Comparison of Conservative FPDs Designs with Traditional Design Using 3DFEA

Introduction: Traditional designs of FPDs are destructive of tooth tissue. Adhesive materials open up the possibility if using alternative designs that are more conservative. However it is important that any proposed new design does not compromise the structural integrity of the restored dentition. 3D FEA provide a good opportunity to examine the stress state for a range of designs of FPDs. Aim of study: Assess the stress distribution for different FPD designs and the materials selected for their fabrication. Materials and methods: A combination of micro-CT, Mimics, FreeForm and Ansys software was used to develop five 3-unit FPD designs, one traditional and four different conservative FPD retainers (II- Partial coverage crowns A, III- Partial coverage B, IV- Inlay A, and V- Inlay B). Two types of bridge materials with an elastic modulus of 95 GPa and 20 GPa were usedThe resin cement had an elastic modulus of 3.5 GPa. A load of 100N was applied on the centre of occlusal surface of the pontic. Results: All designs showed a load path travelling from the loading points toward the gingival aspect of the connector. The maximum principal stress was concentrated in the connecter area at the lingual and gingival surface. The maximum principal stress was 18.9, 22.0, 17.0, 16.0 and 44.4, MPa for the high modulus material compared with 11.0, 13.8, 22.5, 29.9 and 28.5 MPa for the low modulus material in designs I, II, III, IV and V respectively. Conclusion: For the high modulus FPD material designs II, III and IV did not compromise the structural integrity but then higher levels of stress for design V would suggest this design is contra-indicated. For the low modulus material only design II would appear not to compromise the structural integrity.