Regional variations of µTBS of light- and chemically cured resin composite restorations in clinically relevant situations.

PURPOSE To test whether the distance to the mass center of a buildup made of visible-light- or chemically curing composite resin bonded to dentin and cured in one increment has an influence on µTBS. MATERIALS AND METHODS In the experimental groups, one-increment visible-light (Z250) or chemically-cured (TiCore) composite-resins buildups were bonded to flattened bovine dentin surfaces. In the control groups, the same materials were bonded as separate buildups on circumscribed areas to minimize the effect of shearing polymerization contraction. Compound composite/interface/dentin specimens were trimmed out of buildups and tested in tension until detachment; the distances to the mass centers of their respective buildups were recorded as the independent variable. The correlation between µTBS and distances was tested in each group. Slopes and intercepts of regression lines (µTBS to bonded area) were compared in the experimental groups. RESULTS The correlation between µTBS and distances was negative and statistically significant for both experimental groups (p < 0.0001), but not for the two control groups (p > 0.34). CONCLUSION In clinical situations such as direct resin veneering or resin core construction, where a first layer of a light- or chemically cured resin composite is bonded and cured on a broad surface, the µTBS of the interface decreases proportionally to the distance to the mass center of the restoration.