Effect of bleaching on dentin-resin composite interfacial fracture toughness

Objectives: The notchless triangular prism (NTP) specimen fracture toughness test was used to assess the effect of a carbamide peroxide-containing bleaching agent (Perfecta; Premier) on the fracture toughness of a resin composite - dentin interface. Methods: Human molars and premolars (<6 months old) were wet ground on 600 SiC to obtain 4x4x4x4 mm triangular prisms onto which a resin composite (Z250; 3M) was subsequently bonded using SingleBond (3M) to obtain 4x4x4x8 mm NTP specimens. Bonded specimens were randomly divided into groups (n=9) and exposed to four concentrations of bleaching agent (11, 13, 16, and 21%). Exposure took place in 30 min increments for 2 hour/day during the first week and 4 hours/day over the next two weeks. Testing was conducted after a cumulative exposure of 14, 42, and 70 hours. The maximum force required to fracture specimens, using an Instron 4311 universal testing machine at a cross head speed of .1 mm/min, was recorded and used to calculate K_IC. Results: The results are presented in the Table. The results were analyzed using two-way ANOVA and Bonferroni multiple means comparisons (α=.05). Fractured surfaces were characterized using scanning electron microscopy. Conclusions: Interfacial fracture toughness was significantly reduced by exposure to carbamide peroxide.

Table: K_IC (in MPa·m^1/2) (mean ± SD)