Statement of problem
Clinicians must know if a new screw can predictably increase reverse torque after
multiple screw insertion cycles.
Purpose
The purpose of this study was (1) to compare the effect of multiple implant prosthetic
screw insertion and removal cycles on reverse torque, (2) to determine whether a new
screw, after multiple screw insertion cycles, affects reverse torque, and (3) to assess
implant and prosthetic screw thread surface morphology with scanning electron microscopy
(SEM).
Material and Methods
One primary screw was paired with an implant (MT Osseospeed) and inserted to 25 Ncm
torque 9, 19, 29, or 39 times (n=10). Primary screw reverse torque values were recorded
after each insertion. A second, reference screw was then paired with each implant
for a final screw insertion, and reverse torque was measured. Maximum, minimum, median,
and mean values (Pmax, Pmin, Pmedian, and Pmean) were identified for primary screws. A 1-way ANOVA and Tukey HSD post hoc analysis
assessed the influence of multiple screw insertion cycles on Pmax, Pmin, Pmedian, and Pmean values (α=.05). Confidence intervals were used to test differences between reference
(REF) screw data and corresponding DMAX and DMIN (DMAX=Pmax-REF; DMIN=Pmin-REF). The surface topography of an unused implant and screw and of 1 implant and
screw from each group was evaluated with SEM.
Results
Pairwise comparisons showed that 9 or fewer insertion cycles resulted in significantly
greater mean reverse torque (20.9 ± 0.5 Ncm; P<.01). After 19, 29, or 39 cycles, the
second, reference screw achieved significantly greater reverse torque than the minimum
recorded values (P<.05). Implant thread surface morphology changes occurred primarily
during the first 10 insertions.
Conclusions
After 10 screw insertion cycles, a new prosthetic screw should be used with the implant
system tested to maximize screw reverse torque and maintain preload when an abutment
is definitively placed.
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Article info
Footnotes
Supported by an American Academy of Fixed Prosthodontics Tylman Research Grant. First Place, 2008 Stanley D. Tylman Research Award.
Identification
Copyright
© 2011 The Editorial Council of the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.
