الفهرس 
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Abstract
Successful long-term results of dental implants have led to an
increase in their usage in many clinical situations. Since the introduction of
osseointegrated implants for the rehabilitation of edentulous patients,
tremendous awareness and subsequent demand have arisen in the field, where
implant supported fixed prosthesis became widely accepted as an alternative
to conventional prosthesis.
However, some clinical studies have reported variable rates of failure.
Biomechanical factors and stress distribution around implant supported
restorations are the prime factors leading to failure of implants. The
relationship between load factors and implant failure cannot be ignored any
longer because of the high incidence of fractures of components, marginal
bone loss, and loss of Osseointegration in situations of compromised
prosthetic reconstruction and/or extreme load conditions.
The current study evaluated the effect of platform switching
implants and different abutment materials (Titanium and zirconia) on the
stress distribution around Implant supported monolithic full anatomical
zirconia crowns. Stress analysis was measured using mechanical loading
test together with strain gauge.
The following materials were used in the current study:
Implant direct dental implant fixtures.
Implant direct titanium abutments.
Implant direct Zirconia abutments.
inCoris TZI mono blocks.
. Epoxy resin material.
Electrical resistance strain gauges
Two implants were fixed in two anatomically correct mandibular
epoxy resin models restoring posterior missing first molar. Twenty fullanatomical
monolithic zirconia crowns were constructed over 4 sub-groups as
follows:
1. Standard implant-abutment connection with titanium abutment
2. Standard implant-abutment connection with zirconia abutment
3. Platform switching implant-abutment connection with titanium
abutment
4. Platform switching impant-abutment connection with zirconia
abutment
All zirconia crowns were fabricated by CAD/CAM technology. Full
anatomical Zirconia crowns were milled using Cerec Inlab system. Cementing
device was used to cement the crowns to its corresponding abutment using
temporary cement.
Strain was developed around the implants during static loading with a
defined force of 300 N applied to the crown by a universal testing machine,
they were measured using strain gauges at the buccal, the lingual, the mesial
and the distal surfaces along with the long axis of implants. Measurements
were carried out together with specialized software to analyze the strains that
occurred.
Within the limitations of this study, the following conclusions were
drawn as follows:
1. The highest strain was observed in the groups with Standard implantabutment
platform in comparison with the other groups with platform
switching.
2. Regarding the effect of abutment material within the regular platform
and platform switching groups, there was no statistically significant
difference in strain development between the two abutment matertials.
3. The use of platform switching concept might be a successful
approach to overcome bone resorption, due to shifting of stresses away
from the bone-implant interface especially in high stress areas.
4. The abutment material has no influence on the strains induced in the
supporting structures. Both Zirconia and titanium abutments could
withstand the functional loads developed during physiologic chewing in
the molar area. Zirconia abutments could be considered as a valid
esthetic alternative to titanium abutments