Marginal fit and internal adaptation of zirconia complete coverage fixed dental prostheses fabricated by milling versus 3D printing: A systematic review and meta-analysis of in vitro studies

STATEMENT OF PROBLEM: Marginal fit and internal adaptation are critical factors influencing the longevity and biological performance of zirconia complete coverage fixed dental prostheses. With the increasing use of digital fabrication workflows, particularly milling and 3-dimensional (3D) printing, existing in vitro studies report inconsistent and heterogeneous findings regarding accuracy. Therefore, systematic review and meta-analysis are needed to quantitatively compare the marginal fit and internal adaptation of zirconia fixed dental prostheses fabricated by milling versus 3D printing. PURPOSE: The purpose of this systematic review was to evaluate and compare the marginal fit and internal adaptation of zirconia complete coverage fixed dental prostheses fabricated using subtractive (milling) and additive (3D printing) techniques based on in vitro studies. MATERIAL AND METHODS: Electronic databases (PubMed, Medline/Embase, Scopus, Web of Science, and Google Scholar), and manual searches were conducted to identify relevant articles evaluating the effect of milling and 3D printing on the marginal fit and internal adaptation of zirconia fixed dental prostheses. Data were extracted and meta-analyzed. Risk of bias was assessed using the QUIN tool. RESULTS: Of 2205 records identified, 9 in vitro studies met the eligibility criteria; the majority focused on single crowns, and only 1 assessed a 4-unit fixed dental prosthesis. The meta-analysis revealed that milled zirconia prostheses had a statistically better marginal fit (Mean Difference (MD)=-13.12 µm; 95% CI:-20.21 to -6.03; P<.001; I²=91.98%), while no significant difference was found in internal adaptation between the 2 groups (MD=-3.26 µm; 95% CI:-9.41 to 2.88; P=.30; I²=85.93%). CONCLUSIONS: Both fabrication techniques produced clinically acceptable marginal fit and internal adaptation. Milled zirconia prostheses exhibited significantly smaller marginal gaps than 3D printed restorations, whereas internal adaptation did not differ significantly between the 2 techniques.