The influence of humidity on expansion and shrinkage properties of duralay

Reconstruction of the tooth crown using the root structure is one of the common dental treatments. Despite daily increase in using prefabricated metal or fiber reinforced posts, there are still cases in which using casting posts are preferred. Duralay acrylic resin is considered as one of the precisest and most common materials for making post patterns in prepared dental canals. Since acrylic resin’s dimensional changes after its setting is one of the main dentist’s problems while working with it, this study has evaluated the humidity’s effect on duralay’s dimensional changes. In this experimental study, a plated brass mold was used and 60 duralay cylindrical models were made with 10 mm diameter and 12 mm height. These models were coded and then randomly divided into 2 groups (30 case and 30 control).Volume, dimensions (diameter and height) and weight of samples were measured by dilatometer, digital Collis and digital scale respectively.The samples of the control were kept in a dry environment and the samples of the cases group, in the deionized distilled water for 7 days. After this period, volume, dimensions and weight of the samples were re-measured. For minimizing the probability of the errors, each factor was measured 6 times by the researchers. Datas were statistically analyzed using paired t test and student t test. This study showed that duralay’s volume and dimensions decreased in a dry environment which was significant (p<0.05).In a humid environment, duralay’s volume dimensions and weight increased significantly (p<0.05).It was also observed that duralay’s weight increased a little in a dry environment, but it was not significant (p>0.05). According to the results of this study and regarding duralay’s water absorption and dimensional volume expansion, it seems better that send prepared duralay’s post and core patterns to the Laboratory in a dry environment.