Pilot study on accuracy and dimensional stability of impression materials using industrial CT technology

Abstract

Objective: Using computed tomography, scan impressions can be saved and edited as virtual data. The aim of this study was to evaluate the parameters influencing different impression materials and impression trays and their relevance with regard to accuracy and dimensional stability.

Materials and methods: Two alginate impressions (Zhermack Hydrogum®5 and Kaniedenta Tetrachrom®) and a polyether impression (3MEspe Impregum™) were each combined with two acrylic trays (3M Espe Position Tray™ and Profimed Opti-Tray) and CT scanned immediately after impression at the Fraunhofer Institute Development Center for X-ray Technology (EZRT) in Fürth, Germany. Each impression was digitized 10 times on the same day, 3 times after 2 days and twice after 6 days, thus determining the dimensional stability of the various materials. An acrylic model was digitized with a high-resolution µCT research scanner to be used as a reference for assessing the accuracy of the impression materials. For graphic and statistical analysis, VGStudio Max® was used.

Results: Both alginate impressions were less dimensionally stable than the polyether impression material. The Zhermack Hydrogum®5 alginate impression resulted in more deviation (151 µm) after 6 days than the Kaniedenta Tetrachrom® impression. The polyether scans showed a mean deviation of 73 µm. The accuracy of both alginates was similarly precise (mean value: Hydrogum®5 0.129 ± 0.021 mm, Tetrachrom® 0.137 ± 0.002 mm). The type of tray had limited influence on the results of the alginate impressions, while the accuracy of the Impregum™ impression depended on the tray combination chosen.

Conclusion: The accuracy of the alginate impressions is sufficient for clinical use in orthodontics and produced, with correct storage, acceptable results even after 2 days. Hydrogum®5 impressions proved to be slightly more accurate than the reference material but less dimensionally stable than the Tetrachrom® impressions. The 3M Espe Position Tray™ seemed to be more practical due to a better retentive effect compared to the Opti-Tray made by Profimed.