An analytical model to design circumferential clasps for laser-sintered removable partial dentures

• Published in: Dental materials Vol. 34; no. 10; pp. 1474 - 1482
• Main Authors: Alsheghri, Ammar A., Alageel, Omar, Caron, Eric, Ciobanu, Ovidiu, Tamimi, Faleh, Song, Jun
• Format: Journal Article
• Language: English
• Published: England Elsevier Inc 01.10.2018; Elsevier BV
• Subjects: Beam theory (structures); Bicuspid; Chromium; Chromium Alloys - chemistry; Circumferences; Circumferential clasp design; Cobalt; Cobalt–chromium (Co–Cr); Crack propagation; Cross-sections; Curved beams; Deformation; Dental Alloys - chemistry; Dental Casting Technique; Dental Clasps; Dental materials; Dental prosthetics; Dental Stress Analysis; Dentistry; Denture Design; Denture Retention - instrumentation; Denture, Partial, Removable; Dentures; Fabrication; Fasteners; Fatigue; Fatigue failure; Finite Element Analysis; Finite element analysis (FEA); Finite element method; Humans; Laser sintering; Lasers; Materials Testing; Mathematical analysis; Mathematical models; Molars; New technology; Plastic deformation; Plastics; Premolars; Prostheses; Removable partial dentures (RPDs); Retention; Retention force; Stress; Teeth; Tensile stress; Undercut; Undercut; Circumferential clasp design; Cobalt–chromium (Co–Cr); Laser-sintering; Plastic deformation; Fatigue failure; Removable partial dentures (RPDs); Finite element analysis (FEA); Retention force; Stress
• ISSN: 0109-5641; 1879-0097
• DOI: 10.1016/j.dental.2018.06.011

•A model for rational design of laser-sintered circumferential clasps is proposed.•The model adjusts for tooth type, stress, alloy properties, undercut and retention.•The model helps to avoid plastic deformation and fatigue failure in clasps.•Laser-sintered Co–Cr circumferential clasps are vulnerable to failure in premolars. Clasps of removable partial dentures (RPDs) often suffer from plastic deformation and failure by fatigue; a common complication of RPDs. A new technology for processing metal frameworks for dental prostheses based on laser-sintering, which allows for precise fabrication of clasp geometry, has been recently developed. This study sought to propose a novel method for designing circumferential clasps for laser-sintered RPDs to avoid plastic deformation or fatigue failure. An analytical model for designing clasps with semicircular cross-sections was derived based on mechanics. The Euler–Bernoulli elastic curved beam theory and Castigliano’s energy method were used to relate the stress and undercut with the clasp length, cross-sectional radius, alloy properties, tooth type, and retention force. Finite element analysis (FEA) was conducted on a case study and the resultant tensile stress and undercut were compared with the analytical model predictions. Pull-out experiments were conducted on laser-sintered cobalt–chromium (Co–Cr) dental prostheses to validate the analytical model results. The proposed circumferential clasp design model yields results in good agreement with FEA and experiments. The results indicate that Co–Cr circumferential clasps in molars that are 13mm long engaging undercuts of 0.25mm should have a cross-section radius of 1.2mm to provide a retention of 10N and to avoid plastic deformation or fatigue failure. However, shorter circumferential clasps such as those in premolars present high stresses and cannot avoid plastic deformation or fatigue failure. Laser-sintered Co–Cr circumferential clasps in molars are safe, whereas they are susceptible to failure in premolars.