The Effect of Different Bleaching Treatments and Thermal-Mechanical Cycling on the Shear Bond Strength of Orthodontic Brackets

Özet

Objective: The aim of the present study was to compare the shear bond strength (SBS) of orthodontic brackets bonded to the enamelafter at-home and in-office bleaching treatments.Methods: Sixty bovine incisors were subjected to initial color readings and then classified into three groups: CP (16% carbamideperoxide), HP (35% hydrogen peroxide), and C (control). After treatments, new color readout was obtained, and orthodontic bracketswere bonded to the bleached area. Half of the samples of each group (n=10) were subjected to thermal-mechanical cycling (TMC)testing (1,200,000 cycles; 44.2 N; 2 Hz/s), whereas the other half were stored in distilled water at 37 °C for 24 h. Samples were subjectedto the SBS test at a speed of 0.5 mm/min. The mean SBS was analyzed (two-way ANOVA, Bonferroni test, p 0.05) in SBS values between the samples subjected to TMC and the cycled samples in any group.Samples subjected to carbamide peroxide presented lower SBS (p<0.05) than the non-cycled ones. Enamel adhesive fractures werehigher in the bleached groups than in the control group, which presented mixed fractures prevalence, regardless of whether it wassubjected to TMC or not.