Microhardness and color changes of human dentin with repeated intracoronal bleaching

This study investigated the effects of three intracoronal bleaching techniques on the color and microhardness changes of human dentin and compared them to a control group. Twenty-four dentin slabs were derived from extracted maxillary anterior teeth and evenly distributed among four groups. The pulpal surface of each dentin slab was treated with one of the following bleaching techniques: thermocatalytic treatment with 30% hydrogen peroxide, walking bleaching with 2% sodium perborate and a combination treatment that uses both methods. In the control group, the specimens were treated with distilled water. All specimens were subjected to repeated treatment with fresh bleaching pastes on days 0, 7, 14 and 21. During the experimental period, all specimens were placed in individual vials maintained at 37 degrees C and 100% humidity. CIELab color parameters and microhardness (VHN) were evaluated prior to the experiments and seven days after each treatment. All bleaching treatments effectively increased L* values and decreased b* values of dentin. Thermocatalytic bleaching significantly reduced dentin hardness to half its original value after four treatment cycles; whereas, treatment with either walking bleaching or the combined technique did not significantly affect dentin hardness. Because the combination treatment had shown great bleaching efficacy, it can serve as an alternative approach for severely stained teeth.