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UNIVERSITY OF SIENA SCHOOL OF DENTAL MEDICINE PhD PROGRAM “FACTORS AFFECTING ADHESIVE CEMENTATION OF INDIRECT RESTORATIONS” PhD THESIS Nicoletta Chieffi TITLE -Factors affecting adhesive cementation of indirect restorations ACADEMIC YEAR 2004/2005
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17 December 2005 Siena Italy Committee: Promoter Prof. Marco Ferrari Co-Promoter Prof. Carel L. Davidson Prof. Franklin Tay Prof. Manuel Toledano Prof. Raquel Osorio Prof. Piero Balleri Prof. Egidio Bertelli Prof. Romano Grandini TITLE Factors affecting adhesive cementation of indirect restorations CANDIDATE Nicoletta Chieffi
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CONTENTS
Section 1. Introduction
1.1 Some factors potentially affecting the adhesive-resin cement bonding……………….xx
1.1.1 Incompatibility of the polymerization modes between resin cements and
adhesive systems …………………………………………………..........................xx
1.1.2 In vitro and in vivo evidence of adhesive permeability: total-etch vs. self-etch
systems……………………………………………………………………………..xx
1.1.3 Adhesive systems to protect the exposed dentin after tooth preparation…….xx
Section 2. The effect of different bonding procedures on problematic bonds between
simplified adhesives and chemical-cured resin cementation.
2.1 An in vitro study of the effect of the seating pressure on the adhesive bonding of
indirect restorations…………………………………………...………………………….. xx
2.2 The effect of application sustained seating pressure on adhesive luting
procedure…………………………………………………………………………………. xx
Section 3. The final bond of resin cement with adhesive covered dentin before
temporary cementation.
3.1 The effect of pre-sealing tooth preparations with dentin adhesives on permanent crown
cementation: A Pilot Study ………………………………………………………………. xx
3.2 Influence of a resin cement used on control untreated dentin vs. dentin that had been
covered with resin sealers and temporary cement………………………………………... xx
Section 4. The effect of additional monomers on the resin cement bond strength.
4.1 The effect of adding an antibacterial monomer on the bond quality of a luting
cementation system ……………………………………………………………………..... xx
Section 5. Summary, general discussion, conclusions and future research.
5.1 Considering the limits of the currently available adhesive systems and their clinical
implications……………...………………………………………………………………... xx
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Riassunto……………………………………………………………………….…………... xx
Résumé……………………………………………………………………………............... xx
Zusammenfassung………………………………………………………………..………... xx
Resumen……………………………………………………………………...…….………. xx
Sumário…………………………………………………………………………………….. xx
Complete list of references……………………………………………………………….. xx
Acknowledgements…………………………………...……………………………............xx
Section 1. Introduction
1.1 Some factors potentially affecting the adhesive-resin cement bonding.
In dental research, a great deal of attention has constantly focused on adhesive
procedures that have become routine in the daily dental practice. The coupling of resin-
based cements usually requires the adjunctive use of dentin adhesives that are either
total-etch or self-etch in nature. The thesis focuses on some factors that can alter this
adhesive bond.
For a long time dentists and researchers have assumed that resin cements and
composites bond well to dentin adhesives when air inhibition layers are present on the
surface of the cured adhesives, while the weak bonds occur between the adhesive and
the dentin.1,2 With the advent of the modern simplified adhesive systems, which are
more acidic and hydrophilic in nature, the assumption that bond failures occur between
adhesives and dentin and not between adhesives and resin cements may still not be true.
There is evidence3 to suggest that simplified self-etch adhesives may not be compatible
with chemical polymerization mode of resin cements. The incompatibility between
materials is therefore introduced as one of the possible causes of failure in adhesive
procedures and in the light of this, the thesis proposes an in vitro protocol based on the
application of sustained seating pressure during the luting procedure, in order to verify
its effect on the chemical-cured adhesive cementation.
Usually, bonding of resin cement to cured adhesive is achieved in the presence of an
oxygen-inhibited layer of unreacted monomers and oligomers,4 allowing the materials
from both sides to cross the interface and blend together to form an interdiffusion zone,
wherein co-polymerization occurs to initiate a chemical bond.5 Some clinical
procedures, such as long temporary cementation on adhesive sealed dentin can
determine this layer absence during the permanent cementation. To date, this oxygen
inhibition layer’s role, as far as bond strength is concerned, is not clear.6-9 However,
even if one considers this aspect, a further objective of the thesis is to investigate the
coupling of the resin cement to dentin that had been covered with adhesive before and
after temporary cementation.
In order to protect the exposed dentin against bacteria infiltration, the inclusion of
antibacterial molecules in adhesive systems has been proposed by manufactures. A
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further objective of the thesis was therefore to evaluate possible adverse chemical
interactions given by including an added antibacterial monomer in a dual-cured resin
cement prototype and to verify its influence on the final bond strength.
In the present thesis, those factors that can influence indirect restoration bond strength
are evaluated in the paragraphs that follow.
1.1.1 Incompatibility of the polymerization modes between resin cements and adhesive
systems.
To date, dentin adhesives and resin cements are all cured via a free radical
polymerization. Chemical polymerization is traditionally achieved using a binary, redox
catalytic system consisting of a peroxide and an aromatic tertiary amine. On the other
hand, light-activated polymerization proceeds from the activation of a photoinitiator
(i.e. camphoroquinone) to its exited triplet state. This is followed by the reduction of the
activated photoinitiator by an amine accelerator to form an intermediate exited complex,
releasing free radicals on dissociation.10
Initially, the incompatibility of simplified adhesives with chemical-cured resin cement
or composites was thought to be exclusively caused by interaction of the nucleophilic
tertiary amine with the acidic adhesive resin monomers.10,11 Charge-transfer complexes
that are formed between acidic resin monomers and the tertiary amines impeded free
radical generation and resulted in incomplete polymerization of the chemical-cured
resin cement or composite.2
The proposed mechanism has been discussed and assumed as the chemical cause of the
above mentioned incompatibility. To circumvent the problem, alternative reducing
agents (i.e. acrylic sulphinate salts, ascorbic acid or barbituric acid salts) have been
added to simplified adhesives to ensure that optimal polymerization of the resin cements
occurs when used in chemical-cured mode.12
From further studies a research group3,13,14 excluded that inherent chemical resin-
initiator incompatibility could be the only cause of the adverse reactions with simplified
self-etch adhesives. In fact, the authors found similar adverse reactions even when
simplified adhesives were used with light-cured composites. In particular, when some
time elapsed before composite light-activation.
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This issue led the authors to develop an alternative mechanism of the incompatibility in
which water is thought to permeate through the adhesive layer and mechanically
disrupts the coupling between the adhesive and the composite. In the presence of a
slow-setting chemical cured composite, this diffusion process tends to be greater.
Thus, at present, the increased permeability in simplified adhesives provides the second
major reason for the adverse reactions with chemically cured resin cements.
Researchers came to these conclusions through in vivo and in vitro studies, often
combining the results of microtensile tests with the results of microscopy observations.
The permeability phenomena has been morphologically described from different kinds
of analysis (i.e. SEM and TEM). More precisely, the fluid movement throughout the
hybrid layer (dentin-adhesive interface), as well as the fluid movement through the
cured adhesive layer (adhesive-composite interface) was found to lead to different,
peculiar morphological defects. On the base of their location in the different bonding
interfaces and in light of the different materials and methods performed in the
experiments, these defects (i.e. voids, resin globules, honeycomb structures) can be
assumed as the morphological evidence of adhesive permeability.
1.1.2 In vitro and in vivo evidence of adhesive permeability: total-etch vs. self-etch
systems.
Initially, characteristic morphological features were evidenced along the adhesive-
dentin interface of some acetone-based adhesives when a wet bonding technique was
used. This so called “overwet phenomenon” 15observed in total-etch (three-step and
two-step) adhesives was correlated to transudation of dentinal fluid, from tubules that
are opened after acid-conditioning in vital teeth that exhibit a positive pulp-pressure.16
Then, similar structural defects (resin globules and blisters) were observed along the
adhesive-composite interface of self-etch (two-step or one-step) adhesives when used
with auto- or dual-cured resin cements,11,12 or with chemical cured composite or with
delayed light-activated cured composites.2,17 For this “new” phenomenon the authors
had to consider different causes. In fact, simplified self-etch adhesives do not require
the removal of the smear plugs. Moreover, these experiments on hydrated dentin were
not performed under dentin perfusion. In addition, the structural defects were never
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observed along the dentin-adhesive interface, which instead remained intact. The
morphological manifestations were therefore correlated to the osmotic permeability.
The latter mentioned studies provided a precise explanation of what presumably occurs.
In particular, the fluid movement across the cured adhesive should be caused by a
concentration difference between the dentinal tubules (region of low solute
concentration) and the adhesive-composite interface (region of high solute
concentration), resulting in an osmotic pressure gradient. This fluid movement from the
dentin substrate into the unpolymerized interface (i.e. delayed light-activation or slow-
chemical-polymerization), produces an immiscible blend of hydrophobic and
hydrophilic monomers. All this results in the formation of the characteristic
morphological defects observed along the adhesive-composite interface. Emulsion
polymerization of the hydrophobic resin in water results in the formation of resin
globules and resin polymerization around the osmotic blisters produces the honeycomb
resin structures.
Finally, the osmotic permeability associated to simplified self-etch adhesives has been
unequivocally confirmed in a recent in vivo study,18 where the fluid movement across
the adhesive layer has been found, through resin replicas, even in endodontically treated
teeth.
1.1.3 Adhesive systems to protect the exposed dentin after tooth preparation.
Before adhesive permeability knowledge, dentine bonding agents have been
recommended as an effective way of sealing dentinal tubules. Many studies19,20 have
claimed that dentin bonding alone was able to guarantee a tight seal of the tubules.
When applied on vital prepared dentin, the adhesive resin material can infiltrate exposed
collagen network forming a hybrid layer, resin tags and adhesive lateral branches,
thereby decreasing the dentin permeability.21
Indirect restorations often require removal of most of the enamel resulting in an exposed
dentine surface. Dentine is a tissue crossed by tubules 0.6-2.0 m in diameter and these
tubules provides routes for the passage of bacteria, fluids, chemical substances
molecules and ions to and from the dental pulp.22 The prepared teeth are typically
protected by provisional restorations that are retained by temporary cements, that are
often subject to problems that include microleakage, dislodgement and even fracture.
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These all can affect clinical performance and longevity of the restoration, as well as
contribute to potential pulp damage and onset of post-preparation tooth sensitivity, if an
appropriate sealing procedure is not employed. Despite the improved sealing
performance of available adhesives,23 to date, it is not clear how effective this adhesive
barrier is and how long it lasts.24 Moreover, if the adhesive system is placed before the
temporary cement, it is difficult to predict the overall behavior of this dentin substrate
when resin cement is used as the final bond.
In order to “seal” the dentin, self-etch adhesive systems can be used instead of total-etch
systems, since the smear layer in the bonding mechanism is incorporated, thus, less
post-operative sensitivity is expected to occur. On the other hand, among the multiple
bacteria sources that may be implicated in tooth preparation infection, there is also the
smear layer. In particular, Brannstrom25 included: 1) bacterial invasion from the tooth
surface via marginal gap formation between tooth and restorative material; 2) bacteria
present in the dentinal tubules; 3) bacteria present at the dentino-enamel junction; 4)
bacteria recontaminating the surface of tooth prior placing the restoration and 5)
bacteria present in the smear layer. Even when the tooth preparation is sealed
completely, bacteria exisisting in the smear layer can multiply and their toxins and
degradation products can diffuse into the pulp, resulting in irritation and inflammation.26
To reduce the potential risk of pulpal inflammation resulting from bacterial activity, the
incorporation of antibacterial monomer in the adhesive system may represent a possible
alternative solution. However, there are no benefits if the antibacterial agent decreases
the bond strength of the indirect restoration which is bonded with a resin cement by
altering its sealing ability to dentin.
In the present research project, after different bonding procedures, the evaluation of the
bond quality of the luting cementation system represents the trait de union among all the
studies. The experiments were performed in vitro in order to simulate cementation of
indirect restorations. The main laboratory examinations performed were microtensile test
and scanning electron microscopy observations. One microleakage study was included.
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References
1. Tay FR, Pashley DH, Byoung IS, Carvalho RM, Itthagarun A. Single-step
adhesives are permeable membranes. J Dent 2002; 30: 371-382.
2. Tay FR, Pashley DH, Byoung IS, Carvalho RM, Miller M. Single-step, self-etch
adhesives behave as permeable membranes after polymerization. Part I. Bond
strength and morphological evidence. Am J Dent 2004; 7: 271-278.
3. Carvalho RM, Garcia FC, Silva SM, Castro FL. Adhesive-composite
incompatibility, part II. J Esthet Restor Dent 2005; 17:191-195.
4. Nathanson D, Antebi R, Hughes CV. Bonding self-etching adhesives to enamel
and dentin in-vitro. J Dent Res 2005; 83(B): C-122 (Abstr 0262).
5. Chieffi N, Chersoni S, Papacchini F, Vano M, Goracci C, Davidson CL, Tay
FR, Ferrari M. An in vitro study of the effect of the seating pressure on the
adhesive bonding of indirect restorations. (accepted for publication Am J Dent
2005).
6. Truffier-Boutry D, Place E, Devaux J, Leloup G. Interfacial layer
characterization in dental composite. J Oral Rehabil 2003; 30: 74-77.
7. Velazquez E, Vaidyanathan J, Vaidyanathan TK, Houpt M, Shey Z, Von Hagen
S. Effect of primer solvent and curing mode on dentin shear bond strength and
interface morphology. Quintessence Int 2003; 34: 548-555.
8. Kupiec KA, Barkmeier WW. Laboratory evaluation of surface treatments for
composite repair. Oper Dent 1996; 21: 59-62.
9. Finger WJ, Lee KS, Podszun W. Monomers with low oxygen inhibition as
enamel/dentin adhesives. Dent Mater 1996; 12: 256-261.
10. Sanares AME, Itthagarum A, King NM, Tay FR, Pashley FR. Adverse surface
interactions between one-bottle light-cured adhesives and chemical-cured
composites. Dent Mater 2001; 17: 542-556.
11. Mack YF, Lay SCN, Cheung GSP, Chan WK, Tay FR, Pashley DH. Micro-
tensile bond testing of resin cements to dentin and an indirect resin composite.
Dent Mater 2002; 18: 609-621.
12. Carvhalo RM, Pegoraro TA, Tay FR, Pegoraro LF, Silva DH, Pashley DH.
Adhesive permeability affects coupling of resin cements that utilize self-etching
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primers to dentin. J Dent 2004; 32: 55-65.
13. Tay FR, Suh BI, Pashley DH, Prati C, Chuang SF, Li F. Factors contributing to
the incompatibility between simplified-step adhesives and self-cured or dual-
cured composites. Part II. Single-bottle, total-etch adhesive. J Adhes Dent 2003;
5: 91-106.
14. Tay Fr, Pashley DH, Yiu CKY, Sanares, Wei SHY. Factors contributing to the
incompatibility between simplified-step adhesives and self-cured or dual-cured
composites. Part I. Single-step, self-etch adhesive. J Adhes Dent 2003; 5: 27-40.
15. Tay FR, Gwinnet AJ, Pang KM, Wei SH. Variability on microleakage observed
in a total etch, wet-bonding technique under different handling conditions. J
Dent Res 1995; 74: 1168-1178.
16. Itthagarun A, Tay FR. Self-contamination of deep dentin by dentin fluid. Am J
Dent 2000; 13: 195-200.
17. Tay FR, Pashley DH, Garcia-Godoy F, Yiu CK. Single-step, self-etch adhesives
behave as permeable membranes after polymerization. Part II. Silver tracer
penetration evidence. Am J Dent 2004; 17: 315-322.
18. Chersoni S, Acquaviva GL, Prati, Ferrari M, Grandini S, Pashley DH, Tay FR.
In vivo fluid movement through dentin adhesives in endodontically treated teeth.
J Dent Res 2005; 84: 223-227.
19. Moodley D, Grobler SR, Rossouw RJ, Oberholzer TG, Patel N. In vitro
evaluation of two adhesive systems used with compomer filling materials. Int
Dent J 2000; 50: 400-406.
20. Gwinnett AJ, Kanaka J. Micromorphological relationship between resin and
dentin in vivo and in vitro. Am J Dent 1992; 5: 19-23.
21. Ferrari M, Cagidiaco M.C, Vichi A, Mannocci F, Mason PN, Mjor IA. Bonding
of all-porcelain crowns: structural characteristics of the substrate. Dent Mater
2001;17:156-164.
22. Richardson D, Tao L, Pashley DH. Dentin permeability: effect of crown
preparation. Int J Prosthodont 1991;4:219-225.
23. Ferrari M, Garcia-Godoy F. Sealing ability of new generation adhesive-
restorative materials placed on vital teeth. Am J Dent 2002; 15: 117-128.
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24. Elgalaid TO, Youngson CC, McHugh S, Hall AF, Creanor SL, Foye RH. In
vitro dentine permeability: the relative effect of a dentine bonding agent on
crown preparations. J Dent 2004; 32: 413-421.
25. Brännström M. Infection beneath composite resin restorations: Can it be
avoided? Oper Dent 1987; 12: 158-163.
26. Turkun M, Cal E, Toman M, Toksavul S. Effect of dentin disinfectants on the
shear bond strength of all-ceramic to dentin. Oper Dent 2005; 30: 453-460.
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Section 2. The effect of different bonding procedures on problematic bonds
between simplified adhesives and chemical-cured resin cementation.
2.1 An in vitro study of the effect of the seating pressure on the adhesive bonding
of indirect restorations.
Nicoletta Chieffi, Stefano Chersoni, Michele Vano, Cecilia Goracci, Carel L. Davidson,
Franklin R. Tay, Marco Ferrari.
ABSTRACT
Purpose: To evaluate the effect of two different techniques of seating pressure
application on the adhesive-dentin bond of indirect restorations. Methods: Eight non-
carious human third molars were randomly divided in two treatment groups (four teeth
each). Cylindrical composite blocks were luted with a resin cement (Panavia F,
Kuraray). In Group 1, the seating pressure was applied for 5 seconds. In Group 2, the
resin cylinder was maintained under constant pressure during the entire three minute
polymerization period of the resin cement. After storing in distilled water for 24 hours,
0.9 x 0.9 mm sticks were produced from these luted specimens for microtensile bond
testing and SEM examination. Results: The Student t-test showed a significant
difference (p<0.05) in bond strength between Group 1 and Group 2. SEM revealed the
presence of structural defects and resin globules on the seating surface of the
composites. These features were exclusively identified from the Group 1 specimens and
were probably caused by fluid transudation from the underlying dentin through the
simplified self-etch adhesive (ED primer).
Clinical Significance: Pressure application during the entire course of setting of the
dual-cured resin cement improves the bond strength and reduces fluid interference from
the bonded dentin.
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INTRODUCTION
Although posterior composite restorations require minimal intervention and
cavity preparation,1 indirect aesthetic restorations have remained popular among
clinicians as they can overcome some of the limitations associated with direct
composite placement.2 When indirect restorations are luted with thin layers of
contemporary adhesive cements, polymerization shrinkage stresses are reduced in
cavities with high cavity configuration.3 This results in stronger and more durable
bonds to tooth structures4-6 and improvements in the fracture resistance of these
restorations.7,8
Auto-cured or dual-cured resin cements that utilize peroxide/aromatic tertiary
amine catalytic systems are frequently used for bonding of indirect restorations in
conjunction with total-etch or self-etch dentin adhesives.9,10 Self-etch systems are
advantageous in that because they are less technique-sensitive and exhibit a lower
incidence of postoperative sensitivity.11,12 However, when simplified self-etch
adhesives were used with auto-cured or dual-cured resin composites, abnormal features
were reported along the adhesive-composite interface that were deleterious to the
integrity of these.11,13 Conversely, the use of the resin-coating technique, which
involves the application of an additional less hydrophilic resin layer, was found to
improve the bond strength of the resin cements.14-16
Previous studies have examined the effect of the magnitude of seating force on
film thickness of luting cements.17-21 However, little is known about the effect of
seating pressure on the bond strengths of indirect restorations that are coupled to dentin
via the use of auto-cured resin cements. As auto-cured resin cements have longer setting
times than light-cured resin cements,9 there is sufficient time for water to diffuse from
the underlying bonded dentin across the polymerized hydrophilic adhesive layer via an
osmotic gradient.11
This study examined the effect of the seating pressure on the coupling of a dual-
cured resin cement (Panavia F, Kuraray Medical Inc., Tokyo, Japan) to one-step self-
etch adhesive bonded dentin. The null hypothesis tested was that the manner in which
the seating pressure was applied during the setting time of the resin cement has no
influence on the microtensile bond strength of indirectly composite restorations to
dentin.
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MATERIALS AND METHODS
Eight non-carious human third molars that were stored in a 0.5% chloramine T
solution at 4oC were used within one month following extraction. All the teeth were
bonded in their normal hydrated status, as they were retrieved from the storage medium.
The composition of Panavia F is shown in Table I. The operating procedures for the
experimental and control groups are summarized in Table II. Table I. Composition of the material employed in this study.
Material Components Batch # Manufacturer
Panavia F Primer a: HEMA, 10-MDP, 5-NMSA, water, accelerator. Primer b: 5-NMSA, accelerator, water, sodium benzene sulfinate. Paste A: 10-MDP, hydrophobic aromatic dimethacrylate, hydrophobic aliphatic dimethacrylate, hydrophilic dimethacrylate, silanated silica, photoinitiator, benzoyl peroxide. Paste B: hydrophobic aromatic dimethacrylate, hydrophobic aliphatic dimethacrylate, hydrophilic dimethacrylate, sodium aromatic sulfinate, accelerator, sodium fluoride, silanated barium glass.
41170
Kuraray Medical Inc., Tokyo, Japan
Abbreviations- HEMA: 2-hydroxyethyl methacrylate; 10-MDP: 10-methacryoloyloxydecyl dihydrogen phosphate; 5-NMSA: N-methacryloxyl-5-aminosalicylic acid.
Table II. Procedures employed for the two groups and their microtensile bond strengths.
Group designations
Bonding procedures
Pressure applied (MPA)
Laboratory examinations
Microtensile bond strength
(MPa)*
1
Control group
1,249
for 5 sec
9.8 ± 5.7 A
2
Experimental
group
Panavia F
1,249 for 3 min
Microtensile and
SEM
20.7 ± 7.3 B
*Values are means ± standard deviations in MPa. The different superscripts indicates a statistically significant difference (P< 0.05)
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a. MICROTENSILE BOND STRENGTH EXAMINATION
Specimen Preparation
The occlusal enamel was removed using a slow-speed saw with a diamond-
impregnated disk (Isomet, Buehler Ltd., Lake Bluff, IL, USA) under water cooling. The
root of each tooth was cut at the same level, in order to obtained tooth samples with a
standardized height (5mm). A 180-grit silicon carbide paper was used under running
water to create a clinically relevant smear layer on the dentin surface.
Composite cylinders (Tetric-Ceram, Ivoclar-Vivadent, Schaan, Liechtenstein) of
10 mm in diameter and 6 mm in height were prepared using a split aluminum mold, in
order to limit and standardize the bonding area. Prior to cementing procedures, the
bonding surface of each resin cylinder was sandblasted, etched with phosphoric acid,
rinsed with water and dried.
Cementing procedures
The specimens were randomly divided in two treatment groups (N=4). In the
Control group, the resin cement Panavia F (Kuraray Medical Inc., Tokyo, Japan) was
used according to manufacturer’s instructions. ED Primer (A+B) was mixed and
applied with a brush on the dentin surface and left in place for 30 s. After drying the
etched surface with gentle air flow, Panavia F resin cement (A+B) was mixed and
applied on each of the freshly prepared composite cylinder. The composite block was
cemented to the dentin surface using a seating pressure of 1,249 MPa for 5 s. To ensure
optimal polymerization of the resin cement along the exposed margins, a layer of
Oxyguard was applied after removal of the excess cement with a small scaler and left
in place for at least 3 min.
In the Experimental group, the bonding procedures were the same as described
in the Control group, except for the application of the cementation pressure. During the
entire three-minute period that was necessary for the complete polymerization of the
resin cement, the resin cylinder was maintained under a constant seating pressure of
1,249 MPa. The excess cement was removed and the Oxiguard was applied while the
specimen was under pressure. For both groups, in order to standardize the applied
pressure, a metallic tool (Fig. 1) that delivered 10 Kg was used. This resulted in a
seating force of 98,1 N. The pressure [N/m2] was calculated, dividing this force [N] by
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the surface area [m2] of the metal weight. The value obtained was finally converted in
MPa.
Fig. 1 The metallic tool used to standardized the seating pressure application. The tooth was positioned
on the basal surface of the tool and the composite cylinder was cemented, applying the weight on the
upper surface of the tool.
Bond Strength Evaluation
After cementation, all the specimens were stored in water for 24 hours at 37°C.
Each tooth was then sectioned vertically with the Isomet saw into a series of slabs. The
slabs were then sectioned vertically into 0.9 x 0.9 mm sticks, based on the “non-
trimming” version of the microtensile bond testing technique.22 Each stick was
measured using a digital caliper to determine the cross-sectional area. The sticks were
attached to a testing device with cyanoacrylate glue (Zapit, DVA, Corona, CA, USA).
The device was attached to a universal testing machine (Triax digital 50, Controls,
Milano, Italy) and loaded in tension at a crosshead speed of 0.5 mm/min until failure.
Statistical Analysis
After checking for normal distribution with the Kolmogorov-Smirnov test, the
differences in bond strength values between the two groups were tested for statistical
significance using the Student t-test. The level of significance was set at α=0.05.
b. SCANNING ELECTRON MICROSCOPY (SEM)
Specimens Preparation
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After microtensile bond testing, eight pairs (fractured composite and dentin
sides) of specimens from each group were randomly selected for SEM examination.
Each specimen was mounted on metallic stubs, sputtered with gold/palladium and
observed with a SEM (JSM – 6060LV, JEOL, Tokyo, Japan) operating at 10 or 15 kV.
Images of the two complementary debonded interfaces for each fractured
specimen were taken at different standardized magnifications at 100-6,000X. The angle
of observation of the samples was 90°. The SEM evaluation was performed by double-
blinded operators.
RESULTS
a. MICROTENSILE BOND STRENGTHS
The Control group exhibited significantly lower tensile bond strength than the
Experimental group (p<0.05) [Table II], indicating that the application of a sustained
seating pressure during the cementation procedure had a positive effect on the final
bond strength of the resin cement tested.
b. SEM OBSERVATIONS
The most remarkable finding was the observation of structural defects in
fractured specimens derived from the Control group. These defects consisted of
compartmentalized structural entitles that were nearly identical in almost all of the
fractured composite interfaces examined, except for differences in their dimensions (Fig
2a-b; Fig 3). Moreover, the corresponding fractured dentin interfaces in the Control
group featured resin globules that represented the separation phase of resin components
(Fig 4). These features were completely absent in fractured interfaces of the
Experimental group (Fig. 5).
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Fig.2a
Fig. 2b
Fig. 2 SEM image of composite side from Group 1, in which the seating pressure was applied for five
seconds. (a) a representative medium magnification view (1500x) showing structural defects in the
majority of the composite interface (b) A high magnification view (6000x) of a region in (a).
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Fig. 3 SEM image (4000x) of composite side from Group I. The micrograph shows the structural design
of the faults observed.
Fig. 4 SEM image (6000x) of dentin side of a representative high magnification view of a specimen
from Group I. The micrograph shows resin globules.
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Fig. 5 SEM image of composite side from Group II, in which the seating pressure was applied for
three minutes. The micrograph shows a representative medium magnification view (1800x) showing
the absence of structural defects in the composite interface.
DISCUSSION
As the microtensile bond strength of the resin cement was significantly higher
when the seating pressure was maintained throughout the entire setting period of the
cement, we have to reject the null hypothesis tested in this study. Furthermore, the
quality of the debonded interfaces was inferior when the seating pressure was only
applied for 5 s.
The low microtensile bond strength results observed in the Control group are
comparable with those reported in previous studies23,24 when the same resin cement was
used according to the manufacturer’s instructions. It should be stressed that these low
bond strengths were not caused by the incompatibility between acidic simplified dentin
adhesives and the basic amine catalysts in auto/dual-curable resin composite. This is
due to the inclusion of two different types of sulphinate ternary catalyst25 in the ED
primer as well as the Panavia F resin cement (Dr. K. Arikawa, Kuraray, personal
communication). Should such incompatibility exists, it should be reflected in the bond
strength results of both the Control and Experimental groups, and not in the former
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only. Thus, it is logical to assert that the low bond strengths and the observation of
structural defects and resin globules in the Control group was not caused by acid-base
incompatibility of the resin cement system. Indeed, the resin globules seen in ED
primer-treated dentin from the Control group (Fig. 4) had also been identified in
previous studies that employed single-step self-etch adhesives26 or two-step etch-and-
rinse adhesives.23 These globules represent emulsion polymerization of the hydrophobic
components of the resin cement that were in contact with the water that had permeated
through the etched and primed dentin.12
Moreover, the structural defects that were identified from the fractured composite
side of the specimens in the Control group (Fig. 3) had also been reported previously as
“honeycomb structures” or “blisters” in previous studies. Based on SEM and TEM
evaluations,11,12 these defects were located along the adhesive-composite interface. In
those studies, the authors suggested that the blisters were either filled with water that
permeated from dentinal tubules, or represented incompletely polymerized regions
within the primer layer that resulted from the entrapment of water. When stressed to
failure, these blisters may act as stress raisers that expedite crack propagation through
the adhesive-resin cement interface.
In order to improve the coupling of resin cements to hydrated dentin bonded with
simplified adhesives, the application of an additional coat of a more hydrophobic resin
to the primed dentin has been recommended. Although such a technique is useful for
direct composite restorations, it has limited use in the bonding of indirect restorations.
This is because the addition of an additional hydrophobic resin coating would affect the
fit of these indirect restorations. Reduction in the permeability of the primer-cement
system to water derived from the underlying sound dentin may account for the higher
bond strengths observed in the Experimental group (Group 2). Previous studies27,28 that
evaluated the long-term durability of resin bonds to dentin confirmed the inverse
relationship between water penetration through adhesive systems and bond strength
results. The results of this study demonstrated that the detrimental effect of adhesive
permeability associated with simplified self-etch adhesives can be eliminated by the
application of sustained seating pressure during the luting of indirect restorations.
Although, the results of this in vitro study cannot fully predict the clinical behaviour of
the same material applied on vital teeth as no fluid diffusion system was applied, such
23
investigation can contribute to understanding of the adverse interactions29 that occur
between chemical-cured resin cements and simplified self-etch dentin adhesives.
Further studies should be done to test seating pressure effect on auto/dual-curing resin
cements when the pulpal pressure is simulated.
24
REFERENCES
1. Tyas MJ, Anusavice KJ, Frencken JE, Mount GJ. Minimal intervention dentistry-a
review FDI commission project. Int Dent J 2000; 50: 1-12.
2. Versluis A, Douglas WH, Cross M, Sakaguchi RL. Does an incremental filling
technique reduce the polymerization shrinkage stresses? J Dent Res 1996; 75: 871-
878.
3. Feizer AJ, de Gee AJ, Davidson CL. Increased wall-to wall curing contraction in
thin bonded resin layers. J Dent Res 1989; 68: 48-50.
4. El Zohairy AA, de Gee AJ, Mohsen MM, Feilzer AJ. Microtensile bond strength
testing of luting cements to prefabricated CAD/CAM ceramic and composite
blocks. Dent Mater 2003; 19: 575-583.
5. Stewart GP, Jain P, Hodges J. Shear bond strength of resin cements to both ceramic
and dentin. J Prosthet Dent 2002; 88: 277-84.
6. Kramer N, Lohbauer U, Frankenberger R. Adhesive luting of indirect restorations.
Am J Dent 2000; 13: 60-76.
7. Burke FJ, Wilson NH, Watts DC. Fracture resistance of teeth restored with indirect
composite resins: the effect of alternative luting procedures. Quintessence Int 1994;
25: 269-75.
8. Furukawa K, Inai N, Tagami J. The effects of luting resin bond to dentin on the
strength of dentin supported by in direct resin composite. Dent Mater 2002; 18:
136-142.
9. Ogawa T, Tanaka M, Matsuya S, Aizawa S, Koyano K. Setting characteristics of
five autopolymerizing resins measured by an oscillating rheometer. J Prosthet Dent
2001; 85: 170-6.
10. Sanares AM, Itthagarun A, King NM, Tay FR, Pashley DH. Adverse surface
interactions between one-bottle light-cured adhesives and chemical-cured
composites. Dent Mater 2001; 17: 542-556.
11. Tay F, Pashley DH. Have dentin adhesives become too hydrophilic? J Can Dent
Assoc 2003; 69: 726-31.
12. Carvalho RM, Pegoraro TA, Tay FR, Pegoraro LF, Silva NRFA, Pashley DH.
Adhesive permeability affects coupling of resin cements that utilize self-etching
primers to dentin. J Dent 2004; 32: 55-65.
25
13. El Zohary AA, De Gee AJ, Hassan FM, Feilzer AJ. The effect of adhesives with
various degrees of hydrophilicity on resin ceramic bond durability. Dent Mater
2004; 20: 778-87.
14. Jayasooriya PR, Pereira PN, Nikaido T, Tagami J. Efficacy of resin coating on bond
strengths of resin cement to dentin. J Esthet Restor Dent 2003; 15: 105-113.
15. Nikaido T, Cho E, Nakajima M, Tashiro H, Toba S, Burrow MF, Tagami J. Tensile
bond strengths of resin cements to bovine dentin using resin coating. Am J Dent
2003; 16: 41-46.
16. Montes MA, DE Goes MF, Ambrosano GM, Duarte RM, Sobrinho LC. The effect
of collagen removal and the use of a low-viscosity resin liner on marginal
adaptation of resin composite restorations with margins in dentin. Oper Dent 2003;
28: 378-87.
17. Piemjai M. Effect of seating force, margin design, and cement on marginal seal and
retention of complete metal crowns. Int J Prosthodont 2001; 14: 412-416.
18. White SN, Yu Z, Kipnis V. Effect of seating force on film thickness of new
adhesive luting agents. J Prosthet Dent 1992; 68: 476-81.
19. White SN, Kipnis V. Effect of adhesive luting agents on the marginal seating of cast
restorations. J Prosthet Dent 1993; 67: 28-31.
20. Yu Z, Strutz JM, Kipnis V, White SN. Effect of dynamic loading methods on
cement film thickness in vitro. J Prosthodont 1995; 4: 251-5.
21. Wang CJ, Millstein PL, Nathanson D. Effect of cement, cement space, marginal
design, seating aid materials, and seating force on crown cementation. J Prosthet
Dent 1992; 67: 786-90.
22. Shono Y, Ogawa T, Terashita M, Carvalho RM, Pashley EL, Pashley DH. Regional
measurement of resin-dentin bonding as an array. J Dent Res 1999; 78: 699-705.
23. Mak YF, Lai SCN, Cheung GSP, Chan AWK, Tay FR, Pashley DH. Micro-tensile
bond testing of resin cements to dentin and an indirect resin composite. Dent Mater
2002; 18: 609-621.
24. De Munck J, Vargas M, VAN Landuyt K, Hikita K, Lambrechts P, Van Meerbeek
B. Bonding of an auto-adhesive luting material to enamel and dentin. Dent Mater
2004; 20: 963-71.
26
25. Nyunt NM, Imai Y. Adhesion to dentin with resin using sulfinic acid initiator
system. Dent Mater 1996; 15: 175-82.
26. Tay FR, Pashley DH, Byoung IS, Carvalho R, Itthagarun A. Single-step adhesives
are permeable membranes. J Dent 2002; 30: 371-82.
27. Okuda M, Pereira PN, Nakajima M, Tagami J, Pashley DH. Long-term durability of
resin dentin interface: nanoleakage vs. microtensile bond strength. Oper Dent 2002;
27: 289-96.
28. Hashimoto M, Ohno H, Kaga M, Endo K, Sano H, Oguchi H. In vivo degradation
of resin-dentin bonds in humans over 1 to 3 years. J Dent Res 2000; 79: 1385-91.
29. Tay FR, Pashley DH, Suh B, Carvalho R, Miller M. Single-step, self-etch adhesives
behave as permeable after polymerization. PartI. Bond strength and morphological
evidence. Am J Dent 2004; 17: 271-278.
27
Section 2. The effect of different bonding procedures on problematic bonds
between simplified adhesives and chemical-cured resin cementation.
2.2 The effect of application sustained seating pressure on adhesive luting
procedure.
Nicoletta Chieffi, Stefano Chersoni, Federica Papacchini, Michele Vano, Cecilia
Goracci, Carel L. Davidson, Franklin R. Tay, Marco Ferrari
ABSTRACT
Objectives: To evaluate the effect of short versus long application seating pressure on
the bond strength of resin blocks, luted with a dual-cured resin cement (Panavia F) to
pre-coated or non pre-coated dentin with an hydrophobic light-cured adhesive (Clearfil
Protect Bond). Methods: Sixteen non-carious human third molars were randomly
divided in six Groups (4 teeth each). Cylindrical composite blocks were luted with
Panavia F (Group Ia) and with Clearfil Protect Bond with Panavia F (Group IIa) and the
seating pressure was applied for 5 seconds. In Groups Ib, IIb, the two bonding
procedures were respectively repeated, but the resin cylinder was maintained under
constant pressure during the entire three-minute polymerization period of the resin
cement. After storing in distilled water for 24 hours, 0.9 x 0.9 mm sticks were produced
from these luted specimens for microtensile bond testing and SEM examination.
Results: The use of Clearfil Protect Bond with Panavia F produced higher bond
strengths than the use of Panavia F (p<0.05). Extending the time of pressure application
up to 3 minutes increased the bond strength (p<0.001) and improved the integrity of the
interfacial quality.
Significance: The application of sustained seating pressure during luting procedures
and the additional use of a hydrophobic light-cured adhesive both improve the final
bond strength of the resin cement.
28
INTRODUCTION
It has been widely demonstrated that simplified self-etch adhesives can attract
fluid from dentin after polymerization.1-6 This fluid absorption is due to relatively high
concentrations of ionic or acidic monomers in the self-etching primers (in the two-step
systems)1 or in adhesive (in the single-step systems)2-6 essential to enable these systems
to diffuse through the smear layer and demineralize the underlying dentine.7
Recently it was reported that incompatibility may be present when auto-cured
or dual-cured resin cements were used in conjunction with simplified self-etch dentin
adhesives.8,9 Adverse chemical interaction and adhesive permeability were identified
as the two main factors responsible for the reduction in bond strength, when slow
setting resin cements were coupled to bondings on hydrated dentin.10 Even when the
interaction between acidic simplified dentin adhesives and the basic amine catalysts in
dual-curable resin cements may be eliminated by the use of sulphinate-type ternary
catalysts in the self-etching primer and the resin cement,11 adhesive permeability
remains a possible cause of bond strength reduction. This is because auto/dual-cured
resin cements have longer setting times than light-cured resin cements and, in time,
water can diffuse from the underlying bonded dentin across the polymerized
hydrophilic adhesive layer via an osmotic gradient.6 A previous study concluded that
the additional application of a more hydrophobic resin layer resulted in improved
coupling of the dual-cured resin cement to dentin.12 Another recent investigation13
indicated that pressure application during the entire course of the setting of a dual-
cured resin cement improves the bond strength and reduces fluid interference from the
underlying, with bonding covered dentin.
The objective of this study was to evaluate the effect of the sustained seating
pressure on the integrity of the adhesive bond in resin blocks, in order to simulate
indirect restorations, luted with a dual-cured resin cement. The effect of seating
pressure was examined by comparing the use of Panavia F as recommended by the
manufacturer (i.e., resin cement applied to dentin primed with the one-step self-etch
adhesive included in the kit), versus the application of Panavia F to dentin that had first
undergone a bonding procedure with the two-step self-etch adhesive Clearfil Protect
Bond.
29
The null hypotheses tested were that: (a) the application of sustained seating
pressure during the curing of the resin cement has no influence on the microtensile bond
strength of resin blocks to dentin; and (b) the additional application of the two-step self-
etch adhesive has no influence on the microtensile bond strength of the dual-cured resin
cement.
MATERIALS AND METHODS
Sixteen non-carious human third molars that had been stored in a 0.5%
chloramine T solution at 4oC were used within one month following extraction. All the
teeth were submitted to bonding in their normal hydrated status, as they were retrieved
from the storage medium. The composition of the materials is shown in Table I. The
operating procedures for the four experimental and control Groups are summarized in
Table II. Table I. Batch number (#), composition and manufacturer of the materials employed in this study.
Materials Components Manufacturer
Panavia F (# 41170)
Primer a: HEMA, 10-MDP, 5-NMSA, water, accelerator. Primer b: 5-NMSA, accelerator, water, sodium benzene sulfinate. Paste A: 10-MDP, hydrophobic aromatic dimethacrylate, hydrophobic aliphatic dimethacrylate, hydrophilic dimethacrylate, silanated silica, photoinitiator, benzoyl peroxide. Paste B: hydrophobic aromatic dimethacrylate, hydrophobic aliphatic dimethacrylate, hydrophilic dimethacrylate, sodium aromatic sulfinate, accelerator, sodium fluoride, silanated barium glass.
Kuraray Medical Inc., Tokyo, Japan
Clearfil
Protect Bond (#41112)
Primer: HEMA, 10-MDP, 12-MDPB*, hydrophilic dimethacrylate, water Bond: 10-MDP, Bis-GMA, HEMA, hydrophobic dimethacrylate, di-Camphoroquinone; N,N-Diethanol-p-toluidine, silanated colloidal silica, surface treated sodium fluoride.
Kuraray Medical Inc., Tokyo, Japan
Abbreviations- HEMA: 2-hydroxyethyl methacrylate; 10-MDP: 10-methacryoloyloxydecyl dihydrogen
phosphate; 5-NMSA: N-methacryloxyl-5-aminosalicylic acid; 12-MDPB: 12-
Methacryloyloxydodecylpyridinium bromide; Bis-GMA: Bis-Phenol A diglycidylmethacrylate.
*MDPB has been included as for its antibacterial properties.
30
Table II Procedures employed for the four Groups and their microtensile bond strengths.
Values are means (standard deviations) in MPa. Groups with the same superscripts are not significantly different (P>0.05).
a. MICROTENSILE EXAMINATION
Specimen Preparation
The occlusal enamel was removed using a slow-speed saw with a diamond-
impregnated disk (Isomet, Buehler Ltd., Lake Bluff, IL, USA) under water cooling. The
root of all teeth were cut at the same level, in order to obtained tooth samples with a
standardized height (5mm). A 180-grit silicon carbide paper was used under running
water to create a clinically relevant smear layer on the dentin surface.
Composite cylinders (Tetric-Ceram, Ivoclar-Vivadent, Schaan, Liechtenstein) of
10 mm in diameter and 6 mm in height were prepared using a split aluminum mold, in
order to limit and standardize the bonding area. Prior to cementing procedures, the
bonding surface of each resin cylinder was sandblasted, etched with phosphoric acid,
rinsed with water and dried.
Cementing procedures
The specimens were randomly divided in six Groups (N=4). In Group Ia, the
resin cement Panavia F (Kuraray Medical Inc., Tokyo, Japan) was used according to
manufacturer’s instructions. ED Primer (A+B) was mixed and applied with a brush on
the dentin surface and left in place for 30 s. After drying the etched surface with gentle
air flow, Panavia F resin cement (A+B) was mixed and applied on each of the freshly
prepared composite cylinders.
Microtensile bond strength (MPa)*
a B
GROUP DESIGNATION Seating pressure:
for 5 sec. Seating pressure: for 3 min.
I (a & b) Panavia F
9,78 (5,66) C 20,71 (7,31) B
II (a & b) Clearfil Protect Bond + Panavia F
13,03 (7,01) B,C 31,11 (11,85) A
31
In Group IIa, the light-curing self-etch adhesive Clearfil Protect Bond (Kuraray
Medical Inc., Tokyo, Japan) was used according to manufacturer’s instructions. This
material also contains 12-methacryloyloxydodecylpyridinium bromide (MDPB)
monomer to include antibacterial properties which may be useful in cases of vital teeth.
The self-etching primer was applied with a brush on dentin surface and left in place for
20 sec. After drying the etched surface with mild air flow, the bonding was applied on
the etched-primed dentin, gently air flowed and light-cured for 10 sec. Then Panavia F
resin cement (A+B) was mixed and applied on each of the freshly prepared composite
cylinders.
In these two Groups, the composite block was cemented to the dentin surface
using a seating pressure of 1,25 MPa for 5 sec. To ensure optimal polymerization of
the resin cement along the exposed margins, a layer of Oxyguard was applied after
removal of the excess cement with a probe and left in place for at least 3 min.
In Group Ib and in Group IIb, the bonding procedures were the same as
described for Group Ia and Group IIa, except for the application of the cementation
pressure. During the entire three-minute period that was necessary for the complete
polymerization of the resin cement, the resin cylinder was maintained under a constant
seating pressure of 1,25 MPa. The excess cement was removed and the Oxiguard was
applied while the specimen was under pressure. In order to standardize the applied
pressure, a metallic tool (Fig 1) that delivered 10 Kg was used. This resulted in a
seating force of 98,1 N. The pressure [N/m2] was calculated, dividing this force [N] by
the surface area [m2] of the metal weight. The value obtained was finally converted in
MPa.
Bond Strength Evaluation
After cementation, all the specimens were stored in water for 24 hours at 37°C.
Each tooth was then sectioned vertically with the Isomet saw into a series of slabs.
The slabs were then sectioned vertically into 0.9 x 0.9 mm sticks, based on the “non-
trimming” version of the microtensile bond testing technique.14 Each stick was
measured using a digital caliper to determine the cross-sectional area. The sticks were
attached to a testing device with cyanoacrylate glue (Zapit, DVA, Corona, CA, USA).
32
The device was attached to a universal testing machine (Triax digital 50, Controls,
Milano, Italy) and loaded in tension at a crosshead speed of 0.5 mm/min until failure.
Statistical Analysis
The population of bond strength values was normally distributed according to
the Kolmogorov-Smirnov test (p>0.05). The Two-Way ANOVA was applied with
bond strength as the dependent variable, material and pressure application time as
factors. Tukey’s test was used for post-hoc comparisons.
b. SCANNING ELECTRON MICROSCOPY (SEM)
Specimen Preparation
After microtensile bond testing, eight pairs (fractured composite and dentin
sides) of specimens from each Group were randomly selected for SEM examination.
Each specimen was mounted on metallic stubs, sputtered with gold/palladium and
observed with a SEM (JSM – 6060LV, JEOL, Tokyo, Japan) operating at 10 or 15
kV. Images of the two complementary detached interfaces for each fractured specimen
were taken at different standardized magnifications: 100-6,000X.
RESULTS
a. MICROTENSILE BOND STRENGTHS
Bond strength results of the four Groups are shown in Table II.
The selection of the luting material was a significant factor with regard to
obtained bond strength; with Clearfil Protect Bond + Panavia F measuring significantly
higher bond strengths than Panavia F (p<0.05).
Pressure application time was a also significant factor. Extending the time of
pressure application up to 3 minutes significantly increased the bond strength
(p<0.001).
The interaction between cement and time of pressure application was also
significant to obtained highest bond strength. According to the Tukey’s test applied
for post-hoc comparisons, Group IIb achieved the highest bond strength and the
difference was statistically significant (p<0.05). Group Ib and Group IIa were
33
comparable (p>0.05). The latter was comparable to Group Ia, which had the lowest
bond strength.
b. SEM OBSERVATIONS
SEM analysis of the specimens from those Groups where the seating pressure
was sustained for a few seconds, revealed the presence of structural defects. These
defects consisted of compartmentalized structural entities that were nearly identical in
almost all of the fractured composite interfaces examined from Groups Ia (Fig. 2).
Fig. 2 SEM imagine of fracture composite side of a specimen from Group Ia, where the seating pressure
was applied for five seconds. The micrograph (4000x) shows the structural design of the defects
observed.
The most significant result in Group IIa (pre-coated light-cured adhesive dentin,
with a few seconds of pressure application time), was that separation was between the
adhesive and the resin cement (Fig. 3a). Moreover, resin globules that represented the
separation phase of resin components were present between the detached adhesive and
the resin cement (Fig 3b).
34
Fig.3a
Fig.3 b
Fig. 3 SEM image of fractured composite sides of a specimen from Group IIa, where the seating pressure
was applied for five seconds. (a) a medium magnification view (1000x) of composite side, showing
structural defects in most of the adhesive layer, almost completely detached from the resin cement (b) A
high magnification view (4000x) of an area in photo a, showing resin globules.
35
In contrast to this, such features (structural defects and resin globules) were not
found at the fractured interfaces of Group Ib where the seating pressure was sustained
for 3min.
In almost all specimens examined in Group IIb the fracture was located between
the resin cement and the composite resin block and a strong adhesion between the
adhesive layer and the resin cement was present (Fig. 4).
Fig. 4 SEM imagines of dentin side of two different specimens from Group IIb, where the seating
pressure was sustained for three minutes. The micrograph (200x) demonstrates that the fracture was
between the resin cement and the composite block.
DISCUSSION
As the microtensile bond strength of the resin cement was significantly higher
when the seating pressure was maintained throughout the entire setting period of the
cement, the first null hypothesis tested in this study has to be rejected.
If the SEM evaluation had not be performed, we could attribute the lower bond
strength of the control Group to voids caused by air introduced during hand mixing of
the two component pastes of the dual cured cement. However when examining the
micrographs another explanation may be found.
36
As a result of the incompatibility of the absorbed water with the hydrophobic
components in the resin cement, material discontinuity (presence of globules) 15 and
irregular features12,16 along the adhesive-composite interface were previously reported.
The osmotic permeability of the simplified adhesive systems has been described in
experiments performed with pulpal pressure simulations,1,5 and also in those
experiments performed without perfusion system.3,4,17,18 In these latter studies, as well
as in the present investigation, it is reasonable that fluid interferences can be occurred
as the samples were retrieved from the storage medium and bonded in their normal
hydrates status. Still, transmission of dentin fluid through simplified dentin adhesives
was demonstrated to occur in vivo, in endodontically treated dentin.19
It is clear that such structural defects (Fig 2) observed in those Groups where the
seating pressure was only applied for a few seconds, were therefore caused by water
that had permeated through the etched and primed dentin. These defects were even
observed in those samples that had been pre-treated with the hydrophobic light-cured
adhesive (Fig.3 a-b). Thus, it is feasible that permeability of the light-cured self-etch
adhesive may have compromised the ultimate bond strength result of the resin cement.
Apparently the application of a sustained seating pressure suppresses the
absorption of water and the globules formation, resulting in a better quality of the
adhesive interface. These results are in agreement with those obtained in a previous
investigation.13 As a consequence, reduction of water infiltration, coming from the
underlying dentin into the primer-cement system may account for the higher bond
strength as observed in Groups Ib, IIb.
Since Clearfil Protect Bond together with Panavia F, regardless of pressure
application time, had significantly higher bond strengths than Panavia F, the second
null hypothesis tested in this study has also to be rejected. This means that the
additional application of a hydrophobic light-cured adhesive improves the final bond
strength of the resin cement. This latter result confirms those studies20,21 showing that
the application of an additional hydrophilic resin layer improves resin cement bond
strength. Moreover, as the extensive and prolonged antibacterial activity of the
adhesive tested in the present investigation has been previously demonstrated,22,23
clinical protection against oral bacteria can be expected from this product.
Also the selection of cement in combination with pressure application time was
37
found to be significant to obtained highest bond strength. In particular, Group IIb (pre-
coated light-cured adhesive dentin, with 3 min pressure application time) achieved the
highest bond strength among all the other Groups. Thus, it can be speculated that, since
the inherent self-etch adhesive system permeability was eliminated by the sustained
seating pressure, the application of the hydrophobic light-cured adhesive was more
efficient in improving the bond strength of the resin cement, because the
incompatibility factors had been reduced. This finding confirms a previous
investigation,3 showing that when simplified adhesives were bonded to dehydrated
dentin, no compromised bond strength resulted.
An unexpected outcome of this study was the difference in the kind of fracture
observed in Group IIa, located between the adhesive and the resin cement (Fig. 3 a-b)
and in Group II b, between the resin cement and the composite block (Fig. 4). From
SEM analysis, it should be stressed that when the short seating pressure was applied
(Group IIa), the water that had permeated through the adhesive interfered with the
hydrophobic resin cement and resulted in a weaker adhesion. Thus, failure in
adhesive/resin-cement bonding interface resulted. On the other hand, with three
minutes seating pressure, a stronger adhesion between adhesive and resin cement
occurred due to the reduction of the adhesive permeability. Thus, the weakest bonding
interface was between the resin cement and the composite restoration. In order to
improve the adhesion of the latter bonding interface, the composite block surface could
be treated with hydrofluoric acid and bonding.
The results of this study demonstrated that:
To improve coupling of the resin cement to dentin, both the additional self-etch
adhesive containing the light-cured hydrophobic bonding layer and the sustained
seating pressure during cementation are effective. The latter reduces the
incompatibility between simplified-step adhesives and dual-cured resin cements, since
it reduces the adhesive permeability associated with simplified self-etch adhesives.
However, since pulpal pressure was not simulated in this study, the results of this in
vitro study still cannot fully predict the clinical behaviour of these materials applied on
vital teeth.
38
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2. Tay FR, Frankenberger R, Bouillaguet S, Pashley DH, Carvalho RM, Lai
CN. Single-bottle adhesives behave as permeable membranes after
polymerization. I. In vivo evidence. J Dent 2004; 32: 611-21.
3. Tay FR, Pashley DH, Suh B, Carvalho R, Miller M. Single-step, self-etch
adhesives behave as permeable after polymerization. Part I. Bond strength
and morphological evidence. Am J Dent 2004; 17: 271-278.
4. Tay FR, Pashley DH, Garcia-Godoy F, Yiu CK. Single-step, self-etch
adhesives behave as permeable after polymerization. Part II. Silver tracer
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Single-step, self-etch adhesives behave as permeable after polymerization.
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6. Tay FR, Pashley DH, Byoung IS, Carvalho R, Itthagarun A. Single-step
adhesives are permeable membranes. J Dent 2002; 30: 371-82.
7. Yiu CK, Hiraishi N, Chersoni S, Breschi L, Ferrari M, Prati C, King NN,
Pashley DH, Tay FR. Single-bottle adhesives behave as permeable
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8. Ogawa T, Tanaka M, Matsuya S, Aizawa S, Koyano K. Setting
characteristics of five autopolymerizing resins measured by an oscillating
rheometer. J Prosthet Dent 2001; 85: 170-6.
9. Sanares AM, Itthagarun A, King NM, Tay FR, Pashley DH. Adverse surface
interactions between one-bottle light-cured adhesives and chemical-cured
composites. Dent Mater 2001; 17: 542-556.
10. Tay FR, Pashley DH, Yiu CK, Sanares AM, Wei SH. Factors contributing to
the incompatibility between simplified-step adhesives and chemically-cured
39
or dual-cured composites. Part I. Single-step self-etching adhesive. J Adhes
Dent 2003; 5: 27-40.
11. Nyunt NM, Imai Y. Adhesion to dentin with resin using sulfinic acid
initiator system. Dent Mater 1996; 15: 175-82.
12. Carvalho RM, Pegoraro TA, Tay FR, Pegoraro LF, Silva NRFA, Pashley
DH. Adhesive permeability affects coupling of resin cements that utilize
self-etching primers to dentin. J Dent 2004; 32: 55-65.
13. Chieffi N, Chersoni S, Papacchini F, Vano M, Goracci C, Davidson CL, Tay
FR, Ferrari M. An in vitro study of the effect of the seating pressure on the
adhesive bonding of indirect restorations. (accepted for publication Am J
Dent 2005)
14. Shono Y, Ogawa T, Terashita M, Carvalho RM, Pashley EL, Pashley DH.
Regional measurement of resin-dentin bonding as an array. J Dent Res 1999;
78: 699-705.
15. Tay F, Pashley DH. Have dentin adhesives become too hydrophilic? J Can
Dent Assoc 2003; 69: 726-31.
16. Mak YF, Lai SCN, Cheung GSP, Chan AWK, Tay FR, Pashley DH. Micro-
tensile bond testing of resin cements to dentin and an indirect resin
composite. Dent Mater 2002; 18: 609-621.
17. Chersoni S, Suppa P, Grandini S, Goracci C, Monticelli F, Yiu C, Huang C,
Prati C, Breschi L, Ferrari M, Pashley DH, Tay FR. In vivo and in vitro
permeability of one-step self-etch adhesives. J Dent Res 2004; 83: 459-464.
18. Chersoni S, Suppa P, Breschi L, Ferrari M, Tay FR, Pashley DH, Prati C.
Water movement in the hybrid layer after different dentin treatments. Dent
Mater 2004; 20: 796-803.
19. Chersoni S, Acquaviva GL, Prati C, Ferrari M, Grandini S, Pashley DH, Tay
FR. In vivo fluid movement through dentin adhesives in endodontically
treated teeth. J Dent Res 2005; 84: 223-7.
20. Jayasooriya PR, Pereira PN, Nikaido T, Tagami J. Efficacy of resin coating
on bond strengths of resin cement to dentin. J Esthet Restor Dent 2003; 15:
105-113.
40
21. Nikaido T, Cho E, Nakajima M, Tashiro H, Toba S, Burrow MF, Tagami J.
Tensile bond strengths of resin cements to bovine dentin using resin coating.
Am J Dent 2003; 16: 41-46.
22. Imazato S, Tarumi H, Kato S, Ebisu S. Water sorption and colour stability of
composites containing the antibacterial monomer MDPB. J Dent 1999; 27:
279-83.
23. Imazato S, Ehara A, Torii M, Ebisu S. Antibacterial activity of dentine
primer containing MDPB after curing. J Dent 1998; 26: 267-71.
41
Section 3. The final bond of resin cement with adhesive covered dentin before
temporary cementation.
3.1 The effect of pre-sealing tooth preparations with dentin adhesives on permanent
crown cementation: A Pilot Study.
Nicoletta Chieffi, Cecilia Goracci, Marco Simonetti, Francesca Monticelli, Marco Ferrari
ABSTRACT
Objectives: 1. to investigate whether the sealing procedures performed before the
provisional cementation affect the efficacy of the permanent luting procedures, and 2. to
determine the sealing capacity of two different resin-based bonding systems.
Materials and methods: Thirty extracted molars were prepared for full-crowns
restorations. Samples were randomly divided into three groups (10 teeth each). Dentin
desensitizers were applied in two sessions in order to simulate “abutment preparation”
and “cementation appointment”. Dentin treatments included: a “one-bottle” self-curing
adhesive system (Group 1); a self-etching light-curing two component adhesive system
(Group 2); water, that was applied as a control instead of a desensitizing agent (Group
3). Eugenol-free temporary cement was applied on the treated surface and the
specimens were stored in distilled water for 1 week. After the removal of cement, the
adhesive systems and the resin cement was used to finally cement composite crowns to
the abutments. After the luting procedure, specimens were prepared for microleakage
test and for a standardized SEM examination. Dye penetration was statistically
evaluated using the Kruskal-Wallis Non Parametric Analysis of Variance (p<0.05).
Results: Statistical analysis showed no significant difference in the microleakage
exhibited by the three groups (p=0.85). SEM observation of Group 1 and Group 2
revealed a perfect bond between the cement and the adhesive and between the adhesive
and the dentin. Resin replicas of specimens belong to any of the three groups revealed a
gap between the crown and the cement.
Conclusion: This pilot study suggests that the application of the two resinous dentin
coating, before the temporary cementation, does not effect negatively the seal of luted
resin crowns. These findings need to be researched further.
42
INTRODUCTION
Post-operative sensitivity is frequently encountered in vital teeth that have been
prepared for complete–coverage crowns. The prepared teeth are typically protected by
provisional restorations that are retained by temporary cements. Frequently, the patients
suffer from sensitivity during the temporization phase, when the provisional restorations
are removed prior to permanent cementation of the final restorations, following
permanent luting or during any combination of these events.15, 26
Various theories have been presented to explain the mechanism of dentin sensitivity.12
Currently, the most widely accepted theory is the one based on hydrodynamics.
Displacement of fluids is thought to be responsible for the deformation of nerve fibers
located in the dentin tubules.1 Sealing dentin with adhesive resin systems has been
proposed as a means to prevent the undesired fluid movement after mechanical dentin
exposure.13 Any system that obstructs infiltration of exposed dentin is recommended in
preventing dentin sensitivity.23
In an in vivo study, Cuenin et al4 reported the direct relationship between dentin
hypersensitivity and the accessibility of dentin tubules. Pashley20 showed adhesive resin
systems to be effective and reliable in reducing sensitivity.
Suzuki25,26 and Lam14 evaluated the pulpal response following sealing of the prepared
vital dentin with a dentin bonding system and demonstrated how this procedure not only
offered a biologic seal to the vital dentin substrate and tubule complex, but also
prevented post-operative sensitivity that often accompanies complete crown
preparation.
In case of full coverage–crown preparation, millions of dentinal tubules are exposed.7,22
The provisional restoration and the temporary cement are often subject to problems that
include microleakage, dislodgement and even fracture. These all can contribute to the
onset of post-preparation tooth sensitivity and potential pulp damage, if an appropriate
procedure is not employed. This means that all effort has to be given to prevent
hydraulic pressure on the tubule fluids. Such pressure may come along with the
cementation itself when the still unset cement penetrates into dentinal tubules,
displacing an equal volume of dentinal fluid in the pulp.19
Moreover, mastication forces can be transferred into hydraulic pressure.32 This
mechanism is most likely to be the reason why the non-anaesthetized patient
43
experiences pain during crown cementation. Therefore, it is most important to maintain
dentin protection during the provisional phase of treatment and before the permanent
luting of the crown.2,7,18
Some clinical studies3,5,7,14,15,26,31 reported on the efficacy of different adhesive systems
used for preventing sensitivity on prepared vital abutments. When applied on vital
prepared dentin, the adhesive resin material can infiltrate exposed collagen network
forming a hybrid layer, resin tags and adhesive lateral branches, thereby decreasing the
dentin permeability.7
Several types of bonding systems are available in the market. The so called “one-bottle”
and the self-etching priming bond systems were well-accepted by practitioners.
Recently a “one-bottle” self-curing adhesive system (Exite DSC, Ivoclar Vivadent,
Schaan, Liechtenstein) and a self-etching, light-curing, two component adhesive system
(AdheSE, Ivoclar Vivadent) were introduced.
The aims of this study were: 1) to investigate whether sealing tooth preparations with
dentin adhesives before provisional cementation affects the efficacy of the permanent
luting procedures, and 2) to test the null hypothesis that there is no difference in the
ability of the two bonding systems in preventing dye penetration in full-coverage
crowns that are sealed with these adhesives and subsequently luted with a resin cement.
MATERIALS AND METHODS
Specimens Preparation
Thirty molars, extracted for periodontal reasons, were selected for this study. These
teeth were free from decay or previous restoration, and were kept in distilled water until
the experimental time. Each tooth was prepared, for full-crowns restoration, with a 1.5
mm axial and a 2 mm occlusal reduction. The crown margin was positioned in dentin. A
chamfer margin was made on all. The teeth were prepared using diamonds burs in a
high-speed handpiece under constant water cooling.
The following treatments simulated the “preparation appointment” and the “cementation
appointment”.
Preparation appointment- The teeth were randomly divided into three groups of 10
teeth each. The teeth in the first group were treated with a “one-bottle” self-curing,
etch-and-rinse adhesive (Excite DSC). The teeth in the second group were treated with a
44
self-etching, light-curing, two component adhesive system (AdheSE). In the control
group, the teeth were treated only with water.
In Group 1, the Excite DSC was used according to the manufacturer’s instructions. The
conditioning gel (37% phosphoric acid) was applied for 20 s and the substrate was
rinsed with water spray for 15-20 s and then gently dried for 1-2 s. A micro brush,
impregnated with the self-curing activator, was used for the application of the light-
curing solution of the bonding system. One layer of this bonding system was applied
and finally the alcoholic solvent was gently removed with air.
In Group 2, the AdheSE was used, as recommended by the manufacturer. An adequate
amount of AdheSE Primer was applied with a brush. Once the dentin surface was
thoroughly coated with the primer, the product was brushed into the entire surface for
another 15 s. The total reaction time was not shorter than 30 s. The excess AdheSE
Primer was dispersed with a strong stream of air until the mobile liquid film
disappeared. Then, the AdheSE Bond was applied, dispersed with a very weak stream
of air and light-cured for 10 s.
In Group 3, the dentin surface was treated only with water and no adhesive as
desensitizer was applied.
Following removal of the oxygen inhibition layer of the adhesives with a wet cotton
pellet, impressions were taken of the crown preparations using Permadyne (3M ESPE,
Seefeld, Germany) impression material, from which resin crowns (Gradia, GC, Tokyo,
Japan) were fabricated in the laboratory.
After impression taking, a layer of an eugenol-free temporary cement (Temp-Bond NE,
Kerr, Orange, CA, USA) was applied on the surface of each crown preparation. After
setting of the temporary cement, the samples were stored in distilled water for 1 week.
Prior to cementing, the fit of the crowns was observed at 24x magnification under a
dissecting microscope. Crowns were accepted only when no discontinuity or gaps were
found.8
Cementation appointment- Following the one week storage period, the temporary
cement covering the dentin specimens was mechanically removed and the surface was
cleaned with polishing brushes.
45
The dentin surface of each tooth was covered again with the adhesive systems, before
the final cementation: Excite DSC was utilized for the Group 1 and Group 3 and
AdheSE for the Group 2 following manufacturer’s instructions.
The crowns were cemented with a resin cement (Variolink II, Ivoclar Vivadent) without
additional pre-treatment of their inner surfaces. Although we understand that the
bonding of resin composite crowns to resin cements may be improved by silanization,
this procedure was not performed so as the results of the study may be extrapolated to
the cementation of metal, ceramometal, and alumina/zirconia-based all-ceramic crowns.
After cementation, specimens were prepared for the microleakage test.
Dye Penetration
Root surfaces were coated with two layers of nail varnish, up to 1 mm beneath the
cervical margins. The specimens were then immersed in an aqueous solution of 2%
methylene blue solution at room temperature for 24 h and thoroughly rinsed in tap
water.
The teeth were sectioned with a low speed diamond disk (Isomet, Buehler, Lake Bluff,
IL, USA) under water cooling. Each tooth was sectioned into three vertical slices in a
mesiodistal direction.
Microleakage Evaluation
The specimens were observed under a stereomicroscope at 25x magnification, and the
highest score of each sample was recorded. Dye penetration was ranked by two
examiners, and the depth of cervical staining was measured according to the parameters
described in a recent study (Fig 1).10
Fig. 1 Schematic illustration of the dye penetration scale, according to the parameters described in the text
46
Score 0 = no dye penetration; Score 1 = leakage not exceeding the first third of the
cervical wall; Score 2 = penetration past the first third of cervical wall; Score 3 =
penetration not exceeding the middle of the axial wall; Score 4 = penetration up to the
middle of the axial wall. Since data were not normally distributed dye penetration was
statistically evaluated using the Kruskal-Wallis non-parametric analysis of variance.
The significance level was defined at p<0.05.
Scanning Electron Microscopy (SEM) Examination
All slices were evaluated using SEM. The slices were immediately returned to water
after evaluation of the dye penetration and prevented from dehydration. Impressions
(Provil Novo, Heraeus Kulzer, Hanau, Germany) of these slices were taken and a set of
epoxy resin replicas (Alpha Die, Schuetz Dental, Rosbach, Germany) was made for
SEM evaluation. The resin replicas were mounted on metallic stubs and sputtered with
gold in a Balzers device (Balzers Ltd., London, Great Britain). They were examined
using a SEM (Philips 505, Eindhoven, The Netherlands) operating at 10 kV.
All samples were evaluated in double blind for defects/gap at the adhesive interfaces.
Defects were recorder - at dentin(D)/adhesive(A) interface, at adhesive(A)/resin
cement(R) interface and at resin cement(R)/crown(C) interface - as present or not.
RESULTS
The results of the statistical analysis showed no significant difference in the
microleakage exhibited by the three groups (p=0.85). The dye penetration of control
specimens (Group 3) was not significantly different than that of samples treated with
Excite DSC (Group I) or AdheSE (Group II).The frequency and median value of the
scores for each of the tested groups are listed in Table 1. The interface gaps evaluated
using the SEM are reported in Table 2. Table 1 Frequency and median value of the scores for each of the tested groups.
Score 1 Score 2 Score 3 Score 4 Median
Group 1 Excite 6 8 11 5 3 Group 2 AdheSE 7 7 6 10 3
Group 3 Control 7 8 4 11 2.5
47
Table 2 The table shows the number of samples with gaps in each of the tested groups for any adhesive
interface [dentin(D)/adhesive(A) interface; adhesive(A)/resin cement(R) interface; resin
cement(R)/crown(C) interface].
D/A A/R R/C Group 1 Excite 2 / 30
Group 2 AdheSE 4 / 30 Group 3 Control 25 / 30
Some important differences between the groups were observed when the specimens
were examined using SEM.
Resin replicas analysis of Group 1 (Fig. 2) demonstrated the presence of a large gap
between the crown and the resin cement in all samples. Spaces were absent along the
resin cement-adhesive interface and almost absent along the adhesive-dentin interface.
Similar results were obtained from the resin replicas analysis of Group 2 (Fig. 3).
Instead, SEM examination of Control group (Fig. 4) revealed gaps between the crown-
resin cement interface and also between the adhesive-hybrid layer interface in almost all
samples; only the adhesive/resin cement interface was free of gaps.
Fig. 2 SEM image of resin replicas belong to Group 1.
A gap (pointer) could be seen between the crown (C) and the cement (R). Absence of spaces between the
cement/adhesive (A)/dentin (D) interfaces.
48
Fig. 3 SEM image of resin replicas belong to Group 2.
A gap (pointer) could be seen between the crown (C)and the cement (R). Absence of spaces between the
cement/adhesive (A)/dentin (D) interfaces.
Fig. 4 SEM image of resin replicas belong to Group 3.
A gap (arrow) could be identified between the crown (C) and the cement (R) and another big gap
(pointer) between the adhesive (A) and the hybrid layer.
49
DISCUSSION
While it is desirable to reduce sensitivity, it is also important to evaluate the possible
adverse effects of the desensitizing agents on the adhesion of resin to dentin, in terms of
bond strength and microleakage. Several studies3,5,11,15,21,23,24,31 have reported the effects
of desensitizing measures on the bond strength of different bonding systems. Few
studies9,16,32 have reported the effect of tubule coating on the eventual microleakage. In
fact, bonding agent application is meant to be directly covered with the permanent
luting cement, or in the case of direct restorations, with the restorative resin-based
composite. Each handling divergent from this procedure should be regarded as a sort of
contamination with possible negative effects on the ultimate adhesive qualities
(adaptation and bond strength). As most of the dentin substrate consists of intertubular
dentin, which is not likely to form on short term a pathway for infiltration towards the
pulp, this material might be better untouched during the provisional stage and be
“traditionally” conditioned when the permanent luting is being performed. In this view,
it might be preferred to employ an unfilled adhesive resin system such as the first
generation Gluma, which has shown to be an excellent tubule infiltrating desensitizing
agent3,11,24 without forming a coat on the dentin substrate.
The results of SEM observations of this study demonstrated that using both resin
coating materials almost no gaps are formed at dentin/adhesive interface. This
observation can support the hypothesis that following the described dentin coating
clinical procedure an important reduction of postoperative sensitivity can be expected.
Microleakage in this study was assessed using a dye. This method continues to be the
most popular of the techniques, which are currently available, but it presents some
disadvantages.31 The main one it is usually associated with the assigning of the
numerical scoring that, although carried out by more than one examiner, is somewhat
subjective.
Microleakage test results demonstrated no statistically differences in dye penetration
between the specimens pre-coated with the adhesives as desensitizers and the specimens
uncoated. The two dentin-coating materials (Excite DSC and AdheSe) can not reduce
considerably dye penetration of luting resin crown. On the other hand, based on the
SEM observations, neither of the two desensitizers, when used at preparation and
50
cementation appointments, interfered with the adaptation of the resin cement to dentin.
In fact, no gaps between adhesive material and resin cement were noted in all groups.
According to recent studies,5,6 from a clinical point of view, the use of a “one-bottle”
system could be indicated because it simplifies the operative protocol and, at the same
time, it assures an effective protection. In spite of that, we have to consider that,
recently, several studies27,28 demonstrated that no perfect seal can be obtained using
simplified bonding systems, because of they act as a semi permeable membrane.
Although, similar microleakage median values were obtained from the dye penetration
analysis of the three groups selected, some important differences among the groups
were extrapolated from the SEM examination. In fact, the two groups in which adhesive
systems were employed before the temporary cementation showed an almost perfect
bond between the resin cement and the adhesive layer and between the adhesive layer
and the dentin. This indicates that a good seal was achieved for the dentinal tubules and
no interferences of the provisional cement of the dentinal adhesive. Further, after proper
debridement, one may achieve a strong bond between the adhesive (utilized as
desensitizers) and the luting cement. On the other hand, the control group was
characterized by a different SEM characteristic, in which the major gap was observed
between the adhesive and the hybrid layer. Clinically this main result in rapid fluid
movements and post-operative sensitivity on the one hand, and the ingress of bacterial
on the other.
Under the experimental conditions of this study, both total-etch and self-etch adhesive
systems seem to affect not negatively the dentin sealing, without producing negative
consequences during the adhesive luting procedures. However, in order to obtain a good
marginal sealing it is important to pre-treat the inner surface of the crowns, before the
final cementation, when resin crowns are chosen. The high microleakage median values,
registered in any of the groups analyzed, could be related with the absence of the pre-
treatment of the inner surface of the resin crowns before the final cementation. In fact,
resin replicas of specimens belong to any of the three group revealed the presence of a
gap between the crown and the cement.
As no statistically difference was observed in preventing dye penetration between the
two bonding systems selected, and because of SEM examination showed intact bonding
51
interfaces (dentin-adhesive-resin cement) for both the adhesives, we cannot reject the
null hypothesis.
The results of this preliminary in vitro study cannot fully predict the clinical behaviour
of the same materials applied on vital abutments. No artificial aging methods were
applied. Moreover, given the limitations in sample size included in the study, it is
possible that these results may be due to a low power of the study. However, these
findings may be used in future studies which include larger sample sizes to further
evaluate this resin system in the effectiveness of decreasing hypersensitivity in the
clinical setting.
CONCLUSIONS
This pilot study suggests that the application of a resinous dentin coating, before the
temporary cementation, does not effect negatively the seal of luted resin crowns. In
order to make clinical recommendations it is necessary to conduct other studies, both in
vitro and in vivo, using also adequate sample sizes in order to further evaluate this
research question.
52
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1. Brännstrøm M. Aastrom A. The hydrodynamics of dentin: its possible relationship to
dentinal pain. Int Dent J 1972; 22: 219-227.
2. Cagidiaco M.C, Ferrari M, Garberoglio R, Davidson CL. Dentin contamination
protection after mechanical preparation for veneering. Am J Dent 1996; 9: 57-60.
3. Cobb D.S, Reinhardt J.W, Vargas M.A. Effect of HEMA-containing dentin
desensitizers on shear bond strength of a resin cement. Am J Dent 1997; 10: 62-65.
4. Cuenin MF, Scheidt MJ, O’Neal RB, Strong SL, Pashley DH, Horner JA. An in vivo
study of dentin sensitivity: the relation of dentin sensitivity and the patiency of dentin
tubules. J Periodontol 1991; 62: 668-673.
5. Dagostin A, Ferrari M. Effect of resins sealing of dentin on the bond strength of ceramic
restorations. Dent Mater 2002; 18: 304-31.
6. Dagostin A, Ferrari M. In vivo bonding mechanism of an experimental dual-cure
enamel-dentin bonding system. Am J Dent 2001;14:105-108.
7. Ferrari M, Cagidiaco M.C, Vichi A, Mannocci F, Mason PN, Mjor IA. Bonding of all-
porcelain crowns: structural characteristics of the substrate. Dent Mater 2001; 17: 156-
164.
8. Ferrari M, Dalloca L, Kugel G, Bertelli E. An evaluation of the effect of the adhesive
luting on microlealkage of the IPS empress crowns. Pract Periodontics Aesthet Dent
1994; 6: 15-23.
9. Fukushima M, Nakamata T, Okabe T, Yamaga M, Sunda S, Iwaku M. Micro-leakage of
various dentin adhesive systems on root surface caries. J Adhes Dent 1991; 9: 9-23.
10. Jacques LB, Ferrari M, Capel Cardoso PE. Micro-leakage and resin cement film
thickness of luted all-ceramic and gold electroformed porcelain-fused-to-metal crowns.
J Adhes Dent 2003; 5: 145-152.
11. Johnson GH, Lepe X, Bales DJ. Crown retention with use of a 5% glutaraldehyde sealer
on prepared dentin. J Prosthet Dent 1998; 79: 671-6.
12. Krauser JT. Hypersensitive teeth. Part I: Etiology. J Prosthet Dent 1986; 56: 153-155.
13. Krauser JT. Hypersensitive teeth. Part II: Treatment. J Prosthet Dent 1986; 56: 307-
311.
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14. Lam CV, Wilson PR. The effect of dentin surface treatment on pulp ward pressure
transmission during crown cementation: a laboratory study. Int Dent J 1998; 48: 196-
202.
15. Mausner I.K, Goldstein GR, Georgescu M. Effect of two dentinal desensitizing agents
on retention of complete cast coping using four cements. J Prosthet Dent 1996; 75: 129-
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16. Moodley D, Grobler SR, Rossouw RJ, Oberholzer TG, Patel N. In vitro evaluation of
two adhesive systems used with compomer filling materials. Int Dent J 2000; 50: 400-
406.
17. Pashley EL, Comer RW, Simpsn MD, Horner JA, Pashley DH. Dentin permeability:
sealing the dentin in crown preparations. Oper Dent 1992; 17: 13-20.
18. Pashley DH. Dentin permeability, dentin sensitivity, and treatment through tubule
occlusion. J Endod 1986; 12: 465-474.
19. Pashley DH. Smear layer-physiological consideration. Oper Dent 1984; 9: 13-29.
20. Pashley DH, Derkson GD, Tao L, Derkson M, Kalathoor S. The effect of a multi-step
dentin bonding system on dentin permeability. Dent Mater 1988; 4: 60-3.
21. Reinhardt JW, Stephens NH, Fortin D. Effect of Gluma desensitization on dentin bond
strength. Am J Dent 1995; 8: 170-172.
22. Richardson D, Tao L, Pashley DH. Dentin permeability: effect of crown preparation. Int
J Prosthodont 1991; 4: 219-225.
23. Seara SF, Erthal BS, Ribeiro M, Kroll L, Pereira GDS. The influence of a dentin
desensitizer on the microtensile bond strength of two bonding systems. Oper Dent 2002;
27: 154-160.
24. Soeno K, Taira Y, Matsumura H, Atsuta M. Effect of desensitizers on bond strength of
adhesive luting agent to dentin. J Oral Rehabil 2001; 28: 1122-1128.
25. Suzuki S, Cox CF, White KC. Pulpal response after complete crown preparation,
dentinal sealing, and provisional restoration. Quintessence Int 1994; 25: 477-485.
26. Suzuki S. Clinical evaluation of a new resin composite crown system to eliminate
postoperative sensitivity. Int J Periodontics Restor Dent 2000; 20: 499-509.
27. Tay FR, Pashley DH, Suh BI, Carvalho RM, Itthagarun A. Single-step adhesives are
permeable membranes. J Dent 2002; 30: 371-82.
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28. Tay FR, Pashley DH, Peters MC. Adhesive permeability affects composite coupling to
dentin treated with a self-etch adhesive. Oper Dent 2003; 28: 610-21.
29. Taylor MJ, Lynch E. Micro-leakage. J Dent 1992; 20: 3-10.
30. Turki MA, Arpata ES. Penetrability of dentinal tubules in adhesive-lined cavity walls.
Oper Dent 2002; 27: 124-131.
31. Yim NH, Rueggerberg FA, Caughman F, Gardner FM, Pashley DH. Effect of dentin
desensitizers and cementing agents on retention of full crowns using standardized crown
preparations. J Prosthet Dent 2000; 83: 459-65.
32. Zaimoglu A, Aydin AK. An evaluation of smear layer with various desensitizing agents
after tooth preparation. J Prosthet Dent 1992; 68: 450-457.
55
Section 3. The final bond of resin cement with adhesive covered dentin before
temporary cementation.
3.2 Influence of a resin cement used on control untreated dentin vs. dentin that had
been covered with resin sealers and temporary cement.
Nicoletta Chieffi, Fernanda Sadek, Francesca Monticelli, Cecilia Goracci, Simone
Grandini, Carel L. Davidson, Franklin R. Tay , Marco Ferrari
ABSTRACT
Purpose: To evaluate the effects of dentin adhesives employed as resin sealers and
provisional cementation on the bond strengths of a resin cement to dentin. Methods: A
two-step etch-and-rinse adhesive (Excite DSC – Group I) and two-step self-etch
adhesive (AdheSE – Group II) were applied to exposed dentin surfaces prepared from
human molars (N=4). Water was used in lieu of a resin sealer in control Groups 3 and 4.
A eugenol-free provisional cement (except for Group 4) was applied to the treated
surfaces. After storing in distilled water for one week, the provisional cement was
removed and cylindrical composite blocks were luted with a resin cement (Variolink
II). 0.9 x 0.9 mm sticks were produced from these luted specimens for Microtensile
bond testing and SEM examination. Results: One-way ANOVA revealed that neither
the resin sealer nor the temporary eugenol-free cement had a negative effect on the final
bond strength (p>0.05). Mixed failures were predominantly identified from SEM.
Clinical Significance: The use of dentin adhesives as resin sealers before provisional
cementation with a non-eugenol provisional cement does not adversely affect the
retentive strength of indirect restorations bonded subsequently with an adhesive and a
resin cement.
56
INTRODUCTION
In crown and bridge restorations, temporization of the prepared teeth is
obligatory for the patients' aesthetic and functional needs. Sealing of the freshly-
exposed vital dentin during the fabrication of provisional restorations has clinical
merits, as external stimuli may trigger rapid fluid shifts within dentinal tubules, and
contribute to post-operative sensitivity.1 Previous studies2-5 indicated that application of
resin sealers immediately after tooth preparation was able to seal the exposed dentin via
resin infiltration into the tubules.
Traditionally, zinc-oxide eugenol cement was the first choice for temporary
protection of the prepared dentin. However, when the final cementation is planned with
resin cements, the eugenol-containing provisional cements should preferably be
excluded. Although some studies6-9 reported that eugenol-containing provisional
cements did not affect the retention of the final bonded restorations, there were other
studies10-12 that reported the contrary. Similar to other phenolic compounds, eugenol is a
radical scavenger that inhibits the polymerization of resin materials.13 Residual resin
products may also impair hybridization and polymerization of the permanent resin
adhesives due to the reduced wettability/reactivity with the dentin substrate.14 This may
result in compromises in bond strength and marginal seal.
Dislodging of the provisional restoration and temporary cement may result in
contamination of dentinal tubules with moisture, saliva and blood. As these risk factors
may jeopardize bonding to dentin,15 a double-bonding “resin-coating technique” that
consists of sealing dentin with an adhesive before the placement of a eugenol-free
provisional cement has been recommended.16-19 It is not clear whether the subsequent
adhesion of indirect restorations will be adversely affected by this double-bonding
protocol. This study examined the microtensile bond strengths of a resin cement to
dentin that was previously treated with either an etch-and-rinse or a self-etch adhesive
in conjunction with a eugenol-free provisional cement. The null hypothesis tested was
that the use of adhesives as resin sealers and the eugenol-free provisional cement have
no adverse effect on the microtensile bond strengths of indirect composites restorations
coupled with an adhesive and a resin cement to dentin.
57
MATERIALS AND METHODS
Sixteen non-carious human third molars that were stored in a 0.5% chloramine T
solution at 4oC were used within one month following extraction. The occlusal enamel
was removed using a slow-speed saw with a diamond-impregnated disk (Isomet,
Buehler Ltd., Lake Bluff, IL, USA) under water cooling. A 180-grit silicon carbide
paper was used under running water to create a clinically relevant smear layer on the
dentin surface. The teeth were randomly divided into four groups (N=4).
Experimental Design
Two different dentin bonding systems were used in the context of resin sealers
in the first and the second groups. The eugenol-free temporary cement (Tempofix,
Ghimas, Bologna, Italy) was used for the first, second and third groups. The materials
tested in this study and their components are summarized in Table I. The operation
procedures for the four experimental and control groups are summarized in Table II.
Table I. Compositions of the materials employed in this study.
Materials Components Batch # Manufacturer AdheSE Primer: DMA, phosphonic acid acrylate,
initiators, stabilizers in a aqueous solution. Bond: HEMA, DMA, silicon dioxide, initiators, stabilizers.
F25882 Ivoclar-Vivadent, Schaan, Liechtenstein
Excite DSC HEMA, DMA, phosphonic acid acrylate, highlydispersed silicon dioxide, initiators andstabilizers in a an alcohol solution. The ExciteBrush is coated with initiators.
G03703
Ivoclar-Vivadent
Resin cement Variolink II
The monomer matrix is composed of Bis-GMA, urethane DMA, and triethylene glycol DMA. The inorganic fillers are barium glass, ytterbium trifluoride, Ba-Al-fluorosilicate glass, and spheroid mixed oxide. Additional contents: catalyst, stabilizers, and pigments.
F55945 Ivoclar-Vivadent
Abbreviations: DMA: dimethacrylate; HEMA: 2-hydroxyethyl methacrylate
58
Table II. Procedures employed for the four experimental and control groups and their microtensile bond strengths.
Provisional restoration stage Final cementation stage Group
designations Resin Sealer
Temporary Cement
Dentin Bonding Resin Cement
Microtensile bond strength
(MPa)* 1 Excite DSC Tempofix Excite DSC Variolink II 41.2 ± 9.6 A 2 AdheSE Tempofix Excite DSC Variolink II 39.7 ± 8.9 A
3 (control) Water Tempofix Excite DSC Variolink II 40.7 ± 9.2 A 4 (control) Water NIL Excite DSC Variolink II 42.8 ± 5.7 A
* Values are means ± standard deviations in MPa. Groups with the same superscripts are not statistically significant (P>0.05)
In Group 1, Excite DSCc was used according to the manufacturer’s instructions.
The conditioning gel (37% phosphoric acid) was applied for 20 s and the substrate was
rinsed with water for 15-20 s and then gently dried for 1-2 s. A microbrush,
impregnated with the self-curing activator, was used for the application of the light-
curing bonding system. One layer of this mixed ‘dual-cured’ solution was applied and
finally the alcoholic solvent was gently removed with air.
In Group 2, AdheSEc was used as recommended by the manufacturer. An
adequate amount of AdheSE Primer was applied with a brush. The dentin surface was
thoroughly coated with the primer that was agitated for 15 s. The excess AdheSE
Primer was dispersed with a strong stream of air until the mobility of the liquid film
disappeared. Then, the AdheSE Bond was applied, dispersed with a very weak stream
of air and light-cured for 10 s.
In control Groups 3 and 4, the dentin surfaces were treated only with water,
without the use of a dentin adhesive. A layer of the eugenol-free provisional cement
was applied on the surfaces of the first three groups of specimens. After setting of the
temporary cement, the samples were stored in distilled water for one week at 37°C. In
the control Group 4, no provisional cement was applied in order to evaluate the effect of
this cement on the final bond strength.
After mechanical removal of the provisional cement, the surface of each
specimen in Groups 1-3 was re-etched with phosphoric acid for 15 s. A layer of Excite
DSC was applied in the manner described previously. A resin cement (Variolink II,
Ivoclar-Vivadent, Schaan, Liechtenstein) was then employed to cement a freshly
prepared hybrid resin composite cylinder (Tetric-Ceram, Ivoclar-Vivadent, Schaan,
59
Liechtenstein) to the bonded dentin. The composite cylinders (10 mm in diameter by 6
mm in height) were prepared using a special metallic tool (Fig. 1), in order to limit and
standardize the bond area. In control Group 4, adhesive cementation was made directly
on the previously untreated dentin surface.
Fig.1 The metallic tool used for the composite cylinders preparation.
Bond Strength Evaluation
After cementation, all the specimens were stored in water for 24 hours at 37°C.
Each tooth was then sectioned vertically with the Isomet saw into a series of slabs. The
slabs were then sectioned vertically into 0.9 x 0.9 mm sticks, based on the “non-
trimming” version of the microtensile bond testing technique.20 Each stick was
measured using a digital caliper to determine the cross-sectional area. The sticks were
attached to a testing device with cyanoacrylate glue (Zapit, DVA, Corona, CA, USA).
The device was attached to a universal testing machine (Triax digital 50, Controls,
Milano, Italy) and loaded in tension at a crosshead speed of 0.5 mm/min until failure.
Statistical Analysis
All the sticks of each group were pooled together for the statistical analysis. The
distribution of microtensile bond strength data was first checked for normality with the
Kolmogorov-Smirnov test. The data were analyzed with one-way analysis of variance
(ANOVA) and Tukey’s multiple comparison tests with α=0.05.
Scanning Electron Microscopy (SEM)
After microtensile bond testing, several pairs of specimens from each group
were randomly selected for SEM examination. Impressions (Provil Novo, Heraeus
60
Kulzer, Hanau, Germany) of these slices were taken and a set of epoxy resin replicas
(Alpha Die, Schuetz Dental, Rosbach, Germany) was made for SEM evaluation. The
resin replicas were mounted on metallic stubs, sputtered with gold/palladium and
observed with a SEM (JSM – 6060LV, JEOL, Tokyo, Japan) operating at 10 kV.
RESULTS
Bond strength results of the four groups are shown in Table II. No statistically
significant differences were observed among the four groups, indicating that neither the
resin-coating materials nor the provisional eugenol-free cement had an adverse effect
on the final bond strength (p>0.05).
SEM images of the specimens pre-treated with Excite DSC (Fig. 2; A-B) and
AdheSE (Fig. 3) as resin sealers demonstrated resin tags formation and mixed failure
respectively. SEM analysis of the specimens from Control group 3 revealed the
presence of provisional cement remnants that were not completely removed after
phosphoric acid etching and rinsing prior to the application of the Excite DSC adhesive
(Fig. 4). Images from Control group 4 were similar to Groups 1 and 2 (Fig. 5) in that
mixed failures were predominantly observed.
Fig 2a
61
Fig 2b .
Fig.2 SEM images (3500x) of a specimen from Group I with the use of Excite DSC as resin sealer. After
removal of the provisional cement, Excite DSC and Variolink II were employed for the final
cementation. A. The composite side of a fractured stick showing that resin tags were pulled out of the
dentinal tubule, along with fracture within the hybrid layer (H). The hybrid layer that was formed around
the periphery of the dentinal tubules remained attached to the resin tags (open arrowheads). B. The
corresponding dentin side of the fractured stick, showing the patent dentinal tubules that remained after
the resin tags were pulled out.
Fig.3 SEM image (170x) of a specimen from Group 2 with the use of AdheSE as desensitizer). After
removal of the provisional cement, Excite DSC and Variolink II were employed for the final
cementation. A mixed failure mode was observed the composite side of the fractured stick. C: fractured
resin cement; A: fractured adhesive.
62
Fig.4 SEM image (3500x) of a specimen from Control group 3. As the specimen was not pre-coated with
any adhesive, remnants of the provisional cement (open arrowheads) could be identified from the dentin
surface even after subsequent phosphoric acid and rinsing.
Fig.5 SEM image (85x) of a specimen from Control group 4 with no adhesive applied before provisional
cementation, and the use of Excite DSC/Variolink II for the final cementation. A mixed failure mode,
involving fractured resin cement (C) and fractured adhesive (A) could be observed from the composite
side of the fractured stick.
63
DISCUSSION
In line with previously published studies18,21,22 on the evaluation of microtensile
bond strengths to dentin, the microtensile bond assessment was also employed for this
study. Our results showed that the application of the resin-coating material and the use
of provisional cement by itself did not decrease the bond strength values significantly.
Thus, we have to accept the null hypothesis that the use of adhesives as resin sealers
and the eugenol-free provisional cement have no adverse effect on the microtensile
bond strengths of indirect composites restorations coupled with an adhesive and a resin
cement to dentin.
From the SEM analysis, it was evident that those specimens that were not pre-
coated with any adhesive before the provisional cement application showed remnants of
provisional cement, even after phosphoric acid etching (Fig. 4). A possible explanation
is that as the dentin surface was not covered with any adhesive, the simple mechanical
removal of the provisional cement was not effective enough to create a perfectly clean
dentin surface. On the contrary, when the freshly exposed dentin surface was first
sealed with a dentin adhesive prior to the placement of the provisional cement, we
speculate that the comparatively smoother surface rendered by the underlying adhesive-
layer permitted complete removal of the provisional cement, as the latter was not
bonded to the adhesive. In light of these findings, when dentin pre-coating is not
performed, a meticulous cleaning of the dentin substrate should be performed to prevent
a possible reduction in the adhesion of the final restorations.
In this study, a total-etch system (Excite DSC) and a self-etch system (AdheSE) were
selected as resin-coating materials. Dagostin et al.17 concluded that total-etch adhesive
systems first employed as dentin sealers and consecutively as bonding produce
satisfactory final bond strength values. Thus, a similar conclusion may be extrapolated
from the microtensile results of the present study with the double application of Excite
DSC. Although self-etching primers indeed offer some advantages over total-etch
adhesives such as simplification of the chairside procedures, faster manipulation and
reduced technique sensitivity, some investigators pointed out that these materials are
only able to modify or partially remove the smear layer, as compared with total-etch
adhesives and thus might be less effective as bonding.23,24 The bond strength of the
self-etch adhesive tested in this study was higher when compared with recent studies
64
results.23-26 This may be due to the additional application of the total etch system
(Excite DSC), which is the bonding system recommended by the manufacturer of the
Variolink resin cement for the final luting procedure.
A potential problem associated with the resin-coating technique is whether the
subsequently applied adhesive and resin cement may couple effectively with the
original adhesive surface that is devoid of the oxygen inhibition layer after the
placement and the subsequent removal of the non-bonding provisional cement. The
oxygen-inhibited layer primarily consists of unreacted monomers and oligomers25 that
allows the materials from both sides to cross the interface and blend together to form an
interdiffusion zone, wherein co-polymerization occurs to initiate a chemical bond.
Reports on how the oxygen-inhibited layer affects bond strength have been equivocal.
While some reports indicated a positive correlation between the oxygen-inhibited layer
increased bond strength,28,30 others reported that the presence of oxygen-inhibited layer
has no significant influence on bond strength.30,31 In addition, others concluded that the
presence of an oxygen-inhibited layer was in fact detrimental to bonding additional
layers of composite.32,33
Indeed, SEM micrographs of fractured specimens from Groups 1 and 2 revealed
that mixed failure along the interfaces was the predominant mode of failure and that
pure adhesive failure did not occur (e.g. Fig. 3). These observations provided strong
evidence that coupling of the new adhesive to the existing adhesive-covered dentin was
not affected by the depletion of the original oxygen inhibition layer. Our results,
therefore, were consistent with the recent findings that negate the concept that the
oxygen inhibition layer is required for effective coupling of resin composites.34
Söderholm and Roberts35 showed that during repair of composite materials, the amount
of free radicals available in the original resin was reduced to approximately 30%. While
this is certainly applies to the coupling of new resin materials to old, existing resin
composites, the differences may be accounted for by the half-lives of free-radical decay.
It is known that active free radical may remain in polymerized resins for up to 4-5
weeks that slowly decayed with time (Watts DC. personal communication 2004).
Clinically, as most permanent restorations are bonded within 1-2 weeks after the resin-
coating technique, it is reasonable to speculate that sufficient free-radicals remain within
the adhesive-desensitized dentin to ensure optimal coupling between the original
65
adhesive and the new adhesive. Further studies should be done using electron spin
resonance spectroscopy36, to quantify the rate of decay of free radicals in polymerized
resins that are devoid of the oxygen inhibition layers. This will provide important
information on how long clinicians can leave provisional restorations on adhesive-
desensitized dentin without adversely affect the coupling strengths of the final
restorations.
Although it has been demonstrated that clinically, that hybridizing dentin
bondings are able to reduce post-operative sensitivity, 37-46 recent in vitro 47,48 and in
vivo studies 49,50 have shown that simplified total-etch and self-etch adhesives act as
semi-permeable membranes after polymerization. This means that they permit the
continuous transudation of dentinal fluid and do not provide an hermetic seal in vital
deep dentin. Moreover, two of these studies further showed that continuous fluid
transudation through the adhesive-coated dentin persisted even after a period of
temporization with non-bonding provisional cements.47,49 Although the relatively slow
rate of diffusion of dentinal fluid is unlikely to result in post-operative cold sensitivity,
it may interfere with the optimal polymerization of dual-cured or auto-cured
composites50,51 or resin cements in both direct and indirect restoration.52,53 The
permeability of contemporary simplified adhesives may influence the clinician’s
selection of conventional self-etch and total-etch adhesives with comparatively more
hydrophobic, non-solvented coupling resins for the resin-coating technique.54
66
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dentine permeability: the relative effect of a dentine bonding agent on crown
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behave as permeable membranes after polymerization. Part II. Silver tracer
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one-step self-etch adhesives. J Dent Res 2004; 83: 459-464.
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Single-bottle adhesives behave as permeable membranes after polymerization. I. In
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incompatibility between simplified-step adhesives and chemically-cured or dual-
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incompatibility between simplified-step adhesives and self-cured or dual-cured
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71
Section 4. The effect of additional monomers on a resin cement bond strength.
4.1 The effect of adding an antibacterial monomer on the bond quality of a luting
cementation system.
Nicoletta Chieffi, Stefano Chersoni, Federica Papacchini, Michele Vano, Cecilia Goracci,
Carel L. Davidson, Franklin R. Tay, Marco Ferrari
ABSTRACT
Purpose: To examine the bond quality of a luting cement after incorporation of an
antibacterial molecule into the primer. Methods: Eight non-carious human third molars
were randomly divided in two equal groups. Cylindrical composite blocks were luted
with Panavia F (Group I) and Panavia Prototype (Group II) and the seating pressure was
applied during the entire three-minute polymerization period of the resin cement to
minimize fluid interferences from the underlying dentin. After storing in distilled water
for 24 hours, 0.9 x 0.9 mm sticks were produced from these luted specimens for
microtensile bond testing and SEM examination. Results: No statistically difference in
the bond strength between the control Group and the experimental Group was detected
(p>0.05). From SEM analysis, between the two groups, no significant differences were
found.
Conclusions and clinical significance: Addition of an antibacterial monomer (MDPB)
to existing Panavia F luting cementation system does not negatively affect final bond
quality and might extend the application of the cement.
72
INTRODUCTION
Exposure of dentinal tubules during tooth preparation necessitates that they are
adequately sealed as soon as possible to prevent microleakage, bacterial invasion,1-3 and
minimize postoperative sensitivity.4-7 Treatments available to protect the dentin-pulp
system include agents that seal tubules with resins,5,6,8,9 crystal sediments,10-12 or with
both materials.13 Over the past years, different results were reported on the contribution
of adhesive systems regarding dentin sealing. Some studies14-15 claimed that dentin
bonding alone was able to guarantee a tight seal of the tubules. Others16,17 concluded
that dentin bonding did not completely seal dentinal tubules and as a result, they could
not prevent bacterial penetration. More recently, in vitro18,19 and in vivo20,21 studies
have shown that simplified etch-and-rinse and self-etch adhesives behave as permeable
membranes after polymerization. These adhesives permit continuous transmission of
the dentinal fluid and thus do not provide a hermetic seal when they are applied to vital
deep dentin. Additional measures to protect vital teeth are sought in adding antibacterial
agents to self-etch adhesives. It has been demonstrated that the recently introduced
monomer 12-methacryloyloxydodecylpyridinium bromide (MDPB) provides
extensive22,23 and prolonged24 antibacterial activity, before and after polymerization.
The new commercially available, self-etch primer Clearfil Protect Bond (Kuraray
Medical Inc., Tokyo, Japan) contains this antibacterial resin monomer.25,26
Consequently a prototype of Panavia resin cement (Kuraray Medical Inc., Tokyo,
Japan) in which MDPB is included has recently been formulated.
The objective of this study was to investigate whether the quality of bonding of
the new antibacterial monomer-containing Panavia prototype is not negatively affected
by admixing the agent to the primer of the system. Panavia F was used as control.
Micro-tensile bond strength and SEM examination of the interface were used as
parameters for bonding quality.
The null hypotheses tested was that the incorporation of an antibacterial resin
monomer in a dual-cured resin cement does not alter its quality of bonding to dentin.
MATERIALS AND METHODS
Eight non-carious human third molars that were stored in a 0.5% chloramine T
solution at 4oC were used within one month following extraction. All the teeth
73
underwent bonding in their normal hydrated status, as they were retrieved from the
storage medium. The composition of the materials is shown in Table I. The microtensile
bond strengths values for the two groups are showed in Table II.
Table I. Batch number (#), composition and manufacturer of the materials employed in this study.
Materials Components Manufacturer
Panavia F (# 41170)
Primer a: HEMA, 10-MDP, 5-NMSA, water, accelerator. Primer b: 5-NMSA, accelerator, water, sodium benzene sulfinate. Paste A: 10-MDP, hydrophobic aromatic dimethacrylate, hydrophobic aliphatic dimethacrylate, hydrophilic dimethacrylate, silanated silica, photoinitiator, benzoyl peroxide. Paste B: hydrophobic aromatic dimethacrylate, hydrophobic aliphatic dimethacrylate, hydrophilic dimethacrylate, sodium aromatic sulfinate, accelerator, sodium fluoride, silanated barium glass.
Kuraray Medical Inc., Tokyo, Japan
Panavia Prototype
(# 41127)
Primer a: HEMA, 10-MDP, 12-MDPB, dimethacrylate, water. Primer b: 5-NMSA, accelerator, water, sodium benzene sulfinate. Paste A: 10-MDP, hydrophobic aromatic dimethacrylate, hydrophobic aliphatic dimethacrylate, hydrophilic dimethacrylate, silanated silica, photoinitiator, benzoyl peroxide. Paste B: hydrophobic aromatic dimethacrylate, hydrophobic aliphatic dimethacrylate, hydrophilic dimethacrylate, sodium aromatic sulfinate, accelerator, sodium fluoride, silanated barium glass.
Kuraray Medical Inc., Tokyo, Japan
Abbreviations- HEMA: 2-hydroxyethyl methacrylate; 10-MDP: 10-methacryoloyloxydecyl dihydrogen phosphate; 5-NMSA: N-methacryloxyl-5-aminosalicylic acid; 12-MDPB: 12-Methacryloyloxy dodecylpyridinium bromide; Bis-GMA: Bis-Phenol A diglycidylmethacrylate
74
Table II The microtensile bond strengths values for the two investigated groups.
Values are means ± standard deviations in MPa. Groups with the same superscripts differ not statistically significant (P>0.05)
a. MICROTENSILE EXAMINATION
Specimen Preparation
The occlusal enamel was removed using a slow-speed saw with a diamond-
impregnated disk (Isomet, Buehler Ltd., Lake Bluff, IL, USA) under water cooling. All
teeth were cut at the same level, in order to obtain tooth samples with a standardized
height (5mm). A 180-grit silicon carbide paper was used under running water to create
a clinically relevant smear layer on the dentin surface.
Composite cylinders (Tetric-Ceram, Ivoclar-Vivadent, Schaan, Liechtenstein) of
10 mm in diameter and 6 mm in height were prepared using a split aluminum mold, in
order to limit and standardize the bonding area. Prior to cementing procedures, the
bonding surface of each resin cylinder was sandblasted, etched with phosphoric acid,
rinsed with water and dried.
Cementing procedures
The specimens were randomly divided in two groups (N=4). In the Control
Group, the resin cement Panavia F (Kuraray Medical Inc., Tokyo, Japan) was used
according to manufacturer’s instructions. ED Primer (A+B) was mixed and applied
with a brush on the dentin surface and left in place for 30 s. After drying the etched
surface with gentle air flow, Panavia F resin cement (A+B) was mixed and applied on
each of the freshly prepared composite cylinders.
GROUP
Microtensile
bond strength (MPa)*
I Controll Panavia F
20,71 ( ± 7,31) a
II Experimental
Panavia prototype
19,13 ( ± 6,68) a
75
In the Experimental Group, Panavia prototype was used according to the
manufactures instructions and the bonding procedures were the same as described for
the Control.
In the two groups, the composite block was cemented to the dentin surface
using a constant seating pressure of 1,25 MPa that was maintained during the entire
three minutes lasting period required for complete polymerization of the resin cement.
While the specimen was still under pressure, a layer of Oxyguard was applied after
removal of the excess cement with a probe and left in place for at least 3 min to ensure
optimal polymerization of the resin cement along the exposed margins.
In order to standardize the applied pressure, a metallic tool that delivered 10 Kg
was used. This resulted in a seating force of 98,1 N. The pressure [N/m2] was
calculated, dividing this force [N] by the surface area [m2] of the metal weight. The
value obtained was finally converted into MPa.
Bond Strength Evaluation
After cementation, all the specimens were stored in water for 24 hours at 37°C.
Each tooth was then sectioned vertically with the Isomet saw into a series of slabs. The
slabs were then sectioned vertically into 0.9 x 0.9 mm sticks, based on the “non-
trimming” version of the microtensile bond testing technique.27 For each group 120
sample sticks were tested. Each stick was measured using a digital caliper to determine
the cross-sectional area. The sticks were attached to a testing device with cyanoacrylate
glue (Zapit, DVA, Corona, CA, USA). The device was attached to a universal testing
machine (Triax digital 50, Controls, Milano, Italy) and loaded in tension at a crosshead
speed of 0.5 mm/min until failure.
Statistical Analysis
After checking for normal distribution with the Kolmogorov-Smirnov test,
the differences in bond strength values between the two groups were tested for
statistical significance using the Student t-test. The level of significance was set at
α=0.05.
76
b. SCANNING ELECTRON MICROSCOPY (SEM)
Specimen Preparation
After microtensile bond testing, several pairs (fractured composite and dentin
sides) of specimens from the two groups were randomly selected for SEM
examination. Each specimen was mounted on metallic stubs, sputtered with
gold/palladium and observed with a SEM (JSM – 6060LV, JEOL, Tokyo, Japan)
operating at 10 or 15 kV. Images of the two complementary debonded interfaces for
each fractured specimen were taken at different standardized magnifications at 100-
6,000X.
RESULTS
No statistically difference in the bond strength between the Control group and
the Experimental group was detected (p>0.05) [Table II], indicating that the
incorporation of the antibacterial resin monomer in the dual-cured resin cement does
not alter its bond strength to dentin.
SEM images of the specimens treated with Panavia F (Fig. 1) showed interfaces
practically without structural defects. Images from taken from the experimental group
(Fig. 2) were similar to the control group, also without structural irregularities.
Fig. 1 SEM image (1000x) at the composite site of a fractured sample from Group I. The micrograph
shows the absence of structural defects.
77
Fig. 2 SEM image (1000x) at the composite site of a fractured sample from Group II. Note the similarity
with Fig.1.
DISCUSSION
Since the microtensile values of the experimental group were comparable to the
those of the control group, the null hypothesis tested in this study can be accepted. This
means that the monomer (MDPB) incorporated into a dentin bonding system could
potentially provide bactericidal activity without causing an adverse effect on bond
strength. This antibacterial action is more significant in the case of adhesive systems
with a self-etching priming solution since the demineralized smear layer is not
removed but only incorporated into the hybrid layer by absence of a rinsing procedure.
This implies that residual bacteria may remain at the interface between the tooth and
the luting material, constituting a possible cause of secondary caries and damage to the
pulp. MDPB is a compound of the antibacterial agent quaternary ammonium and a
methacryloyl group, and the antibacterial agent is covalently bound to the polymer
matrix by copolymerization of MDPB with other monomers when the material is
cured.24 Problems with antibacterial additions may arise when chemical incompatibility
with the adhesive monomers occurs as the technical proprieties of the bonding agent
78
can be impaired by the addition of the antibacterial substances, or the material may
become toxic (Schmalz G, personal communication). This latter event can be avoided
by applying the material at a safe distance from the pulp, that is when the dentin barrier
is equal/thicker than 500 µm no toxicity is detectable with glutaraldehyde-free dentin-
bonding agents (Schmaltz G, personal communication). Yet, admixing a monomer
containing the antibacterial agent remains a potential factor of chemical
incompatibility. As such, also simplified self-etch systems exhibit chemical
incompatibility with auto or dual curing resin cements.28,29,30 The reduced procedure of
the simplified one-step or two-step self-etch adhesive systems is associated with an
increase of hydrophilic components in the material in order to facilitate bonding to
intrinsically wet dentine surface.31,32 These adhesion-promoting monomers have the
general structural formula of a hydrophilic group at one end and a monomethacrylolyl
group at the other, which are connected with a linking group.33 As a result, the material
itself becomes more hydrophilic and capable of attracting dentinal fluid34,35 which
affects the final bond strength between the adhesive layer and the greater hydrophobic
components of the resin cement.36,37 When MDPB is incorporated in adhesion-
promoting monomers, covalent bonding of both the bactericide and the hydrophilic
group of adhesion promoting monomers to polymer matrix occurs after curing. The
antibacterial agent dodecylpyridinium bromide remains pendant from the polymer
network and, while the immobilized bactericide can act on bacteria that contact the
surface, it is not clear how the immobilized agent acts on the affinity with water.23
An inverse relationship between water absorption and bond strength of the
adhesive resin systems has been demonstrated in literature.38,39 Based on our
microtensile and SEM results it can be assumed that the antibacterial monomer did not
significantly change the water absorption and thus does not interfere with the final bond
strength of the resin cement.
Moreover, the presence of an oxygen-inhibited layer in acidic self-etch adhesives
was found to be a possible cause of the adverse reaction with self-cured resin
cements.28,30 Hydrophilic groups are thought to show affinity with water molecules by
hydrogen bonding to oxygen.23 However, alternative reducing agents (i.e. benzoyl
peroxide-tertiary aromatic amine and sulphinic acid salts) have been used with dentin
adhesive containing acidic resin monomers in order to improve their bonding with
79
chemical-cured composites.28 According to these authors the improved bond strength
derived from a better affinity between the salts of sulphinic acid and the acid-etched
dentin, as well as from a more complete polymerization of the acidic resin monomers.28
Similarly, the inclusion of two different types of sulphinate ternary catalyst agents40 in
Panavia F system, as well as in the prototype version tested in the present investigation,
may have contributed to the results obtained.
Some of the procedures used in this study, such as the application of a sustained
seating pressure during the composite block cementation, or the use of only the chemical
cured mode of the polymerization in the dual-cured resin cement, differ from the daily
practice. Although clinicians during cementation usually apply a seating force that does
not envelop the entire polymerization period of the resin cement, in particular, during the
auto cured resin cement with a longer setting time, it has to be emphasized that fluid
interferences can occur from the underlying dentin.33 In a recent investigation,34 the
maintained seating pressure protocol was demonstrated to reduce the fluid movement
and by consequence an increase in the bond strength, which was related to a lower
hydrophilicity of the material used. Even if, as in the present investigation no pulpal
pressure was simulated, it may be expected that water interference at the adhesive
interface is present since the specimens were bonded in their normal hydrated status, as
they were retrieved from the storage medium19,42,43.
As in the present investigation, the bond strength and the SEM micrographs of
Panavia F and Panavia prototype were almost identical, it can be hypothesized that the
sustained seating pressure had the same effect on the two materials, notwithstanding
their different composition, which evidently has the same effect on the water
absorption.
From the results of this in vitro study, it can be concluded that for protection of
the dentin and the pulp, resin cements containing the antibacterial molecule (MDPB)
can be used without affecting the final bond strength.
80
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dentinal sealing, and provisional restoration. Quintessence Int 1994; 25: 477-
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3. Pashley EL, Comer RW, Simpson MD, Horner JA, Pashley DH. Dentin
permeability: sealing the dentin in crown preparations. Oper Dent 1992; 17:13-
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4. Kolker JL, Vargas MA, Armstrong SR, Dawson DV. Effect of desensitizing
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5. Suzuki S. Clinical evaluation of a new resin composite crown system to
eliminate postoperative sensitivity. Int J Prosthodont 2000; 20: 499-509.
6. Cobb D.S, Reinhardt J.W, Vargas M.A. Effect of HEMA-containing dentin
desensitizers on shear bond strength of a resin cement. Am J Dent 1997; 10: 62-
65.
7. Cuenin MF, Scheidt MJ, O’Neal RB, Strong SL, Pashley DH, Horner JA, Van
Dyke TE. An in vivo study of dentin sensitivity: the relation of dentin
sensitivity and the patency of dentin tubules. J Periodontol 1991; 62: 668-673.
8. Nikaido T. Nakaoki Y. Ogata M. Foxton R. Tagami J. The resin-coating
technique. Effect of a single-step bonding system on dentin bond strengths. J
Adhes Dent 2003; 5: 293-300.
9. Baba N, Taira Y, Matsumura H, Atsuta M. Surface treatment of dentin with
GLUMA and iron compounds for bonding indirect restorations. J Oral Rehabil
2002; 29: 1052-1058.
10. Seara SF, Erthal BS, Ribeiro M, Kroll L, Pereira GDS. The influence of a dentin
desensitizer on the microtensile bond strength of two bonding systems. Oper
Dent 2002; 27: 154-160.
11. Haveman CW, Charlton DG. Dentin treatment with an oxalate solution and
glass ionomer bond strength. Am J Dent 1994; 7: 247-251.
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12. Gillam DG, Mordan NJ, Sinodinou AD, Tang JY, Knowles JC, Gibson IR. The
effects of oxalate-containing products on the exposed dentin surface: an SEM
investigation. J Oral Rehabil 2001; 28: 1037-1044.
13. Tay FR, Pashley DH, Mak YF, Carvalho RM, Lai SCN, Suh BI. Integrating
oxalate desensitizers with total-etch two-step adhesive. J Dent Res 2003; 82:
703-707.
14. Moodley D, Grobler SR, Rossouw RJ, Oberholzer TG, Patel N. In vitro
evaluation of two adhesive systems used with compomer filling materials. Int
Dent J 2000; 50: 400-406.
15. Gwinnett AJ, Kanaka J. Micromorphological relationship between resin and
dentin in vivo and in vitro. Am J Dent 1992; 5: 19-23.
16. Al-Turki M, Akpata ES. Penetrability of dentinal tubules in adhesive-lined
cavity walls. Oper Dent 2002; 27: 124-131.
17. Akpata ES, Sadiq W. Post-operative sensitivity in glass-ionomer vs adhesive
resin-lined composites. Am J Dent 2001; 14: 34-8.
18. Elgalaid TO, Youngson CC, McHugh S, Hall AF, Creanor SL, Foye RH. In
vitro dentine permeability: the relative effect of a dentine bonding agent on
crown preparations. J Dent 2004; 32: 413-421.
19. Chersoni S, Suppa P, Breschi L, Ferrari M, Tay FR, Pashley DH, Prati C. Water
movement in the hybrid layer after different dentin treatments. Dent Mater
2004; 20: 796-803.
20. Chersoni S, Suppa P, Grandini S, Goracci C, Monticelli F, Yiu C, Huang C,
Prati C, Breschi L, Ferrari M, Pashley DH, Tay FR. In vivo and in vitro
permeability of one-step self-etch adhesives. J Dent Res 2004; 83: 459-464.
21. Tay FR, Frankenberger R, Bouillaguet S, Pashley DH, Carvalho RM, Lai CN.
Single-bottle adhesives behave as permeable membranes after polymerization. I.
In vivo evidence. J Dent 2004; 32: 611-21.
22. Imazato S, Ebi N, Tarumi H, Russell RR, Kaneko T, Ebisu S. Bactericidal
activity and cytotoxicity of antibacterial monomer MDPB. Biomaterials 1999;
20: 899-903.
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23. Imazato S, Tarumi H, Kato S, Ebisu S. Water sorption and colour stability of
composites containing the antibacterial monomer MDPB. J Dent 1999; 27: 279-
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24. Imazato S, Ehara A, Torii M, Ebisu S. Antibacterial activity of dentine primer
containing MDPB after curing. J Dent 1998; 26: 267-71.
25. Imazato S, Tarumi H, Ebi N, Ebisu S. Cytotoxic effects of composite
restorations employing self-etching primers or experimental antibacterial
primers. J Dent 2000; 28: 61-7.
26. Imazato S, Torii Y, Takatsuka T, Inoue K, Ebi N, Ebisu S. Bactericidal effect of
dentin primer containing antibacterial monomer
methacryloyloxydodecylpyridinium bromide (MDPB) against bacteria in human
carious dentin. J Oral Rehabil 2001; 28: 314-9.
27. Shono Y, Ogawa T, Terashita M, Carvalho RM, Pashley EL, Pashley DH.
Regional measurement of resin-dentin bonding as an array. J Dent Res 1999; 78:
699-705.
28. Sanares AME, Itthagarun A, King NM, Tay FR, Pashley D. Adverse surface
interactions between one-bottle light-cured adhesives and chemical-cured
composites. Dent Mater 2001; 17: 542-556.
29. Tay FR, Pashley DH, Yiu CK, Sanares AM, Wei SH. Factors contributing to the
incompatibility between simplified-step adhesives and chemically-cured or
dual-cured composites. Part I. Single-step self-etching adhesive. J Adhes Dent
2003; 5: 27-40.
30. Suh BI, Feng L, Pashley DH, Tay FR. Factors contributing to the incompatibility
between simplified-step adhesives and chemically-cured or dual-cured
composites. Part III. Effect of acidic resin monomers. J Adhes Dent 2003; 5: 283-
291.
31. Yiu CK, Hiraishi N, Chersoni S, Breschi L, Ferrari M, Prati C, King NN,
Pashley DH, Tay FR. Single-bottle adhesives behave as permeable membranes
after polymerization. II. Differential permeability reduction with an oxalate
desensitizer. J Dent 2005 (article in press).
32. Tay FR, Pashley DH, Byoung IS, Carvalho R, Itthagarun A. Single-step
adhesives are permeable membranes. J Dent 2002; 30: 371-82.
83
33. Imazoto S, Imai T, Russel RRB, Torii M, Ebisu S. Antibacterial activity of cured
dental resin incorporating the antibacterial monomer MDPB and adhesion-
promoting monomer. J Biomed Mater Res 1998; 39: 511-515.
34. Tay FR, Pashley DH, Byoung IS, Carvalho R, Itthagarun A. Single-step
adhesives are permeable membranes. J Dent 2002; 30: 371-82.
35. Tay F, Pashley DH. Have dentin adhesives become too hydrophilic? J Can Dent
Assoc 2003; 69: 726-31.
36. Carvalho RM, Pegoraro TA, Tay FR, Pegoraro LF, Silva NRFA, Pashley DH.
Adhesive permeability affects coupling of resin cements that utilize self-etching
primers to dentin. J Dent 2004; 32: 55-65.
37. Mak YF, Lai SCN, Cheung GSP, Chan AWK, Tay FR, Pashley DH. Micro-
tensile bond testing of resin cements to dentin and an indirect resin composite.
Dent Mater 2002; 18: 609-621.
38. Okuda M, Pereira PN, Nakajima M, Tagami J, Pashley DH. Long-term
durability of resin dentin interface: nanoleakage vs. microtensile bond strength.
Oper Dent 2002; 27: 289-96.
39. Hashimoto M, Ohno H, Kaga M, Endo K, Sano H, Oguchi H. In vivo
degradation of resin-dentin bonds in humans over 1 to 3 years. J Dent Res 2000;
79: 1385-91.
40. Nyunt NM, Imai Y. Adhesion to dentin with resin using sulfinic acid initiator
system. Dent Mater 1996; 15: 175-82.
41. Chieffi N, Chersoni S, Papacchini F, Vano M, Goracci C, Davidson CL, Tay
FR, Ferrari M. An in vitro study of the effect of the seating pressure on the
adhesive bonding of indirect restorations.(accepted for publication Am J Dent
2005)
42. Tay FR, Pashley DH, Suh B, Carvalho R, Miller M. Single-step, self-etch
adhesives behave as permeable after polymerization. Part I. Bond strength and
morphological evidence. Am J Dent 2004; 17: 271-278.
43. Tay FR, Pashley DH, Garcia-Godoy F, Cynthia KYY. Single-step, self-etch
adhesives behave as permeable after polymerization. Part II. Silver tracer
penetration evidence. Am J Dent 2004; 17: 271-278.
84
Section 5. Summary, general discussion, conclusions and future research.
5.1 Considering the limits of the currently available adhesive systems and their clinical
implications.
Over the years, various clinical applications have been proposed for adhesive systems.
The thesis concentrates on when these adhesive materials are used during indirect
restorations as materials manufactured exclusively for use with resin cement, as
adhesive dentinal “sealers” before temporary cementation and as material with
adjunctive antibacterial proprieties.
The research reported in Section 2 confirms that, among factors potentially affecting the
coupling of resin cement to dentin, fluid interference from the dentin substrate through
the simplified self-etch adhesive system, still represents the major problem in terms of
final dual-cured resin cement bond strength.
Simplified bonding strategies proposed by dental manufactures have been well accepted
by dentists because they are not time-consuming. Moreover, the different bonding
mechanism of self-etch systems has circumvented some of the clinical problems
associated with the traditional total-etch bonding procedures. Self-etch systems do not
remove the smear plugs, as a result the hydraulic conductance through the dentinal
tubules is reduced and less postoperative sensitivity compared with that of total-etch
systems occurs.1,2 In addition, the bonding mechanism of these materials goes back to a
dry bonding to smear layers. With self-etch adhesives the technique sensitivity of wet
bonding associated with total-etch adhesives is reduced because more hydrophilic and
acidic monomers are used, which enable these materials to etch and prime through
smear layers and into underlying intact dentin.3,4
On the other hand, hydrophilic resin systems attract water because of their higher
concentrations of hydrophilic and ionic resin monomers.5 This is the case above all with
one-step self-etch systems. As a result, an impervious seal of the exposed dentin could
not be achieved even when bonding is performed in the laboratory on the flat dentin
surface and without the additional influence of pulpal pressure, as morphologically
evidenced by SEM analysis performed in the studies showed in Section 2, as well as by
previous literature data.6,7 The fluid moves through the self-etch primed dentin and
when it comes into contact with the slow-setting resin cement, adverse interactions
85
occur. These adverse interactions may be responsible for the unexpected premature
decoupling of self-cured, core buildup composites that are bonded with single-bottle
adhesive systems in vivo,8 and for the low bond strength value results in vitro, as seen in
the present study, as well as in previous research.9,10 These issues led to important
clinical implications, also found by other researchers.11 It is suggested to avoid the
treatment of dentin surfaces with these acidic adhesives before luting indirect
restorations with dual-cure resin composite cements.
On the contrary, the maintained seating pressure during the entire time of dual-cured
resin cement setting, improves the bond strength by reducing incompatibility factors
(Section 2.1). In light of the encouraging results obtained with the application of a
sustained seating pressure, it is important to confirm how effective this is against fluid
interference, when the pressure pulp is simulated. In addition, in order to exclude other
chemical causes of the incompatibility, the same cementation procedure should be
repeated on dehydrated dentin substrate. These further studies could be clinically
relevant as a new alternative to circumvent simplified adhesive permeability when
indirect restorations require dual-cured resin cements.
In order to overcome, at least in part, the problem of the permeability of simplified one-
step systems (in which the resin cement is directly coupled to primed dentin without an
additional resin coating) previous studies12,13 have proposed the dentin coverage with an
additional layer of a greater hydrophobic bonding resin, before the resin cement
application. In order to evaluate the significance of the added hydrophobic layer, the
second study presented in Section 2 was carried out. This study shows that although
fluid flow across bonded dentin cannot be totally eliminated, bond strength of resin
cement is substantially improved by the additional application of the greater
hydrophobic adhesive layer. The maximum bond strength is obtained with
simultaneously applying the maintained seating pressure, which avoids fluid
interferences, permitting a superior bond between the adhesive layer and the resin
cement, resulting in adhesive-resin cement interfaces completely intact at SEM
evaluation.
A potential clinical problem with the use of such a resin coating is the adverse effect on
the fit of the indirect restorations. However this can be overcome if the impression is
taken after coating the teeth with the additional layer.14
86
When dealing with microleakage prevention after tooth preparation,15,16 two papers
were included in the thesis (Section 3.1 and Section 3.2). The study presented in Section
3.2 concluded that the use of dentin adhesives as resin sealers before provisional
cementation with a non-eugenol provisional cement does not adversely affect the
retentive strength of indirect restorations bonded subsequently with an adhesive and a
resin cement.
The traditional opinion that a perfect seal could be achieved if dentin tubules and spaces
within the demineralized collagen matrix were completely infiltrated by adhesive resin,
was based on the assumption that polymerized resins used for bonding are nonporous
and impermeable to fluid movement.17 To date, it is well known that potential leakage
pathways within the hybrid layer and the adhesive layer may both contribute to slow
fluid flow across a dentin-adhesive joint.18,19
However, while water and small ions such as fluoride can certainly move across
adhesive-sealed dentin, one wonders if large molecules, such as glucose, bacterial
products or hydrolytic enzymes, can permeate from the outside, through the adhesive
and dentin, into the pulp.20 Moreover, the relatively slow diffusion of dentin fluid across
the adhesive is unlikely to result in severe postoperative sensitivity.3 In spite of these
logical hypothesis, to date, it appears hard to clinically recommend these materials as
dentinal “sealers”. Thus, the conclusions found in Section 3.2 are influenced by the
difficulty to achieve an impervious seal of the exposed dentin with adhesive systems.
To circumvent the partial protection offered by adhesives systems, it appears useful to
employ therapeutic solutions in which adhesive systems used as resin sealers are helped
with the simultaneous use of treatments with crystals, or with agents providing
antibacterial activity. Taking this into account, the study in Section 4.1 was carried out
and the results obtained suggest that the dual cured resin cement tested, containing the
antibacterial molecule (MDPB) in the primer, does not affect the final bond strength,
and thus can be safety used in order to protect the exposed dentin and the pulp.
Moreover, recently a new technique that uses crystals (oxalate) after acid-etching of
dentin, prior to adhesive application, has been developed.21,22 Reduction in dentin
permeability is thus achieved via subsurface tubular occlusion that does not interfere
with subsequent resin infiltration.
87
In this way of reconsidering the adhesive sealing, the use of adhesive systems to protect
the exposed dentin surface still appears to be effective. When considering the potential
factors affecting the final bond between adhesive and resin cement, the results of the
study presented in Section 3.2 are relevant when referred to the influence that the
oxygen inhibition layer may have on the bonding mechanism. Our observations provide
strong evidence that coupling of the new adhesive to the existing adhesive-covered
dentin is not affected by the depletion of the original oxygen inhibition layer. Further
research could be done in this direction, in order to know how long dentists can leave
provisional restorations on adhesive-covered dentin without adverse affects on the
coupling strength of the final restorations.
The following conclusions can be made:
1. To improve coupling of the resin cement to dentin, both the additional self-etch
adhesive containing the light-cured hydrophobic bonding layer and the sustained seating
pressure during cementation are effective. The latter reduces the incompatibility
between simplified-step adhesives and dual-cured resin cements, since it drastically
reduces the adhesive permeability associated with simplified self-etch adhesives.
2. The use of dentin adhesives as resin sealers before provisional cementation with a
non-eugenol provisional cement does not adversely affect the retentive strength of
indirect restorations bonded subsequently with an adhesive and a resin cement.
3. In order to protect the dentin and the pulp, resin cements containing the antibacterial
molecule (MDPB) can be used without affecting the final bond strength.
According to clinical needs, adhesive systems should be able to bond well to dentin
substrate which is hydrophilic in nature and to resin composites or cements that are
hydrophobic in nature, seal hermetically the dentinal tubules in order to protect exposed
dentin against bacteria, prevent post-operative hypersensitivity, provide high bond
strength immediately but also in time, finally they should be easy to handle and time
saving. Researchers and dentists require that these materials solve a lot of clinical
problems. On the base of these stimuli, over the last years, manufactures have tried to
improve the features of these materials, but in spite of the collaboration between
research, clinical experience, and manufactures, the final ambitious objective of a
versatile bond still remains.
88
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89
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