Shear Bond Strength of Orthodontic Stainless Steel Bracket in Bovine Teeth Submitted to Bleaching Agents

The purpose of this in vitro study was to determine the influence of bleaching agents in the shear bond strength of orthodontic stainless steel bracket. The samples were composed by 90 bovine lower central incisors, which were divided into three groups named G1 (not submitted to bleaching), G2 (bleached with carbamide peroxide at 16%-Whiteness HP - FGM ®) and G3 (bleached with hydrogen peroxide at 35%-Whiteness HP, FGM ®). The teeth were stored in distilled water at a temperature of 37oC for 24 hours and 30 days was expected for the bonding of brackets Gemini 3M (3M - Unitek ®), after a wait period of 30 days the brackets were placed to all groups of samples, applied with the composite Transbond XT (3M/ESPE®). The shear bond test was performed in material testing machine EMIC DL 2000, carried under a deformation speed of 0.5 mm / min. The G1 presented an average strength of 6,05 (±3,47) MPa, while the G2 presented an average resistance of 2,52 (±1,69) MPa, and the G3 demonstrated 1,58 (±1,17) MPa. The results concluded that the dental bleaching induced, in the experimental model used, significant reduction of shear strength of brackets bonded to dental elements subjected to both in-home and in-clinic bleaching. These findings suggest that adherence of the resin used in the placement of the brackets was damaged by bleaching. Therefore, the most affected in the analysis of shear bond strength was first the in-clinic bleaching, followed by in-home bleaching and at last the control group and the greater the concentration of bleach is less shear strength. So it is suggested to perform the bleaching treatment after orthodontic treatment.