VERTICAL DISTORTION IN DISTAL-EXTENSION RIDGES AND PALATAL AREA OF CASTS MADE BY DIFFERENT TECHNIQUES

A coordinate measurement machine with laser probe was used to measure the vertical distortion of the casts produced by use of three types of impression materials (irreversible hydrocolloid, condensation silicon e, and addition silicone) and two types of trays (stock and custom tra ys), Results indicated that all impression groups showed positive vert ical distortion (ranging from 0.00566 to 0.30299 mm) at the edentulous ridges and palatal area, The amount of the vertical distortion was gr eatest at the palatal area and was followed by the high edentulous rid ge and the low edentulous ridge, Addition silicone, with either custom tray or stock tray, was the most accurate impression material, Conden sation silicone was more accurate than irreversible hydrocolloid in cu stom tray impression, However, in stock tray impression the irreversib le hydrocolloid was more accurate than the condensation silicone, The results suggest that, with careful manipulation, irreversible hydrocol loid with stock tray impression may provide a satisfactory cast for fa bricating the framework of a distal extension removable partial dentur e.