title: Beneficial effects of hydroxyapatite on enamel subjected to 30% hydrogen peroxide.
abstract: OBJECTIVE
  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 DeltaE 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.
authors.affiliation: Key Laboratory for Oral Biomedical Engineering, Ministry of Education, School and Hospital of Stomatology, Wuhan University, 237 Luoyu Road, Wuhan 430079, PR China.
authors.forename: Tao
authors.initials: T
authors.lastname: Jiang
authors.forename: Xiao
authors.initials: X
authors.lastname: Ma
authors.forename: Zhejun
authors.initials: Z
authors.lastname: Wang
authors.forename: Hua
authors.initials: H
authors.lastname: Tong
authors.forename: Jiming
authors.initials: J
authors.lastname: Hu
authors.forename: Yining
authors.initials: Y
authors.lastname: Wang