Statement of problem
Accurate recording of implant locations is required so that definitive restorations
are properly supported and do not place additional stress on the implants. Angulated
implants may result in inaccurate impressions, and the impression technique may affect
the accuracy of the definitive cast.
Purpose
The purpose of this study was to determine the effect the combined interaction of
impression technique, implant angulation, and implant number has on the accuracy of
implant definitive casts.
Material and methods
One definitive stone cast was fabricated for each of 6 experimental groups and 1 control
group. All 7 definitive casts had 3 implants arranged in a triangular pattern creating
a plane. In the 6 experimental groups, the center implant was perpendicular to the
plane of the cast while the outer implants had 5, 10, or 15 degrees convergence towards
or divergence away from the center implant. The control definitive cast had all 3
implants parallel to each another and perpendicular to the plane of the cast. Five
open tray and 5 closed tray addition silicone impressions were made of each definitive
cast. Impressions were poured with type IV dental stone, and a fine tip measuring
stylus was used to record multiple axis (X-Y-Z) coordinates on the top surface of
the implant hex and on the cast base. Computer software was used to align the data
sets and vector calculations determined the difference in degrees between the implant
angles in the definitive cast and the duplicate casts. Statistical analysis used repeated-measures
ANOVA (α=.05) with post-hoc tests of significant interactions.
Results
The angle errors for the closed and open tray impression techniques did not differ
significantly (P=.22). Implant angulations and implant numbers differed in average angle errors but
not in any easily interpreted pattern (P<.001). The combined interaction of impression technique, implant angulation, and
implant number had no effect on the accuracy of the duplicate casts compared to the
definitive casts (P=.19).
Conclusions
The average angle errors for the closed and open tray impression techniques did not
differ significantly. There was no interpretable pattern of average angle errors in
terms of implant angulation and implant number. The magnitude of distortion was similar
for all combinations of impression technique, implant angulation, and implant number.
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Article info
Footnotes
Supported by the Tylman Grant from The American Academy of Fixed Prosthodontics; awarded first place in Tylman Research Award competition.
Presented at the 56th Annual Meeting of the American Academy of Fixed Prosthodontics, February 2007, Chicago, Ill.
Identification
Copyright
© 2007 The Editorial Council of the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.
