title: Effect of hydrogen peroxide concentration on enamel color and microhardness.
abstract: OBJECTIVE
  The aim of this study was to investigate the effect of hydrogen peroxide gels with different concentrations (20%, 25%, 30%, and 35%) on enamel Knoop microhardness (KNH) as well as on changes in dental color (C).
  
  
  METHODS
  Cylindrical specimens of enamel/dentin (3-mm diameter and 2-mm thickness) were obtained from bovine incisors and randomly divided into six groups (n=20), according to the concentration of the whitening gel (20%, 25%, 30%, 35%, control, thickener). After polishing, initial values of KNH0 and color measurement, assessed by spectrophotometry using the CIE L*a*b* system, were taken from the enamel surface. The gels were applied on the enamel surface for 30 minutes, and immediate values of KNHi were taken. After seven days of being stored in artificial saliva, new measures of KNH7 and color (L7* a7* b7*, for calculating ΔE, ΔL, and Δb) were made. Data were submitted to statistical analysis of variance, followed by Tukey test (p<0.05).
  
  
  RESULTS
  Differences in gel concentration and time did not influence the microhardness (p=0.54 and p=0.29, respectively). In relation to color changes, ΔE data showed that the 35% gel presented a higher color alteration than the 20% gel did (p=0.006).
  
  
  CONCLUSIONS
  Bleaching with 35% hydrogen peroxide gel was more effective than with the 20% gel, without promoting significant adverse effects on enamel surface microhardness.
authors.forename: A B
authors.initials: AB
authors.lastname: Borges
authors.forename: R F
authors.initials: RF
authors.lastname: Zanatta
authors.forename: A C S M
authors.initials: AC
authors.lastname: Barros
authors.forename: L C
authors.initials: LC
authors.lastname: Silva
authors.forename: C R
authors.initials: CR
authors.lastname: Pucci
authors.forename: C R G
authors.initials: CR
authors.lastname: Torres
mesh_terms: D000818:Animals; D002417:Cattle; D003116:Color; D003743:Dental Enamel / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D005782:Gels; D006244:Hardness / Q000187:drug effects*; D006861:Hydrogen Peroxide / Q000008:administration & dosage / Q000009:adverse effects / Q000494:pharmacology*; D013053:Spectrophotometry; D014073:Tooth Bleaching / Q000009:adverse effects / Q000379:methods; D058205:Tooth Bleaching Agents / Q000008:administration & dosage / Q000009:adverse effects / Q000494:pharmacology*
chemical_list: D005782:Gels; D058205:Tooth Bleaching Agents; D006861:Hydrogen Peroxide