Dimensional Stability of Light - Cured Acrylic Resin Special Tray Material

Objective: To determine the linear dimensional shrinkage of light-cured acrylic resin special tray material stored in a dry-environment. Method: A meta – analysis of dimensional stability of chemically-cured acrylic resin special tray materials was conducted. Twenty specimens with configurations of 2 x 4.2 x 20mm as set out in the guidelines of the American Society for Testing Materials were fabricated using a custom-made Perspex template. The length of the template (20mm) served as the standard to compare possible dimensional changes. The specimens were cured in a light-polymerizing unit for 3min. Thereafter, the specimens were removed from the template and placed in the curing unit again for 3minutes to ensure complete polymerization. Using a digital Vernier scale the specimens were measured 3 times at time intervals of 30 min, 1 hr, 24, 36 and 48 hrs following polymerization and the values of each were recorded. The Mean, Median and Interquartile ranges of the shrinkages from the standard of 20mm were calculated. The Wilcoxon Signed Rank test was used to evaluate the extent of shrinkage over time. Results: The Medians in mm of the shrinkages recorded at the different time intervals were as follows: At 30min: 0,230; at 1 hr: 0,245; at 24hours: 0,200; at 36hours: 0,265 and at 48hours: 0,280. Shrinkages at the different time intervals were highly significant compared to the standard. According to the Wilcoxon Signed Rank test, the changes in shrinkage over time were not significantly different. Conclusions: The results show that significant linear shrinkage occurred initially, thereafter a steady but insignificant decrease in shrinkage over time. Thus, special trays made from this material may be used immediately after polymerization.