Numerical Simulation Of In Vivo Intraosseous Torsional Failure Of A Hollow-Screw Oral Implant

Background Owing to the complexity and magnitude of functional forces transferred to the bone-implant interface, the mechanical strength of the interface is of great importance. The purpose of this study was to determine the intraosseous torsional shear strength of an osseointegrated oral implant using 3-D finite element (FE) stress analysis implemented by in vivo failure torque data of an implant. Methods A Ø 3.5 mm × 12 mm ITI® hollow screw dental implant in a patient was subjected to torque failure test using a custom-made strain-gauged manual torque wrench connected to a data acquisition system. The 3-D FE model of the implant and peri-implant circumstances was constructed. The in vivo strain data was converted to torque units (N.cm) to involve in loading definition of FE analysis. Upon processing of the FE analysis, the shear stress of peri-implant bone was evaluated to assume torsional shear stress strength of the bone-implant interface. Results The in vivo torque failure test yielded 5952 μstrains at custom-made manual torque wrench level and conversion of the strain data resulted in 750 N.cm. FE revealed that highest shear stress value in the trabecular bone, 121 MPa, was located at the first intimate contact with implant. Trabecular bone in contact with external surface of hollow implant body participated shear stress distribution, but not the bone resting inside of the hollow. Conclusion The torsional strength of hollow-screw implants is basically provided by the marginal bone and the hollow part has negligible effect on interfacial shear strength.PubMe

Assessment

In order to achieve an adequate oral rehabilitation after reconstruction of the jaw, a consistent prosthetic treatment is necessary. The main determinants of implant stability are the mechanical properties of the bone tissue at the implant site, and how the contact between the implant neck and the cortical bone plate is achieved. If we presume a correct surgical technique and a good implant design, the bone density determines the primary implant stability at the time of surgery. A stable implant can exhibit different degrees of displacement or resistance to load, which corresponds to varying degrees of stability. Conversely, a failed implant shows clinical mobility on the macroscale, as the implant is surrounded by a fibrous scar tissue. An increasing degree of micro-mobility is present until clinical failure of the implant. This suggests that techniques to measure and to monitor implant micro-motion/stability could give the clinician the opportunity to optimize implant treatment. Insertion torque, Periotest, and resonance frequency analysis are suitable to measure primary implant stability. Nevertheless, the resonance frequency analysis is the only method that can detect variations in different bone densities, which may be measured even during the follow-up of the implant