Clinical acceptability of orthodontic retainers fabricated from stored alginate impressions

The purpose of this study was to determine the clinical acceptability of orthodontic retainers fabricated from stored alginate impressions. In the laboratory, alginate impressions were made of a standard dentoform. In the clinic, maxillary alginate impressions were made of the teeth of 20 dentate adults. In each case, sets of stone models were made either immediately or after the impressions had been stored for 24 or 72 hours at high humidity. The linear dimensions of the three sets of dentoform models were compared with one another and with the standard dentoform. No differences were found. Claspless acrylic retainers were fabricated on the models from the adult subjects. The retainers were positioned in the subjects' mouths and evaluated for snap fit, stability, cervical margin fit, and self-retention. With the use of these criteria, 95% of the retainers made from impressions that were poured immediately were clinically acceptable. When impressions were stored 24 and 72 hours, the percentages of acceptable retainers were 80% and 90%, respectively. The differences in percentage of clinically acceptable retainers were not statistically significant. When impressions are stored at high humidity, a large percentage of clinically acceptable orthodontic retainers can be made from models poured as long as 72 hours after the impression is made.