Case-specific finite elements analysis of CAD/CAM prostheses to identify design flaws prior to manufacture

Purpose: To apply a design optimization strategy to dental prostheses machining to verify whether this approach can detect flaws occurring in the CAD process and to estimate the influence of the type of material on the occurrence of fractures in restorations. Methods: The stereo lithography interface format of a 4-unit (from canine to first molar) fixed dental prosthesis designed by a conventional dental CAD process was converted into a Finite Element Analysis (FEA) model. This basic model was coupled to the mechanical properties of feldspathic ceramic, lithium disilicate ceramic (LS2) and zirconia (ZrO2) to create three FEA models with different mechanical properties. The models were constrained along the abutment housing surfaces of the canine and the first molar, respectively. Finally, a simulated load of 50 N was applied vertically to the occlusal surface of the first premolar. Results: The FEA showed a stress peak concentration between the second connectors and the second premolar. The stress peak overcame the ultimate tensile stresses of feldspathic and lithium disilicate ceramics; conversely, the ultimate tensile stress of zirconia was not overcome. A geometrical flaw was identified in the 4-unit fixed dental prosthesis. The flaw was sensitive to tensional stress and could lead to failure of the component.