The effect of different surface preparation methods and various aging periods on bond strength for composite repair

The aim of this in vitro study was to evaluate the effect of various aging periods and different surface preparation methods on microtensile bond strength (μTBS), for repairing a nanohybrid composite resin in combination with a three-step etch&rinse adhesive system. 112 composite resin blocks were formed by using a current universal nanohybrid composite resin (Harmonized, Kerr) and the samples were divided into 4 groups according to surface preparation methods (n=28): Control Group (Unrepaired sound composite blocks); Er,Cr:YSGG Laser group; Air Abrasion Group; Silicon carbide (SiC) group. All samples were then divided into 4 subgroups according to various aging periods: No aging; Aging by 10,000 thermocycling; Aging by 30,000 thermocycling; Aging by 50,000 thermocycling. The surface topography of one randomly selected sample from each group was examined by a Scanning Electron Microscope (SEM). In the groups with surface preparation process, the nanohybrid composite repairs were bonded to the sample surfaces, using a three-step etch&rinse adhesive (Optibond FL, Kerr) according to the manufacturer's recommendations. Consequently, 1x1x8 mm sized beams were obtained from all samples under water cooling and 30 beams from each group were subjected to μTBS test with a crosshead speed of 1.0 mm/min. The fracture modes were evaluated under a stereomicroscope at x10 magnification. The data were analyzed by using Two-Way Analysis of Variance, Post-hoc Bonferroni and Chi-Square tests (p=0.05). When different surface preparation methods were evaluated together, no aging and 10,000 times thermocycling groups showed higher μTBS values than those aged with 30,000 and 50,000 thermocycling (p<0.05). When all aging periods were evaluated together, the surface preparation with Air Abrasion provided higher μTBS compared to Laser and SiC (p<0.05). When the interactions of various aging periods with different surface preparation methods were examined; it was found that there were significant differences in terms of μTBS between surface preparation methods, in addition various aging periods resulted in significant changes in μTBS values in Control, Laser and Air Abrasion groups (p<0.05). In terms of fracture mode distributions, there were statistically significant differences among the surface preparation methods (p<0.001), while no significant difference was found among various aging periods (p>0.001). SEM images were in accordance with μTBS findings. Within the limitations of this in vitro study; it was concluded that various aging periods, different surface preparation methods and the interaction of these factors with each other affected the μTBS, when repairing the tested nanohybrid composite resin by using a three-step etch&rinse adhesive system. Key words: Repair, Composite Resin, Etch&Rinse Adhesive, Micro Tensile Bond Strength