الفهرس 
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Abstract
The research presented in this study evaluated the effect of coping
thickness and processing technique on the fracture resistance of ceramic
copings under static and cyclic conditions.
A total number of 60 all-ceramic lithium disilicate non-anatomical
copings were constructed. According to the construction technique, the
copings were divided into two equal groups, thirty copings each
group 1: Heat pressing (n=30)
group 2: CAD/CAM milling (n=30)
Each group was further subdivided into three equal subgroups according
to the coping margin thickness, 10 copings each:
Subgroup A: The copings had margin thickness 0.5 mm. (n=10(
Subgroup B: The copings had margin thickness 0.7mm. (n=10)
Subgroup C: The copings had margin thickness 1 mm. (n=10)
Each subgroup was further subdivided into two divisions (n=5);
division (C) with cyclic loading and (NC) without cyclic loading.
For the purpose of standardization, three master dies were machine
milled with three margin thicknesses (0.5 mm, 0.7 mm and 1mm). A
uniform die preparation was made to simulate the dimensions of a
prepared maxillary first premolar to receive all-ceramic non anatomical
copings.
An anti-rotational occluso-axial bevel was made on all dies to prevent
rotation and to assure the exact reproducibility of placement of copings
over the dies.
All of the copings were constructed following the manufacturer’s
recommendations and cemented to their respective epoxy resin dies using
resin cement.
Half of the samples were subjected to cyclic loading, (10000 cycles)
using a computer controlled testing machine.
All of the samples were loaded until fracture using the same computer
controlled testing machine. Load under compression was applied at a
cross head speed of 1 mm/min until failure. Fracture load values were
recorded for each subgroup.
Data were collected in the form of tables of mean values and standard
deviations. The collected data were then statistically analyzed. Data
analysis was performed in several steps.
Descriptive statistics for each group results was performed. One way
ANOVA followed by pair-wise Tukey’s post-hoc tests was performed to
detect significance between the three coping thicknesses. Separate
student t-test to detect significance between main groups was done.
Finally three-way ANOVA to evaluate the effect of processing technique,
coping thickness and cyclic loading on the fracture resistance.
Statistical analysis was performed using Graphpad Prism-4 statistics
software for Windows. P values which were 0.05 or less were considered
to be statistically significant in all tests.
The following results were obtained:
1) Fracture resistance of IPS e.max copings (Press and CAD/CAM) was
affected significantly by cyclic loading.
2) CAD/CAM copings had significantly higher mean fracture resistance
than press copings.
3) Increasing the copings margin thickness significantly increased the
fracture resistance mean value.
Conclusions:
Within the limitations of this study, the following conclusions could be
drawn:
1) CAD/CAM technique showed improved strength than heat pressed
technique, regardless the thickness of the ceramic coping.
2) 0.5 mm thickness coping, constructed using both pressing and milling
techniques has sufficient strength to withstand average masticatory
forces in the premolar region (222 to 445 N)
3) Fracture resistance of lithium disilicate ceramic copings decreased
significantly after cyclic loading .