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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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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

4

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.

10

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

11

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.

12

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

17

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

18

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).

20

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

22

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

REFERENCES

1. Hashimoto M, Tay FR, Ito S, Sano H, Kaga M, Pashley DH. Permeability of

adhesive resin films. J Biomed Mater Res B Appl Biomater 2005 (article in

press).

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

penetration evidence. Am J Dent 2004; 17: 315-322.

5. Itthagarun A, Tay FR, Pashley DH, Wefel JS, Garcia-Godoy F, Wei SHI.

Single-step, self-etch adhesives behave as permeable after polymerization.

Part III. Evidence from fluid conductance and artificial caries inhibition. Am

J Dent 2004; 17: 394-400.

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

membranes after polymerization. II. Differential permeability reduction with

an oxalate desensitizer. J Dent 2005 (article in press).

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

REFERENCES

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.

53

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-

34.

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.

54

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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43. Ferrari F, Garcia-Godoy F. Sealing ability of new generation adhesive-restorative

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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

penetration evidence. Am J Dent 2004; 17: 315-322.

49. 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.

50. 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.

51. 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-etch adhesive. J Adhes Dent 2003; 5:27-

40.

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incompatibility between simplified-step adhesives and self-cured or dual-cured

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70

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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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restorative materials placed on vital teeth. Am J Dent 2002; 15:117-128.

2. Shiro S, Cox CF, White KC. Pulpal response after complete crown preparation,

dentinal sealing, and provisional restoration. Quintessence Int 1994; 25: 477-

485.

3. Pashley EL, Comer RW, Simpson MD, Horner JA, Pashley DH. Dentin

permeability: sealing the dentin in crown preparations. Oper Dent 1992; 17:13-

20.

4. Kolker JL, Vargas MA, Armstrong SR, Dawson DV. Effect of desensitizing

agents on dentin permeability and dentin tubule occlusion. J Adhes Dent 2002;

4: 211-221.

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.

81

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.

82

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-

83.

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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Acknowledgements