Three-dimensional Change of Elastomeric Impression Materials During the First 24 Hours: A Pilot Study

It was already known that dental impression materials undergo dimensional changes after mixing, which can affect the accuracy of dental restorations. Prior research has shown that polymerization shrinkage occurs in these materials, but the exact timeline and extent of this change remain unclear. No prior work had resolved the behavior of dimensional changes in different types of elastomeric materials over the first 24 hours. This uncertainty drove the need for a more precise and continuous measurement method. Existing studies often rely on traditional methods that may not capture real-time volumetric changes. This gap motivated the use of a novel noncontact imaging system to track shrinkage dynamically. The study aimed to address the lack of detailed data on how different materials behave in the critical early hours after preparation. Understanding these changes is essential for optimizing clinical workflow and minimizing errors in dental impressions.

The aim of this work was to assess the volumetric changes in three types of elastomeric impression materials over the first 24 hours after mixing. The specific problem addressed was the lack of detailed data on how these materials shrink in the early period following preparation. The motivation came from the need to improve the accuracy of dental impressions by understanding when and how much shrinkage occurs. The study focused on evaluating low-viscosity polyvinyl siloxane and two vinyl polyether silicone materials. It was already known that polymerization shrinkage affects impression accuracy, but the timing and magnitude of this effect remained uncertain. The researchers proposed to use a calibrated noncontact imaging system to capture continuous data. This approach allowed for precise tracking of dimensional changes at 30-second intervals. The goal was to determine whether shrinkage patterns varied between materials and over time.

The study involved three impression materials: a low-viscosity polyvinyl siloxane and two vinyl polyether silicone formulations. Each material was prepared according to manufacturer guidelines and placed on a measurement pedestal. A noncontact video imaging system was used to track volumetric changes continuously for 24 hours. Measurements were recorded every 30 seconds to capture dynamic shrinkage patterns. The device used was a calibrated volumetric change measuring system. Data collection began immediately after material preparation to ensure early changes were captured. Statistical analysis included Kruskal-Wallis and Dunn’s tests to compare shrinkage between groups. Evaluated parameters included mean shrinkage at specific time points and maximum shrinkage values. The study design allowed for repeated measurements across 10 trials per material to ensure reliability.

All three materials showed significant volumetric shrinkage over 24 hours, with p-values below 0.001. Aquasil LV and EXA'lence LB had similar shrinkage rates throughout the 24-hour period (p=0.92). Between 10 and 15 minutes after preparation, all materials demonstrated similar shrinkage (p=0.19). EXA'lence Monophase had significantly greater shrinkage at the recommended first pour time (p=0.002) compared to the other two materials. The 24-hour mean shrinkage for EXA'lence Monophase was higher than for Aquasil LV and EXA'lence LB (p<0.008). Shrinkage between recommended first pour and 24 hours was also greater for EXA'lence Monophase (p=0.003). Aquasil LV and EXA'lence LB showed similar shrinkage at the first pour time (p=0.89). Maximum shrinkage occurred at 16 hours for Aquasil LV and 20 hours for EXA'lence LB, followed by some relaxation behavior.

The authors proposed that all three materials exhibited significant polymerization shrinkage over 24 hours. The results suggest that dimensional changes continue beyond the recommended removal time. The study found that shrinkage patterns varied between materials and over time. EXA'lence Monophase demonstrated greater shrinkage than the other two materials at key time points. The researchers propose that pouring impressions at the earliest recommended time may be prudent to minimize dimensional changes. No prior work had resolved the extent of shrinkage after the recommended first pour time. The findings suggest that up to 20–30% of total shrinkage occurs after the recommended pouring time. The authors suggest that these results may inform clinical practices regarding timing for impression pouring.