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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 AP-X) 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°C for one week; old - water storage for six months. The SBS was tested. The fracture mode was assessed under 40× 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.