Benign designs for resin-bonded non-metal fixed partial dentures milled by cerec system (CAD/CAM)

Developing conservative FPD designs in term of the preservation of tooth structure is not just a matter of cutting from the crown to form abutment. These designs need to prove that they show benign behaviour under occlusal forces. The aim of this study was to develop new single layer non-metal 3-unit posterior FPD designs as an alternative to the traditional FPD design without compromising the structure integrity of the natural dentition. The group designs were traditional, two different partial coverage crowns and two different inlay retained FPD. The CEREC CAD/CAM system was employed using a modified designing method and two resin bonded non-metal materials were used for the fabrication of these bridges. A series of tests were conducted in order to identify I) the volume of tooth structure loss with different designs 2) the ability of the CAD/CAM system to produce full-thickness FPD restorations 3) the fracture resistance of these restoration and 4) 2D and 3D FEA models were later developed involving some highly innovative steps. Micro CT, MIMICS and FreeForm DeskTop were used to create the 3D model. For meshing these models, due to the complexity of the 3D model, a sectional meshing technique was used by mechanical APDL and Workbench Ansys Y 12. The FEA data were compared with the results from the practical experiments. XIX Abdulsalam AI-Zahawi Benign non-metal fixed partial denture The results of the in vitro tests revealed that the four conservative designs showed less tooth structure loss compared with the traditional design and the inlay design was less than the partial coverage crown retained FPD. The CEREC CAD/CAM system was able to produce the suggested FPD designs in a full-thickness as an alternative to producing framework FPD. The fracture resistance test revealed that there is no significant influence of designs on the fracture strength excluding design V. The results showed that no fractures of the bridges in design V were recorded during the test. The FPD fabricated from the low elastic modulus material PEEK showed a higher fracture strength than one with the high elastic modulus ceramic. Part of the 2D FEA results showed agreement with the practical test results especially that the site of high stress concentration and the fracture site were at the gingival side of the connector. Nevertheless the 2D FEA results showed that there were many differences with the 3D FEA results. These differences include the overestimation in the stress level in the 2D FEA compared with 3D FEA model and the high stress located at the inlay cavity wall, which was difficult to see in the 2D FEA. 3D FEA results were in agreement with fracture strength tests results and these include that there is no influence of the partial coverage crown retained FPDs on the stress compared with the traditional design, the fracture site and the location of the higher stress were unaffected by the designs. Although both inlay retained FPD designs show more conservative preparations than partial crown retainers, they were found to be more destructive to the abutment teeth structure under a concentrated load. The clinical significant of this research project is that it is possible to create more conservative FPD designs without compromising the structure integrity of the restored dentition. xxEThOS - Electronic Theses Online ServiceGBUnited Kingdo