# How does fluoride prevent tooth decay?

Fluoride is a common active ingredient in tooth paste to prevent dental caries. It is also added or removed from the water supply in some communities for the same reason, but in children only.

My understanding is that the fluoride in tooth paste reacts with minerals in saliva then bonds to the tooth enamel. The fluoride in water is ingested and is somehow added to the developing bones and teeth of growing children, to the benefit of making decay resistant teeth.

What is the biochemical pathway of each process? A perfect answer will also discuss fluorosis and when that occurs and why.

Your understanding is correct to some extent. Tooth enamel mostly consists of a mineral called hydroxyapatite ($$ce{Ca_{10}(PO4)6(OH)2}$$) (Staines et al, 1981). Though this makes enamel the strongest material in the body, it is susceptible to degradation. In acidic environment, hyrdoxyapatite gets dissolved and leads to cavities (Brown, p. 688). The reaction is:

$$ce{Ca_{10}(PO4)6(OH)2_{(s)}~+~8~H+_{(aq)} -> 10~Ca^{2+}_{(aq)}~+~6~HPO4^{2-}_{(aq)}~+~2~H2O_{(l)}}$$

To overcome this, fluoride is added in toothpastes. Fluoride ($$ce{F-}$$) reacts with hydroxyapatite of enamel to form fluoroapatite via demineralization and remineralization cycle. The 3 main mechanisms through which it happens are (Rošin-Grget et al, 2013):

1. Iso-ionic exchange of $$ce{F-}$$ for $$ce{OH-}$$ in apatite: $$ce{Ca_{10}(PO4)6(OH)2~+~2~F- -> Ca_{10}(PO4)6F2~+~2~OH-}$$

2. Crystal growth of fluorapatite from a supersaturated solution:

$$ce{10~Ca^{2+ }~+~6~PO4^{3-}~+~2~F- -> Ca_{10}(PO4)6F2}$$

3. Apatite dissolution with $$ce{CaF2}$$ formation:

$$ce{Ca_{10}(PO4)6(OH)2~+~20~F- -> 10~CaF2~+~6~PO4^{3-}~+~2~OH-}$$

Instead of preventing cavities, fluoride just controls the rate of formation of cavities (i.e. it repairs, not prevents, tooth decay), due to which its repeated exposure on enamel throughout the day is important (Cate et al, 2013). However, the effects of fluoride are minimal once it gets swallowed (Ismail et al, 2008).

Talking about fluorosis, the cause behind it is dissolution of hydroxyapatite due to higher concentration of fluoride (see the 3rd point in mechanisms, it requires higher level of fluoride to occur). Apart from this, formation of fluorohydroxyapatite is also a cause of fluorosis, the reaction being:

$$ce{Ca_{10}(PO4)6(OH)2~+~F- ~+~H+ -> Ca_{10}(PO4)6(OH)F + H2O}$$

Dissolution of fluoroapatite causes depletion of enamel layer, causing fluorosis.

References:

1. M. Staines, W. H. Robinson and J. A. A. Hood (1981). "Spherical indentation of tooth enamel". Journal of Materials Science. 16 (9): 2551-2556. doi:10.1007/bf01113595.

2. Wikipedia contributors. "Tooth enamel." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 25 Apr. 2017. Web. 1 May. 2017.

3. Rošin-Grget, K; Peroš, K; Sutej, I; Bašić, K (Nov 2013). "The cariostatic mechanisms of fluoride". Acta medica academica. 42 (2): 179-88. doi:10.5644/ama2006-124.85. PMID 24308397. Retrieved 31 March 2014.

4. ten Cate FM. Contemporary perspective on the use of fluoride products in caries prevention British Dental Journal 214, 161 - 167 (2013) PMID 23429124

5. Ismail AI, Hasson H; Hasson (2008). "Fluoride supplements, dental caries and fluorosis: a systematic review". J Am Dent Assoc. 139 (11): 1457-68. doi:10.14219/jada.archive.2008.0071.

## New evidence on how fluoride fights tooth decay

In an advance toward solving a 50-year-old mystery, scientists are reporting new evidence on how the fluoride in drinking water, toothpastes, mouth rinses and other oral-care products prevents tooth decay.

Their report appears in the ACS journal Langumir.

Karin Jacobs and colleagues explain that despite a half-century of scientific research, controversy still exists over exactly how fluoride compounds reduce the risk of tooth decay. That research established long ago that fluoride helps to harden the enamel coating that protects teeth from the acid produced by decay-causing bacteria. Newer studies already found that fluoride penetrates into and hardens a much thinner layer of enamel than previously believed, lending credence to other theories about how fluoride works.

The report describes new evidence that fluoride also works by impacting the adhesion force of bacteria that stick to the teeth and produce the acid that causes cavities. The experiments -- performed on artificial teeth (hydroxyapatite pellets) to enable high-precision analysis techniques -- revealed that fluoride reduces the ability of decay-causing bacteria to stick, so that also on teeth, it is easier to wash away the bacteria by saliva, brushing and other activity.

## New evidence on how fluoride fights tooth decay

In an advance toward solving a 50-year-old mystery, scientists are reporting new evidence on how the fluoride in drinking water, toothpastes, mouth rinses and other oral-care products prevents tooth decay. Their report appears in the ACS journal Langumir.

Karin Jacobs and colleagues explain that despite a half-century of scientific research, controversy still exists over exactly how fluoride compounds reduce the risk of tooth decay. That research established long ago that fluoride helps to harden the enamel coating that protects teeth from the acid produced by decay-causing bacteria. Newer studies already found that fluoride penetrates into and hardens a much thinner layer of enamel than previously believed, lending credence to other theories about how fluoride works.

The report describes new evidence that fluoride also works by impacting the adhesion force of bacteria that stick to the teeth and produce the acid that causes cavities. The experiments — performed on artificial teeth (hydroxyapatite pellets) to enable high-precision analysis techniques — revealed that fluoride reduces the ability of decay-causing bacteria to stick, so that also on teeth, it is easier to wash away the bacteria by saliva, brushing and other activity.

## Where to Find Fluoride

Fluoride can be found in a number of dental hygiene products, specifically toothpaste where it exists in low doses. For severe instances of decay or weakened enamel, a dentist may prescribe extra strength toothpaste that contains higher levels of fluoride (roughly 5,000 ppm), which is only available with a doctor’s authorization. In addition, dentists typically will administer topical fluoride to children until their teenage years during their regular checkups. This ensures that children’s teeth stay strong enough to fight cavities during their formative years.

While fluoride has been proven to help strengthen teeth and prevent cavities, it’s important to maintain good dental habits as well. Brushing twice a day and flossing at least once a day will ensure your teeth and gums stay plaque-free and ultimately will help to fight tooth decay. In addition, visiting your dentist twice a year helps guarantee the best dental health possible.

## 5. DISCUSSION

The term oral health is very complex and comprehensive concept, which includes a number of parameters which essentially define and determine oral health. We also mentioned that according to the World Health Organization (WHO) in 1965, oral health is essentially a 𠇌ondition of healthy and functioning teeth and their supporting structures, including the health of all parts of the oral cavity involved in chewing”. For this study, we clearly and unambiguously seen and proved that only chewing function is not only in preserving oral and overall health status and human health, there are aesthetics and phonics (6).

The wider issue of this study, in the sense to estimate the quality of general health status of oral health and to assess the status of representation of dental caries in relation to sex and chronological age by determining the degree of influence of the use of certain methods in the treatment of dental caries in different age and gender categories ( Table 7 ).

### Table 7

Concentrations of selected agents for topical application

So the main problem of this study was to investigate the possibility of improving the quality of general dental health status by the treatment with 0.5% NaF, in children aged 8� years, with the application of methods of topical fluoridation.

For the purpose of this survey selected is a sample of school children aged 8 to 15 who use medical and dental services of regional ambulance MZ “Zalik” in Mostar. The study included 108 subjects, divided into two sub-samples (control group of 40 subjects and experimental group of 68 subjects).

The control group consisted of children in whom was followed multiple factors (children who have a need for dental treatment, but the same was not apply, except for regular controls and tips for self-hygiene and the use of various protective preparations in dental hygiene. The experimental group consisted of children who are was involved in the six-month treatment of topical therapy fluoridation NaF 0.5% (five percent sodium fluoride).

Results of obtained general descriptive indicators of the teeth health status in the total number of respondents are presented in tables and graphs the frequency distribution of values of the parameters under the health status of teeth and the same is clearly observable differences in the values of the studied parameters and the initial and final dental examination. As we have mentioned earlier DMFT index represents the sum of the number of decayed, extracted and teeth with fillings, and as such is both a very good indicator of oral health (7,8). In the analysis of the obtained data investigated parameters to assess oral health it is determined DMFT index and for the control and experimental group of subjects at the initial and final dental examination.

This mini research aimed to investigate the studied sample population, the effects of the application of methods fluoridation on dental health status of children from 8 to 15 years, and that we obtain certain information and guidance in caries prevalence as well as the assessment of the presence or homogeneity within the studied population. Awareness of various socioeconomic condition of the company in our country, are very important for the general idea of dental caries in children and early adolescence. It has been shown that countries in transition have the highest value DMFT-index, and in such a reorganization of our country.

Unemployment, inflation, low family income, lack resolved hygienic sanitation facilities life, primarily inadequate housing conditions without basic hygiene, poor diet, low level of health awareness among parents, as well as the growing privatization of the dental profession, represent the main external risk factors which favor the emergence and spread of decay within the most vulnerable population of children transition period of growing permanent teeth and falling dairy teeth (9,10).

So the results of this mini-survey will not be able to use as a scientific, exact population indicator, but be sure that we will reach a very important knowledge about the effects of the application of methods of fluoridation, its duration, which in practice will give one particular contribution to improving health care quality status teeth within the studied population.

It’s understandable that you’d want to know, is fluoride bad for your teeth? Rest assured that research over 70 years has shown that adding fluoride to water has led to the reduction of tooth decay by 40-60%. 5 The British Dental Association also recommends that everyone should brush with a fluoride toothpaste for at least two minutes, twice a day. 6

Fluoride helps strengthen the enamel on your teeth. 7 The enamel protects a soft layer of a substance called dentine, and if the dentine is exposed because the enamel is weak, you can get sensitive teeth. 8

## Toothpaste-Makers' Point of View

Fluoride offers one way to strengthen teeth and does have potential benefits, says Darryl Bosshardt, a spokesman for Redmond, which makes a fluoride-free toothpaste, Earthpaste. But tooth decay is not caused by fluoride deficiency, he says, and fluoride supplementation can't reverse active cavities.

"It can also have some potential negative aspects that some consumers would like to avoid if possible," he says. As one of many examples, he cited a study finding fluoride-containing toothpaste ingestion as a main source of fluoride toxicity, according to the Association of Poison Control, especially in young children.

"We are also quick to point out that a non-fluoride toothpaste may not be the best option for everyone. However, we similarly acknowledge that mandatory fluoride supplementation in all water supplies and in all oral care products may also not be the ideal solution for everyone.'' He encourages people to weigh the pros and cons with their dentist.

While toothpaste with fluoride ''is the best choice for oral health, we also recognize that not all the people that choose our brand want fluoride in their toothpaste, and we offer a fluoride-free alternative," says Rob Robinson, a spokesman for Tom's of Maine. The fluoride-free toothpaste from Tom’s does not carry an anti-cavity claim.

## Is Sodium Fluoride Linked to Cancer?

It is unlikely that sodium fluoride ingestion contributes to the development of any type of cancer, according to the American Cancer Society. A 2016 study concluded that there is no relationship between fluoride consumption and childhood or adolescent osteosarcoma, the form of bone cancer people believed was linked to fluoride. Most modern research supports this assertion.

The myth of sodium fluoride causing cancer arose in 1991 when scientists tested doses of sodium fluoride on rats and found that some males developed osteosarcoma. Since then many studies have shown that this connection does not apply to humans.

You might want to approach similar myths with a healthy skepticism. There is a popular conspiracy theory, for example, that the government uses sodium fluoride to make citizens docile and easy to control.

## How does fluoride strengthen teeth and why add it to the public water supply?

People of all ages benefit from fluoride in both their toothpaste and drinking water. While the amount of fluoride a person uses should be tailored to factors including age, stage of growth and development and risk for dental decay, scientific evidence indicates that optimum levels of fluoride in drinking water can reduce cavities by 30 percent.

Since fluoride was first added to municipal water supplies in 1945, there has been a significant decline in tooth decay and tooth loss in the United States. But when children ages 8 and under are exposed to too much fluoride, they can develop what is known as dental fluorosis, which causes white speckling or pitting on tooth surfaces.

And in 2007, the Centers for Disease Control reported a marked increase in fluorosis in American teens since the 1980s.

To address the potential for over-fluoridation, the U.S. Department of Health and Human Services and the Environmental Protection Agency in January proposed changes in the recommended amounts of fluoride in public water supplies—lowering the level from a range of 0.7 to 1.2 milligrams per liter of water to 0.7 milligrams per liter.

The current scientific consensus is that public water fluoridation is safe and effective, and the proposed change in recommend levels simply takes into consideration other possible sources of fluoride to which children are exposed today.

Fluoride’s anti-decay mechanism is well established. Tooth decay occurs when certain types of bacteria found in dental plaque break down dietary sugars and produce acid. These acids can dissolve tooth enamel and dentin, which is directly below the enamel, by leaching calcium and phosphate minerals from these hard tooth tissues. This process—called demineralization—eventually causes cavities. When fluoride becomes chemically incorporated in the tooth, it makes the enamel more resistant to demineralization, thus preventing the decay process.

Many toothpastes contain fluoride, which the teeth absorb during brushing. But for some patients who are at high risk for decay, including children or those with chronically dry mouth, using a fluoride toothpaste might not be enough. When added to drinking water at a concentration of one part per million, fluoride ions bathe the teeth when they are secreted in the saliva.

The spike in the prevalence of fluorosis could be a result of the proliferation of fluoridated products on the market today: over-the-counter toothpastes and rinses, fluoride supplements and topical treatments applied during dental visits.

The new federal recommendations take these other sources of fluoride exposure into account while attempting to balance its decay-fighting benefits against the risk of fluorosis.

One complicating factor is that Americans now drink nearly 3 billion gallons of bottled water each year. Because different brands of bottled water vary in fluoride content, some people may not be consuming protective levels of fluoride. In addition, some water filtration systems eliminate most of the fluoride in the water. For example, while carbon filtration does not affect fluoride levels, a reverse osmosis system can remove as much as 95 percent of fluoride from water.

Too little fluoride increases the risk of tooth decay, and more than half of all children develop cavities before age 11. Dentists and physicians should evaluate the fluoride intake of children and discuss with their parents or caretakers ways to ensure kids are getting the appropriate amount of fluoride.