biologic aspects protection of the pulp and dentin adhesion

135

CHAPTER 4

BIOLOGIC ASPECTS: PROTECTION OF THE PULP AND DENTIN ADHESION

D. Pansecchi , F. Brenna , P. Ferrari , L. Breschi , G. Dondi dall ’ Orologio , M. Gagliani , L. Fadini , and A. Cerutti

Protection of the Pulp Functions of the Dental Pulp Trauma Defense Mechanisms Pulp Damage Natural Communication Routes between the Endodontium and the

Periodontium Protective Bases Enamel-Dentin Adhesives

Pulp-Dentin Protection with Adhesive Techniques Esthetics and Function in Relation to the Internal Biologic Structures Direct Restoration with Pulp-Dentin Protection of Two Class I Cavities with

Esthetic Adhesive Materials Direct Pulp Capping with Adhesive Techniques Materials for Direct Pulp Capping Case Reports of Direct Pulp Capping

136

Innovations in the Field of Dentin Adhesion Clinical Problems and Applications Clinical Classifi cation Selecting the Adhesive System Main Errors and the Operator Factor

Composites and Glass-Ionomer Cements Clinically Relevant Product Updates Evidence-Based Dentistry Toxicity

Light-Curing Units Light Curing Curing Lamps Degree of Conversion of Composites Polymerization Techniques Clinical Use of Curing Lamps

137

PROTECTION OF THE PULP D. Pansecchi

Biologic Aspects: Protection of the Pulp and Dentin Adhesion Chapter 4

Th e following character istics make the dental pulp unique compared with any other body tissue:

• Pulp is surrounded by unyielding walls of dentin and therefore cannot expand in response to infl am-matory lesions.

• Vascularization is terminal ar teriolar, which reduces the pulp ’ s ability to regenerate itself after an injury; one or mor e arterioles enter the tooth through the apic al foramen, and smaller v essels can enter the pulp thr ough lateral channels.

• Innervation lacks proprioceptive sensory mechanisms.

• It is composed almost entirely of specialized loose connective tissue and a highl y sophisticated cell population: odontoblasts in the outer area near the dentin, and fi broblasts, lymphocytes, macrophages, and undiff erentiated mesenchymal cells in the inner portion of the tissue.

FUNCTIONS OF THE DENTAL PULP

Th e dental pulp has four major functions: dentinogenic, defensive, sensory, and nutritive.

Figure 4-2 shows the radiographs of 8-, 25- and 79-year-old patients. Th ese are sound teeth with healthy pulp that exhibit ph ysiologic responses to pulp vitalit y and percussion tests and that radiographic ally do not show any sign of c alcifi cation or root resorption but a normal lamina dura and a per iodontal space of normal width.

Th e incisor and the pulp of the 8-year-old are healthy, and the tooth has an immature apex housed within very thin walls of dentin. Likewise, the pulp of the incisor of the elder ly patient (79 y ears old) is health y, with severe reduction of the pulp chamber and the r oot canals owing to the continuous deposition of dentin by the odontoblasts over the years.

TRAUMA

Figure 4-3 shows pulp that has aged pr ematurely, as it belongs to a young patient (tooth 9). Th e pulp chamber and root canal have clearly disappeared. Th is is a sign of pulp damage and c an be obser ved as the r esult of

Dentinogenic function: Odontoblasts are responsible for dentin formation and c an generate a process of collagen fi ber mineralization from the predentin ( Figure 4-1 ).

Defensive function: Th e pulp responds to insults — bacterial, iatrogenic, and traumatic (restorative techniques) — with an infl ammatory process.

Sensory function: Th e pulp responds to injury with pain. Th is is one of the most impor tant functions of the pulp.

Nutritive function: Intake of nutr ients and water required for dentin metabolism.

Figure 4-1

trauma with injur y of the neur ovascular bundle. Th e crown is discolored as a result of degradation of hemo-globin released from the red blood cells that infi ltrated the dentinal tubules.

Th is kind of aging is fr equently asymptomatic, and often the patient comes to obser vation because of unsightly dental cr own discoloration or the onset of periodontal symptoms caused by pulp necrosis; in some cases it is noted on x-ray images. Th e following clinical case ( Figure 4-4 ) is the r esult of trauma. Th is young patient (21 years old) presents a buccal supracrestal and palatal subcrestal complete cr own-tooth fracture complicated by pulp exposure (Ellis Class V fracture). Figures 4-5 and 4-6 also show the outcome of the trauma.

138

Chapter 4 Biologic Aspects: Protection of the Pulp and Dentin Adhesion

Figure 4-2 Radiographs of three patients aged 8 (A) , 25 (B), and 79 (C).

A B C

Figure 4-3 A, Radiograph of tooth 9 showing a prematurely aged pulp and disappearance of the pulp chamber and root canal. B, Upper left central incisor (9). Clinical appearance of the dental crown; note the change in color.

A B

139


Figure 4-4 A 21-year-old patient with a buccal supracrestal and palatal subcrestal complete crown-tooth fracture complicated by pulp exposure (Ellis Class V fracture). Unfortunately, this case required a root-canal treatment.

A B

C D

Figure 4-5 The coronal fragment was removed, and after detachment of a partial-thickness fl ap the patient underwent an osteotomy and osteoplasty. Later the operative site was isolated with a rubber dam, and after endodontic treatment the coronal fragment was bonded with the aid of a carbon-fi ber post.

A B C

Continued

140

Th e evidence suggests that under restorations bacte-rial multiplication occurs only in the presence of micro-cracks and infi ltration.

In restorative dentistry, the most important means of pulp protection — aside from prevention — is the removal of root caries.

According to Langeland (1987) , pulp r eactions caused by initial caries can be reversed by removing the carious dentin.

Recurrent caries with pulpal inv olvement are often the result of residual bacteria under restorations, which are able to proliferate thanks to the nutrients that reach them via microleakage or that spread from the pulp.

Th e key factors for a successful c aries treatment are as follows:

• Complete removal of softened infected dentin • Best possible fi t between restorative material and

the enamel-dentin substrate to pr event bacterial growth and r einfection of the dentin tubular system ( Figure 4-12 )

Protection of the dentinal tubules exposed by cavities or prosthetic abutment pr eparation is cr ucial for the preservation of pulp vitality, in order to avoid the passage of bacteria and toxins into the pulp. Th is can be achieved with hermetically sealed r estorations able to pr event marginal microleakage and bacter ial invasion ( Figure 4-13 ).

WHAT THE PULP SHOULD BE PROTECTED FROM In the ear ly 1970s the piv otal studies of Br ä nnstr ö m clarifi ed that the gr eatest threat to pulp and dentin integrity is represented by bacteria and their metabolic products ( Figures 4-7 and 4-8 ).

As early as 1927 Gr owell hypothesized that pulp infl ammation was attributable to bacterial infection.

Marginal bacterial infi ltration or microleakage: Infection of the microgap between the restoration material and cavity walls that inexorably leads to bacterial invasion along the dentinal tubules up to the pulp.

Restorative materials do not c ause any signifi cant pulp reactions, even when they are in contact with the pulp.

Microleakage Microleakage is the c linically undetectable passage of bacteria, fl uids, and molecules betw een the cavity wall and the restoration ( Figures 4-9 to 4-11 ).

It is important to maintain the integrity of the mar-ginal seal over time. According to Br ä nnstr ö m (1984) , when the bacteria nested in the dentin ar e deprived of nutrients, they probably die.


Figure 4-6 Checkups after 1 year ( A and B ) and after 2 years ( C and D ).

A B C D

141


Figure 4-7 A, Marginal deterioration and wear of composite Class II restoration. B, X-ray fi lm of the right lower fi rst molar (30). Wide radiolucent area under the composite restoration (secondary caries). The radiolucency around the mesial root also involves the bifurcation. The recurrent caries under the old restoration caused pulp necrosis.

A B

Figure 4-8 First and second upper left premolars (12 and 13). Faulty, infi ltrated, and anatomically incorrect restorations. The margins show the presence of secondary caries.

Figure 4-9 Amalgam restoration with serious margin fl aws and fracture of the fi lling mass. Recurrent caries under the old restorations caused pulp necrosis.

142


A

C

B

Figure 4-10 First and second right lower molars (30 and 31). A, Preoperative image. Old composite restorations heavily worn with infi ltration and secondary recurrent caries. B, Postoperative image. C, One-year checkup.

Figure 4-11 First and second right premolars (4 and 5). A, Composite restorations with serious marginal fl aws and infi ltration. B, Postoperative image. Gold-ceramic crown on tooth 4; composite restoration on tooth 5.

A B

143


Figure 4-12 Pulp damage may be caused by a traumatic insult but also by tooth decay, erosion, and abrasion. The bacterial colonization of the pulp causes irreversible pulpitis, which over time will lead to pulp necrosis. A, First upper right molar (3). Old amalgam fi lling and severely infi ltrated composite restoration. B, Preoperative radiograph with necrotic pulp and periradicular lesion. C, Recurrent caries under the old restoration (which caused pulp necrosis). D, Full occlusal coverage amalgam restoration. E, X-ray checkup after 1 year.

A B

C

E

D

NON – HERMETICALLY SEALED RESTORATIONS

144


Th e defenses of the pulp-dentin complex against bacterial invasion as w ell as natural and iatr ogenic stimuli are:

1. Dentinal pain 2. Infl ammation of the pulp 3. Pathologic sclerotic dentin 4. Tertiary dentin (or reactive dentin)

INNER AND OUTER DENTIN Inner dentin is character ized by a high tubular densit y (45,000 to 65,000 tubules/mm 2 ) with an average diam-eter of 2.5 to 3.0 micr ons, whereas the outer dentin exhibits fewer tubules (15,000 to 20,000/mm 2 ) with a reduced diameter of 0.8 micr ons (the dentinal tubules are spaced far ther apart, with as m uch as 96% inter-tubular dentin). Th is is impor tant because dentin permeability is dir ectly proportional to the number and diameter of the exposed tubules and inv ersely pro-portional to dentin thickness.

Dentin close to the pulp is eight times more perme-able than the outer dentin. Th e preparation for a pros-thetic crown on molars cr eates an ar ea of 3 to 4 cm 2 (potential opening of 6 to 12 million tubules) (P ashley, 1989).

During preparation of the abutment it is impor tant to know the thickness of the residual dentin in order to protect the pulp, as the dentin near the pulp is about eight times more permeable than the outer dentin.

PROTECTION OF THE PULP Another way to protect the pulp-dentin complex is b y using a rubber dam.

“ I disinfect and protect the exposed dentin v ery easily by isolating the operative site with a r ubber dam ” ( Monari, 2000 ).

Th e factors that aff ect the r esponse of the pulp in restorative dentistry are:

• Preoperative conditions of the pulp • Size of the preparation • Method of cavity preparation and cleaning • Tissue changes in dentin and permeabilit y • Amount and pathogenicit y of bacter ia at the

tooth-restoration interface

DEFENSE MECHANISMS

Th e pulp-dentin complex defends itself against bacterial invasion: 6 hours after cavity preparation, dentin perme-ability is reduced by approximately 75% ( Pashley, 1983 ).

Th e reaction of the pulp depends essentiall y on the type and amount of bacterial metabolism products that reach the pulp chamber; the response of the pulp — that is, the ability of odontoblasts to pr oduce irregular sec-ondary dentin or tertiary dentin in the inner portion of the tissue and sc lerotic dentin in pr oximity of the surface at an early stage; and the infl ammatory reaction, which can cause pulpal necrosis if it is too str ong.

Dentin

Primary dentin: Produced during odontogenesis until tooth eruption.

Secondary dentin: Deposited slowly for the life of the tooth on the pulp side and below the primary dentin, leading to gradual r eduction of the pulp chamber.

Physiologic sclerotic dentin: Sealed peritubular dentin below the enamel layer; it is the r esult of natural aging.

Tertiary dentin: Secondary or reactive dentin or irregular or reparative dentin formed on the pulp side. It is produced when the pulp is subjected to irritant stimuli that can induce the reaction of the odontoblasts with the apposition of new tissue, in order to preserve pulp vitality.

Pathologic sclerotic dentin: Th is is apposed on the surface, just below the ar ea of the lesion. High mineralization associated with progressive obliteration of the lumen of dentinal tubules. First biologic barrier capable of signifi cantly reducing dentin permeability.

Figure 4-13 Lower fi rst right molar (3). Full occlusal coverage amalgam restoration.

145


PREPARATION OF THE ABUTMENT FOR A FULL CROWN Abutment preparation for a full cr own aff ects all the dentinal tubules. Th is is an extreme case.

Increasing the depth of the preparation increases the risk of pulp damage owing to the higher number of dentinal tubules that ar e larger in diameter. According to Perrini (1985), 0.5 to 1 mm of dentin c an safely be removed without damaging the pulp .

In the c ase of the fi rst upper molar , which has a mesialized pulp chamber, removal of the mesial dentin wall should be per formed very carefully ( Figure 4-14 ).

TEMPORARY RESTORATION It is essential to pr otect the pulp-dentin complex fr om bacterial, chemical, physical, and thermal insults in the period between tooth preparation and defi nitive cemen-tation of the dir ect or indir ect prosthetic restoration ( Figure 4-15 ).

During prosthetic preparations of full cr owns, removal of tooth str ucture exposes a large number of dentinal tubules.

Pulp Necrosis Caused by Periodontal-Prosthetic Treatments in Vital Teeth A study conducted b y Ferrara (1991) examined the frequency of periradicular lesions after pulp necrosis of vital teeth used as abutments in per iodontal-prosthetic treatments. Th e teeth had been reduced at least 2 years before the beginning of the study, and at the time they were sound and had no history of trauma. Periradicular

Recommendations for Pulp Protection

• Completely remove carious tissue • Use the instruments carefully • Avoid overheating, dehydration, mechanical

trauma • Avoid excessive pressure and the use of w orn

rotary instruments • Work under a constant jet of water ( Fitzgerald

and Heys, 1991 )

Th e following thr ee key considerations m ust be made:

• Th e real status (histology) of the pulp at the time of restoration cannot be ascertained.

• Th e eff ect of the iatrogenic trauma of preparation cannot be assessed. Excavation and dr ying can deal the fi nal blow to the pulp , which is alr eady damaged (even if asymptomatic).

• Th e countless variables related to materials, dentin substrate, and c linical procedures should be considered.

Another important point is the lac k of corr elation between the histologic status of the pulp and its clinical aspect, as w ell as the complete lac k of corr elation between pain intensit y and the extent of pulp involvement.

PULP DAMAGE

In restorative dentistry the pulp c an sometimes get injured during cavity preparation, but in health y pulps this damage is reversible.

In prosthetic dentistry, pulp damage can occur during preparation of the abutment, impression taking, or the phase of provisional restoration and its cementation.

Other factors that c an damage the pulp ar e the eff ects of the per iodontal disease and its tr eatment on the endodontium.

Th ere is cer tainly a gr eat need to pr otect the pulp-dentin complex, which is r epeatedly traumatized by very invasive preparation with the exposur e of millions of tubules and the amputatio n of millions of odontoblast processes (large wound). Th erefore prompt disinfecting treatment and isolation from the oral envi-ronment is fundamental.

Th e pulp-dentin complex c annot use its natural defense mechanisms, such as formation of ter tiary dentin or reactive sclerosis, because they need a cer tain amount of time to de velop.

Figure 4-14 Upper right fi rst molar (3, section). Note the position of the mesialized pulp chamber.

146


Figure 4-15 The tooth is protected during the period between preparation and fi nal cementation of the crown.

A

B

lesions were found in 22.6% of cases, and the percentage increased when per iodontal involvement was mor e severe. A pr evious study b y Bergenholtz and N yman (1984) yielded similar results.

Th e purpose of temporary restorations is to pr event the cumulative eff ect of irr itative, bacterial, chemical, and other kinds of stimuli on the pulp, the consequences of which c an make r oot-canal treatment necessary. Th erefore the pretreatment status of the pulp (which is unknown), together with removal of dentin around the perimeter of the tooth and possible bacter ial coloniza-tion of the dentinal tubules in the e vent of length y prosthetic treatments, may cause secondary caries of the prosthetic abutment or at the interface with the restor-ative material.

Th erefore precision of the margins as well as optimal internal adaptation of the pr ovisional (relining) is very important. Th is prevents dissolution of the temporar y cement owing to infi ltration of saliva, imprecise margins, and/or excessive thickness of the cement ( Fichera, 2004 ).

NATURAL COMMUNICATION ROUTES BETWEEN THE ENDODONTIUM AND THE PERIODONTIUM

Th e pulp-dentin complex and the per iodontium com-municate with each other via major r outes that form a direct bridge between the dental pulp and the per i-odontium and permit the mutual passage of infl amma-tory and degenerative insults.

Th e communication routes are represented by den-tinal tubules, the apic al foramen, and lateral channels ( Figures 4-16 and 4-17 ).

DENTINAL TUBULES AND THE APICAL FORAMEN Th e dentinal tubules run from the pulp to the amelo-dentinal junction and the cemento-dentinal junction, with a diameter of about 2.5 micr ons on the pulp side and about 1 micr on at the opposite end (see Figure 4-17 ).

147


Figure 4-16 First lower molar.

1

2

3

4

1. Foramen with apical delta

2. Lateral channel

3. Accessory channel at the bifurcation

4. Dentinal tubules

A

B

Figure 4-17 Dentinal tubules.

Th e dentinal tubules may contain bacter ia and thus allow the passage of to xins and other substances produced during a degenerative infl ammatory process of the pulp.

Under normal conditions, dentinal tubules do not communicate with the per iodontium because of the presence of the radicular cement. Periodontal disease (with exposed r oot surface), congenital absence of cement, and r oot planing c an create communication between the dentinal tubules and the oral environment.

Th e apical foramen is the main route of communica-tion between the endodontium and the per iodontium and represents the main exchange channel for diseases in both directions ( Figures 4-18 to 4-21 ).

Figure 4-18 Apical foramen of the mesio-vestibular root of the fi rst upper right molar (3).

Figure 4-19 Lower diaphanized premolar.

148


Figure 4-20 Upper right lateral incisor (7). Postoperative radiograph showing two confl uent channels.

Figure 4-21 Second lower left premolar (20). Postoperative radiograph: apical delta.

LATERAL CANALS Lateral canals are quite common and c an be found along the entire root surface and at the bifur cation of multiradicular teeth.

According to a study on the mor phology of r oot canals conducted by Walter Hess (1925) , the occurrence of lateral canals is estimated to be about 43.5%.

Some authors have suggested a corr elation between lateral canals and periodontal disease and treatment.

Lateral canals unquestionably act as a point of exit of the disease toward the endodontium-periodontium;

the hypothesis of the point of entr y in the opposite direction is still being inv estigated. Th e larger lateral canals contain pulp and fi bers that are closely connected with the main canal ( Figure 4-22, A and B ).

INFLUENCE OF PERIODONTAL DISEASE AND PERIODONTAL TREATMENT ON THE ENDODONTIUM Some authors agr ee that the per iodontal disease c an cause pulp alterations ( Craney, 1925 ; Cahn, 1927 ; Bauchwitz, 1932 ; Seltzer and colleagues, 1963 ; Rubach and colleagues, 1965 ; Staml, 1966; Bender and Seltzer, 1972 ; Seltzer, 1975), whereas others believe that per i-odontal disease c annot aff ect the pulp ( Mazur and Massler, 1964 ; Smukler and Tagger, 1976; Bergenholtz and Lindhe, 1978 ; Czarnecki and Schilder, 1979 ; Tor-abinejad and colleagues, 1985 ).

Pulp damage in the course of per iodontal disease can occur only in the case of advanced periodontopathy, when bacterial plaque covers all the apical foramina ( Figure 4-23 ).

Figure 4-22 A, Diaphanized upper right central incisor (8); lateral channels at the apical third. B, Upper left central incisor (9). Postoperative radiograph: large lateral channel on the mesial aspect of the root.

A

B


Figure 4-23 Upper right fi rst molar (3).

Langeland and co-w orkers (1974) identifi ed retro-grade pulpitis caused by periodontal disease. Retrograde infl ammation of the pulp c an lead to pulp necr osis. Regarding the infl uence of the per iodontal treatment on the endodontium, Schilder (1978) argued that r et-rograde pulpitis can be caused by periodontal treatment. For instance, sectioning a vascular pedic le of a large lateral channel with a curette can lead to pulp necrosis. Th e periodontal treatment can cause pulp necrosis when the blood supply to the pulp through an accessory canal is interrupted by a cur ette (periodontal curettage — sectioning of a lateral v essel — loss of blood suppl y resulting in ischemia and pulp necr osis) ( Figures 4-24 to 4-26 ).

149

Figure 4-24 Forty-fi ve – year-old patient with an acute alveolar abscess. The preoperative radiographic examination showed substantial radiolucency at the apex and on the distal aspect of the root of the left upper incisor (10). The lesion was fi stulized buccally and in the gingival sulcus. The tooth did not respond to vitality tests. There was no history of trauma, and no coronal caries was detected. Mild chronic adult periodontitis with slow progression. Vertical atrophy of the bony ridge was noted on the distal aspect of tooth 10; there was a limited bucco-distal pocket of 9 mm at the fi stulous tract of the gingival sulcus (the endodontic drainage simulated a periodontal problem). The cavity was prepared without anesthesia, which confi rmed the diagnosis of pulp necrosis and the periapical lesion of endodontic origin. The endodontic drainage was left in place until complete resolution of the acute symptoms.

A B

150


Figure 4-25 The postoperative radiograph showed a signifi cant lateral channel at the cervical third on the distal side of the root. The diagnosis was primary periodontal lesion with secondary endodontic involvement, pulpitis, and retrograde pulp necrosis because of periodontal treatment. The radiographic checkup a few months later confi rmed the healing of the bone (with a residual probing depth of 5 mm) and the good conditions of the gum. Furthermore, the signs of the previous periradicular lesion were no longer detectable.

A B

Figure 4-26 A, Checkup after 7 years. B, X-ray checkup after 7 years.

A B

Regarding the possibility of pulp infection secondary to periodontal disease, this is a v ery rare fi nding and occurs only when the per iodontal disease exposes the root apex, thus connecting the pulp with the oral envi-ronment. In this c ase the tissue c an become infected and we may fi nd retrograde infl ammation of the pulp with subsequent retrograde pulpitis or necr osis caused by periodontal disease.

PROTECTIVE BASES

Several materials can be used as pr otective bases for cavities, such as c alcium hydroxide [Ca(OH) 2 ], simple

varnishes, cavity liners, Intermediate Restorative Mate-rial (IRM), and glass-ionomer cements (GICs) ( Figures 4-27 and 4-28 ).

WHY USE A PROTECTIVE BASE? Why use a pr otective base? What do w e expect from it?

Protective bases aim to do the following: • Reduce postoperative sensitivity • Protect the pulp from thermal, chemical, and bac-

terial stimuli • Induce the formation of ter tiary and pathologic

sclerotic dentin

151


can even dissolve partially or entirely over time (Pashley 1991).

Displacement of the base dur ing amalgam compac-tion maneuvers is also frequent.

Dental pulp responds to stimuli with dentinal sc le-rosis and apposition of r eactive dentin at the corr e-sponding pulp area, without the need for a pr otective base ( Figure 4-29 ).

Calcium Hydroxide Th e features and indications of Ca(OH) 2 can be sum-marized as follows:

• It adds a lay er of mater ial to the c avity with a consequent decrease in the r esistance, retention, and stability of the restoration.

• It cannot be applied on the entire exposed dentin.

• Reduce the amount of r estoration material • Improve cavity geometry

Thermal Insulation According to the study conducted b y Piperno and Spiering (1982 to 1984), a 2-mm pr otective base (0.5 mm calcium hydroxide and 1.5 mm zinc oxyphos-phate) results in a 20% r eduction in a 60 ° C heat stimulus.

Th e cavity should be at least 4 mm deep in order to place an amalgam layer of at least 1.5 to 2 mm.

CHARACTERISTICS AND TYPES OF PROTECTIVE BASES No base c an withstand marginal infi ltration. A wide space can form under the r estoration, and the cement

Figure 4-27 Preoperative radiograph of the fi rst and second right lower molars (30 and 31).

Figure 4-28 First and second right lower molars (30 and 31). Cavity base of calcium hydroxide.

Figure 4-29 Third lower left molar (17). A, Old and faulty amalgam restoration. B, Preoperative radiograph: radiolucency under the amalgam restoration. C, Dissolution of the cavity base (calcium hydroxide). The base is mechanically fragile and tends to disappear over time.

A B C

152


Furthermore, GICs: • Can be consider ed the ideal r eplacement for

dentin • Provide a layer of “ fl exible ” material that can dis-

sipate the mechanical and thermal str ess applied on the restoration

• Can prevent and reduce marginal infi ltration Th e GIC should ne ver be etched (this applies to

fi rst-generation glass ionomer cement).

Use of Glass-Ionomer Cements

• Restoration of deciduous teeth • Liner • Cavity base • Defi nitive cement in prosthetic dentistry

GIC can be placed over Ca(OH) 2 in order to prevent its dissolution by action of the etching agent and the primer ( Figure 4-30 ).

Because of its low pH, it should not be used in direct contact with the pulp but should be placed onl y on residual dentin that is at least 0.5 mm thick.

Placement of GIC as a cavity base permits reduction of the C factor b y improving the shape of the c avity.

Mineral Trioxide Aggregate Composition and Physical Properties

Mineral trioxide aggregate (MTA) is a pow der com-posed of small h ydrophilic silicate, phosphate, and tri-calcium oxide particles with the addition of silicon oxide and bism uth oxide, which make it radiopaque . Th e pH var ies from 10.2 r ight after mixing to 12.5 after curing, which corresponds to the pH of c alcium hydroxide. Th e latter is a high value , which explains its antimicrobial activity. It has low solubilit y and w orks well even in the pr esence of moisture. It exhibits low resistance to compression.

Indications (Ford, 1996; Torabinejad and Chivian, 1999 ) include the following:

• Retrograde fi llings or endodontic surger y • Direct pulp capping • Repair of perforation or stripping • Apexifi cation • Internal resorptions

DIRECT PULP CAPPING Pulp exposure may occur accidentall y (e.g., during a prosthetic preparation), during caries excavation, or during a traumatic event.

• It does not adhere to the dentin. • It shows low resistance to compression. • It needs to be pr otected (Copalite). • It is soluble in acids (etching). • It washes out if ther e is no marginal sealing

( Barnes, 1980 ). • It is used for dir ect pulp capping. When preparing mesial-occlusal-distal (MOD) cav-

ities for amalgam r estoration, it is advisable to add 0.5 mm of calcium hydroxide because, according to the study by Farah and colleagues (1975 to 1983) , this reduces the r estoration ’ s resistance to fractur e by 50% compared with c avities that hav e no pr otective base.

Bacterial growth within c alcium hydroxide after 2 years of permanence in the oral c avity has also been demonstrated.

Cavity Varnishes Cavity varnishes ar e solutions of r ubber or natural (copal) or sy nthetic (cellulose nitrate) r esins dissolved in a volatile solvent (Copalite contains copal plus ether). Th eir placement in the cavity is diffi cult, and a minimum thickness of 2 to 5 micr ons should be ensur ed. Th e varnishes form a semipermeable membrane .

Cavity Liners Cavity liners are similar to the previous solutions, with calcium hydroxide and zinc oxide added in suspension. Th ey produce a thicker layer (12 to 40 microns). Accord-ing to Pashley and colleagues (1986, 1989) , varnishes and liners do not pr ovide the desired isolation barr ier for the restoration.

IRM IRM may cause an infl ammatory reaction of the pulp when placed inside c avities whose distance fr om the pulp is less than 0.5 mm ( Br ä nnstr ö m and co-workers, 1981 ).

Glass-Ionomer Cements Th e main featur es of GICs ( Wilson and Kent, 1972 ; Mount and colleagues, 1994 ) are as follows:

• Biocompatibility • Cariostatic action thr ough fl uoride release

(moderate) • Ease of use • Good chemical and mechanical adhesion to dental

structures • Compressive strength similar to that of dentin

153


is treatment of the preparation with an adhesive system. Th e use of dentin-enamel adhesiv es, which permit removal of the smear layer and formation of the hybrid layer, creates a pr otective barrier that is m uch more eff ective than what c an be achieved with liners or var-nishes ( Anderlini, 2001 ).

Th ese current treatments cannot off er an absolute guarantee that there will be no microcracks between the restoration and the c avity walls, but compar ed with traditional methods they have a better chance of decon-taminating, sealing, and insulating the pulp-dentin system aff ected by the preparation. Th e research seems to off er compelling r easons for consider ing these biocompatible enamel-dentin sy stems, and their clinical use has not established any contraindications so far ( Nakabayashi and colleagues, 1991 ; Pashley and colleagues, 1992 ; Stanley, 1993 ).

Th e aims of enamel-dentin adhesion ar e as follows ( Oddera and colleagues, 1996 ):

• Retention and stability of the restoration • Opposition and absorption of shrinkage stress • Perfect marginal fi t • Absence of cracks and microleakage • Sealing of the pulp-dentin complex • Reduction of postoperative sensitivity • Structural reinforcement of the restored tooth Of these goals, the seal is unquestionabl y the most

important ( Figure 4-31 ).

Th e results of studies on the success rate of dir ect pulp capping are quite divergent. On the basis of long-term considerations (10 y ears), Roulet recommends to avoid pulp capping.

CONCLUSION Pulp infl ammation is not c aused by the to xicity of restorative materials. Th e evidence shows that the problem lies in the presence of bacteria. Without bacte-rial contamination the pulp c annot be compromised.

Direct Pulp Capping with Adhesive Systems

Authors in Favor Cox, 1998 Liebenberg, 1999 Cox, 2000

Authors in Disagreement Gwinnet and Tay, 1998 Hebling, 1999 Pereira, 2000 Prati, 2000

ENAMEL-DENTIN ADHESIVES

With any t ype of restoration, the safest and c linically most feasible means to protect the pulp-dentin complex

Figure 4-30 A, Second upper left molar (15). Preoperative image. B, Cavity base: glass-ionomer cement (GIC). C, Postoperative image.

A B

C

154


• Treatment of the dentin • Moisture (dry or wet bonding) • Sclerotic dentin • Any mistake in product applications Th e factors that aff ect adhesion to the dentin ar e as

follows ( Anderlini, 2000 ): • Dentin substrate • Materials • Operator

Dentin Substrate Th e same cavity may contain diff erent types of dentin (e.g., sound, sclerotic).

Certainly the most important parameter to consider is whether the dentin is superfi cial or deep . Th e best

ADHESIVE STEP Th e crucial step in this pr eparation involves the adhe-sion, a delic ate and cr itical phase for the outcome of restoration.

Th e type of adhesion depends mainl y on the quality of the hybrid and especially the marginal layers.

A porous marginal h ybrid layer (MHL) facilitates the formation of marginal gaps, infi ltration, marginal nano-infi ltration, and, consequently, secondary caries and black spots ov er time ( Figure 4-32 ) ( Prati and colleagues, 1998 ).

Th e daily clinical problems to be faced when using these materials are as follows:

• Choice of the adhesive system • Treatment of the enamel

Figure 4-31 A, First and second right lower molars (30 and 31). Preoperative image: composite restorations worn, damaged, and infi ltrated. B, Postoperative image.

A B

Figure 4-32 Interface between composite (R) and dentin (D) , resin tags and hybrid layer.

R

H

D

155


results in terms of adhesion c an be obtained on the superfi cial dentin.

Other variables are dry or wet; coronal or radicular; deciduous or permanent teeth; tubular or atubular , young or old; density of tubules; amount of intertubular dentin; distance from the pulp; and amount of organic matter and available substrate for the adhesion mechanisms.

Materials and Operator As far as materials are concerned, the following factors can aff ect the quality of dentin adhesion:

• Condition of the products • Defective products • Mechanical properties of materials • Light-curing or dual-curing materials • One-, two-, three-step dentin-enamel adhesives • Acid concentration • Type of band • Lamp effi ciency • Inappropriate lubrication of handpieces • Impurities from the air-water sy ringe Factors that ar e operator dependent inc lude the

following: • Proper use of products • Etching time • Proper rinsing of the etching agent

• Drying method • Primer or solvent evaporation • Cavity shape • Filling method • Curing time and methods • Isolation of the operative site • Salivary contamination Th e condition of the materials is crucial. For instance,

because adhesives have an acetone base , continuous opening and closing of the package may cause acetone evaporation, which could aff ect the eff ectiveness of the product.

It is imperative that the operator isolate the operative site with a rubber dam.

Dentin Conditioning Dentin conditioning is the most cr itical step of the whole composite restoration ( Figure 4-33 ):

• Application of 30% to 40% orthophosphoric acid for 10 to 15 seconds

• Rinsing with a copious amount of water • Drying It is impor tant to av oid overdrying, particularly in

special cases ( Figures 4-34 to 4-36 ). Th e level of dentin moistur e is c linically diffi cult to

control, and of ten it is unc lear how to dr y the c avity and to what extent.

156


Figure 4-33 Enamel: 15 seconds (A). Dentin: 10 seconds (B). Rinsing time: at least as long as etching time (C). Primer: 1 minute (D). Bonding, curing: 40 seconds (E).

A B

C

E

D

157


INVASIVE EXTRACANALAR SUPRAOSSEOUS RESORPTION ( “ PINK TOOTH ” )

Figure 4-34 A 16-year-old patient who came to observation because he was worried about a tooth that had turned pink (upper right central incisor) (A). The patient showed a large invasive extracanalar supraosseous resorption of tooth 8. The preoperative radiograph showed a radiolucent area with hazy margins, with the profi le of the canal superimposed on the radiolucency of the defect. The tooth responded positively to pulp vitality tests (B).

A B

Figure 4-35 Opening of a partial-thickness fl ap (A) and curettage of the infl ammatory tissue responsible for the lesion (B). The rubber dam was placed intraoperatively (C), and restoration was performed with an esthetic material (D). Postoperative image (E) and radiographic checkup (F).

A B C

D E F

Figure 4-36 At the 1-year checkup (A), the pulp was vital (B).

A B

158


layer, leading to dissolution of the adhesive and the col-lagen fi brils together with their binding r esins.

According to some studies, what occurs is hydrolytic degradation of the adhesive system associated with the formation of marginal gaps with secondar y caries and detachment of the restoration.

Studies on one-, two-, and thr ee-step adhesive systems found a h ybrid layer of poor qualit y and degradation from water exposure ( Hashimoto and colleagues, 2000 ; Tay and colleagues, 2002 ; Tay and Pashley, 2003 ; Breschi and colleagues, 2003 ; Breschi and colleagues, 2004 ; Pashley and colleagues, 2004 ).

Recent studies hav e shown that adhesiv e systems provide only a par tial seal of the dentin, that they ar e permeable to fl uids, and that such permeability increases progressively over time ( Bouillaguet and colleauges, 2000 ; Tay and colleagues, 2002 ; Tay and colleagues, 2003 ).

Adhesive systems cannot provide a complete seal to the exposed dentin.

Moreover, as noted, the adhesiv e system tends to become more permeable over time ( Chersoni and col-leagues, 2004 ).

Th e development of ne w adhesive systems should strive to r educe permeability in or der to pr ovide the clinician with reliable and durable adhesive systems.

References Anderlini G : Adesione oggi. Parte II. Fattori che infl uenzano la

qualit à dell ’ adesione , Riv Ital Stomatol 2 : 79 - 95 , 2000 . Anderlini G : Adesione oggi. Parte II, sez I II. Fattori che infl u-

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Drying of the Dentin

• Th e water is fi rst suctioned with a saliva ejector . • Air syringe for a few seconds from at least 5 to 6 cm

(this yields the worst results). • Absorbent paper points. • Synthetic brush. • Sponges or cotton pellets ( De Goes and co-workers,

1997 ). Th e degree of dentin moistur e will also depend on

the type of solvent in the pr imer ( Figure 4-37 ): • Acetone-based adhesives: wet bonding (K anko,

1992) • Water-based adhesives: dry bonding • Alcohol-based adhesives: intermediate

Clinical Applications It has been demonstrated that the same type of adhesive applied by diff erent operators can yield diff erent results in terms of bond str ength ( Ciucchi, Bouillaguet, and Russel, 1997 ).

CONCLUSION AND OUTLOOK An ideal universal adhesive would be desirable , but it has not been made yet. Products that are easy to apply, guarantee predictable long-term r esults, and contain antibacterial monomers are needed.

FAILURE OF THE ADHESIVE BOND Unfortunately, there is a problem here, as the contem-porary adhesive systems believed to be useful for pr o-tecting the exposed dentin c annot ensure an adequate seal and instead show pr ogressively increasing permeability.

Water, lactic acid, salivary esterases, and proteolytic enzymes can penetrate and pass thr ough the h ybrid

Figure 4-37 Drying of enamel and dentin.

159


Kanka J : Resin bonding to wet substrate. Part I. Bonding to dentin , Quintessence Int 23 ( 1 ): 39 - 41 , 1992a .

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Liebenberg WH : Esperienza clinica di inc appucciamento pulpare intenzionale con un adesivo , J Adhes Dent 1 : 345 - 363 , 1999 .

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Pashley DH , et al : Eff ects of the smear lay er copalite and o xalate on microleakage , Oper Dent 11 : 95 - 102 , 1986 .

Pashley DH , et al : Considerazioni cliniche sulla microinfi ltrazione , Prog Odontoiatr 6 : 7 - 15 , 1989 .

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Pashley DH , et al : Collagen degradation by host-derived enzymes during aging , J Dent Res 83 : 216 - 221 , 2004 .

Pereira JC , Segala AD , Costa CAS : Human pulp response to direct capping with an adhesiv e system: histologic study , J Dent Res 76 : 180 , 1997 .

Pereira JC , et al : Incappucciamento diretto con un sistema adesiv o nell ’ uomo , Am J Dent 3 : 139 - 147 , 2000 .

Perrini N : La prevenzione del danno pulpare in protesi , Riv Odon-toiatr Amici Brugg 5 : 219 - 235 , 1993 .

Piperno S , et al : Th ermal discomfort of teeth related to presence of cement bases under amalgam r estorations , Oper Dent 7 : 92 - 96 , 1982 .

Pitt Ford TR , et al : Using mineral tr ioxide aggregate as a pulp-capping material , J Am Dent Assoc 127 ( 10 ): 1491 - 1494 , 1996 .

Prati C , et al : Resin infi ltrated dentin lay er formation of ne w bonding system , Oper Dent 23 : 185 - 194 , 1998 .

Roulet JF , et al : Incappucciamento pulpare: studio r etrospettivo , J Endod 9 : 525 - 528 , 2000 .

Rubach WC , Mitchell DF : Periodontal disease, accessory canals and pulp pathosis , J Periodontol 36 : 34 , 1965 .

Schilder H : Perio-endo relationship , Boston , 1978 , Continuing Edu-cation Course. BUSGD .

Seltzer S , Bender IB , Ziontz M : Th e interrelationship of pulp and periodontal disease , Oral Surg 16 : 1474 , 1963 .

Br ä nnstr ö m M , Nyborg H : Pulp reaction to composite resin restora-tion , J Prosthet Dent 27 : 181 - 188 , 1972 .

Br ä nnstr ö m M , Nordenwall KJ , et al : Pulpal reaction to I RM cements: an intermediate restorative material containing eugenol , J Dent Child 4 : 259 - 263 , 1981 .

Br ä nnstr ö m M : Smear layer: pathological and treatment consider-ations , Oper Dent (suppl) 3 : 35 , 1984 .

Breschi L , Gobbi P , Lopez M , Prati C , Falconi M , Teti G , Mazzotti G : Immunocytochemical analysis of dentin: a double labeling technique , J Biomed Mater Res 67a : 11 - 17 , 2003 .

Breschi L , Prati C , Gobbi P , Pashley DH , Mazzotti G , Teti G , Perdigao J : Immunohistochemical analysis of the collagen fi brils included inside the h ybrid layer: a FE ISEM study , Oper Dent 29 : 538 - 546 , 2004 .

Cahn LR : Th e pathology of pulps found in p yorrhetic teeth , Dent Items Interest 49 : 598 , 1927 .

Chersoni S , et al : Water movement in the hybrid layer after diff erent dentin treatments , Dent Mater 20 : 669 - 676 , 2004 .

Ciucchi B , Bouillaguet S , Russel C : Dentin bonding b y general practitioners: the battle of the bond. Part l , J Dent Res 1997 . Abstract .

Cox CF , Hafez AA , et al : Biocompatibility of primer, adhesive and resin composite system on non-exposed pulps of non-human pr i-mates , Am J Dent 10 : 55 - 63 , 1998 .

Cox CF , et al : Biocompatibilit à di sistemi adesivi verso polpe esposte in denti di pr imati , Am J Dent 11 : s55 - s63 , 1998 .

Craney AG : Die Patologisch-anatomischen Ver ä nderungen der Pulpa Bei Pyorrhea Alveolaris , Kor Bl F Z ahn 49 : 317 , 343, 369 , 1925 .

Crowell WS : Physical chemistry of dental cements , J Am Dent Assoc 14 : 1030 - 1048 , 1972 .

Czarnecki RT , Schilder H : A histological evaluation of the human pulp in teeth with varying degrees of periodontal disease , J Endod 5 : 242 , 1979 .

Farah JW , et al : Eff ect of cement bases on str esses in amalgam restorations , J Dent Res 54 : 10 - 15 , 1975 .

Farah JW , et al : Eff ect of cement bases thic knesses on MOD amalgam restorations , J Dent Res 62 : 109 - 111 , 1983 .

Ferrara A : Necrosi pulpare conseguente a trattamento pr otesico-parodontale in denti vitali , G It Endod 1 : 5 - 9 , 1991 .

Fichera G : Il restauro provvisorio in protesi fi ssa , Dentista Moderno 10 : 21 - 59 , 2004 .

Fitzgerald M , Heys RJ : A clinical and histologic al evaluation of conservative pulpal therap y in human teeth , Oper Dent 16 : 101 - 112 , 1991 .

Gwinnett AJ , Tay FR : Early and intermediate time response of the dental pulp to an acid etch technique in vivo , Am J Dent 11 : 35 - 44 , 1998 .

Gwinnett AJ , Tay FR : Risposta pulpare all ’ incappucciamento diretto nell ’ uomo , Am J Dent 11 : s35 - s44 , 1998 .

Hashimoto M , et al : In vivo degradation of r esin dentin bonds in humans over 1 to 3 y ears , J Dent Res 79 : 1385 - 1391 , 2000 .

Hebling J , Giro EMA : Biocompatibility of an adhesiv e system applied to exposed human dental pulp , J Endod 25 ( 10 ): 676 - 682 , 1999 .

Hess W , Zurcher E : Th e anatomy of the ro ots canals of the t eeth of the p ermanent dentition , New York , 1925 , William and Wood Co .

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Tay FR , Pashley DH : Water treeing: a potential mechanism for degradation of dentin adhesives , Am J Dent 16 : 6 - 12 , 2003 .

Torabinejad M , et al : A histologic e valuation of dental pulp tissue of a patient with per iodontal disease , Oral Surg 59 : 198 , 1985 .

Torabinejad M , et al : Sealing ability of a mineral trioxide aggregate when used as a root-end fi lling material , J Endod 19 ( 12 ): 591 - 595 , 1993 .

Torabinejad M , Chivian N : Clinical applications of mineral trioxide aggregate , J Endod 25 ( 3 ): 197 - 205 , 1999 .

Wilson AD , Kent BE : A new translucent cement for dentistr y , Br Dent J 15 : 133 - 135 , 1972 .

Seltzer S , Sinai I , August D : Periodontal eff ects of root perforation before and during endodontic procedures , J Dent Res 49 : 333 , 1970 .

Spierings TAM , et al : Th e infl uence of restorative dental materials on heat transmission in human teeth , J Dent Res 63 : 1096 - 1100 , 1984 .

Stanley HR : Pulpal responses to conditioning and bonding agent , J Esthet Dent 5 ( 5 ): 208 - 214 , 1993 .

Tay FR , et al : Adhesive permeability eff ects composite coupling to dentin treated with a self etch , Adhes Oper Dent 28 ( 5 ): 610 - 621 , 2003 .

Tay FR , et al : Single step adhesiv es are permeable membranes , J Dent 30 : 371 - 382 , 2002 .

Tay FR , et al : How can nanoleakage occur in self-etching adhesiv e systems that demineraliz e and infi ltrate simultaneously? J Adhes Dent 4 : 255 - 269 , 2002 .

161

PULP-DENTIN PROTECTION WITH ADHESIVE TECHNIQUES * F. Brenna


ESTHETICS AND FUNCTION IN RELATION TO THE INTERNAL BIOLOGIC STRUCTURES

During initial checkups it has become increasingly fre-quent to see patients whose mouths embody what pro-fessional and home prevention have contributed to oral health. Such high standar ds meet the expectations of clinicians committed to motivating patients and making them aware of the importance of preventing caries and periodontal disease ( Figure 4-38 ).

More and more often, however, we fi nd patients who present problems arising from recent dental treatment performed with adhesive materials and techniques.

Esthetic adhesive products have now replaced tradi-tional materials for restorations in the lateral and pos-terior sector of the oral c avity. For these products to be applied correctly, the operator m ust master these ne w techniques, which should be per formed precisely and professionally from the very beginning. Th e two bite-wings of the mouth shown in Figure 4-38 clearly reveal teeth that could be a source of problems and complaints for the patient.

* In memory of Carlo Zerosi.

Close observation of the images shows that most of the problems involve teeth that hav e already been treated (secondary disease), probably as a r esult of inadequate knowledge of techniques and adhesiv e materials that may have been used hastil y and without proper isolation of the operativ e site ( Figures 4-39 to 4-42 ).

In this specifi c case, the patient r eported extensive pain in the poster ior sectors that was se vere at the two right upper premolars. With the help of radiographs the case was pr operly diagnosed. Th erefore we can agree with Davidson, who as far back as 1989 reported restor-ative failures that may have been caused by the misuse of composites. Composites, unlike traditional materials,

Figure 4-38 Front image of the dental arches during a fi rst visit before professional oral hygiene. The situation appears to be optimal.

Figure 4-39 Right lateral view.

Figure 4-40 Left lateral view.

162


Figure 4-41 Right-side bitewing showing iatrogenic problems (red circles).

Figure 4-42 Left-side bitewing showing not only iatrogenic lesions (red circles) but also other defects due to primary caries (yellow circles). It is clear that the former are more abundant than the latter.

are very diffi cult to control because of the shrinkage that follows self-curing or photocur ing. Th ose failures are caused by infi ltration of bacter ia that can easily pene-trate the har d tissues as a r esult of light-cur ing shrinkage or the substances that harden resinous mate-rials. Some researchers report that mild transitional histologic pulp changes may occur even after the use of simple professional bleaching (home bleaching tr eat-ment for 2 w eeks with 10% c arbamide peroxide) ( Pohjola and colleagues, 2002 ). Th ese fi ndings can easily be explained by the fact that such agents open pr efer-ential channels in the enamel and dentin, thus creating structures that allow semidirect contact with the vulner-able dental pulp ( Figures 4-43 and 4-44 ).

Figure 4-43 Initial image.

Figure 4-44 Outcome of home bleaching treatment with the custom tray technique and 10% carbamide peroxide.

Th e aim of this section is to pr ovide tools that c an help manage dentin and pulp pr otection after caries removal and before fi nal restoration.

When dealing with dir ect or indirect restoration in the lateral sectors of the mouth using esthetic adhesiv e materials, the c linician must address three basic problems:

• Dentin and pulp pr otection after removal of primary or secondary caries

• Prevention of postoperativ e dentin-pulp h yper-sensitivity

• Esthetic and functional restoration of the occlusal morphology with r espect to the basic cr iteria of occlusion

163


Th e fi rst two points are addressed in this section, and we will try to clarify these aspects, providing guidelines to improve the c linical success rate. For the last point, the reader is referred to Chapter 10 on direct and indi-rect restorations.

To simplify the pr ocess, we will descr ibe a c linical case from start to fi nish to illustrate all the phases of a direct restoration, going step by step.

DIRECT RESTORATION WITH PULP-DENTIN PROTECTION OF TWO CLASS I CAVITIES WITH ESTHETIC ADHESIVE MATERIALS

Th e teeth to be treated are two lower molars exhibiting primary carious lesions of the occlusal surfaces on clini-cal examination ( Figure 4-45 ).

Figure 4-45 Occlusal view of two lower molars with primary carious lesions.

Figure 4-46 The radiograph taken with the parallel-beam technique shows the extent of the carious lesions of both teeth.

If the diagnostic examination had been limited to simple clinical observation, the extent of the lesion would easily have been under estimated because the lesion ’ s invasiveness is appr eciable only with a radio-graphic examination ( Figure 4-46 ).

In fact, the periapical radiograph — taken with a Rinn holder and using the parallel-beam technique — shows that the lesions aff ecting the tw o teeth ar e deep and involve large portions of dentin, subjecting the pulp to inevitable infective stress from bacterial contamination. Nevertheless, it is impor tant to underscore that of ten such deep lesions can be completely asymptomatic and are detected only during a checkup. It is known that the lack of symptoms is a favorable condition for the entire tooth-restoration complex. Figure 4-47 shows the cavity outline prepared using a coarse c ylindric diamond bur mounted on a r ed-band reduction contra-angle hand-piece, after proper isolation of the operativ e site with the rubber dam.

Th e bottom of the c avity looks dar k and irr egular, and it is easy to distinguish the sc lerotic dentin, which cannot be consider ed healthy and fr ee of infectiv e agents.

Examination of the undermined dentin should be careful and accurate. When the dentin is soft on tactile examination, it should not be removed with a rose-head bur cutter mounted on a blue-band contra-angle hand-piece, but only with shar p sterile manual exc avators, used very carefully until the infected tissue has been removed completely ( Figure 4-48 ).

After complete manual and mechanic al removal of the infected dentin, the cavity is cleansed, with no mac-roscopic bacterial residua ( Figure 4-49 ). Scanning elec-tron microscope (SEM) observation ( Figure 4-50 ) reveals the high level of clinical cleansing and a count-less number of “ open routes ” (dentinal tubules) that must be c losed to ensur e a per fect seal, a good bond between tooth and r estoration, and defi nitive isolation of the pulp.

Th e dentin and borderline enamel can then be con-sidered ready for initial disinfection, which m ust be followed by chemical decontamination to dissol ve the last bacterial remnants and the smear lay er in the fi rst few microns of the dentinal tubules that hav e been cleansed mechanically. Aqueous solutions are used for this purpose, applied with ster ile cotton pellets soaked in a benzalkonium chloride – based disinfectant or sub-stances containing Cetr exidin or 0.2% chlorhexidine; 37% orthophosphoric acid gel is applied afterward with a syringe for 30 seconds on the dentin and 40 seconds on the peripheral enamel of the c avity ( Figure 4-51 ).

164


Manual Removal of Deep Car ious Dentin

Why should removal of deep carious dentin be carried out only with manual excavators?

Because this prevents the bacteria nested in the carious tissue from spreading to the deep lay ers owing to the fast r otary motion impressed by the mechanical strength of the bur.

Th e latter would permit invasion of the dentinal tubules in the dentin-pulp dir ection, as shown by the SEM microscope image.

Dentinal tubules completely invaded by the bacteria responsible for the infection. It is easy to understand how these “ routes ” invaded by bacteria can rapidly lead the infectious agents toward the pulp, triggering the full sequence of infl ammatory processes that can cause pulpal hyperemia complicated by possible irreversible pulpitis. (Courtesy Professor E. Milia, University of Sassari, Italy).

Th e steps described previously are followed by thor-ough rinsing with water for at least 15 seconds to remove any acid residue. Th is completes the etching of enamel and dentin. Th e drying step, which should always follow rinsing, should be c areful and pr ecise, avoiding

overdrying to allow the chemical agents of the adhesive systems to maximize their binding to the biologic struc-tures being prepared. Th e basic concept is that or tho-phosphoric acid-etched dentin and enamel should not be excessively dried but should be slightly moist to allow

Th e Elastic Adhesive Base as Cavity Coating

Left, From top to bottom, we can observe the layers of composite resin and adhesive that interconnect with the tubular structures, providing adhesion, sealing, and protection of the pulp. Right, Intrapulpal terminals of nerve fi bers that surround the basal poles of the odontoblasts. (Left, Courtesy Professor M. Gagliani. Right, Courtesy Dr. E. Tosco. )

CompositeComposite

AdhesiveAdhesive

Hybrid LayerHybrid Layer

Dentin andDentin anddentinal tubulesdentinal tubules

Composite

Adhesive

Hybrid Layer

Dentin anddentinal tubules

Using the elastic adhesive base as cavity coating is a simple and fast method that pr ovides the following:

• Perfect fi lling of all recesses and undercuts. • Control over the formation of air micr obubbles

that could trigger unwanted contraction of the nerve fi ber, the coronal extension of the ner ve plexus that covers the odontoblasts. It seems that these small anatomic str uctures contract into the peritubular space via a hydropneumatic mechanism called the

“ pumping eff ect ” — described years ago by Br ä nnstr ö m — stimulated by the pressure exerted by the occlusal forces. Th is triggers a painful, immediate, punctiform nerve stimulus that can impede the masticatory function.

• Protection of pulp and dentin in a single step , preparing the cavity to receive direct or indirect conventional or adhesive material to be used for conser vative restoration of the tooth.


Enamel and dentin conditioning and applic ation of the enamel-dentin adhesive are followed by the light-curing phase, carried out with halogen lamps — preferably the latest generation — that exploit light energy in diff erent ways according to clinical needs and timing (to examine the chemical-physical properties of these procedures, see the section entitled “ Light-Curing Units ” by Massimo Gagliani and colleagues). For the clinical case presented here, a light-emitting diode (LED) light source was used in a soft-start mode at 650 mW/cm 2 for 10 seconds for each tr eated surface (see Figure 4-52 ).

Once the fi rst seal was obtained by applying adhesive systems, the inner lining of all exposed dentinal surfaces was performed. Th is operation should be carried out only with adhesive materials. Currently, the most accepted procedure calls for placing a 0.5-mm fl uid composite layer

the hydrophilic substances contained in most adhesiv e agents to interconnect properly with the speciall y pre-pared biologic structures.

Th e steps that follow acid etching ar e critical and diff er according to the type of adhesive system used (see the section entitled “ Innovations in the Field of Dental Adhesion ” by Paolo Ferrari and Lorenzo Breschi).

In the c ase in question, a tw o-step system was employed, encompassing — after application of or tho-phosphoric acid — rinsing, partial drying, and condi-tioning of enamel and dentin surfaces with a fl uid agent that serves as a pr imer and bonding agent.

Th e mechanical placement of conditioning and adhesive fl uids is important. Consequently, it is best to use small brushes that, rubbed vigorously on the dentin for at least 40 seconds, ensure perfect penetration of the fl uids in the dentinal tubules ( Figure 4-52 ).

165

Figure 4-47 Cavities prepared and only partially cleansed.

Figure 4-48 Removal of deep carious dentin with a manual vanadium excavator.

Figure 4-49 Cavity cleansed after caries removal. It is advisable to disinfect the exposed dentin with sterile cotton pellets and liquid chlorhexidine for 1 minute.

Figure 4-50 Patent dentinal tubules ready to be sealed. (Courtesy Professor L. Breschi.)

Continued

166


Figure 4-51 Application of orthophosphoric acid (37%) on enamel (40 seconds) and dentin (30 seconds).

Figure 4-52 Application of primer plus bonding agent with disposable brushes (40 seconds).

Figure 4-53 Light curing with halogen lamp for 40 seconds in each cavity.

Figure 4-54 The elastic base should be applied using the appropriate clinical technique: magnifying glasses or microscope, rubber dam, and probe in order to spread the fl owable composite on the bottom of the cavity. The nerve fi ber extensions around the odontoblasts must be blocked in order to prevent their activation as a result of the “ pumping effect ” responsible for postoperative occlusal pain.

( Dietschi and S preafi co, 1997 ) on the bottom of the cavity with a long and pointed explorator y probe ( Figures 4-53 and 4-54 ) in order to completely “ line ” all the dentin pr eviously treated by means of adhesiv e systems.

Th e following steps are aimed at completing the res-toration, which can be direct or indirect.

In this case we opted for the former , and the teeth were restored with composites accor ding to the ana-tomic multiple lay ering technique to obtain the ideal anatomy of the teeth, respecting bioesthetic and func-tional principles as w ell as occ lusal and gnathologic aspects ( Figures 4-55 to 4-60 ).

To provide exhaustive information on this c ase, we have illustrated the direct restoration phases, performed with hybrid microfi lled composite placed in the cavities in multiple layers alternated with light curing, with the layering technique. Th e deeper layers of the c avity are restored with opaque and dar ker dentinal masses, fol-lowed by increments of transpar ent enamel moving toward the occlusal portions.

Small amounts of characterization materials can also be used and ar e placed deepl y among the masses of dentin and enamel in or der to confer gr eater trans-lucency and enhance the esthetic qualities of the restoration.

167


COMPOSITE PLACEMENT WITH THE MULTIPLE LAYERING TECHNIQUE

Figure 4-55 The fi rst layer of composite is placed in the cavity in an attempt to restore the morphology of the mesio-buccal cusp. At this stage, visual recall of the tooth before the removal of carious tissue and of the condition of the other teeth is important. Simple observation of the anatomy will determine decisions on cusp inclination and the depth of the occlusal fossae.

A B

A B

C

Figure 4-56 Characterization of the fossae. It is advisable to place the pigmented resin with a very sharp probe that allows proper application of the characterization material, which will be placed only at the pits and/or fi ssures areas.

Continued

168


Figure 4-57 Completion of anatomic shaping through the placement of dentin and then enamel masses. Each layer is light cured for 20 seconds. The last polymerization step (1 minute) may be performed by covering the occlusal surface with a glycerin gel to achieve more complete hardening of the composite in the absence of oxygen (Roulet, 1991).

A

B

C

Figure 4-58 Occlusal check of centric and lateral contacts with articulating papers (40 microns thick). If needed, the touchups can be performed with fi ne-grain diamond burs, preferably mounted on a red-band reduction contra-angle handpiece.

A

B

C

169


Figure 4-59 Direct midsize composite restorations require operating times that are 20% to 50% compared with silver amalgam restorations (Osborne, 1991). These times are needed to ensure adequate protection of pulp and dentin, restore proper functional morphology, and check postoperative sensitivity.

A B

Figure 4-60 The black-and-white image, without the chromatic effect, shows the precision of the dental anatomy accuracy in its fi nest details.

170


Occlusal Anatomy: A “ Biofunctional ” Problem or a “ Cultural ” One?

Neutralization of postoperative sensitivity is a biofunctional problem, whereas the type of restoration depends strictly on the cultural approach. Indeed, if the dentin and pulp ar e well protected, then the same pr inciple should also apply to the remaining occlusal part of restoration. Increments should consist of small amounts of material placed sequentially inside the cavity, always followed by light curing, and alternating the use of enamel, dentin, and clear masses of composite. Th e current means, technologies, and materials yield good results.

In recent years, the layering technique has been sim-plifi ed enormously. Many authors r ecommend placing no more than three layers of composite resin above the inner coating made with an elastic base of fl owable composite.

Th is makes it possible to obtain a sur face morphol-ogy that meets functional principles. Light-curing pig-ments can be added to the design of gr ooves and pits.

DIRECT PULP CAPPING WITH ADHESIVE TECHNIQUES

So far w e have detailed the curr ent direct techniques with composite for pulp and dentin pr otection during restoration of a tooth aff ected by primary caries. A possible complication is pulp exposur e during caries

Figure 4-61 A, Accidental exposure of the coronal-most portion of the vital pulp of an upper third molar after cavity preparation. Clinical view (B) and optic microscope image (C) ( Mj ö r, 2002 ).

removal or preparation of the deep dentin. What is the best way to proceed?

Direct exposure of the pulp during cavity preparation is a very common iatrogenic event in restorative den-tistry, an occurrence that requires a swift decision by the operator ( Figure 4-61 ), who must choose between the following:

• Root-canal treatment • Actions to protect the exposed pulp, also choosing

which methods and/or mater ials to employ It is impor tant to note that if the patient does not

report a set constellation of sy mptoms such as diff used and irradiated pain, especially if exacer bated by hot stimuli and/or mild per cussion of the tooth; repeated pain after intake of hypertonic substances such as sugar or particularly salty foods; or change in the pain inten-sity between the supine and standing position — all of which are events that indic ate toxic-infective involve-ment of the pulp — it will be possible to pr otect the exposed pulp b y direct capping with appr opriate materials.

Th ree materials are most commonly used in r estor-ative dentistry to protect and promote repair phenom-ena at the pulp exposur e area:

• Calcium hydroxide – based materials (powder, paste, self-hardening paste af ter mixing with catalyst)

• Adhesive systems • MTA-based materials Th e dentist will perform direct pulp capping using the

most suitable of these thr ee materials in the following circumstances:

• If in the pr eoperative phase the patient did not report any pain at the tooth in question that might

A B C

171


suggest recent pulp involvement, such as thermal sensitivity (generalized pain after intake of hot or cold substances), or pain af ter intake of h yperos-molar substances (ov erly sweet or salt y food or drinks), or pain in response to pressure (percussion or strong mastication forces)

• If the pr eoperative radiographic image does not show evident penetrating caries in the deep dentin adjacent to the pulp

• If the operative site is per fectly isolated through proper placement of a rubber dam to control per-colation of harmful substances such as plaque , saliva, and/or blood, and good disinfection of the pulp and health y residual dentin has been per-formed with appropriate means such as a chlorhex-idine solution

Figure 4-62 Bur in action during cavity preparation.

Figure 4-63 Selective etching of enamel and dentin with orthophosphoric acid at different concentrations.

Figure 4-64 This histologic section shows the thin dentin layer of tissue between cavity and pulp, which is about to be affected by bacterial infection. (Courtesy Dr. E. Tosco, University of Ancona, Italy.)

Dentin

Cavity

Pulp

At this point a distinction m ust be made. In the past many sources attributed the cause of pulp

infl ammation to var ious cofactors, such as the use of rotary instruments that could irremediably overheat the pulp ( Figure 4-62 ), chemicals such as orthophosphoric acid or other substances contained in cements, and/or common preparations in contact with the dentin and/or enamel ( Figure 4-63 ).

However, it is now co mmonly known and pr oven that the real cause of pulp infl ammation is invasion b y bacterial contaminants ( Figure 4-64 ).

Dentin that is invaded by bacteria or caries leaves no hope for maintaining pulp vitality, even in a very young tooth (see the c linical case illustrated in Figures 4-65 to 4-68 ).

172


Figure 4-65 Tooth of a very young patient in which — despite the absence of symptoms and isolation of the operating site with a rubber dam — any pulp capping treatment is contraindicated owing to the high bacterial invasiveness of the carious lesion.

Figure 4-66 Preoperative radiologic image of the tooth. The radiograph shows the temporary restoration material covering the large carious lesion. Note the area of coronal radiolucency, unequivocal signs of the decay that involves the pulp chamber. The probability of bacterial invasion of the pulp is very high.

Figure 4-67 After receiving the fi rst medication, the young patient could not be recontacted. A few months later she returned to resume treatment, and the radiologic examination performed at that time showed a midsize periapical lesion at the mesial root of the fi rst permanent molar, which proved the necrosis of the pulp. A root-canal treatment performed immediately with traditional techniques resolved the periapical osteolytic process.

Figure 4-68 The following checkup, 12 months later, showed good healing of the periapical lesion, justifying resumption of the treatment plan for the fi nal restoration. Note the physiologic development of roots of the adjacent teeth, which did not sustain any iatrogenic insult.

CASE PRESENTATION

173


MATERIALS FOR DIRECT PULP CAPPING

In restorative dentistry there are three schools of thought regarding the br oad term of “ direct pulp capping ” if one m ust protect the pulp with accepted methods and mater ials. Th e fi rst suggests the use of calcium hydroxide; the second, which emerged in the early nineties once adhesiv e systems were perfected, is called direct pulp capping with adhesiv e techniques; and the third employs MTA-based materials. To date, I have not used MTA for this pur pose, although it has been approved by the U.S. Food and D rug Administration (FDA) for dir ect pulp c apping and as permanent medication.

Based on current knowledge, I prefer to use a single type of mater ial — from contact with the pulp to the fi nal restoration, and on the basis of c linical and scien-tifi c facts — that when applied corr ectly has long pr o-duced very satisfactory results, confi rmed above all by close monitoring over the years.

Until a few years ago c linical dentistry chiefl y pro-tected the dentin areas in proximity and in direct contact with the pulp using mater ials containing c alcium hydroxide. Th anks to the scientifi c experiments brought to the c linical forefront by studies conducted b y the Scandinavian and U .S. schools in the se venties and eighties by Br ä nnstr ö m, Cvek, Mijor, Bergenholtz, and others, the dental w orld has al ways been or iented toward the safe use of these methods applied to protect the dentin and exposed pulp (see the sectio n entitled “ Protection of the P ulp ” by Davide P ansecchi, which covers the topic extensively).

At the same time , it is inter esting to anal yze the contribution of some U.S. schools on the use of adhesive materials to protect the exposed pulp.

Th e early nineties mar ked the thir d adhesive revolution — the fi rst was the clinical introduction of the etching concept ( Buonocore, 1955 ); the second the creation of Bow en ’ s resin (1961), which, applied af ter the etching agent, allowed the chemic al-mechanical bonding between dental surfaces and composites — with the rise of thr ee-step dentin adhesiv es. Th is demon-strated the possibilit y of etching both enamel and dentin to impr ove biologic, chemical, ultrastructural, and, above all, adhesive conditions, revealing new clini-cal landscapes considered inconceivable until then.

We are referring to the possibilit y of placing in contact with the deep dentin, and therefore the dentinal tubules, acidic substances such as orthophosphoric acid or others that, thanks to the conditioning of the fi rst microns of exposed tubules, create an adhesiv e mesh

known as the “ hybrid layer ” (for further information see the section entitled “ Innovations in the Field of Dentin Adhesion ” by Paolo Ferrari and Lorenzo Breschi).

After the de velopment of adhesiv e systems that in turn underwent further classifi cations and changes, always aimed at ensuring better and more extensive use by clinicians, many researchers focused on the c linical use of these mater ials to ensure protection and a good seal of the deeper lay ers of prepared dentin.

It is interesting to note that in the second half of the nineties the team fr om the Univ ersity of Alabama in Birmingham, coordinated by Professor Cox, com-mented that the clinical use of calcium hydroxide, valid as it may hav e been, had been r endered obsolete b y adhesive systems, considered to be protective materials for pulp and dentin ( Cox and co-workers, 1996 ) ( Figure 4-69 ).

Statement of Use of Calcium Hydroxide ( Cox and Colleagues, 1996 )

Benefi ts • Bactericidal and bacteriostatic • Excellent endodontic medication • Neutralizes the low pH of cements • Stimulates cellular enzyme systems • Halts internal resorptions • Stimulates healing and reparation of the dentin

because of high pH • Acts as a good temporar y cement • Inexpensive

Figure 4-69 This image, courtesy of Professor C. Cox, highlights a fl aw in the dentin bridge after degradation of calcium hydroxide.

Dentin

DB

ZnO

Ca(OH)2

174


Disadvantages • No biologic role in the stimulation of primary

dentin • Not the only stimulus for formation of the

dentin bridge • No biologic role in the stimulation of secondary

dentin • Not the only stimulus for sclerosis of the tubules • Does not stimulate apexifi cation or root

development • No adhesion to vital dentin • Deteriorates during amalgam condensation • Etching acids degrade its inter face • Deteriorates 1 to 2 y ears after placement • Can be found in the pulp cells 2 y ears after

pulp capping • Often associated with secondar y caries • Undergoes degradation with occ lusal loads

Th e histologic image in Figure 4-70 shows the dete-rioration of the calcium hydroxide protective base, with pathologic infi ltration responsible for the infl ammatory reaction of the odontoblast lay er, which w ould favor the spread of the lesion to the whole pulp ( Cox and colleagues, 1996 ).

Th e histologic section in Figure 4-71 demonstrates that a good seal achie ved with the careful use of adhe-sive resins and composite mater ials can encourage the formation of a dentin bridge between the exposed pulp and the cavity base. Th is represents the desired result in any clinical case without previous pathologic conditions of the pulp, and where the best c linical approach is to maintain tooth vitality. Extensive literature supports the validity and eff ectiveness of direct capping with etching and composite r esins, underscoring formation of the dentin bridge; the studies of Niinuma (1999) , White and co-workers (1994) , and Ciavarelli and co-workers (1999) support this thesis, whereas other authors, such as Cehreli and colleagues (2000) have a diff erent opinion.

Some scientifi c papers hav e reported satisfactory results after placement of adhesive materials on exposed noninfl amed pulps (Snuggs and colleagues, 1993; Kita-sako and colleagues, 2001 ). Th ese works have empha-sized the impor tant role of adhesiv es in pr eventing bacterial infi ltration at the tooth-r estoration interface, also attributing the successful outcome to the excellent seal obtained with composite r estorations.

Other researchers ( Gwinnett and Tay, 1998 ; Pamei-jer, 1998 ) obtained totall y diff erent and contrasting

Figure 4-70 The image shows how the calcium hydroxide allowed the formation of a tunnel through the dentin bridge (Db), resulting in infl ammation of the odontoblast layers, involving the deep pulp tissue. Pulp capping was performed with self-hardening calcium hydroxide: 2-year checkup. (Courtesy Professor C. Cox, through research collaboration with the Department of Restorative Dentistry, UCLA, School of Dentistry).

Pulp

Pathological cell reactionDb

TunnelCa(OH)2

Figure 4-71 Formation of the dentin bridge between composite restoration and pulp.

Pulp

Dentin

Dentin

Dentin bridgeComposite

results, reporting poor outcomes with the use of adhesive-resinous materials on the exposed pulps of monkeys and humans. Failures included the presence of active infl ammatory infi ltrations and the absence of the dentin bridge.

An important aspect that, despite the diff erent opin-ions (the pr esence or absence of infl ammation of the pulp subjected to dir ect capping with adhesive resins), is underscored by several researchers is that pulp infl am-mation after application of resins for direct pulp capping can be considered reversible and does not e volve into pulp necrosis ( Kitasako and colleagues, 2001 ).

175


I agree with the majority of researchers and clinicians on one thing: Infl ammation of the dental pulp is unquestionably a consequence of bacter ial invasion caused by microleakage and not by the type of material used for pulp capping ( Wataha and colleagues, 1994 ).

CASE REPORTS OF DIRECT PULP CAPPING

Here we describe clinical cases in which the pulp , exposed for diff erent reasons, was tr eated by capping with adhesive resins and other restorative materials.

DIRECT PULP CAPPING WITH TOTAL ETCH TECHNIQUE AND SILVER AMALGAM: 11 YEARS OF PULP VITALITY Figure 4-72 shows a sil ver amalgam r estoration on tooth 19 of a 13-y ear-old girl, performed as an emer-gency procedure in November 1996 at the Department of Restorative Dentistry of Polo San Paolo (University of Milan, Italy). Th e tooth did not exhibit specifi c dentinal-pulpal symptoms, despite the fact that the carious lesion was deep and penetrating. On removal of the carious tissue, during the fi nishing stage with manual excavators the mesio-bucc al pulp horn was accidentally exposed. After hemostasis of the exposed bleeding pulp was achieved by compression with sterile cotton pellets soaked in a 30-v olume solution of 10% hydrogen peroxide, the dentin was tr eated with an etching agent (37% or thophosphoric acid) for 40 seconds (20 seconds on the pulp). After extensive rinsing with water a pr imer and a bonding agent (All-Bond 2, Bisco) w ere applied accor ding to the

Figure 4-72 Direct capping with adhesive systems and silver amalgam (1996).

manufacturer ’ s instructions, and after light curing of the bonding material (40 seconds) a silver amalgam restora-tion (Phaesalloy) was applied. After shaping and fi nish-ing, the postoperativ e radiograph show ed penetration of the restoration material inside the pulp chamber and slight enlargement of the per iodontal space of the mesial root. Th e patient was seen again a week later for a checkup and to polish the restoration, and she did not report any abnormal sy mptoms. Th e fi rst radiographic and instrumental vitality checkup (pulp tester, Analytic Technology) took place 18 months after the fi rst inter-vention ( Figure 4-73 ), and the tooth that under went direct pulp capping did not show any sensitive or func-tional alteration.

From a radiologic standpoint, the tooth exhibits a radiopaque area at the apex of the distal c anal and cal-cifi cations, possibly of infl ammatory origin, from the stress sustained by the pulp.

Deciduous tooth shedding continued as expected, and the growth of permanent teeth was normal. During this period the patient did not r eport any pr oblem aff ecting tooth 19. Th e patient was regularly recalled for an annual radiologic chec kup and instrumental moni-toring of tooth vitalit y. Figure 4-74 shows that the lamina dura around the mesial root is perfectly restored. New carious lesions can be noted at the inter proximal spaces, revealing the patient ’ s high susceptibilit y to caries; she was advised to r esume restorative treatment at the hospital ’ s department of restorative dentistry.

Th e patient is under constant obser vation through annual checkups ( Figure 4-75 ). So far, the tooth that underwent direct pulp capping and silver amalgam res-toration has r esponded positively to vitalit y tests. Th e

Figure 4-73 Checkup after 18 months (1998).

176


Figure 4-74 Checkup after 5 years (2001). Pulp stability, new carious lesion.

Figure 4-75 Checkup after 11 years (2007).

radiographic examination does not show any pathog-nomonic sign of pulp-per iapical alterations.

TRAUMA OF A PERMANENT FRONT TOOTH IN A BOY Accidental traumas, particularly as a r esult of spor ts, typically lead to the loss of a tooth fragment, often complicated by exposure of the pulp . Th ese complica-tions are even more problematic when the tooth in question is permanent and is located in the front region in a young boy with many years ahead of him and thus high expectations in terms of both functio n and esthetics.

Nicola, aged 12, fell while skiing, and the ski hit his two front permanent central incisors. Th e blow was strong and hard. Needless to say, the coronal fragments could not be found in the snow , given their color. He was immediately taken to a dentist who w orked at the tourist resort, who applied emergenc y medication of reinforced zinc oxide – eugenol (Caulk IRM, Dentsply) ( Figure 4-76 ). Th e patient was then seen about a w eek after the trauma, and on that occ asion a per iapical radiograph was taken af ter his par ents provided informed consent. In the inter val between the fi rst medication and the visit the patient did not r eport any pathologic symptoms ( Figure 4-77 ).

Th e vitality of the tooth was checked via instrumen-tal examinations. At this point the r esponse could still have been a false positiv e, given the shor t amount of time that had elapsed since the initial trauma. Th e defi nitive assessment regarding pulp vitality or necrosis had to be postponed to a later chec kup (40 days).

After administration of anesthesia, the temporar y restoration was removed from the tooth ( Figure 4-78 ), revealing extensive exposure of the pulp with no signs of bleeding.

After the lesion was isolated with a r ubber dam, it was carefully disinfected (0.20% chlorhexidine solution without alcohol) ( Figure 4-79 ).

Th e tooth with the extensiv e pulp lesion was disin-fected and subjected to pulp capping in rapid sequence ( Figures 4-80 and 4-81 ). At the end of the fi rst session, the tooth was pr otected and sealed fr om the outside environment, which ensured a better seal than the pr e-vious emergency restoration ( Figure 4-82 ).

Impressions were taken with pr ecision impression material in or der to fabr icate — through diagnostic waxing — silicon templates for the dir ect restoration to be performed at the next appointment ( Figure 4-83 ).

Th e direct restoration was made with the anatomic multiple increment technique using masses of compos-ite, starting on the palatal side . Th e restoration was completed by layering diff erent composite colors, inter-posing characterization materials, and shaping the surface ( Figure 4-84 ).

Th e checkup showed satisfactory morphologic and chromatic recovery of the r estored tooth ( Figure 4-85 ).

Radiographic examination and electrical testing were performed 18 months later to assess the maintenance of vitality and the dentin-pulp seal achie ved via direct pulp capping with adhesive techniques and composite materials ( Figure 4-86 ).

177


Figure 4-76 Temporary medication of tooth 9 after trauma. Observation 1 week after the accident.

Figure 4-77 Radiograph. Note that the temporary medication covers the pulp exposed by trauma.

Figure 4-78 Removal of temporary restoration. Note the extensive exposure of the pulp.

Figure 4-79 Disinfection of the lesion.

Figure 4-80 Application of the etch and prime-bond adhesive system (LB 200, Kuraray Medical).

Figure 4-81 Coating with fl owable composite (Tetric Flow, Ivoclar-Vivadent).

Continued

178


Figure 4-82 Radiograph taken at the end of the fi rst session, after direct capping with an adhesive system and fl owable composite. Note the seal and the good radiopacity of the employed materials.

Figure 4-83 Second session. Two impressions were taken with precision materials and were used to manufacture a wax reconstruction of the missing portion. It was then used to create a silicone template as an aid for the palatal restoration of the tooth. A base color was also chosen. The tooth was restored with the direct technique using composite materials.

A B C

Figure 4-84 The direct restoration was performed by anatomic multiple layering technique using masses of composite, starting at the palatal side until complete restoration of the shape was achieved by layering the different composite colors. Right after removal of the rubber dam, which causes dehydration of the natural tooth, the color of the restoration looks different. It takes a few days to achieve good chromatic integration with the adjacent teeth.

A B C

179


Figure 4-85 The checkup shows satisfactory morphologic and chromatic recovery of the restored tooth.

Figure 4-86 Checkup after 18 months. Pulp vitality and maintenance of the pulp-dentin seal, obtained with direct capping with adhesive techniques and composites, were assessed at this time.

Guidelines for Direct Pulp Capping with Adhesive Techniques

1. Th ere must not be any endodontic sy mptoms at the time of the pr ocedure. Th e patient should not report any kind of sensitivit y of the tooth on which direct pulp capping will be performed.

2. Minor accidental exposures must be treated in a caries-free environment if possible.

3. Swift intervention is essential in the c ase of pulp exposure caused by trauma. Th e tooth and mucosa aff ected by trauma must be disinfected with chlorhexidine-based solutions.

4. Small areas of exposed pulp in y oung subjects have a better chance of healing .

5. Th e tooth must always be isolated with a rubber dam.

6. Obtain hemostasis of the exposed pulp through compressions with small ster ile cotton pellets soaked in a 30-v olume solution of 10% hydrogen peroxide.

7. Use three-step (etching acid + primer + bonding) or two-step (self-etch + bonding) adhesive systems.

8. Cover the exposed pulp tr eated with adhesive systems with a layer of fl owable composite.

9. Restore the tooth with dir ect or indirect techniques using composite or ceramic materials.

10. Perform periodic checkups: in the fi rst year a checkup at 6 and 12 months (x-ray examination and electric vitality testing, recording the values), followed by annual checkups with the same pr ocedures.

CONCLUSION

In addition to the c linical recommendations proposed in these guidelines, other scientifi c and clinical recom-mendations are excerpted from a book by Professor Ivar Mj ö r (2002) . A combination of factors play s a key role in successful direct pulp c apping. Biologic parameters should always be taken into consideration. With the introduction of adhesive resin – based materials for these procedures, the following factors should be taken into account during treatment planning:

180


1. Selection of the c ase is cr ucial. Pulp capping should be av oided when the pulp is infl amed. Dentists should av oid using to xic or allergenic materials that can trigger pulp reactions. Eugenol is a potent allergen and is also toxic when applied to soft tissues. Many r esin-based materials are allergenic, and some c an even be toxic. Calcium hydroxide mixed with water pr oduces necrotic areas when applied to sof t tissues, but minimal lesions in the pulp tissues. Th e healing potential is higher in y oung pulp compar ed with that of adults or elderly patients.

2. Calcium hydroxide used as a base and medication material has a long scientifi c and clinical history. Adhesives and composite materials can be placed directly on the pulp wound, and papers have been published that testify to healing af ter use of the total etching technique and adhesive resins on the exposed pulp. A favorable prognosis depends on simple and safe applic ation of the base mater ial. Th e long-term c linical experience in direct pulp capping with adhesive materials is not as vast as the literature about calcium hydroxide. Neverthe-less, increasingly encouraging e vidence is now being collected.

3. Th e fi nal restoration after direct pulp c apping should ensure a per fect seal to pr event bacterial infi ltration. Th is seal will be of paramount impor-tance until a pr oper dentin br idge has formed, guaranteeing impermeability. Zinc oxide – eugenol cements may be a valid temporar y barrier, but their physical properties are not suffi cient to guar-antee their use as defi nitive restorations. Properly applied composite mater ials may be consider ed valid defi nitive restorations. Th ese materials are especially recommended if the margins of the res-toration lie on the enamel. Considering that the same type of material can be applied from direct protection of the pulp thr ough defi nitive tooth restoration, it can be argued that such techniques make clinical procedures faster and safer.

When I r eviewed texts that hav e helped mold our scientifi c and clinical culture, with regard to restoration materials and dental pulp I found se veral clinical rec-ommendations proposed by Fabio Toff enetti (1983) that are still relevant today, and I would like to conclude this chapter by citing the suggestions of the fi rst presi-dent of the A ccademia Italiana di Conser vativa (AIC, Italian Academy of Restorative Dentistry):

• Perform an oral hygiene session before therapy. • Remove soft superfi cial infected dentin.

• Isolate the site. • Avoid reinfection by using c lean and ster ile

instruments. • Irrigate to prevent dehydration. • Use atraumatic burs. • Avoid pressure. • Work in short intervals. • Cool the burs with a water jet. • Carefully cleanse and disinfect. • Dry briefl y in a single step . • Apply a suitable cavity base. • Perform atraumatic restoration. • Use biocompatible restoration materials. • Shape the occlusion properly. • Finish without generating heat.

References Anderlini G : Modern guidelines for dental restoration , Bologna , 1994 ,

Chap VI. Preparazioni per restauri diretti. Edizioni Mar tina , pp 588-589 .

Bouillaguet S , Ciucchi B : Protection of the pulpo-dentin complex with adhesive resins .

Br ä nnstr ö m M : Dentin and pulp in r estorative dentistry , J Endod 1982 .

Cehreli ZC , Targut M , Olmez S , et al : Short-term human primary pulpal response after direct pulp capping with fourth-generation dentin adhesives , J Clin Pediatr Dent 25 : 65 - 71 , 2000 .

Cerutti A , Mangani F , Putignano A : Adhesive Aesthetic Dentistry — Educational Multimedia , 2007 , Quintessenze Int .

Ciavarelli L , De Fazio P , Scarano A , Piattelli A : Histological analy-sis of direct capping with enamel dentin bonding sy stem in vivo , J Dent Res 78 : 219 , 1999 . Abstract .

Cox CF , S ü bay RK , Ostro E , et al : Tunnel defects in dentin bridges: their formation following direct pulp capping , Oper Dent 21 : 4 - 11 , 1996 .

Dietschi D , Spreafi co R : Adhesive metal free restorations. Current concepts f or the esthetic t reatment of posterior teeth , 1997 , Quintessence Books .

Gwinnett AJ , Tay FR : Early and immediate time r esponse of the dental pulp to an acid etch technique in viv o , Am J Dent 11 : 535 - 544 , 1998 .

Kitasako Y , Shibata S , Pereira PNR , Tagami J : Short-term dentin bridging of mechanic ally-exposed pulps c apped with adhesiv e systems , Oper Dent 25 : 155 - 162 , 2001 .

Mj ö r IA : Pulp-dentin biology in restorative dentistry , Chicago , 2002 , Quintessence Books .

Niinuma A : Newly developed resinous direct pulp c apping agent containing calcium hydroxide (MTAYA-1-Ca) , Int Endod J 32 : 470 - 475 , 1999 .

Pameijer CH , Stanley HR : Th e disastrous eff ects of the “ total etch ” technique in vital pulp c apping in pr imates , Am J Dent 11 : 545 - 554 , 1998 .

Pohjola RM , Browing WD , Hickman ST , et al : Sensitivity and tooth whitening agents , J Esthet Restor Dent 14 : 85 - 91 , 2002 .

Prati C : Protection of dentin and pulp . Chap. 1 , pp. 17 - 26 .

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Riethe P : Caries prevention and conser vative therapy , Padua , 1992 , Piccin .

Roulet JF , Wilson N , Fuzzi M : Advances in operative dentistry , Vol. 1 , Milan , 2002 , Quintessenz Verlags-Scienza e Tecnica Dentistica Edizioni Internazionali .

Toff enetti F : La conservativa — Manuale Atlante. Materiali da ottura-zione e polpa , 1983 , Istituto per la Comunicazione Audiovisiva .

Vanini L , Mangani F , Klimovskaia O : Composites and adhesion. In: Th e restoration of anterior teeth , Viterbo , 2003 , Promoden .

Wataha JC , Hanks CT , Strawn SE , Fat JC : Cytotoxicity of com-ponents of r esins and other dental r estorative materials , J Oral Rehabil 21 : 453 - 462 , 1994 .

White KC , Cox CF , Kanka J III , et al : Pulpal response to adhesive resin system applied to acid etched vital dentin: dump versus dry primer application , Quintessence Int 25 : 259 - 268 , 1994 .

182

INNOVATIONS IN THE FIELD OF DENTIN ADHESION P. Ferrari and L. Breschi


Th e application of enamel-dentin adhesives is one of the basic procedures of every specialized branch of modern dentistry ( Osborne and S ummitt, 1998 ; Sharma and Roulet, 1998). Th ese products are used as sealants and for direct and indirect esthetic restorations, preendodon-tic treatments, cementation of posts and pr eprosthetic reconstructions, cementation of v eneers, crowns and bridges, periodontal splinting, bonding of or thodontic brackets, and treatment of dentin hypersensitivity.

Th e use of adhesiv es can be regarded as a phase of paramount importance, one of the most delic ate and crucial steps aff ecting the outcome of the r estoration.

Th e main functions of the adhesiv e system are as follows:

1. Sealing, in or der to permit corr ect long-term maintenance of the restoration

2. Distributing forces, to ensur e proper functional rehabilitation of the tooth

3. Opposition of separation, an essential feature for restorative material retention and to counteract shrinkage

Th e fi rst prerequisite for a proper approach to adhe-sive dentistry is correct isolation of the operativ e site, which can be achieved only with a rubber dam.

In fact, the literature shows that any contamination of tooth surfaces by bodily fl uids such as saliva, blood, or crevicular fl uids can create signifi cant problems in terms of the qualit y of the adhesiv e bond, drastically reducing bond strength ( Johnson and colleagues, 1994 ; Kaneshima and colleagues, 2000 ; Park and Lee, 2004 ).

Goals of Enamel-Dentin Adhesion ( Lutz, Krejci, and Oddera, 1996 )

• Retention and stability of the restoration • Counteraction and absorption of shrinkage stress • Perfect marginal adaptation without gaps and

microleakage • Hermetic sealing of the pulp-dentin complex • Reduction of postoperative sensitivity • Reinforcement of the restored dental structure

CLINICAL PROBLEMS AND APPLICATIONS

Th e main issues r elating to the applic ation of enamel-dentin adhesive systems are as follows:

1. Choice of adhesive system 2. Treatment of enamel and dentin, including scle-

rotic dentin 3. Drying procedure and moisture retention of the

substrate 4. Application techniques of the var ious products Before proceeding with an anal ysis of the var ious

clinical problems, it is fundamental to be familiar with the compositions and c lassifi cations of modern adhe-sives, in order to facilitate the dentist ’ s orientation in a fi eld that continues to e volve.

BASIC COMPOSITION OF MODERN ADHESIVES Modern adhesive systems call for thr ee basic phases ( Pashley, 1984 ; Van Meerbeek and co-w orkers, 2003 ; Acquaviva and co-workers, 2004 ):

1. Etching : Using an acid-etch conditioner to achieve surface demineralization by removing hydroxy-apatite and increasing free surface energy

2. Priming : Using an adhesion pr omoter (primer) aimed at increasing the wettability of the adhesive on the substrate

3. Bonding : Using a bonding agent (fl uid resin or bonding) that c an infi ltrate the substrate and create the actual bond

CLASSIFICATION OF ENAMEL-DENTIN ADHESIVES Th e classifi cation of enamel-dentin adhesiv es can be based on several factors including the following:

• Th e mechanism of action against the dentin substrate

• Th e number of c linical steps and products used • Th e type of solvent

Action on the Substrate With reference to dental substrate it is impor tant to mention the smear lay er, which consists of an

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amorphous layer that is 1 to 5 micr ons thick and is composed of organic and inorganic denatur ed debris, contaminants and bacteria deposited on the sur face of the tooth after the use of manual and/or r otary instru-ments ( Pashley, 1984 ). It is also important to remember that the smear layer has been reported on both enamel and dentin. Th erefore systems can be distinguished as follows ( Acquaviva and colleagues, 2004 ):

• Th ose that remove the smear layer • Th ose that dissolve the smear layer

Number of Clinical Steps and Products Used Th e most widely known and used classifi cation is based on the number of clinical steps involved ( Van Meerbeek and colleagues, 2003 ):

• Th ree-step systems: Th ree traditional separate and distinct steps — etching, primer, bonding.

• Two-step systems: Two steps, achieved by com-bining primer plus bonding or etching plus priming: • Etching, primer and bonding • Etching and primer, bonding

• One-step systems (one-component systems): Th e three solutions ar e combined in a single c linical application.

It should be underscor ed that, despite their name , one-component adhesives often require initial etching with a specifi c product and ar e not pur ely “ one-step ” systems. Similarly, many one-step sy stems are not all-in-one — that is, available in a single container and requiring mixing just before use.

As noted, the two-step systems are divided into self-etching and pr imer (combining the etching agent and primer) and self-priming and adhesiv e (combining the primer and bonding agent in a single solution).

Th e three-step systems — the oldest — are among the most widel y tested and w ell-known adhesives, and today they ar e still consider ed the gold standar d by many r esearchers ( Van Meerbeek and colleagues, 1998 , Van Meerbeek and colleagues, 2003 ; Acquaviva and colleagues, 2004 ; Breschi and colleagues, 2008 ).

Solvent Types

As far as solvent characteristics are concerned, adhesives can be distinguished as acetone-, alcohol-, and water-based adhesives ( Perdig ã o and colleagues, 2000 ). As we will see, this distinction has important clinical implica-tions, especially for drying of the c avity ( Perdig ã o and colleagues, 2000 ).

CLINICAL CLASSIFICATION

Th e previous distinctions and considerations allow us to draw up a c linical classifi cation that divides modern adhesives into four basic gr oups, which in turn form two broad categories: etch-and-rinse and self-etching. Th ere are also GICs, which, being self-adhesives, do not require separate adhesive systems and represent a sepa-rate group ( Van Meerbeek and colleagues, 2003 ; Acqua-viva and colleagues, 2004 ).

Th e fi rst category, etch-and-rinse, is characterized by total etching of enamel and dentin with a strong acid that can remove the smear layer and includes the following:

• Th ree-step etch-and-rinse systems, with three tra-ditional steps of etching agent, primer, and bonding agent, applied separately

• Two-step etch-and-rinse systems, also called self-priming adhesives, characterized by an etching phase similar to the thr ee-step systems, followed by an agent that combines primer and bonding in a single product

Th e second c ategory, called self-etching but recently also referred to as etch-and-dry ( Breschi and colleagues, 2008 ), as it is character ized by drying of the etching agent on the substrate and not by rinsing, encompasses adhesives that dissolve the smear lay er and simultane-ously infi ltrate the dentin. Th ese adhesive systems can be divided into the following:

• Two-step self-etching, characterized by an etching agent and pr imer combined in a pr oduct that should not be r insed (to pr event removal of the primer) but only dried; this means a step in which the bonding has to be applied and cur ed

• One-step self-etching, characterized by a sy stem that combines etching plus pr imer plus bonding in a single product (pure one-step, one-component system)

ETCH-AND-RINSE SYSTEMS Systems That Remove the Smear Layer Th e etch-and-rinse technique envisions total etching ( Fusayama and colleagues, 1979 ) — that is, the simulta-neous etching of enamel and dentin with a str ong acid (usually 35% to 37% orthophosphoric acid) — and subse-quent rinsing with water to remove the acid completely from the tooth surface. Th e acid function is exerted:

• On the enamel to remove the thin smear layer, or rather the debr is produced by manual or r otary instruments, and exposing sur face irregularities and the characteristic enamel prisms


• On the dentin to remove both the smear layer and smear plugs (plugs of debris that occlude the open-ings of dentinal tubules), and on demineralization of the dentin sur face by fl aring the tubule open-ings and exposing the collagen fi brils of the inter-tubular dentin

Th is group also comprises two categories of adhesive systems: three-step (etching, primer, bonding) and two-step (etching, primer + bonding) systems, depending on whether the primer and bonding agent ar e separate or combined. Both adhesiv e systems have a common etching phase.

Enamel Etching

Th e enamel etching technique dates to the mid-1950s. It was pioneer ed by Buonocore ’ s studies and is still employed successfully ( Buonocore, 1955 ).

Th e use of or thophosphoric acid leads to the formation of a thr ee-dimensional complex on the enamel surface, with a signifi cant increase in the ar ea available for bonding and fr ee surface energy, resulting in greater wetting and bonding capabilities ( Buonocore, 1955 ).

Th e use of orthophosphoric acid is recommended in concentrations from 30% to 40%. Th e recommended times range from 15 to 60 seconds; according to some authors the ideal time is 30 to 45 seco nds ( Barkmeier and colleagues, 1986 ; Cagidiaco and Ferrari, 1995 ).

Dentin Etching

Acid etching of the dentin sur face followed by rinsing leads to complete removal or dissolution and infi ltration of the smear lay er ( Nakabayashi, Kojima, and Masu-hara, 1982 ).

ENAMEL-DENTIN ADHESIVE CLASSIFICATION Three-Step Etch-and-Rinse 1. Etching 2. Primer 3. Bonding

Two-Step Etch-and-Rinse 1. Etching 2. Primer + bonding

Etching Primer Bonding

+ +

Self-Etching (Two Steps) 1. Etching + primer 2. Bonding

All-in-One (One-Step One-Component) 1. Etching + primer + bonding in a single application

Etching Primer + Bonding

+

Etching + Primer Bonding

+

Etching + Primer + Bonding

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185


With etch-and-rinse adhesives, the applic ation of orthophosphoric acid not only removes the smear layer, but it also demineraliz es a layer of surface dentin 3 to 5 microns thick by removing the inorganic component and exposing a mesh of collagen fi bers at the inter tu-bular and peritubular dentin level, which is an ideal area for micromechanical anchoring ( Figure 4-87 ).

Given the impor tance of the impr egnation process in determining bond strength and its stability over time, it is crucial to preserve integrity and prevent the collapse of this three-dimensional mesh because of maneuvers that cause excessive drying of the etched cavity. Several studies have shown that the mor e interfi brillar space

Figure 4-87 Orthophosphoric acid etching of enamel and dentin. The application of 37% orthophosphoric acid on enamel and dentin for 15 seconds removes debris caused by cutting instruments (mechanical or manual). The enamel surface changes from amorphous and poorly characterized (A) to the characteristic “ prismatic ” disposition of hydroxyapatite crystals (B). Application of acid on the dentin with smear layer (C) makes the tubules open and demineralizes intertubular dentin (D).

A B

C D

there is, the gr eater the bond str ength ( Pashley and Carvalho, 1997 ).

Infi ltration of the adhesiv e within the exposed col-lagen fi bers leads to formation of the “ hybrid layer ” or area of r esin-infi ltrated dentin ( Nakabayashi, Kojima, and Masuhara, 1982 ) ( Figure 4-88 ).

Ideally, the adhesive resin should be able to impr eg-nate the entire demineralized area. In the case of incom-plete impregnation the h ybrid layer will be par tially porous and is referred to as “ hybridoid. ”

Several studies have evaluated the eff ect of diff erent types of acids and applic ation times. Th e most widel y used is 35% to 37% or thophosphoric acid gel for 15

186


Figure 4-88 Formation of the hybrid layer occurs because of penetration of the adhesive between the collagen fi brils and within the dentinal tubules. A, Optical microscope image of the hybrid layer (HL) of Prime & Bond NT (two-step etch-and-rinse) that reveals the smooth adaptation to the dentin (D) and proper adhesion of the composite (C). B, Scanning electron microscope (SEM) images of Scotchbond 1 that show the formation of the hybrid layer (HL) and resin tags (RT) within the dentin tubules (D). C, SEM image of Peak SE Bond (two-step self-etching system) demonstrating that the formation of a proper hybrid layer (HL) and resin tags is easily achievable even without orthophosphoric acid etching. D, SEM image of Tri-S (one-step self-etching system) showing the formation of a thin hybrid layer (HL).

C

HL

D

A

C

RT

HL

D

B

C

HL

D

C

D HL

C

A

D

seconds. Th ere is extensiv e documentation indic ating that prolonged etching time does not incr ease bond strength, but instead cr eates an unstable h ybrid layer because the increased demineralization is not followed by adequate impr egnation of collagen fi brils ( Van Meerbeek and colleagues, 2003 ; Breschi and colleagues, 2008 ). Even the rinsing phase is of utmost impor tance

in order to remove the etching gel completely and avoid any silica residue (the aggregating agent required for the gel formulation) on the dentin sur face.

Th is is follow ed by drying (never excessive) of the dentin sur face and the applic ation of pr imer and bonding (as a single solution or in separate steps).

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Figure 4-89 A, Selective enamel etching (15 seconds). B, Total etching of enamel and dentin.

A B

Three-Step Etch-and-Rinse Systems: Clinical Application Etching

Th e etching gel is applied to the enamel sur face for 15 seconds, and then the dentin is etched for 15 more seconds ( Figure 4-89 ). Th e etched area must be rinsed thoroughly to remove any acid r esidue. Drying requires no special precautions because the subsequent application of the pr imer will ensure proper “ wetting ” (hydration) of the exposed collagen fi brils ( Pashley and Carvalho, 1997 ). Th e issues related to the treatment of the dentin after rinsing the etching agent chiefl y involve the diffi cult clinical monitoring of dentin moistur e level, and the choice of c avity drying methods and timing ( Figure 4-90 ). Distinctions in the type of cavity drying have to do with the characteristics of the solvent contained in the adhesiv e. It should be underscor ed, however, that often it is c linically diffi cult to assess the dentin drying method corr ectly and achie ve adequate

Figure 4-90 A, Total etching of enamel and dentin. B, Drying of the cavity.

A B

dentin moisture. Several authors hav e researched the problem of dentin dr ying, and various techniques have been proposed ( Kanka, 1992 ; De Goes and colleagues, 1997 ) including the following:

• Air syringe (for a few seconds) • Blotting paper (endodontic paper points) • Synthetic brushes • Pellets • Absorbent sponges • Rewetting : strong drying followed by rehydration

with a special aqueous solution (H EMA 35%) Th e procedure employing absorbent sponges seems

to be one of the most c linically eff ective in achieving a constant level of dentin moistur e ( Figure 4-91 ). Th e procedure that yields the worst results in terms of drying is the one that uses the air sy ringe.

Primer

Apply a copious amount of pr imer on the sur face, ensuring uniform coverage of the etched sur face.

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Figure 4-91 Drying of the cavity with an absorbent sponge.

Th e primer should be rubbed properly on the surface by applying it in several layers to ensure proper wetting of the cavity; this step is followed by drying to evaporate the solvent.

Th e material should be reapplied if there are “ chalky ” areas, as they should instead be shiny and c learly wet-table by the adhesive system.

Th e primer can be applied in m ultiple layers, and then air should be blown on it indir ectly for 3 to 5 seconds to remove any excess and allow the sol vent to evaporate ( Figure 4-92 ).

Bonding

Th e bonding agent should be br ushed inside the cavity and gently blown, taking c are to cr eate a thic k even layer. Th en it is gentl y air dried to allow the sol vent to evaporate before proceeding with the cur ing phase.

Figure 4-92 Application of primer.

Advantages and Disadvantages

Th ese adhesive systems have several advantages. Th ey can be used on diff erent substrates, including

metals and ceramics (by means of appropriate coupling agents).

Generally they can also be dual cured, which is useful in case of indirect restorations.

Th e most frequently reported disadvantages are the need for careful sequential application of the pr oducts and strict observance of the timing of the applic ation.

Adhesive Classifi cation Based on the Type of Solvent

• Acetone-based adhesives — Very moist dentin covered by a clinically visible fi lm of water ( wet bonding ) ( Kanka, 1992 ). Acetone is a highly volatile solvent, which tends to disloc ate the residual water during evaporation ( Perdig ã o and colleagues, 2000 ).

• Water-based adhesives — Dentin less humid, drier ( dry bonding ). Th e water in the adhesiv e is able to rehydrate the cavity.

• Alcohol-based adhesives — Intermediate drying, moist and glossy dentin.

Two-Step Etch-and-Rinse System: Clinical Application Etching

Etching is similar to that in the pr evious system, but it is important not to dry the etched dentin too much, in order to ensure adequate porosity of the substrate and thus facilitate the infi ltration of the collagen fi brils exposed by etching.

Primer and Bonding

Th e primer – bonding agent should be applied liberall y to attain uniform coverage of the etched surface. If there are chalky-looking areas, it should be reapplied, prefer-ably using a continuous brushing technique or rubbing the adhesive into the cavity in order to promote the best possible impregnation of the substrate.

Application of the adhesiv e should last at least 30 seconds to ensure proper impregnation, after which air should be blown to ensur e evaporation of the sol vent, after which it must be cured properly.

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Th e advantages of these adhesiv e systems versus the previous ones ar e their r elative speed and ease of clinical use.

Th e disadvantages are related to the fact that numer-ous studies have shown the following:

• Th ey exhibit lower adhesion values than the cor-responding three-step systems.

• Acetone-based adhesives can lose their eff ective-ness if part of the sol vent evaporates and if more layers are needed.

• Some systems are not compatible with self-curing or dual composites (composites for buildups and resin cements).

SELF-ETCHING ADHESIVE OR ETCH-AND-DRY SYSTEMS Systems That Dissolve the Smear Layer Systems that dissolve the smear layer are characterized by an etching agent that incor porates the primer (thus becoming a self-etching pr imer, two-step self-etching adhesive) or that combines the thr ee steps in a single clinical phase (one-step self-etching). Th erefore these systems should not be r insed after application in order to avoid removal of the pr imer.

Depending on the acidit y (low, intermediate, high) they dissolve the smear layer by infi ltration, but gener-ally they do not r emove it completely ( Van Meerbeek and colleagues, 2003 ).

On the enamel, self-etching systems produce diff er-ent changes depending on their pH ( Breschi and colleagues, 2003 ):

• pH greater than 4: Little or no modifi cation of the enamel.

• pH 2 to 4: Mixed pattern of etched and unetched areas.

• pH below 2: Th e surface pattern exhibits morpho-logic characteristics similar to those pr oduced by orthophosphoric acid.

Nevertheless, the fact that self-etching adhesiv e systems with a pH of less than 2 c an lead to a demin-eralization pattern on the enamel similar to that created by orthophosphoric acid fails to pr ove that the c linical effi cacy is comparable to that of the etch-and-r inse technique. Several clinical studies hav e consistently underscored that the use of 35% or thophosphoric acid leads to better adhesion on the intact nongr ounded enamel.

Two additional systems belong to this gr oup: • Two-step self-etching sy stems: also c alled self-

etching and pr imer systems; characterized by the association of etching and pr imer, followed by bonding

• One-step self-etching: one-component in a single step, using a solution containing all the ingredients


Th e advantage of these adhesiv e systems is the sim ul-taneous conditioning and impr egnation of the dentin, which simplifi es the clinical procedure, minimizing the eff ect of the operator and, above all, reducing postop-erative sensitivity.

Th e main disadvantage lies in adhesion to the enamel, which is not as eff ective and reliable as that obtained with systems using or thophosphoric acid. Th e clinical recommendation for ov ercoming this pr oblem is to perform selective etching of the enamel with 35% orthophosphoric acid (as in the etch-and-r inse tech-nique) and then apply the adhesive system on the pre-etched enamel and unetched dentin.

It should be noted that wher eas the etch-and-r inse adhesive systems are characterized by purely micro-mechanical adhesion to the dentin, the two-step self-etching systems have an additional chemical component owing to the bond between the residual hydroxyapatite on collagen fi brils and specifi c functional monomers contained in the adhesive mixtures.

Such chemical adhesion seems to play a key r ole in the long-term stabilit y of bond str ength ( Van Meerbeek and colleagues, 2003 ; Yoshida and colleagues, 2004 ; De Munck and colleagues, 2005 ).

Two-Step Self-Etching Systems: Clinical Application Etching and Primer

A generous amount of self-etching primer is applied to the enamel and dentin according to the time indic ated by the manufacturer, and then the excess is blown away gently. During application the continuous brushing tech-nique may be indicated to renew the acid on the tooth surface continuously.

Bonding

Th e bonding agent is applied b y creating a thick even layer on the c avity surface. Air is then blown gentl y in order to obtain an adhesive layer with a uniform thick-ness and to allow e vaporation of the sol vent. Proper curing is then per formed.

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Th e advantages of these adhesiv e systems are as follows:

• Very fast application, without the need for rinsing • Less postoperative sensitivity than with etch-and-

rinse adhesives • Excellent adhesion on normal dentin (but less so

on sclerotic dentin) • Possibility of self- or dual-cur ing systems Th e disadvantages include poor enamel etching if not

preceded by orthophosphoric acid.

One-Step Self-Etching Systems: Clinical Application Etching, Primer, and Bonding

Th e adhesive system should be rubbed on the substrate for 10 to 20 seconds accor ding to the t ype of system.

Th e application allows sim ultaneous demineraliza-tion, conditioning, and infi ltration of the tooth.


Th ese adhesive systems off er several advantages includ-ing the following:

• Quick and simple application • Minimal operator eff ect Th e disadvantages are as follows: • Poor adhesion to unprepared enamel • Poor in vitro adhesion both on dentin and enamel

compared with previous systems • Poor stability over time r esulting from aging of

the adhesive interface • Th e need for many lay ers in order to be eff ective • Incompatibility with self- or dual-cur ing systems It has recently been demonstrated that the low degree

of polymerization of this t ype of adhesive may be one of the causes of adhesion loss with aging .

It is advisable to incr ease curing time in or der to prolong the life and stabilit y of the adhesive bond.

SCLEROTIC DENTIN Sclerotic dentin is unquestionabl y not the ideal sub-strate for optimal adhesion. Th erefore several ways to improve the quality of the adhesiv e bond on this t ype of surface have been proposed to date.

Some authors r ecommend mechanical removal of the sclerotic portion with burs, whereas others suggest using an adhesiv e with a str ong acid such as 32%

to 35% or thophosphoric acid, in or der to pr oduce strong etching action ( Van Meerbeck and colleagues, 1994; Nakajima and colleagues, 2000 ; Cadenaro and colleagues, 2005 ).

SELECTING THE ADHESIVE SYSTEM

Th e choice of adhesiv e system can often be infl uenced by the constant marketing of newly developed advanced products and their highly touted adhesive properties.

Th e results of the studies, both in vitr o and in viv o, performed by the most accr edited researchers are of paramount importance, because without their suppor t it would become extremely diffi cult to choose a reliable system.

Other factors that can guide the dentist ’ s preferences are cavity size and the amount of enamel and dentin available.

Enamel : Dentin Ratio

• Small shallow cavity (prevalence of enamel) • Th ree-step etch-and-rinse system

• Wide deep cavity (abundant dentin) • Two-step self-etching system

• Endodontic cementation (dentin only) • Th ree-step etch-and-rinse system or self-

adhesive cement

For example, when dealing with a small shallow cavity (adhesion mainly on the enamel), the etch-and-rinse technique may be advisable , as etching c an easily be managed ( Figure 4-93 ). However, in deep c avities characterized by adhesion to the dentin it might be preferable to use a self-etching adhesiv e system, possi-bly with selective preetching of the enamel with ortho-phosphoric acid ( Figure 4-94 ), as ther e are fewer problems with cavity drying and product application.

Th e considerations for endodontic cementation ar e more complex, given the w ell-known problems with adhesion to intraradicular dentin ( Figure 4-95 ).

In this c ase, etch-and-rinse adhesive systems have shown higher adhesion values than self-etching systems. Moreover, it should be noted that pr omising results have been obtained with cementation systems based on the use of self-hardening cement or resin cements with self-adhesive properties because of the sim ultaneous presence of a glass-ionomer component.

191


A B

C D

Small Shallow Cavity Removal of the existing metal restoration and cavity preparation are followed by selective etching of the enamel for 30 seconds and subsequent dentin etching for 15 more seconds. After the gel has been rinsed away thoroughly, the cavity must be dried carefully, avoiding overdrying and aiming to maintain a certain degree of humidity. The adhesive is then applied (in this case, two-step etch-and-rinse) and cured. The layering of composite masses completes the restoration.

Figure 4-93 Example of small shallow cavity. A, Isolation of the operative site. B, Removal of the existing restoration and cavity preparation. C, Application of the etching agent on the enamel. D, Application of the etching agent on the dentin.

Continued

Continued

192


E, Drying of the cavity. F, Application of primer and bonding. G, Curing. H, Final restoration.

E F

G H

Figure 4-93, cont’d

193


Figure 4-94 Example of a wide deep cavity. A, Isolation of the operative site (rubber dam). B, Preparation of the cavity (large amount of dentin affected). C, Application of the matrix band and enamel-dentin adhesive. D, Layering of the marginal ridge. E, Final restoration.

A B

C

E

D

Wide Deep Cavity In a large cavity with a greater amount of exposed dentin, a two-step self-etching adhesive system may be indicated, possibly after selective enamel etching with orthophosphoric acid.

194


Figure 4-95 Adhesive cementation of endodontic posts. A, Application of the adhesive. B, Placement of the posts.

A B

Endodontic Cementation The etch-and-rinse technique is advisable for adhesive cementation of endodontic posts.

MAIN ERRORS AND THE OPERATOR FACTOR

Errors can involve the application of the etching agent, primer, or bonding agent and can be classifi ed according to the kind of adhesive system that was used ( Franken-berger and colleagues, 2000 ).

ETCH-AND-RINSE SYSTEM Etching and Primer Prolonged Dentin Conditioning, Over-Etching

Dentin etching times of mor e than 15 seconds lead to excessive removal of mineral matter and the exposur e of too many collagen fi bers with respect to the impreg-nation ability of the adhesiv e system. Th is implies the presence of exposed collagen fi brils within the h ybrid layer as a r esult of inadequate penetration of r esin monomers, leading to r educed bond strength and sig-nifi cantly increasing postoperative sensitivity.

Excessive Drying of the Dentin

Application of the adhesive on overdried collagen fi bers can lead to incomplete penetration and thus the forma-tion of a “ porous ” hybrid layer unsuitable for long-term bonding.

Numerous studies hav e shown that the bigger the interfi brillar space (r elated to the h ydration level of dentin), the greater the bond strength.

Instant Drying of the Primer

It is essential that the pr imer be lef t long enough to penetrate the collagen fi bers eff ectively and create the ideal condition for the subsequent bonding application. Generous application in multiple layers is always advis-able to ensure good impregnation of the etched dentin.

Excessive Drying of the Primer

Excessive drying can hamper pr oper adhesion; the dentin should be moist af ter etching to avoid the “ col-lapse ” of collagen fi bers (reduction of the interfi brillar space).

Inadequate Solvent Evaporation

After generous application of the bonding agent, the surface should be dried carefully to ensure proper evap-oration of the solvent.

SELF-ETCHING SYSTEM Excessive or Inadequate Enamel Etching

Several clinical studies hav e shown that var ious self-etching systems are unable to etch the enamel properly.

Th erefore we recommend selective preetching of the enamel with orthophosphoric acid, which signifi cantly improves the adhesion and stabilit y of the r estoration margins over time.

195


Inadequate Solvent Evaporation

It is essential to dr y the self-etching and pr imer agent properly (for the tw o-step adhesives) and r emove as much solvent as possible when w orking with one-step systems in order to improve the mechanical properties and reduce degradation of the adhesiv e interface over time.

GENERAL CLINICAL PROBLEMS Proper Mixing

It is impor tant to remember to shake the pr oducts to mix the var ious components pr operly. After use the containers should be c losed immediately to avoid the rapid evaporation of the solvent, which seriously under-mines adhesion. Proper handling of products is essential for the eff ectiveness of the adhesive bond.

Inadequate Curing

It is always advisable to incr ease the cur ing time with respect to the manufacturer ’ s recommendations in order to increase the degree of pol ymerization and improve the mechanical properties. Careful periodic inspection of the cur ing lamps is also essential ( Cadenaro and colleagues, 2005 ).

Incompatibility between Adhesive Systems and Bleaching Products

All whitening sy stems leave residual active oxygen in the dental substrate , which aff ects polymerization of dental adhesive systems and r esin composites. It is important to postpone adhesiv e restoration by at least 15 days after the bleaching pr ocedure has been com-pleted ( Breschi and colleagues, 2007 ).

Operator

Th e “ operator variable ” also seems to play an important role in the eff ectiveness of the adhesive bond. Some studies hav e shown that the applic ation of the same adhesive system by diff erent operators c an yield diff erent results in terms of bond str ength ( Ciucchi, Bouillaguet, and Russel, 1997 ; Frankenberger and colleagues, 2000 ).

DURATION OF BOND STRENGTH Th e adhesive bond is subject to change and degradation over time, which determine w ell-known clinical prob-lems such as pigmentation, marginal discoloration, the lack of a seal, and even the development of secondary

caries ( De Munck and colleagues, 2005 ; Breschi and colleagues, 2008 ).

Diff erent factors act on the var ious components of the hybrid layer to c ause the failur e of the adhesiv e interface.

In general, aging of the adhesive monomers and col-lagen fi brils can be noted ( Breschi and colleagues, 2008 ).

Among the phenomena that determine the degrada-tion of resin monomers, we can cite hydrolytic degrada-tion, or degradation of pol ymer chains af ter water exposure ( Hashimoto and colleagues, 2000 ). It has been noted that the greater the hydrophilicity of the adhesive system, the higher the degradation rate . Th e hydrophi-licity of adhesive systems follows this order:

1. One-step self-etching systems: More hydrophilic and therefore highly permeable and r eadily degradable

2. Two-step etch-and-rinse systems: Intermediate hydrophilicity and permeability, average stability

3. Th ree-step etch-and-rinse and tw o-step self-etching systems: Characterized by highly hydro-phobic bonding and thus low permeabilit y and high stability over time

Recent studies hav e also r evealed the pr esence of microscopic water bubbles on the adhesiv e surface (known as “ droplet phenomenon ” ) ( Figure 4-96 ), con-fi rming the hypothesis of the permeabilit y of adhesive systems, which behave like “ semipermeable membranes ” ( Chersoni and colleagues, 2004 ).

Because hydrolytic degradation depends on the intrinsic permeability of simplifi ed systems ( Breschi and colleagues, 2008 ), the duration of the inter face adhesive appears to be as follows:

Figure 4-96 The droplet phenomenon.

196


• Poor: One-step self-etching systems • Average: Two-step etch-and-rinse systems • High: Th ree-step etch-and-rinse and tw o-step

self-etching systems Other aging phenomena c an lead to degradation of

collagen fi brils that ar e not completel y hybridized ( Pashley and colleagues, 2004 ). Such fi brils can be attacked by the enzymes of the dentin matr ix (matrix metalloproteinases [MMPs]), whose activation seems ascribable to the applic ation of adhesiv e systems ( Mazzoni and colleagues, 2006 ). In fact, the release and activation of these enz ymes leads to pr ogressive thin-ning and disappearance of collagen fi brils, as shown by studies conducted both in vitr o and in viv o (Carrilho and colleagues, 2006, 2007a, 2007b ). It has r ecently been shown that the c linical use of chlorhexidine — a common antibacterial agent with inhibitor y properties against MMPs — applied as a pr imer on the etched dentin before adhesive application can prevent the destruction of collagen, contributing to maintenance of the bond ov er time ( Carrilho and colleagues, 2007b ; Breschi and colleagues, 2008 ).

CONCLUSION

Today dentine adhesion is still a constantl y evolving fi eld, and this underscor es the need for easy-to-appl y products with predictable long-term results. Th e three-step etch-and-rinse and two-step self-etching systems are the gold standar d in terms of adhesiv e bond stability.

Future research in the fi eld of enamel-dentin adhesion will also focus on monomers with pharmaco-logic properties such as antibacter ial monomers ( Imazato and colleagues, 2000 ), monomers with self-diagnostic properties from fl uorescent biosensors that can detect pH changes at the infi ltration site, and self-repair properties through the induction of remineraliza-tion and the formation of r eactive dentin ( Tay and Pashley, 2002 ).

Following are several tips for the correct use of adhe-sive systems:

1. Use an additional hydrophobic layer. Th e presence of hydrophilic monomers in simplifi ed adhesive systems (two-step etch-and-rinse and one-step self-etching systems) decreases the stability of the adhesive bond, and therefore it is always advisable to use an adhesive system that envisions a hydro-phobic layer to r educe water absor ption and stabilize the hybrid layer over time ( Breschi and colleagues, 2008 ).

2. Improve polymerization. Increasing the cur ing time of simplifi ed adhesive systems with respect to the manufactur er ’ s recommendation means better curing and permeabilit y reduction, with a good chance of impr oving the per formance of these adhesiv es ( Cadenaro and colleagues, 2005 ).

3. Use MMP inhibitors. It is belie ved that the use of metalloproteinase inhibitors, such as chlorhexi-dine, as primers on etched dentin can reduce deg-radation of the adhesiv e interface over time b y inhibiting the activit y of the dentin enz ymes responsible for the degradation of collagen fi bers ( Carrilho and colleagues, 2007a, 2007b ; Breschi and colleagues, 2008 ).

4. Improve impregnation of the adhesiv e compo-nent in the substrate . Diff erent ways to enhance impregnation of the substrate hav e recently been proposed, such as the extended application of the dentin adhesive system, more vigorous mechani-cal application of the adhesive with a microbrush, and the use of specifi c electrical impulses during adhesive application ( Breschi and colleagues, 2006 ; Pasquantonio and colleagues, 2007 ).

References Acquaviva GL , Breschi L , Di Lenarda R , et al : Adesione e adesivi

fra ricerca e clinica: stato dell ’ arte , Dent Mod 9 : 25 - 57 , 2004 . Barkmeier WW , Shaff er SE , Gwinnett AJ : Eff ect of 15 vs 60

seconds enamel and acid conditioning on adhesion and morphol-ogy , Oper Dent 11 : 111 , 1986 .

Breschi L , Cadenaro M , Antoniolli F , et al : Extent of polymeriza-tion of dental bonding systems on bleached enamel , Am J Dent 20 : 275 - 280 , 2007 .

Breschi L , Cammelli F , Visintini E , et al : Infl uence of chlorhexidine concentration on the durabilit y of etch and r inse dentin bonds: a 12-month in vitro study , J Adhes Dent (in press) , 2008 .

Breschi L , Mazzoni A , Pashley DH , et al : Electric impulse-assisted application of self-etch adhesiv es to dentin , J Dent Res 85 : 1092 - 1096 , 2006 .

Breschi L , Mazzoni A , Ruggeri A Jr , et al : Dental adhesion review: aging and stability of the bonded interface , Dent Mater 24 : 90 - 101 , 2008 .

Breschi L , Perdigao J , Lopes MM , et al : Morphological study of resin-dentin bonding with TEM and in-lens FESEM , Am J Dent 16 : 267 - 274 , 2003 .

Buonocore MG : A simple method for incr easing the adhesion of acrylic fi lling materials to enamel surfaces , J Dent Res 34 : 849 - 853 , 1955 .

Cadenaro M , Antoniolli F , Sauro S , et al : Degree of conversion and permeability of dental adhesives , Eur J Oral Sci 113 : 525 - 530 , 2005 .

Cagidiaco MC , Ferrari M : Bonding to dentin , Livorno , 1995 , De Batte O & F .

Carrilho MRO , Carvalho RM , Goes MF , et al : Chlorhexidine pre-serves dentin bond in vitr o , J Dent Res , 86 : 90 - 94 , 2007a .

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Carrilho MRO , Geraldeli S , Tay FR , et al : In vivo preservation of hybrid layer by chlorhexidine , J Dent Res 86 : 529 - 533 , 2007b .

Chersoni S , Suppa P , Grandini S , et al : In vivo and in vitro perme-ability of one-step self-etch adhesiv es , J Dent Res 83 : 459 - 464 , 2004 .

Ciucchi B , Bouillaguet S , Russel C : Dentin bonding b y general practitioners — Th e battle of the bonds. Part 1 , J Dent Res 76 , 1997 . (Abstract 981) .

De Goes MF , Ferrari Pachane GC , Garcia-Godoy F : Resin bond strength with diff erent methods to remove excess water from the dentin , Am J Dent 10 : 298 - 301 , 1997 .

De Munck J , Van Landuyt K , Peumans M , et al : A critical review of the durability of adhesion to tooth tissue: methods and results , J Dent Res 84 : 118 - 132 , 2005 .

Frankenberger R , Kramer N , Petschelt A : Technique sensitivity of dentin bonding: eff ect of applic ation mistakes on bond str ength and marginal adaptation , Oper Dent 25 : 324 - 330 , 2000 .

Fusayama T , Nakamura M , Kurosaki N , Iwaku M : Non-pressure adhesion of a new adhesive restorative resin , J Dent Res 58 : 1364 - 1370 , 1979 .

Hashimoto M , Ohno H , Kaga M , et al : In vivo degradation of resin-dentin bonds in humans ov er 1 to 3 y ears , J Dent Res 79 : 1385 - 1391 , 2000 .

Imazato S , Tarumi H , Ebi N , Ebisu S : Cytotoxic eff ects of compos-ite restorations employing self-etching pr imers or exper imental antibacterial primers , J Dent 28 : 61 - 67 , 2000 .

Johnson ME , Burgess JO , Hermesch CB , Buikema DJ : Saliva con-tamination of dentin bonding agents , Oper Dent 19 : 205 - 210 , 1994 .

Kaneshima T , Yatani H , Kasai T , et al : Th e infl uence of blood con-tamination on bond str engths between dentin and an adhesiv e resin cement , Oper Dent 25 : 195 - 201 , 2000 .

Kanka J : Eff ect of resin primer solvents and surface wetness on resin composite bond strength to dentin , Am J Dent 5 : 213 - 215 , 1992 .

Lutz F , Krejci I , Oddera M : Restauri estetici nei settori posteriori — manuale operativo , Zurich , 1996 , Verlag PPK .

Mazzoni A , Pashley DH , Nishitani Y , et al : Reactivation of quenched endogenous proteolytic activities in phosphoric acid-etched dentine by etch and r inse adhesives , Biomaterials 27 : 4470 - 4476 , 2006 .

Nakabayashi N , Kojima K , Masuhara E : Th e promotion of adhesion by the infi ltration of monomers into tooth substrate , J Biomed Mater Res 16 : 265 - 273 , 1982 .

Nakajima M , Sano H , Urabe I , et al : Bond strengths of single-bottle dentin adhesives to c aries-aff ected dentin , Oper Dent 25 : 2 - 10 , 2000 .

Osborne JW , Summitt JB : Extension for prevention: is it r elevant today? Am J Dent 11 : 189 - 196 , 1998 .

Park J , Lee C : Th e infl uence of salivary contamination on shear bond strength of dentin adhesive systems , Oper Dent 29 : 437 - 442 , 2004 .

Pashley DH : Smear layer: physiological considerations , Oper Dent 3 : 13 - 29 , 1984 .

Pashley DH , Carvalho RM : Dentine permeability and dentine adhesion , J Dent 25 : 355 - 372 , 1997 .

Pashley DH , Tay FR , Yiu CKY , et al : Collagen degradation by host-derived enzymes during aging , J Dent Res 83 : 216 - 221 , 2004 .

Pasquantonio G , Tay FR , Mazzoni A , et al : Electric device improves bonds of simplifi ed etch and rinse adhesives , Dent Mater 23 : 513 - 518 , 2007 .

Perdig ã o J , Frankenberger R , Rosa B , Breschi L : New trends in dentin/enamel adhesion , Am J Dent 13 : 25D - 30D , 2000 .

Sharma SJ , Roulet JF : Adhesion: the silent r evolution. 2nd Euro-pean Symposium on Adhesive Dentistry , J Adhes Dent 1 : 285 - 287 , 1999 .

Tay RT , Pashley DH : Dental adhesives of the futur e , J Adhes Dent 4 : 91 - 103 , 2002 .

Van Meerbeek B , Braem M , Lambrechts P , Vanherle G : Morpho-logical characterization of the interface between resin and sclerotic dentin , J Dent 22 : 141 - 146 , 1994 .

Van Meerbeek B , De Munck J , Yoshida Y , et al : Buonocore memo-rial lecture. Adhesion to enamel and dentin: current status and future challenges , Oper Dent 28 : 215 - 235 , 2003 .

Van Meerbeek B , Perdig ã o J , Lambrechts P , Vanherle G : Th e clinical performance of adhesives , J Dent 26 : 1 - 20 , 1998 .

Yoshida Y , Nagakane K , Fukuda R , et al : Comparative study on adhesive performance of functional monomers , J Dent Res 83 : 454 - 458 , 2004 .

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COMPOSITES AND GLASS-IONOMER CEMENTS Giovanni Dondi dall ’ Orologio


CLINICALLY RELEVANT PRODUCT UPDATES

Curing of polymer-based materials is associated with a volume reduction ranging from 1.5% to 6% ( Kleverlaan and Feilzer, 2005 ). Consequently, shrinkage problems have driven manufacturing companies to de vise new composites with a v olume contraction of less than 1% ( Weinmann, Th alacker, and G uggenberger, 2005 ). Composite polymerization produces internal str ess, which is considered more important than the dimen-sional change of the mater ial inside the c avity because it could lead to bond loss at the tooth-composite inter-face, cuspal defl ection, and enamel crac k, all of which are primary factors in the potential failur e of restora-tions ( Ferracane, 2008 ). Th e magnitude of stress depends on composite stiff ness, fl ow properties, degree of con-version, and the anchorage determined b y the adhesive system on cavity walls ( Kinomoto and Torii, 1998 ).

Complete polymerization of the mater ial is cr ucial for exploiting the best mechanic al properties of the material. Th e highest possible level of conversion (60% to 70%) is achieved by respecting the principle of energy density (mJ/cm 2 ) given by the power of the lamp unit at the distal end of the light guide for the duration of exposure, considering that adhesiv e systems require 8000 mJ/cm 2 , as do cer tain nanoparticle composites of the latest generation, whereas hybrid composites usually require 16,000 mJ/cm 2 (Sagaguchi and F erracane, 2001).

A lamp with a pow er of 400 mW/cm 2 thus needs a time of 20 or 40 seconds, respectively, to r each the energy density required.

Th e distance between the distal end of the light guide and the surface of the mater ial decreases the power by about 50% e very 10 mm ( Suh, 1998 ), which must be taken into account during curing of the occlusal surface of composites placed on the cer vical step. Transdental curing decreases the cur ing light intensit y fourfold to fi vefold ( L ö esche, 1999 ), which explains the excellent laboratory results achieved with the technique de vised by Lutz ( Lutz and Kr ejci, 1986 ), as incomplete

polymerization of the material because of loss of power during transparietal light curing reduces stress and thus permits better marginal fi t, albeit at the expense of the strength of the mater ial and thus the life of the restoration.

It is impor tant to r emember that the minim um curing time is 10 to 15 seconds — 20 seconds with the latest products — to allow the monomer chains to be transformed into polymers. On the other hand, a lamp with a power of less than 150 mW/cm 2 does not lead to complete polymerization even with longer exposure times. Th e studies of Versluis (1998) have shown that shrinkage moves away fr om the fr ee surface, going toward the walls wher e the composite is bound. Th e diff erent methods of composite lay ering — horizontal, vertical, and oblique — are designed to increase the free surface and decrease the C-factor, but there are no clini-cal or laborator y data available to indic ate the most appropriate technique. Versluis (1996) demonstrated that the bulk technique w ould instead lead to low er cuspal defl ection (from 20% to 50%). It is c lear that layers of composite up to 2 mm thick are required for better control over the mater ial and pr oper curing, whereas the pol ymerization of layers 3 mm thick can halve composite har dness (Knoop har dness number [KHN]) ( Versluis, Tantbirojn, and Douglas, 1998 ) owing to inadequate curing. Regarding the mechanical properties of composites, the literature reports a high degree of approximation. As noted, composites have an elastic modulus ranging from 13 to 27 GPa, consistent with that of dentin, which has a compr ession modulus of 14, a fl exural modulus of 30, and a tensile modulus of 18.5 GP a ( Van Meerbeek and colleagues, 1993 ; Craig, 1998 ), whereas the tensile modulus of compos-ites varies according to the fi ller but is far low er than that of dentin. For example, under stress-strain analysis ( Kleverlaan and Feilzer, 2005 ) Filtek Z100 exhibits a 3.5-GPa tensile modulus with 2.56% shr inkage and 23.5-MPa contraction str ess; Filtek Supreme has a tensile modulus of 3.7 GPa, 2.51% shrinkage, and 13.9-MPa contraction str ess; and Tetric Flow shows a


1.9-GPa tensile modulus, 4.9% shrinkage, and 7.6-MPa contraction stress. Th is demonstrates that higher fl owability — despite the higher shr inkage value — produces less str ess. Because of these character istics, many researchers have investigated the use of a deform-able liner that can absorb the stress ( Van Meerbeek and colleagues, 2001 ). Choi, Condon, and Ferracane (2000) observed that the use of a nonfi lled adhesive placed in very thick layers can decrease stress signifi cantly; Fer-racane (2008) showed that the use of a r esin-modifi ed glass-ionomer (RMGI) as a liner on the dentin reduces polymerization shrinkage stress of composites b y over 50%. Besnault (2004) reported that tr eatment with a self-etching adhesive before application of RMGI increases the bonding of cement on the dentin by about 50%.

Th e use of fl owable composite as a liner to reduce stress has also been tested, but there is no clinical evidence that such methods will enhance c linical

success rates ( Lindberg, Van Dijken, and Hoersted, 2005 ).

With regard to wear resistance, a recent highly quali-fi ed clinical trial ( Palaniappan and colleagues, 2008 ) shows that there is still a signifi cant diff erence between the behavior of the composite and the enamel, even if the features of the former hav e decidedly improved.

Product information of clinical relevance is provided by spectrophotometric analysis of composites ( Khurana and colleagues, 2007 ), where the ability to test samples of materials by assessing br ightness, hue, chroma, and translucency according to the parameters of the Inter-national Commission on Illumination (Commission Internationale de l ’ Eclairage [CIE]), allows us to con-sider as obsolete both the Munsell color system and the empirical methods of sample pr eparation, which leave the choice of color in the limbo of subjectiv e artistic sensibility with no scientifi c basis ( Figures 4-97 to 4-101 ).

199

Figure 4-97 Fracture of teeth 8 and 9.

Figure 4-98 Restoration of tooth 9.

Figure 4-99 Restoration of tooth 8.

Figure 4-100 Final result after polishing.

200


Figure 4-101 Spectrophotometric analysis.

A B

It is v ery diffi cult for the user to understand the conversion of color into numbers. Moreover, the shade guides of the same pr oducer (e.g., Vita) diff er greatly from one another — often dentin and enamel masses of the same product do not refl ect the natural color of the tissues, where the enamel is br ighter, less color ed, greener, and mor e translucent than the dentin — and even the same reference symbol (e.g., A3) for compos-ites of diff erent brands corr esponds to v ery diff erent colors in 90% of c ases. In fact, the same masses of dentin and enamel of tw o successive generations of composites of the same brand (such as S upreme-Supreme XT, 3M-ESPE) are visibly diff erent from each other ( d ’ Alanno and colleagues, 2006 ).

A further contribution to the diffi culty of translating into clinical terms the results of laboratory research was given by Heintze (2007) in a sy stematic review of the literature, which reached the shocking conclusion that bond strength is not r elated to micr oleakage or gap formation and that micr oleakage has no eff ect on increased sensitivity, marginal discoloration, and sec-ondary caries. For these reasons, the microleakage test should be eliminated. Heintze also noted that according to laboratory data, 13 out of 20 adhesive systems should not have attained c linical success, whereas the c linical data reported the failure of only 4 of these products. In short, the laborator y results do not confi rm the inter-mediate endpoints. As stated by Watts (2004) , the labo-ratory may pr ovide a basis for selection, given the complex preparation required by a clinical trial, but the reference for operativ e choices should be suppor ted only by the le vel of e vidence. According to the

American Health Car e Research Program (AHCRP; 1992) and the Centr e for Evidence-Based Medicine (CEBM; 2005), laboratory investigations have a le vel of evidence of 5, so they hav e no validit y or c linical predictability, and the same holds tr ue for expert opin-ions. Very low r elevance is also attr ibuted to studies classifi ed as c ase series, with a le vel of e vidence of 4, which are useful for gaining experience with a material or technique befor e starting a pilot study , a phase 2 clinical trial, or a study on a larger sc ale with a control group or phase 3 c linical trial.

Th e current clinical research guidelines w ere pub-lished in 1996 in the C ONSORT statement ( Begg, Cho, and Eastwood, 1996 ). Th e 22 points of the check-list permit the optimal organiz ation and development of the r esearch; the medic al journals with a higher impact factor (such as the New England Journal of Med-icine, BMJ, AMJ, and Th e Lancet ) readily adopted the new guidelines and r equire that at least some of the main parameters be met.

EVIDENCE-BASED DENTISTRY

A clinical trial is a prospective longitudinal study with a control group, with at least two operators acting on a group of patients selected according to strict criteria of inclusion and exclusion, with a sample size whose power is at least 80% for a super iority or equivalence study design with a preestablished minimal clinically impor-tant diff erence. Th e possibility of randomizing the study increases its qualit y, especially when the methods ar e devised by an independent monitor thr ough a design

201


tied to computerization and the use of sealed envelopes. Th e inclusion of an independent and blind examiner — better yet, two — with an intrarater and interrater agree-ment > 75% ensures greater objectivity. Th e application of hazard ratio parameters, absolute and r elative risk reduction, odds ratios, and 95% confi dence intervals (meaning that the researcher is confi dent that the values in the consider ed range will inc lude the r eal but unknown data for 95% of the population) makes it pos-sible to anal yze the r esults correctly. Based on these parameters it is easy to identify gr oss errors contained in certain articles such as that of Loguercio and col-leagues (2003) , who, in a randomiz ed double-blind clinical trial — therefore theoretically a level 1B on the evidence scale, with high quality — does not explain how the operator can be blind to two products, one being in a paste form (compomer) and the other in a pow der-liquid form (RMGI). Th e low number of r estorations at checkup (28 distributed among 10 patients) means a severe type II error (false negative), whereas it is stated that the diff erent retention between the two materials (78.5% versus 93%) is not statistic ally signifi cant.

Another frequent and err oneous citation is that of Skeeters (1998) , whose results after 15 years are reported to support the validit y of composites in the poster ior sectors. Th e abstract reports 59 Class I and I I restora-tions; the generalization of the fi gure, which does not specify the number of r estorations per c lass, in itself represents a signifi cant inaccuracy, implying the impos-sibility of determining the pow er of the sample . Th is gap is aggravated by the lack of specifi cation even at the 15-year checkup, for which the success of 19 r estora-tions out of 20 (95%) is r eported.

Th e small number of r estorations assessed b y the author means a study with low pow er. In addition, the high number of patients with restorations (40) who did not show up for the chec kup implies the w orst-case scenario, as if all the r estorations that could not be fol-lowed up were classifi ed as failures. Consequently the fi nal result is onl y 19 successes out of 59 r estorations (35%). For the same r easons, the r esults reported by Gaengler, Hoyer, and Montag (2001) after 10 years — a 74.2% success rate of the 194 initial restorations — must be downsized to 23.8%, because 24 failur es resulting from caries or prosthetic treatment with a cr own were disregarded, and 108 restorations were not followed up.

In recent literature, however, there are correct and important articles: those of Peumans (2007a) on the results at 5 y ears of tw o self-etching sy stems with or without enamel etching with or thophosphoric acid with 29 r estorations and 100 patients; and Peumans

(2007b) with the results at 7 years on the treatment of noncarious cervical lesions with the follow-up of 51 patients out of the initial 71, and 114 r estorations out of 142, with an overall success rate of 11% and annual success rate of 1.5%. Th e study by Van Dijken (2007) can also be mentioned, with the results at 13 years of a clinical trial comparing an etch-and-rinse system with a self-etching adhesiv e system, with follow-up of 98 patients out of the initial 119, and 275 restorations out of 337. Van Dijken ’ s study show ed 4.1% and 2.0% annual success rates for the etch-and-r inse system and the self-etching system, respectively.

GUIDELINES Th e ultimate goal of c linical research is to pr opose guidelines that are systematic recommendations aimed at helping clinicians and patients make decisions regard-ing specifi c clinical conditions on the basis of the following:

• Th e best evidence from clinical research • Evidence complemented b y clinical expertise

(experience plus knowledge) of the operator • Th e patient ’ s needs and rational pr eferences for

choosing the best treatment for the specifi c case According to the Amer ican College of Car diology,

which presented updates in 1995, 2001, and 2005, guidelines should be rational, accurate, objective, impar-tial, and timely. Guidelines can stem from expert opin-ions, consensus, and, above all, evidence.

Prospective cohort studies, clinical trials, and ran-domized clinical trials (RCTs) make it possible to suggest grade B le vel 2 r ecommendations in the fi rst two cases, and grade A le vel 1D (RCTs with at least 100 cases at follow-up) or higher (1C, 1B, 1A) recom-mendations for RCTs with 500 to 10,000 c ases.

Th e possibility of per forming systematic reviews of clinical trials makes it possible to achie ve the highest evidence level for the r esults. In this r egard, another rather unprofessional trend is to publish narrativ e reviews that uninformed authors report to support their theses and that careless readers translate into their oper-ative choices.

Torabinejad (2005) concisely but compr ehensively examined the diff erences between a narrativ e and a systematic review, in which the biggest discr epancy is the lack (in the former) of inc lusion and exclusion cri-teria without assessment of the evidence. Consequently, the fi nal results are a mixture of studies that c annot be compared with one another . A pr ime example is the narrative review performed by Manhart (2004) on the survival of direct and indirect restorations in posterior

202


sectors, in which pr ospective and r etrospective case series, cross-sectional studies, and c linical trials were evaluated using the same method. Recently, in the fi eld of restorative dentistry (Hickel and colleagues, 2004) there likewise seems to be a gr owing need for mor e scientifi c contributions. Suffi ce it to say that from 2004 to 2008 three RCTs, on average, on dir ect restorative dentistry were presented at the annual International Association for Dental Research conference.

TOXICITY

Regarding the dispute about the alleged to xicity of amalgam, which all national and international bodies and institutional committees have defi nitively ruled out, a further important contribution comes from two RCTs ( Bellinger and colleagues, 2006 ; DeRouen and col-leagues, 2006 ) with 507 children ages 8 to 10 years and 534 children ages 6 to 10 years, respectively, divided into two groups. Half were selected for amalgam fi llings and half for composite restorations, with an average of 18.7 amalgam surfaces versus 21.3 composite surfaces in the fi rst study and 15 sur faces of both mater ials in the second. After 5 years the neurologic and kidney evalu-ation of the tw o groups did not show any diff erences. A fi nal consideration is the need for pr oper analysis of political decisions that go against scientifi c evidence.

Th e article entitled “ Has Dental Amalgam Been Torpedoed and Sunk? ” ( Jones, 2008 ) discusses the ban in eff ect in Norway since January 1, 2008 on the use of amalgam fi llings. Th e ban was motivated by the irratio-nal attempt to divert media attention from the govern-ment ’ s belated response and inadequate measures after the discovery in 2003 of the wreck of a German U-864 submarine, sunk during World War II off the coast of Bergen in February 1945 with a c argo of 65 tons of mercury, and ther efore with enormous potential for pollution. In the ar ticle, Jones stated the following:

• A patient with 10 amalgam sur faces in his or her mouth would have a mer cury intake into the blood that would be only 2% of the World Health Organization ’ s Acceptable Daily Intake ( WHO ADI 40 mcg/day) for mer cury, with no adv erse health eff ects.

• Th e environmental impact of mer cury from 800,000 dental offi ces worldwide would represent 0.04% to 0.2% of the total w orldwide environ-mental mercury pollution from all sources.

Th e author ’ s conclusion that “ banning ‘ dental amalgam ’ is a politic al issue that will hav e no impact on total w orldwide mercury pollution ” but that

unfortunately will r educe the benefi ts of amalgam is similar to the conc lusion of Re (2008) , and both ar e absolutely and completely sharable, as they are evidence based.

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Bellinger DC , Trachtenberger F , Barregard L , et al : Neuropsycho-logical and renal eff ects. Eff ects of dental amalgam in children. A randomized clinical trial , JAMA 295 : 1775 - 1783 , 2006 .

Besnault C , Attal SP , Ruse D , Degrange M : Self-etching adhesives improve the shear bond str ength of a RMGIC to dentin , J Adhes Dent 6 : 55 - 59 , 2004 .

Choi KK , Condon JR , Ferracane JL : Th e eff ects of adhesiv e thickness on pol ymerization contraction stress of composite , J Dent Res 79 : 812 - 817 , 2000 .

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d ’ Alanno M , Fazzi F , Lorenzi R , Dondi dall ’ Orologio G : Color diff erence between Supreme and Supreme XT , IADR-PEF Dublin 2006 (abst 604) .

DeRouen T , Martin MD , Leroux BG , et al : Neurobehavioral eff ects of dental amalgam in children. A randomized clinical trial , JAMA 295 : 1784 - 1792 , 2006 .

Ferracane JL : Placing dental composites — A stressful experience , Oper Dent 33 : 247 - 257 , 2008 .

Gaengler P , Hoyer I , Montag R : Clinical evaluation of poster ior composite restorations: the 10-y ear report , J Adhes Dent 3 : 185 - 194 , 2001 .

Heintze SD : Systematic Reviews: I. Th e correlation between labora-tory tests on marginal qualit y and bond strength. II. Th e correla-tion between marginal quality and clinical outcome , J Adhes Dent 9 : 77 - 106 , 2007 .

Hickel R , Roulet JF , Bayne S , et al : Recommendation for conducting controlled clinical studies of dental r estorative materials , J Adhes Dent 9 ( suppl 1 ): 121 - 147 , 2007 .

Jones D : Has dental amalgam been torpedoed and sunk? J Dent Res 87 : 101 , 413 , 2008 .

Khurana R , Tredwin CJ , Weisbloom M , Moles DR : A clinical evaluation of the individual r epeatability of thr ee commercially available color measuring devices , Br Dent J 203 : 675 - 680 , 2007 .

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Loguercio AD , Reis A , Barbosa AN , Roulet JF : Five-year double-blind randomized clinical evaluation of a RMGI and PMR in NCCLs , J Adhes Dent 5 : 323 - 332 , 2003 .

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Lutz F , Krejci I : Elimination of polymerization stress at margins of posterior composite resin restorations: a new technique , Quintes-sence Int 17 : 777 - 784 , 1986 .

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development of elastic modulus of a model light-activated com-posite during polymerization , J Esthet Dent 13 : 121 - 130 , 2001 .

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204

LIGHT-CURING UNITS M. Gagliani , L. Fadini , and A. Cerutti


Since their intr oduction in the 1970s, light-curing resins have radically changed composite placement and shaping. Today various types of cur ing lamps permit clinically acceptable and rapid composite polymerization.

We can cite the many uses of cur ing lamps in the various branches of dentistr y, which range fr om com-posite curing for the placement of orthodontic brackets to preventive sealing of deciduous pits in pediatric den-tistry, and fr om the cementation of cosmetic indir ect restorations to the placement of r oot-canal posts, to name onl y the most r ecent applications ( Camilotti and colleagues, 2008 ; dos Santos Alves Morgan and colleagues, 2008 ; Jim é nez-Planas and colleagues, 2008 ; Palomares and colleagues, 2008 ).

Over the years, however, the term “ light curing ” has acquired a special meaning , especially because of its more specifi c use, which is r elated to r esin composite materials employed in direct restorative dentistry.

Th e choice of curing lamp and its clinical use is very important because, as detailed b y Drummond (2008) , the degree of conversion of composite r esins is crucial to achieve good mechanical behavior and higher stabil-ity of the restorations over time ( Schulze and colleagues, 2003 ; Sarafi anou and colleagues, 2007 ).

In addition, we must not overlook the fact that recent fi ndings underscore the impor tance of proper conver-sion of the adhesive systems not only for the life of the restoration, but also for limiting the harmful eff ects of free monomers on the pulp sy stem as a r esult of their inadequate inclusion in the pol ymer network ( Hosoda and colleagues, 1991 ; Galler and colleagues, 1998; Schedle and colleagues, 1998 ; Santerre, Shajii, and Leung, 2001 ; Tabatabaee and colleagues, 2009 ).

LIGHT CURING

Irradiation of composite resin with a visible-light lamp, properly calibrated to emit light at specifi c wavelengths, triggers the pol ymerization process, which is the physical-chemical reaction that converts the monomers in the composite r esin into pol ymers and that ulti-mately modifi es the mater ial consistency from semi-fl uid to hard enough to bear the mastic atory loads.

Th is phenomenon is generated by the physical action of the light on a chemic al agent, called a photoinitiator, contained in the same composite r esin ( Figure 4-102 ). A schematic look can help us understand the phenom-enon: A composite resin is formed by the combination of monomers (high-viscosit y liquids) and substances called fi llers.

MONOMERS Among the most widel y used monomers, the methac-rylate type plays a key role, and the var ious diff erences in terms of concentration confer mechanical diff erences in the composite without modify ing the essence of the curing process.

INORGANIC MATRIX OR FILLER Th e fi ller added to composites is usuall y a vitr eous material, with S iO 2 in the form of cr ushed crystalline quartz. Th e size of the par ticles is of gr eat importance because it aff ects the strength, texture, and contraction of the material during the polymerization reaction. Th e fl ow properties of composites are largely determined by the amount of free resin. Th erefore a certain amount of unbound resin is needed to confer a good degr ee of viscosity and adequate hand ling properties. Currently, so-called “ hybrid composites, ” consisting of a combina-tion of macrofi ller and microfi ller particles, are used for clinical purposes. Th ey have a fi ller content of about 85% by weight (74% volume), and therefore the amount of base resin is lowered to about 15% b y weight (26% volume). Th is increase in the fi ller percentage reduces polymerization shrinkage and improves the mechanical properties of the composite, and the small par ticle size of the fi ller ensures good polishing.

However, the detailed descr iption of composite materials goes beyond the scope of this chapter ; for a more in-depth discussion see the section entitled “ Com-posites and Glass-Ionomer Cements . ”

PHOTOPOLYMERIZATION Th is process consists of the union of monomer mole-cules through the chemical reactions briefl y described in this section (see Figure 4-102 ).

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Figure 4-102 1 and 2, Diagram of the monomer contained within the composite material, coupled with the photoinitiator molecules. 3 and 4, Polymerization reaction. Short chains are initially formed, and bound together they produce longer and stronger molecular clusters.

1. Initial semiliquid status

Photoinitiatingmonomers

2. Light exposure

Photoinitiating monomers generate high-energy free radicals

3. The free radicals begin the formation of polymer chains

4. Cross-linked polymers

Th e essential factor for tr iggering the pr ocess are substances called photoinitiators; among them, cam-phorquinone (CQ) still plays a dominant r ole, but we must also mention tertiary amines and other chemicals that for proprietary reasons often are not indicated in full ( Figure 4-103 ). All of these molecules ar e elicited by light energ y of a specifi c wavelength; for CQ it is about 468 nm, but analogous wav elengths may be equally active on its isomers or similar ones.

Once activated by this wavelength, an alpha-diketone, such as CQ or 1-phenyl-1,2-propanedione (PPD) in its excited state, reacts with the other r esin component: dimethylaminoethyl methacrylate.

During the reaction a hydrogen atom is transferr ed to the oxygen of the photoactivated ketone group, trans-forming it into a h ydroxyl group. Th e remaining electron of the dimeth ylaminoethyl methacrylate molecule (free radical) fi nally triggers the pol ymer-ization reaction.

Akin to what occurs in the chemically activated com-pounds, this is follow ed by reduction of the activated photoinitiator by an accelerator, an aliphatic or aromatic tertiary amine. Th is leads to the formation of an inter-mediate excited complex (exciplex), which in turn releases free radicals by dissociation. With a relatively broad spectrum in the visible r egion (400 to 550 nm; peak at 468 nm), the radiation promotes electron exci-tation of one of the two carbonyl groups of CQ, which lasts fractions of a second.

If during this phase one molecule of amine is met, it becomes a fr ee radical that c an attack a monomer to promote its bond with another , yielding to a pol ymer chain.

Figure 4-103 Camphorquinone (CQ) still plays a major role in the polymerization reaction, and its wavelength requires a specifi c activation.

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During activation each radic al can simultaneously incorporate about 50 monomers into the polymer chain. Tertiary amines used in light-cur ing composites ar e generally less nuc leophilic (electron-rich compounds with a high affi nity for chemical species with few elec-trons) than those used in self-cur ing materials, owing to the inc lusion of electronegative groups, which sub-tract electrons. Furthermore, the rate of formation of free radicals in photoactivated sy stems is much greater than in chemic ally activated ones. Th erefore the competition between the a cid-base reaction (acid

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monomers free in the inhibition lay er or basic amine) and the redox reaction with formation of fr ee radicals favors the latter , whereas the former is likel y to be suppressed.

In order to avoid spontaneous polymerization (where free radicals are formed continuously ), composites contain small amounts of inhibitors that react with free radicals, neutralizing them.

Indeed, the pol ymerization reaction can be pr opa-gated only when all the inhibitor molecules ar e exhausted. Th e addition of diff erent concentrations of inhibitor to the r esin permits pr ecise control of the processing time of the composite . Hydroquinones are often used as inhibitors. Another inhibiting factor is represented by the oxygen transferred to the composite from the ambient air . Oxygen tends to conv ert highly reactive radicals into relatively stable hydrogen perox-ides, which — if present in a suffi cient concentration — can alter polymer quality. Th is explains the eff ect that oxygen plays on the outer layers of composite material. On the one hand it pr events complete polymerization, but on the other it makes the material that is not bound to the pol ymer network available for the subsequent layers of composite . From a c linical standpoint, when placement of composite has been completed, in the most superfi cial areas the operator can limit this inter-action by isolating the site with water-soluble gl ycerin or Mylar matrix bands.

Th e formation of a polymer network — a particularly fast and violent reaction once it is triggered — determines the persistence of monomer radic als trapped in the polymer matrix. Th ese molecules in turn tend to combine into polymers that, once completed, confer additional stiff ness to the composite mater ial.

Th e phenomenon is known as postpolymerization. Most of the possible conv ersion is r eached within minutes of irradiation, but a signifi cant increase in con-version and in the properties of the polymer — including a certain amount of contraction — is observed even after 24 hours. As previously mentioned, the polymerization process is a chain r eaction that leads to formation of a macromolecular complex from the monomer.

Th e monomer, regardless of whether it is Bis-GMA or any other component of the methacr ylate-based resin matrix, has two C = C double bond sites, each at an extremity of the molecule. Th ese double bonds deter-mine monomer aggr egation by addition thr ough a radical reaction. Th e reaction is tr iggered by the pres-ence of free radicals, or high-energy molecules that are extremely unstable and r eactive, usually produced by a photoactivatable initiator . Once formed, the fr ee

radicals open the double C = C bonds in the monomer ’ s methacrylate groups, and the chain r eaction leading to the formation of a pol ymer with a high molecular weight and a cr oss-linked three-dimensional structure begins. Th e initiator also r equires activation and is decomposed by an activator or accelerator.

Th is reaction is slow at fi rst but becomes increasingly faster. For explanatory purposes, we can divide it into two basic phases: pregel and postgel. Th e gel point (or hardening point) represents the point at which the reac-tion starts and af ter which the conv ersion of the monomer into a pol ymer is no longer r eversible. Th e curing process starts during the pr egel phase. In this phase the internal fl ow of the composite is still possible, polymer chain formation has just star ted, and the resin material is still sof t and c an adapt mor phologically. After the gel point, the composite becomes so stiff that it prevents any further internal fl ow. Shrinkage stress is no longer compensated for b y the intr insic fl owability of the composite and is distr ibuted along the tooth-composite interface ( Stansbury, 2000 ).

Radical Polymerization 1. Low degree of conversion, the polymer chains

are in a diluted solution (no contact betw een the chains)

2. “ Intermediate ” conversion, between low and high conversion

3. High degree of conversion, the chains tend to become tangled

“ Intermediate ” Conversion (Gel Effect, Trommsdorff Effect, or Self-Acceleration) 1. Th e polymer chains lose mobilit y. 2. Th e termination rate decreases. 3. Th e concentration of radicals increases. 4. Th e degree of polymerization increases. 5. Molar mass increases.

During photopolymerization, self-acceleration happens when at maxim um light exposure bulk pol y-merization of the mater ial occurs, producing heat of reaction (Trommsdorff eff ect), which leads to an addi-tional increase in polymerization speed and viscosit y.

CURING LAMPS

Curing lamps are composed of a light sour ce (usually halogen incandescent or other types, as described later)

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that emits light within the visible spectr um; the light output is suitabl y fi ltered so that onl y wavelengths of about 460 to 480 nm converge on the tip . Filtering involves the dispersion of available energ y through a cooling system. Th erefore only the wavelengths needed to elicit the photoinitiator , which is indispensable for triggering the curing process ( Figures 4-104 and 4-105 ), are available. Th e power of the lamp , measured in milliwatts/cm 2 , varies according to the t ype of basic light source and initial power; the light output area can vary in width owing to the fact that the tip diameters of curing lamps vary from 6 to 12 mm. Th e minimum power required to ensure adequate pol ymerization — a composite mass about 2 mm thick with a diameter comparable to the tip emplo yed — is established b y International Organization for S tandardization (ISO)

Emittedlight

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Figure 4-104 Simplifi ed diagram of a conventional light-curing lamp, which can be halogen, micro-xenon, or plasma. Emission of visible light from the source should be fi ltered properly, because the light needed to trigger the polymerization reaction must have a wavelength of 400 to 500 nm (blue light).

Filter

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Figure 4-105 This image illustrates the extent of energy dispersion: About 90% of the original emission must be dissipated before reaching the distal end of the light guide.

standards and corr esponds to irradiation b y a light source with a pow er of 400 mW/cm 2 for 40 seconds. Th e result is an energ y of 16,000 mJ . Th ese reference data should be kept in mind dur ing curing, because theoretically such a level could also be achieved through 20-second irradiation using a lamp with an output of 800 mW/cm 2 .

Later we will see that this is not always true and that high powers always generate severe contraction stress, which is harmful to the enamel-adhesiv e and dentin-adhesive interfaces.

TYPES OF CURING LAMPS Today there are several types of curing lamps available on the market, and they can be divided into two major subgroups:

• Lamps with fi ltered visible light sources, or lamps that diff er only in the t ype of bulb that pr ovides the primary light energy before fi ltering: • Halogen lamps • Plasma lamps • Micro-xenon lamps

• Lamps that emit light at a specifi c wavelength for photoinitiators, around 460 to 480 nm: • Laser lamps • LED lamps

Halogen Lamps Today halogen lamps still r epresent the benchmar k; they are composed of a conv entional halogen light source with the fi lament inside a glass bulb . To avoid early deterioration of the fi lament from oxidation, the bulb is fi lled with a noble gas. As previously mentioned, the light emitted fr om the bulb is concentrated with the aid of a r efl ector, and it trav els within an optic al fi ber bundle at the tip of the optic al conductor; unwanted wavelengths are eliminated with specifi c fi lters ( Rueggeberg, 1999 ; Althoff and Hartung, 2000 ).

In the 1990s, “ programmable ” lamps w ere intro-duced, in which both the power output (milliwatts) and the time (shorter or longer) of the source light could be set. Such lamps allow the specialist to determine the total amount of energy needed to lengthen the gelifi ca-tion phases of the resin restoration material and also to convert it optimall y to conf er physical characteristics that will endure.


Th e advantages of the system are related to their struc-tural simplicity, easy management of light intensity, and low operating cost. At the same time, the disadvantages

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are by no means negligible, as the light source is subject to a strong decline in light intensit y over time (Barga and colleagues, 1994). Th is occurs bec ause of w ear of the fi lament and the subsequent deposit of par ticles inside the bulb ( Figure 4-106 ) ( Martin, 1998 ; Miyazaki and colleagues, 1998 ). Refl ectors also lose eff ectiveness because of constant ov erheating ( Rueggeberg, Twiggs, and Caughman 1996 ).

Th e graph in Figure 4-107 shows the tr end of the emission spectrum typical of a halogen lamp . Wave-lengths above 500 nm and below 400 nm are fi ltered.

Plasma Lamps With respect to halogen lamps, the basic source is rep-resented by bulbs in which light is generated b y high voltage between the anode and c athode, producing an electrical discharge inside a metal bulb where the envi-ronment is saturated with noble gas — usually xenon — in the plasma state . Excitation at the atomic le vel contributes to the formation of light.

Th e light source develops high heat (adequate cooling is thus needed) and very high power. Light is conveyed through a fl exible tube fi lled with a clear gel to a hand-piece with a tip made of optical glass fi bers. In this case the light emitted by the bulb also travels through fi lters to produce the desired spectrum. In recent models the fi lter is located at the tip to avoid rapid decay as a result of the enormous amount of heat generated by the light source.

Figure 4-106 Medium-power programmable halogen lamp (Demetron-Kerr, USA) (A) and a high-power lamp (EMS, Switzerland) (B).

A B

Figure 4-107 Characteristic emission spectrum of a traditional halogen lamp. The power is represented by the area under the curve, so that the larger and higher the curve, the greater the power of the lamp (mW/cm 2 ).

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Th e spectrum of emitted light is limited; the energy peak is concentrated around 470 nm without any emis-sion below 440 nm ( Figure 4-108 ).


Plasma lamps, which have been on the market for about a decade, enjoyed momentary success before fl aws that limit their range of use w ere observed. Th e high power produced — over 1200 mW/cm 2 — calls for v ery rapid application during polymerization, often of no mor e than 10 seconds. Th is causes a sort of “ hesitation ” in the

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Figure 4-108 Note the high emission peak of a plasma lamp, but with a characteristic narrow-band emission. This problem makes plasma lamps particularly composite-sensitive.

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formation of pol ymer chains, which ar e thus shor ter, leading to less satisfactory mechanical properties of the cured material ( Feng, Carvalho, and S uh, 2008 ). In addition, it was shown that shrinkage stress is con-stantly transmitted to the adhesiv e interface. Further-more, the de velopment of heat makes r estorations of deep cavities problematic because of the need to av oid overheating the pulp. Last but not least, spare parts can be very expensive.

Micro-Xenon Lamps Micro-xenon curing lamps ar e very similar to plasma lamps.

Changes adopted by the automotiv e industry (e.g., in the bulbs used for head lights) made it necessar y to shorten the distance betw een the tw o poles (c athode and anode), leading to a signifi cant reduction in the voltage needed for the ar c of light. Th e result was a reduction in heat and an exponential increase in the life of the bulb. Whereas the average life of the bulb for a plasma lamp is about 1000 hours (as stated b y manu-facturers), that of a micr o-xenon lamp is about 10,000 hours.

Ten seconds of pr eheating are needed to achie ve maximum power, and because of this “ delay ” the lamp is constantly lit and the illumination cycle (light inten-sity) is determined b y the opening and c losing of a diaphragm. Th e emission spectr um of micr o-xenon lamps is very irregular, but it covers the whole spectrum between 400 and 500 nm better than plasma lamps ( Figure 4-109 ). Th ey also hav e powers of mor e than 1000 mW/cm 2 , and therefore during application of the

Figure 4-109 Similarly to what is illustrated in Figures 4-107 and 4-108 , this image underscores the different emission spectrum characteristics of a micro-xenon lamp.

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light source they generate a gr eat deal of str ess in the resin material and at the inter faces.

Argon Laser Lamps Argon laser lamps emit electromagnetic radiation in the narrow band of the spectr um from 458 to 514 nm, which includes the absorption peak of C Q. Th e waves emitted by lasers ar e coherent (same fr equency and phase) and not div ergent. Argon laser emits a narr ow, collimated beam on a specifi c sample, showing a much more consistent density at the same distance . Light is transmitted through an optical fi ber with a v ery small diameter.


Th is type of lamp has several problems, as it is expensive (including spare parts), can be cumbersome to use, and is quickly outdated owing to technologic pr ogress. Misuse can easily aff ect the surr ounding tissues, and prolonged use (up to 30 seconds) cr eates the r isk of necrosis with crac king of the composite 5 day s after application.

LED Lamps LED lamps are completely innovative with respect to halogen lamps ( Figure 4-110 ).

Light energy is generated by the passage of electrical current through the LED chip, which consists of n-p semiconductor junctions interposed between an active site ( Sze, 1981 ). Th e n site is cov ered with electr ons, whereas the p site is positiv ely charged. When voltage is applied to the L ED chip, the positive and negative

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Figure 4-110 A, Light-emitting diode (LED) lamp by Dentsply. B, Elipar 2 LED lamp (3M). C, MiniLED LED lamp (Satelec).

A

C

B

charges leave their sites and meet at the activ e site. Th e union of these charges produces a photon emission. Th e light spectrum emitted b y LED lamps is par ticularly narrow (440 to 490 nm), with a peak of around 470 nm ( Mills, 1995 ; Nomoto, 1997 ; Fujibayashy and col-leagues, 1998 ; Mills, Jandt, and Ashworth, 1999 ) ( Figure 4-111 ).

Th is wavelength, falling perfectly within the absorp-tion spectrum of the CQ photoinitiator, depends mainly on the presence of a blue salt in the cr ystal structure of the active site: gallium nitride ( Nakamura, Mukai, and Senoh, 1994 ; Smith and King, 2000 ). As a result, LED lamps — unlike halogen lamps — do not r equire special fi lters to eliminate the wav elengths that are unsuitable for triggering the polymerization process.


Th e advantages of the LED system are as follows: • Life of thousands of hours with constant light

emission ( Mills, Jandt, and Ashworth, 1999 ; Jandt, Mills, and Blackwell, 2000 )

• Minimum heat generation ( Kurachi and col-leagues, 2001 ; Porko and colleagues, 2001 ; Uhl, Mills, and Jandt, 2003 )

• Silent operation coupled with easy handling (small size) and practicality (cordless)

Th e disadvantages inc lude fragility and cost. Based on the number of hours of polymerization, the duration and light emission of an LED lamp far exceed those of halogen and plasma lamps. Furthermore, a 20-second exposure time is not suffi cient for proper curing.

Figure 4-111 Emission spectra of several LED lamps of the latest generation. All of them seem to have similar spectra, differing only in a slight elevation of the emission peak.

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BluphaseRadiiplusDentsplyMRS 1

Despite the need for additional inv estigations to determine the appropriate clinical protocols for second-generation LED lamps with composite resins designed to be cured by these new light sources, the new LED technology represents a viable alternativ e to conv en-tional halogen lamps.

With their reliability, the lack of heat generation, and curing potential, these high-pow er lamps — especially those of second generation — are capable of curing resin materials in the same amount of time as traditional halogen lamps.

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• Matrix hardness • Flexural modulus and fl exural strength • Fracture resistance • Compressive strength • Tensile strength • Diametral tensile strength • Wear resistance • Composite creep ( Lovell, Lu, and Elliott, 2001 ) In any e vent, mechanical properties depend greatly

on the formation of a pol ymer network, which is not equivalent to conversion ( Sideridou and Tserki, 2002 ). Th e formation of a network occurs during the propaga-tion of polymer chains and includes a mixture of linear, interrelated, interwoven, and interpenetrating segments. All of them combined determine the pr operties of the material ( Figures 4-112 and 4-113 ). Bond densit y is

DEGREE OF CONVERSION OF COMPOSITES

Polymer properties are largely determined by the degree of conversion of composite or the extent of polymeriza-tion. Th is value indicates the number of double bonds in the methacr ylate groups involved in the cur ing process.

After polymerization of methacr ylate-based light-cured composites, we can see a signifi cant number of unreacted methacrylate groups ( Cook, Beech, and Tyas, 1984 ) with incomplete conv ersion of double bonds (50% to 75%), which depends on the per centage of monomer and fi ller, the initiator system, and the curing mode ( Peutzfeldt and Asmussen, 2004 ). Th is results in 25% to 65% r esidual unsaturation r epresented by the free methacrylate groups, which provide the parameter for assessing the degree of conversion.

Th e polymerization reaction is self-limiting: Th e increase in system viscosity causes a severe reduction in the mobility of reactive groups owing to formation of a highly ramifi ed polymer network ( Ferracane, 1985 ). Monomer viscosity greatly infl uences the degree of con-version of the matr ix. In fact, diff usion of radicals will be faster in a low-viscosity monomer, such as TEGDME, and slower in a viscous composite with a high content of Bis-GMA ( Sideridou and Tserki, 2002 ). A high content of Bis-GMA monomer corr esponds to a high content of unreacted methacrylate groups.

Because of incomplete conv ersion, the unr eacted monomer, like the photoinitiator that did not react (and its photoreactive products), can be eluted in saliva, pos-sibly causing allergic reactions or stimulating bacterial growth around the r estorations ( Carmichael, Gibson, and Walls, 1997 ; Hansel and colleagues, 1998 ; Reichl and colleagues, 2002 ; Walther and colleagues, 2002 ). Th e unreacted monomer c an also act as a plasticiz er, reducing the mechanical strength of the restoration and increasing fl uid absorption ( Lovell, Newman, and Bowman, 1999 ). Th e oxidation of unreacted methacry-late groups can cause colorimetric changes in compos-ites ( Sideridou and Tserki, 2002 ) or the formation of formaldehyde, which is potentiall y allergenic ( Oysaed, Ruyter, and Sj ø vik Kleven, 1988 ).

Th e extent of pol ymerization in composites is expressed by the degree of conversion of C = C bonds in the monomer into C-C bonds character istic of the polymer (Svendsen and Ruyter, 1978 ).

Th e degree of conv ersion aff ects both the ph ysical and mechanical properties of pol ymers ( Rueggeberg and Craig, 1988 ; Sideridou and Tserki, 2002 ). Its increase will in fact incr ease the following:

Figure 4-112 Example of a fl exural strength test in its most widely known form.

Figure 4-113 System codifi ed by ACTA University in Amsterdam to produce a microfl exural test with samples of the same size as the tip of the curing lamp.

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between one lay er of cur ed composite and the one placed after it (incr emental technique) ( Pelissier and colleagues, 2000 ).

Even in these c ases it should be r emembered that, based on analysis of the collected data, the thickness of the composite profoundly aff ects the degree of conver-sion. In a study w e conducted on second-generation LED lamps, we observed that when they are used with exposure times of about 40 seconds they pr ovide a depth of polymerization and degree of monomer con-version that are signifi cantly higher than those obtained with a control halogen lamp, not only on the surface of the material but also in the inner lay ers ( Figures 4-115 to 4-117 ).

POLYMERIZATION TECHNIQUES

Th e process described so far is similar to what occurs when polymerization is c arried out consistentl y — or, rather, when the light source is activated at its maximum power over a giv en period of time . Th e eff ects of the pregel and postgel phases aff ect the dentin-enamel and composite interface. In fact, it has been obser ved that the energy at which the composite shr inks during polymerization greatly stresses the bond with the enamel-dentin adhesive as w ell as the dentin itself (shrinkage stress). Th is abrupt curing process would then detach the adhesiv e system from the hard dental tissue interface, damaging the margin seal, which is

associated with an incr ease in mechanic al properties and stability. In any c ase, polymers with similar con-version values may hav e diff erent bond densities ( Peutzfeldt and Asmussen, 2004 ). Th erefore it is under-standable that conversion alone cannot be predictive of the performance of a restoration.

In light-cured composites the degr ee of conversion decreases as one mov es away fr om the composite surface, because of the attenuation of light intensit y during its passag e through the mater ial ( Hansen and Asmussen, 1993 ; Gagliani, Fadini, and Ritzmann, 2002 ).

It has been observed that the polymerization process of composites continues for at least 1 day af ter activa-tion ( Figure 4-114 ).

Moreover, exposure of the mater ial to a gradual increase in temperature can produce a further increase in the degree of conversion and cross-linking. Th is phe-nomenon raises the segmental mobilit y of the polymer network and can reduce the residual unsaturation that is constantly observed at the end of pol ymerization at room temperature ( Bagis and Rueggeberg, 2000 ). Th e degree of conv ersion at the sur face of the composite resin can be completely diff erent from that of the inner mass. Th is happens because of diff usion of oxygen on the surface layer, which partially (or completely) inhib-its polymerization.

Residual unsaturation, with a high number of r eac-tive methacrylate groups, permits the inter facial bond

Figure 4-114 The graph shows the fl exural strength of a composite material (Enamel Plus A3, Micerium) cured with three different light sources. Note the differences in fl exion between the samples analyzed immediately and those examined after 24 hours. Nevertheless, the immediate data refl ect those that emerged after the full conversion.

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Figure 4-115 Conversion dynamics of the material assessed through fl exural tests. Note the different resistance in the immediate phase obtained with the LED light source compared with the halogen light (MiniLED [Satelec] versus Demetron 501 halogen). Composite EvoCeram A3 Tetric (Ivoclar Vivadent, Luxembourg).

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process — to a time when it c annot compromise the strength of the bond with the dentin.

If activated slowly, the process can be tolerated well by enamel-dentin adhesiv es and does not undermine the integrity of the bond with the dentin substrate . In all the described cases this process can occur because of two specifi c strategies: the use of low light-emission power and short exposure to light.

Th e next step — the one intended to confer a suitable degree of pol ymerization — is the one that m ust be characterized by higher powers and longer exposure to the light source.

SOFT-START POLYMERIZATION Initial irradiation of composites with low-intensit y light makes it possible to extend the pregel polymeriza-tion of the r esin. In fact, resin contraction str ess is largely absorbed by the polymer being formed, as long as a certain molecular mobility is still possible (viscous fl ow phenomenon). As the reaction progresses, the resin becomes more rigid and contraction stress is transmit-ted to the adhesive interface.

Th is moment of the pol ymerization process coin-cides with the gel point. Soft-start polymerization with a low-intensity start would delay the gel point, creating conditions favorable to the formation of a pr oper mar-ginal seal ( Tay, 2001 ). Soft-start polymerization is designed to limit contraction str ess of the r esin while ensuring an appropriate temporary degree of conversion and good curing depth.

Diff erent modes of sof t-start polymerization have thus been designed with diff erent times and powers.

Step Mode Th e lamp is used for a shor t initial period (about 10 to 12 seconds) with a low-intensit y light, equal to about 150 to 200 mW/cm 2 .

Th e intensity increases rapidly to 700 to 800 mW/cm 2 , a level maintained until the end of polymerization.

Ramp Mode Ramp mode entails a gradual increase in light intensity. In 10 to 15 seconds of irradiation, intensity increases from zero to a maximum value that is then maintained for the duration of exposur e.

Pulse Mode Light energy is delivered in cycles that are repeated for the duration of pol ymerization — that is, fl uctuations between 400 and 750 mW/cm 2 every 2 seconds.

crucial for sealing the resin restoration material against the bacteria-rich oral fl uid.

Over the past tw o decades, many r esearchers have tackled this problem in various ways, and many of them arrived empirically at the solutions descr ibed ahead.

It should be noted that all the descr ibed techniques conceal a common pr inciple that in simple terms aims to shift the postgel phase — namely the stage where the composite resin is irreversibly transformed, generating stress at the inter faces from the ine vitable shrinkage

Figure 4-116 Conversion of different composites with different polymerization sources (FreeLight 2 [3M], Demetron LED MiniLED [Satelec], and Demetron 501 [Kerr], with halogen source). Note the uniformity of values, albeit with minor differences from the affi nity with the source lamp. Composites: Point 4 (Kerr), Enamel Plus (Micerium), Tetric EvoCeram (Ivoclar Vivadent).

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Figure 4-117 Conversion of the composite material polymerized with different curing times (20 and 40 seconds) with a Demetron LED lamp (Kerr) at 800 mW/cm 2 and a Demetron 501 halogen lamp (Kerr) at 600 mW/cm 2 for 40 seconds. Note the uniformity of curing achieved in depth with the LED source.

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of restorations depends on the intr insic properties of materials, operating technique , indications for tr eat-ment, and patient-related factors (e.g., caries suscepti-bility, dental class, occlusal relationships of the restored tooth, and parafunctions). For these reasons, in order to achieve clinical success the choice of r estorative tech-nique as well as clinical and operating rigor are crucial.

Th e cementation phase — essential for the fav orable long-term prognosis of the r estoration — and the most suitable materials and techniques ar e currently being debated.

Th e determining factors for pr oper execution of adhesive cementation depend on substrate character is-tics, the ph ysical and mechanic al properties of the cement, the eff ectiveness of the adhesiv e techniques, and the loc ation of the tooth-r estoration margin (because adhesion to the enamel is mor e predictable than that on dentin). It is common knowledge that contamination by saliva signifi cantly aff ects the bond strength between composite and substrate . Conse-quently it is important to emphasize that it is essential to use a rubber dam.

Criteria for Inlay Cementation

• Mechanical: For micromechanical and chemical adhesion

• Structural: To increase resistance of the restoration

• Biologic: For the hermetic sealing of the space between tooth and restoration

• Esthetic: To ensure seamless color integration between the tooth and the r estoration

Cementation of indir ect restorations can be per-formed either with light-curing materials alone or with dual-cure materials ( Irie and Suzuki, 2001 ; Magne and Belser, 2002 ; Hannig and Bott, 2003 ; Ferrari, Dagostin, and Fabianelli, 2003 ). A review of the literature shows the advantages and disadvantages of each c lass of materials.

• Light-curing composites ar e easy to hand le, permit greater control over curing time, and promote the formation of w ear-resistant margins (because they contain a high per centage of fi ller), but their exc lusive photoactivation r epresents a disadvantage.

• Among the advantages of dual-cur ing materials, it should be noted that they hav e a self-cur ing component, which fav ors conversion even with low radiation energy. However, their great fl uidity

Pulse-Delay Mode Pulse-delay mode is suitable for pol ymerization of the composite layer placed on the margin of the c avity or surface of the restoration.

With this mode , polymerization is tr iggered by a low-intensity light pulse (300 mW/cm 2 for 2 seconds) ( Kanca, 1999 ) suffi cient to cure the top lay er of com-posite so as to allow immediate fi nishing and polishing. Th e fi rst 2 seconds of polymerization are followed by a 5-minute interval, during which the composite material is left to self-cure. During the waiting time the r esin can absorb much of the contraction str ess through the phenomenon of viscous fl ow (or internal fl ow) until the gel point is reached.

Finally, after a 5-minute delay, the curing process is completed with 600 mW/cm 2 for 10 seconds.

Despite the “ long ” wait between the two polymeriza-tions, this time frame can be used for the fi rst fi nishing of the outer layer of the composite at the chair .

CLINICAL USE OF CURING LAMPS

POLYMERIZATION TECHNIQUES FOR CEMENTATION OF INDIRECT CERAMIC AND/OR COMPOSITE RESTORATION Th e need for alternativ es to amalgam fi llings and the demand of patients for highly esthetic restorations have led to the growing popularity of ceramic mater ials and resin-based composites in tooth r estoration, a choice whose eff ectiveness has been demonstrated b y long-term studies ( Fuzzi and Rappelli, 1999 ; Da Rosa and colleagues, 2006 ).

Indirect composite r esin ( M ö rmann, 1982 ; James and Arovesky, 1983 ; Blankeneau, Kelsey, and Cav el, 1984 ) or ceramic r estoration entails the use of a thin layer of composite mater ial as a cementing agent. Th e technique off ers several advantages:

• Polymerization shrinkage aff ects only the slight amount of luting mater ial

• Better tooth morphology can be recreated • Extremely precise contact areas can be attained • Multiple restorations can be performed in just one

sitting • A higher degree of conversion of the material can

be achieved in the case of composite inlays Disadvantages include the need for two sessions and

the assistance of a dental technician. Th e clinical evidence and the results reported in the

literature demonstrate that the pr ognosis of these t ype

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the lower viscosity of the sy stem and the incr eased frequency of collisions betw een groups and unreacted radicals below vitrifi cation temperature.

Th is implies that the fr ee volume available for the radicals is not distr ibuted but is concentrated in ar eas of diff erent sizes and cannot be distributed ( Bausch, de Lange, and Davidson, 1981 ; Lovell, Newman, and Bowman, 1999 ; Lovell and colleagues, 2001 ).

Th e relationship between conversion and tempera-ture has been inv estigated extensively ( Maff ezzoli and colleagues, 1994 ; Elliott, Lovell, and Bowman, 2001 ; Lovell and colleagues, 2001 ; Trujillo, Newman, and Stansbury, 2004 ). Nevertheless, little is known about the preheating eff ect on conversion at diff erent depths and irradiation times. Ideally, preheating the composite at 54 ° or 60 ° C before its placement in the c avity, which makes the material more uniform and easier to hand le, would improve adaptation of the uncur ed resin to the cavity walls, potentially minimizing microleakage.

It has been demonstrated extensively that preheating light-cured composites increases the conversion degree of the monomer, which thus improves the properties of the cementing agent ( Draughn, 1981 ; Lovell and col-leagues, 1999 ; Stansbury, 2000 ; Mak and colleagues, 2002 ; Trujillo, Newman, and Stansbury, 2004 ; Daronch and colleagues, 2007 ). Th e former aspect contrasts the decrease in light energ y (Ciucci and colleagues, 1997) that reaches the cement af ter passage through the res-toration (see Figure 4-118 ).

In vitro studies hav e demonstrated that with the interposition of inlays of increasing thickness (2, 3, and 4 mm) between the cur ing lamp and the cementing agent, the degr ee of conv ersion of micr ohybrid

is a disadvantage, and they also require the mixing of two components (pow der-liquid or paste-paste), which can result in porosity and air trap-ping, thus aff ecting adhesion of the material to the tooth substrate.

Th e physical and mechanical properties of compos-ites are closely related to the degree of conversion of the monomer into a pol ymer ( Caughman and colleagues, 1991 ; Leloup and colleagues, 1991 ; Ferracane, 1995 ; Kawaguchi and colleagues, 1996 ; Shaji and S anterre, 1999 ; Ogunyinka and colleagues, 2003; Goldsmith and colleagues, 2003; S ä ilynoja and colleagues, 2004 ).

In light-activated sy stems the degree of conversion decreases as the distance betw een the lamp and the material increases, owing to the attenuation of radiant energy during its passage thr ough the r estoration ( Aravamudhan, Rakowski, and F an, 2006 ; Obici and colleagues, 2006 ). Musanje and Darvell (2006) investi-gated the infl uence of composite inlay thickness on the degree of conv ersion of the cementing mater ial. Th e collected data showed a signifi cant reduction in radiant energy as the thickness of the samples increased, which agrees with pr evious studies ( McCabe and Carr ick, 1989 ; Wassell, Walls, and McCabe, 1995 ). Even if we were to assume that attenuation depends in part on the percentage of the fi ller and the distribution, shape, uni-formity, and r efractive index of the par ticles, a dir ect comparison cannot be made because of a lack of precise data on fi llers.

Th is fi nding, supported by studies on the conversion of fl owable light-curing composite r esins used for cementing inlays of incr easing thickness, has c learly demonstrated the inadequacy of this c lass of materials, as they do not guarantee acceptable pol ymerization when used to cement inlays thicker than 3 mm ( Vieno and colleagues, 2007 ) ( Figure 4-118 ).

As far as dual mater ials are concerned, it has been ascertained that direct radiation yields the best mechan-ical properties and a mor e suitable pol ymer structure, suggesting that the impr ovement of radiation condi-tions (e.g., longer irradiation times and multidirectional irradiation) is still needed to overcome the infl uence of the restoration thickness ( Meng, Yoshida, and Atsuta, 2008 ).

Th e temperature at which polymerization takes place aff ects the conversion of the monomer and consequently the polymer properties ( Bausch, de Lange, and David-son, 1981 ; Lovell, Newman, and Bowman, 1999 ; Lovell and colleagues, 2001 ). Radical mobility increases with temperature (because of an increase in free volume), and this causes additional pol ymerization as a r esult of

Figure 4-118 Verifi cation of the conversion through micro-Raman analysis of self-curing and light-curing composites for the cementation of composite inlays. Note that although some materials have a dual polymerization induction system, they do not have the same degree of conversion in the deep areas as they do on the surface.

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colleagues, 1989 ). Th e type III and IV gold allo ys employed for post and cor es are inert, with a modulus of elasticity and coeffi cient of thermal expansion similar to those of enamel, and they hav e good r esistance to compression, meaning that they can withstand occlusal forces. Metal alloys have also been tested over the years, but their har dness represents a major disadvantage because it increases the risk of fracturing the tooth.

Gold post and cores have two major drawbacks: • Color: Th e post is of ten visible through the new

all-ceramic restorations; to ov ercome this shor t-fall, gold posts and cores whose coronal portion is covered with ceramic have been introduced.

• Two dental appointments and the collaboration of the dental technician are required.

Prefabricated posts can instead be adapted and placed in a single session. Th ey come in a number of v ersions diff ering in material, shape, and design. Th e ideal mate-rial for a post should have physical properties (modulus of elasticity, compressive strength, and coeffi cient of thermal expansion) similar to those of dentin. Prefab-ricated posts should not be subject to corr osion and should bond easily and strongly to radicular dentin with a suitable luting cement, forming a single unit that resembles the sound tooth ( Cheung, 2005 ).

Prefabricated posts ar e available in stainless steel, titanium, titanium allo ys, gold-plated brass, ceramic, and fi ber-reinforced polymers. Th e last type of material is made of c arbon fi bers or silica surrounded by epoxy resin and has a fl exural modulus similar to that of dentin, which may r educe the incidence of r oot frac-tures ( Martinez-Insua and colleagues, 1998 ; Sirimai, Rii, and Morgano , 1999 ). Fiber-reinforced posts ar e designed to be connected to composites for cementa-tion and restoration by means of an adhesive. Th e con-nection between fi ber-reinforced posts and radicular dentin has been clarifi ed by in vivo studies ( Ferrari and Mannocci, 2000 ; Ferrari, Vichi, and Grandini, 2001 ; Vichi, Grandini, and Ferrari, 2001 ): SEM studies have clearly shown the presence of a hybrid layer, resin tags, and lateral branches of adhesiv e. An eff ective bond minimizes the wedge eff ect of the post inside the canal. In addition, compared with gold abutment posts, it requires only minimal removal of dentin (for the inser-tion of a r elatively short and narrow post) and engen-ders a lower risk of root fracture ( Pontius and Hutter, 2002 ), and retention is not r elated to the shape of the post (parallel versus conical).

Because fi ber-reinforced posts are metal free, they do not cause allergies or corr osion. Th ey also ensure good esthetics in the most visible ar eas of the oral c avity

light-curing composites, subjected to preheating at 54 ° C in a dedicated furnace, is similar to that obtained b y dual materials, if the energy is kept constant and regard-less of the t ype of light sour ce (LED or halogen) that is used ( Acquaviva and colleagues, 2008 ; Adami and colleagues, 2008 ).

It should be underscor ed that a dual mater ial or a preheated fi ller reduces the infl uence of the inlay thick-ness on the degr ee of conv ersion of the cementing material.

Although this result was predictable for dual com-posites, the application of heat to a fi lled composite is extremely interesting. However, it should be empha-sized that to achie ve clinical success, the adhesiv e cementation phase plays a pivotal role, which is why it should be performed with extreme accuracy and preci-sion, according to standar dized protocols and al ways with a rubber dam.

CURING TECHNIQUES FOR THE CEMENTATION OF ENDODONTIC POSTS Clinical and experimental studies have established that the predictable outcome of the tr eatment of a se verely compromised tooth with pulp inv olvement is deter-mined not onl y by the execution of good r oot-canal treatment, but also by proper restoration of the tooth.

Endodontically treated teeth ar e subject to dr ying over time, which modifi es the collagen netw ork of dentin. Furthermore, because of the massiv e loss of tissue as a r esult of trauma or c aries, these teeth ar e fragile and more prone to fracture than vital teeth. As a result, when endodontic ally treated teeth ar e being restored, the use of an endodontic post may be advisable in some cases. Th e sole function of the post is to hold the core of the r estoration to suppor t the cor onal portion, and it does not hav e a tooth-r einforcing function.

Th e aim of modern r estorative dentistry is to use materials with similar ph ysical properties, bonded together, for the successful maintenance of tooth func-tion. Because preparation of the post space can increase the risk of root fractures and endodontic failures, place-ment of the post is a decision that should be w eighed carefully after examining the residual amount of sound dental tissue and the mor phology of the tooth in question.

Th ere are two basic t ypes of posts: customized and prefabricated.

Customized gold post and cores have been used for years as a basis for restoring endodontically treated elements, with a six-y ear success rate of 90.6% ( Bergman and

217


have shown no adv erse eff ects on the marginal seal ( Mannocci, Ferrari, and Watson, 2001 ; Mezzomo, Massa, and Libera, 2003 ) and post retention ( Burns and colleagues, 2000 ) when the channels ar e fi lled with a eugenol-based sealer and the post is cemented with a resin-based material, provided that the walls of the root canal have been c leansed properly ( Boone and colleagues, 2001 ).

Another aspect to consider is removal of the layer of demineralized collagen with a proteolytic agent such as sodium hypochlorite. SEM studies have demonstrated that this improves the bond of the r esin to the r oot-canal walls, allowing penetration of resin tags inside the dentinal tubules ( Varela and colleagues, 2003 ).

Lastly, removal of the smear lay er with acid etching and wet bonding to the dentin should be meticulous and avoid any contamination. Cementation of a metal post using a composite makes its r emoval extremely complex if the tooth needs or thograde retreatment, which increases the r isk of r oot fracture; the r emoval procedure is easier with a fi ber-reinforced post ( Faria da Silva and colleagues, 2007 ).

Th e performance of adhesives placed in the channels can be aff ected by lack of moisture control, the presence of a thic k smear lay er, diffi cult access when hand ling the material, diffi cult curing of the adhesive system, and complex cavity confi guration (the amount of composite material placed in the c anal should thus be minimal) ( Carter and colleagues, 1983 ; Sokol, 1984 ; Davidson and Feilzer, 1997 ). Th is makes the expectation of achiev-ing a single unit composed of the material and radicular dentin unrealistic. Th e retention of fi ber posts is attrib-utable more to fr iction than to r eal adhesion to the intraradicular dentin ( Reeh, Douglas, and Messer , 1989 ). Th erefore diff erent mechanical properties of composites can increase the coeffi cient of friction ( Oliveira, Denehy, and Boyer, 1987 ).

To achieve optimal mechanical properties the com-posite cement should be cur ed adequately ( Guzy and Nicholls, 1979 ). Dual-cure cements w ere designed to exploit the benefi ts off ered by both light-cur ing and self-curing components. Th e rationale was to hav e a material with an extended working time and the ability to achieve a high degree of conversion, in both the pres-ence and the absence of light ( Trope, Maltz, and Tron-stad, 1985 ). In any case, some dual-cure cements depend primarily on activation b y light energ y, because the degree of conversion is likely to be inadequate without a light-curing lamp ( Morgano, 1996 ; Heydecke, Butz, and Strub, 2001 ). During cementation of the post the exposed marginal ar eas are easily accessible b y light;

(especially below all-ceramic restorations). It is impor-tant to note that in the event of endodontic retreatment this class of posts can be removed with relative ease.

Retrospective studies have confi rmed the high success rate of this treatment, which is considered reliable and predictable.

Cementation of the Post Among the most commonly used luting cements — zinc phosphate, polycarboxylate, GICs, resin-based cements, and resin-ionomer hybrid cements — zinc phosphate has the longest history of success. In addition to having an extended working time, it is compatible with the zinc oxide – eugenol contained in most endodontic r oot-canal cements. In c ases of endodontic failur e, a metal post cemented with zinc phosphate c an be r emoved easily, and the r isk of root fracture is much lower than with a metal post str ongly bonded to the radicular dentin with a composite cement.

Th e most ser ious drawback of pol ycarboxylate and GICs is microleakage. Moreover, the modulus of elas-ticity of these cements is m uch lower than that of zinc phosphate and dentin.

Th e potential bond with dentin led to the widespread use of r esin-based composites for cementation. Some authors are doubtful about the micr oleakage and ther-mocycling of these mater ials ( Tjan, Grant, and D unn 1991 ; Scianamblo, 2002 ), whereas others have demon-strated improvements in post r etention ( Standlee and Caputo, 1992 ; Chan, Harcourt, and Brockhurst, 1993 ; Nissan, Dmitry, and Assif, 2001 ; Varela and colleagues, 2003 ); reduced microleakage ( Bachicha and colleagues, 1998 ; Mannocci, Ferrari, and Watson, 2001 ; Reid, Kazemi, and Meiers, 2003 ); and gr eater resistance to tooth fracture ( Bachicha and colleagues, 1998 ) when the posts are cemented with a composite cement.

Th e procedure for adhesive cementation of the com-posite to the radicular dentin walls should be performed very carefully to impr ove the bond and minimiz e microleakage.

First of all, dentin walls should be c leansed of any residual gutta-percha and sealer to ensur e the pr oper bond of resin to the dentin. Th is can be achieved through thermal or mechanic al removal of gutta-per cha or a combination of these tw o systems. Th is phase is fol-lowed by thorough cleansing of the canal walls (prefer-ably with a long microbrush and pumice dust). Rinsing of the root-canal space can be performed with an irriga-tion syringe or the air-water spray gun. It is generall y believed that eugenol-based endodontic cements inhibit polymerization of composite cements, but some studies

218


Bachicha WS , DiFiore PM , Miller DA , et al : Microleakage of endodontically treated teeth restored with posts , J Endod 24 : 703 - 708 , 1998 .

Bagis YH , Rueggeberg FA : Th e eff ect of post-cur e heating on residual, unreacted monomer in a commercial resin composite , Dent Mater 16 : 244 - 247 , 2000 .

Baratieri LN , De Andrada MA , Arcari GM , Ritter AV : Infl uence of post placement in the fractur e resistance of endodontic ally treated incisors v eneered with dir ect composite , J Prosthet Dent 84 : 180 - 184 , 2000 .

Barghi N , Berry T , Hatton C : Evaluating intensity output of curing lights in private dental offi ces , J Am Dent Assoc 25 : 992 - 996 , 1994 .

Bausch JR , de Lange C , Davidson CL : Th e infl uence of temperature on some physical properties of dental composites , J Oral Rehabil 8 ( 4 ): 309 - 317 , 1981 .

Bergman B , Lundquist P , Sj ö gren U , Sundquist G : Restorative and endodontic results after treatment with c ast posts and cor es , J Prosthet Dent 1 : 10 - 15 , 1989 .

Blankeneau RJ , Kelsey WP , Cavel WT : A direct posterior restorative resin inlay technique , Quintessence Int 5 : 515 - 516 , 1984 .

Boone KJ , Murchison DF , Schindler WG , Walker WA : Post reten-tion: the eff ect of sequence of post-space preparation, cementation time, and diff erent sealers , J Endod 27 : 768 - 771 , 2001 .

Bott B , Hannig M : Eff ect of diff erent luting mater ials on the marginal adaptation of c lass I ceramic inlay r estorations in vitro , Dent Mater 19 : 264 - 269 , 2003 .

Burns DR , Moon PC , Webster NP , Burns DA : Eff ect of endodontic sealers on dowels luted with resin cement , J Prosthodont 9 : 137 - 141 , 2000 .

Camilotti V , Grull ó n PG , Mendon ç a MJ , et al : Infl uence of diff er-ent light curing units on the bond strength of indirect resin com-posite restorations , Braz Oral Res 22 ( 2 ): 164 - 169 , 2008 .

Carmichael AJ , Gibson JJ , Walls AW : Allergic contact dermatitis to bisphenol-A-glycidyldimethacrylate (BIS-GMA) dental r esin associated with sensitivit y to epoxy resin , Br Dent J 183 ( 8 ): 297 - 298 , 1997 . Review .

Carter JM , Sorensen SE , Johnson RR , et al : Punch shear testing of extracted vital and endodontic ally treated teeth , J Biomech 16 : 841 - 848 , 1983 .

Caughman WF , Caughman GB , Shifl ett RA , et al : Correlation of cytotoxicity, fi ller loading and cur ing time of dental composites , Biomaterials 12 : 737 - 740 , 1991 .

Chan FW , Harcourt JK , Brockhurst PJ : Th e eff ect of post adaptation in the r oot canal on r etention of posts cemented with var ious cements , Aust Dent J 38 : 39 - 45 , 1993 .

Cheung W : A review of the management of endodontically treated teeth: post, core and the fi nal restoration , J Am Dent Assoc 136 : 611 - 619 , 2005 .

Ciucchi B , Bouillaguet S , Delaloye M , Holtz J : Volume of the internal gap formed under composite r estorations in vitro , J Dent 25 : 305 - 312 , 1997 .

Cook WD , Beech DR , Tyas MJ : Resin-based restorative materials — a review , Aust Dent J 29 ( 5 ): 291 - 295 , 1984 . Review .

Da Rosa RPA , Cenci MS , Donassollo TA , et al : A clinical evaluation of posterior composite r estorations: 17-year fi ndings , J Dent 34 : 427 - 435 , 2006 .

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however, because it is irradiated ther e is a signifi cant reduction of radiant energ y owing to sc attering within the cement and the presence of shadow zones as a result of tooth morphology and the shape of the post ( Sorensen and Martinoff , 1985 ), as well as the increased distance between the lamp tip and the mater ial to be cured.

Th e use of fi ber-reinforced composite posts, charac-terized by the abilit y to transmit light, increases the depth of cure of the resin ( Sorensen and Martinoff , 1984 ; Kane and Burgess, 1991 ; Baratieri and colleagues, 2000 ; Gagliani, Fadini, and Ritzmann, 2002 ), as reported by several studies. On the other hand, no study has investi-gated the extent to which a translucent post increases the degree of conv ersion of dual composite cements. It should also be added that fi ber distribution within the post is unpredictable, and that light transmission occurs only along the axial component, which does not guaran-tee uniform conversion of the cementing material.

In vitro and ex vivo studies on dual materials used to cement endodontic posts and cured through a translu-cent post showed a decrease in the degree of conversion — although it was not statistic ally signifi cant — in the deepest areas. Th is makes it likely that conversions will be unacceptable as depth incr eases.

Th ese data underscore the need to use a dual-cur ing material to cement endodontic posts, because only the self-curing component can ensure an adequate monomer conversion at increased depth.

As far as light curing is concerned, there is no univo-cal guideline on irradiation time and the amount of radiant energy to apply. Th e characteristics of individual materials are enhanced b y various polymerization conditions.

Special thanks to F rancesca Cerutti, Alessandro Chisoli, Alessandro Malinverni and Dar io Mezzanzanica for their valuable collaboration: Th is chapter could not hav e been written without them.

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biologic aspects protection of the pulp and dentin adhesion

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