Stannous Fluoride Blocks Tooth Decay American Dental Association okays Procter & Gamble's SnF2-containing toothpaste as useful caries preventive agent Procter & Gamble's basic research into the chemistry of tooth decay and its prevention resulted in a top honor this week: The American Dental Association has recognized P&G's Crest toothpaste, which contains stannous fluoride ( S n F 2 ) , as an effective decay preventing agent. Underlying ADA's blessing is P&G's extensive work in the chemical mechanisms of tooth decay and how stannous fluoride acts to slow it down. These data on tooth decay, developed at P&G's Miami Valley laboratories near Cincinnati, have led directly to Crest and its impressive performance over an eight-year clinical program. Carried out by various university dental schools and state health agencies, the clinical tests show that a regular Crest brushing regimen reduces caries formation by from 21 to 57%, compared with control groups. The relatively broad range is due to the varying conditions under which each test was carried out. Crest is the first dentifrice to get such approval from the dental group's Council on Dental Therapeutics.
ADA cautions, however, that the toothpaste is not a cure-all and isn't a substitute for water fluoridation. Beneficial effects of fluoridation, brushing with the stannous fluoride dentifrices and topical application (by a dentist ) of fluoride compounds may be additive, ADA notes. SnF2 Activity Shown. Stannous fluoride came to P&G's attention soon after scientists at Indiana University discovered that the compound inhibits caries. P&G chemists began working to learn why. Along with the tin compound, sodium fluoride was also considered as a possibility. But it was soon rejected, as it isn't as effective as stannous fluoride, says Dr. William J. Griebstein, head of P&G's basic dental research. Alongside the studies on stannous fluoride's mechanism in stopping or delaying tooth decay, P&G chemists began to come up with data showing what's behind tooth decay itself. Acid attack on tooth enamel is the most important factor in early stages of caries formation, Dr. Griebstein says. P&G chemists found that the
SPECIAL SAW SECTIONS TEETH. Procter & Gamble designed this saw to section teeth as thin as 25 to 35 microns. Stained sections showed that teeth start to decay by demineraiization
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reaction rates of acid with enamel are nothing unusual; they obey all the known laws of kinetics. So much so, in fact, that caries were induced in isolated teeth in the Miami Valley laboratory. The acidic buffer system used for in vitro caries formation is sodium lactate plus lactic acid, together with a water soluble organic compound of high molecular weight ( agar or gelatin, for example ). The sodium lactate-lactic acid buffer is similar to what exists in the human mouth, and a lab-induced cavity forms in the same way that natural decay does. Source of the acid system in natural decay is the bacterial coating (plaque) on teeth. Progress of decay in the lab teeth (furnished by dentists) is followed by sectioning a tooth on a specially designed saw. The sections, about 30 microns thick, are appropriately stained and studied under a light microscope. Observed by this technique: The first stage of decay begins in the enamel just below the surface of the tooth, rather than at the surface as had been generally thought.
SECTION SHOWS LESION. Carious lesion in thin section, cut with the saw at left and stained with acid, extends along a crack down through enamel into the dentin. Magnification: 200X
Staining of the sections shows that decay begins as a demineralization inside the enamel. Enamel is almost completely hydroxyapatite (containing calcium and phosphorus in a 1.67:1 molar ratio), with a small (about 1%) amount of protein. During demineralization, calcium and phosphate ions are freed. Cause of the demineralization, says Dr. Griebstein, is apparently the diffusion of hydrogen ions and undissociated lactic acid past the enamel surface into the area just beneath it. The calcium and phosphate ions freed by the acid's action probably diffuse outward. Demineralization progresses downward into the tooth's dentin, as well as outward until it breaks through the surface. Then bacteria enter the cavity, and full-blown decay is under way. The early stages of demineralization in a tooth (too early for a dentist's attention) are P&G's area of interest. The affected areas appear white and are dubbed "white spots." Stannous Fluoride Forms Layer. Using electron microscopy techniques, the dental research team found that a hard layer exists on sound, stannous fluoride-treated teeth. Dr. Griebstein's group believes that the coating consists of one or more tin phosphates (probably including tin hydroxyapatite), calcium fluoride, tin oxide, and perhaps other materials. This layer prevents acid diffusion through the enamel. But the surprising find is stannous fluoride's action when white spots have already formed or during the early stage of decay. Stannous and fluoride ions diffuse past the enamel's surface and into the white spots, in addition to forming the outside layer. In these cases, tin concentration is heavy on the surface, low in the area between the surface and white spot, and again heavy within the demineralized area. Fluoride concentration, too, is high on the surface, then diminishes inside the tooth. This behavior of the stannous fluoride, says Dr. Griebstein, probably stops or slows down the demineralization process. In this way, decay is halted or slowed even after it has actually started. Just why the tin compound behaves this way is now being looked into. Other research projects under way include the nature of the bacterial plaque on teeth, and investigating other compounds which may behave as well as, or even better than, stannous fluoride.
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