Pouring Time and Cast Porosity of Alginate Substitute Impression Materials

Alginate impression materials are the most frequently used dental impression material.  However these materials have limitations and only one cast from each impression can be made.  Alginate substitute materials made from polyvinyl silicone eliminate some of these problems but cast porosity is noted with these materials. 

OBJECTIVES: To determine and compare the effect of 4 pouring times on surface porosity of Type IV stone models made from four alginate substitute (poly vinyl siloxane) impression materials.

METHODS: Four alginate substitute materials Position Penta, AlgiNot, Status Blue and Silgimix and four experimental versions of one alginate substitute material (Silgimix) were used and compared. Following the manufacturers' instructions, impressions were made of a glass cement mixing slab and placed in an incubator (37ēC, 83%RH) until set. Casts were poured in ADA Type IV vacuum mixed stone at four different time intervals (10, 30, 45, 60 minutes), yielding five specimens for each time period. To quantify the surface porosity a metal grid was used as a framework to divide the cast into twenty equal squares (12.25x12.25mm). Each square was then evaluated under magnification and given a porosity index score from 0 to 4 (0=no porosity, 1=0-25%, 2=25-50%, 3=50-75%, 4=75-100%). The number of squares with the same score was recorded for each sample and the data analyzed using ANOVA and Tukey/Kramer post-hoc tests (p=0.05).

RESULTS: Mean porosity index observed for the 4 different materials and the 4 experimental versions showed that significant differences were found between each material (p<0.0001) and time of pour (p=.0001). Degassing occurred with all materials and decreased with time for most. CONCLUSIONS: Within the range of materials and times examined in this study it can be concluded that a limitation of alginate substitute materials is the degassing which has a significant effect on model porosity.  Supported in part by Sultan.