Clinical uses of rubber impression materials and electroforming of casts and dies in pure silver

Abstract

DIGEST OF THE LITERATURE pertaining to the physical properties of the rubber impression materials shows agreement among the investigators as to its accuracy, dimensional stability, and ability to recover after deformation in removal from severe undercuts. The research of Skinner and Cooper,1 Jorgensen,” Rosenteil, Fairhurst and others,’ and the Thiokol Chemical Corporation” confirms the belief of the author that the synthetic rubber base is a desirable impression.material which possesses qualities equal to those of the hydrocolloids. Variables inherent to the hydrocolloids are not found in the synthetic rubber impression materials which may lay claim to some valuable properties of their own. Notable among them is the surface density and fine detail imparted to stone casts and individual dies recovered from such impressions. Casts and dies need not be processed immediately as in the case of the hydrocolloids but may be poured at a convenient time. The rubber base neither gives up nor takes water from the hydrocal material during setting. This property results in an extremely accurate cast that exhibits a harder surface than casts poured in the hydrocolloid impressions. The ability of the Thiokol base synthetic rubber material to take a plate of pure silver to electroform casts and dies enhances it as an impression material for most prosthodontic procedures, including the making of individual crowns and inlays of either gold or porcelain. A comparison of electroformed silver with stone dies for processing inlays favors the metal type of die because of the better marginal definition, strength, ease of waxing, and finishing. The detail and accuracy of the silver dies produced by electrodeposition over rubber impressions is unsurpassed. Undercuts that have not been eliminated in the preparation are faithfully reproduced in the impression and die and, if they are not recognized and eliminated in the wax-up, they will prevent the precise seating of the crown or inlay. The circular gouging by diamond and cross-cut cylindrical instruments in the preparation of parallel walls constitutes small but precise undercuts that may prevent the proper seating of the casting. Attention to detail in the elimination of undercuts and other shortcomings in our preparations will be rewarding in the satisfaction one receives from the production of superior restorations. The rubber base material may be used for impressions in most clinical and laboratory procedures where hydrocolloid, alginate, modeling compound, or zinc oxide and eugenol pastes have been the materials of choice. For single and multiple inlays and crowns, multiple abutments for fixed and removable partial dentures, and for complete dentures, this versatile material may be used for the production of