Effect of Installation Protocol on Initial Preload Loss in Dental Implant Abutment Screws.
Restorative dentistry is turning increasingly to implant-supported restorations as a
means to replace missing teeth. Nearly all implant-supported restorations involve at
least one screwed joint. The purpose of the screw in these joints is to create a
clamping force, called preload, between the joint members. If the preload in such a
joint is degraded, the screwed joint can become ... read moremore susceptible to failure. Often
screwed joints will experience some initial loss of preload after they are first
tightened. The purpose of this in-vitro study is to determine whether a dental implant
abutment screw installation protocol that includes retightening of the screw; or
tightening followed by loosening and retightening of the screw, can decrease the amount
of initial preload loss. The study used 139 M1.6 titanium abutment screws of two
different seating surface geometries in a simulated implant/abutment assembly that
included a strain gauge for direct measurement of joint preload. Following tightening to
25N-cm, preload was recorded for 2-12 hours. Preload loss and residual preload were
evaluated at 2 hours. Without retightening, mean preload loss was 2.0% for the screw
with the flat seating surface and 3.4% for the screw with the tapered seating surface.
The simple retightening protocol produced the lowest mean preload loss, 0.8% for the
flat screw, and 1.0% for the tapered screw. Without retightening, mean residual preload
was 373N for the flat screw 228N for the tapered screw. Tightening, loosening and
retightening produced the highest mean residual preload for the tapered screw (238N).
Neither of the retightening procedures had a statistically significant effect on mean
residual preload for the flat screw (p > .05), though tightening, loosening and
retightening cut the range of residual preload by more than half compared to tightening
alone. Scanning electron microscopy, white light interferometry, and profilometry were
utilized to examine the contact surfaces after testing. Based on the results of this
study, installation protocols involving retightening should be considered as a means to
decrease relative preload loss, increase residual preload, and decrease variability in
preload for dental implant abutment screws.
Thesis (M.S.)--Tufts University, 2013.
Submitted to the Dept. of Mechanical Engineering.
Advisor: Thomas James.
Committee: Anil Saigal, and James Hannoosh.
Keywords: Mechanical engineering, Biomedical engineering, and Dentistry.read less