In-vitro mechanical performance of three CAD-CAM bar designs for implant-supported metal-resin hybrid prostheses: a preliminary pilot study

Abstract

Background Implant-supported hybrid metal–resin prostheses are widely used to rehabilitate edentulous patients. However, fractures of the veneering resin and screw complications remain common mechanical failures. Advances in CAD-CAM design and laser sintering technology may improve the structural integrity of these restorations. Aims To conduct a preliminary in-vitro evaluation of the fracture resistance of veneering resin in three CAD-CAM–designed bar configurations fabricated by laser sintering, describing their mechanical behavior and failure patterns under compressive stress. Methods Three bar designs (inverted T, L-shaped, and Ackerman circular) were digitally created and manufactured in cobalt–chromium using laser sintering. Each bar was veneered with autopolymerizing acrylic resin and subjected to compressive loading up to 1000 N at a 30° angle, in accordance with ISO 14801. Simultaneously, acoustic emission analysis was performed to detect microcracks and structural failures. Results No fractures of the veneering resin were observed. Mechanical failures occurred as deformation or fracture of prosthetic screws, beginning at 600 N. Acoustic emission detected early microcracks between 160 N and 400 N, and main fracture peaks between 627 N and 871 N. Among the three samples, the inverted T-shaped bar sustained the highest load before failure in this pilot test. Conclusion In this pilot in-vitro study, the veneering resin showed high resistance under simulated masticatory loading. The combination of CAD-CAM design, laser-sintered fabrication, and retentive elements may enhance mechanical performance. Further studies with larger sample sizes and cyclic loading are warranted to validate these preliminary findings.