Abstract
The purpose of this study is to examine the impression accuracy of posts and cores using the combined reversible hydrocolloid and irreversible hydrocolloid, especially at various angles between the direction of the posts and the path of withdrawal of the impression tray. Five master models of clear acrylic resin and an impression tray of base metal were made particularly for this study. Each master model had two posts: one, in a parallel direction; the other, at a definite angle (0°, 10°, 20°, 30° and 40°) to the path of withdrawal of the impression tray. The permanent distortions of post impressions were measured on the standardized photographs with a profile projector.
The results are as follows:
(1) The distortions increased in proportion to the degree of angle and the depth of the measuring points.
(2) Dentloid and Hydrostick showed comparatively low distortions at 10°, 20°, but the distortions at 30°, 40° were considerable. A maximum distortion (0.40 mm) was found at the end of the 40° post with Dentloid.
(3) For reversible hydrocolloid, a radial pin proved to be effective in preventing distortion of the post impression and improving the impression accuracy.
