A systematic review on influence of printing layer thickness on the marginal and internal fit of 3D-printed fixed dental prostheses

The purpose of this study is to systematically review the effect of printing layer thickness and build orientation on the marginal and internal fit of 3D-printed fixed dental prostheses (FDPs). A systematic search was conducted in PubMed, Scopus, Web of Science, and Cochrane Library up to August 2025 following PRISMA guidelines (PROSPERO: CRD42024591005). Comparative studies assessing the impact of layer thickness on marginal gap (MG), internal gap (IG), or absolute marginal discrepancy (AMD) of 3D-printed FDPs and crowns were included. Risk of bias was assessed using a modified CONSORT tool. Thirteen in vitro studies met the eligibility criteria. Thinner layers (20-50 μm), particularly at 50 μm, improved marginal and internal fit compared to thicker layers (100 μm). Intermediate build orientations (45°-60°) minimized discrepancies, while extreme orientations (0° and 90°) increased stair-stepping effects. Marginal gap values generally ranged from 40 to 120 μm, within clinical acceptability. Subtractive (milled) restorations consistently showed superior fit compared to additive manufacturing. Layer thickness and build orientation significantly influence the fit of 3D-printed FDPs. A layer thickness of 50 μm at intermediate build orientations (45°-60°) provides the best adaptation. Milling remains the gold standard for precision, although optimized 3D-printing parameters can achieve clinically acceptable accuracy. Optimizing 3D-printing parameters-especially using 50 μm layer thickness with intermediate build orientations-enhances the marginal and internal precision of FDPs. While 3D printing is suitable for provisional restorations, milled prostheses remain preferable for definitive restorations requiring the highest accuracy.