Marginal Fit of Metal Copings Fabricated by Selective Laser Melting: An In Vitro Study

Introduction: Marginal adaptation is a key determinant of the clinical success and longevity of fixed dental restorations. Poor marginal fit is associated with microleakage, secondary caries, and periodontal disease. Selective laser melting (SLM), an additive manufacturing technique (AM), has been introduced as an alternative for fabricating metal restorations, offering high precision and reduced fabrication errors compared with conventional casting techniques.
Objective: This in vitro study evaluated the vertical marginal gap (VMG) of metal copings fabricated using SLM with two finish line thicknesses.
Materials and Methods: A sound human mandibular first molar was prepared for a porcelain-fused-to-metal crown with standardized dimensions. Two finish line configurations were created: a 1.0 mm round shoulder on the buccal surface and a 0.7mmround shoulder on the lingual surface. The prepared tooth was digitally scanned, and 20 standardized resin dies were fabricated using a three-dimensional (3D) printing system. Twenty metal copings were designed using computer-aided design and manufacturing (CAD/CAM) software and fabricated using SLM under identical manufacturing parameters. The specimens were then cemented and sectioned in the buccolingual direction using a standardized guide. VMG was measured at predefined marginal points under a stereomicroscope at high magnification, and the digital images were analyzed using specialized software. Data were statistically analyzed using the Mann–Whitney U test, with significance set at p ≤ 0.05.
Results: The SLM metal copings showed a total median marginal gap of 24.53 μm (IQR: 10.97–37.68 μm) with total median marginal gap in buccal margins of 20.82 μm (IQR: 9.96–29.18 μm), whereas the lingual margins showed a total median of 29.13 μm (IQR: 19.07–48.60 μm). Additionally, the marginal fit varied significantly between the buccal and lingual surfaces (p < 0.001).
Conclusion: The SLM technique showed there is a marginal gap, though it demonstrated a high marginal accuracy, that remained within clinically acceptable limits. Finish line thickness significantly affected marginal fitness.