Effect of manipulative variables on the accuracy of crown wax patterns.

An instrument was developed to carve wax patterns in a reproducible manner. The methods of wax application to the die and wax removal during carving were similar to routine laboratory procedures. The wax patterns were invested in stone with the dies on which they were prepared, and sectioned to allow the determination of their adaptation on sectioned samples. Shrinkage of wax patterns on dies was found to create a marginal gap at shoulders and bevels. Further shrinkage observed after removal from the die was attributed to relaxation of elastic stresses in the wax. Carving of bevels improved adaptation to the die for samples with large gaps at the shoulder. This improved adaptation can be attributed to plastic deformation in the wax bevel. Remodeling of pattern margins was found to improve adaptation to the die, especially if carried out after the pattern was removed and replaced on the die. Remodeling the margin should involve heating with a spatula of a narrow band of wax around the margin up to the axial die wall over the entire shoulder width.