Biomechanical Assessment Of Implant Supported Removable Partial Denture:3-D Finite Element Analysis Study

Main problem For years, removable partial denture (RPD) have been used extensively for rehabilitation of partial edentulous patients although major shortcomings exist. Clinically, as an endeavor to overcome these problems, endosseous implants have been used for support of RPD, stabilization and maintaining the alveolar bone.Aims of the study The purposes of the study were to evaluate the effects of implant in implant supported RPD, including its length and number on stress values and stress distribution within abutment tooth, periodontal ligament, bone, alveolar mucosa, and implant, as well as on the displacement of both abutment tooth and RPD.Materials and methods The3-dimensional finite element analysis method was selected to evaluate the stress values, distribution and displacement in four geometric3-D models which were prepared by NX (CAD/CAM/CAE) software package and CT scan of patient mandible, composed of:mandibular segment, abutment tooth and distal extension RPD without implant support, or with implant (14mm and10mm in length), or with two short implants (7mm). All implants have the same diameter3.4mm. In separate load cases,350N vertical,175N oblique and70N horizontal forces were utilized to simulate the multidirectional chewing forces. Stress distribution and Von Mises stress values were assessed for simulated oral tissues and implants. Also3-D displacement of two measuring points (one for abutment tooth and the other for RPD) were evaluated, using NX Nastran software.Results Use of implant for support of RPD, reduced the Von Mises stress values within abutment tooth, periodontal ligament and alveolar mucosa, and increased the Von Mises stress values within cortical bone under three loading conditions, while for Cancellous bone, long implant(14mm L.) caused more Von Mises stress values under oblique load. Decreasing the length of implant caused marked increase in the Von Mises stress within cortical bone. For implants with14and10mm (L.), the stress was mostly concentrated within abutment part, and in the upper segment of the main body of the implant. Use of two short implants reduced the stress within cortical bone and produced more favorable distribution of stress within implants, abutment tooth and simulated oral structures. Use of implant caused marked reduction in displacement of measuring points at abutment tooth and RPD under all loading conditions.Conclusions Use of implant in association with RPD not only provide vertical support for the RPD, but also provide a bracing effectiveness, and reduce lateral movements of the extension base against oblique and horizontal loads applied on the removable denture, furthermore reduce the action of reciprocal arm on the abutment tooth, provide more stress relief within abutment tooth and its corresponding periodontal ligament, also reduce the displacement of both abutment tooth and RPD. Use of two short implants, in association with RPD highly reduce Von Mises stress values in all supporting structures relative to longer implant length, and under three loading conditions, as well as a dramatic reduction in displacement at abutment tooth and RPD.