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Abstract Perception and awareness of esthetics truly changed over centuries. Porcelain-fused to metal (PFM) restorations are not considered as esthetic solutions any more. High strength all-ceramic materials succeeded to replace the metal substructure. Zirconia in particular represented a promising core material owing to its unique properties. Unfortunately, insufficient translucency was behind the demand of veneering that creates a multiphase structure. The veneering technique and the design of the core structure have an effect on the reliability of veneered zirconia restorations. This study is performed to examine the effect of the veneering technique and core marginal configuration on the fracture resistance of zirconia-based all-ceramic crowns. Twenty stainless steel dies were machined to simulate an allceramic molar crown preparation with standardized dimensions and 1mm wide rounded shoulder around the entire circumference. Twenty zirconia cores (IPS e.max ZirCAD) were constructed, one for each die, using the Cerec inLab CAD/CAM System, which comprised acquiring an optical impression (with the Cerec-3 acquisition unit) for each die, designing the restorations with inLab 3.65 software and finally milling the cores in the inLab MC XL milling unit. The inLab 3.65 software was utilized to create the two margin designs of zirconia cores: chamfer design (n=10), and butt joint design (n=10), after milling sintering of copings was done. Five samples of each group were veneered with one of the veneering techniques: manual veneering technique, CAD/CAM veneering technique. The CAD/CAM veneering, with (IPS e.maxCAD), was done using the Cerec inLab CAD/CAM System, which comprised acquiring an optical impression (with the Cerec-3 acquisition unit) for each zirconia core, designing the veneering caps with inLab 3.65 software and finally milling them in the inLab MC XL milling unit. After milling, crystallization firing cycle was held to crystallize the partially crystallized lithium disilicate veneering caps. Joining of the two parts was done with an intermediate low fusing ceramic material (IPS e.max Ceram) through a sintering firing cycle. The manual veneering technique with (IPS e.max Ceram) was done conventionally and according to manufacturer recommendations. All specimens were subjected to a continuous compressive testing in a universal testing machine. Fracture loads were recorded, and then failed specimens were retrieved and examined microscopically. Data were statistically analyzed using t-test analysis and Bonferroni’s Multiple Comparison test. The results of this study showed that the sintering of a CAD/CAM-milled veneering cap to the zirconia core led to a significant increase of mechanical stability. The effect of margin design was significant with CAD/CAM veneering technique despite being non-significant with manual veneering technique. |