How to give teeth a fluoride 'apatite.' (new treatment that is not soluble in saliva)

How to give teeth a fluoride 'apatite'

For 30 years, dentists have been treating teeth topically with fluoride to make them more resistant to cavities. This treatment typically incorporates fluoride into the tooth as calcium fluoride. However, notes American Dental Association (ADA) chemist Laurence Chow, research has shown that because calcium fluoride is soluble in saliva, topically applied fluoride can leach out of treated teeth completely within a week or two and even result in a "net loss of tooth mineral and fluoride." Together with Walter E. Brown, Chow has developed a new treatment that not only makes teeth incorporate more fluoride but also bonds the chemical in a form, known as fluorapatite, that is not soluble in saliva -- features they have demonstrated in humans.

Their chemical treatment is nontoxic, Chow says, and can be delivered much as fluoride is today, as an ingredient in toothpaste, mouth rinses, gels -- even in chewing gum. Chow and Brown, who work at the ADA's Paffenbarger Research Center at the National Bureau of Standards in Gaithersburg, Md., have just received a patent for their treatment. They are awaiting Food and Drug Administration approval of a three-year human study to confirm what they have already shown in animals: that the fluoride they can bind into teeth will translate into fewer cavities.

Their technique involves treating teeth with aqueous solutions or gels that will cause some of the apatite -- a structural mineral in tooth enamel -- to convert into dicalcium phosphate dihydrate, or DCPD. Because it is very unstable, DCPD will react with any fluoride in the mouth -- from toothpaste, water or food. Fluoride picked up by tooth enamel in this reaction is converted back to an apatite. But instead of the previous hydroxy apatite, it's an even more stable mineral, fluorapatite.

The treatment's DCPD-forming compounds do not contain fluoride, Chow points out; they simply make the tooth enamel more reactive so that it will incorporate any fluoride more readily and securely. Moreover, Chow says, "The process is essentially self-limiting. As the tooth becomes richer in fluoride, it no longer responds to the treatment as much," so even daily use should not overfluoridate teeth. But because teeth are constantly demineralizing and remineralizing -- dissolving and laying down new mineral -- the treatment is not permanent, but instead should be part of a regular dental-care program.

Right now, the challenge is to deliver the treatment to the cavity-prone areas--between teeth, along the gum line and in crevices on the grinding surfaces. In addition, Chow says, several researchers are trying to harness the technique's ability to remineralize teeth as a means of repairing teeth in the early stages of decay.