Stress Distribution of Different Endocrown Retained Bridge Designs Replacing Missing Upper First Molar (Finite Element Analysis Study)

Objective: To evaluate stress of three different endocrown retained bridges designs restoring missing maxillary first molar, under regular masticatory forces via 3D finite element analysis. Methods: In this study three different bridge designs models restoring missing upper first molar were suggested: Design A: Bridge retained with endocrown on both abutments, Design B: Bridge retained with an endocrown on the second molar and with a full coverage retainer on the second premolar and Design C: Bridge retained with an endocrown on the second premolar and with a full coverage retainer on the second molar, then analyzed and compared. The three different endodontic models were created on 3Matics (Materialize, NV, USA). Sound freshly extracted upper second premolar and second molar were scanned by high resolution cone beam CT (Planmeca Promax 3D Mid, Planmeca OY, Finland). The second premolar and the second molar were modified to receive an endocrown as the first design and one by one in combination with fully covered retainers as second and third designs. A cylinder of 4 mm diameter was modeled as connectors standardized with 4*4 mm buccolingual and occlusogingival dimensions. The same, 3-matic version 7.01 (Materialise, NV, USA) was used to manipulate the STL files and merge the three teeth (crowns) in the proposed bridge geometric model. Bone was simplified as a cylinder, where the bottom area of the cortical bone cylinder was set to be fixed in place as a boundary condition. The applied load cases were vertically 300N and oblique 45 º from the vertical plane prior to performing linear static analysis. Results: The three bridge designs showed acceptable and equivalent effect on bone. While, teeth behavior showed high Von Mises stress under the bridge design retained with endocrown on both abutments. From total deformation point of view, both teeth and bone were nearly not affected by bridge design, and the three bridge designs showed acceptable amount of total deformation. Conclusion: within limitations of this study it can be concluded that, Bone is not sensitive to bridge design, the endocrown retained bridge at both abutments showed the maximum stresses on teeth finish line and The endocrown retained bridge at the molar abutment showed the best behavior at teeth, On the other hand it raises the bridge stress by about 50% in comparison to two endocrown retainers.