Effect of carbamide peroxide bleaching agents on tensile strength of human enamel

Objectives. The aim of this study was to evaluate the effects of low concentrations of carbamide peroxide bleaching agents (CP) on the ultimate tensile strength of enamel (UTS). Methods. Resin composite structure was built-up on the bonded occlusal surface of 12 sound third molars to facilitate specimen preparation for microtensile testing. The bonded teeth were sectioned in a bucco-lingual direction in slices approximately 0.7 mm thick. Each slice was trimmed with a fine diamond bur to reduce the buccal, internal slope enamel of the cusps to a dumb-bell shape with a cross-sectional area at the ‘neck’ of less than 1 mm2. The sample was randomly divided into six groups of 10 specimens each: Control (C—untreated); Opalescence 10% (O10), Opalescence 15% (O15), Opalescence 20% (O20), Whiteness 10% (W10) and Whiteness 16% (W16). Specimens in each group received the application of the CP for 6 h/day, at 37 °C, during 14 days and were stored in artificial saliva in between each application. After the bleaching regimen, specimens were tested with the microtensile method at 0.5 mm/min. Data were analyzed by ANOVA and Tukey test (5%). Results. Mean tensile strengths were (MPa): C=47.5±6.2a; O10=37.6±5.8b; O15=33.2±6.0b; O20=31.2±3.5b; W10=32.5±6.1b; W16=30.6±7.7b. Specimens subjected to the bleaching regimen presented significantly lower UTS than the control group. No differences were found among the type and concentration of the bleaching agents. Significance. Results suggested that bleaching enamel with CP could significantly reduce its UTS within a 14 days treatment.