The Etching Effect of Co2 Laser on The Shear Bond Strength of Bleached Teeth

Abstract

Background: Tooth discoloration is one of the great esthetic problems in dentistry, Despite vital bleaching, is often considered a first step to improve the appearance of teeth, reports are controversial about the effect of bleaching on the shear bond strengths (SBS) of brackets. Etching of enamel surface can be carried out by acid or laser, there was controversial about the efficiency of CO2 laser as enamel surface etchant Objective: The aim of the present study is to detect if there is a significant reduction in SBS of bleached teeth, and to detect the effect of CO2 laser as etchant on both bleached and normal teeth. Methods and materials: Forty non-carious first premolars are divided into 2 main groups: None- bleached (A) and Bleached (B) groups, of 20 specimens for each group, then the groups were subdivided into 2 subgroups (10 specimens for each subgroup). Group (B) teeth were bleached with chemically activated 40% hydrogen peroxide, while group (A) teeth were left without bleach- ing. The subgroups teeth (A1 and B1) were etched with CO2 laser and the subgroups (A2 and B2) were etched with 37% phosphoric acid. After bracket bonding, samples were then thermally cycled for 500 cycles between( 5°C and 55°C). Debonding was performed with a shearing force using the universal testing machine, then ANOVA and LSD test were used to specify if there was a significant difference between groups. Results: there was the nonsignificant difference in mean SBS of both phosphoric acid etching and CO2 laser etching in both bleached and normal surface enamel specimens A and B groups. Whereas there was a significant difference in mean shear bond strength between the CO2 laser etched and the phosphoric acid etched groups with highest mean values in the phosphoric acid etched subgroups, Conclusion: The results of this in vitro study suggest that hydrogen peroxide bleaching does not affect the shear bond strength of metal orthodontic brackets when bonding occurred 1 week after bleaching and CO2 laser etching has low shear bond strength values making it not suitable for clinical use.