The evolution of dental implants 171

Fig. 5-72. Weinberg's subperiosteal implant is a latticed framework that straddles the jaw. A, The implant before placement; B, the implant in place, straddling the crest of the maxilla and lying under the periosteum. (From Weinberg, W. D.: Subperiosteal implantation of a Vitallium artificial abutment, J.A.D.A. 40 [5] :549, 1950. Copyright American Dental Association. Reprinted by permission.)

Fig. 5-73. Other Weinberg implants were constructed by eliminating the four uprights and adding solid posts to the implant, simplifying suturing around the posts.

secure. The danger of its being moved on its axis, which is quite possible with the screw post implant, is minimized by the extreme width of the implant. Because it makes its own site as it is tapped in, it is immediately stable.

A 2-year follow-up is extremely promising so far, and indications are that the blade will become very popular because of its design, adaptability, and ease of insertion. Linkow now prefers its over all other implant designs and uses it whenever the site's anatomy permits.

SUBPERIOSTEAL IMPLANTS

One of the greatest difficulties with subperiosteal implants has been deciding when and where to use

them. An implant designed to be set over bone must be used only when the alveolar bone has greatly re-sorbed so that there is very little left between the superior and inferior cortical plates. While alveolar bone is a highly active type of bone relying upon the natural stimulation provided by Sharpey's fibers or the substitute stimulation provided by a false periodontal membrane, the dense cortical bone is relatively inactive. Its stimulation comes primarily from the muscles for which it serves as an attachment site. As long as the extensions of the implant rest mainly on dense cortical bone, the little remaining basal and cortical bone stay relatively unchanged.

Because the resorption of alveolar bone leaves the mandibular canal close to, if not right at, the crest of the mandible, great care must be taken in designing a subperiosteal implant to take stress off the crest and to divert it around the flanks of the implant. The flanks also help secure the implant against side-to-side movements of the jaws.

Whereas the endosseous implant is held secure by healed bone, only the healed soft tissues of the mouth lie over the subperiosteal implant. This means that the way in which the implant is fitted to the bone must provide the means of preventing dislodgment from normal movements of the mouth. The evolution of the subperiosteal implant is thus the story of trying to shape some kind of frame that will fit the jaw closely enough to prevent movement, yet be painless to the wearer.

One of the earliest designers of a subperiosteal implant was the Swedish practitioner Gustav Dahl,