Fracture toughness of two dentin adhesives

Abstract

Purpose Test the hypothesis that a self-etching adhesive is more likely to fail at the dentin-adhesive interface than an etch-and-rinse adhesive. Materials and methods Forty-eight composite-dentin short rod chevron-notched specimens were prepared. XP Bond and G Bond were used as adhesives. After 7 days in distilled water at 37 °C, each specimen was tested (cross-head speed = 0.05 mm/min). Fractured surfaces were inspected and characterized as interfacial failures, composite failures or a combination of interfacial and composite failures. The fracture toughness values ( K IC) of the two adhesives were compared (Student's t-test and Weibull statistics). Results Of the specimens bonded with XP Bond, 50% failed at the dentin-adhesive interface, 42% at both the dentin-adhesive and composite interface and 8% in the composite alone. Of the specimens bonded with G Bond, 41% failed at the dentin-adhesive interface, 53% at both the dentin-adhesive and composite interface and 6% in the composite alone. The K IC values of the two adhesives differed significantly ( p < 0.05). XP Bond had a K IC of 0.77 ± 0.11 MNm −3/2 ( n = 17), while G Bond a K IC of 0.62 ± 0.21 MNm −3/2 ( n = 12). Conclusion The high percentage of mixed failures did not support the hypothesis that the dentin-adhesive interface is clearly less resistant to fracture than the adhesive–composite interface. The finding that cracks occurred in 6–8% in the composite suggests that defects within the composite or at the adhesive–composite interface are important variables to consider in adhesion testing.