Influence of convergence angle and cement space on adaptation of zirconium dioxide ceramic copings

Objective. The purpose of the present study was to evaluate the influence of total convergence angle and cement space on internal and marginal adaptation of posterior zirconium dioxide (zirconia) ceramic copings. Material and methods. Seventy-two standardized mandibular first molar zirconia copings were fabricated with nine parameters: three different total convergence angles (6°, 12°, and 20°) with three different computer-fixed cement spaces (10, 30, and 60 µm). Marginal adaptation was assessed to measure vertical discrepancy between the coping and abutment by direct viewing. Internal adaptation was evaluated using the cement replica technique with a laser microscope. The Kruskal-Wallis test and Wilcoxon rank-sum test were performed to test for differences in internal space and marginal discrepancy values (α=0.05). Results. The median of mean internal spaces/marginal discrepancies ranged from 54.0/27.4 to 128.1/77.8 µm. Statistically significant differences in the internal spaces were found between groups with 6° and 20° convergence angle, regardless of cement space. The different cement spaces did not have any significant influence on the 12° and 20° convergence angle groups. The 60-µm cement space group exhibited statistically smaller marginal discrepancies than the 10-µm cement space group in all the different convergence angles. Conclusions. Within the limitations of the present study, the internal spaces of zirconia ceramic copings may decrease as the convergence angles of abutments increase. The computer-fixed cement space might influence the marginal adaptation of zirconia ceramic copings. The internal and marginal adaptation of zirconia ceramic copings obtained was within the range of clinical acceptance.