An In Vitro Assessment of the Effects of Three Surface Treatments on Repair Bond Strength of Aged Composites

Objective: This study evaluated the effectiveness of three surface treatments on repair shear bond strength (SBS) of aged composites. Methods: A total of 120 cylindrical samples made of a micro-hybrid composite (Clearfil APX) were randomly assigned to one control and three experimental groups (n=30) after water storage (3 weeks). All experimental groups included surface roughening with diamond burs. Subsequent treatments were provided as follows: group 1-only (self-etching) bonding; group 2-silane and bonding; and group 3-phosphoric acid etching, silane, and bonding. The composites were repaired with the same brand and were aged (water storage [48 hours] and thermocycling [2000 cycles]). Each group was divided into two subgroups (each, n=15): new-water storage at 37 degrees C for one week; old-water storage for six months. The SBS was tested. The fracture mode was assessed under 40x magnification. Results: Mean SBS values (MPa) for the study subgroups were as follows: control (new: 3.38 +/- 1.6; old: 1 +/- 0.76), group 1 (new: 27.3 +/- 1.8; old: 25.7 +/- 1.9), group 2 (new: 59.1 +/- 7.9; old: 50.8 +/- 4.6), and group 3 (new: 48.5 +/- 8.6; old: 39 +/- 3.5). Significant influence of the conditioning method and the duration of water storage was observed (p<0.01 [two-way analysis of variance {ANOVA}]). The SBS of all groups were significantly different (all p values <0.01 [Tukey]). Longer water storage time significantly reduced repair bond strength in all experimental groups (p <0.01). Although the control group and group 1 showed approximately 100% and 75% adhesive failures, respectively, groups 2 and 3, respectively, demonstrated about 75% mixed and cohesive failures. Weibull analysis showed that groups 2 and 1 had the lowest and highest probabilities of failure among the experimental groups, respectively. Conclusion: All experimental groups produced acceptable SBS levels; however, use of silane and bonding systems showed the most superior results. Acid etching reduced the SBS.