Marginal Fit of Selective Laser Melting Cobalt-Chromium Bar Versus Cast Bar on Mandibular Edentulous Casts with Two Implants Supported Over Denture: An In vitro Study

Objectives: To evaluate and compare the fit of Cobalt Chromium customized bar fabricated with different manufacturing processes cast metal bar, and SLM metal bar utilizing USB-digital microscope.Methodology: A physical mandibular edentulous cast was digitized and imported into Blender Dental for virtual model creation. Digital implant planning involved placement of two parallel bone-level implants with a 14 mm inter-implant distance. The virtual model was 3D printed, and embedded with two implant analogs. Scan abutments were attached, scanned, and imported into Exocad for bar design. Twelve bars were fabricated: six using Selective Laser Melting (SLM) with Co-Cr alloy (Group I) and six using a combined digital-analog method (Group II). A USB-digital microscope was used to evaluate the marginal fit at the implant-abutment interface. Results: Paired t-tests demonstrated significantly higher marginal fit values for casted frameworks compared to 3D-printed counterparts on buccal (56.05±7.65µm vs. 34.19±6.03µm, p=0.003) and overall surfaces (50.0±2.62µm vs. 39.93±4.71µm, p=0.002). While a trend towards higher fit was observed for cast frameworks on the proximal surface (54.39±8.25µm vs. 45.17±7.62µm, p=0.08), it did not reach statistical significance. Repeated Measures ANOVA revealed significant surface-related variations in marginal fit within both groups. In the cast group, the lingual surface exhibited the poorest fit (39.55±4.94μm), while in the SLM group, the buccal surface demonstrated the least favorable fit (34.19±6.03μm).Conclusions: This study demonstrated that both SLM and casted Co-Cr bars exhibited clinically acceptable marginal fit. However, SLM-fabricated bars demonstrated superior marginal fit at the implant-abutment interface in comparison to cast bars.