Optimum concentration and application time of 1,6-hexanediol as a dentin primer.
The optimum concentration and application time for an experimental dentin primer composed of an aqueous solution of 1,6-hexanediol were determined by measuring the wall-to-wall polymerization contraction gap width of a commercial light-activated resin composite in a cylindrical dentin cavity prepared in an extracted human molar. Contraction gap formation was completely prevented only when the dentin cavity wall was primed with 45 wt% 1,6-hexanediol for 60 s. There were no significant differences in tensile bond strength among primers composed of 20.0-57.5 wt% 1,6-hexanediol. These results suggest that the optimum concentration and application time are 45 wt% and 60 s, respectively.
Bonding Efficacy of Erythritol Methacrylate Solutions as Dentin Primers
The bonding efficacy of aqueous solutions of two kinds of erythritol methacrylates as dentin primers was examined by measurement of the polymerization contraction gap of a light-activated resin composite in a cylindrical dentin cavity and the tensile bond strength of the composite to the flat dentin surface. The dentin surface was cleaned with neutralized 0.5 mol/L EDTA and pre-treated with a meso-erythritol or penta-erythritol methacrylate solution, followed by application of a commercial dentin bonding agent (Clearfil New Bond) and a resin composite. Among the tested primers, a 40% meso-erythritol methacrylate solution was shown to be the most effective because, in contrast to the other primers, contraction gap formation by the composite was prevented in all tested specimens.
Evaluation of Lapping Grains based on Shape Characteristics.
The shape and size of abrasive grains during lapping varies complicately and irregularly. In this study, the aspect ratio of grain size and the fractal dimension of the grain external form were used as shape characteristics of grain in order to evaluate grains with lapping time. The results obtained are summarized as follows : (1)The fractal dimension increases due to microscopic fracture and decreases due to macroscopic fracture or attritious wear. (2)The aspect ratio and the fractal dimension, which are grain shape characteristicsis of the macroscopic shape and the microscopic surface complication of grain respectively, can be used for evaluating grain shape variation during lapping.