Dimensional changes in plaster cast models due to the position of the impression tray during setting

Abstract

Introduction: The objective of this study was to assess whether the positioning of the impression tray could cause distortion to plaster casts during gypsum setting time.Materials and Methods: Fifteen pairs of master models were cast with alginate impression material and immediately filled with gypsum. Impressions were allowed to set with the tray in the noninverted position (Group A) or in the inverted position (Group B). The plaster models were digitized using a laser scanner (3Shape R-700, 3Shape A/S, Copenhagen, Denmark). Measurements of tooth size and distance were obtained using O3d software (Widialabs, Brazil) measurement tools. Data were analyzed by paired t-test and linear regression with 5% significance.Results and Conclusion: Most of the measurements from both groups were similar, except forthe lower intermolar distance. It was not possible to corroborate the presence of distortions due to the position of the impression tray during gypsum setting time.