Effect of Core Design on Metal-ceramic Implant-supported Crown Failure

Objectives: The aim of this study was to evaluate the fracture resistance of both implant-supported screw- and cement-retained porcelain fused to metal (PFM) single crowns with three different framework designs, submitted or not to mechanical cycling. Material and methods: Thirty implant-supported metal-ceramic single molar crowns were fabricated and divided into 3 Groups (n=10, each): Group 1(control group) - cement-retained without screw access hole (SAH); Group 2 - screw-retained with SAH in metal; and Group 3 - screw-retained with SAH in porcelain. Half of each group was artificially aged through dynamic loading in water (106 cycles; load: 100 N; frequency: 2 Hz) and, whereas, the other half was not subjected to artificial aging. Subsequently, all specimens were loaded occlusally until fracture occurred using a universal testing machine. Values of maximum fracture resistance were compared using 2-way ANOVA and Tukey's test (p≤.5),. Results: The values of non aged and aged (average) were, respectively, G1 – 2190.10N – 2215.05N (2202.58N), G2 – 1428.48N – 1444.75N (1436.62N) e G3 –1412.13N – 1433.59N (1422.86N) showed that cemented prostheses presented higher resistance than groups 2 and 3 (p=.000013), which were not significantly different from each other (G1 > G2 = G3) and no significants differences were found between specimens aged and non aged (p=.86). Conclusion: Occlusal discontinuity of the porcelain on screw-retained PFM crowns affects their resistance, and the metallic support on the SAH did not reinforce the porcelain structure, with or without artificial aging. However, both screw- and cement-retained PFM crowns displayed resistance values acceptable for daily clinical use.