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Researches Regarding the Biomechanics Behaviour of some Impressions Biomaterials Used in Dentistry

The dimensional stability of impression materials is a variable with an impact on the accuracy of dental prostheses; alongside with other factors including the modifications occurred during the material preparation or the impression techniques. The study was based on a laboratory simulation of a clinical situation. The impression materials were: Alginate; Addition silicon materials-AFFINIS and FLEXITIME; Condensation silicon materials-SPEEDEX and OPTOSIL; Polyvinyl siloxane materials-EXPRESS. The impressions were taken at 37 ̊C at 100 per cent humidity and mould in IV class gypsum at intervals of 0 min, 30 min, 1 h, 8 hr, 24 hr and 48 hr. There were taken 3 impressions for each time interval, for each material type as well as for the 2 storage conditions, with a total number of 252 impressions. The measurements of this study were limited to the linear dimension, being observed the changes occurred in one direction, although contraction is a volumetric modification. The statistic assessment of the measurement data obtained in the case of the same type of addition silicon materials recorded an increase of the volumetric contraction type in dry environment and in longer time intervals. The Express material has less significant deformation at room temperature, compared to its being exposed to moist environment. The least significant deformations were recorded in the case of polyether materials automatically mixed.