Alteração dimensional de moldes de polissulfeto e poliéter sob influência do tempo de confecção do modelo

Abstract

The delay in pouring of elastomers impressions can be the cause of possible dimensional alterations of the working casts, mainly when they are under influence of other factors that interfere on its dimensional stability. The purpose of this research was to test the hypothesis that the delay in pouring of the casts after the attainment of impressions of polysulfide and polyether has influence in dimensions of the model obtained, using a method that simulates the conditions of the practical clinic. It had been used a polysulfide (Permlastic - Kerr) and a polyether (Impregum 3M ESPE) to mold a master model with two pillars: 1 first human premolar and 1 first human molar prepared for fixed partial denture with three elements. Six reference points had been established in each tooth, resulting in seven measurements: (mesiodistal, buccopalatine and cervico-occlusal for both, and the interpillars distance). Molds were obtained with acrylic resin custom-trays, stored for the times of 30min, 2h and 12h (n = 10) and poured with dental stone type IV (Vel-Mix - Kerr). Three examiners measured the master model and the samples in an optical microscope (Mitutoyo). The measurements of each sample had been compared with the master model by means of Student s t test, and between groups by means of two-way ANOVA, and Tukey s test (P<.05). The average distances for polysulfide varied from 0 to 23&#956;m for the time of 30min, 4 to 30&#956;m for 2h and 1 to 22&#956;m for 12h of storage. For the polyether, it was from 1 to 43&#956;m for 30min, 2 to 44&#956;m for 2h, and 0 to 23&#956;m for 12h. The polysulfide and the polyether generated models with alterations in at least one of the distances, but only one of them was influenced by the storage time. Almost all the alterations were clinically acceptable.