الفهرس 
coverOnly 14 pages are availabe for public view
 |  | from | 160 |  |  |
| | | from | 160 | | |
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.