368 Theories and techniques of oral implantology

Fig. 9-111. Internally threaded implants were then "hand-ratcheted" into the bone. (From Linkow, L. I.: Internally threaded endosseous implants, Dent. Concepts 10:16-20, 1967.)

Fig. 9-112. The plaster index with the gold copings and duplicate implant shafts is seen, as well as the wax inter-occlusal record of centric relation.

index should include the three gold copings, the copper rods, and the duplicate shafts [Fig. 9-112].) A master stone model was poured into the plaster index. After it hardened, it was articulated with the model of the opposing jaw (Fig. 9-113). Two integral units—the mesostructure and the superstructure—were fabricated from the master stone model.

The mesostructure was constructed as two separate units, one for each side of the jaw. Thus, if an implant in the left quadrant, for example, became troublesome, the operator needed to remove only the mesostructure on the involved side. Each mesostruc-

Fig. 9-113. The master stone model. (From Linkow, L. I.: Internally threaded endosseous implants, Dent. Concepts 10:16-20, 1967.)

ture contained two set screws for insertion into the implant shafts and two units to accept the screws of the superstructure (Fig. 9-114) .

To fabricate the mesostructure, the set screws were partially inserted in the duplicate hollow-threaded implant shafts, leaving a good portion of the screw sticking out of the shaft. The amount of protrusion desired was determined by occlusal clearance there should be at least 2 mm. between the heads of the screws and the occlusal surfaces of the opposing teeth. When the height of the screws had been adjusted, a wax-up of the mesostructure was accomplished. The wax was built up to a proper bulk, with no undercuts around the set screws. The wax-up also contained at least four sets of internal threading to accept the set screws of the superstructure and thus stabilize it. These threaded units were made separately. Hollow-threaded shafts that were duplicates of the implant shafts were fabricated with the line angles of their shafts undercut with a carborundum disk. The separate shafts were then placed strategically in the wax mesostructure, and wax was built up around them. The wax-up was then sprued, invested, and cast. The duplicated shafts were locked permanently into position in the gold casting.

The cast mesostructure was then tried on the master model (Fig. 9-115). It included the four set screws for insertion into the implant shafts and four threaded shafts to accept the superstructure's screws.

The superstructure was fabricated as a full arch splint, a restoration that reduced the buccolingual movements of the teeth and implants more than any other type of prosthesis.