Factors affecting the fit of metal‑based restorations fabricated by selective laser melting: A systematic review

The marginal and internal fit of fixed dental prostheses (FDPs) plays a crucial role in their long-term clinical success. Although selective laser melting (SLM) has become a widely used additive manufacturing technique for FDP fabrication, conclusive evidence regarding the factors influencing the fit of SLM-fabricated FDPs is still lacking.

This systematic review aimed to evaluate the influence of tooth preparation design and manufacturing parameters on the marginal and internal fit of FDPs fabricated using SLM.

The study followed the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines, with an electronic search conducted in 4 databases and manual searches up to July 2025. Following the population, intervention, comparison, outcome, study design (PICOS) framework, the population included tooth-supported metal-based FDPs fabricated via SLM; the intervention involved tooth preparation designs and manufacturing parameters; the comparison included designs or parameters not associated with fit; the outcome was marginal and internal fit; and the study design included in vitro, animal, and human studies. The risk of bias in in vitro studies was assessed using the Quality Assessment Tool for In Vitro Studies, while the Risk of Bias in Non-randomized Studies of Interventions tool was used for nonrandomized clinical studies.

Sixteen studies comprising 14 in vitro and 2 quasi-experimental clinical studies were included. Key factors influencing the fit of SLM-fabricated FDPs included tooth finish line and preparation design, printing orientation, and printing parameters such as lamination layer thickness and laser settings. Evidence regarding the effects of alloy type and postprocessing steps, including heat treatment and ceramic veneering, remained inconsistent. Among the in vitro studies, 8 of 14 were assessed as having a medium risk of bias, while 6 demonstrated a low risk. Of the 2 nonrandomized clinical studies, one was rated as having a serious overall risk of bias, whereas the other showed a low risk.

Within the limitations of current evidence, clinically acceptable fit was associated with cobalt chromium alloys printed at 0 or 30 degrees with a 25- to 50-µm layer thickness and optimized laser parameters. In contrast, a 90-degree printing orientation often resulted in marginal gaps exceeding acceptable thresholds.