Abstract
Objective:The aim of this study was to evaluate the effects of carbamide peroxide-based bleaching agents (CPG) containing fluoride (CF) or calcium (CCa) on the ultimate tensile strength of enamel (UTS).Method:A "cube-like" resin composite structure was built-up on the occlusal surface of twenty-two sound third molars to facilitate specimen preparation for the micro-tensile test. The restored teeth were serially sectioned in buccal-lingual direction in slices with approximate 0.7 mm thickness. 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 0.5 mm2. The samples were randomly divided into 12 groups (n=11). The control groups were not submitted to the bleaching regimen. Specimens were treated with 10% CPG gel or with 10% CPG formulations containing CF (0.2% and 0.5%) or CCa (0.05% and 0.2%). Bleached groups received the application of the 10% CPGs for 6 hours/day at 37° C, during 14 consecutive days and were stored in artificial saliva (AS) or 100% relative humidity (RH) among each application. After bleaching, specimens were tested with the microtensile method at 0.5 mm/min. Data were analyzed by two-way ANOVA and Tukey test (5%).Results:No significant difference was observed between groups stored in AS or RH. Specimens treated with CF or CCa presented similar UTS as unbleached control groups.Conclusion:Either 10% CPG formulations containing CF or CCa can preserve the UTS after bleaching regimen.
Highlights
Previous bleaching methods were more aggressive due to application of 30 to 35% hydrogen peroxide in combination with a heat lamp or a heating element, microabrasion and etching with 37% phosphoric acid
There is no agreement about the effects of bleaching on enamel, since scanning electron microscopy investigations of bleached enamel surfaces have shown little or no topographic alterations[17,22], while surface changes after carbamide peroxide bleaching have been reported
Two-way analysis of variance (ANOVA) detected a statistically significant difference among bleaching materials (p = 0.00002), no significant difference between specimens stored in artificial saliva and relative humidity (p = 0.738) and failed to identify any factor interactions (p = 0.542)
Summary
Previous bleaching methods were more aggressive due to application of 30 to 35% hydrogen peroxide in combination with a heat lamp or a heating element, microabrasion and etching with 37% phosphoric acid. Home bleaching techniques using 10% carbamide peroxide gel in a mouthguard have been considered less invasive, safe for soft tissues and an effective method to bleach vital teeth[13]. Since contemporary concepts in Esthetic Dentistry recommend less invasive techniques without tooth damage, the use of home bleaching techniques has become popular for whitening stained and discolored teeth[14,18]. There is no agreement about the effects of bleaching on enamel, since scanning electron microscopy investigations of bleached enamel surfaces have shown little or no topographic alterations[17,22], while surface changes after carbamide peroxide bleaching have been reported. The alterations include increased porosity, pitting, erosion and demineralization of enamel prisms periphery[1,9,12,15,23,27]. Chemical composition, mechanical and physical properties of bleached human enamel have demonstrated conflicting evidences[1,4,10,11,20,24,25,26]
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