An investigation into the comparative accuracy of five types of elastic impression materials commonly used in restorative dentistry

Abstract

Numerous types of impression materials are currently available for use by the dental practitioner for the fabrication of cast restorations. No two materials do, however, resemble each other in all aspects, yet all seem to be capable of producing satisfactory results if manipulated correctly. However, the availability of a second cast is often necessary for the successful completion of a dental restoration. It is, therefore, advantageous if multiple casts can be retrieved from the original impression in lieu of having to make multiple impressions. The claim is often made that the more recent elastomeric materials are capable of producing such a result. The purpose of this study then, was to evaluate and compare the accuracy of first and second generation casts obtained from the same impression. Ten impressions of a Bureau of Standards die for full crown preparations were made utilizing the following impression materials. 1) Polysulfide 2) Polyether 3) Silicone 4) Polyvinylsiloxane 5) Reversible Hydrocolloid The impressions were poured in dental stone, and after retrieval of the first generation dies, a second pour was made on all the impressions excepting those obtained from the hydrocolloid material. Five dies were selected for each group of materials from both the first and second generation dies and castings were fabricated on these. The remaining dies were stored at room temperature and humidity for measuring purposes. An additional ten impressions were made, utilizing the polyether and polyvinylsiloxane materials, stored for six days at room temperature and humidity and then poured in dental stone. Castings were then fabricated on each of these dies. A further five castings were manufactured directly on the master die. All castings were then seated on the master die and marginal discrepancies were measured with a calibrated light microscope. A casting manufactured on the master die was then in turn seated on the working dies and marginal discrepancies measured to establiish whether the dies were oversized. Castings from each group of impression materials were then seated on the measuring dies and the marginal discrepancies measured. First and second pour castings were also interchanged with each other and marginal discrepancies measured. The results indicated that when castings were obtained from the first generation dies, the polyether and hydrocolloid materials produced the most accurate dies, whilst the polyvinylsiloxane material produced second generation dies at 48 hours comparable in accuracy to first generation dies produced at 24 hours. The polyether material proved to be the most accurate when a period of six days elapsed prior to pouring of the dies. Considering the above mentioned statistically confirmed facts, it becomes clear that no one material provides optimum results under all circumstances, and materials should therefore be selected to provide their optimum characteristics for the specific purpose required.