Comparison of Marginal And Internal Fit of 3D-Printed Versus Milled Zirconia Crowns: An in Vitro Study

Abstract

Background
The accuracy of marginal and internal adaptation is an important determinant of the biological, mechanical, and clinical performance of indirect dental restorations. Zirconia crowns are increasingly fabricated using computer-aided design and computer-aided manufacturing (CAD/CAM). Conventional subtractive milling of presintered zirconia is an established manufacturing technique, whereas additive manufacturing or three-dimensional (3D) printing of zirconia has emerged as an alternative that may reduce material waste and permit fabrication of complex geometries. However, differences in shrinkage, printing resolution, layer deposition, debinding, and sintering may influence the final fit of printed restorations.
Aim
The present in vitro study was designed to compare the marginal and internal fit of monolithic zirconia crowns fabricated using 3D-printing and conventional CAD/CAM milling techniques.
Materials and Methods
A standardized mandibular first molar preparation was digitally designed and duplicated to produce 40 identical dies. Forty monolithic zirconia crowns were fabricated using an identical CAD design. Specimens were divided into two groups: Group I, 3D-printed zirconia crowns (n=20), and Group II, milled zirconia crowns (n=20). Following fabrication, sintering and standardized finishing procedures, marginal and internal discrepancies were assessed using a non-destructive digital triple-scan protocol. Measurements were obtained at standardized marginal, cervical, axial, and occlusal reference locations. The primary outcomes were mean marginal gap and mean internal gap. Independent-samples t tests were used for normally distributed data, with statistical significance set at α=0.05.
Results
The dataset showed a lower mean marginal discrepancy for milled crowns than for 3D-printed crowns. The corresponding internal discrepancy also showed a lower mean value for the milled group. Both manufacturing techniques remained within the commonly cited clinically acceptable range for marginal adaptation. The between-group difference was statistically significant in the illustrative dataset.
Conclusion
Within the limitations of this experimental model, the proposed study supports the hypothesis that conventional milling may provide more predictable marginal adaptation than 3D printing of zirconia, while both techniques may provide clinically acceptable internal adaptation. Nevertheless, the performance of additive zirconia is strongly influenced by printer technology, zirconia formulation, layer thickness, orientation, debinding, sintering protocol, and software compensation.