Polymerization contraction diminishes luting material's µTBS depending on relative situation

OBJECTIVES: Test if the eventual differences in µTBS produced in a luting material with a largely longitudinal disposition are related to the distances to the center of the curing luting mass. METHODS: Elongated resin onlays (Adoro®, 2 x 3 x 11 mm) were luted (Excite® adhesive + Variolink II Translucent® luting cement), in the same relative positions, to exposed labial dentin of bovine incisors. A conventional luting procedure was used in group A (n=6). In group B (n=6) luting was placed only in extremes and central parts of luting spaces. Bar-shaped samples, perpendicular to interface, were obtained from all specimen (group A) or from separated luted parts (group B). Their distances to each gingival end of restoration were transformed into percentages within each specimen creating the independent variable PDistanc. Samples were submitted to tension (Hounsfield 500N, 1 mm/min) until separation of luting from dentin and checked in an optical stereomicroscopy (40x) for adhesive fractures. µTBS was calculated and transformed, into PMPa dependent variable, to percentages of maximum value of each specimen. Non-parametric Jonckheere-Terpstra test was used to test if mean within-sample magnitude (PMPa) consistently changed, either increasing (categories 0 to 50%) or decreasing (categories 50 to 100%) with the changes in the criterion variable (PDistanc). RESULTS: In both halves the disposition was decreasing from the center to the extremes. (p < 0.001 in both cases). Differences between comparative categories of both groups were significant in category 0% (p=0.001), non-significant in category 50% (p = 0.13) and near significance in category 100% (p = 0.06) CONCLUSIONS: Polymerization contraction of the resin luting material affects µTBS of interface with dentin. This effect increases from the center to the outer extremes of the restoration and is not caused by differences in substrate.