Bone and teeth, as anyone who has ever studied them has learned, are mostly mineral. In the case of tooth enamel the mineral content is more than 99 percent and in the case of bone the figure is 65 percent. The mineral, called hydroxyapatite, is also found in the earth's crust; and when mined, the processed result is a white powder. For years researchers have been trying to form this powder into artificial bone and teeth, but with only limited success.
Recently, though, a University of Texas chemist, Richard Lagow, has synthesized hydroxyapatite in forms that are virtually identical to bone and teeth. Tests so far have been very encouraging, and the day may soon come when orthopedic surgeons make bones to order and dentists put in false teeth that, to the body, aren't false at all.
A Tooth for a Tooth
Lagow originally started working work hydroxyapatite in the early 1970s, while he was on the faculty at MIT. An undergraduate student of his was interested in becoming a research physician and Lagow came up with a project for him: the synthesis of tooth enamel. Lagow recalls, "Our goal at that time was to be able to fill cavities with tooth enamel. Nothing to do with bone."
The student must have gotten a passing grade because he produced what was essentially tooth enamel. There were only a few small problems. One was the size of the tooth-like piece that could be manufactured. "We were successful then, but we could only make things as big as a pearl," says Lagow. A second problem was in the temperature required: too high to be used on the inside of someone's mouth.
Lagow left MIT in 1976 and came to the University of Texas. He brought along with him the synthetic tooth enamel process, but it languished until 1980. Then another of Lagow's students, Paul J. Capano, took up the task. Several years later, the result was a 1,200-page doctoral thesis - and the ability to synthesize large chunks of hydroxyapatite. Capano - now at Dow Chemical - and Lagow formed a research team with two others: Dr. Ed Farris, a Dallas dentist, and Dr. J.L. Matthews, executive director of the Baylor Medical Research Foundation in Dallas. The group investigated the use of this bone substitute, and their initial results were announced in 1987, although studies still continue.
Why did Lagow's team succeed where others failed? Lagow cities two main reasons. First, no one realized how important and successful bones and teeth made out of pure hydroxyapatite would be. Lagow says, "I think that anybody that would have recognized that and was willing to put in a lot of time could do the same thing we did."
The second reason lies in the composition and character of hydroxyapatite itself. Bone substitutes fall under the heading of bioceramics, and most researchers in the field, naturally, are ceramicists. And just as naturally, standard ceramic techniques have been employed in research with the hydroxyapatite: The material being worked on is heated up and pressed together. Hydroxyapatite, a complex calcium phosphate, unfortunately, is inert up to a high temperature and then decomposes - part of the molecule breaks off and escapes as steam. A fraction of what results is water soluble, and the rest is spongy, sticky, and extremely weak. In the past an additive,
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