CARMEN SAVIN, MAGDA-ECATERINA ANTOHE, ADRIANA BALAN, ANA SIRGHE, LAURA GAVRILA STUDY REGARDING THE ELASTIC IMPRESSION BIOMATERIALS DIMENSIONAL STABILITY In order to have an accurate impression, dimensional modifications must be under control throughout the impression stages, considering they are highly influenced by the variability level during polymerization.The factors with an influence on dimensional stability are:impression material width, tensile modulus, temperature during the imprinting process, storage humidity, the time lapse between imprinting and casting. The study focuses on dimensional modifications of varied elastic impression materials, considering both testing and impression techniques are done in similar conditions in order to assess accurately the behaviour of varied impression materials.Material and methods:The study was based on a laboratory simulation of a clinical situation. There were used two 6-year maxillary molars in the position they have in the oral cavity. A 3 mm wax layer was added during the next stage its width being checked with an Ivoclar mechanical vernier. The surface parallelism was subsequently checked using a parallelograph and there was taken an individual tray made of photopolymer acrylic. 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 addition materials were significantly superior in terms of contraction time, as compared to the previous case, granting higher accuracy to the end product. The Silagum Light presented an increased volumetric contraction in moist environment, the contraction being more significant in longer time intervals. The Xantopren L blue material has a reduced deformation gradient in less than 48 h.