Effect of marginal forms on marginal leakage of CEREC crowns

Methods: Extracted human mandibular molars were prepared with three different marginal forms (n = 20 each); (1) chamfer, (2) shoulder with rounded axiogingival line angle (rounded shoulder), and (3) shoulder. The margins were placed about 2 mm occlusally from the CEJ. Each tooth was set in the left first molar position of a plaster mandibulary typodont model, and optical impression with a CCD camera was taken with a handheld technique. Ceramic crowns were fabricated and seated with dual-cured resin cement. For marginal leakage evaluation, specimens were stressed under a mechanical axial load cycle of 1.3 kgf, 98 cycles/min for 24 hours immersing in 0.2% basic fuchsin. They were then cut mesiodistally through their center, and the degree of dye penetration was scored at two interfaces (ceramic/cement and cement/tooth) with a 4-level scale. The cement thickness was measured with a stereomicroscope at 4 marginal points. Kruskal Wallis and Mann Whitney tests were used for the analysis of the marginal leakage, and 1-way ANOVA and Bonferroni test for the cement thickness. The leakage and the cement thickness were correlated with Spearman test.

Results: The rounded shoulder and shoulder groups showed less marginal leakage than the chamfer group (p < 0.0159, Mann Whitney test). The mean marginal cement thickness was approximately 50 um in all the groups, and there was no significant difference among the three groups (p > 0.05, ANOVA). There was no correlation between the cement thickness and the leakage (p > 0.05, Spearman test).

Conclusion: Under the limitations of this study, CEREC 3 crowns with the rounded shoulder and shoulder margins provided less marginal leakage than those with the chamfer margin.