No description available.

No description available.

A research report submitted to the faculty of health sciences, University of the Witwatersrand, Johannesburg, in partial fulfillment of the requirements for the degree of Master of Density Johannesburg, 2017 / MT2017

No description available.

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.

No description available.

No description available.

Thesis (doctoral)--University of Göteborg, 1991. / Extra t.p. with thesis statement inserted. Includes bibliographical references.

Thesis (doctoral)--University of Göteborg, 1991. / Extra t.p. with thesis statement inserted. Includes bibliographical references.

Thesis (doctoral)--University of Göteborg, 1991. / Extra t.p. with thesis statement inserted. Includes bibliographical references.