The Journal of Adhesive Dentistry, 03/2009

Purpose: The objective of this study was to examine whether one-step self-etching adhesives (1-SEAs) really have an advantage over multistep systems. Materials and Methods: Nine one-step self-etching adhesives (Absolute, Adper Prompt L-Pop, Clearfil S3 Bond, GBond, Hybrid Bond, iBond, One-up Bond F Plus, Optibond All-in-one and Xeno III) were included in this study. One twostep self-etching adhesive (Clearfil SE Bond) and one three-step etch-and-rinse adhesive (Optibond FL) served as controls. Their microtensile bond strength to bur-cut enamel and dentin was determined using a standardized protocol and the respective adhesive/dentin interface of these adhesives was characterized by transmission electron microscopy. Statistical analysis was performed with the Kruskal-Wallis nonparametric test. Results: Regarding bond strength, the control adhesives tended to perform superior to the one-step adhesives. However, a significant difference between the control adhesives and some one-step adhesives could not always be demonstrated, partly due to the statistical setup of this study. Interface analysis by electron microscopy showed wide variation among the one-step adhesives, depending on their composition and their acidity. 1-SEAs also exhibited two different kinds of droplets, depending on their hydrophilicity. Hydrophobic HEMA-free 1-SEAs such as G-Bond were prone to phase separation, while especially HEMA-containing hydrophilic 1-SEAs, such as Clearfil S3 Bond and Xeno III were predisposed to forming osmosis-induced droplets. Hybrid bond, Absolute, and iBond featured both phase separation as well as osmosis. Optibond All-in-one exhibited a clustering reaction of the filler particles upon solvent evaporation. All adhesives including the control adhesives showed signs of nanoleakage, indicating that all adhesives are to some extent permeable to water. A definitive conclusion with regard to quantitative assessment of nanoleakage was much hindered by inconsistencies in the silver deposition. The application procedure of some 1-SEAs sometimes proved as elaborate and time consuming as those of the two-step adhesive Clearfil SE Bond. Conclusion: Considering bond strength and application procedure, 1-SEAs are not always a better alternative to multistep adhesives. Keywords: adhesion, adhesive, one-step self-etching, phase separation, droplets, bonding effectiveness

Purpose: To investigate the effect of 0.2% and 2% chlorhexidine (CHX) used as a therapeutic primer on the long-term bond strengths of two etch-and-rinse adhesive systems. Materials and Methods: Adper Scotchbond 1XT (SB1) and XP-Bond (XPB) were evaluated. Etched dentin substrates were assigned to 6 treatment groups: (1) 0.2% CHX + SB1; (2) 2% CHX + SB1; (3) SB1 (control); (4) 0.2% CHX + XPB; (5) 2% CHX + XPB; (6) XPB (control). Composite buildups were made and beams prepared for microtensile bond strength testing. Beams were divided into 3 subgroups and either immediately pulled to failure or stored in artificial saliva for 6 or 12 months prior to testing. Data were evaluated with three-way ANOVA. Additional adhesive interfaces were prepared to investigate nanoleakage expression by TEM. Results: SB1 and XPB showed similar immediate bond strength values with or without CHX pretreatment (p > 0.05). After 12 months, bonds fell from 43.9 ± 9.5 MPa to 20.1 ± 5.4 MPa and from 39.6 ± 9.4 MPa to 14.2 ± 5.0 MPa in control specimens for SB1 and XPB respectively, while bond fell only from 41.9 ± 9.6MPa to 33.2 ± 8.3 MPa and 38.3 ± 8.9 MPa to 26.5 ± 10.9 (for SB1 and XPB, respectively) when 0.2% CHX was previously used. CHX concentration did not affect bond strength values (0.2% vs 2%, p > 0.05). Nanoleakage increased during aging in controls, but reduced silver deposits were found in CHX-treated specimens. Conclusion: Chlorhexidine significantly reduced the loss of bond strength seen in control bonds. Since no bacterial growth was present in the aging conditions, the results of this study suggest that endogenous factors thought to degrade the adhesive interface can be inhibited by CHX. Further in vivo trials should confirm the role of CHX in bond durability. Keywords: chlorhexidine, dental bonding systems, hybrid layer, aging, dentin

Purpose: To investigate the micromechanics and damage accumulation of the enamel/adhesive interface using submodelling and element deactivation methods. Materials and Methods: A finite element (FE) macromodel of the enamel/adhesive/ceramic interface subjected to shear bond testing was generated for mechanical analysis. The FE micromodel was constructed at the upper enamel/adhesive interface where stress concentration was found. The morphology of the micromechanical interlockings at the bonded interface was assigned based on a scanning electron micrograph. Boundary conditions of the micromodel were determined from the macromodel's results. Furthermore, an iterative code with the element deactivation method was used to calculate the microdamage accumulation. Parallel experiments were performed to validate the simulation. Results: The micromodel results demonstrated that stress concentration within the adhesive mainly occurred at the upper corner near the enamel/adhesive interface and the base of the resin tags. A simulated fracture path was found at the base of the resin tags along the enamel/adhesive interface. The morphological observation of fracture patterns obtained from in vitro testing corresponded with the simulation results. Conclusion: This study showed that the FE submodelling and the element deactivation approaches could better simulate the micromechanical responses and the microdamage accumulation noted at the enamel/adhesive interface. Keywords: micromechanics, enamel bonding, interface, finite element analysis, damage accumulation

Purpose: The present study was undertaken to determine the content and the constituent elements of inorganic fillers as well as the radiopacity of 15 recently introduced bonding agents and to compare their radiodensities with those of enamel and dentin by using a transmission photodensitometer. Materials and Methods: The content of inorganic fillers was determined by the ashing method. In addition, x-ray microanalysis was used to identify the constituent elements of the inorganic fillers. In the measurement of the radiopacity, specimens 10 mm in diameter and 0.9 mm in thickness were fabricated from the 15 different bonding agents (n = 3 each) for a total of 45 specimens. Human premolars were longitudinally sectioned into 1.0-mm-thick slices to include both enamel and dentin, then ground to final thickness of 0.9 mm. The optical densities of enamel, dentin, the bonding agents, and an aluminum (Al) step wedge were obtained from radiographic images by transmission photodensitometry. The Al equivalent (mm) for each material was calculated by using the linear regression equation of the log of the normalized optical density and Al thickness (mm) obtained from the step wedge. A linear regression of the logarithm of the normalized optical density and Al thickness (mm) was plotted. Results: The inorganic filler content ranged from 0.0 wt% to 43.5 wt%. Silicon and aluminum were the main constituent elements of the inorganic fillers; however, the resins contained different kinds of inorganic fillers. These elements have high and low atomic numbers. The surface reaction type pre-reacted glass-ionomer (S-PRG)-filled bonding agent (FII) had a filler content of 43.5 wt% and contained B, Si, Sr, Na, F and Al as its elemental constituents. The relative radiopacities expressed as equivalent thickness of Al were ranked ordinally. Fourteen of the 15 adhesive resins had radiopacity values that fell below that value for dentin, whereas the FII resin showed a radiopacity that was equal to or greater than that of dentin but below that of enamel (p 0.05). Conclusion: The radiopacity of bonding agents depended on their filler content and the presence of heavier atoms of elements in the filler. Keywords: bonding agent, filler, radiopacity, densitometer, Al equivalent

Purpose: This study evaluated the resin-dentin microtensile bond strength (µTBS) of ethanol/water- (Single Bond, [SB] 3M ESPE), ethanol- (Optibond Solo Plus, [OP] Kerr) and acetone-based (One-Step, [OS] Bisco) two-step etch-and-rinse adhesives in the presence or absence of their respective solvents to dry and wet dentin. The ultimate tensile strength (UTS) and the degree of conversion (DC) of the materials were also evaluated. Materials and Methods: Solvent-based and solvent-free adhesives were vigorously applied to occlusal dentin surfaces after phosphoric acid etching. Composite crowns were built up incrementally. After 24-h water storage, the specimens were sectioned in x and y directions to obtain bonded sticks (1.0 mm2) which were immediately tested in tension (0.5 mm/min). The data were analyzed by three-way ANOVA and Tukey's test (α = 0.05). For the UTS measurement, hourglass-shaped specimens of adhesives were prepared and tested in tension. FTIR analysis was used to verify the DC of adhesives. The data from UTS and FTIR was analyzed by two-way ANOVA and Tukey's test (α = 0.05). Results: High µTBS values were obtained for SB and OS, regardless of the presence or absence of solvents or the moisture condition of dentin. A lower µTBS mean was observed for the solvent-free OP compared to its solvent-based version. Significantly higher UTS values were obtained for all adhesives after removal of solvents. The DC of OS in the solvent-based condition was lower than SB and OP. After removal of solvents, only OS showed a significant increase in the DC. Conclusion: The presence of solvents was not essential for SB and OS to achieve high bond strength values to both dry and wet dentin when applied under vigorous application. Keywords: adhesive systems, moisture degree, microtensile bond strength, solvents

Purpose: The objective of this in vitro study was to compare the degree of microleakage of composite restorations performed by lasers and conventional drills associated with two adhesive systems. Materials and Methods: Sixty bovine teeth were divided into 6 groups (n = 10). The preparations were performed in groups 1 and 2 with a high-speed drill (HD), in groups 3 and 5 with Er:YAG laser, and in groups 4 and 6 with Er,Cr:YSGG laser. The specimens were restored with resin composite associated with an etch-and-rinse two-step adhesive system (Single Bond 2 [SB]) (groups 1, 3, 4) and a self-etching adhesive (One-Up Bond F [OB]) (groups 2, 5, 6). After storage, the specimens were polished, thermocycled, immersed in 50% silver nitrate tracer solution, and then sectioned longitudinally. The specimens were placed under a stereomicroscope (25X) and digital images were obtained. These were evaluated by three blinded evaluators who assigned a microleakage score (0 to 3). The original data were submitted to Kruskal-Wallis and Mann-Whitney statistical tests. Results: The occlusal/enamel margins demonstrated no differences in microleakage for all treatments (p > 0.05). The gingival/dentin margins presented similar microleakage in cavities prepared with Er:YAG, Er,Cr:YSGG, and HD using the etch-and-rinse two-step adhesive system (SB) (p > 0.05); otherwise, both Er:YAG and Er,Cr:YSGG lasers demonstrated lower microleakage scores with OB than SB adhesive (p 0.05). Conclusion: The microleakage score at gingival margins is dependent on the interaction of the hard tissue removal tool and the adhesive system used. The self-etching adhesive system had a lower microleakage score at dentin margins for cavities prepared with Er:YAG and Er,Cr:YSGG than the etch-and-rinse two-step adhesive system. Keywords: microleakage, Er:YAG laser, Er, Cr:YSGG laser, etch-and-rinse, adhesive system, self-etching primer

Purpose: This study evaluated the effect of surface treatments of the prepolymerized adhesive layer in the immediate dentin sealing technique (IDS) on the microtensile bond strength of two-step etch-and-rinse adhesive systems. Materials and Methods: The occlusal dentin surfaces of 60 human third molars were exposed and Adper Single Bond 2 (SB) or Prime & Bond NT (PB) adhesive systems were applied (control groups). Immediately afterwards, the temporary cement RelyXTemp NE was applied on the bonded dentin surface, and the teeth were stored in artificial saliva for 48 h or 4 months. After the storage time, the temporary cement layer was removed and the following surface treatments were applied: aluminum oxide (AO), 37% phosphoric acid (PA), or AO+PA. Next, a second adhesive layer was applied for each adhesive system, and a composite resin block restoration (Z250) was built. The specimens were cut and submitted to microtensile strength (µTBS) testing. The adhesive layer thickness (ALT) was evaluated in other specimens from all groups by SEM. The fracture pattern was evaluated in all sticks tested by SEM. µTBS and ALT values were analyzed with two-way ANOVA and Tukey's test (α = 0.05). Results: The highest µTBS, similar to the control, was obtained with aluminum oxide and phosphoric acid (AO+PA) for both adhesives systems. The use of aluminum oxide alone (AO) or associated with phosphoric acid (AO+PA) showed values close to those of the control groups in relation to the ALT. The failure pattern was the same for control groups and AO +PA groups. Conclusion: Dentin prehybridization can improve the adhesive bond strength if the bonded surface is treated with airborne aluminum oxide particle abrasion associated with 37% phosphoric acid, followed by application of a second adhesive layer. Keywords: microtensile bond strength, prehybridized dentin, resin coating technique, storage time

Purpose: To compare the short- and long-term sealing ability of root canal fillings consisting of AH-26 and laterally compacted gutta-percha in combination with a self-etching dentin bonding system and the Epiphany-Resilon system. Materials and Methods: Ninety-eight single-rooted human teeth were used in this study. The root canals were prepared using the step-back technique. Sodium hypochlorite 5% was used as the irrigant solution. The teeth were divided into 4 groups. In groups 1, 3, and 4, irrigation with ethylene diamine tetracetic acid (EDTA) 15% was used to remove the smear layer. In the specimens of all groups, a final irrigation with 5 ml distilled water was performed. In groups 1 and 2, the Nanobond bonding system was used. The specimens in groups 1 to 3 were obturated with AH-26 and laterally compacted gutta-percha. In the last group (4), the Epiphany-Resilon system was used. Microleakage was measured at 7 days, 1 month, and 1 year using a fluid transport model. Two specimens from each group and 4 where only Nanobond had been applied were prepared and examined in a scanning electron microscope. Results: The Epiphany-Resilon system and the group obturated with AH-26 sealer and gutta-percha, in combination with the self-etching bonding system after removal of the smear layer with EDTA, demonstrated similar sealing ability. Kruskal-Wallis and Mann-Whitney tests showed that he results for these two groups were statistically significanty better than the other groups (p 0.05). All the groups examined showed increased apical leakage over time, but the increase was statistically significant after one year only in the case of the Epiphany-Resilon system. Conclusion: The use of a self-etching bonding system improved the sealing ability of AH-26 sealer only after removal of the smear layer. Significantly higher microleakage over time was only observed with the Epiphany-Resilon system. Keywords: self-etching bonding agents, resin-based sealers