The evolution of dental implants 195

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homoaital transplant is alive at the start and remains alive, while the homostatic transplant is progressively revitalized by the recipient tissue.

In recent years, as information has accumulated about all types of organ transplants, interest in trans-planting teeth has revived. Chronologically, the most important animal experiments in tooth transplantation have been undertaken by Huggins on dogs (1934) ; Sutro on cats (1939) ; Lapshinsky on cats and dogs (1940) ; Hahn on dogs (1941) ; Willfane on rats (1942) ; Shapiro on cats (1945) ; Avery on salamanders (1950) ; Fleming on guinea pigs (1952); Sata on rabbits (1955); Agnew on monkeys (1955) ; and Cserepfalvi on dogs (1955). Trans-plantation of teeth in humans has been reported by Pafford (1955) , Hale (1956) , and Apfel (1956) .

Cserepfalvi's reports on successful transplantation of human teeth are of interest. His donor teeth were extracted from young children to facilitate orthodontic treatment. According to Cserepfalvi, the success of his method depends on several factors. The tooth to be utilized, while unerupted or even partially erupted, must be in the stage of development in which the root structure is still only partially formed. The tooth sac must be uninjured during removal and used immediately or stored at 2° C. in Hank's balanced salt solution or another suitable medium for not more than 20 days.

When considering the suitability of a site, the operator must determine that the socket is deep enough to permit firm contact between the trans-planted tooth and the bone wall and that the surface of the socket is smooth and free from blood clots. Undue strain on the tooth must be avoided for a period of 3 weeks after transplantation.

Successful results are enhanced by careful surgical technique and careful handling of the transplant. Fortunately, in homotransplantation of teeth the blood group, Rh factor, tissue incompatibility, or immunobiologic reactions play an insignificant role.

In reports published in 1923 and 1925, Haas called attention to the fact that after clinical death the various cells and tissues of some organs would subsist for a limited period of time. In 1955 and again in 1959, Cserepfalvi suggested that teeth from a recently dead individual might prove valuable for tooth transplant investigations. In his 1955 study he found that the homotransplantation of a tooth obtained from a recently sacrificed dog gave the same result as with a tooth obtained from a living animal. He also observed that there was no significant difference in the healing processes of either type of trans-planted tooth, nor were there significant histologic

differences noted in these transplanted teeth when removed for examination. Further transplantation experiments were conducted with teeth removed from animals sacrificed 6, 9, and 12 hours previously. The results of these experiments were unsatisfactory.

Encouraged by the results obtained by transplanting teeth from freshly sacrificed dogs to live dogs, Cserepfalvi performed the first human tooth trans-plantation using cadaver teeth. None of the four transplanted cadaver teeth was rejected, although they did not become as firmly embedded as teeth transplanted from live subjects.

The problem of tooth sensitivity involved in a transplant procedure has been approached in a number of ways. Some investigators use a fluoride paste on the teeth to desensitize them so that they will be more readily acceptable when transplanted. If and when the nerve inside the transplanted tooth should be removed seems debatable. Some investigators advise removal of the nerve before the tooth is inserted, some have had good results leaving it in-tact, and others recommend removal a week or two after the tooth has been transplanted. No matter which method is preferred, the fate of the transplant follows one of three courses.

First, the transplanted tooth can become ankylosed to the bone, function quite well for a number of years, but eventually fail because of root resorption. The rate of resorption is determined by such factors as the occusal surface hardness of the natural tooth's enamel or of the restoration covering it; the pressure per square inch of the patient's bite; the density of the alveolar bone surrounding the trans-planted tooth; and harmful personal habits, such as clenching the teeth and bruxism.

Second, the tooth may be rejected immediately or within a few weeks or months after transplantation. In this situation the tooth is probably unstable at the onset or loosens soon after its insertion as granulation, and epithelial tissues form between it and the adjacent bone.

Third, the transplanted tooth may be accepted and develop a normal periodontal membrane around its surface with no root resorption.

Tooth reimplantations

Linkow has been performing numerous autogenous tooth reimplantations, which are a form of trans-plantation. The reimplantations are done when a tooth must be extracted because of a large periapical cyst or granuloma, a failure of root canal therapy to clear up an infection, or an inability to perform an apicoectomy without involving the antral floor or