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Purpose: To evaluate (1) the initial and long-term microtensile bond strengths of two-step self-etch adhesives with different degrees of conversion (DC); (2) the elastic modulus of the respective adhesive resins; (3) the water sorption of the respective adhesive resins., Materials and Methods: Two two-step self-etch adhesives, Clearfil SE Bond (CSE) and Clearfil SE Bond 2 (CSE2) were used in this study. The DC was determined using ATR/FT-IR with a time-based spectrum analysis. Midcoronal flat dentin surfaces of 24 human molars were prepared with 600-grit SiC paper for microtensile bond strength (µTBS) testing. CSE and CSE2 were applied to the dentin surfaces according to the manufacturer's instructions, followed by composite buildups. The µTBS was measured after water storage for 24 h, 6 months, and 1 year. The elastic modulus (before and after 1 month of water immersion) was determined by the three-point flexural bending test and water sorption values by the water sorption test., Results: CSE2 showed significantly higher DC than CSE. The µTBS of CSE2 was significantly higher than that of CSE in all water storage periods. One-year water storage decreased the µTBS of CSE; however, it did not decrease that of CSE2. Regarding the polymerized adhesive resins, the elastic modulus of CSE2 was significantly higher than that of CSE before and after water immersion (p < 0.001), and the water sorption of CSE was higher than that of CSE2., Conclusions: The higher DC of adhesive resins of two-step self-etch adhesives resists water aging and improves the initial bond strengths and durability of the resin-dentin bond.

Objective: To evaluate the effect of base layer thickness of DyadFlow(DF) self-adhesive resin on dentin bonding strength., Methods: Twenty extracted intact human molars were randomly selected and the occlusal surface of each molar was prepared by removing the enamel and exposing the dentin surface. The prepared molars were divided, randomly and equally, into 4 groups. For groups G0.5, G1.0 and G2.0, DF was applied directly on the dentin surfaces following the manufacturer's instruction, and for group GOB, OptiBond All-in-One(OB) self etching adhesive was applied on the dentin surface before using DF. The base layer thickness of DF was 0.5 mm, 1.0 mm, 2.0 mm, 2.0 mm for groups G0.5, G1.0, G2.0 and GOB, respectively. Composite crown were built up on each tooth, then the samples were sectioned longitudinally into sticks with proximately 1.0 mm2 bonding area(for microtensile bond strength[MTBS] testing) or slabs (for bonding interface observation with SEM). Fifteen sticks were obtained for each group. The fracture surface was also observed using SEM and the fracture type of each specimen was determined., Results: The MTBS were: GOB (20.19±3.11) MPa>G0.5 (8.65±1.58) MPa>G1.0 (6.65±1.13) MPa>G2.0 (5.70±0.60) MPa(P<0.05). Bonding interface fracture B2 was most frequently observed for all groups: G0.5: 14/15, G1.0: 13/15, G2.0: 14/15 and GOB: 13/15., Conclusions: The MTBS decreased when the base layer thickness of DF increased. Direct application of DF self-adhesive resin on dentin surface adhesive restorations should be concerned.

Objective: To investigate the effect of filler content on microtensile bond strength (Μ-TBS) in Class I cavities., Method and Materials: Experimental composites with filler contents of 80%, 76%, 70%, 60%, and 50% by weight were used. Polymerization shrinkage was measured with Acuvol, and a three-point flexural test was performed to determine flexural properties. For evaluation of Μ-TBS, 25 extracted human molars were randomly divided into five groups and Class I cavities were prepared. After filling with one of the experimental composites and curing for 40 seconds, teeth were serially sectioned perpendicular to the cavity floor. Stick-shaped samples were tested with a microtensile tester. Statistical analysis was conducted using ANOVA and Pearson correlation tests., Results: Significant correlations were found between filler content and polymerization shrinkage (r = -0.973, P < .05) and the filler content and Young modulus (r = 0.891, P < .05). Different filler contents in the experimental composites had no significant effect on Μ-TBS or flexural strength., Conclusion: In a Class I cavity model, this in vitro study showed that the filler content did not influence the flexural strength of experimental composite resins and had no effect on the microtensile bond strength between composite resin and dentin.