الفهرس 
AcknowledgementOnly 14 pages are availabe for public view
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Abstract
The present study was designed to evaluate the effect of different
occlusal veneer preparation designs of CAD/CAM generated Zirconia
reinforced Lithium Silicate (ZLS) , on fatigue resistance and stress
distribution using Finite Element Analysis (FEA) method.
A total of fifty four human mandibular molars were prepared to receive
ZLS Occlusal veneers with three different preparation designs and
accordingly were divided into three groups (n=18):
group I (Conventional Design): Planar occlusal veneer preparation design.
group II (Occlusal veneer with circumferential preparation): Modified
occlusal veneer preparation design with circumferential finish line.
group III (Occlusal veneer with intracoronal cavity extension): Modified
occlusal veneer preparation design with intracoronal extension.
All samples’ Occlusal veneers were constructed from Zirconia
reinforced Lithium Silicate Ceramic blocks (Vita Suprinity) using the CEREC
CAD/CAM system.
All samples were subjected to Step Stress test on a universal testing
machine to determine fatigue resistance. All the data were collected, tabulated
and statistically analyzed. Microscopic examination of fractured samples was
carried out using the stereomicroscope and the scanning electron microscope
to determine modes of failure.
Stress distribution was evaluated by 3D Finite element analysis test. 3D
digital model was generated by CBCT scanning and Reverse engineering.
The components of the model were assembled using Solidworks software and
then imported in ANSYS software to carry out the analysis.
The highest mean±SD values were recorded for group II
(Circumferential Preparation) ; (890.57±211.53N) followed by group I
(Planar Preparation) mean±SD values; (883.54±135.91 N) while the lowest
mean±SD values were recorded for group III (Intracoronal Cavity
extension) (875.57±143.52 N). The difference between groups was
statistically non-significant as indicated by ANOVA test (p=0.9814<0.05).
The results of 3D finite element analysis showed that the three
preparation designs yielded low Von-Mises stresses within the factor of safety
with enamel in cervical region being least safe when subjecting the models to
average bite force of 500 N. The stress distribution among different layers of
the model differed, where group I (Planar Occlusal veneer preparation)
delivered equivalent stresses to the occlusal veneer as well as transferring
stresses to the center of the tooth and cervical area concentrated towards
lingual and distal areas with maximum stresses at center of occlusal veneer.
While for group II (Circumferential occlusal veneer preparation design) the
maximum stresses were developed at the occlusal veneer center and less
stresses at lingual as well as distal halves of the tooth structure. In the
meantime group III (Intracoronal extension occlusal veneer preparation
design ) generated maximum amount of stresses among the three groups,
where it delivered less stresses to the occlusal veneer and transferred larger
stresses towards the center of the tooth and cervical area concentrated towards
lingual and distal areas.