ACCURACY OF THE IMPRESSION TECHNIQUE USING THERMOFORMING POLYMETHYL METHACRYLATE TRAY

Abstract

Statement of problem. Use of the conventional dental impression procedure is problematic in patients who have difficulty opening their mouth, difficulty breathing through their nose or tendency to gag.

Purpose. It is necessary to make individual trays more comfortable for patients during impression taking procedure. It was reported at the KAP Annual Meeting 2001 Seoul that an improved impression technique was suitable for this purpose. In this study, the accuracy of the improved dental impression method for implant was compared with the conventional dental impression method.

Material and methods. An oral simulator was made from clear acrylic resin block which had similar form of edentulous ridge. For setting up the standard, five fixtures were installed on it. Study casts were made using two kinds of impression techniques. One was the conventional method that was taken using silicone impression material and an individual resin tray under connection of inter-fixture relation. The other was the improved method in which was the connection of the impression coping and the thermoformed polymethyl methacrylate tray. In addition, two different study casts were made from the improved impression body. The coordinates of the fixture on the study model were measured by three-dimensional coordinate measuring equipment. Then the distances between each fixture were calculated and compared with that of oral simulator. Accuracy of the each impression method was also assessed.

Results. The differences of inter-fixture dimension between study casts and simulator in the improved impression technique showed 0.014{pm}0.016mm and 0.017{pm}0.022mm, respectively and that of the conventional method was 0.017{pm}0.014mm. There was no significant difference between the improved impression technique and conventional method.

Conclusion. The improved impression technique is useful for multiple support implants.