Fit Alteration of Presintered Co-Cr and Zirconia Multiple-Unit Prostheses After Ceramic Layering

The fit alteration after ceramic layering of soft Cobalt-Chromium (Co-Cr) and zirconia is poorly documented. This study compared the marginal and internal fit of presintered Co-Cr and zirconia three-unit fixed dental prostheses before and after ceramic veneering.

Co-Cr master model was prepared and duplicated 60 times to receive three-unit fixed dental prostheses (FDPs). Sixty dies were prepared, scanned and assigned to 3 groups (n = 20/group), to receive the FDPs made of presintered Co-Cr (CS), presintered zirconia (CZ) and cast Ni-Cr (Wi). Each framework was seated on its specific cast. A replica technique was used for marginal and internal discrepancy measurements in mesiodistal and buccolingual planes. Frameworks were ceramic veneered. Results were compared before and after ceramic layering within each group. Data were analyzed using the Levene, t test, and ANOVA (α = 0.05).

Significant difference was found when gaps were compared within groups for CS and CZ but not for Wi. At the abutments level, significant difference was found for both premolars and molars in the buccolingual planes (p < 0.001). A multiple comparison between materials tested showed significant differences between presintered and cast Ni-Cr. No significant difference was detected between CS and CZ (p = 1.000).

Although ceramic layering increased the discrepancy for presintered Co-Cr and zirconia, the marginal adaptation remained clinically acceptable.