الفهرس 
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Abstract
The idea of this study is to propose a technique to salvage osseointegrated implant with damaged internal threads using Ni-Cr or
zirconia post and core.
Post and core specimens were fabricated from Zirconia and NiCr to
precisely fit the post space in the prepared implant fixtures. The
specimens were randomly divided into 7 groups (n=10) depending on the
post and core material and the duration of simulated intra-oral function.
group (1): Zirconia post and core control group; immediate
placement, no fatigue test is carried out. group (2): NiCr post and core
control group; immediate placement, no fatigue test is carried out. Group
(3): Zirconia post and core group were subjected to 5 months fatigue test.
group (4): NiCr post and core group were subjected to 5 months fatigue
test. group (6): NiCr post and core group were subjected to 2 years
fatigue test. group (7): NiCr post and core group were subjected to 3
years fatigue test.
Specimens were sandblasted and cemented to the prepared implant
fixtures. Immediate placement group served as control group. Fatigue
resistance test was executed using the chewing simulator simultaneously
with thermo-cycling to mimic the intra-oral function in 5 months, 1 year,
2 years, and 3 years durations. Tensile bond strength test was then applied
to surviving specimens. SEM surface topography testing was done to
bonded and de-bonded specimens after their sectioning.
All zirconia specimens failed in fatigue resistance test as well as in
the tensile bond strength test where they all fractured and didn’t dislodge.
The zirconia specimens testing results were excluded from the statistical
analysis.
NiCr specimens testing showed no results in 5 months, 1 year, and
2 years durations. 40% of specimens’ dislodgement occurred at three
years duration in fatigue resistance test. Bond strength tensile tests’
results showed no significance till the first year duration, which had a
decrease in bond strength of 16.32% in 2 years and 54.32% in three
durations.
SEM testing to surface topography of randomly selected bonded
specimen showed continuous cement layer between post and implant
fixture fitting surfaces. De-bonded specimens showed generalized mixed
adhesive/cohesive fractures in the cement layer on the surface of the post
and on the internal surface of implant fixture.
Conclusion:
Within the limitation of this in-vitro study it can be concluded that
in cases of damaged implants’ internal threads the presented technique
using NiCr post and core provides a valid technique for their salvation
giving promising results under function.