title: Effect of tooth whitening strips on fatigue resistance and flexural strength of bovine dentin in vitro.
abstract: OBJECTIVE
  To determine the effects of whitening strips on bovine dentin fatigue resistance and flexural strength in vitro.
  
  
  METHODS
  A total of eighty bovine dentin specimens (2x2x17mm) were treated with either: control glycerine gel on plastic film wrap or whitening strips containing 9.5% hydrogen peroxide. Treatment was applied for 30 minutes, twice a day, for 1- or 4-weeks. After the last treatment, ten specimens per group were randomly selected to undergo fatigue testing (106 cycles, 3Hz, 20N) while the other ten were subjected to flexural strength testing after ten days of storage in artificial saliva. Kaplan-Meier method with a log rank test, Wilcoxon test and Cox regression were used to assess fatigue test results (p<0.05). One-way ANOVA and Tukey's tests were used to compare the flexural strength results (p<0.05).
  
  
  RESULTS
  There were significant differences in survival during the fatigue test among the groups (p<0.001). Treatment (control or bleach) was a significant factor for specimen survival (p<0.001, Exp(B) = 33.45). There were significant differences in mean flexural strength (p<0.001). No significant difference was found between "1-wk control" and "4-wk control". The mean flexural strength and fatigue resistance of the "4-wk bleach" were significantly lower than all the other groups.
  
  
  CONCLUSIONS
  The use of whitening strips reduced the fatigue resistance and flexural strength of bovine dentin in vitro. Until the effect of whitening strips on mechanical properties of human dentin is fully elucidated, it remains prudent to advise patients to avoid excessive direct use of whitening strips on dentin.
authors.affiliation: Restorative Dentistry, Department of Clinical Sciences, Faculty of Dentistry, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Laura E
authors.identifier: http://orcid.org/0000-0002-4670-6952
authors.initials: LE
authors.lastname: Tam
authors.affiliation: Restorative Dentistry, Department of Clinical Sciences, Faculty of Dentistry, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Namhee
authors.initials: N
authors.lastname: Kim
authors.affiliation: Restorative Dentistry, Department of Clinical Sciences, Faculty of Dentistry, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Grace M
authors.initials: GM
authors.lastname: De Souza
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D002417:Cattle; D003804:Dentin / Q000187:drug effects* / Q000502:physiology*; D008422:Materials Testing; D055595:Mechanical Phenomena; D011934:Reagent Strips / Q000009:adverse effects*; D014073:Tooth Bleaching / Q000009:adverse effects*
chemical_list: D011934:Reagent Strips