Mechanical fracture is a common cause of failure for 3-unit dental bridges, particularly, the all-ceramic structures. The purpose of the present study was to evaluate the effect of convergence angles of the abutments on the distribution of the mechanical stresses, within the prosthesis and at the restoration-abutments interface of a 3-unit all-ceramic bridge. The 3-D geometrical data of the second premolar and first and second molar teeth were obtained using ATOS scanner system and utilized for reconstruction of a surface model of the 3-unit bridge in I-Deas as solid modeler software. This was then transferred to MSC/Nastran software for mesh generation and finite element analysis. Two FE models were developed with different convergence angles, including 171900 and 168700 tetrahedral solid four-node elements. The models were subjected to two different prosthesis material and three different load cases. Therefore, twelve cases were analyzed and compared. Aforementioned comparing indicated that the maximum tensile stresses occur on the gingival surface of the second premolar retainer, and at the tooth/restoration interface on the marginal distal surface of the second molar. The peak tensile stress was relatively lower for the model with the higher convergence angles but the difference was not significant. Changing the prosthesis material from IE2 to Dicor decreased the stresses within the prosthesis; however, the safety factor was still higher for IE2 due to its higher mechanical strength. The load condition found to have an important role in the mechanical stresses observed.

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