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.