Fracture toughness of two dentin adhesives

Test the hypothesis that a self-etching adhesive is more likely to fail at the dentin-adhesive interface than an etch-and-rinse adhesive.

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).

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).

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.