USING DOUBLE-POURED ALGINATE IMPRESSIONS TO FABRICATE BLEACHING TRAYS

Esthetic and diagnostic treatment often requires two casts of one arch , one for baseline and one for alterations (diagnostic wax-up, bleachi ng tray, occlusal analysis). The purpose of this study was to compare the accuracy of stone casts generated from a second pour of a properly handled alginate impression with first-poured casts. A maxillary dent oform was indexed with six reference spaces (#8-15, 9-2, 2-15, and inc isal-to-gingival of #3, 9, 14). Irreversible hydrocolloid (Jeltrate) i mpressions were made in perforated steel trays by a single investigato r. Impression material was spatulated for 1 minute. The seated impress ion and dentoform were wrapped in a damp paper towel to simulate intra oral conditions, and allowed to set for 2 minutes. Upon separation, th e impression was stored in a damp towel for 5 minutes. The impression was poured in cast stone (Microstone) according to the manufacturer's instructions. The stone-filled impression was immediately rewrapped in a damp paper towel and allowed to set for 45 minutes at room temperat ure. Upon removal of the stone, the impression was rinsed with cold wa ter, shaken dry, and repoured in the same manner. Ten impressions were made: the first five impressions were poured to make casts for Group A, then repoured as described above for casts for Group B. The remaini ng five impressions were poured once to make casts for Group C. The si x spaces of each cast were measured three times in random order using a dial caliper and the space average calculated for the cast. At each space, analysis of variance showed no significant difference among Gro ups A, B, or C (P < 0.05). When alginate impressions that have been po ured with cast stone are kept moist during stone setting and repoured within 45 minutes, two casts can be generated from one impression with the same degree of accuracy as two casts made from taking two separat e impressions, providing the alginate does not tear during first cast removal.