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

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 By JANET RALOFF

It's the ultimate in painless dentistry -- some might even say "natural" dentistry. By harnessing chemical reactions that involve fluoride, calcium and phosphate, researchers are developing new weapons for the war on cavities. A major focus is the development of month rinses that work as synthetic "supersalivas." Generally envisioned as a homebased addition to a regular brushing and flossing regimen, they're being aimed not only at fighting decay but also at strengthening teeth and even repairing developing cavities.

One of the pioneering treatments, based on such a mouth rinse, has been used for more than 10 years in the experimental management of people with otherwise rampant, uncontrollable tooth decay. Other treatments will undergo clinical trials in the next few years. None is expected to put the dentist out of work. In fact, as an adjunct to the mechanical dentistry best symbolized by the pick and drill, these treatments promise to help preserve much of the dentist's handiwork -- from fillings to caps and crowns -- that might otherwise be lost as subsequent decay eroded the teeth onto which these were anchored.

In the mouth, a process of demineralizing and remineralizing -- a dissolving and reforming of tooth mineral -- occurs continually at the surface of teeth. Plaqueforming bacteria, which thrive on the fermentable carbohydrates in food, create weak acids (SN: 3/29/86, p. 203). It's these acids that demineralize teeth. Saliva contains the constituents needed to remineralize them again. Carious lesions, or caries, form when demineralization exceeds remineralization.

In its first stages, a carious lesion does not contain an actual "cavity"; the tooth mineral just becomes more porous and "spongy" as swiss-cheese-like holes begin to form within it. When perforations become too numerous and too large, a hole or cavity forms, or the weakened tooth breaks.

"We have shown over 20 years that wherever one side of a tooth touches another, there's a (carious) lesion," says Leon Silverstone, director of the University of Colorado's Oral Sciences Research Center in Denver. Crowded teeth, therefore, always harbor decay. "In fact," he says, "by the time a lesion is clincally detectable, it may have existed just below the tooth surface for about three years." Using microscopy, he explains, "we have shown that in the typical person there are probably at least 20 lesions that are small but cannot be seen by our best available diagnostic techniques" -- like visual inspection or dental X-rays.

Such findings have convinced Silverstone that dental researchers should give up focusing on the impossible: preventing lesions. He says, "We must instead concentrate on stopping them from growing" into true cavities.

An approach being taken by his lab and several others is to create a mouth rines that outperforms saliva, the body's natural remineralizer. The "calcifying fluids" Silverstone and his colleagues are developing contain a solution of calcium and phosphate, together with a small quantity of fluoride. Calcium and phosphate are the remineralizing constituents of saliva. Flouride serves as a catalyst to speed the preciptation of calcium phosphate -- in the form of a hydroxy apatite -- onto or into teeth.

But that's not fluoride's only role. It is able to inhibit the activity of some bacterial enzymes and their acid-producing processes, and at extremely high concentrations it can also kill some plaque bacteria. Even more important, it tends to become incorporated into the apatite (as a fluoridated hydroxy apatite, or "fluorapatite"), creating a mineral that is actually less dissolvable by acids (SN: 3/8/86, p. 150). And, Silverstone says, because the remineralized fluoridated-apatite crystal will be larger than the crystal it replaces, it will have a smaller surface-to-volume ratio. With a smaller exposed surface, acid erosion -- or dissolution -- becomes a more lengthy process.

In designing a superior remineralizing solution, Silverstone says, the real trick is to tailor its chemistry so that it deposits new apatite crystals where you need them. And that may not be on the tooth surface.

The acid attack that initiates a carious lesion begins the process of decay by dissolving apatite crystals from a tooth surface. Silverstone's research has shown that within a few hours a new layer of hydroxy apatite crystals will form over the initial surface attack. This cover repairs only some of the decay; the rest is buried. Over time, the buried decay will grow as more and more mineral is lost from this "white spot lesion." But its growth is invisible to the dentist, Silverstone says, because the actual tooth surface is hard and apparently healthy. "This is also why it's so difficult to stop a very early cavity," Silverstone points out. "It's covered by a solid, intact surface."