The evolution of dental implants 189

Ring inserts

Another type of retainer relying on implants em-bedded in the mucosa is that of John E. Brennan, which was filed in the U. S. Patent Office in 1952 (Fig. 5-108). Because of the complexity of relating the variety and number of interlocking parts, it is doubtful that many such implants were successful.

Supraplants

The supraplant—or superplant—was introduced by Dahl in 1951 and has been extensively used by Lennart Izikowitz of Sweden. It is a fixed extension saddle denture used primarily in posteriorly free-end saddle areas. The anterior portion fits over prepared abutment teeth, and a metal saddle bearing the restorations rests on the soft tissue covering the alveolar crest over the edentulous area. A bar extends from the posterior portion of the metal saddle; this is implanted under the mucosa to stabilize the free end of the bridge (Fig. 5-109).

The supraplant is indicated when the patient can-not tolerate a removable appliance or when it is impossible to utilize a conventional fixed partial denture. It is also practical when the alveolar bone is not high enough for an endosseous implant. The saddle of a supraplant is also sometimes used to bridge the gap between two teeth with a large edentulous span between them. If the prognosis is doubtful for the posterior abutment, it may be extracted and the saddle extended and modified to a free-end supraplant. The supraplant is also sometimes used to replace cantilevered bridges in order to reduce the torque action caused by the hanging pontic on the anterior abutment or abutments.

The supraplant has several advantages over conventional appliances and, in certain situations, over subperiosteal implants. Experimental studies by Dahl have indicated that movement of the natural tooth abutment roots is less pronounced when supraplants are used instead of removable prostheses. The rigidity of the supraplant also proved mechanically superior to that of a removable prosthesis with a stress-distributing attachment.

One main advantage of a supraplant over a subperiosteal implant is that a large span of missing teeth can be replaced with a fixed extension saddle denture; this procedure involves only very minor surgery. Still another point in its favor is that the supra-plant can be inserted much sooner after an extraction than can a subperiosteal implant. Also, a supra-plant can be used where the mucosa is very thin, a situation that sometimes contraindicates a subperios-

teal implant. Unlike the subperiosteal implant (for which removal is a complicated procedure) the supraplant is easy to move and reinsert if it should fracture. Because the extension included in a supra-plant bears on the bone only indirectly, the risk of resorption is negligible (Fig. 5-110).

The supraplant is unsuitable for hypochondriacs or for patients with poor oral hygiene, as are all implants. It is also contraindicated in cases where there have been recent extractions in the intended saddle areas. A 6-month healing period is advised, although the operation can be performed after 3 months in some cases. Flabby, hypertrophied ridges can present problems and, until the excess mucoperiosteal tissue is removed surgically and the site again reviewed, the procedure should not be under-taken. Major parafunctions of the masticatory muscles may also contraindicate the use of supraplants. Severely mobile natural tooth abutments can also preclude use of the supraplant if splinting of the loose teeth is not practical.

In 1959 and 1960, Izikowitz performed clinical, radiologic, and histologic studies to assess the clinical value of the supraplant. Although his results were most encouraging, he had certain reservations. Be-cause of the fixed saddles, the patient must adhere to a strict oral hygenic routine and must be recalled every 3 or 4 months to check for any tissue damage caused by the saddles. Also, and this is vital from the beginning, the peripheral borders of the saddle must be smooth and rounded to ensure maximum success of the prosthesis.

Magnetic implants

In certain situations, conventional dentures incorporating magnets that are attracted to magnets buried in the mandibular bone have been successful. Early reports of this type of procedure came in the 1950's from Mossdorf, the Frenchman Donday, and the American Stanley J. Behrman. Behrman pre-pared cavities in the bone in the area of the first and second mandibular molars on both sides of the arch to accommodate magnetized chrome-cobalt alloy implants covered by a tantalum mesh (Fig. 5-111). To attract the denture to the buried magnets, Behrman processed magnets either inside the acrylic teeth or inside the denture itself. In this manner, the attraction between the two sets of magnets helped hold the denture to the mucosal tissue.

Properly fitted, the magnetic implants may last many years, and Behrman has reported excellent results (Fig. 5-112). However, certain definite dis-