| Summary: | Purpose
It is known that distortions can occur during impression making and the pouring of
casts, and that this distortion may produce inaccuracies of subsequent castings,
especially long span castings for implant superstructures. The purpose of this study
was to compare the ability of different impression materials to reproduce the positions
of 5 implant analogues on a master model, in terms of their accuracy and the accuracy
of a resultant cast, relative to the master model.
Method
The master model was a stainless steel model with 5 implant analogues. The
impression materials used were impression plaster (Plastogum), a polyether
(Impregum Penta), and two polyvinyl siloxane materials (Aquasil Monophase and
Aquasil putty with light body wash). Five impressions were made with each
impression material and cast in Satin stone under controlled conditions. The positions
of the implants on the master model, the impression copings, and the implant
analogues in the subsequent cast were measured using a co-ordinate measuring
machine which measures within 4μm of accuracy.
Results
Statistical analysis using a one factor t-test indicated that distortion occurred in all the
impression materials, but inconsistently. Aquasil Monophase reproduced the master
model most accurately. Although there was no significant distortion between the
Aquasil monophase impressions and the master model or between the impressions and
their casts, there were distortions between the master model and the master cast, which highlighted the cumulative effects of the distortions. Impregum’s performance
proved to be the most reliable in terms of predictability. Plastogum displayed
cumulative distortion and with Aquasil putty with light body, these impression
materials had the least reliability.
Conclusions
Some of the distortions observed are of clinical significance and likely to contribute to
a lack of passive fit of any superstructure. The unpredictability of such distortions
may mean that the future of accurate impressions and superstructures may lie in the
digital world.
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