title: Separate contribution of enamel and dentine to overall tooth colour change in tooth bleaching.
abstract: OBJECTIVE
  The aim of this study was to evaluate the separate contribution of enamel (E) and dentine (D) to the colour change of tooth which subjected to 10% carbamide peroxide (CP) gels using a novel recombined enamel-dentine (Recombined-ED) study model.
  
  
  METHODS
  120 enamel-dentine (ED) samples (four homogeneous premolar ED from each patient; total=30×4 ED) were involved in the present study. Two homogeneous ED samples were bleached with 10% CP and the other two ones were stored in artificial saliva for one, two or four weeks. After treatment, four kinds of layers were prepared from each four homogeneous ED samples by removing enamel or dentine part: bleached-enamel (BE), bleached-dentine (BD), control-enamel (CE) and control-dentine (CD). Initial and final colour records of samples were taken with a spectrophotometer in CIELab system. The contribution of enamel/dentine to the colour change of tooth (CTCC) was calculated by measuring the colour difference ΔE between two different enamel-dentine combinations (ΔE between BE/BD and CE/BD for enamel; ΔE between BE/BD and BE/CD for dentine). Translucency parameter (TP) was obtained by calculating the colour difference between enamel on black and white backings.
  
  
  RESULTS
  ED and recombined-ED were significantly correlated in L(*)a(*)b(*) values both for unbleached samples and bleached samples. Bleaching resulted in a significant colour change (ΔE) of E, D and ED samples. The TP of BE was significantly lower than that of CE. The CTCC of enamel was significantly higher than that of dentine all through the time points.
  
  
  CONCLUSIONS
  Enamel played a more important role than dentine in tooth bleaching due to the changes in translucency and colour.
authors.affiliation: Key Laboratory for Oral Biomedical Engineering, Ministry of Education, School and Hospital of Stomatology, Wuhan University, Wuhan, PR China.
authors.forename: Xiao
authors.initials: X
authors.lastname: Ma
authors.forename: Rong
authors.initials: R
authors.lastname: Li
authors.forename: Yue
authors.initials: Y
authors.lastname: Sa
authors.forename: Shanshan
authors.initials: S
authors.lastname: Liang
authors.forename: Lili
authors.initials: L
authors.lastname: Sun
authors.forename: Tao
authors.initials: T
authors.lastname: Jiang
authors.forename: Yining
authors.initials: Y
authors.lastname: Wang
mesh_terms: D000077463:Carbamide Peroxide; D003116:Color; D003124:Colorimetry; D003743:Dental Enamel / Q000187:drug effects* / Q000502:physiology; D003804:Dentin / Q000187:drug effects* / Q000502:physiology; D006801:Humans; D008027:Light; D008954:Models, Biological; D010545:Peroxides / Q000008:administration & dosage / Q000494:pharmacology*; D012542:Scattering, Radiation; D014073:Tooth Bleaching; D058205:Tooth Bleaching Agents / Q000494:pharmacology*; D014508:Urea / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology
chemical_list: D010545:Peroxides; D058205:Tooth Bleaching Agents; D000077463:Carbamide Peroxide; D014508:Urea