Effect of prolonged direct and indirect peroxide bleaching on fracture toughness of human dentin

Statement of the Problem: The effects of prolonged exposure to peroxide bleaching agents on dentin structural integrity are uncertain. Purpose: To evaluate the effect of in vitro prolonged tooth bleaching on the fracture toughness (K-1C) of human dentin. Materials and Methods: Dentin from recently extracted molar teeth was directly or indirectly treated to simulate a prolonged at-home (10% carbamide peroxide or 3% hydrogen peroxide, 6 hours/day, 5 days/week for 8 weeks) or in-office (30% hydrogen peroxide, 1 hour/week for 8 weeks) bleaching regimen (N = 8/group). Placebo gel and distilled water acted as control materials. Compact tension test specimens (approximately 4.60 x 4.50 x 1.60 mm) were prepared from coronal dentin and tensile loading was applied at a rate of 10 mm/min 24 hours after the last bleaching session. Results were analyzed using analysis of variance and Tukey's test (p < 0.05). For direct bleach application, the treatment materials were applied onto dentin that was already prepared as compact tension specimens. For indirect bleach application, bleach was applied to the enamel of intact teeth prior to specimen preparation. Results: There was a significant decrease in dentin K-1C after 8 weeks of direct bleach treatment (p < 0.05). There were no significant differences between the bleach and control groups after 8 weeks of indirect bleach treatment (p = 0.19). Conclusions: The in vitro fracture resistance of dentin was reduced after the prolonged use of bleach products that were applied directly to dentin.