Full mapping tensile bond strength of luting in search for differences due to centripetal curing shrinkage.

OBJECTIVES: testing if hypothetical transverse centripetal strains due to polymerization contraction of luting materials produce differential alterations in its bonding to luted structures, depending on distances to the center of the luting mass, and if this effect is C-factor related. Two hypotheses were tested: (1) there is a statistically significant decreasing relationship between the bonding strength and the transverse distances to the center of the luting material, and (2) there is a statistically significant difference between bonding strengths among luting spaces with different configuration factors. METHODS: 10 PMMA (15 mm O) pairs of cylinders were cemented (Scotchbond Universal adhesive & Relyx Universal, both chemically cured) in a compliant setup under two (20 and 70 N) luting forces forming 2 groups (5 samples each), resulting in different C-factors. Whole samples were sectioned in x and y directions obtaining non-trimmed beams from all along the luting surfaces. Their relative positions in each sample were assessed before separating and categorized (10 categories) according to their distances to the center of the sample. All beams were tested in tension and, because of their uneven bonding areas and to balance its influence, UTS results were transformed into UTS(res). First hypothesis was tested trough a linear relationship between UTS(res) and distances to vertical centers per samples. Second hypothesis was tested using Mann-Whitney U tests to compare UTS(res) between groups, along all categories. Further Weibull analysis was applied. RESULTS: ANOVA's p of the regression UTS(res) - categories were statistically significant for all samples in group 70 N and for all except one in group 20 N: first hypothesis is partially maintained. Although Mann-Whitney tests p comparing UTS(res) of both groups for all categories but the first were statistically significant this hypothesis was maintained relying in Weibull analysis. SIGNIFICANCE: bonded attachment of cemented materials decreases from centers to outbounds in plane, extensive surfaces, and this decrease is C-factor related.