Cast ejector

Abstract

A process for forming a removable dental cast embedded with a plastic, threaded, cast ejector button, and apparatus for fabricating a plurality of cast ejector buttons comprised of a mold device including an upper plate containing a plurality of mold cavities, and a base plate incorporating coil spring means for resiliently maintaining the upper plate in a predetermined spaced-apart and open relation thereto and a plurality of rigid support elements attached, at their bottom ends, in vertically-upright relation on the base plate and slidably engaged, at their upper ends, in a bottom opening in each upper plate-mold cavity and extending in overlapping relation into the respective cavity. The upper ends of each rigid support element are threaded so that, when the mold cavities are poured with and filled by a suitable material, in the plastic flow form that is allowed to set for a specified period, a separate and internally threaded plastic cast ejector button is formed in each cavity.

I claim: 
     
       1. In a method of making and using a master cast having a plastic button embedded therein, flush with the surface thereof, said button having a threaded aperture in an exposed side thereof for facilitating removal of said master cast from an article to be molded thereabout, the improvement comprising: (a) forming a negative impression, of a shaped object of which reproduction is desired, in a first hardenable impression material and allowing said material to harden; (b) casting a second hardenable material against said first hardenable material and in the impression therein in a mold and allowing said second hardenable material to partially harden only thereby forming a positive casting; (c) securing .[.a cast.]. .Iadd.said .Iaddend.plastic button on a flat slab, with the side of said button having said aperture disposed against said slab; (d) depositing and manually shaping a third hardenable impression material about said button and against said slab to completely cover exposed portions of said button; (e) inverting said mold and disposing partially hardened said second impression material against said third hardenable impression material; (f) mixing abutting portions of said second and third impression materials and manually shaping said materials to a desired configuration and allowing said materials to harden thereby forming a hardened master cast containing a threaded plastic insert; (g) removing said hardened master cast from said slab and inserting said master cast in a mold and casting a fourth hardenable material about said master cast leaving a surface of said button having said aperture exposed and allowing said fourth hardenable material to harden; and (h) threadably engaging a threaded member with threads of said aperture and using said member removing said master cast from hardened said fourth hardenable material. .Iadd. 2. The method of making a master dental cast and duplicating mold therefor comprising the steps of: (a) forming a negative impression of a patient's tooth and gum structure in a suitable impression material contained in a dental impression tray; (b) pouring said negative impression with dental stone or the like to form a positive cast and allowing said stone to partially set; (c) temporarily affixing a plastic button on a flat slab, said button having a threaded recess facing said slab; (d) covering and surrounding said button on the slab with additional dental stone in the unhardened state; (e) inverting said tray and, with said positive cast centered on said threaded recess, joining the partially set dental stone of the positive cast with that on said slab to bond the two together; (f) allowing the dental stone to harden; (g) removing the joined positive cast and additional stone from said slab, and the tray and impression material from the positive cast, leaving a master dental cast having a flat surface with said plastic button embedded therein; (h) pouring a hydrocolloid or the like mold material about said master cast in a duplicating mold, leaving the flat surface of the master dental cast containing said button exposed, and allowing said mold material to set; (i) threading a handle into said button; and (j) holding said flask in one hand and the handle in the other, ejecting said master cast from the set mold material with a quick snap-like straight outward pull. .Iaddend..Iadd. 3. In a master dental cast made of dental stone or the like having on one side a replica of the tooth and gum structure of a patient and having the reverse side a flat surface, the improvement comprising a plastic button embedded in said stone and centrally located relative to said tooth and gum structure, said button having a threaded recess centrally located relative to the tooth and gum structure with the open end of said recess substantially flush with said flat surface, and means for locking said button in the stone. .Iaddend.