Rinsing away decay; while new inroads in chemical dentistry aren't likely to make the dentist's drill obsolete, they may reduce the need for drilling and even more serious dental work - includes related article on saliva

Science News, April 19, 1986 by Janet Raloff

But by varying the relative proportions of calcium to phosphate in the remineralizing fluid, he is learning how to target where new apatite is deposited. "When you have high calcium, you remineralize the outer surface of a tooth," he says. "As you start dropping the calcium, you begin remineralizing inside the tooth." Based on these findings, he's already developed a series of calcifying fluids that he says "are very effective at remineralizing lesions."

By using them to fill in a lesion's swisscheese-like holes, people should be able to repair caries naturally, he says, before the decay develops into a full-fledged cavity. Silverstone suspects that these fluids ultimately will be marketed as mouth rinses in a range of formulations, each designed to tackle decay from a different cause or in a different type of tissue -- for example, in tooth enamel, or in root tissue. Similar work is under way at the University of Iowa's Dows Institute in Iowa City.

The remineralizing rinse being developed at the University of Rochester (N.Y.) contains, in addition to the standard calcium, phosphate and fluoride, several additives to enhance the transport of the remineralizing chemicals through the enamel, which acts as a molecular sieve. One of the additives, strontium, reduces the solubility of apatite and tooth enamel, particularly when delivered in conjunction with fluoride, says John Featherstone, who chairs the oral biology department at the university's Eastman Dental Center. And tartrate, his studies indicate, enhances the transport of calcium through the enamel to buried carious lesions.

In 14-day tests, he reports, a rinse with these additives rehardened the deepseated carious lesions Featherstone and his colleagues had initiated in human tooth enamel. In one preliminary test of its ability to work under real-world conditions, the researchers embedded tiny test slabs of enamel into temporary dental bridges worn by subjects for two weeks. A one-minute-per-day swish of the rinse through the teeth reduced the depth of the buried caries 25 percent more than did saliva exposure alone in similar, artificially developed lesions.

The most widely used of the synthetic-saliva remineralizing solutions was developed about 15 years ago at the University of Rochester by dental pathologist Erling Johansen and chemist Thor O. Olsen. Previously, they had found that certain mineral crystals appeared to survive -- even grow -- in the acid environment of active caries. Chemical analysis of these crystals showed their fluoride content to be 20-to 30-fold higher than that of normal tooth materials.

"I realized that if I could change the normal crystals to the same chemistry as those observed in the carious lesions, they should have the same cariostatic (properties)," recalls Johansen, now dean of the Tufts School of Dental Medicine in Boston. And the fluoride-and-mouth-rinse treatment that he and colleagues have now used on more than 1,500 persons is designed to do just that.