Fracture toughness of two dentin adhesives

PurposeTest 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 methodsForty-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 (KIC) of the two adhesives were compared (Student's t-test and Weibull statistics).ResultsOf 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 KIC values of the two adhesives differed significantly (p < 0.05). XP Bond had a KIC of 0.77 ± 0.11 MNm−3/2 (n = 17), while G Bond a KIC of 0.62 ± 0.21 MNm−3/2 (n = 12).ConclusionThe 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.