Effect of cross-sectional surface area on bond strengths between resin and dentin

This study was conducted to determine the effect of the bonding area on the micro-shear and micro-tensile bond strengths of four dentin adhesive systems (Scotchbond MP Plus, 3M Dental Products, St. Paul, MN; OptiBond FL, Kerr Corp., Orange, CA; OptiBond Solo, Kerr Corp., Orange, CA; One-Step, Bisco, Inc., Itasca, IL).

Sixty extracted human molars were cut vertically and occlusal enamel removed, one half of the tooth was used for tensile testing and one half for shear. The occlusal dentin was bonded according to manufacturers' directions with a resin composite block and sectioned to obtain up to three square bar-shaped specimens, which were shaped with a high speed diamond bur on a lathe to produce cylindrical specimens of 1.2, 1.4 or 2.0 mm diameter at the bonded interface. The bonds were stressed in shear or tension at a crosshead speed of 1 mm min-1. The mean bond strengths were compared using one-way ANOVA, two-way ANOVA and Student's t-test. The fractured surfaces were examined under a scanning electron microscope and the frequency of fracture modes was compared using the Kruskal-Wallis and Mann-Whitney U tests.

For all materials, the 2.0 mm diameter group showed significantly lower bond strengths than the 1.2 mm diameter group in both shear and tensile tests (p < 0.05). Most specimens of 1.2 mm or 1.4 mm diameter exhibited adhesive failure at the interface between the dentin and the adhesive resin.

The results indicate that small surface areas of test specimens are associated with higher bond strengths and that the effect on tensile and shear values is similar.