The Limitations of Transplants

Ecuadorian Indians faced up to the problem in the days before Columbus; so did U.S. dentists around the time of the Revolution: if someone had a hole in his jawbone where a tooth had just been extracted, why not fill it with any fresh, healthy-looking tooth that happened to be available? The answer seemed especially logical since many of these transplants apparently worked.

The price paid to donors for front teeth went up to 4 guineas a tooth in New York in 1772. The trouble was that neither the Indians nor the colonial dentists knew anything about immune mechanisms and the rejection of transplants. Most of the transplanted teeth fell out a couple of years later.

Last week scores of dentists met in Manhattan to trade up-to-the-minute data on the feasibility and success of tooth transplants. It soon became apparent that, although they have learned much about rejection mechanisms, they still do not know enough.

Crown & Root. A tooth is not a sim ple cutting or grinding tool, but a complex piece of living matter. The part that shows, which dentists call the crown, is made of bonelike dentine wrapped in an enamel shell. The part that is hidden, which dentists call the root, consists of bonelike materials surrounding the root canal, which is filled with soft tissue, blood vessels and the tooth's nerve.

So much of the tooth seems to be inert that some dental surgeons hoped that a transplant would not set off rejection reactions. They thought it might be possible to graft teeth from one person to another in much the same way as the bloodless cornea of the eye can be grafted, and for essentially the same reasons. Some dentists at last week's meeting claimed successes in person-to-person transplants that have lasted from two to four years. But they had no X rays to show that the roots were still healthy. Soon, their colleagues predicted, the crowns would drop off.

Fact is, concluded Cornell University's Dr. Stanley J. Behrman, teeth are far from immune to the processes of graft rejection. Even their enamel, he said, may touch off an immune reaction. The root is slowly whittled away by scavenger cells in the bloodstream of the tooth's new owner, and is replaced with soft tissue or new bone, which is why the crown eventually falls off.

Wisdom Growth. But all the experts agreed that transplantation of a tooth inside the patient's own mouth is indeed worthwhile. The likeliest occasion for using this technique is when an adolescent or young adult loses one of his first molars (as one in three does) because of decay. Then, if the patient has a "wisdom tooth" that has not yet broken through, or is threatening to become impacted, the dentist removes it and uses it to replace the lost molar. This young, "budding" tooth will take root and grow just like any other tooth, except that it will never develop a nerve connection. Since all the tissues are the patient's own, there is no problem of graft rejection. And the problems of surgical technique have been pretty well solved. Decay in the transplant can be treated as in any other tooth.

Los Angeles' Dr. Harland Apfel has tried six homotransplants (person to person), and all have failed. But he has done 350 autotransplants (with the patients' own teeth), and 97% are now successful. Homotransplants of teeth, with long-term success, will have to await the finding of safer and more effective drugs or new techniques to check the rejection process.

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