Stannous Fluoride

OVERVIEW

Stannous fluoride (STAN-us FLOR-ide) is a lustrous, white crystalline solid with a salty and bitter taste. The only application of any consequence for stannous fluoride is as an additive in toothpastes. Its function is to strengthen tooth enamel and reduce the rate of tooth decay.

KEY FACTS

OTHER NAMES:

Tin(II) fluoride; tin difluoride

FORMULA:

SnF₂

ELEMENTS:

Tin, fluorine

COMPOUND TYPE:

Binary salt (inorganic)

STATE:

Solid

MOLECULAR WEIGHT:

156.71 g/mol

MELTING POINT:

213°C (415°F)

BOILING POINT:

850°C (1560°F)

SOLUBILITY:

Soluble in water; insoluble in ethyl alcohol, ether, and chloroform

The first hints that fluorides might be helpful in preventing tooth decay were reported as early as 1901. Fluorides are binary compounds of the element fluorine, compounds containing one element other than fluorine. Sodium fluoride (NaF), potassium fluoride (KF), and stannous fluoride are typical fluorides. But solid scientific evidence for the role of fluorides in preventing tooth decay was not available until the 1940s. Even then, the idea of adding fluorides to toothpastes to reduce the risk of tooth decade was hampered by researchers' inability to find suitable fluoride compounds to use for this purpose. One research team working on this problem was that of Joseph C. Muhler (1923–1996), then an undergraduate student at Indiana University, and one of his instructors, Harry G. Day (1906–). Muhler and Day discovered that stannous fluoride was significantly more effective at preventing cavities than other fluorides they had tested. Furthermore, the compound could be incorporated into toothpastes without affecting their other properties. Their first research paper on the subject was published in 1950. The information discovered by Muhler and Day was sold to the Proctor & Gamble company, which released the first toothpaste containing stannous fluoride—Crest®—in 1955.

HOW IT IS MADE

Stannous fluoride is made commercially by reacting stannous oxide (SnO) with hydrofluoric acid (H₂F₂) in an oxygenfree environment.

COMMON USES AND POTENTIAL HAZARDS

The primary use of stannous fluoride is in toothpastes, dental rinses, and fluoride treatments for teeth. Fluorides prevent tooth decay in two ways. First, fluorides kill bacteria that cause tooth decay. Second, fluorides react with other chemicals in the mouth to make new enamel to replace enamel destroyed by bacteria or worn away by mechanical processes. Studies suggest that stannous fluoride also has other beneficial effects, including preventing gingivitis (inflammation of the gums) and bad breath.

Stannous fluoride does have some disadvantages as an additive in tooth care products. For example, it has a somewhat bitter and unpleasant taste. Today, a number of alternatives have been developed for stannous fluoride as an additive in dental products. The most successful of these alternatives is sodium monofluorophosphate (MFP), which is now the most popular anti-decay additive in toothpastes. Some research suggests that another compound, stannous hexafluorozirconate, may be even more effective than either stannous fluoride or MFP as a decay preventive compound.

Stannous fluoride is a classic example of a compound that must be used in moderation. In small concentrations, it appears to be completely safe for human uses. In larger doses, it may have some health risks. For example, in concentrations of more than two parts per million, stannous fluoride (and other fluorides) may causes fluorosis, a mottling (brownish coloring) of the teeth and changes in bone composition. Individuals who work with pure stannous fluoride may also be at risk from exposure to its powder or dust. It is an irritant and may cause inflammation of the skin, eyes, or respiratory system. Symptoms may include coughing, wheezing, and shortness of breath. These effects do not occur, however, at the level at which stannous fluoride occurs in tooth care products.

Interesting Facts

• The effects of fluorides in preventing tooth decay were first observed by a young dentist named Frederick S. McKay in Colorado Springs, Colorado, in 1901. McKay noticed that many of his patients had unattractive brown stains on their teeth. But the rate of tooth decay among these patients was very low. He concluded that both the brown stains and the low rate of tooth decay were caused by unusually high levels of fluorides in the local water supply.

FOR FURTHER INFORMATION

"How Crest Made Business History." Working Knowledge, Harvard Business School. http://hbswk.hbs.edu/item.jhtml?id=4574&t=bizhistory (accessed on November 15, 2005).

McCoy, Mike. "What's That Stuff: Fluoride." http://pubs.acs.org/cen/whatstuff/stuff/7916sci4.html (accessed on November 15, 2005).

"Stannous Fluoride." International Programme for Chemical Safety. http://www.intox.org/databank/documents/chemical/stanflur/eics0860.htm (accessed on November 15, 2005).

Walter, Patricia A. "Dental Hypersensitivity: A Review." The Journal of Contemporary Dental Practice (May 15, 2005): 107-117.

See AlsoSodium Fluoride