الفهرس 
Review of literatureOnly 14 pages are availabe for public view
 |  | from | 156 |  |  |
| | | from | 156 | | |
Abstract
This study was designed to investigate, in vitro, the cervical
marginal accuracy and fatigue failure after dynamic loading of allceramic
crowns IPS Empress 2 (Conventional lost wax,
Injectable heat – pressed) and IPS e.max CAD (CAD / CAM
milling, Cerec inLab) using two types of finish lines (deep
chamfer, and shoulder finish line).
Specially designed stainless steel dies were constructed and
a total number of 40 all-ceramic Lithium disilicate nonanatomical
crowns were constructed and classified into two
equal groups, twenty each, according to the technique of
construction [lost wax technique, and CAD / CAM milling
technique (Cerec inLab)]. Each of the previously mentioned two
groups was subdivided into two equal subgroups, ten each,
according to the type of finish line used (deep chamfer, and
shoulder finish line).
The IPS Empress 2 crowns were constructed following a
standard procedure using a specially designed and fabricated
counter split die for the purpose of crown samples
standardization. Also, the IPS e.max CAD crowns were
fabricated with the same standard dimensions as controlled by
the Cerec in Lab software
The samples were tested to determine vertical cervical
marginal accuracy using a stereomicroscope using a fixed
magnification of 40X, then for fatigue failure under dynamic
loading using (Lloyd) universal testing machine, after
Summary
11 8
duplicating the stainless steel dies into epoxy resin dies, and
then a randomly selected fractured all-ceramic crown of each
group was analyzed using SEM, at 1500X magnification.
IPS Empress 2 crowns with shoulder finish line group
recorded the lowest cervical marginal discrepancy mean (35.73
μm), IPS e.max CAD crowns with chamfer finish line group
recorded the highest cervical marginal discrepancy mean
(60.29 μm), while IPS Empress 2 crowns with chamfer finish
line and IPS e.max CAD crowns with shoulder finish line
groups recorded intermediary cervical marginal discrepancy
means (45.01 μm and 58.74 μm) respectively.
IPS Empress 2 crowns with shoulder finish line group
recorded the highest fatigue failure mean (1038 N), IPS e.max
CAD crowns with shoulder finish line group recorded the lowest
fatigue failure mean (735.4 N), while IPS Empress 2 crowns
with chamfer finish line and IPS e.max CAD crowns with
chamfer finish line groups recorded an intermediary fatigue
failure mean values (986.4 and 919.5 N) respectively.
The scanning electron photomicrographs showed more
granular surfaces of IPS Empress 2 crowns compared to that of
IPS e.max CAD crowns, also microscopic isolated surface
flaws and flakes were present, and finally, microcracks within
the glassy phase were noticed on the fractured surfaces of all
crowns, which seemed to be more numerous and smaller in the
IPS e.max CAD crowns, but less in number and larger in the
IPS Empress 2 crowns.
Summary
11 9
Under the limitations of this study, several conclusions could
be detected:
1. With regards to the recorded levels of the suggested
acceptability for vertical cervical marginal accuracy
and for fatigue failure under dynamic loading, the
four tested groups had acceptable marginal fit and
strength, which leads to clinical success.
2. Posterior crowns made from IPS Empress 2
(Conventional lost wax, Injectable heat – pressed)
are more accurately fit and stronger than those
made of IPS e.max CAD (CAD / CAM milling, Cerec
inLab).
3. The use of a shoulder finish line is recommended for
all ceramic crowns, as the marginal gaps were
greater for the chamfer finish line specimens,
although the fracture strength of the all ceramic
crowns with a chamfer finish line was higher than
that of the crowns with a shoulder finish line
4. CAD / CAM milling, Cerec inLab, is a recent
technique that allows easy and rapid construction of
restorations, but still effort must be done in order to
improve precision and strength.