A Comparison of Precision of Fit, Rotational Freedom, and Torque Loss with Copy-Milled Zirconia and Prefabricated Titanium Abutments

Purpose: The present study sought to compare copy-milled zirconia abutments with standard prefabricated titanium abutments in terms of horizontal and vertical misfit, rotational freedom, and torque loss. Materials and Methods: Twenty regular-platform implants (Brånemark, Nobel Biocare) with a standard external-hexagon implant-abutment interface were divided into two groups. In one group, prefabricated titanium abutments (Easy Abutment, Nobel Biocare) were used; in the other group, custom-made zirconia abutments were fabricated using the Zirkonzahn milling system. Measurements of geometry, rotational freedom, and marginal discrepancy were performed using a video measuring machine. To measure torque loss, each abutment was torqued to 32 Ncm and then loosened with a digital torque wrench. The torque loss values were reported as a percentage of the applied torque. Results: Rotational freedom and horizontal misfit were significantly higher with the customized abutments. There were no statistically significant differences in vertical misfit or in mean percentage of torque loss between the two groups. Conclusions: Within the limitations of this study, it could be concluded that copy-milled zirconia abutments do not fit as accurately as prefabricated titanium abutments. However, the less precise fit of customized zirconia abutments does not seem to affect their ability to maintain the applied torque. Keywords: copy milling, dental implant-abutment interface, fit, rotational freedom, torque, zirconia