Beneficial effects of hydroxyapatite on enamel subjected to 30% hydrogen peroxide

Objectives: To evaluate the effect of combination of hydroxyapatite (HA) and hydrogen peroxide (HP) on color, microhardness and morphology of human tooth enamel. Methods: Forty-eight human dental blocks were obtained from 12 pairs of premolars and were randomly divided into four groups. Group DW was treated with distilled water, group HP with 30% HP, group HA + DW with HA mixed with distilled water and group HA + HP with HA mixed with 30% HP. Baseline and final color measurements and microhardness test were carried out before and after bleaching experiments. Two specimens from each group were selected for morphological investigation after final tests. Results: The LIE of group HP and HA + HP were significantly higher than those of group DW (p = 0.000 and p = 0.000) and group HA + DW (p = 0.000 and p = 0.000). The percentage microhardness loss of group HA + HP was significantly lower than that of group HP (p = 0.047), but significantly higher than those of group DW (p = 0.000) and group HA + DW (p = 0.000). The obvious variation of morphology was only observed on enamel surfaces in group HP. Conclusions: This study suggested that combination of HA and HP was effective in tooth whitening. HA could significantly reduce the microhardness loss of enamel caused by 30% HP and keep enamel surface morphology almost unchanged. (C) 2008 Elsevier Ltd. All rights reserved.