The influence of the cutting speed on bond strength and integrity of microtensile specimens

Objectives To verify the influence of cutting speed during microtensile specimen preparation, on bond strength values and on the sample microscopic integrity of a single-bottle adhesive system to enamel and dentin. Methods Thirty sound human third molars were restored with light-cured Excite and Tetric Ceram according to manufacturersʹ instructions, being half in ground enamel [E], and half in flat dentin [D]. After 24 h storage in distilled water at 37 °C, the restored teeth were sectioned in x and y-axes under different cutting speed: 100, 200 or 400 RPM, obtaining stick shaped specimens with cross-sectional area of 1.0 mm2. Five specimens from each experimental group were randomly selected before being loaded for SEM analysis, while the remaining samples were subjected to the microtensile bond strength test. Because the variance of dentin specimens was significantly higher than the variance of enamel samples, analysis of the influence of the cutting speed was performed separately, by subtrate. Results The mean values in MPa were calculated including/excluding premature failures: E1: 24.67/27.31a; E2: 24.03/25.81a; E4: 19.06/21.52b; D1: 35.80/36.33A; D2: 35.84/36.65A; D4: 37.78/38.50A. In the SEM analysis, better integrity of the dentin specimens was observed when compared to the enamel samples, for which the integrity was greater in the lower cutting speed groups. Significance It can be concluded that the cutting speed is an important factor that should be considered, mainly when enamel is involved, since it may affect the bond strength results and the integrity of the specimens.