Comparison of shear bond strength relative to two testing devices

Dentin adhesives are characterized on the basis of their bond strength to dentin; however, great variation exists within the same material depending on the testing apparatus. To realistically compare bond strengths, the testing mechanisms must be the same.

The purpose of this investigation was to use 2 testing devices to evaluate the shear bond strength of 3 single-bottle adhesives with their multistep counterparts.

The occlusal surfaces of 120 freshly extracted third molars were ground to expose the dentin and polished with 600-grit silicon carbide paper. Three single-bottle, (Optibond Solo Plus, 3M Single Bond, and Excite) and 3 multistep adhesives (Optibond FL, 3M MultiPurpose Plus, and Syntac) were each used to bond a composite cylinder (made from a 2.379 +/-.001-mm diameter by 4-mm-high mold) of Tetric Ceram to 20 teeth. The specimens were stored in 100% humidity for 24 hours. The shear bond strength at failure was measured in kilograms and converted to megapascals for each material, using a knife (conventional method) and an Ultradent testing device on a universal testing machine (Instron) at a loading rate of 0.5 mm/min. A 2-way analysis of variance (ANOVA) test was performed comparing the 2 testing devices and the materials at P<.05. Where significant, a 1-way ANOVA test was conducted among the materials for each test group, and a Tukey multiple comparison test was used to determine significant differences among the materials tested (P<.05). An independent Student t test at P<.05 was used to determine significance between testing devices.

The results showed that Optibond Solo Plus (26.85 +/- 8.76 MPa), Optibond FL (25.40 +/- 4.44 MPa), 3M Single Bond (28.12 +/- 5.01 MPa), and 3M MultiPurpose Plus (34.40 +/- 7.90 MPa) had significantly higher bond strengths when tested with the Ultradent testing device. The mean values for Excite (19.47 +/- 6.17 MPa) and Syntac (20.20 +/- 7.07 MPa) were also higher with the Ultradent testing device, but the difference was not significant.

Within the limitations of this study, all bonding agents tested resulted in higher mean shear bond strengths when tested with the Ultradent testing device compared with the unrestricted knife. The single-step bonding agents exhibited mean bond strengths comparable to their multistep counterparts.