Evaluation of bond strength of composite resins applied ph-cycling model and different repair methods

Aim: The aim of this study was to evaluate the effect of two different repair methods (Er: YAG laser and bur) with or without silane application on the microtensile bond strength of a nanohybrid composite aged with two different aging methods (pH cycling and thermocycling). Material and Methods: Composite resin blocks (Clearfil Majesty Esthetic , Kuraray, Japan) were prepared (5 mm x 6 mm x 6 mm) and randomly assigned into two groups for aging process: (a) pH cycling (b) thermocycling (5,000 cycles). After aging, the blocks were assigned to one of the following repair procedures: (1) Er:YAG laser (LightWalker STE-E, Fotona Medical Lasers, Ljubljana, Slovenia) (2) Er:YAG laser + silane (3) bur (4) bur + silane and (5) negative control and (6) positive control (cohesive strength of the resin). Resin composite (Clearfil Majesty Esthetic) was bonded to the conditioned substrates incrementally and light polymerized. Repaired samples were thermocycled (5,000 cycles).The microtensile bonding test was performed at a crosshead speed of 0,5 mm/min. Failure modes were classified using a stereomicroscope. The data were analyzed using Scheirer-Ray-Hare, Kruskal-Wallis Mann-Whitney U tests, Chi-square and Z tests with Bonferroni correction (p=0,05). Results: No statistically significant difference was found between the aging methods applied to filling material (p=0,821) and the interaction of applied surface treatments and aging (p=0,289). All repair procedures achieved bond strength values higher than the negative control group but they did not reach the composite's cohesive bond strength. Failure modes distribution was found statistically different according to repair procedure and also aging methods (p<0,05). Conclusion: The bond strengths of the composite resins were similar to those of applied thermal cycling and the pH cycling model with no difference between the different repair methods.