THE EFFECT OF TEMPERATURE-CHANGES ON THE DIMENSIONAL STABILITY OF POLYVINYL SILOXANE AND POLYETHER IMPRESSION MATERIALS

Statement of problem. Dental impressions are commonly mailed to remote dental laboratories and can be subjected to extreme temperature chang es; however, the effects of these temperature changes on the accuracy of elastomeric impression materials are unknown. Purpose. This study e valuated the dimensional changes of polyether and polyvinyl siloxane i mpression materials as a function of storage temperature. Material and methods. A total of 144 impressions were made of a stainless steel di e similar to ADA Specification No. 19. Half of the impressions were ma de in perforated custom trays and the other half in solid trays. Measu rements of the vertical and horizontal lines on the impressions were m ade at 10 minutes, 1 hour, 24 hours, and 26 hours, and storage tempera tures ranged from 4 degrees C to 40 degrees C. Results. Changes in sto rage temperature had a statistically significant effect on the dimensi onal stability of the horizontal and vertical lines. However, overall dimensional changes were extremely small. Conclusions. Storing both im pression materials at 4 degrees C for 24 hours and then allowing the i mpressions to reach room temperature resulted in a slightly expanded i mpression that partially compensated for the contraction that occurred from polymerization shrinkage. Similar results occurred for polyether material only, when stored at 40 degrees C.