The importance of adhesive area delimitation in a microshear bond strength experimental design

The purpose of this study was to assess the influence of adhesive area delimitation on the microshear bond strength of different adhesives to dentin.

Eighteen bovine incisors were sectioned and the exposed dentin surfaces were prepared with 600-grit SiC paper. These teeth were randomly divided into three groups, according to the adhesive to be applied: two-step etch-and-rinse Adper Single Bond 2 (3M ESPE), two-step self-etching Clearfil SE Bond (Kuraray), and one-step Clearfil S3 Bond (Kuraray). On each dentin surface, 4 samples were built up with the composite resin Z100 (3M ESPE); on 2 of these, a suggested area delimitation technique was employed. After 24 h of storage in water at 37°C, samples were subjected to the microshear bond strength test, and the failure modes were evaluated under optical and scanning electron microscopes. The obtained results were statistical analyzed using two-way ANOVA and Tukey's test.

Groups without area delimitation presented significantly higher bond strength results (p < 0.05) and a higher incidence of cohesive failures. In these groups, fractures tended to occur beyond the limits of the actual adhesive area, while the area restriction technique succeeded in avoiding this phenomenon. The three adhesives performed similarly when area delimitation was employed (p > 0.05), but Clearfil S3 Bond showed significantly higher bond strength results when no area delimitation was taken into account (p < 0.05).

The extension of the adhesive area beyond the limits of the composite cylinder may play an important role in the results of microshear bond strength tests, while the suggested area delimitation technique may lead to less questionable outcomes.