The Journal of Adhesive Dentistry, 02/2012

Purpose: To assess the microshear bond strength of 3 experimental adhesives with different degrees of hydrophilicity after 1, 7 and 90 days of storage. Materials and Methods: The bonding effectiveness of three experimental two-step etch-and-rinse adhesives (bis- GMA, bis-EMA/bis-GMA, polybutadiene [C6H12]) and one commercial adhesive (Single Bond) to sound hydrated dentin was determined using the microshear test with delimitation of the adhesive area after 1, 7, and 90 days of storage in water at 37°C. Two-way ANOVA was performed at the 0.05 probability level. The fractures were classified as adhesive, cohesive in dentin, cohesive in resin, and mixed. Results: The experimental adhesives showed values in the range of 11.31 to 12.96 MPa, with polybutadiene (PBH) showing the lowest bond strengths, bis-GMA the highest, and bis-EMA/bis-GMA intermediary values. Single Bond yielded bond strengths of approximately 24 MPa. Water storage decreased the bond strength in all adhesives. Adhesive fractures were predominant in experimental adhesives, while mixed fractures were the most frequent type in the Single Bond group. Conclusion: The experimental dentin adhesives of this study were able to form resin tags, but they could not penetrate into the collagen fibers and form hybrid layers. The resulting low bond strength decreased with increasing length of storage. Keywords: adhesion, solubility parameters, microshear, hydrophilicity

Purpose: To determine whether bonds of contemporary etch-and-rinse adhesives made with ethanol-wet bonding are stronger and more durable than those made with water-wet bonding, and to explore the possible reasons for the bonding results. Materials and Methods: Flat surfaces of midcoronal dentin were made in extracted human third molars. The dentin surfaces were randomized into 6 groups according to bonding techniques (water- vs ethanol-wet bonding) and dental adhesives [Single Bond 2 (SB), Prime Bond NT (PB), and Gluma Comfort Bond (GB)]. After etching and rinsing, dentin surfaces were either left water-moist or immersed in ethanol. Following adhesive application and composite buildups, the bonded teeth were sectioned into beams for microtensile bond strength evaluation with or without NaOCl challenge. The morphology of the hybrid layer was analyzed with SEM. The wettability of water- vs. ethanol-saturated dentin was evaluated. The concentrations of non-volatile ingredients in the adhesives were compared. Results: Compared to water-wet bonding, ethanol-wet bonding yielded similar (p > 0.05 for PB and GB) or higher (p 0.05 for SB) 24-h bond strength, displayed significantly higher bond strength after chemical challenge (p 0.05, for all three adhesives), and produced more even hybrid layers. Moreover, ethanol-saturated dentin exhibited a lower contact angle than water-saturated specimens, and the concentrations of non-volatile ingredients of the adhesives decreased in the order of SB > GB > PB. Conclusion: Ethanol-wet bonding could improve the bonding efficacy of contemporary etch-and-rinse adhesives, probably due to the good wettability of ethanol-saturated dentin and the structure of the hybrid layer. Moreover, this positive effect of ethanol-wet bonding might be influenced by the composition of adhesives. Keywords: dentin bonding, ethanol-saturated dentin, hybrid layer, wettability

Purpose: To evaluate the scrubbing effect of self-etching adhesive systems on the microtensile bond strengths to sodium hypochlorite-treated dentin. Materials and Methods: The occlusal surfaces of 36 extracted human third molars were horizontally cut to expose sound dentin. The dentin surfaces of the teeth were treated with 6% NaOCl aqueous solution for 30 s or none. After water rinsing for 10 s and air drying, a 2-step (Clearfil Protect Bond) or 1-step (Clearfil S3 Bond or Bond Force) self-etching adhesive was applied with or without a scrubbing technique, and resin composite (Clearfil AP-X) crowns were built up. The bonded specimens were stored in water for 24 h and then subjected to the microtensile bond test at a crosshead speed of 1.0 mm/min. Data were analyzed using three-way ANOVA and Bonferroni multiple comparisons (p 0.05). Results: The NaOCl-treated dentin exhibited significantly lower bond strength with the tested self-etching adhesive systems than did the normal dentin (p 0.05). Using a scrubbing technique for the tested self-etching adhesive systems significantly improved the µTBS to NaOCl-treated dentin (p 0.05), whereas there was no significant difference in µTBS to normal dentin between a scrubbing and nonscrubbing technique (p > 0.05). Conclusion: Using a scrubbing technique for applying self-etching adhesive systems to NaOCl-treated dentin was effective in improving the compromised bonding. Keywords: sodium hypochlorite, scrubbing, dentin, bond strength, adhesives

Purpose: The use of sodium hypochlorite (NaOCl) can decrease the bond strength of 4-META/MMA-TBB resin cement to root dentin. The aim of this in vitro study was to evaluate the effect of sodium toluene sulfinic acid (SA) as a pretreatment to increase bond strength to NaOCl-treated dentin. Materials and Methods: The root canal dentin of bovine teeth was treated with 6 methods: group 10-3 (10% citric acid/3% ferric chloride; control); group SA; group NC (sodium hypochlorite/10-3 solution); group NS-10-3 (NaOCl + sulfinic acid + 10-3 solution); group HSA-10-3 (NaOCl +H2O2 +NaOCl + sulfinic acid + 10-3 solution); group HO-10-3 (NaOCl + H2O2 + NaOCl +10-3 solution). The roots were then filled with Super-Bond C&B (SB) or Super-Bond sealer (SBS). Samples were stored in distilled water for 24 h at 37°C and then cross sectioned into five slabs (0.8 mm thick) that were subjected to "trimming" microtensile bond strength testing. All treated dentin surfaces and resin/dentin bond interfaces were analyzed under SEM. Results: Compared with the control, NaOCl treatment significantly decreased the resin/dentin bond strengths. However, SA treatment following NaOCl irrigation resulted in no significant differences of bond strength values. Conclusion: Sulfinic acid was effective in restoring 4-META/MMA-TBB resin cement bond strength after NaOCl irrigation. Keywords: dentin bond strength, resin cement, sodium hypochlorite, sodium toluene sulfinic acid

Purpose: To evaluate whether Nd:YAG laser irradiation of etched and unetched dentin through an uncured adhesive affected the microtensile bond strength (µTBS). Materials and Methods: Flat dentin surfaces were created in 19 extracted human third molars. Adper Single Bond (SB) adhesive was applied over etched (groups 1 to 3) or unetched dentin (groups 4 to 6). The dentin was then irradiated with a Nd:YAG laser through the uncured adhesive, using 0.75 or 1 W power settings, except for the control groups (groups 1 and 4). The adhesive was light cured and composite crowns were built up. After 24 h, the teeth were sectioned into beams, with cross-sectional areas of 0.49 mm2, and were stressed under tension. Data were statistically analyzed using two-way ANOVA and Tukey's test (α = 5%). Dentin surfaces of fractured specimens and the interfaces of untested beams were observed under scanning electron microscopy (SEM). Results: Acid etching, laser irradiation, and their interaction significantly affected bonding (p 0.05). Laser irradiation did not improve bonding of etched dentin to resin (p > 0.05). However, higher µTBS means were found on unetched lased dentin (groups 5 and 6), but only in comparison to group 4, where neither lasing nor etching was performed. Groups 4 to 6 showed the lowest µTBS means among all groups tested (p 0.05). Laser irradiation did not change the characteristics of the hybrid layers created, while solidification globules were observed on lased dentin surfaces under SEM. Conclusion: Laser irradiation of dentin through the uncured adhesive did not significantly improve the µTBS in comparison to the suggested manufacturer's technique. Keywords: dentin adhesives, lasers, dentin, tensile bond strength

Purpose: To evaluate the ceramic-to-dentin bond following luting with light- and dual-curing resin composites using different adhesive techniques. Materials and Methods: Dentin surfaces from 160 human molars were ground flat and randomly divided into eight groups (n = 20). Vita Mark II ceramic disks measuring 2 and 4 mm in thickness were bonded to the dentin with one of the following luting systems: Syntac/Tetric Ceram (ST), Syntac/Variolink II (SV), OptiBond Solo Plus/ Prodigy (OP), OptiBond Solo Plus/Nexus 2 (ON). Two different irradiation times (60 s, 120 s) were used per luting system, each without (-PC) and with (+PC) precuring the respective adhesive layer. After storage in water for 24 h at 37°C, the bonded specimens were sectioned perpendicularly to the adhesive interface into 1-mm-thick sticks. Three sticks per specimen were loaded to failure under tension in the Zwicki 1120. Failure analysis was performed using a scanning electron microscope (SEM). Results: Four-way ANOVA showed that the ceramic thickness, the type of luting system used, and the adhesive precuring had a significant effect on the microtensile bond strength. The longer irradiation times did not significantly increase the bond strength. The highest values were recorded with SV/+PC (27.9 ± 4.3 MPa) and the lowest with ST/-PC (10.2 ± 3.5 MPa). Under the SEM, failed specimens that had not been precured showed significantly more exposed dentin than those which had been precured (chi-square test). Conclusion: The precuring step of light-curing bonding systems and the use of dual-curing luting composites were shown to optimize the dentin bond under thick ceramic layers. Keywords: ceramic-to-dentin bond, luting system, light curing, dual curing, precuring, bonding effectiveness

Purpose: To evaluate the effect of cement shade, light-curing unit, and water storage on tensile bond strength (σ) of a feldspathic ceramic resin bonded to dentin. Materials and Methods: The dentin surface of 40 molars was exposed and etched with 37% phosphoric acid, then an adhesive system was applied. Forty blocks of feldspathic ceramic (Vita VM7) were produced. The ceramic surface was etched with 10% hydrofluoric acid for 60 s, followed by the application of a silane agent and a dual-curing resin cement (Variolink II). Ceramic blocks were cemented to the treated dentin using either A3 or transparent (Tr) shade cement that was activated using either halogen or LED light for 40 s. All blocks were stored in 37°C distilled water for 24 h before cutting to obtain non-trimmed bar-shaped specimens (adhesive area = 1 mm2 ± 0.1) for the microtensile bond strength test. The specimens were randomly grouped according to the storage time: no storage or stored for 150 days in 37°C distilled water. Eight experimental groups were obtained (n = 30). The specimens were submitted to the tensile bond strength test using a universal testing machine at a crosshead speed of 1 mm/min. The data were statistically analyzed using ANOVA and Tukey's posthoc tests (a = 0.05). Results: The mean bond strength values were significantly lower for the corresponding water stored groups, except for the specimens using A3 resin cement activated by halogen light. There was no significance difference in mean bond strength values among all groups after water storage. Conclusion: Water storage had a detrimental effect under most experimental conditions. For both cement shades investigated (Tr and A3) under the same storage condition, the light-curing units (QTH and LED) did not affect the mean microtensile bond strengths of resin-cemented ceramic to dentin. Keywords: cement shade, ceramic, polymerization source, microtensile bond strength

Purpose: To evaluate the influence of dynamic fatigue on fracture load and failure mode of different types of adhesive zirconia restorations. Materials and Methods: Eighty adhesive cantilever fixed dental prostheses (CFDP) were fabricated and assigned to four equal groups (n = 20) using the following materials and techniques. Group 1: machine copy-milling zirconia (Cercon), group 2: manual copy-milling technique (ZirkonZahn), group 3: slip casting technique (Vita In-ceram Zirconia), group 4: metal-ceramic CFDP. Specimens in groups 1and 2 received selective infiltration-etching surface treatment, specimens in group 3 were acid etched with hydrofluoric acid and silanated, while those of group 4 were airborne particle abraded. All specimens were bonded with resin cement (Panavia F2.0) and thermocycled (5000 cycles/ 5 to 55°C). Then, half the number of the specimens of each group (n = 10) underwent dynamic loading (one million cycles at alternating loads between 10 and 40 N in a water bath at 37°C). All specimens were subjected to one-cycle loading to failure to evaluate fracture resistance. One-way and two-way ANOVA and Bonferroni post-hoc tests were used to analyze the data (α = 0.05). The intaglio surfaces of fractured specimens were examined using stereomicroscopy and scanning electron microscope (SEM). Results: Statistical analysis revealed that the failure load of metal (413 ± 26 N) and machine copy-milled zirconia (368 ± 24 N) restorations was significantly higher (F = 129, p 0.001) than manually copy-milled (316 ± 18) and In-ceram zirconia (210 ± 17) restorations. Dynamic fatigue significantly (p 0.03) reduced failure load of the manually copy-milled and In-ceram zirconia restorations, while metal and machine copy-milling zirconia restorations were not influenced by fatigue. Conclusions: The fatigue strength of adhesive zirconia restorations is influenced by cyclic loading and the technique used to manufacture these restorations. Keywords: zirconia, adhesive cantilever fixed prosthesis, cyclic loading, fatigue

Purpose: This study evaluated a dual-curing composite along with different dentin adhesive systems for 1 year under water storage, as a new bonding method of root fragments in complete vertical root fracture. Materials and Methods: Bovine root fragments were bonded with the dual-curing resin composite Clearfil DC Core Automix (DCA) and one of three adhesive systems: two-step self-etching adhesive Clearfil SE Bond (SE), one-step self-etching adhesive Tokuyama Bond Force (BF), one-step dual-curing self-etching adhesive Clearfil DC Bond (DC). Microtensile bond strength (µTBS)/ultimate tensile bond strength (UTS), FE-SEM ultramorphology of fracture modes, and adhesive dentin interface were observed after water storage for periods of up to one year. The data were analyzed with two-way ANOVA. Results: µTBS was influenced by "dentin adhesive system" (F = 324.455, p 0.001) and "length of water storage" (F = 8.470, p 0.001). SE yielded significantly higher µTBS, regardless of storage period (p 0.05) and maintained the initial µTBS without a significant change after 1 year of water storage (p > 0.05). From 24 h to 1 month, BF showed significantly higher bond strength than DC. UTS of DCA was influenced only by the curing mode of the material (F = 5.051, p = 0.027), but not by the length of water storage (F = 0.053, p > 0.05). Conclusion: Two-step self-etching adhesive systems and dual-curing composite core material can be considered as a suitable bonding method for complete root fractures. Keywords: root fracture, luting, self-etching adhesives, dual-curing composite, bonding

Purpose: To investigate the effect of a prefabricated tribochemical coating of FRC (fiber-reinforced composite) posts with and without aging on the pull-out forces compared to posts without conditioning. Materials and Methods: Post space preparations were performed on 108 extracted anterior teeth. Thirty-six uncoated FRC posts (DentinPost) and 72 prefabricated tribochemically coated FRC posts (DentinPost Coated) were used at a length of 12 mm. Thirty-six of the coated posts were thermally aged. FRC posts (n = 9) were placed using DentinBuild or MultiCore Flow foundation composite resins or Panavia F2.0 or RelyX Unicem resin cements. Following water storage (37°, 24 h) and thermocycling (5000 cycles, 5° to 55°C, 30 s), pull-out force testing was performed. Fracture modes were assessed using a light microscope. Data were analyzed statistically (1-way and 3-way ANOVA, Bonferroni-Dunn correction, α = 0.05). Results: Significantly higher pull-out forces of posts luted with Panavia F2.0 were observed for the coated and coated/aged FRC posts compared to the unconditioned posts (control group, p 0.001). The pull-out forces of tribochemically coated FRC posts luted with MultiCore Flow were significantly lower than of coated posts luted with Panavia F2.0 (p 0.001). Coated/aged FRC posts exhibited similar pull-out forces for the tested luting composite resins (p > 0.05). Except for DentinBuild (coated posts), more mixed or cohesive fractures were assessed for coated and coated/aged FRC posts than for unconditioned FRC posts. Conclusion: Prefabricated tribochemical coating of FRC posts provided a stable interface between coating and post and remained stable over time. Keywords: root posts, FRC posts, surface coating, resin cement, core buildup composite, silica coating, aging

Purpose: To evaluate the clinical performance and postoperative sensitivity of noncarious Class V restorations with and without the use of a potassium oxalate-based desensitizing agent over a period of 18 months. Materials and Methods: One hundred forty cervical lesions (40 patients) were selected and randomly divided into four groups: group 1 (G1) - teeth restored with the application of a potassium oxalate-based desensitizing agent (BisBlock) after acid etching and before the application of the adhesive Adper Single Bond 2; group 2 (G2) - teeth restored using the same adhesive system used in G1, without the use of any desensitizing agent; group 3 (G3) - similar to G1, but using the adhesive One-Step; group 4 (G4) - similar to G3, but without the application of BisBlock. All restorations were evaluated (double blind) after 1 week and 2, 6, 12, and 18 months according to the modified USPHS criteria. The McNemar and chi-square tests were used to analyze the results (p = 0.05). Results: There were no statistical differences between groups restored with or without the use of a desensitizing agent for postoperative sensitivity. After 18 months, retention rates proved to be statistically significantly lower for One-Step than Adper Single Bond 2. Conclusion: The use of potassium oxalate-based desensitizing agent did not decrease postoperative sensitivity when it was used under composite resin restorations. Keywords: clinical evaluation, dentin desensitizer, potassium oxalate, dentin hypersensitivity, noncarious cervical lesions