An Experimental Study on Distortion of Wax Patterns Caused by Loading Force

Abstract

This experimental study has been performed to investigate the distortion of wax patterns caused by the loading force, and to examine the influence of the angle of the axial wall of the crown, the kind of inlay wax, and the manipulation for waxes on the distortion.
a) Wax patterns for crowns were made on the plaster dies, employing metal original dies. The axial dimensional change caused by the loading force on the occlusal surface and the axial wall of the wax patterns was measured by use of the optical fiber transducer for detection.
b) The metal sprue pin 2 mm in diameter was inserted in the center of the occlusal surface, and the tension produced when the sprue pin was pulled out was measured. The results obtained were as follows:
(1) A large amount of distortion on the axial surface of the wax pattern caused by the vertical load at the central region was observed at the occlusal, central, or marginal region. Furthermore, the distortion of both the occlusal and marginal regions was conspicuous in comparison with that in the central region, and a concave-shaped distortion was found on the axial surface.
(2) Concerning the relationship between the distortion, which was brought about when the wax pattern was pressed between the thumb and index finger, and the duration which was left after the preparation of the wax pattern, the distortion observed when the wax pattern was left at 1 hour or 24 hours after taking off was smaller in amount than that observed immediately thereafter.
(3) The tension loaded for pulling out the wax pattern from the plaster die was approximately 3kg, and the axial surface of the wax pattern was noticed to shrink.