title: Effects of different bleaching time intervals on fracture toughness of enamel.
abstract: OBJECTIVE
  This study was designed to evaluate the influence of different time intervals of a vital home bleaching procedure on the fracture toughness of bovine enamel.
  
  
  METHODS
  Labial aspects of 48 bovine incisors were prepared and stored in artificial saliva. The samples were divided into four groups (n = 12) according to the different time intervals of the bleaching procedure: 0, 2, 4, and 6 weeks. The experimental groups were subjected to the bleaching agent; 15% Opalescence PF according to manufacturer's instructions. The fracture toughness (FT) of enamel was assessed using Vickers hardness indentation. Then, FTs were compared statistically by one-way ANOVA (α = 0.05).
  
  
  CONCLUSIONS
  Different tested time intervals did not significantly influence the fracture toughness of bovine enamel following treatment with 15% carbamide peroxide (P = 0.05)
  
  
  CONCLUSIONS
  15% Opalescence PF after 6 weeks did not reduce the fracture toughness of human enamel compared with the baseline, 2 and 4-week values.
authors.affiliation: Department of Operative Dentistry, Dental School and Dental Research Center of Mashhad University of Medical Sciences, Mashhad, Iran.
authors.forename: Hamideh
authors.initials: H
authors.lastname: Ameri
authors.forename: Marjaneh
authors.initials: M
authors.lastname: Ghavamnasiri
authors.forename: Akram
authors.initials: A
authors.lastname: Abed