ATlLLA SERTGÖZ*, (University of Marmara, Faculty of Dentistry, Department of Prosthodontics)
The aim of this study was to investigate the effect of three different occlusal materials (resin, composite, porcelain) and four different framework materials (gold, Ag-Pd, Co-Cr, Ti alloys) on stress distribution of an implant-supported mandibular fixed prosthesis and surrounding bone, utilizing three dimensional (3D) finite element analysis (FEA) method. 3D finite element model of a typical complete-arch fixed prosthesis, with 16 mm bilateral cantilever extension, was performed in a simulated mandibular bone with I-DEAS (Structural Dynamics Research Corporation, Ohio) FEA software on a VAX computer. To simulate the clinical situation, the model was not supported at the bottom, and some bending was allowed by fastening the mandibular bone at both distal ends. A total of 172 N vertical load was applied to the model. Generated stress patterns and values were calculated at the occlusal and framework materials, connection screws, implants and surrounding cortical and spongy bones.
No variation was found in stress values of the cortical and spongy bones surrounding the implants as a function of both occlusal and framework materials. However, when the gold alloy and resin combination was used as material for the superstructure, the highest tensile (189.2 MPa) and compressive (-165.2 MPa) stresses were calculated at the gold screws connecting the implants to the superstructure. In addition, at the gold screws for the Co-Cr alloy and porcelain combination, the lowest tensile (118.7 MPa) and compressive stress (-115,6 MPa) values were calculated.
It was concluded that (1) elasticity of the superstructure did not have any effect on the stress patterns and values of the cortical and spongy bones surrounding the implants. (2) using more elastic materials for the superstructure increased the potential risk of the prosthetic failure due to concentrated stresses at the connection screws.