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Effect of saliva contamination on bond strength of resin luting cements to dentin
journal of dentistry 37 (2009) 923–931
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Effect of saliva contamination on bond strength of resin luting cements to dentin C.W.M. Chung a, C.K.Y. Yiu a,*, N.M. King a, N. Hiraishi a, F.R. Tay b a
Paediatric Dentistry and Orthodontics, Faculty of Dentistry, The University of Hong Kong, Prince Philip Dental Hospital, 34 Hospital Road, Pokfulam, Hong Kong SAR, China b Department of Endodontics, School of Dentistry, Medical College of Georgia, Augusta, GA, USA
article info
abstract
Article history:
Objectives: This study examined the effect of saliva contamination on the microtensile bond
Received 16 January 2009
strength (mTBS) of resin luting cements to dentin.
Received in revised form
Methods: For RelyX ARC (ARC, 3M ESPE), dentin surfaces were etched with 32% phosphoric
13 July 2009
acid. The subgroups were: ARC-control (uncontaminated), ARC-I (saliva contamination,
Accepted 28 July 2009
blot-dried), ARC-II (saliva contamination, rinse, blot-dried) and ARC-III (saliva contamination, rinse, re-etch, rinse, blot-dried). For Panavia F 2.0 (PF, Kuraray), the subgroups were: PFcontrol (uncontaminated), PF-I (saliva contamination, dried), PF-II (saliva contamination,
Keywords:
rinse, dried), PF-III (primer, saliva contamination, dried), PF-IV (primer, saliva contamina-
Resin cement
tion, dried, primer re-applied) and PF-V (primer, saliva contamination, rinse, dried, primer
Saliva
re-applied). Composite blocks were luted onto dentin using the two cements. Bonded
Contamination
specimens were sectioned into 0.9 mm 0.9 mm beams for mTBS testing. Representative
Microtensile bond strength
fractured beams were prepared for fractographic analysis.
Dentin
Results: For ARC, salivary contamination of etched dentin (ARC-I) significantly lowered bond strength ( p = 0.001). Rinsing saliva off with water (ARC-II) restored bond strength to control level. Re-etching dentin surface after rinsing (ARC-III) resulted in the lowest bond strength ( p < 0.001). For PF, salivary contamination of dentin before (PF-I) and after application of primer (PF-III and PF-IV) significantly lowered bond strength ( p < 0.001). Rinsing saliva off with water and re-application of primer (PF-II and PF-V) improved bond strength. Conclusion: Saliva contamination during luting deteriorated the bond quality of resin cements. Decontamination by rinsing with water was most effective in restoring the bond strength of RelyX ARC. Decontamination by water-rinsing and primer re-application after rinsing improved the bond strength of Panavia F 2.0. # 2009 Elsevier Ltd. All rights reserved.
1.
Introduction
Indirect composite resin restorations are stronger and more durable due to their higher filler content and better degree of conversion. They exhibit a significantly lower mean annual failure rate than direct techniques.1 Resin cements are increasingly used for luting all-ceramic, metal or composite indirect
restorations, due to their excellent mechanical properties, better bond strengths and improved aesthetics when compared to conventional cements.2 They have the ability to bond to both restoration and tooth surface. Additionally, they have been shown to exhibit reduced dissolution in the oral environment.3 Currently, adhesives are used to bond resin cement to tooth surface and they are classified as either etch-and-rinse or self-
* Corresponding author. Tel.: +852 2859 0251; fax: +825 2559 3803. E-mail address: [email protected] (C.K.Y. Yiu). 0300-5712/$ – see front matter # 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.jdent.2009.07.007
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etch adhesives.4 Bonding resin cement to tooth structure is challenging, as the preparation of the hydrophilic dentin surface for application of the hydrophobic resin cement is a technique sensitive procedure and is time consuming.5 Resin cements that incorporated self-etch adhesive are becoming more popular because of their ease of use and lack of postoperative sensitivity.6 As dental adhesives and tooth surfaces are very vulnerable to fluid contamination,7,8 it is important to keep the bonding substrate free of contamination. The contaminants present in the oral cavity may be in the form of saliva, blood or plasma. The effect of saliva contamination on the bond strength of adhesive systems to dentin is controversial. Several studies7– 10 have shown that saliva contamination significantly reduced bond strength of dentin adhesives; others reported contradictory results.11,12 No studies have explored the effect of saliva contamination on the bond strength of resin cements to dentin. The multi-step application of resin cements via the etch-and-rinse and self-etch approaches may increase the risk of saliva contamination during the luting procedures when moisture control is inadequate. It is therefore of clinical importance to determine the effect of saliva contamination on bond strength of resin cement to dentin, as this may affect the durability of indirect aesthetic restorations. The objective of this study was to evaluate the effect of salivary contamination on the microtensile bond strength of two resin luting cements to dentin and to determine the best decontamination method to re-establish the original resin– dentin bond strength. The null hypothesis tested was that salivary contamination has no effect on the microtensile bond strength of two resin luting cements to dentin.
2.
Materials and methods
2.1.
Tooth preparation
polymerization, the partially polymerized cylindrical composite blocks were placed inside a composite inlay processing chamber (Dentacolor1 XS, Heraeus Kulzer GmbH & Co. KG, Wehrheim, Germany) and heat-cured at 100–110 8C for 5 min. The bonding surface of each composite was ground with #180grit SiC paper to create a roughened surface. The composite was etched with 32% phosphoric acid gel (Uni-Etch, Bisco Inc., Schaumburg, IL, USA) for 15 s and rinsed for 10 s. A mixture of Clearl SE Primer and Porcelain Bond Activator (Kuraray Medical Inc.) was applied for 5 s on each bonding surface of composite and dried.
2.3.
Two types of resin luting cements, RelyX ARC (3 M ESPE, St. Paul, MN, USA) and Panavia F 2.0 (Kuraray Medical Inc., Tokyo, Japan) were investigated in this study (Table 1). The two resin cements were used according to the manufacturers’ instructions. RelyX ARC is a resin cement used in conjunction with a two-step etch-and-rinse adhesive. Phosphoric acid (32%) was used to prepare dentin. Adper Single Bond 2 (3M ESPE), a twostep etch-and-rinse adhesive was applied on the dentin surface before luting with RelyX ARC. Panavia F 2.0 is used with a one-step self-etch adhesive. The dentin was prepared with ED primer, followed by luting with Panavia F 2.0. After the resin cement was applied on dentin surface, the composite block was placed under a constant seating pressure of 3.0 kg (40 g/mm2) that was maintained for 3 min. The selection of 3.0 kg was based on a previous study, in which such a greater seating force enhanced interfacial adaptation and subsequently improved bond strength of resin cements.13,14 For Panavia F 2.0, Oxyguard II was liberally applied around the resin cement to ensure complete anaerobic polymerization. Light-curing was then performed from four parallel directions for 20 s along the cement interface using an Optilux light-curing unit at 600 mW/cm2.
2.4. Fifty caries-free human third molars that had been stored in a 0.5% chloramine T solution at 4 8C were used within 1 month after extraction. The teeth were collected after the patients’ informed consent had been obtained under a protocol reviewed and approved by the Institutional Review Board of the University of Hong Kong. The occlusal enamel and roots of the teeth were removed using a slow-speed saw (Isomet, Buehler Ltd., Lake Bluff, IL) under water lubrication to form 5– 6 mm thick crown segments that were devoid of enamel. A #600-grit silicon carbide (SiC) paper was used under running water for 30 s to create a smear layer on the surface of the coronal dentin.
2.2.
Cylindrical composite block preparation
A heat and light-activated hybrid resin composite (ESTENIA C&B, Kuraray Medical Inc.) was used for the experiment. Layers of composite were dispensed into flat Teflon molds (5 mm thickness, 10 mm diameter). The uncured composite was initially light-cured using a quartz–tungsten–halogen light-curing unit (Optilux 500, Demetron Research Corporation, Danbury, CT, USA) operated at 600 mW/cm2. To improve
Cementation of indirect composite blocks
Experimental design
The teeth were randomly allocated to ten groups according to the different surface contaminations. Five teeth were assigned per control group and per type of contamination for each resin luting cement. Whole saliva was collected from a single individual to standardize the saliva for all surface contaminations. Fresh saliva is considered an acceptable material to be used in saliva contamination testing.15,16 The teeth were treated as follows: The RelyX ARC specimens were divided into four groups based on different contamination and decontamination procedures (Fig. 1): ARC-control: without saliva contamination. The teeth were luted with RelyX ARC luting cement following the manufacturer’s instructions. ARC-I: following etching, saliva was applied to the dentin surface with a microbrush, left undisturbed for 10 s and then blot-dried carefully. ARC-II: following etching, saliva was applied to the dentin surface with a microbrush, left undisturbed for 10 s, rinsed with water then blot-dried carefully.
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Table 1 – Composition and application of the tested luting resin cements. Product
Dentin treatment
Composition
RelyX ARC (ARC) Two-step etch-and-rinse resin luting cement
1. Etch with phosphoric acid 2. Apply Adper Single Bond 2 and light cure
Adper Single Bond 2 (Lot: 6JF): Ethanol, Bis-GMA, silane-treated silica, HEMA, glycerol 1,3-dimethacrylate, copolymer of acrylic and itaconic acids, diurethane dimethacrylate, water. Dual cure-filled resin cement (Lot: EYGH): Bis-GMA, TEDGMA, zirconia filler, silica.
Panavia F2.0 (PF) One-step self-etch resin luting cement
1. Apply ED primer 2.0 for 30 s and air-dry gently
ED primer 2.0A (Lot: 00226A): HEMA, 10-MDP, 5-NMSA, water, accelerator ED primer 2.0B (Lot: 00105A): 5-NMSA, accelerator, water, sodium benzene sulfinate. Paste A (Lot: 00239A): 10-MDP, hydrophobic aromatic dimethacrylate, hydrophobic aliphatic dimethacrylate, hydrophilic dimethacrylate, silanated silica, photoinitiator, benzoyl peroxide Paste B (Lot: 00128A): hydrophobic aromatic dimethacrylate, hydrophobic aliphatic dimethacrylate, hydrophilic dimethacrylate, sodium aromatic sulfinate, accelerator, sodium fluoride, silanated barium glass.
Abbreviations: Bis-GMA: bisphenol A diglycidyl ether dimethacrylate; HEMA: 2-hydroxyethyl methacrylate; TEDGMA: triethylene glycol dimethacrylate; 10-MDP: 10-methacryoloyloxydecyl dihydrogen phosphate; 5-NMSA: N-methacryloxyl-5-aminosalicylic acid. Note: The brand name of Adper Single Bond 2 is used in Latin America and Oceania, while Adper Scotchbond 1 XT is used in Europe, Adper Single Bond Plus in the USA and Adper Single Bond 1 XT in South Africa.
ARC-III: following etching, saliva was applied to the dentin surface with a microbrush, left undisturbed for 10 s, rinsed with water, re-etched then blot-dried carefully. The Panavia F 2.0 specimens were similarly divided into six groups based on different contamination and decontamination procedures (Fig. 2): PF-control: without saliva contamination. The teeth were luted with Panavia 2.0 luting cement following the manufacturer’s instructions.
PF-I: prior to application of ED primer, saliva was applied to the dentin surface with a microbrush, left undisturbed for 10 s and then dried with oil-free compressed air. PF-II: prior to application of ED primer, saliva was applied to the dentin surface with a microbrush, left undisturbed for 10 s, rinsed with water, and then dried with oil-free compressed air. PF-III: following application of ED primer, saliva was applied to the dentin surface with a microbrush, left undisturbed for 10 s and then dried with oil-free compressed air. PF-IV: following application of ED primer, saliva was applied to the dentin surface with a microbrush, left undisturbed for 10 s, dried with oil-free compressed air and ED primer re-applied. PF-V: following application of ED primer, saliva was applied to the dentin surface with a microbrush, left undisturbed for 10 s rinsed with water, dried with oil-free compressed air and ED primer re-applied. Details of the luting procedures for each resin cement are presented in Figs. 1 and 2.
2.5.
Fig. 1 – Luting procedures for RelyX ARC (ARC groups).
Measurement of microtensile bond strength
After storage in distilled water at 37 8C for 24 h, the luted teeth were sectioned occluso-gingivally into serial slabs, and further sectioned into 0.9 mm 0.9 mm composite-dentin beams, according to the ‘‘non-trimming’’ technique of the microtensile test.17 Eight beams were retrieved from the two widest slabs of each tooth. Five teeth from each group yielded 40 beams for bond strength evaluation. The exact dimension of each beam was measured using a pair of digital calipers. Each beam was attached to the test apparatus with a cyanoacrylate adhesive and stressed to failure under tension using a universal testing machine Model 4440 (Instron, Inc., Canton, MA, USA) at a crosshead speed of 1 mm/min. Beams that
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2.6.
Statistical analysis
The bond strength data obtained were analyzed using a statistical software package (SigmaStat Version 2.03, SPSS, Chicago, IL, USA). As the normality (Kolmogorov–Smirnof test) and homoscedasticity assumptions (Levene test) of the data appeared to be valid, a one-way ANOVA was used separately for each resin cement to examine the effect of saliva contamination on microtensile bond strength. The total number of tested beams in each group was used in the statistical analysis, with each individual beam considered as a statistical unit. Multiple comparisons were carried out using the Bonferroni and Student–Newman–Keuls test, with statistical significance set at a = 0.05.
Fig. 2 – Luting procedures for Panavia F 2.0 (PF groups).
exhibited premature failure during specimen preparation were recorded as null bond strength and those values were included in the statistical analysis. The fractured surfaces were examined under scanning electron microscopy (SEM) to determine the failure mode. Failures were classified as (1) adhesive failure along the cement–dentin interface, (2) adhesive failure along the cement–composite interface, (3) cohesive failure within resin cement, (4) mixed failure of 1 and 3 and (5) mixed failure of 2 and 3. Representative fractured beams from each subgroup with microtensile bond strength close to the mean bond strength of that group were selected for fractographic analysis by SEM. The fractured sides of the specimens were air-dried, sputter-coated with gold/palladium, and examined using a SEM (FEI Quanta 200 3D, Oregon, USA) operating at 10–20 kV.
3.
Results
3.1.
Microtensile bond strength
Microtensile bond strength results of ARC and PF to dentin are shown in Table 2. One-way ANOVA showed that for ARC groups, saliva contamination (ARC-I) of the etched dentin surface resulted in a significant reduction (20.6 3.8 MPa, p = 0.001) in dentin bond strength from the control group (23.8 2.7 MPa). Rinsing the saliva with water (ARC-II) restored the bond strength of ARC to the control level (23.9 2.8 MPa, p > 0.05). Re-etching the dentin surface following water rinsing (ARC-III), however, resulted in the lowest bond strength among the ARC groups (17.4 3.5 MPa, p < 0.001). For PF, all the experimental groups had significantly lower bond strengths than the control group (24.0 2.9 MPa, p < 0.005). Saliva contamination of dentin before (PF-I) and after primer application (PF-III) significantly lowered the bond strength to 61% (14.8 2.9 MPa) and 54% (13.0 4.3 MPa) of the control values ( p < 0.001), respectively. Rinsing the saliva off the dentin surface with water (PF-II) as well as re-application
Table 2 – Microtensile bond strengths of resin cements to dentin. Surface treatment ARC-control ARC-I ARC-II ARC-III
RelyX ARC a
23.8 2.7 (0:40) [0/28/1/5/6] 20.6 3.8b (2:38) [13/3/0/20/2] 23.9 2.8a (0:40) [4/33/0/0/3] 17.4 3.5c (0:40) [33/0/0/6/1]
Surface treatment PF-control PF-I PF-II PF-III PF-IV PF-V
Panavia F 2.0 24.0 2.9a (0:40) [1/11/1/11/16] 14.8 2.9c (0:40) [11/0/3/25/1] 20.5 3.4b (0:40) [16/1/3/16/4] 13.0 4.3c (1:39) [7/16/1/6/9] 8.1 3.7d (3:37) [12/3/6/14/2] 18.5 4.3b (1:39) [23/1/9/4/2]
Values are means standard deviations. Beams that failed prematurely were recorded as null bond strength and included in the statistical analysis. The number of specimens is shown in parenthesis: (the number of premature failure: the actual number of beams prepared). For each resin luting cement, groups identified with the same letters were not significantly different ( p > 0.05). Numbers in square brackets are the number of specimens classified into five fracture modes [1/2/3/4/5]: [1] adhesive failure along the cement– dentin interface; [2] adhesive failure along the cement–composite interface; [3] cohesive failure within resin cement; [4] mixed failure of 1 and 3; [5] mixed failure of 2 and 3.
journal of dentistry 37 (2009) 923–931
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Fig. 3 – (A) Low magnification view of ARC-control. Presence of coarse polishing lines confirmed adhesive failure at the composite–cement (RC) interface. (B) High magnification view of ARC-I showing failure along the dentin interface. Partially open dentinal tubules and incompletely polymerized resin were observed on the dentin surface. D: fractured dentin. (C) High magnification view of ARC-III demonstrating failure at the adhesive–dentin interface. Over-etching of peritubular and intertubular dentin with incomplete resin penetration.
of primer on saliva-contaminated, primer-treated dentin after water rinsing (PF-V) restored the bond strength to 85% (20.5 3.4 MPa) and 77% (18.5 4.3 MPa) of control values, although the bond strengths were still significantly different ( p < 0.005) from control. Re-application of ED primer directly on saliva-contaminated, primer-treated dentin surface without water rinsing (PF-IV) resulted in the lowest bond strength in the PF groups (8.1 3.7 MPa, p < 0.001).
3.2.
Examination of fractured interfaces
The failure modes are summarized in Table 2. Morphological differences were observed between the fractured interfaces of the specimens in the ARC and PF groups. The SEM micrographs of the dentin sides of representative fractured beams from ARC and PF groups are shown in Figs. 3 and 4. In the ARCcontrol and ARC-II groups, the majority of failures were adhesive failures along the composite–cement interface. By contrast, in ARC-I and ARC-III groups, the mode of failure was largely a mixed failure involving both the composite–cement interface and along the dentin interface. As the fracture patterns were similar for both ARC-control and ARC-II groups, only representative SEM micrograph from ARC-II group is shown. Presence of coarse polishing lines on cement surface confirmed adhesive failure along cement–
adhesive interface (Fig. 3A). High magnification view of the fractured cement revealed air-voids that were incorporated during hand mixing of the two component pastes of the dualcured cement (not shown). Representative adhesive failure along dentin surface from ARC-I group is shown in Fig. 3B. Partially open dentinal tubules and incompletely polymerized resin were found on the dentin surface. Similarly, representative adhesive failure along dentin surface from ARC-III group is shown in Fig. 3C. Over-etching of peritubular and intertubular dentin with incomplete resin penetration were observed. In PF-control group, failures were predominantly adhesive at the composite–cement interface and mixed failures. Representative SEM micrograph from the PF-control group is shown in Fig. 4A and B. Saliva contamination on dentin prior to application of ED primer (PF-I group) increased adhesive failure along dentin. Remnants of a mixture of saliva and resin prevented proper etching and resin infiltration into demineralized dentin (not shown). Similarly, saliva contamination after application of ED primer (PF-III group) and reapplication of ED primer on saliva-contaminated, primertreated dentin surface (PF-IV group) showed increased cohesive failure within cement. There was a marked increase in porosities in the fractured primer layer when comparing PF-IV with PF-III (Fig. 4C). Several droplets could
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Fig. 4 – (A) Low magnification view of PF-control displaying mixed adhesive failures. Presence of coarse polishing lines confirmed adhesive failure at the composite–cement (RC) interface and fine polishing lines validated adhesive failure along the dentin surface. D: fractured dentin. (B) High magnification view of the fractured dentin surface from PF-control revealed well infiltrated hybrid layer with hybridized resin tags. D: fractured dentin. (C) High magnification view from PF-IV demonstrating cohesive failure at the cement–adhesive interface. There is a marked increase in porosity observed in the fractured primer layer. RC: fractured resin cement; P: fractured primer layer. (D) High magnification view of PF-II showing failure along the dentin surface with fractured resin tags at the surface of hybrid layer. Circular, rosette-like fracture pattern (arrows), originating from a patent dentinal tubule (arrowheads), was identified on the dentin surface. D: fractured dentin. (E) High magnification view of PF-V showing adhesive failure at the adhesive–dentin interfaces. The fractured primer layer appeared thickened, porous and unevenly infiltrated into the dentinal tubules. Several droplets (arrows) were found in association with the dentinal tubules. P: fractured primer layer; D: fractured dentin.
be found in the fractured primer layer. Decontamination by rinsing with water before (PF-II group) primer application had a majority of adhesive failure along dentin surface. Circular, rosette-like fracture pattern (20 mm in diameter) originating from a patent dentinal tubule orifice could be identified on the dentin surface (Fig. 4D). Decontamination
by rinsing with water on primed dentin surface similarly resulted in increased failure along dentin interface (PF-V group). The dentin surface was demineralized with open dentinal tubules incompletely infiltrated by resin (Fig. 4E). Several droplets were found in association with the dentinal tubules.
journal of dentistry 37 (2009) 923–931
4.
Discussion
The present study investigated the effect of saliva contamination on the microtensile bond strength of two resin luting cements to dentin, and the effect of different types of decontamination methods. The results of the study demonstrated that saliva contamination decreased the microtensile bond strengths of both RelyX ARC and Panavia F 2.0 to dentin. Thus, we have to reject the null hypothesis that saliva contamination has no effect on the microtensile bond strength of resin luting cements to dentin. Contamination by saliva, blood and gingival crevicular fluid is a major clinical problem encountered during restorative dental treatment, especially when the cavity margins are near or at the gingival margins. As demonstrated by previous studies, contamination of the tooth surface prior to or during the bonding procedures can result in decreased quality of the bond, which may result in microleakage or loss of restorative material.7,18 Isolation of the working field is essential with any bonding procedure. Good isolation may be achieved with the use of rubber dam. Saliva is a very dilute solution, composed of more than 99% water. Saliva also contains immunoglobulins, glycoproteins, enzymes (e.g. a-amylase), mucins, nitrogenous products, and a variety of electrolytes.19 Excess water from saliva had been reported to cause overwetting of dentin surfaces and reduced bond strength of dentin adhesives.20 Salivary glycoproteins may also be adsorbed and accumulated on the bonded surface, thus interfering with proper adhesion.20 It has also been shown that high molecular weight macromolecules in saliva may diffuse into the dentin tubules.21 These macromolecules may compete with hydrophilic monomers during the hybridization process, reducing the bond strength.22 Additionally, it has been previously shown that Bis-GMA in composite is degraded by enzymes present in human saliva, and this hydrolytic activity may similarly contribute to the breakdown of the bonded interfaces.23,24 There have been minimal studies which investigated the effect of saliva contamination on the bond strength of resin luting cements. The performance of resin luting cement depends on the quality of dentin hybridization and degree of polymerization of adhesive and cement at the bonded interface. In group ARC-I, the dentin surface was simply blot-dried following contamination with saliva. The bond strength this group was significantly lower than the control group. Blotting dry dentin surface was not sufficient to eliminate saliva contamination. After investigation of the failure modes under SEM, it was found that group ARC-I had majority of failures along the dentin surface, which was not observed in ARCcontrol or ARC-II groups. Viewing at higher magnification, incompletely polymerized adhesive resin was seen on the dentin surface (Fig. 3C). These results correlated with previous reports which showed that bond strength of two-step etchand-rinse adhesives was affected by saliva contamination.7,8 In the present study, we found that for RelyX ARC, the bond strength was re-established when the saliva was rinsed with water and the dentin surface blot-dried before the application of Adper Single Bond (ARC-II). Rinsing with water may have removed the contaminants in saliva and in addition, provided the dentin with an optimal water content to facilitate moist
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bonding with the etch-and-rinse adhesive. The hydrophilic self-priming adhesive was therefore able to form a good hybrid layer and provide a strong bond between the dentin and resin luting cement. Additionally, the SEM images of ARC-control and ARC-II groups were similar and showed that the majority of failures were adhesive which occurred at the composite– cement interface (Fig. 3A), confirming the strong bond of luting cement to dentin in the absence of saliva contamination or following decontamination, which exceeds the cohesive strength of the cement. In experimental group ARC-III, the dentin surface was contaminated with saliva, followed rinsing with water and reetching of the dentin surface prior to application of the adhesive. The bond strength of this group was the lowest in the ARC groups. It appears that the action of re-etching the dentin was detrimental to the adhesive surface structure. Investigation under SEM showed the majority of failures involved the adhesive–dentin interface. It has previously been demonstrated that the demineralized dentin layer becomes too thick following re-etching, thereby preventing optimal penetration of adhesive monomers.25,26 Re-etching the dentin after saliva contamination had been shown to increase microgap formation at resin–dentin interface.27 As a result, most failures in the ARC-I and ARC-III groups were adhesive along the dentin interface, indicating a weak link between Adper Single Bond and dentin. Hence, for ARC group, decontamination by water rinsing is the most reliable method for restoring the bond strength. For Panavia F 2.0, all five experimental groups had bond strength values that were significantly lower than the control group. Similar to previous studies 8–10,28 freshly prepared, uncontaminated dentin was used as the bonding substrate in the control group. However, such saliva-free dentin surface is difficult to achieve clinically. In contrast to the ARC groups, more adhesive failures were observed in the PF groups when self-etch primers were used. This could be attributed to increased permeability of the bonded interfaces, which may have compromised the ultimate bond strength of the resin cement.29,30 Greater concentration of hydrophilic resin monomers in the ED primer and the lack of additional hydrophobic resin coating render these simplified self-etch adhesives extremely permeable and allow water transportation across the etched and primed dentin. Water transudation may further be facilitated by the slow polymerizing rate of ED primer in the self-curing mode. The lower bond strengths observed in the PF-I, PF-III and PF-IV groups may be explained by the incomplete removal of saliva constituents. This is in agreement with previous studies which showed reduced bond strength in one-step self-etch adhesives following saliva contamination.9,10 When viewed under SEM, PF-control group had a majority of mixed adhesive failure between the composite–cement and adhesive–dentin interfaces (Fig. 4A and B). By contrast, SEM images of group PF-I show a majority of failures along the dentin surface. ED primer is water-based and does not contain additional solvent such as ethanol or acetone to dissolve the salivary glycoproteins and remove saliva contaminants.31 This could have compromised the demineralization and infiltration of ED primer into dentin. In groups PF-III and PF-IV, there were more mixed failures involving the cement-adhesive and adhesive–dentin inter-
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faces. Saliva remnants were still partially observed primed dentin surface even after drying. ED primer contains 30–50% HEMA. It is functions as a polymerizable solvent for the other resin monomers such as 10-MDP and 5-NSMA (Table 1). As it is highly hydrophilic, water from saliva may be retained to form permeable hydrogels at the primer–cement interface.32 With group PF-III, the retained water from saliva could have affected the rate and extent of polymerization of primer and hydrophobic resin cement, resulting in a porous, weakened surface between the resin cement and adhesive.33 With PF-IV, the porosities in the primer layer were even more marked. SEM micrograph of PF-III and PF-IV groups showed several droplets on the fractured primer surface, indicating water, air or saliva might have been trapped between the primer layers during rinsing and air-drying (Fig. 4C). These water or air droplets render the primer layer weaker and lower the bond strength. Thus, air-drying alone only spread the saliva over the salivacontaminated surface and might not effectively eliminate saliva contamination. Direct application of ED primer on saliva-contaminated dentin or primed dentin surface following air-drying is not recommended for decontamination. For groups PF-II and PF-V in which water rinsing occurred, although the bond strengths were raised to 85% (PF-II) and 75% (PF-V) of control values, they were still significantly different from control. There was also possibly incomplete removal of the contamination in these two groups, but more likely the dentin surface was exposed to more water from rinsing, and therefore may have been too moist for the self-etching adhesive. Examination under SEM showed that groups PF-II and PF-V had mixed failures involving the cement–adhesive and adhesive–dentin interfaces. Incomplete removal of water from rinsing may prevent proper etching and hybridization on some areas of dentin.34 Several unique rosette-like structures were observed emerging from patent dentin tubules were observed under SEM (Fig. 4D). These structures were also seen in PF-control group. These blisters were either filled with water that permeated from the dentinal tubules, or represented incompletely polymerized regions within the primer layer that resulted from the entrapment of water.29 The water used to rinse the saliva contamination may have remained trapped within some dentinal tubules after which the primer was applied to the dentin surface. Conversely, group PF-V showed a demineralized surface not infiltrated by resin (Fig. 4E). Incomplete removal of water from rinsing as well as transudation of water from open dentinal tubules resulted in several water droplets on dentin surface. Thus, in contrast to the ARC groups, decontamination by water rinsing is more unpredictable in the PF groups and may not be easily accomplished on primed dentin surfaces. This study was an in vitro study, and the laboratory results may not correlate with the clinical setting. The present study did not investigate the consequences of saliva contamination occurring on cured adhesive layer prior to luting with ARC. However, previous studies have shown that saliva contamination after polymerization of cured adhesive layer presented a detrimental effect on dentin bond strength.9,10 This could be explained by the adsorption of glycoproteins onto the poorly polymerized, oxygen inhibited adhesive surface, compromising the polymerization between the adhesive and resin composite.31 Furthermore, the presence of excess water on
cured adhesive may also compromise the setting of the overlying RelyX ARC resin cement.30 Re-application of the adhesives after drying or rinsing the contamination reestablished the bond strength.9 Further studies are needed to confirm these results with RelyX ARC cement.
5.
Conclusion
Within the limits of this study, it may be concluded that: 1. Saliva contamination of dentin surfaces during luting deteriorated the bond quality of RelyX ARC and Panavia F 2.0. 2. For RelyX ARC, decontamination by rinsing with water was effective for restoring the bond strength, while re-etching decreased the bond strength. 3. For Panavia F 2.0, decontamination by rinsing with water and re-application of primer after rinsing improved the bond strength.
references
1. Manhart J, Chen H, Hamm G, Hickel R. Buonocore Memorial Lecture. Review of the clinical survival of direct and indirect restorations in posterior teeth of the permanent dentition. Operative Dentistry 2004;29:481–508. 2. McCabe JF, Walls AWG. Applied dental materials. 8th ed. Oxford: Blackwell Science; 1998. 3. White SN, Sorensen JA, Kang SK, Caputo AA. Microleakage of new crown and fixed partial denture luting agents. Journal of Prosthetic Dentistry 1992;67:156–61. 4. Van Meerbeek B, De Munck J, Yoshida Y, Inoue S, Vargas M, Vijay P, et al. Buonocore memorial lecture. Adhesion to enamel and dentin: current status and future challenges. Operative Dentistry 2003;28:215–35. 5. Yoshida Y, Van Meerbeek B, Nakayama Y, Snauwaert J, Hellemans L, Lambrechts P, et al. Evidence of chemical bonding at biomaterial-hard tissue interfaces. Journal of Dental Research 2000;79:709–14. 6. Christensen GJ. Should resin cements be used for every cementation? Journal of American Dental Association 2007;138:817–9. 7. Hiraishi N, Kitasako Y, Nikaido T, Nomura S, Burrow MF, Tagami J. Effect of artificial saliva contamination on pH value change and dentin bond strength. Dental Materials 2003;19:429–34. 8. Park JW, Lee KC. The influence of salivary contamination on shear bond strength of dentin adhesive systems. Operative Dentistry 2004;29:437–42. 9. Sattabanasuk V, Shimada Y, Tagami J. Effects of saliva contamination on dentin bond strength using all-in-one adhesives. Journal of Adhesive Dentistry 2006;8:311–8. 10. Yoo HM, Oh TS, Pereira PN. Effect of saliva contamination on the microshear bond strength of one-step self-etching adhesive systems to dentin. Operative Dentistry 2006;31: 127–34. 11. Taskonak B, Sertgoz A. Shear bond strengths of saliva contaminated ‘one-bottle’ adhesives. Journal of Oral Rehabiliatation 2002;29:559–64. 12. van Schalkwyk JH, Botha FS, van der Vyver PJ, de Wet FA, Botha SJ. Effect of biological contamination on dentine bond strength of adhesive resins. Journal of the South African Dental Association 2003;58:143–7.
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13. Chieffi N, Chersoni S, Papacchini F, Vano M, Goracci C, Davidson CL, et al. Effect of the seating pressure on the adhesive bonding of indirect restorations. Amercian Journal of Dentistry 2006;19:333–6. 14. Goracci C, Cury AH, Cantoro A, Papacchini F, Tay FR, Ferrari M. Microtensile bond strength and interfacial properties of self-etching and self-adhesive resin cements used to lute composite onlays under different seating forces. Journal of Adhesive Dentistry 2006;8:327–35. 15. Hitmi L, Attal JP, Degrange M. Influence of the time-point of salivary contamination on dentin shear bond strength of 3 dentin adhesive systems. Journal of Adhesive Dentistry 1999;1:219–32. 16. Vassilakos N, Arnebrant T, Glantz PO. Adsorption of whole saliva onto hydrophilic and hydrophobic solid surfaces: influence of concentration, ionic strength and pH. Scandinavian Journal of Dental Research 1992;100:346–53. 17. Shono Y, Terashita M, Shimada J, Kozono Y, Carvalho RM, Russell CM, et al. Durability of resin–dentin bonds. Journal of Adhesive Dentistry 1999;1:211–8. 18. Duangthip D, Lussi A. Microleakage and penetration ability of resin sealant versus bonding system when applied following contamination. Pediatric Dentistry 2003;25:505–11. 19. Humphrey SP, Williamson RT. A review of saliva: normal composition, flow, and function. Journal of Prosthetic Dentistry 2001;85:162–9. 20. Xie J, Powers JM, McGuckin RS. In vitro bond strength of two adhesives to enamel and dentin under normal and contaminated conditions. Dental Materials 1993;9:295–9. 21. Pashley DH, Nelson R, Kepler EE. The effects of plasma and salivary constituents on dentin permeability. Journal of Dental Research 1982;61:978–81. 22. el-Kalla IH, Garcia-Godoy F. Saliva contamination and bond strength of single-bottle adhesives to enamel and dentin. American Journal of Dentistry 1997;10:83–7. 23. Finer Y, Santerre JP. Salivary esterase activity and its association with the biodegradation of dental composites. Journal of Dental Research 2004;83:22–6.
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24. Lin BA, Jaffer F, Duff MD, Tang YW, Santerre JP. Identifying enzyme activities within human saliva which are relevant to dental resin composite biodegradation. Biomaterials 2005;26:4259–64. 25. Hashimoto M, Ohno H, Endo K, Kaga M, Sano H, Oguchi H. The effect of hybrid layer thickness on bond strength: demineralized dentin zone of the hybrid layer. Dental Materials 2000;16:406–11. 26. Pashley DH, Ciucchi B, Sano H, Horner JA. Permeability of dentin to adhesive agents. Quintessence International 1993;24:618–31. 27. Duarte SJ, Lolato AL, de Freitas CR, Dinelli W. SEM analysis of internal adaptation of adhesive restorations after contamination with saliva. Journal of Adhesive Dentistry 2005;7:51–6. 28. Townsend RD, Dunn WJ. The effect of saliva contamination on enamel and dentin using a self-etching adhesive. Journal of the American Dental Association 2004;135:895–901. 29. Carvalho RM, Pegoraro TA, Tay FR, Pegoraro LF, Silva NR, Pashley DH. Adhesive permeability affects coupling of resin cements that utilise self-etching primers to dentine. Journal of Dentistry 2004;32:55–65. 30. Hiraishi N, Yiu CK, King NM, Tay FR. Effect of pulpal pressure on the microtensile bond strength of luting resin cements to human dentin. Dental Materials 2009;25:58–66. 31. Eiriksson SO, Pereira PN, Swift Jr EJ, Heymann HO, Sigurdsson A. Effects of saliva contamination on resin–resin bond strength. Dental Materials 2004;20:37–44. 32. Tay FR, King NM, Chan KM, Pashley DH. How can nanoleakage occur in self-etching adhesive systems that demineralize and infiltrate simultaneously? Journal of Adhesive Dentistry 2002;4:255–69. 33. Jacobsen T, Soderholm KJ. Some effects of water on dentin bonding. Dental Materials 1995;11:132–6. 34. Chiba Y, Rikuta A, Yasuda G, Yamamoto A, Takamizawa T, Kurokawa H, et al. Influence of moisture conditions on dentin bond strength of single-step self-etch adhesive systems. Journal of Oral Science 2006;48:131–7.
available at www.sciencedirect.com
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Effect of saliva contamination on bond strength of resin luting cements to dentin C.W.M. Chung a, C.K.Y. Yiu a,*, N.M. King a, N. Hiraishi a, F.R. Tay b a
Paediatric Dentistry and Orthodontics, Faculty of Dentistry, The University of Hong Kong, Prince Philip Dental Hospital, 34 Hospital Road, Pokfulam, Hong Kong SAR, China b Department of Endodontics, School of Dentistry, Medical College of Georgia, Augusta, GA, USA
article info
abstract
Article history:
Objectives: This study examined the effect of saliva contamination on the microtensile bond
Received 16 January 2009
strength (mTBS) of resin luting cements to dentin.
Received in revised form
Methods: For RelyX ARC (ARC, 3M ESPE), dentin surfaces were etched with 32% phosphoric
13 July 2009
acid. The subgroups were: ARC-control (uncontaminated), ARC-I (saliva contamination,
Accepted 28 July 2009
blot-dried), ARC-II (saliva contamination, rinse, blot-dried) and ARC-III (saliva contamination, rinse, re-etch, rinse, blot-dried). For Panavia F 2.0 (PF, Kuraray), the subgroups were: PFcontrol (uncontaminated), PF-I (saliva contamination, dried), PF-II (saliva contamination,
Keywords:
rinse, dried), PF-III (primer, saliva contamination, dried), PF-IV (primer, saliva contamina-
Resin cement
tion, dried, primer re-applied) and PF-V (primer, saliva contamination, rinse, dried, primer
Saliva
re-applied). Composite blocks were luted onto dentin using the two cements. Bonded
Contamination
specimens were sectioned into 0.9 mm 0.9 mm beams for mTBS testing. Representative
Microtensile bond strength
fractured beams were prepared for fractographic analysis.
Dentin
Results: For ARC, salivary contamination of etched dentin (ARC-I) significantly lowered bond strength ( p = 0.001). Rinsing saliva off with water (ARC-II) restored bond strength to control level. Re-etching dentin surface after rinsing (ARC-III) resulted in the lowest bond strength ( p < 0.001). For PF, salivary contamination of dentin before (PF-I) and after application of primer (PF-III and PF-IV) significantly lowered bond strength ( p < 0.001). Rinsing saliva off with water and re-application of primer (PF-II and PF-V) improved bond strength. Conclusion: Saliva contamination during luting deteriorated the bond quality of resin cements. Decontamination by rinsing with water was most effective in restoring the bond strength of RelyX ARC. Decontamination by water-rinsing and primer re-application after rinsing improved the bond strength of Panavia F 2.0. # 2009 Elsevier Ltd. All rights reserved.
1.
Introduction
Indirect composite resin restorations are stronger and more durable due to their higher filler content and better degree of conversion. They exhibit a significantly lower mean annual failure rate than direct techniques.1 Resin cements are increasingly used for luting all-ceramic, metal or composite indirect
restorations, due to their excellent mechanical properties, better bond strengths and improved aesthetics when compared to conventional cements.2 They have the ability to bond to both restoration and tooth surface. Additionally, they have been shown to exhibit reduced dissolution in the oral environment.3 Currently, adhesives are used to bond resin cement to tooth surface and they are classified as either etch-and-rinse or self-
* Corresponding author. Tel.: +852 2859 0251; fax: +825 2559 3803. E-mail address: [email protected] (C.K.Y. Yiu). 0300-5712/$ – see front matter # 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.jdent.2009.07.007
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etch adhesives.4 Bonding resin cement to tooth structure is challenging, as the preparation of the hydrophilic dentin surface for application of the hydrophobic resin cement is a technique sensitive procedure and is time consuming.5 Resin cements that incorporated self-etch adhesive are becoming more popular because of their ease of use and lack of postoperative sensitivity.6 As dental adhesives and tooth surfaces are very vulnerable to fluid contamination,7,8 it is important to keep the bonding substrate free of contamination. The contaminants present in the oral cavity may be in the form of saliva, blood or plasma. The effect of saliva contamination on the bond strength of adhesive systems to dentin is controversial. Several studies7– 10 have shown that saliva contamination significantly reduced bond strength of dentin adhesives; others reported contradictory results.11,12 No studies have explored the effect of saliva contamination on the bond strength of resin cements to dentin. The multi-step application of resin cements via the etch-and-rinse and self-etch approaches may increase the risk of saliva contamination during the luting procedures when moisture control is inadequate. It is therefore of clinical importance to determine the effect of saliva contamination on bond strength of resin cement to dentin, as this may affect the durability of indirect aesthetic restorations. The objective of this study was to evaluate the effect of salivary contamination on the microtensile bond strength of two resin luting cements to dentin and to determine the best decontamination method to re-establish the original resin– dentin bond strength. The null hypothesis tested was that salivary contamination has no effect on the microtensile bond strength of two resin luting cements to dentin.
2.
Materials and methods
2.1.
Tooth preparation
polymerization, the partially polymerized cylindrical composite blocks were placed inside a composite inlay processing chamber (Dentacolor1 XS, Heraeus Kulzer GmbH & Co. KG, Wehrheim, Germany) and heat-cured at 100–110 8C for 5 min. The bonding surface of each composite was ground with #180grit SiC paper to create a roughened surface. The composite was etched with 32% phosphoric acid gel (Uni-Etch, Bisco Inc., Schaumburg, IL, USA) for 15 s and rinsed for 10 s. A mixture of Clearl SE Primer and Porcelain Bond Activator (Kuraray Medical Inc.) was applied for 5 s on each bonding surface of composite and dried.
2.3.
Two types of resin luting cements, RelyX ARC (3 M ESPE, St. Paul, MN, USA) and Panavia F 2.0 (Kuraray Medical Inc., Tokyo, Japan) were investigated in this study (Table 1). The two resin cements were used according to the manufacturers’ instructions. RelyX ARC is a resin cement used in conjunction with a two-step etch-and-rinse adhesive. Phosphoric acid (32%) was used to prepare dentin. Adper Single Bond 2 (3M ESPE), a twostep etch-and-rinse adhesive was applied on the dentin surface before luting with RelyX ARC. Panavia F 2.0 is used with a one-step self-etch adhesive. The dentin was prepared with ED primer, followed by luting with Panavia F 2.0. After the resin cement was applied on dentin surface, the composite block was placed under a constant seating pressure of 3.0 kg (40 g/mm2) that was maintained for 3 min. The selection of 3.0 kg was based on a previous study, in which such a greater seating force enhanced interfacial adaptation and subsequently improved bond strength of resin cements.13,14 For Panavia F 2.0, Oxyguard II was liberally applied around the resin cement to ensure complete anaerobic polymerization. Light-curing was then performed from four parallel directions for 20 s along the cement interface using an Optilux light-curing unit at 600 mW/cm2.
2.4. Fifty caries-free human third molars that had been stored in a 0.5% chloramine T solution at 4 8C were used within 1 month after extraction. The teeth were collected after the patients’ informed consent had been obtained under a protocol reviewed and approved by the Institutional Review Board of the University of Hong Kong. The occlusal enamel and roots of the teeth were removed using a slow-speed saw (Isomet, Buehler Ltd., Lake Bluff, IL) under water lubrication to form 5– 6 mm thick crown segments that were devoid of enamel. A #600-grit silicon carbide (SiC) paper was used under running water for 30 s to create a smear layer on the surface of the coronal dentin.
2.2.
Cylindrical composite block preparation
A heat and light-activated hybrid resin composite (ESTENIA C&B, Kuraray Medical Inc.) was used for the experiment. Layers of composite were dispensed into flat Teflon molds (5 mm thickness, 10 mm diameter). The uncured composite was initially light-cured using a quartz–tungsten–halogen light-curing unit (Optilux 500, Demetron Research Corporation, Danbury, CT, USA) operated at 600 mW/cm2. To improve
Cementation of indirect composite blocks
Experimental design
The teeth were randomly allocated to ten groups according to the different surface contaminations. Five teeth were assigned per control group and per type of contamination for each resin luting cement. Whole saliva was collected from a single individual to standardize the saliva for all surface contaminations. Fresh saliva is considered an acceptable material to be used in saliva contamination testing.15,16 The teeth were treated as follows: The RelyX ARC specimens were divided into four groups based on different contamination and decontamination procedures (Fig. 1): ARC-control: without saliva contamination. The teeth were luted with RelyX ARC luting cement following the manufacturer’s instructions. ARC-I: following etching, saliva was applied to the dentin surface with a microbrush, left undisturbed for 10 s and then blot-dried carefully. ARC-II: following etching, saliva was applied to the dentin surface with a microbrush, left undisturbed for 10 s, rinsed with water then blot-dried carefully.
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Table 1 – Composition and application of the tested luting resin cements. Product
Dentin treatment
Composition
RelyX ARC (ARC) Two-step etch-and-rinse resin luting cement
1. Etch with phosphoric acid 2. Apply Adper Single Bond 2 and light cure
Adper Single Bond 2 (Lot: 6JF): Ethanol, Bis-GMA, silane-treated silica, HEMA, glycerol 1,3-dimethacrylate, copolymer of acrylic and itaconic acids, diurethane dimethacrylate, water. Dual cure-filled resin cement (Lot: EYGH): Bis-GMA, TEDGMA, zirconia filler, silica.
Panavia F2.0 (PF) One-step self-etch resin luting cement
1. Apply ED primer 2.0 for 30 s and air-dry gently
ED primer 2.0A (Lot: 00226A): HEMA, 10-MDP, 5-NMSA, water, accelerator ED primer 2.0B (Lot: 00105A): 5-NMSA, accelerator, water, sodium benzene sulfinate. Paste A (Lot: 00239A): 10-MDP, hydrophobic aromatic dimethacrylate, hydrophobic aliphatic dimethacrylate, hydrophilic dimethacrylate, silanated silica, photoinitiator, benzoyl peroxide Paste B (Lot: 00128A): hydrophobic aromatic dimethacrylate, hydrophobic aliphatic dimethacrylate, hydrophilic dimethacrylate, sodium aromatic sulfinate, accelerator, sodium fluoride, silanated barium glass.
Abbreviations: Bis-GMA: bisphenol A diglycidyl ether dimethacrylate; HEMA: 2-hydroxyethyl methacrylate; TEDGMA: triethylene glycol dimethacrylate; 10-MDP: 10-methacryoloyloxydecyl dihydrogen phosphate; 5-NMSA: N-methacryloxyl-5-aminosalicylic acid. Note: The brand name of Adper Single Bond 2 is used in Latin America and Oceania, while Adper Scotchbond 1 XT is used in Europe, Adper Single Bond Plus in the USA and Adper Single Bond 1 XT in South Africa.
ARC-III: following etching, saliva was applied to the dentin surface with a microbrush, left undisturbed for 10 s, rinsed with water, re-etched then blot-dried carefully. The Panavia F 2.0 specimens were similarly divided into six groups based on different contamination and decontamination procedures (Fig. 2): PF-control: without saliva contamination. The teeth were luted with Panavia 2.0 luting cement following the manufacturer’s instructions.
PF-I: prior to application of ED primer, saliva was applied to the dentin surface with a microbrush, left undisturbed for 10 s and then dried with oil-free compressed air. PF-II: prior to application of ED primer, saliva was applied to the dentin surface with a microbrush, left undisturbed for 10 s, rinsed with water, and then dried with oil-free compressed air. PF-III: following application of ED primer, saliva was applied to the dentin surface with a microbrush, left undisturbed for 10 s and then dried with oil-free compressed air. PF-IV: following application of ED primer, saliva was applied to the dentin surface with a microbrush, left undisturbed for 10 s, dried with oil-free compressed air and ED primer re-applied. PF-V: following application of ED primer, saliva was applied to the dentin surface with a microbrush, left undisturbed for 10 s rinsed with water, dried with oil-free compressed air and ED primer re-applied. Details of the luting procedures for each resin cement are presented in Figs. 1 and 2.
2.5.
Fig. 1 – Luting procedures for RelyX ARC (ARC groups).
Measurement of microtensile bond strength
After storage in distilled water at 37 8C for 24 h, the luted teeth were sectioned occluso-gingivally into serial slabs, and further sectioned into 0.9 mm 0.9 mm composite-dentin beams, according to the ‘‘non-trimming’’ technique of the microtensile test.17 Eight beams were retrieved from the two widest slabs of each tooth. Five teeth from each group yielded 40 beams for bond strength evaluation. The exact dimension of each beam was measured using a pair of digital calipers. Each beam was attached to the test apparatus with a cyanoacrylate adhesive and stressed to failure under tension using a universal testing machine Model 4440 (Instron, Inc., Canton, MA, USA) at a crosshead speed of 1 mm/min. Beams that
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2.6.
Statistical analysis
The bond strength data obtained were analyzed using a statistical software package (SigmaStat Version 2.03, SPSS, Chicago, IL, USA). As the normality (Kolmogorov–Smirnof test) and homoscedasticity assumptions (Levene test) of the data appeared to be valid, a one-way ANOVA was used separately for each resin cement to examine the effect of saliva contamination on microtensile bond strength. The total number of tested beams in each group was used in the statistical analysis, with each individual beam considered as a statistical unit. Multiple comparisons were carried out using the Bonferroni and Student–Newman–Keuls test, with statistical significance set at a = 0.05.
Fig. 2 – Luting procedures for Panavia F 2.0 (PF groups).
exhibited premature failure during specimen preparation were recorded as null bond strength and those values were included in the statistical analysis. The fractured surfaces were examined under scanning electron microscopy (SEM) to determine the failure mode. Failures were classified as (1) adhesive failure along the cement–dentin interface, (2) adhesive failure along the cement–composite interface, (3) cohesive failure within resin cement, (4) mixed failure of 1 and 3 and (5) mixed failure of 2 and 3. Representative fractured beams from each subgroup with microtensile bond strength close to the mean bond strength of that group were selected for fractographic analysis by SEM. The fractured sides of the specimens were air-dried, sputter-coated with gold/palladium, and examined using a SEM (FEI Quanta 200 3D, Oregon, USA) operating at 10–20 kV.
3.
Results
3.1.
Microtensile bond strength
Microtensile bond strength results of ARC and PF to dentin are shown in Table 2. One-way ANOVA showed that for ARC groups, saliva contamination (ARC-I) of the etched dentin surface resulted in a significant reduction (20.6 3.8 MPa, p = 0.001) in dentin bond strength from the control group (23.8 2.7 MPa). Rinsing the saliva with water (ARC-II) restored the bond strength of ARC to the control level (23.9 2.8 MPa, p > 0.05). Re-etching the dentin surface following water rinsing (ARC-III), however, resulted in the lowest bond strength among the ARC groups (17.4 3.5 MPa, p < 0.001). For PF, all the experimental groups had significantly lower bond strengths than the control group (24.0 2.9 MPa, p < 0.005). Saliva contamination of dentin before (PF-I) and after primer application (PF-III) significantly lowered the bond strength to 61% (14.8 2.9 MPa) and 54% (13.0 4.3 MPa) of the control values ( p < 0.001), respectively. Rinsing the saliva off the dentin surface with water (PF-II) as well as re-application
Table 2 – Microtensile bond strengths of resin cements to dentin. Surface treatment ARC-control ARC-I ARC-II ARC-III
RelyX ARC a
23.8 2.7 (0:40) [0/28/1/5/6] 20.6 3.8b (2:38) [13/3/0/20/2] 23.9 2.8a (0:40) [4/33/0/0/3] 17.4 3.5c (0:40) [33/0/0/6/1]
Surface treatment PF-control PF-I PF-II PF-III PF-IV PF-V
Panavia F 2.0 24.0 2.9a (0:40) [1/11/1/11/16] 14.8 2.9c (0:40) [11/0/3/25/1] 20.5 3.4b (0:40) [16/1/3/16/4] 13.0 4.3c (1:39) [7/16/1/6/9] 8.1 3.7d (3:37) [12/3/6/14/2] 18.5 4.3b (1:39) [23/1/9/4/2]
Values are means standard deviations. Beams that failed prematurely were recorded as null bond strength and included in the statistical analysis. The number of specimens is shown in parenthesis: (the number of premature failure: the actual number of beams prepared). For each resin luting cement, groups identified with the same letters were not significantly different ( p > 0.05). Numbers in square brackets are the number of specimens classified into five fracture modes [1/2/3/4/5]: [1] adhesive failure along the cement– dentin interface; [2] adhesive failure along the cement–composite interface; [3] cohesive failure within resin cement; [4] mixed failure of 1 and 3; [5] mixed failure of 2 and 3.
journal of dentistry 37 (2009) 923–931
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Fig. 3 – (A) Low magnification view of ARC-control. Presence of coarse polishing lines confirmed adhesive failure at the composite–cement (RC) interface. (B) High magnification view of ARC-I showing failure along the dentin interface. Partially open dentinal tubules and incompletely polymerized resin were observed on the dentin surface. D: fractured dentin. (C) High magnification view of ARC-III demonstrating failure at the adhesive–dentin interface. Over-etching of peritubular and intertubular dentin with incomplete resin penetration.
of primer on saliva-contaminated, primer-treated dentin after water rinsing (PF-V) restored the bond strength to 85% (20.5 3.4 MPa) and 77% (18.5 4.3 MPa) of control values, although the bond strengths were still significantly different ( p < 0.005) from control. Re-application of ED primer directly on saliva-contaminated, primer-treated dentin surface without water rinsing (PF-IV) resulted in the lowest bond strength in the PF groups (8.1 3.7 MPa, p < 0.001).
3.2.
Examination of fractured interfaces
The failure modes are summarized in Table 2. Morphological differences were observed between the fractured interfaces of the specimens in the ARC and PF groups. The SEM micrographs of the dentin sides of representative fractured beams from ARC and PF groups are shown in Figs. 3 and 4. In the ARCcontrol and ARC-II groups, the majority of failures were adhesive failures along the composite–cement interface. By contrast, in ARC-I and ARC-III groups, the mode of failure was largely a mixed failure involving both the composite–cement interface and along the dentin interface. As the fracture patterns were similar for both ARC-control and ARC-II groups, only representative SEM micrograph from ARC-II group is shown. Presence of coarse polishing lines on cement surface confirmed adhesive failure along cement–
adhesive interface (Fig. 3A). High magnification view of the fractured cement revealed air-voids that were incorporated during hand mixing of the two component pastes of the dualcured cement (not shown). Representative adhesive failure along dentin surface from ARC-I group is shown in Fig. 3B. Partially open dentinal tubules and incompletely polymerized resin were found on the dentin surface. Similarly, representative adhesive failure along dentin surface from ARC-III group is shown in Fig. 3C. Over-etching of peritubular and intertubular dentin with incomplete resin penetration were observed. In PF-control group, failures were predominantly adhesive at the composite–cement interface and mixed failures. Representative SEM micrograph from the PF-control group is shown in Fig. 4A and B. Saliva contamination on dentin prior to application of ED primer (PF-I group) increased adhesive failure along dentin. Remnants of a mixture of saliva and resin prevented proper etching and resin infiltration into demineralized dentin (not shown). Similarly, saliva contamination after application of ED primer (PF-III group) and reapplication of ED primer on saliva-contaminated, primertreated dentin surface (PF-IV group) showed increased cohesive failure within cement. There was a marked increase in porosities in the fractured primer layer when comparing PF-IV with PF-III (Fig. 4C). Several droplets could
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Fig. 4 – (A) Low magnification view of PF-control displaying mixed adhesive failures. Presence of coarse polishing lines confirmed adhesive failure at the composite–cement (RC) interface and fine polishing lines validated adhesive failure along the dentin surface. D: fractured dentin. (B) High magnification view of the fractured dentin surface from PF-control revealed well infiltrated hybrid layer with hybridized resin tags. D: fractured dentin. (C) High magnification view from PF-IV demonstrating cohesive failure at the cement–adhesive interface. There is a marked increase in porosity observed in the fractured primer layer. RC: fractured resin cement; P: fractured primer layer. (D) High magnification view of PF-II showing failure along the dentin surface with fractured resin tags at the surface of hybrid layer. Circular, rosette-like fracture pattern (arrows), originating from a patent dentinal tubule (arrowheads), was identified on the dentin surface. D: fractured dentin. (E) High magnification view of PF-V showing adhesive failure at the adhesive–dentin interfaces. The fractured primer layer appeared thickened, porous and unevenly infiltrated into the dentinal tubules. Several droplets (arrows) were found in association with the dentinal tubules. P: fractured primer layer; D: fractured dentin.
be found in the fractured primer layer. Decontamination by rinsing with water before (PF-II group) primer application had a majority of adhesive failure along dentin surface. Circular, rosette-like fracture pattern (20 mm in diameter) originating from a patent dentinal tubule orifice could be identified on the dentin surface (Fig. 4D). Decontamination
by rinsing with water on primed dentin surface similarly resulted in increased failure along dentin interface (PF-V group). The dentin surface was demineralized with open dentinal tubules incompletely infiltrated by resin (Fig. 4E). Several droplets were found in association with the dentinal tubules.
journal of dentistry 37 (2009) 923–931
4.
Discussion
The present study investigated the effect of saliva contamination on the microtensile bond strength of two resin luting cements to dentin, and the effect of different types of decontamination methods. The results of the study demonstrated that saliva contamination decreased the microtensile bond strengths of both RelyX ARC and Panavia F 2.0 to dentin. Thus, we have to reject the null hypothesis that saliva contamination has no effect on the microtensile bond strength of resin luting cements to dentin. Contamination by saliva, blood and gingival crevicular fluid is a major clinical problem encountered during restorative dental treatment, especially when the cavity margins are near or at the gingival margins. As demonstrated by previous studies, contamination of the tooth surface prior to or during the bonding procedures can result in decreased quality of the bond, which may result in microleakage or loss of restorative material.7,18 Isolation of the working field is essential with any bonding procedure. Good isolation may be achieved with the use of rubber dam. Saliva is a very dilute solution, composed of more than 99% water. Saliva also contains immunoglobulins, glycoproteins, enzymes (e.g. a-amylase), mucins, nitrogenous products, and a variety of electrolytes.19 Excess water from saliva had been reported to cause overwetting of dentin surfaces and reduced bond strength of dentin adhesives.20 Salivary glycoproteins may also be adsorbed and accumulated on the bonded surface, thus interfering with proper adhesion.20 It has also been shown that high molecular weight macromolecules in saliva may diffuse into the dentin tubules.21 These macromolecules may compete with hydrophilic monomers during the hybridization process, reducing the bond strength.22 Additionally, it has been previously shown that Bis-GMA in composite is degraded by enzymes present in human saliva, and this hydrolytic activity may similarly contribute to the breakdown of the bonded interfaces.23,24 There have been minimal studies which investigated the effect of saliva contamination on the bond strength of resin luting cements. The performance of resin luting cement depends on the quality of dentin hybridization and degree of polymerization of adhesive and cement at the bonded interface. In group ARC-I, the dentin surface was simply blot-dried following contamination with saliva. The bond strength this group was significantly lower than the control group. Blotting dry dentin surface was not sufficient to eliminate saliva contamination. After investigation of the failure modes under SEM, it was found that group ARC-I had majority of failures along the dentin surface, which was not observed in ARCcontrol or ARC-II groups. Viewing at higher magnification, incompletely polymerized adhesive resin was seen on the dentin surface (Fig. 3C). These results correlated with previous reports which showed that bond strength of two-step etchand-rinse adhesives was affected by saliva contamination.7,8 In the present study, we found that for RelyX ARC, the bond strength was re-established when the saliva was rinsed with water and the dentin surface blot-dried before the application of Adper Single Bond (ARC-II). Rinsing with water may have removed the contaminants in saliva and in addition, provided the dentin with an optimal water content to facilitate moist
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bonding with the etch-and-rinse adhesive. The hydrophilic self-priming adhesive was therefore able to form a good hybrid layer and provide a strong bond between the dentin and resin luting cement. Additionally, the SEM images of ARC-control and ARC-II groups were similar and showed that the majority of failures were adhesive which occurred at the composite– cement interface (Fig. 3A), confirming the strong bond of luting cement to dentin in the absence of saliva contamination or following decontamination, which exceeds the cohesive strength of the cement. In experimental group ARC-III, the dentin surface was contaminated with saliva, followed rinsing with water and reetching of the dentin surface prior to application of the adhesive. The bond strength of this group was the lowest in the ARC groups. It appears that the action of re-etching the dentin was detrimental to the adhesive surface structure. Investigation under SEM showed the majority of failures involved the adhesive–dentin interface. It has previously been demonstrated that the demineralized dentin layer becomes too thick following re-etching, thereby preventing optimal penetration of adhesive monomers.25,26 Re-etching the dentin after saliva contamination had been shown to increase microgap formation at resin–dentin interface.27 As a result, most failures in the ARC-I and ARC-III groups were adhesive along the dentin interface, indicating a weak link between Adper Single Bond and dentin. Hence, for ARC group, decontamination by water rinsing is the most reliable method for restoring the bond strength. For Panavia F 2.0, all five experimental groups had bond strength values that were significantly lower than the control group. Similar to previous studies 8–10,28 freshly prepared, uncontaminated dentin was used as the bonding substrate in the control group. However, such saliva-free dentin surface is difficult to achieve clinically. In contrast to the ARC groups, more adhesive failures were observed in the PF groups when self-etch primers were used. This could be attributed to increased permeability of the bonded interfaces, which may have compromised the ultimate bond strength of the resin cement.29,30 Greater concentration of hydrophilic resin monomers in the ED primer and the lack of additional hydrophobic resin coating render these simplified self-etch adhesives extremely permeable and allow water transportation across the etched and primed dentin. Water transudation may further be facilitated by the slow polymerizing rate of ED primer in the self-curing mode. The lower bond strengths observed in the PF-I, PF-III and PF-IV groups may be explained by the incomplete removal of saliva constituents. This is in agreement with previous studies which showed reduced bond strength in one-step self-etch adhesives following saliva contamination.9,10 When viewed under SEM, PF-control group had a majority of mixed adhesive failure between the composite–cement and adhesive–dentin interfaces (Fig. 4A and B). By contrast, SEM images of group PF-I show a majority of failures along the dentin surface. ED primer is water-based and does not contain additional solvent such as ethanol or acetone to dissolve the salivary glycoproteins and remove saliva contaminants.31 This could have compromised the demineralization and infiltration of ED primer into dentin. In groups PF-III and PF-IV, there were more mixed failures involving the cement-adhesive and adhesive–dentin inter-
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faces. Saliva remnants were still partially observed primed dentin surface even after drying. ED primer contains 30–50% HEMA. It is functions as a polymerizable solvent for the other resin monomers such as 10-MDP and 5-NSMA (Table 1). As it is highly hydrophilic, water from saliva may be retained to form permeable hydrogels at the primer–cement interface.32 With group PF-III, the retained water from saliva could have affected the rate and extent of polymerization of primer and hydrophobic resin cement, resulting in a porous, weakened surface between the resin cement and adhesive.33 With PF-IV, the porosities in the primer layer were even more marked. SEM micrograph of PF-III and PF-IV groups showed several droplets on the fractured primer surface, indicating water, air or saliva might have been trapped between the primer layers during rinsing and air-drying (Fig. 4C). These water or air droplets render the primer layer weaker and lower the bond strength. Thus, air-drying alone only spread the saliva over the salivacontaminated surface and might not effectively eliminate saliva contamination. Direct application of ED primer on saliva-contaminated dentin or primed dentin surface following air-drying is not recommended for decontamination. For groups PF-II and PF-V in which water rinsing occurred, although the bond strengths were raised to 85% (PF-II) and 75% (PF-V) of control values, they were still significantly different from control. There was also possibly incomplete removal of the contamination in these two groups, but more likely the dentin surface was exposed to more water from rinsing, and therefore may have been too moist for the self-etching adhesive. Examination under SEM showed that groups PF-II and PF-V had mixed failures involving the cement–adhesive and adhesive–dentin interfaces. Incomplete removal of water from rinsing may prevent proper etching and hybridization on some areas of dentin.34 Several unique rosette-like structures were observed emerging from patent dentin tubules were observed under SEM (Fig. 4D). These structures were also seen in PF-control group. These blisters were either filled with water that permeated from the dentinal tubules, or represented incompletely polymerized regions within the primer layer that resulted from the entrapment of water.29 The water used to rinse the saliva contamination may have remained trapped within some dentinal tubules after which the primer was applied to the dentin surface. Conversely, group PF-V showed a demineralized surface not infiltrated by resin (Fig. 4E). Incomplete removal of water from rinsing as well as transudation of water from open dentinal tubules resulted in several water droplets on dentin surface. Thus, in contrast to the ARC groups, decontamination by water rinsing is more unpredictable in the PF groups and may not be easily accomplished on primed dentin surfaces. This study was an in vitro study, and the laboratory results may not correlate with the clinical setting. The present study did not investigate the consequences of saliva contamination occurring on cured adhesive layer prior to luting with ARC. However, previous studies have shown that saliva contamination after polymerization of cured adhesive layer presented a detrimental effect on dentin bond strength.9,10 This could be explained by the adsorption of glycoproteins onto the poorly polymerized, oxygen inhibited adhesive surface, compromising the polymerization between the adhesive and resin composite.31 Furthermore, the presence of excess water on
cured adhesive may also compromise the setting of the overlying RelyX ARC resin cement.30 Re-application of the adhesives after drying or rinsing the contamination reestablished the bond strength.9 Further studies are needed to confirm these results with RelyX ARC cement.
5.
Conclusion
Within the limits of this study, it may be concluded that: 1. Saliva contamination of dentin surfaces during luting deteriorated the bond quality of RelyX ARC and Panavia F 2.0. 2. For RelyX ARC, decontamination by rinsing with water was effective for restoring the bond strength, while re-etching decreased the bond strength. 3. For Panavia F 2.0, decontamination by rinsing with water and re-application of primer after rinsing improved the bond strength.
references
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