The effect of manufacturing technique on marginal gap in inlay, onlay, veneer, and endocrown restorations: a systematic review and metaanalysis

Purpose: The purpose of this systematic review and meta-analysis was to compare the marginal fit of indirect partial restorations, such as inlays, onlays, and endocrowns, fabricated using milling (subtractive manufacturing) and 3D printing (additive manufacturing) techniques. Materials and Methods: This review was conducted according to the PRISMA guidelines and utilized the PICO framework to define the research question. A comprehensive literature search was performed on PubMed, Scopus, and Web of Science databases for studies published in English between January 1, 2015, and April 1, 2025. The search targeted studies that directly compared milled and 3D-printed indirect partial restorations and reported marginal gap values in a numerical format. Statistical analysis was performed using a random-effects model, and outcomes were synthesized using the Standardized Mean Difference (SMD) with 95% Confidence Intervals (CI). Results: A total of 16 studies, comprising 257 milled samples and 287 3D-printed samples, were included in the meta-analysis. The overall pooled analysis found no statistically significant difference in marginal gap values between milled and 3D-printed partial restorations (p = 0.62). However, subgroup analyses revealed varying trends. For occlusal veneers, milled restorations showed a smaller marginal gap than 3D-printed restorations; however, this difference was not statistically significant (SMD = -1.86, 95% CI: -18.24 to -14.53, p = 0.39). Conversely, inlays and onlays showed a non-significant trend favoring 3D printing (SMD = 0.87, 95% CI: -0.26 to 2.00, p = 0.11). Conclusion: This systematic review and meta-analysis conclude that there is no overall statistically significant difference in marginal fit between milled and 3D-printed indirect partial restorations.