title: Effect of tray-based and trayless tooth whitening systems on microhardness of enamel surface and subsurface.
abstract: OBJECTIVE
  To evaluate the effect of tray-based and trayless tooth whitening systems on surface and subsurface microhardness of human enamel.
  
  
  METHODS
  Enamel slabs were obtained from recently extracted human third molars. Specimens were randomly assigned to six groups according to tooth whitening treatment (n = 10): 6.0% hydrogen peroxide (HP) (Crest Whitestrips), 6.5% HP (Crest Professional Whitestrips), 7.5% HP (Day White Excel 3), 9.5% HP (Day White Excel 3), 10% carbamide peroxide (Opalescence), and a control group (untreated). Specimens were treated for 14 days following manufacturers' recommended protocols, and were immersed in artificial saliva between treatments. Enamel surface Knoop microhardness (KHN) was measured immediately before treatment, and at days 1, 7, and 14 of treatment. After treatment, subsurface microhardness was measured at depths of 50-500 microm. Data were analyzed for statistical significance using analysis of variance.
  
  
  RESULTS
  Differences in microhardness for treated vs. untreated enamel surface were not statistically significant at any time interval. For 6.5% and 9.5% HP, there was a decrease in surface microhardness values during treatment, but at the end of treatment the microhardness values were not statistically different from the baseline values. For the enamel subsurface values, no differences were observed between treated vs. untreated specimens at each depth. Trayless and tray-based tooth whitening treatments do not significantly affect surface or subsurface enamel microhardness.
authors.affiliation: Department of Operative Dentistry, School of Dentistry, The University of North Carolina at Chapel Hill, 302 Brauer Hall, CB#7450, Chapel Hill, NC 27599-7450, USA. teixeire@dentistry.unc.edu
authors.forename: Erica C N
authors.initials: EC
authors.lastname: Teixeira
authors.forename: André V
authors.initials: AV
authors.lastname: Ritter
authors.forename: Jeffrey Y
authors.initials: JY
authors.lastname: Thompson
authors.forename: Ralph H
authors.initials: RH
authors.lastname: Leonard
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Swift
mesh_terms: D000077463:Carbamide Peroxide; D002985:Clinical Protocols; D003743:Dental Enamel / Q000648:ultrastructure*; D004338:Drug Combinations; D006244:Hardness; D006801:Humans; D006861:Hydrogen Peroxide / Q000008:administration & dosage / Q000627:therapeutic use; D016877:Oxidants / Q000008:administration & dosage / Q000627:therapeutic use; D010545:Peroxides / Q000008:administration & dosage / Q000627:therapeutic use; D012464:Saliva, Artificial / Q000737:chemistry; D013997:Time Factors; D014073:Tooth Bleaching / Q000295:instrumentation* / Q000379:methods; D014508:Urea / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000627:therapeutic use
chemical_list: D004338:Drug Combinations; D016877:Oxidants; D010545:Peroxides; D012464:Saliva, Artificial; D000077463:Carbamide Peroxide; D014508:Urea; D006861:Hydrogen Peroxide