Effects of Tooth Bleaching and Desensitization on Shear Bond Strength of Orthodontic Brackets

To evaluate the effects of beyond cold light whitening and desensitization on shear bond strength of orthodontic metal brackets.

Ninety-eight extracted human premolars were randomly divided into seven groups (n = 14). Group 1 was the control (no treatment). Group 2 underwent bleaching, followed by bonding after 24 h. Group 3 received desensitization, then bonding after 24 h. Group 4 combined bleaching and desensitization, with bonding after 24 h. Groups 5, 6, and 7 followed the same procedure as Group 4, but bonding occurred 1, 2, and 3 weeks later, respectively. All samples were stored in 37°C artificial saliva after treatment and bonded with 3 M light-cure composite resin using halogen light. Shear bond strength was tested with a universal testing machine (INSTRON 5848). Adhesive remnant index (ARI) scores were assessed post-debonding. Statistical analysis was conducted using Analysis of Variance (ANOVA), Tukey's test, and chi-square tests, with significance set at p < 0.05.

The shear bond strength 24 h after bleaching (7.5 ± 1.77 MPa) was significantly lower than the control (12.24 ± 3.71 MPa, p < 0.05). Desensitization alone (11.68 ± 3.49 MPa) showed no significant difference compared with the control (p > 0.05). Shear bond strength significantly decreased 24 h after bleaching and desensitization (p < 0.05) but recovered to control levels after 1 week (p > 0.05). ARI scores showed no significant differences.

(1) Brackets bonded 24 h after bleaching or combined treatment showed reduced shear bond strength but were clinically acceptable; (2) The use of nano-biomaterial desensitizers slightly reduces the shear strength of brackets, but it will repair the damage of teeth caused by bleaching; (3) The impacts of bleaching and desensitization gradually reduce and return to normal levels after 1 week.