الفهرس 
Fracture Resistance And Mode Of Failure Assesment of Cad-On Veneered Pekkton Versus Cad-On Veneered Zirconia Crowns after One Year Of Clinical Simulation (A Randomized In Vitro Study)
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Abstract
This study was carried out to evaluate the fracture resistance and mode of failure of of CAD-On milled PEKK core veneered by lithium disilicate compared to CAD-On milled zirconia core veneered by lithium disilicate.
Methodology: 30 freshly extracted molars were embedded in epoxy blocks. A uniform 1.5 mm axial reduction (100 taper) and 1,5 mm occlusal reduction with a 3600 deep chamfer finish line (1 mm thickness) was prepared on all teeth. Scanning and designing of the restorations were done and the final design was split in the software into core and veneer layers to be milled separately. Fusion of the veneer to the core was the only manual step done in crown construction; it was done using low fusing glass material (IPS e.max Crystall./ Connect) in the control zirconia group and using adhesive resin cement (multilink) in the PEKK group as recommended by the manufacturer. All the crowns were adhesively cemented on their corresponding preparations using Duo-link adhesive resin cement. All the specimens were subjected to thermo-mechanical fatigue loading for 150,000 cycle simulating one year’ clinical service before static load to fracture was applied. Fracture resistance was evaluated using a universal testing machine. . After fracture of the specimens, they were evaluated under a scanning digital microscope to determine the mode of failure.
Results: It was found that Zirconia group recorded statistically significant higher fracture resistance mean value than PEKK group mean value. Regarding the mode of failure it was found that. 62.5% of PEKK crowns exhibited veneer-core fractures while 37.5% of specimens showed the fracture veneer-core & tooth (cohesive - Catastrophic failure).
In Zirconia group, 50% of the crowns exhibited partial delamination of the veneering ceramic in addition to 25% with a core delaminated completely - between the core and veneering ceramic (adhesive -repairable fracture). Only 25% of Zirconia crowns exhibited veneer-core fractures (cohesive - Catastrophic failure)
Conclusions: Zirconia veneered by lithium disilicate exhibit higher fracture resistance than PEKK veneered by lithium disilicate. Both PEKK and Zirconia veneered by lithium disilicate by multi-layering technique showed clinically acceptable fracture resistance values exceeding the oral masticatory forces.Mode of failure in veneered ziconia more favorable than veneered PEKK