Comparison of intra- and intertooth resin-dentin bond strength variability.

Purpose: The aim of this study was to investigate the intra- and intertooth microtensile bond strength variability of two adhesive systems applied to dentin.
Materials and Methods: Twenty human third molars were ground to expose a flat dentin surface. Two adhesive systems (Single Bond and One Step) were applied according to the manufacturers' instructions and composite resin crowns were constructed incrementally. After 24 h in distilled water at 37 degrees C, each tooth was longitudinally sectioned in both "x" and "y" directions under 300 rpm to obtain sticks with a cross-sectional area of 0.8 mm2. The sticks from each tooth were tested at a crosshead speed of 0.5 mm/min. The fracture pattern of each stick was microscopically analyzed after debonding (400X). A mixed model with adhesive as a fixed variable, tooth as a random variable, and bonded area included as a covariate, was employed for the data treatment. In this model, all observations have the same variance, which is the sum of two components: the variance of the random effect (intertooth) and the variance of the errors (intratooth).
Results: The intratooth variability was greater than the intertooth variability.
Conclusion: The intratooth variability is higher than the intertooth variability. Sticks from the same tooth cannot be considered as an experimental unit, since it does not fulfill all ANOVA requirements.