ABSTRACT
Aim: The aim of this study was to evaluate vertical marginal gap of CAD-CAM milled PEKK as a framework material to be veneered with CAD-On lithium disilicate glass ceramic as compared to milled zirconia framework veneered with CAD-On lithium disilicate glass ceramic.
Methodology: 14 natural teeth requiring full coverage crown were prepared.
A uniform 1.5 mm axial reduction and 1,5 mm occlusal reduction with a 3600 deep chamfer finish line was prepared . 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. 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 .Vertical marginal gap was assessed using stereomicroscope before and after thermomechanical aging for all the specimens.
Results: regardeless to material type ,totally it was found that after mechanical aging the marginal gap mean value was higher (54.36±13.73 µm) than before (47.39±10.88 µm) and this was statistically non-significant (P=0.1741 > 0.05) as indicated by two way ANOVA followed by pair-wise Tukey's post-hoc tests

Conclusions: Zirconia showed lower mean marginal gap distance, the mean marginal gap distance of all tested specimens were within the acceptable clinical value which is less than 12o µm , pekk can be used as a definitive fixed restoration and CAD ON veneering technique can be used as a novel technique for pekk veneering.