Abstract: A tubular hollow molded body is formed with a resin having a bending resistance; the hollow molded body is inserted into a mold; a resin with less stress relaxation is injected into both ends of the hollow molded body through a connecting path to mold a bellows intermediate; the resin moved into the connecting path of the bellows intermediate is removed; and a cut is put in the hollow molded body to mold a bellows portion.

Abstract: A mold assembly and sprue configuration for dental investment casting includes a ring shaped casing, a base and a cover all made of resilient plastic material and fictionally engaged with each other. The base includes a raised neck having a top surface with a sighting bead for use in mounting wax forms on the sprue, positioned within the casing. The sprue includes a post for engaging a blind bore in a hub of the base. The cover includes a downwardly extending plug which extends into the body of the casing, and a curved lip with recess for facilitating the pouring of investment solution into the mold. The sprue has three spokes and a ring which are all triangular in cross-section to reduce the amount of metal needed in the precision casting to be made with the invention and also to provide a convenient flat upper surface for mounting wax forms to the sprue.