Enamel fluoride

Bacteria on the surface of our teeth metabolize sugars to produce lactic acid, which lowers the pH enough to slowly dissolve tooth enamel. Fluoride inhibits tooth decay because it forms fluorapatite, Cal0(PO4)6F2, which is more acid resistant than hydroxyapatite. 

Fluoride is tenaciously held by the inorganic phase of enamel. In solution at concentrations of less than 100 ppm it replaces hydroxyl ions in the apatite lattice, which is partially converted to fluorapatite. Above this level a second phase of calcium fluoride is formed. These substances have been demonstrated, both in vitro and on the enamel surface where the concentration of fluoride is highest, to be for practical purposes less soluble in slightly acid solutions than is unsubstituted hydroxyapatite. Fluoride likewise becomes concentrated in regions of local demineralization such as enamel defects and areas of incipient caries. Here it replaces hydroxyl ions on the surface of damaged hydroxyapatite crystals, the fluorapatite surface so formed being less vulnerable to further acid attack than if it had remained as hydroxyapatite. Thus in both healthy and carious enamel, fluoride effectively decreases solubility and promotes remineralization of the inorganic phase. 

A fluorinated surfactant in toothpastes containing potassium fluoride enhances fluoroapatite formation and inhibits caries [204]. A fluorinated surfactant formulation (1% Lodyne S-110), which consists of an amphoteric fluoroalky-laminocarboxylic acid and a nonionic fluoroalkylamide synergist, in the toothpaste increases enamel-fluoride interactions. A fluorinated surfactant in pharmaceutical formulations and in toothpaste must be nontoxic for the intended purpose. 

The presence of fluorine as a soluble fluoride in drinking water to the extent of 2 ppm may cause mottled enamel in teeth, when used by children acquiring permanent teeth in smaller amounts, however, fluorides are added to water supplies to prevent dental cavities. 

Fluoridation of potable water suppHes for the prevention of dental caries is one of the principal uses for sodium fluoride (see Water, municipal WATER treatment). Use rate for this appHcation is on the order of 0.7 to 1.0 mg/L of water as fluoride or 1.5 to 2.2 mg/L as NaF (2). NaF is also appHed topically to teeth as a 2% solution (see Dentifrices). Other uses are as a flux for deoxidiziag (degassiag) rimmed steel (qv), and ia the resmelting of aluminum. NaF is also used ia the manufacture of vitreous enamels, ia pickling stainless steel, ia wood preservation compounds, caseia glues, ia the manufacture of coated papers, ia heat-treating salts, and as a component of laundry sours. 

Fluorides. Most woddwide reductions in dental decay can be ascribed to fluoride incorporation into drinking water, dentifrices, and mouth rinses. Numerous mechanisms have been described by which fluoride exerts a beneficial effect. Fluoride either reacts with tooth enamel to reduce its susceptibihty to dissolution in bacterial acids or interferes with the production of acid by bacterial within dental plaque. The multiple modes of action with fluoride may account for its remarkable effectiveness at concentrations far below those necessary with most therapeutic materials. Fluoride release from restorative dental materials foUow the same basic pattern. Fluoride is released in an initial short burst after placement of the material, and decreases rapidly to a low level of constant release. The constant low level release has been postulated to provide tooth protection by incorporation into tooth mineral. 

The addition of therapeutic or cosmetic agents to dentifrices has paralleled advances in knowledge about factors affecting the human dentition. Agents added to dentifrices can act directly on the host tooth stmcture or on specific oral accumulations, for example, the principal action of fluoride is on the tooth enamel. The primary action of an abrasive, however, is on an accumulated stained pellicle. Oral accumulations of interest to preventive dentistry are dental pellicles, dental plaque, dental calculus (tartar), microbial populations responsible for oral malodor, and oral debris (food residues, leukocytes, etc). Plaque is most important because of its potential to do harm. 

Fluorinated polymers stand out sharply against other construction materials for their excellent corrosion resistance and high-temperature stability. In this respect they are not only superior to other plastics but also to platinum, gold, glass, enamel and special alloys. The fluorinated plastics used in process plants are polytetrafluorethylene (PTFE), fluorinated ethylene/ propylene (FEP), polytrifiuoromonochlorethylene (PTFCE) and polyvinyl fluoride (PVF). They are much more expensive than other polymers and so are only economical in special situations [59]. 

Stannous fluoride is used in toothpastes and dental rinses to protect tooth enamel from attack by bacteria—cavities (also known as dental caries). It was the first fluoride used for that purpose, in the toothpaste Crest. 

The addition of fluoride ions to domestic water supplies (in the form of NaF) is now widespread and has resulted in a dramatic decrease in dental cavities. Fluoridated toothpastes, containing either tin(II) fluoride or sodium monofluorophos-phate (MFP, Na2FP03), are also recommended to strengthen tooth enamel. 

C04-0008.Tooth enamel consists, in part, of CajfPOq)] (OH). Tin(II) fluoride (toothpaste labels call it... 

Chamberlain Powers, 1976 Jendresen Trowbridge, 1972). The addition of stannous fluoride to the cement increases dissolution, but this is an advantage rather than a disadvantage, for the fluoride released is taken up by neighbouring enamel (Bitner Weir, 1973). 

The most important modification of these materials was the discovery of the effect of adding stannous fluoride (Foster Dovey, 1974, 1976). Originally added to provide fluoride release, it was found to improve the mixing qualities of the cement and to increase strength by about 50 %. This is reflected also in improved adhesion to enamel and dentine (Section 5.7.4). 

Glass polyalkenoate cement has a unique combination of properties. It adheres to tooth material and base metals. It releases fluoride over a long period and is a cariostat. In addition it is translucent and so can be colour-matched to enamel. New clinical techniques have been devised to exploit the unique characteristics of the material. 

Bitner, T. J. Weir, S. H. (1973). Fluoride uptake and acid solubility of enamel exposed to carboxylate cement containing MFP. Journal of Dental Research, 52, 157-62. 

Shimoke, H., Komatsu, H. Matsui, I. (1987). Fluoride content in human enamel after removal of the applied glass ionomer cement. Journal of Dental Research, 66, Special Issue 131, Abstract No. 196. 

Thornton, J. B., Retief, D. H. Bradley, E. L. (1986). Fluoride release from and tensile bond strength of Ketac-Fil and Ketac-Silver to enamel and dentine. Dental Materials, 2, 241-5. 

It is superior to the zinc phosphate cement for bonding orthodontic bands to teeth (Clark, Phillips Norman, 1977). It has greater durability and there is less decalcification in adjacent tooth enamel. This latter beneficial effect must arise from the release of fluoride which is absorbed by the enamel, so protecting it in a clinical situation where caries-produdng debris and plaque accumulate. 

Hallsworth, A. S. Weatherall, J. A. (1969). The microdistribution, uptake and loss of fluoride in human enamel. Caries Research, 3, 109-18. 

Wei, S. H. Y. Sierk, D. L. (1971). Fluoride uptake by enamel from zinc phosphate cement containing stannous fluoride. Journal of the American Dental Association, 83, 621—4. 

Stannous fluoride, a compound of tin and fluorine, is much less dangerous. It is added to drinking water and toothpaste to strengthen the enamel in the teeth of the user. Another compound of fluorine is teflon, a plastic made of carbon and fluorine, which is used in kitchenware. The fluorine-containing compound freon is used in air-conditioners and refrigerators, and is harmless. 

CCP in milk is mentioned in connection with casein above (Section VI.C). Fluorapatite is a major constituent of phosphate rocks, and a constituent, probably important, of human tooth enamel for those whose drinking water contains significant amounts of naturally occurring or added fluoride. Fluorapatite is significantly less soluble than hydroxyapatite - the relationship between the solubilities of fluorapatite and hydroxyapatite parallels (but is much less extreme than) that between calcium fluoride (Ksp — 3.9 x 10 11 mol3 dm-9) and calcium hydroxide (Ksp = 7.9 x 10 6 mol3 dm 9). Calcium diphosphate, Ca2P207, is believed to be the least soluble of the calcium phosphates. 

---