Influence of mechanical cycling on loosening of retention screw in cemented and screwed fixed partial dentures fabricated with titanium and zirconia cad/cam system. In vitro analysis and non-linear analysis by 3D-FEA.
The metal free implant-supported prostheses fabricated with zirconia by the CAD/CAM system have shown excellent clinical performance in short time. However, there is little scientific evidence to prove its long-term success. Considering that the future involving zirconia and CAD/CAM technology is still unknown, this study will evaluate the influence of mechanical cycling on 12-unit implant-supported fixed partial denture (FPD) fabricated by the CAD/CAM system through in vitro analysis and nonlinear analysis by three-dimensional finite element method (3D-FEA). This study will be conducted in 2 phases: (1) in vitro analysis: Twenty-four implant-supported FPDs with 6 implants will be fabricated using the CAD/CAM system to obtain 4 groups (n=6). The groups will be divided according to the framework material (zirconia or titanium) and type of prosthesis (cemented or screw-retained prosthesis). The samples will be submitted to detorque evaluation using manual torque gauge before and after mechanical cycling. The mechanical cycling will be carried out in a electromechanical equipment for chewing fatigue test with loading of 100N at 2Hz during 1x106 cycles; (2) computational analysis: Two three-dimensional standard models will be fabricated to represent a complete edentulous maxilla simulating the insertion of 6 implants. Each model will represent screw-retained implant-supported prosthesis and cemented implant-supported prosthesis. So, the 4 groups of phase 1 it will be also simulated in phase 2. The finite element software will generate the finite element mesh according to the properties of materials, boundary conditions and loading. Furthermore, contact elements will be inserted between the mechanical components of the implant-supported system to insert the preload. The 4 groups will be submitted to nonlinear transient dynamic analysis by the 3D-FEA. Data from in vitro analysis will be submitted to statistical analysis and data from dynamic analysis will be qualitatively and quantitatively evaluated through the stress maps.
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