Objective: To study the effect of different cores and fracture resistance in hot pressable ceramic systems. Methods: Twenty-four extracted human maxillary molars were regularly prepared for full crown restorations under the control of a parallel milling instrument. Likewise, twenty-four similarly shaped metal cores were milled with industry machinery. An additional twenty-four resin cores were fabricated by cementing prefabricated posts into the natural (molar) teeth canals and building up the cores with a Core-Paste (Den-Mat) core build-up composite resin. Each core group was then divided into three sub-groups for three hot pressable ceramic restorations (at a thickness of 1.5mm): Cerinate (Den-Mat), Ips-Empress (Ivoclar-Vivadent), and Optec-OPC (Jeneric/Pentron, Willingford). The crowns were then pressed according to the manufactures instructions. Then, the finished crowns were cemented with flowable composite resin, and cured for 40 seconds from all directions. Lastly, the cemented crowns were vertically loaded until a failure appeared with a universal testing machine. Significant differences of fracture loads between the experimental groups were analyzed by one-way ANOVA. Results: The fracture resistance for crowns cemented on the natural teeth and composite resin (Core Paste) were significantly higher than crowns cemented on metal cores. Conclusion: Different core bases may significantly affect the fracture resistance of full ceramic crowns. Natural teeth and cores made with a composite resin (Core-Paste from Den-Mat) can better support full ceramic crowns.

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