Precision of mounting in articulator of models with a acrylic cover ( such as accutrac) using different types of Gypsum

Abstract

The goal of this research was to investigate the changes in the position of the upper model when fixed to the articulator using three types of gypsum. A model with a base of acrylic resin was made to simulate the die systems such as AccuTrac (Whaledent, USA) that have a plastic base on top of the gypsum model, keeping it from having contaet with the fixing material. The model was fixed to the articulator using three types of gypsum, Group 1 (tiype II plaster - Ultra-cal herodent, Vigodent), Group 2 (type III stone - Herodent Soli-Rock., Vigodent) e Grupo 3 (type IV stone especial - Vel-Mi. Kerr). Ten mountings were made using each type of gypsum. The movements of the model resulting from dimensional change of the gypsum used in the mounting were recorded by four micrometric precision comparative clocks (Mitutoyo Corporation, J apan). Three of them were positioned on top of the upper branch of the articulator and one was positioned under the model. The results were submitted to variance analysis and Tukey's test at a levei of 5%, and showed that ali groups had a statiscally significant difference among them. Group 4 was the only one that had a predominant mean contraction (-3mm ± 3,7). Groups 2 and 3 had a predominant mean expansion, although Group 3 (124mm ± 9,5) had a significantly larger expansion than Group 2 (55mm ±3,2). The results allowed us to conclude that the smallest change in the position of the model occurred when special stone gypsum was used (Group 4).