Adaptation of Zirconia Ceramic Copings with Different Finish Line Designs

Objectives: The purpose of the present study was to evaluate the marginal and internal adaptation of partially sintered zirconium dioxide (zirconia) ceramic copings with three different finish line designs. Methods: Three steel dies were prepared for maxillary central incisor crowns with the following finish line designs: a shoulder (S), a rounded shoulder (RS), and a chamfer (C) preparation. Twenty-four standardized partially sintered zirconia ceramic copings were fabricated using a CAD/CAM system (Cercon smart ceramics) for the three tested groups (n=8). The marginal adaptation was assessed by measuring the vertical discrepancy, which measured parallel to the abutment axis the distance between the outer restoration margin and the preparation line. The measurements were performed at 60 different points across the entire circumference of each coping. Internal adaptation was measured with the cement space replica technique using two different silicone pastes. The marginal and internal discrepancy was measured in a laser microscope (1LM21W) at a magnification of x250. The data were statistically analyzed (Kruskal-Wallis, Mann-Whitney U with the Bonferroni correction, p<0.05). Results: The following median values were obtained marginal/internal adaptation: S, 84.8/116.8; RS, 61.2/71.8; and C, 64.0/49.4 (µm). There were no significant differences among the three groups for marginal adaptation. On the other hand, significant differences in the internal adaptation were found among all groups. Conclusions: Within the limitations of the present study, the internal adaptation of partially sintered zirconia ceramic copings is affected by finish line design. The adaptation values reported in the present study were within the clinically acceptable range. Supported in part by a Grant-in-Aid for Scientific Research (C 17592048) from JSPS and a Grant from Sato Fund, Nihon University School of Dentistry for 2006.