title: Effect of home bleaching systems on enamel nanohardness and elastic modulus.
abstract: OBJECTIVE
  The purpose of this study was to evaluate the nanohardness and elastic modulus of human enamel after treatment with tray and strip bleaching systems.
  
  
  METHODS
  Fifty-five human enamel samples were exposed to five different bleaching agents. Nanoindentations were made before and after bleaching treatments following the manufacturer's directions using a Nanoindenter XP (MTS Systems Corporation, Oak Ridge, TN, USA). Nanohardness and elastic modulus measurements were obtained and the results were statistically analyzed using a repeated measures analysis of variance with a post-hoc Tukey-Kramer multiple comparison test.
  
  
  RESULTS
  Nanohardness and elastic modulus measurements showed decrease of mean values for each group except the control which remained the same. There were significant differences due to time (before and after treatment) and material effects in nanohardness (P<0.0001) and elastic modulus (P=0.0241). Measurements after treatment showed significant decrease in nanohardness between all groups and the control group. There was a significant difference in hardness between CP and TO after treatment. Additionally, there were significant differences in elastic modulus between the control group when compared to OB and TO after treatment. While there were significant changes in the elastic modulus due to treatment for both CP and TO, there were no significant differences between any of the groups after treatment.
  
  
  CONCLUSIONS
  Nanohardness and elastic modulus of human enamel were significantly decreased after the application of home-bleaching systems.
authors.affiliation: Division of Restorative and Prosthetic Dentistry, The Ohio State University College of Dentistry, Columbus, OH 43218-2357, USA. azer.1@osu.edu
authors.forename: Shereen S
authors.initials: SS
authors.lastname: Azer
authors.forename: Camilo
authors.initials: C
authors.lastname: Machado
authors.forename: Eliana
authors.initials: E
authors.lastname: Sanchez
authors.forename: Robert
authors.initials: R
authors.lastname: Rashid
mesh_terms: D000077463:Carbamide Peroxide; D003743:Dental Enamel / Q000187:drug effects*; D004338:Drug Combinations; D055119:Elastic Modulus / Q000187:drug effects; D006244:Hardness / Q000187:drug effects; D006801:Humans; D006861:Hydrogen Peroxide / Q000009:adverse effects*; D016877:Oxidants / Q000009:adverse effects*; D010545:Peroxides / Q000009:adverse effects*; D014073:Tooth Bleaching / Q000009:adverse effects*; D014508:Urea / Q000009:adverse effects / Q000031:analogs & derivatives*
chemical_list: D004338:Drug Combinations; D016877:Oxidants; D010545:Peroxides; D000077463:Carbamide Peroxide; D014508:Urea; D006861:Hydrogen Peroxide