Finite Element Analysis of an Implant-Assisted Removable Partial Denture

Purpose: This study analyzes the effects of loading a Kennedy class I implant-assisted removable partial denture (IARPD) using finite element analysis (FEA). Standard RPDs are not originally designed to accommodate a posterior implant load point. The null hypothesis is that the introduction of posteriorly placed implants into an RPD has no effect on the load distribution. Materials and Methods: A Faro Arm scan was used to extract the geometrical data of a human partially edentulous mandible. A standard plus regular neck (4.8 × 12 mm) Straumann R � implant and titanium matrix, tooth roots, and periodontal ligaments were modeled using a combination of reverse engineering in Rapidform XOR2 and solid modeling in Solidworks 2008 FEA program. The model incorporated an RPD and was loaded with a bilateral force of 120 N. ANSYS Workbench 11.0 was used to analyze deformation in the IARPD and elastic strain in the metal framework. Results: FEA identified that the metal framework developed high strain patterns on the major and minor connectors, and the acrylic was subjected to deformation, which could lead to acrylic fractures. The ideal position of the neutral axis was calculated to be 0.75 mm above the ridge. Conclusion: A potentially destructive mismatch of strain distribution was identified between the acrylic and metal framework, which could be a factor in the failure of the acrylic. The metal framework showed high strain patterns on the major and minor connectors around the teeth, while the implant components transferred the load directly to the acrylic. It has been suggested that the placement of one or more implants posteriorly in conjunction with a removable partial denture (RPD) will overcome the problems associated with mandibular Kennedy class I RPDs. A mandibular Kennedy class I RPD can rotate during function due to a resiliency mismatch between the supporting teeth and soft tissue. 1-3 Placing two distal im- plants transforms a Kennedy class I to a pseudo Kennedy class III, which provides better support and eliminates the fulcrum line created by the occlusal rests. The additional support can result in a higher bite force. 4,5 The conversion is sometimes achieved by incorporating implant components into a preexist- ing RPD. 6-9 However, converting an RPD to an implant-assisted RPD (IAPRD) can lead to fracturing of the framework and/or acrylic. 10-13