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 CADCAM–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.