الفهرس 
Vertical marginal gap assessment of cad on veneered pekk crowns versus cad on veneered zirconia crowns : Vertical marginal gap assessment of cad on veneered pekk crowns versus cad on veneered zirconia crowns (A Randomized in vitro study)
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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 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 .Vertical marginal gap was assessed using
stereomicroscope of the two groups before and after thermomechanical aging for all the specimens.
Results: PEKK group recorded statistically significant (P<0.05) higher marginal gap mean value
(59.97±2.541 µm) than Zirconia group (41.79±4.424 µm). 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
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Conclusions: Within the limitations of this study, 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 restorations that have an
acceptable marginal gap distance and CAD ON veneering technique can be used as a novel
technique for PEKK veneering