Research and Education Abutment screw loosening in angulation-correcting implants: An in vitro study
The Journal of Prosthetic Dentistry
Available online 10 July 2018
Statement of problem
Techniques
that allow angulation correction for screw-retained implant-supported
restorations are now available. However, whether angulation correction
built into the head of the implant affects abutment screw loosening is
unclear.
Purpose
The purpose of this in vitro
study was to assess abutment screw loosening in angulation-correcting
implants and straight implants subjected to simulated nonaxial occlusal
loading.
Material and methods
Seven
external connection 12-degree angulation-correcting implants and 7
straight implants were embedded in an acrylic resin housing, and
titanium abutments were secured with titanium screws tightened to 32
Ncm. Each specimen was secured in a tooth wear
machine and subjected to 1 000 000 cycles of 50-N nonaxial load to
simulate 1 year of clinical service. The mean abutment screw removal
torque values were calculated, and the association between number of
cycles and the abutment screw removal torque was analyzed using a linear
mixed-effects model and statistical software (α=.05)
Results
The
mean abutment screw torque loss was 59.8% for the angulation-correcting
implant group and 68.7% for the straight implant group. A statistically
significantly greater mean abutment screw removal torque was recorded
in the angulation-correcting implant group compared with the straight
implant group after 1 000 000 cycles (P=.019).
Conclusions
A
significant loss of abutment screw torque was found in both implant
groups with increased cycles of occlusal loading. The
angulation-correcting implants resisted screw loosening significantly
more than the straight implants because of the reduced angle of abutment
screw loading.
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