Fatigue Failure Load of Molars with Thin-Walled Prosthetic Crowns Made of Various Materials: A 3D-FEA Theoretical Study

PURPOSE: The aim of the study was to compare the fatigue lifetime of thin-walled molar crowns made of all-ceramic CAD/CAM materials under three different cyclic load conditions. METHODS: The crowns were fatigued using a range of forces similar to which crowns in the molar region might be subjected. Crowns of two thin-walled thicknesses (0.7 mm and 1.1 mm) were prepared from Zirconia and lithium disilicate. Numerical methodologies to simulate the behavior of a restored tooth were applied to evaluate the fatigue lifetimes under multiple cyclic loading; 50 N, 100 N, 150 N. An 8 mm hemispherical indenter was used to simulate the mechanical stress of opposing teeth during mastication, and applied the fatigue load at the center of the crowns. RESULTS: The results show that the predicted survival rates for 0.7 mm and 1.1 mm Zirconia crowns were not significantly different. The number of life cycles predicted for Zirconia under all fatigue loads indicates that these crowns can live longer than five clinical years (when crowns are in service). However, crowns made from lithium disilicate also can be predicted to survive longer than five clinical years (under load up to 100 N). Crowns made of lithium disilicate should have 1.1 mm thickness to survive longer than five clinical years (when crowns are in service). CONCLUSION: Zirconia crowns exhibit significantly higher fracture resistance compared with lithium disilicate crowns, making them better suited to handle higher masticatory loads encountered in the posterior region of the mouth. Lithium disilicate can survive more than five clinical years (when their thickness is 1.1 mm).