The Dimensional Stability of Elastomeric Dental Impression Materials

High accuracy dental impression is usually a first step during fabrication of indirect restorations that have to be seated in or on prepared teeth. The dimensional stability of the impression material could have an influence on the accuracy of the final restoration. Elastomeric materials (additioncured silicones and condensationcured silicones) are most frequently used as the impression material in fixed prosthodontics. The composition and the type of the chemical reaction determine the urgency to cast or digitize the impression. The aim of this study was to asses the dimensional stability of addition and condensation cured silicones in time. Stainless steel model of two cylinders with the spherical top was fabricated. First, individual tray of acrylic resin was made according to the standard procedure. Addition and condensation cured silicon impressions were taken using monophase technique in acrylic tray. Impressions were cast in type IV dental stone after different periods of time, and dental stone replica models were made. Master model and dental stone replica models were scanned using Carl Zeiss Coordinate measuring machine Contura G2 with associated volumetric probing tolerance of 1μm. Processing was done using Calypso software. Addition and condensation cured silicon impressions were cast after different periods of time. Master model and dental stone replica models were scanned and the differences between the models were measured. The dimensional differences between the master model and the replica models occurred due to the dimensional instability of the impression material. The differences were significantly greater when condensation cured silicon impression material was used comparing to the addition cured silicon impression material. Both condensation and addition silicon showed satisfactory dimensional stability if cast according to the manufacturer’s instructions. If so, the linear dimensional changes did not exceed 1%. Keyword: elastomers, dental impression materials, fixed partial denture.