Effects of surface finish and fatigue testing on the fracture strength of CAD-CAM and pressed-ceramic crowns

Statement of problem. All-ceramic molar sl crowns can be fabricated with CA D-CAM or laboratory meth ods with different materials, and a polished or ov en-glazed surface. Purpose. This in vitro study determined the fracture strength of various al l-ceramic crowns, with and without prior cyclic loading. Material and methods. Standardized molar crowns were fabricated with a. CAD -CAM machine (Cerec 2), software with machinable ceramic materials (Vita Ma rk II and ProCAD), and also conventional heat-pressed IFS Empress crowns fa bricated at 2 dental laboratories. Groups of 40 crowns of each material wer e manufactured with either a polished or an oven-glazed surface finish. Cyc lic loading that Simulated. oral conditions were performed on half of each group. Afterward, all crowns were loaded until catastrophic failure. Results. Fracture lends of the polished ProCAD crowns without Frier cyclic loading was 2120 +/- 231 hi, significantly higher than that of the polished Vita Mark II crowns (1905 +/- 235 N), but was nor significantly different from the strength of 2 laboratory-fabricated Empress crowns. Oven-glazing o f ProCAD crowns improved the fracture strength significantly up to 2254 +/- 186 N. Prior cyclic lending decreased the strength of all tested crowns si gnificantly, but the reduction was less for the Cc res crowns than the Empr ess crowns. Conclusion. Cerec ProCAD crowns demonstrated significantly greater strength than the Vita Mark II crowns, better resistance to cyclic loading and lowe r failure probability than the laboratory-fabricated IFS Empress crowns. Pr ior cyclic lending significantly reduced the strength of all-ceramic crowns , but had less effect on Cerec crowns than oil the IFS Empress crowns. Oven -glazing of ProCAD crowns resulted in significantly higher strength and hig her resistance to cyclic loading than surface polishing.