Measuring and modeling the insertion torque of dental implant.

Background : The insertion torque of a dental implant is generally regarded as a measure of its primary stability. Yet, dental implants vary enormously in terms of their geometry and the corresponding osteotomy, so that prior to experimentation, it is desirable to have a reliable predictive tool that assesses the insertion torque for a given configuration. We report here on finite element modeling of the insertion process and its validation using in vitro experiments. Aim/Hypothesis : To model the implant insertion torque as a function of the geometrical parameters of the implant and the corresponding osteotomy. Material and Methods : Artificial cortical and trabecular bone specimens (Bonesim) were characterized by tension and compression tests to determine their basic mechanical and failure properties. The first phase of the tests in the implants development process is evaluation of the implantation torque by in vitro experiments – drilling and implantation machine. With this machine the following parameters can be controlled – implantation speed (rpm) and force on the implant (N). By these tests, we can evaluate the torque during the implantation in vitro of the implant and the force applied on it. The next phase consisted of devising a finite element model which duplicates the experimental geometry, in which the implant undergoes frictional interaction with the bone specimen. The analyses are three- dimensional and fully nonlinear. The various phases of the insertion process are characterized, and the contribution of each bone type is outlined. The outcome is t he determination of the evolution of the torque as the insertion progresses until full placement, as opposed to often reported point wise measurements of the maximum torque, for example. The numerical model is updated iteratively until a satisfactory replication of the experimentally measured insertion torque is obtained. Once this validation phase is achieved, the various geometrical parameters can be confidently modified to examine any future alternative design configuration, keeping in mind the goal to obtain the desirable sufficiently high values of the insertion torque. Conclusions and Clinical Implications : This research has shown that the insertion torque can be reliably modeled when physical parameters are used in the numerical simulations. Having validated the hybrid numerical- experimental approach, it appears that a reliable calibrated numerical tool is available to investigate all kinds of geometrical modifications to the implant and osteotomy design, thereby providing a tool to perform virtual experiments which save both time and experimental costs. It is recommended that a similar approach be adopted to further investigate additional issues in the mechanics of implant dentistry.