Influência do tipo de material de moldagem e do tempo para vazamento do molde na estabilidade dimensional dos modelos de gesso

Abstract

A delay in pouring elastomeric impressions may be the cause of cast dimensional alterations, resulting in a bad adaptation of the restorative prosthetic. This study aims to evaluate, in-vitro , the influence of differents elastomeric materials and the time passed to pour the cast on its dimensional alteration, by means of a method which simulates the conditions found in the clinical practice. Four elastomers, polysulphide (Permlastic), polyether (Impregum F), condensantion silicone (Zetaplus/Oranwash) and addition silicone (Adsil), were used to reproduce an upper cast in which a molar and premolar were previously prepared to receive a fixed prosthesis. Six reference points were stablished on each tooth and four distances between these points were analysed: mesiodistal (MD), vestibulopalatine (VP), cevicoocclusal (CO) premolar and interdental (Int) distance, between the distal of the premolar and the mesial of the molar. Were obtained 120 impressions (n=10) by the relining technique, stored for 30min, 2h and 12h and poured with type IV gypsum. The measurements were evaluated by three examiners by using a measuring microscope. The data obtained for the VP, CO and Int distances were subjected to variance analysis (4x3) and Tukey test. The data obtained for the MD distance were subjected to non-parametric tests Kuskal-Wallis and Dunn. For all the tests, a 5% reliance level was used. The interaction material x storage time was statistically significant (p<0.05) for the VP and /co distances. When evaluated for the same time, the materials showed statistically significant dimensional alterations between themselves. The time gone between the impression and the cast pouring influenced on its dimensional accuracy. The various materials presented different dimensional behaviours when evaluated at the same period of time. The time gone between the impression and the cast pouring mustn t be neglected by the dentist.