The Journal of Adhesive Dentistry, 06/2008

Purpose: To evaluate microtensile bond strength and interfacial nanoleakage expression of adhesive interfaces created by XP-Bond on human deproteinized dentin immediately after bonding and after 6 months of artificial aging. Materials and Methods: Noncarious human molars were selected, middle/deep dentin substrates were exposed, and either assigned to group 1 (XP-Bond applied on collagen-depleted dentin) or to group 2 (XP-Bond applied in accordance with manufacturers' instructions). In group 1, the etched dentin surface was treated with 10% NaOCl for 60 s to remove the exposed demineralized organic matrix before XP-Bond application. Composite/dentin beams were obtained in accordance with the microtensile nontrimming technique and either pulled to failure after 24 h or after 6 months' artificial aging. Data were analyzed with two-way ANOVA and Tukey's post-hoc test (p < 0.05). Interfacial nanoleakage evaluation was performed on additional adhesive interfaces to quantify the amount of silver tracer along the interface. Results: The use of NaOCl before XP-Bond application (group 1: 18.9 ± 5.8 MPa) reduced immediate bond strength by 62% compared to controls (group 2: 49.9 ± 10.3 MPa; p < 0.5). After 6 months of artificial aging, the bond strength of groups 1 and 2 significantly decreased to 10.1 ± 2.7 MPa and 35.2 ± 8.7 MPa, resp (p < 0.05). Interfacial nanoleakage expression along XP-Bond adhesive interfaces was increased either by sodium hypochlorite or by artificial aging. Conclusion: The role of collagen fibrils is pivotal for the bonding of XP-Bond to dentin, as decreased immediate bond strength and reduced bond stability over time was found on collagen-depleted dentin. Keywords: dental bonding systems, dentin, sodium hypochlorite, collagen, hybrid layer

Purpose: To estimate the in vitro reliability of typical self-etching and etch-and-rinse adhesives of various application protocols. Materials and Methods: The following adhesives were applied on flat dentin surfaces of extracted human teeth (n = 223): self-etching two-step adhesives: AdheSE (AH), Clearfil SE Bond (CL), OptiBond SE (OS); one-step adhesives: Adper Prompt L-Pop (ADP), Adper Prompt (AD), and Xeno III (XE); all-in-one adhesive: iBond (IB); etch-and-rinse threestep adhesives: OptiBond FL (OF), two-step Gluma Comfort Bond (G), Excite (E) and Prime & Bond NT (PB). Composite buildups were prepared using a microhybrid composite, Opticor New. Shear bond strength was determined after 24 h of storage at 37°C in distilled water. The results were analyzed with a nested ANOVA (adhesive, type of adhesive) followed by the Fisher post-hoc tests of group homogeneity at α = 0.05. A two-parameter Weibull distribution was used to calculate the critical shear bond strength corresponding to 5% probability of failure as a measure of system reliability. Results: ANOVA revealed a significant decrease (p < 0.001) in the mean shear bond strength as follows: AH=CL=OS=G=E=OF>AD=IB=XE>PB=ADP, but no significant difference (p > 0.48) between the etch-and-rinse and self-etching adhesives. The corresponding characteristic bond strength of Weibull distribution ranged between 24.1 and 12.1 MPa, Weibull modulus between 8.3 and 2.1, and the critical shear bond strength varied from 16.0 to 3.0 MPa. Conclusion: Pronounced differences in the critical shear bond strength suggest reliability variations in the adhesive systems tested, which originate from chemical composition rather than type of adhesive. Keywords: bond strength, dentin adhesive system, reliability, Weibull analysis

Purpose: The aim of this study was to evaluate the microshear bond strength of three current adhesives to normal and caries-affected dentin, and to examine the correlation between dentin nanoindentation hardness and bond strength. Materials and Methods: Nanoindentation hardness of dentin and microshear bond strength of Clearfil SE Bond, Clerafil Tri-S Bond (Kuraray Medical) and Single Bond (3M ESPE) were measured on caries-affected and normal dentin. Modes of fracture for the bonding tests and the resin/dentin interfaces were observed using SEM. Data were analyzed at a statistical significance level of p < 0.05. Results: Significantly lower hardness values were recorded for caries-affected dentin compared to normal dentin. Two-way ANOVA showed that bonding material, type of dentin, and the interactions of these two factors had significant effects on bond strength. A significant correlation was found between dentin hardness and microshear bond strength. However, ANCOVA analysis revealed that the effect of dentin type was not only due to the mechanical properties of dentin. One-way ANOVA with Tukey's HSD test revealed that the mean bond strength of normal dentin with Tri-S Bond was significantly lower than that with SE Bond and Single Bond; however, bond strengths to caries-affected dentin showed no significant difference between the three adhesives. Conclusion: All three adhesives showed lower bond strength to caries-affected dentin than to normal dentin. The differences between adhesives were not significant with caries-affected dentin as the bonding substrate. Dentin mechanical properties are not the only factors responsible for lower bond strength to caries-affected dentin. Keywords: nanoindentation, microshear bond strength, caries-affected dentin, etch-and-rinse adhesive, self-etching adhesive

Purpose: The aim of this study was to evaluate the influence of ultrasonic treatment on the microtensile bond strength of self-etching adhesives to dentin. Materials and Methods: Forty-two human molars were wet ground occlusally until dentin was exposed. Clearfil S3 Bond, Futurabond NR (one-bottle) and Clearfil SE Bond (two-bottle) self-etching bonding systems were used in this study. In control groups, bonding procedures were performed according to the manufacturers' instructions. In the experimental groups, bonding materials were applied with an ultrasonic scaler. When using Clearfil SE Bond, the ultrasonic device was used either during priming or the bonding stage. The composite was then built up to 5 mm in height. Each tooth was serially sectioned into rectangular beams. The beams were categorized also according to positional status as marginal or central. Beams were subjected to microtensile testing after 24 h of water storage. Failure modes were observed with a stereomicroscope and classified. Randomly selected tested beams from each group were examined with SEM. Results: Three-factor ANOVA results indicated that the adhesive bonding system had a significant effect on bond strength (p < 0.001), whereas ultrasonic agitation and the position of the tested beam (marginal vs central) had no effect on bond strength (p > 0.05). Failure after the test was commonly due to adhesive breakdown associated with partial cohesive failure in the dentin. The mean (SD) microtensile bond strengths to dentin for S3 Bond, Futurabond NR, Clearfil SE Bond in the control group were 44.3 (11.7), 35.3 (12.0), 25.1 (8.8), resp, and in the ultrasonic group 39.3 (14.2), 31.3 (13.5), 35.5 (13.5) at priming and 32.6 (16.2) at bonding. Conclusion: Ultrasonic agitation during application of self-etching adhesives had no effect on bonding performance of the self-etching adhesive. Keywords: composite resin, dentin, ultrasonic, dentin bonding agents, self-etching, single-step adhesives

Purpose: The effects of incremental filling technique and flowable liner on the bond strength of resin composite in different sized cavities were investigated in this study. Materials and Methods: Two sizes of cylindrical Class I cavities were prepared in bovine dentin (98.1 mm3 and 21.2 mm3). A light-curing resin composite (Clearfil Photocore) with a self-etching primer adhesive (Clearfil SE Bond) was used to bulk fill the cavities (C-factor 5), with and without flowable liner (Clearfil FLOW-FX) or incremental filling (2 layers, Cfactor 3). As control, a 3-mm or 5-mm buildup was placed on the flat dentin surface (C-factor 0.2). After 24 h storage in 37°C water, the microtensile bond strength was measured at a crosshead speed of 1 mm/min. Mode of failure in the fractured specimens was observed using a scanning electron microscope. The obtained results were statistically analyzed. Results: In large cavities, incrementally filled and lined cavities showed higher bond strength values than the bulk-filled subgroup (p < 0.05). However, in small cavities, neither the incremental technique nor flowable liner improved the bond strength. Conclusion: Not only the filling techniques but also the cavity size affected the bond strength to the cavity floor in cylindrical Class I cavities. Keywords: cavity size, incremental technique, flowable liner, C-factor, microtensile bond strength

Purpose: To assess the effect of adhesive application and aging on the bond durability of resin cement to etched and silanized feldspathic ceramic. Materials and Methods: Twenty blocks (6.4 x 6.4 x 4.8 mm) of feldspathic ceramic (Vita VM7) were produced. The ceramic surfaces were conditioned with 10% hydrofluoric acid gel for 60 s and silanized. They were then randomly divided into two groups. While half of the group received no adhesive, in the other half, a layer of adhesive (Scotchbond Multi-Purpose Plus) was applied. Each ceramic block was then placed in its silicone mold with the treated surface exposed. The dual-cured resin cement (Variolink II) was injected into the mold over the treated surface and polymerized. Specimens were sectioned to achieve nontrimmed bar specimens (approximately 12 sticks/block) that were randomly divided into 2 groups: a) non-aged - microtensile bond test immediately after sectioning; b) aged-thermocycling (TC) 12,000 times, 5°C to 55°C, and water storage (50 days). The microtensile bond strength test was performed in a universal testing machine (crosshead speed: 1 mm/min). The failure types were examined using an optical light microscope and SEM. Bond strength results were analyzed using two-way ANOVA and Tukey's test (α = 0.05). Results: The adhesive application affected the bond strength results significantly (p = 0.0001) (without adhesive > with adhesive). While aging conditions did not reduce the bond strength in the groups that received no adhesive (20 ± 5.3 MPa non-aged and 21.5 ± 5.6 aged) (p = 0.1698), it significantly affected the bond strength results of the group with adhesive application (18 ± 4.4 MPa to 14.4 ± 4.7 MPa) (p < 0.001). All groups showed mainly mixed type of failures between the ceramic and the resin cement (81% to 100%). The group in which no adhesive was applied presented a higher incidence of cohesive failure of ceramic after aging (18%) than those of the other groups. Conclusion: The use of adhesive did not improve resin cement adhesion to the etched and silanized feldspathic ceramic after long-term thermocycling and water storage. Keywords: acid etching, bond durability, glass ceramic, microtensile test, resin cement

Purpose: To evaluate in vitro the influence of fiber reinforcement on the failure loads of resin composite beams, simulating cantilevered two-unit resin-bonded fixed dental prostheses, and compare the results with similarly obtained failure loads of ZrO2 and CoCr beams of a comparable design. Materials and Methods: Peel tests were performed using resin composite, fiber-reinforced resin composite, and zirconia beams, simulating two-unit cantilevered resin-bonded fixed dental prostheses, luted with Panavia F2.0 onto flat-ground buccal surfaces of bovine mandibular incisors. The recorded failure loads were compared with those of CoCr beams of a similar size and design from earlier research. Finite element analysis revealed the stress concentrations within the cement layers at failure. Results: The failure loads (N) of the peel tests, depending on the beam type and including the type of failure, were statistically analyzed. The highest failure values were obtained with the fiber-reinforced resin composite beams, which were luted with the exposed fibers directly on the bovine enamel. Finite element analysis showed that peak stress locations depend on the beam type and facilitate the explanation of the different failure modes. Conclusion: Fiber-reinforcement of simulated two-unit cantilevered resin composite resin-bonded fixed dental prostheses does not necessarily lead to higher failure loads. This study identified significant differences in peel failure loads between identical specimens, depending on whether or not the fiber reinforcement was exposed on the luting surface. Further research needs to be carried out regarding the combination of resin composite and fiber reinforcement. Keywords: fiber-reinforced resin composites, zirconia, failure load, nonmetal

Purpose: To investigate the effect of two different smear layer thicknesses treated with different dentin conditioners on the bond strength of glass-ionomer adhesive to dentin. Materials and Methods: Fifty human molars were used. Each tooth was sectioned in a mesiodistal direction into halves, using a low-speed diamond disk. The 100 halves were randomly divided into 10 equal groups. Groups I to V for the thick smear layer and groups VI to X for the thin smear layer. Eighty halves were used for shear bond strength testing, while the remaining 20 halves were used for SEM evaluation of the adhesive/dentin interface. After each dentin pretreatment, the glass-ionomer adhesive was applied over the conditioned dentin surfaces for all tested groups and restored with resin composite cylinders. Each half with its attached composite cylinder was subjected to shear load at crosshead speed of 0.5 mm/min until failure occurred. The dentin surfaces for SEM evaluation were treated as described for shear bond strength testing. The samples were examined using SEM operated at 30 kv, and the resin/dentin interface was examined at 1500X. Results: Two-way ANOVA showed that there was no significant effect of the smear layer thickness on shear bond strength. There was a significant effect of the different conditioners used (p = 0.001). The interaction of the two independent variables (smear layer thickness and the dentin conditioners) showed no significant difference in the shear bond strength to dentin. The common feature in all evaluated specimen interfaces was the presence of a hybrid layer of different thicknesses with no visible resin tags. Conclusions: The shear bond strength of the glass-ionomer adhesive to dentin proved to be independent of the smear layer thickness. The use of dentin conditioner prior to the application of the glass-ionomer adhesive appeared to be an important step to improve its bond strength to dentin. Glass-ionomer adhesive failed to produce resin tags regardless of the type of dentin conditioner used. Keywords: glass-ionomer adhesive, bond strength, smear layer, dentin conditioners

Purpose: To evaluate the effects of pretreatment (silanization) and thermocycling on bond strengths of 2 core materials to 3 different types of fiber posts. Materials and Methods: Bond strengths of prefabricated glass (group 1), quartz (group 2), and individually formed glass fiber posts (group 3) to either a flowable or a highly viscous composite resin core material were measured using a pushout design. All posts were investigated with or without the application of a silane. Half of the specimens were stored in distilled water for 28 days, and were subsequently subjected to thermocycling (5000 cycles, 5 to 55°C), whereas the other half was investigated after 24-h water storage. Results: Bond strengths were significantly affected by thermocycling (p < 0.0005), post type (p < 0.0005), and pretreatment (p < 0.0005), but not by the core material (p = 0.149; four-way ANOVA). Posts of group 3 demonstrated significantly higher bond strengths than all other posts, even after thermocycling (p < 0.05; Tukey-B). Conclusion: While silanization had negligible effects, thermocycling drastically reduced bond strengths regardless of pretreatment, post type, or core material. The higher bond strengths between the group 3 posts and the flowable composite resin core material might result in improved stability of the core for postendodontic restorations. Keywords: fiber posts, composite resin core materials, push-out bond strengths, silanization, thermocycling