The Dimensional Stability of Elastomeric Dental Impression Materials

Abstract

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 (addition-cured silicones and condensation-cured 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%.

Measurement of dental crown wear —<i>In vitro</i> study

“…Volumetric probing uncertainty test (P test) and volumetric length measuring uncertainty (E test) has already been recommended by ISO 10360-2 as accuracy tests for CMMs 17) . In previous studies, CMM served as a reference scanner for testing the accuracy of different lab scanners 10,39,40) or dental impressions 41) . Therefore, we consider that it is not needed to conduct control scanning of dental crowns and we restrain from further data comparison.…”

EVALUATION THE FATIGUE RESISTANCE AND COLOR STABILITY OF ACETAL RESIN AND BRE- FLEX (2nd EDITION) IN KENNEDY CLASS I REMOVABLE PARTIAL DENTURE. AN IN-VITRO STUDY

“…The modified master cast was duplicated as conventional manner (17) , 20 refractory casts were poured on the silicon mold then, The wax pattern of the major connector and the saddles were waxed and casted at first as usual with chrome -cobalt alloy the finished and polished after the casting procedure was done the refractory models were randomly divided into 2 groups 10 model in each group.…”

Dimensional Stability and Accuracy of Silicone – Based Impression Materials Using Different Impression Techniques – A Literature Review

“…The second stage comes after the extraction of the impression and lasts in some materials up to an hour, until the polymerization is fully completed. During that time, some dimensional changes on the impression material are possible, and, with its completion, the time convenient for casting of the impression begins [13].…”