Fatigue Testing of Two Porcelain-Zirconia All-Ceramic Crown Systems

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Objective: To evaluate the mouth-motion step-stress fatigue behavior of two porcelain-zirconia all ceramic crown systems and compare their failure modes with clinical observations. Methods: The average dimensions of a mandibular first molar crown were imported into CAD software; a tooth preparation was modeled by reducing proximal walls by 1.5mm and occlusal surface by 2.0mm. The CAD-based tooth preparation was made by rapid prototyping and used as a master die to fabricate all-ceramic crowns with 1.0mm porcelain veneered on 0.5mm Y-TZP cores (Lava veneer + LAVA frame, 3M/ESPE, and Ceramco PFZ + CERCON frame, Dentsply). Crowns were cemented on aged (60 days in water) composite (Z100, 3M/ESPE) reproductions of the die. Three crowns from the LAVA group were subjected to single cycle load to failure for stress profile design; remainder subjected to step-stress mouth motion fatigue (three step-stress profiles). All mechanical testing was performed by sliding a WC indenter of 6.25mm diameter 0.7mm lingually down the mesio-distal cusp. Master Weibull curves and reliability for missions of 50,000 cycles at 200 N load were calculated (Alta Pro 7, Reliasoft). Results: Single load to failure showed fractures through the zirconia core. Reliability for a 200 N X 50K cycle mission is presented in the Table. In fatigue loading, failure occured by formation of large chips within in the veneer originating from the contact area. Zirconia core surfaces were not exposed. This is the failure mode reported in clinical studies of zirconia crowns. No failures through the core were observed for either crown system. Conclusions: No significant difference in fatigue behavior was observed between the LAVA and CERCON systems; fatigue loading reproduces failure modes observed clinically.supported by NIDCR PO1 DE10976.