Failure load of CAD/CAM-generated all ceramic posterior endocrowns
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PURPOSE: To evaluate and compare the failure load of milled and bonded IPS e.max CAD and VITA ENAMIC endocrowns used in the restoration of endodontically molar teeth. MATERIALS AND METHODS: Typodont tooth # 30 was prepared with a central cavity to support the endocrowns. Fifty-eight epoxy resin dies were made from a physical impression of the prepared tooth and scanned with an intra oral scanner (Cerec AC, Dentsply-Sirona). The designed restorations were milled from two different materials: VITA ENAMIC (n=30) and IPS e.max CAD (n=28). Following adhesive cementation, half of the endocrowns of each group were subjected to thermal aging, each specimen was obliquely loaded until failure. Four groups were tested: group 1 (Enamic endocrowns without thermocycling), group 2 (Enamic endocrowns + thermocycling), group 3 (e.max endocrowns without thermocycling) and group 4 (e.max endocrowns + thermocycling). The fracture mode characteristics were identified. RESULTS: There was a significant difference in the mean failure loads between group 4 and group 3 at P ≤ 0.05; also between group 4 and group 1 at P ≤ 0.05. Group 1 had the highest value of 2301 N. A visual inspection of all tested endocrowns revealed four different failure modes; 1-Adhesive failure, 2-Cohesive failure, 3-Mixed failure and 4-Fracture Initiation In Crown Propagating Through Die. CONCLUSION: Thermocycling decreased the load to failure significantly for IPS e.max CAD endocrowns. Mode of failure 4 and 1 were the dominant failure modes for VITA ENAMIC and IPS e.max CAD respectively.