Fracture Resistance and Marginal Adaptation of 3D-Printed Versus Milled Resin-Based Permanent Crowns: A Systematic Review and Meta-Analysis.

OBJECTIVE: To systematically compare the fracture resistance (N) and marginal gap (μm) of 3D-printed versus CAD/CAM-milled resin-based permanent crowns using meta-analytic methods. MATERIALS AND METHODS: A systematic search of PubMed/MEDLINE, Scopus, and Web of Science was conducted from inception to the search date. Eligible studies were in vitro investigations directly comparing 3D-printed and milled full-coverage resin-based crowns and reporting quantitative outcomes for fracture resistance and/or marginal gap. Risk of bias was assessed using the QUIN tool. Random-effects meta-analyses were performed using standardized mean differences (SMDs). RESULTS: Fourteen studies were included (16 study conditions for fracture resistance; 13 for marginal gap). In the primary molar-only analysis, milled crowns demonstrated significantly higher fracture resistance than 3D-printed crowns (SMD -1.49; 95% CI: -2.25 to -0.73; p < 0.001), with the most consistent effect observed under aged conditions (SMD -1.75; 95% CI: -2.31 to -1.19; I2 = 47%). For marginal gap, the primary pooled analysis was non-significant and exhibited extreme heterogeneity (I2 = 99.8%). However, a sensitivity analysis restricted to tooth-supported, direct-measurement conditions (k = 10) showed significantly smaller marginal gaps for 3D-printed crowns (SMD -2.31; 95% CI: -3.47 to -1.14; p = 0.002). CONCLUSIONS: Milled resin-based crowns demonstrated higher fracture resistance, particularly under simulated aging conditions, whereas 3D-printed crowns showed superior marginal adaptation under methodologically comparable conditions. Given the low to very low certainty of evidence and substantial heterogeneity, these findings should be interpreted cautiously, and their clinical relevance remains to be confirmed by well-designed clinical studies.