Feb. 18 (UPI) -- Fluoride helps prevent tooth day -- but too much of it can actually negatively affect oral hygiene, a new analysis has suggested.
In findings published Tuesday in Science Signaling, researchers have expanded their understanding of how a condition called fluorosis develops.
Fluorosis, or over-exposure to fluoride in childhood, can result in damage to tooth enamel, the coating that protects teeth from chemicals in food and drinks that cause decay and, ultimately, cavities.
In general, the risk for fluoride over-exposure in the United Stats "is low because water fluoridation is controlled and in some regions is in fact de-fluoridated because the naturally available water can contain high levels of fluoride," study co-author Rodrigo Lacruz, associate professor of basic science and craniofacial biology at New York University College of Dentistry, told UPI.
He added, however, that "consumers should make sure they follow the recommendations established by health organizations and dental professionals because when used under these guidelines, fluoride has many positive effects."
Fluoride, often a main ingredient in toothpastes, works to prevent cavities by promoting "mineralization" -- which causes the residual chemicals in food and drinks that remain on teeth to break down, preventing decay -- and making the enamel on teeth more resistant to acid.
As Lacruz noted, the mineral is added to drinking water in the United States and elsewhere, but usually at controlled levels -- typically targeted to 0.7 milligrams per liter, as recommended by the federal Public Health Service.
While low levels of fluoride are beneficial, too much of the mineral can cause fluorosis, a discoloring -- usually yellowing -- of the tooth enamel. The condition occurs when children between birth and around nine years of age -- the age at which teeth are forming -- are exposed to high levels fluoride.
According to the U.S. Centers for Disease Control and Prevention, approximately one in four Americans between 6 and 49 years of age has some degree of fluorosis.
Lacruz and his colleagues analyzed the effects of exposing tooth enamel cells taken from rodents to fluoride at levels on the higher end of the range found in most American drinking water -- 1.2 milligrams per liter and above. The levels they used matched those found in areas where fluorosis is more common.
In general, the researchers report that exposing enamel cells to higher amounts of fluoride disrupted their ability to take in and store calcium, which is necessary to strengthen teeth and bones. The researchers also noted that excessive fluoride slows the development of enamel cells, adversely affecting enamel's ability to rejuvenate and strengthen itself.
The researchers repeated their experiment using early-stage kidney cells from humans, but they did not observe the same effects when kidney cells were exposed to fluoride. This indicates that enamel cells are different from cells forming tissue in other parts of the body, they said.
"More research should be encouraged on how dental enamel cells handle high fluoride and how do they differ from other cells of the body in coping with the stresses imposed by fluoride as fluoridation is so common," Lacruz said.
In the meantime, he added, "parents should monitor the amount of fluoridated toothpaste used by young children and not let them swallow toothpaste when brushing teeth. Dispensing toothpaste in a transverse fashion rather than along the length of the toothbrush helps, but a pea size amount of toothpaste is what should be aimed for in children."