title: Bleaching agents with varying concentrations of carbamide and/or hydrogen peroxides: effect on dental microhardness and roughness.
abstract: OBJECTIVE
  To evaluate the effect of low and highly concentrated bleaching agents on microhardness and surface roughness of bovine enamel and root dentin.
  
  
  METHODS
  According to a randomized complete block design, 100 specimens of each substrate were assigned into five groups to be treated with bleaching agents containing carbamide peroxide (CP) at 10% (CP10); hydrogen peroxide (HP) at 7.5% (HP7.5) or 38% (HP38), or the combination of 18% of HP and 22% of CP (HP18/CP22), for 3 weeks. The control group was left untreated. Specimens were immersed in artificial saliva between bleaching treatments. Knoop surface microhardness (SMH) and average surface roughness (Ra) were measured at baseline and post-bleaching conditions.
  
  
  RESULTS
  For enamel, there were differences between bleaching treatments for both SMH and Ra measurements (p = 0.4009 and p = 0.7650, respectively). SMH significantly increased (p < 0.0001), whereas Ra decreased (p = 0.0207) from baseline to post-bleaching condition. For root dentin, the group treated with CP10 exhibited the significantly highest SMH value differing from those groups bleached with HP18/CP22, HP7.5, which did not differ from each other. Application of HP38 resulted in intermediate SMH values. No significant differences were found for Ra (p = 0.5975). Comparing the baseline and post-bleaching conditions, a decrease was observed in SMH (p < 0.0001) and an increase in Ra (p = 0.0063).
  
  
  CONCLUSIONS
  Bleaching agents with varying concentrations of CP and/or HP are capable of causing mineral loss in root dentin. Enamel does not perform in such bleaching agent-dependent fashion when one considers either hardness or surface roughness evaluations. CLINICAL SIGNIFICANCE Bleaching did not alter the enamel microhardness and surface roughness, but in root dentin, microhardness seems to be dependent on the bleaching agent used.
authors.affiliation: Department of Restorative Dentistry, School of Dentistry of Ribeirão Preto, University of São Paulo (USP), São Paulo, Brazil. jujfaraoni@yahoo.com.br
authors.forename: Juliana Jendiroba
authors.initials: JJ
authors.lastname: Faraoni-Romano
authors.forename: Alessandra Gonçalves
authors.initials: AG
authors.lastname: Da Silveira
authors.forename: Cecilia Pedroso
authors.initials: CP
authors.lastname: Turssi
authors.forename: Mônica Campos
authors.initials: MC
authors.lastname: Serra
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D000077463:Carbamide Peroxide; D002417:Cattle; D003743:Dental Enamel / Q000187:drug effects*; D003804:Dentin / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D004338:Drug Combinations; D006244:Hardness / Q000187:drug effects*; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D010545:Peroxides / Q000494:pharmacology*; D011897:Random Allocation; D013499:Surface Properties / Q000187:drug effects; D014073:Tooth Bleaching / Q000009:adverse effects*; D014508:Urea / Q000031:analogs & derivatives* / Q000494:pharmacology
chemical_list: D004338:Drug Combinations; D010545:Peroxides; D000077463:Carbamide Peroxide; D014508:Urea; D006861:Hydrogen Peroxide