Effects of cyclic loading on the shear bond strength of metal orthodontic brackets bonded to resin composite veneer surface using different conditioning protocols

BACKGROUND: The aim of this research is to evaluate cyclic (CSBS) and static shear bond strengths (SSBS) of metal orthodontic brackets bonded to composite laminates using different conditioning protocols. METHODS: A total of 80 direct nanofilled composite laminate veneers were prepared on permanent incisors and divided into four equal groups according to different surface treatments. In group 1, diamond bur was used. In group 2, microetcher (50-μm alumina particles) was utilized. In group 3, 38% phosphoric acid treatment for 60 s was done. In group 4 (control group), metal brackets were bonded to the untreated veneer surfaces using no-mix adhesive resin. SSBS testing was carried out for ten specimens, while CSBS testing was done for another ten specimens from each group. The data were subjected to analysis of variance and Scheffe post hoc test. The chi-square test was used to determine significant differences in the adhesive remnant index scores among different groups. RESULTS: Statistically significant difference was only found between SSBS of brackets bonded when surface treatment was done using the diamond bur, microetcher, and the phosphoric acid at P < 0.05. With regard to CSBS, the use of bur treatment and microetching achieved the highest values; however, there was no significant difference between these two groups. With phosphoric acid, surface treatment achieved the lowest CSBS value; there was no significant difference between this group and the control group. The SSBS was significantly higher than CSBS in all groups. CONCLUSIONS: Roughening composite laminate veneers with either diamond bur or microetcher could be used successfully as an alternative to provide higher bond strength than phosphoric acid surface treatment. Cyclic loading significantly decreased bond strength.