Effect of Different Milling Devices on Marginal Fit of CAD/CAM Zirconia Copings on Implant Stock Abutments

Purpose: To compare the marginal fit and internal surface roughness of CAD/CAM zirconia copings milled with three-and five-axis milling devices. Materials and Methods: A total of 40 titanium implant stock abutments (4.8 mm in diameter, 4 mm in height) screwed to dental implants (4.1 mm in diameter) embedded in resin were considered phantoms and included in this in vitro study. All 40 phantoms were scanned with the same intraoral scanner, and virtual wax-ups of zirconia copings were created from these images and exported as STL files. Two copings were milled from each resulting STL file-one using a three-axis milling device and the other using a five-axis milling device. After milling, zirconia copings underwent high-speed sintering before being analyzed for marginal fit (ie, marginal gap measurement) and observation of internal surface roughness with scanning electron microscopy (SEM). Statistical comparisons between groups were assessed with Mann-Whitney U test. Results: Median marginal gap values were 34.80 mu m (95% CI: 0.00 to 173.98) for the five-axis milling device group and 141.97 mu m (95% CI: 82.13 to 163.46) for the three-axis milling device group. A statistically significant difference in marginal gap was found between both milling device groups (P = .039). In addition, qualitative SEM analysis indicated a higher internal surface roughness for the three-axis milling device group. Conclusion: Within the limitations of this study, the present findings suggest that five-axis milling devices outperform three-axis milling devices for milling CAD/CAM zirconia copings from intraoral scans of implant stock abutments.