Abstract
Background: Numerous factors have an effect on the accuracy of an impression and resultant cast, and these include: impression material, impression technique, tray selection, impression disinfection, storage time of impression before pouring, stone type used for fabrication of cast. Up to now, there has been little research conducted on the effect of contact time of a cast with an impression, on the dimensional stability of a cast. Objectives: The purpose of this study was to evaluate the effect of the contact time of silicone impression materials with stone casts, on the dimensional stability of resultant casts. Materials and Methods: A total of 44 impressions were made from a stainless steel master model, with each one of two silicone impression materials (Elite HD+ and Speedex), and poured with Elite Master Type IV. The thickness of the light-body material (1 mm) was provided by using four copings. The resulting casts from each material were placed in four groups (n = 11) after each contact time with the impression (1 hour, 24 hours, 48 hours, 1 week). Distance between anterior and posterior abutments was measured for the casts and master model. Data were analyzed by two-way analysis of variance and a Tukey test. Results: The relationship between the dimensional stability of the casts and the simultaneous effect of the impression material and contact time of the cast with the impression was not statistically significant (P = 0.099). Type of impression material on the dimensional stability of the cast had no significant effect (P = 0.163). Increased contact time of the cast with the impression resulted in increased dimensional change (P < 0.001). Conclusions: Dimensional stability of the casts after different contact time with the impression was acceptable. The best time to separate the cast from the impression was one hour after pouring the impression
Highlights
Numerous factors have an effect on the accuracy of an impression and resultant cast, and these include: impression material, impression technique, tray selection, impression disinfection, storage time of impression before pouring, stone type used for fabrication of cast
The two-way analysis of variance showed that only the effect of the independent variable of contact time on the dimensional stability of the casts was significant, but the type of impression material did not have any significant effect
In order to make each prosthesis with good adaptation, it is important to have an accurate impression combined with a cast which has high dimensional stability [1, 8]
Summary
Numerous factors have an effect on the accuracy of an impression and resultant cast, and these include: impression material, impression technique, tray selection, impression disinfection, storage time of impression before pouring, stone type used for fabrication of cast. Objectives: The purpose of this study was to evaluate the effect of the contact time of silicone impression materials with stone casts, on the dimensional stability of resultant casts. Many previous studies have been carried out to identify the most effective factors on dimensional accuracy of impressions and resultant casts, so that the most appropriate material and technique can be used in every situation. The type of material used for making the cast and the proper pouring time for each impression material, can have an effect on the accuracy of the dental cast [5, 6]. The silicone impression material can be hydrophilic or hydrophobic and as a result of these characteristics, increasing the contact time between the cast and the impression can have an effect on the dimensional stability of the casts. In a study by Marquezan et al increasing the contact time between the alginate mold and the cast did not have any effect on the dimensional stability of the cast [8]
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