title: Enamel microhardness and shear bond strength after treatment with an 18% carbamide peroxide bleaching varnish.
abstract: OBJECTIVE
  To evaluate the microhardness and shear bond strength of human enamel treated with an 18% carbamide peroxide bleaching varnish.
  
  
  METHODS
  40 dental enamel slabs were embedded and ground flat, dividing them into four groups (n=10) which received the varnish application for 14 consecutive days: (G1) one daily varnish application; (G2) two daily varnish applications with an interval of 15 minutes; (G3) two daily varnish applications with an interval of 5 hours. After varnish application, the slabs were immersed in artificial saliva changed daily. The control group (G4) consisted of slabs (n=10) that did not receive any varnish treatment and were maintained in artificial saliva for 14 days. Microhardness tests were performed with Knoop indentation with a load of 25 grams for 5 seconds at the beginning of the treatment (baseline values) and after 7 and 14 days. Cylinders were made with microhybrid resin composite and one-bottle adhesive system for shear bond strength tests. Using a universal testing machine with a speed of 0.5 mm/minute to obtain the values in MPa.
  
  
  RESULTS
  The Kruskal-Wallis test showed no changes in microhardness values among groups after 7-day varnish application, although there was a decrease in microhardness values when using an 18% carbamide peroxide varnish twice a day with a time-interval of 5 hours between applications (P < 0.05). For enamel shear bond strength, ANOVA test (P > 0.05) did not show significant differences among the groups (G1=15.8; G2=15.2; G3=19.0; G4=15.1).
authors.affiliation: Department of Restorative Dentistry, São Leopoldo Mandic Research Center, Campinas, São Paulo, Brazil.
authors.forename: Robson Tetsuo
authors.initials: RT
authors.lastname: Sasaki
authors.forename: Maria Cinthia
authors.initials: MC
authors.lastname: Barbosa
authors.forename: Flávia Martão
authors.initials: FM
authors.lastname: Flório
authors.forename: Roberta Tarkany
authors.initials: RT
authors.lastname: Basting
mesh_terms: D000268:Adhesiveness; D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry; D000077463:Carbamide Peroxide; D045424:Complex Mixtures / Q000737:chemistry / Q000494:pharmacology; D003188:Composite Resins / Q000737:chemistry*; D001840:Dental Bonding; D003743:Dental Enamel / Q000187:drug effects / Q000648:ultrastructure*; D017220:Dentin-Bonding Agents / Q000737:chemistry; D004338:Drug Combinations; D006244:Hardness; D006801:Humans; D008422:Materials Testing; D016877:Oxidants / Q000737:chemistry* / Q000494:pharmacology; D010545:Peroxides / Q000737:chemistry* / Q000494:pharmacology; D012464:Saliva, Artificial / Q000737:chemistry; D033081:Shear Strength; D013314:Stress, Mechanical; D013997:Time Factors; D014073:Tooth Bleaching; D014508:Urea / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology
chemical_list: C475021:Colgate Simply White Clear Whitening Gel; D045424:Complex Mixtures; D003188:Composite Resins; D017220:Dentin-Bonding Agents; D004338:Drug Combinations; C444701:Filtek Z250; D016877:Oxidants; D010545:Peroxides; D012464:Saliva, Artificial; C115612:single bond; D000077463:Carbamide Peroxide; D017438:Bisphenol A-Glycidyl Methacrylate; D014508:Urea