title: Effects of bleaching gels on the surface microhardness of tooth-colored restorative materials in situ.
abstract: OBJECTIVE
  The purpose of this study was to evaluate the effects of a home bleaching gel containing 15% carbamide peroxide on the surface microhardness of four tooth-colored restorative materials in situ.
  
  
  METHODS
  Four types of tooth-colored restorative materials, including a nanocomposite resin (Filtek Z350), a packable composite resin (Filtek P60), a polyacid-modified composite (Dyract AP), and a glass-ionomer cement (Ketac Molar Easymix), were used in this study. Each material was divided into two groups equally (n=18): bleaching group and control group. Thirty-six Chinese volunteers were recruited and stone casts were constructed for their upper jaws. Two of the four types of restorative materials were randomly selected and mounted on the first or second molar of the cast for each subject. With respect to each material selected, two specimens from each group were put at a random side. Then custom-fabricated trays containing specimens were fabricated. The participants wore the tray in the daytime, and applied the bleaching gel for the side containing specimens of bleaching group during the night. Surface microhardness measurements were obtained on the top surface of each sample on the different time periods.
  
  
  RESULTS
  There was a statistically significant increase in the surface microhardness of Ketac Molar Easymix due to the exposure to 15% carbamide peroxide, while it produced a significant decrease for Dyract AP. Following immersing in saliva without bleaching agent, Ketac Molar Easymix showed a significant increase in surface microhardness.
  
  
  CONCLUSIONS
  The effects of 15% carbamide peroxide on surface microhardness were material dependent. Immersing in saliva produced a surface hardening effect of glass-ionomer cement.
authors.affiliation: Department of Prosthodontics, School and Hospital of Stomatology, Wuhan University, Wuhan 430079, PR China.
authors.forename: Hao
authors.initials: H
authors.lastname: Yu
authors.forename: Qing
authors.initials: Q
authors.lastname: Li
authors.forename: Manal
authors.initials: M
authors.lastname: Hussain
authors.forename: Yining
authors.initials: Y
authors.lastname: Wang
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D000077463:Carbamide Peroxide; D020770:Compomers; D003188:Composite Resins; D003793:Dental Restoration, Permanent / Q000379:methods; D004338:Drug Combinations; D005260:Female; D005899:Glass Ionomer Cements; D006244:Hardness; D006801:Humans; D008297:Male; D003765:Models, Dental; D053761:Nanocomposites; D016877:Oxidants; D010545:Peroxides; D013499:Surface Properties; D014073:Tooth Bleaching; D014508:Urea / Q000031:analogs & derivatives*
chemical_list: D020770:Compomers; D003188:Composite Resins; D004338:Drug Combinations; D005899:Glass Ionomer Cements; D016877:Oxidants; D010545:Peroxides; D000077463:Carbamide Peroxide; D014508:Urea