Relationship between adhesive thickness and microtensile bond strength

This study evaluated the effect of the thickness of the adhesive resin laye r of two commercially available resin bonding systems on bond strengths (Si ngle Bond and Liner Bond 2V). The adhesive of Single Bond contains ethanol and water as solvents and is applied using the moist-bonding technique. The adhesive of Liner Bond 2V contains no solvents and is applied after a self -etching primer treatment. Forty-six caries-free molars were ground flat to expose the dentin surface and polished with #800-grit silicon carhide pape r under running water. A vinyl tape punched with a 6 mm diameter hole was t hen placed on the dentin surface to demarcate the area for bonding. The thi ckness of the adhesive resin layer was varied by stacking an increasing num bers of vinyl tapes together. The teeth were randomly divided into two grou ps and treated with either Clearfil Liner Bond 2V or Single Bond. They were further divided into subgroups according to the number of tapes placed on the dentin surface. After the bonding procedures the teeth were incremental ly restored with Clearfil AP-X resin composite, building a 5 mm high crown to produce sufficient bulk for the microtensile bond test and stored in tap water at 37 degreesC for 24 hours. The teeth were then sectioned along the ir long axis into 0.7 mm thick slabs and trimmed for the microtensile bond test using a super-fine diamond bur. The thickness of the adhesive resin la yer was then measured with a light microscope and the slabs tested in tensi on at a crosshead speed of 1 mm/minute. The results were subjected to stati stical analysis by a one-way analysis of variance and linear regressions wi th 95% confidence intervals. The thickness of the Clearfil Liner Bond 2V adhesive layer ranged from 5 mm -1500 mm, and for Single Bond, it varied from <7.5 mm-430 mm. For Clearfil Liner Bond 2V, bond strengths increased significantly as the thickness of b onding layer increased (p<0.05). However, the bond strengths of the Single Bond decreased significantly with increased thickness of the bonding layer (p<0.05).