title: Effect of bleaching agents on the hardness and morphology of enamel.
abstract: OBJECTIVE
  The goal of the present laboratory study was to analyze the effect of two home bleaching agents (Opalescence 10%, Ultradent, and Hi-Lite II, Shofu) as well as the separate solutions of 10% carbamide peroxide primary components (3% hydrogen peroxide and 7% urea) on enamel microhardness and surface morphology.
  
  
  METHODS
  Thirty human molars stored in water for no longer than 3 months were selected. Their facial and lingual surfaces were embedded in acrylic resin, and the specimens were polished with up to 600-grit sandpaper. The 30 molar sections were divided into five groups as per treatment modality (n = 6); group 1, 10% carbamide peroxide bleach with carbopol (Opalescence, Ultradent); group 2, oxygen-free gel bleach (Hydroxylite, Hi-Lite II, Shofu); group 3, 3% hydrogen peroxide with carbopol (Dermus Pharmacy, Florianópolis, SC, Brazil); group 4, 7% urea treatment (Dermus Pharmacy); and control, group 5, artificial saliva (Dermus Pharmacy). Prior to treatment, six indentations (Vickers) were made on each of the six surfaces in each group under a load of 100 g for 30 seconds. Bleaching procedure was conducted for 3 hours per day for 2 weeks, the control group excepted. Following each bleaching session, the specimens were washed with deionized water and kept in artificial saliva at 37 degrees C, this solution being changed daily. Pre- and post-treatment microhardness data were analyzed using a two-way analysis of variance. In a similar way, 30 other specimens underwent the same procedures. After the bleaching period, the samples were observed under the scanning electron microscope.
  
  
  RESULTS
  Specimens submitted to bleaching treatment with 3% hydrogen peroxide gel as described in this study showed a significant reduction of surface microhardness (p < .0001). The other treatment modalities had no effect on surface microhardness. No morphologic alterations were observed on enamel submitted to bleaching gel of 10% carbamide peroxide (Opalescence), oxygen-free gel (Hi-Lite II, Shofu), or 7% urea solution compared with the control (artificial saliva). However, the specimens bleached for 3 hours per day for 2 weeks with 3% hydrogen peroxide gel presented areas of mild erosion. The effect, nevertheless, was not uniform, occurring with varying intensity on all samples of enamel bleached with 3% hydrogen peroxide.
  
  
  CONCLUSIONS
  Bleaching treatment conducted with two home bleaching agents (Opalescence 10%, Ultradent, and Hi-Lite II, Shofu) had no adverse effects on enamel microhardness or on surface morphology. Bleaching with 3% hydrogen peroxide can have a negative effect on enamel hardness and surface morphology when performed as described in this study.
authors.affiliation: Department of Operative Dentistry, Federal University of Santa Catarina, Florianópolis, Brazil. guilherme_lopes@ig.com.br
authors.forename: Guilherme Carpena
authors.initials: GC
authors.lastname: Lopes
authors.forename: Leandro
authors.initials: L
authors.lastname: Bonissoni
authors.forename: Luiz Narciso
authors.initials: LN
authors.lastname: Baratieri
authors.forename: Luiz Clóvis C
authors.initials: LC
authors.lastname: Vieira
authors.forename: Sylvio
authors.initials: S
authors.lastname: Monteiro
mesh_terms: D000180:Acrylic Resins; D000704:Analysis of Variance; D000077463:Carbamide Peroxide; D003743:Dental Enamel / Q000187:drug effects* / Q000648:ultrastructure; D003747:Dental Enamel Solubility / Q000187:drug effects; D004337:Drug Carriers; D004338:Drug Combinations; D006244:Hardness; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D008855:Microscopy, Electron, Scanning; D008963:Molar; D016877:Oxidants / Q000494:pharmacology*; D010545:Peroxides / Q000494:pharmacology; D011145:Polyvinyls / Q000494:pharmacology; D012464:Saliva, Artificial; D013223:Statistics as Topic; D013696:Temperature; D013997:Time Factors; D014073:Tooth Bleaching; D014077:Tooth Erosion / Q000139:chemically induced; D014508:Urea / Q000031:analogs & derivatives* / Q000494:pharmacology
chemical_list: D000180:Acrylic Resins; D004337:Drug Carriers; D004338:Drug Combinations; D016877:Oxidants; D010545:Peroxides; D011145:Polyvinyls; D012464:Saliva, Artificial; C093177:tooth-bleaching agent, Opalescence; C006912:carboxypolymethylene; D000077463:Carbamide Peroxide; D014508:Urea; D006861:Hydrogen Peroxide