The influence of tray type and other variables on the palatal depth of casts made from irreversible hydrocolloid impressions.

STATEMENT OF PROBLEM: There are conflicting data regarding the effect of various factors on the palatal depth of casts made from irreversible hydrocolloid impressions.

PURPOSE: This study examined the influence of tray type, water temperature, pouring technique, and stone expansion on the palatal depth of casts.

MATERIAL AND METHODS: Irreversible hydrocolloid impressions were made of a model under simulated oral conditions. Palatal depth was measured relative to a reference plane with a microscope. The reference planes were standardized by subjecting the data to three 2-dimensional mathematic rotations. A 2-factor analysis of variance (alpha=.05) was used to determine whether differences existed among tray types and among palatal locations.

RESULTS: The palatal depth of the casts increased approximately 0.06 mm compared with the master model with all but 2 variables. Statistical testing revealed that increased depth was not attributable to water temperature (52 degrees F or 72 degrees F) or tray type (custom resin, perforated metal, metal rimlock, or rimlock with built-up palate). Custom resin tray impressions poured with a lower expansion stone and perforated tray impressions inverted onto a base made from the same mix of stone resulted in casts with palatal depths most similar to that of the master model (P<.001).

CONCLUSIONS: Casts with palatal contours of comparable accuracy were obtained with the use of a stock metal or customized tray and the use of differing water temperatures to mix the impression material.