title: Effect of different time periods of vital bleaching on flexural strength of the bovine enamel and dentin complex.
abstract: OBJECTIVE
  The aim of this in vitro study was to evaluate the effect of 20% carbamide peroxide (CP) on the flexural strength (FS) of bovine enamel and dentin complex.
  
  
  METHODS
  One hundred sound bovine teeth were selected for use. Blocks (2 x 3 x 8 mm) from the middle portion of the facial surfaces of each crown were sectioned from the teeth. The specimens were randomly divided into five groups (n=20) based on the time period of vital bleaching. Group 1 comprised the control group kept in artificial saliva. The experimental groups subjected to immersion in 20% CP, Opalescence, for four, six and eight weeks, respectively (eight hours daily). Mechanical testing was performed 24 hours after the last treatment using an Instron Universal Testing Machine with a crosshead speed of 0.5 mm/min. The results were analyzed by one-way analysis of variance (ANOVA) and Tukey's test (a=0.05).
  
  
  RESULTS
  Mean values for FS were 141.27, 103.06, 120.71, 130.23, and 117.90 (Mpa), respectively. Statistically significant differences in FS were noted among the groups. A statistically significant difference was observed between Group 2 (two week bleach) and the control.
  
  
  CONCLUSIONS
  Application of 20% CP bleach for two weeks provided significant decreases in FS of bovine enamel and dentin complex. Similar decreases were not observed among the other groups.
authors.affiliation: Department of Operative Dentistry, School of Dentistry, Dental Research Center, Mashhad University of Medical Sciences, Mashhad, Iran. dr_marjaneh@yahoo.com
authors.forename: Marjaneh
authors.initials: M
authors.lastname: Ghavamnasiri
authors.forename: Sara
authors.initials: S
authors.lastname: Abedini
authors.forename: Alireza
authors.initials: A
authors.lastname: Mehdizadeh Tazangi
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D000077463:Carbamide Peroxide; D002417:Cattle; D003743:Dental Enamel / Q000187:drug effects; D003799:Dental Stress Analysis; D003804:Dentin / Q000187:drug effects; D004338:Drug Combinations; D016877:Oxidants / Q000008:administration & dosage / Q000633:toxicity*; D010545:Peroxides / Q000008:administration & dosage / Q000633:toxicity*; D018583:Pliability / Q000187:drug effects; D013997:Time Factors; D014073:Tooth Bleaching / Q000009:adverse effects*; D014508:Urea / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000633:toxicity
chemical_list: D004338:Drug Combinations; D016877:Oxidants; D010545:Peroxides; D000077463:Carbamide Peroxide; D014508:Urea