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Toxicology Reflections

Drinking Water Fluoridation

19 Comments

Assessing the risk posed by a substance to human health can be a tremendous scientific challenge. Gathering scientifically sound data on exposure, evaluating all possible adverse outcomes and the levels needed to reach such effects, assessing the uncertainties surrounding the issue, can take years, decades, even generations. Once all that work is done, however, the process is usually fairly simple. A simple comparison of what is believed to be a safe level and what is believed to be out there does the job.

In many cases, the decisions that follow the conclusions reached by the risk assessment are even more challenging than the assessment itself.  This is commonly the case when more than one risk are to be compared at once and against each other, or when the costs and benefits of a certain decision need to be weighed. In these cases, the lines between scientific, political and moral principles start getting blurred.

Probably no human health issue could better exemplify this than Water Fluoridation, or the addition of fluoride to the drinking water supply as a preventive treatment against tooth decay.

In early the 20th century, tooth decay was a major health issue with nearly every individual across most age groups in the United States presenting the disease. (Centers for Disease Control, 1999). No effective measures were available at the time. Those “treated” for the disease by tooth extraction, would soon develop gastrointestinal problems due to poor mastication. Those who didn’t get the treatment, commonly developed serious oral infections and in many cases died of septicemia (Selwitz et al.).

Epidemiological studies in the 30’s and 40’s uncovered a correlation between a dental condition known as “Colorado Brown Stain” and lower incidence of dental caries. Patients with Colorado Brown Stain were usually restricted to areas of naturally high levels of fluoride in water. The teeth of these individuals, although were stained with yellow/brown spots, presented significantly lower numbers of caries. (Ripa, 1993)

The Colorado Brown Stain would later been known as dental fluorosis and its underlying causes would be linked to the reaction of the hydroxyapatite in the teeth enamel with the fluoride on the water to form a harder and more pH-resistant fluoride-rich variant (Aoba and Fejerskov, 2002).

A few years after that discovery, in 1945 the city of Grand Rapids, Michigan, would become the first city in the world to supplement their municipal water supply with fluoride salts. Many US cities followed shortly. The phenomena would make it across the boarder in only one year, and in 1946 Brantford, ON would become the first Canadian city to adopt this strategy.

Since then thousands of cities across the world have opted for this health policy, and currently 16,412 US cities, serving 62.2% of the US population provide some sort of water fluoridation (Bailey W et al., 2008). Other countries suchas United Kingdom, Ireland, Australia and, as mentioned, Canada join the US on this effeort. Some other European countries such as Germany or Finland, implemented water fluoridation for a number of years, but eventually ceased their programmes.

In 1999, The Centre for Control Deaseases in the United Sates, named Water Fluoridation one of the Ten Great Public Health Achievements in the 20th Century (Centers for Disease Control, 1999). The controversy surrounding the real effectiveness, safety and even morality of the policy still continues and it could also be placed among the most contentious public health topics of the century.

During the next weeks, I will explore the different aspects of this controversial issue. From the more scientific aspects such as the  physiological and microbiological processes involved in tooth decay and tooth re-mineralization, the toxicological effects of fluoride, or the exposure levels (both from natural and human sources) to the more socio-political and moral views around the topic.

References

Aoba, T., Fejerskov, O., 2002. Dental Fluorosis: Chemistry and Biology. Critical Reviews in Oral Biology & Medicine 13, 155-170.

Bailey W, Duchon K, Barker L, W., M., 2008. Populations receiving optimally fluoridated public drinking water – United States, 1992–2006. Morbidity and Mortality  Weekly Reports 57, 737–741

Centers for Disease Control, 1999. Achievements in Public Health, 1990-1999:  fluoridation of drinking water to prevent dental caries. Morbidity and Mortality  Weekly Reports, 933-940.

Ripa, L.W., 1993. A half-century of community water fluoridation in the United States: review and commentary. Journal of public health dentistry 53, 17-44.

Selwitz, R.H., Ismail, A.I., Pitts, N.B., Dental caries. The Lancet 369, 51-59.

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19 thoughts on “Drinking Water Fluoridation

  1. This is a really interesting topic! Saskatoon fluoridates its drinking water at a concentration of about 0.7 mg/L (www.saskatoon.ca). I wonder how this compares with other cities and how close it is to the acute and chronic toxic concentration.

    http://www.saskatoon.ca/DEPARTMENTS/Utility%20Services/Water%20and%20Wastewater%20Treatment/Water%20Treatment%20Plant/Pages/Frequently%20Asked%20Questions.aspx#fluoride

  2. People may also be interested in looking at which Canadian cities have banned the addition of fluoride to their drinking water http://o.canada.com/2013/05/01/hows-that-fluoride-free-water-treating-you/. For these cities you would be looking at the baseline concentration of fluoride because they obviously don’t add it post treatment. For the most part, I would think that surface water (vs. groundwater) sources are not as likely to have naturally occurring fluoride concentrations sufficent to significantly decrease caries.

  3. You touch an important aspect: background concentrations. I will touch more on this topic when i write about exposure assessment in future weeks. For now, i can mention that the number of communities receiving optimal (on the 0.7 mg/L level recommended by Health Canada) is surprisingly high. Although this obviously varies geographically. To give you an idea, the Saskatchewan Community fluoride data 2010 (Dental Health Promotion Working Group of Saskatchewan, 2011) identifies a total of 48 communities with fluoride levels naturally occurring at the optimal level or near it. Fifty eight communities, on the other side, supplement their water with fluoride to achieve the same levels in the same province.

    As I mentioned, these distribution depends largely on geography and geological factors, with communities sourcing their water supply on ground water usually presenting higher natural fluoride levels.

    References

    Dental Health Promotion Working Group of Saskatchewan (2011). Saskatchewan Community Fluoride Data 2010. Saskatchewan ministry of health.

  4. Author –
    The level at which Saskatoon is supplementing their drinking water is (0.70 mg/L) is exactly the recommended level established by Health Canada (Health Canada, 2011), which is also supported by Saskatchewan Health (Dental Health Promotion Working Group of Saskatchewan, 2011). According to the Health Canada guidelines, levels of fluoride in fluoridated drinking water systems vary from 0.46 to 1.1 mg/L on average across Canada, with over 75% of the Canadian population on a water system reviving fluoride in their water at concentrations of less than 0.6 mg/L, and fewer than 2% of the population receiving community water at levels over 1.0 mg/L.

    The Health Canada guidelines also set a maximum acceptable concentrations (MAC) of 1.5mg/L. It is important to note that this value is based on aesthetic endpoints based on levels related to the onset of staining due to dental Fluorosis.

    Dental Health Promotion Working Group of Saskatchewan, 2011. Saskatchewan Community Fluoride Data 2010. In: Saskatchewan ministry of health (Ed.).
    Health Canada, 2011. Guidelines for Canadian Drinking Water Quality: Guideline Technical Document – Fluoride. Health Canada, Ottawa, ON.

  5. I have heard of a higher incidence of tooth decay in children who rely primarily on bottled water (i.e. those culligan water coolers, etc) at home. Do you know if there is any truth to this? This study indicates that bottled water does not follow flouridation guidelines: http://courses.washington.edu/h2owaste/bottled_water.pdf

  6. I also find this topic to be very interesting and look forward to reading more about it through the coming weeks. I am curious how fluorination in the water may compare to areas without fluorination where children are given dietary fluoride supplements. Are the same benefits in decreasing caries seen?

  7. Author –
    Before we start trying to understand the controversy regarding water fluoridation we should take a moment to look at the way in which fluoride interacts with teeth structure.

    The external layer of human teeth, or dental enamel, mainly consist of a calcium phosphate-based mineral known as hydroxyapatite with a molecular formula of Ca5(PO4)3(OH). The processes by which human tissue is able to create a solid structure, such as teeth, based on this compound are highly complex, but are mainly driven by enzyme-assisted precipitation processes that occur in the late stages of embryonic development.

    Once developed, adult teeth are not re-generated and they rely on the hardness of hydroxyapatite (5 on Mohs hardness scale) (Staines et al., 1981) to maintain its performance through the life-spam of an adult human.

    Hydroxyapatite, however, presents a significant vulnerability, and this is its low acid-resistance. Normal Saliva pH lies around 7.4 (Dawes C, 2003). Fermentable sugars adhering to teethe structures, especially on rugged areas are used by bacteria such as Streptococcus mutans and Lactobacillus spp producing weak organic acids in the process. With the addition of these acids, pH values fall below a critical value (usually around pH 5.5) resulting in demineralization of tooth (Selwitz et al.).

    When this phenomena is allowed in a recurrent manner, tooth decay processes become prevalent, and the newly created cavities, become optimal environments for bacterial populations (Selwitz et al.). With time, the bacterial infection could make it to the deeper layers of the tooth structure and eventually make it into the blood stream if not cut in time.

    Fluoride, when in solution in the mouth can interact with the mobilized calcium and phosphate ions to create fluouroapatite (Ca5(PO4)3F) by substitution of the hydroxyl radical. Fluoroapatito can precipitate over the existing dental structures and act as a protecting blanket over the existing hydroxyapatite dental structures due to the higher pH resistance (pH4.5) (Aoba and Fejerskov, 2002)

    At the same time as acting as a pH-protective blanket, fluoride dissolved in the mouth fluids has ben proven to act as a antimicrobial as well as to difficult bacterial adhesion into the teeth structures (Loskill et al., 2013)

    All these benefits will play a major role on the decisions made by different administrative bodies on the effectiveness of water fluoridation as a cdental caries preventive tool. Like any other substance, however, the levels of fluoride exposure at which these beneficial effects are observed and those at which negative effects appear will need to be evaluated in detail. During the next few weeks, emphasis will be made on these aspects.

    Aoba, T., Fejerskov, O., 2002. Dental Fluorosis: Chemistry and Biology. Critical Reviews in Oral Biology & Medicine 13, 155-170.

    Dawes C, 2003. What Is the Critical pH and Why Does a Tooth Dissolve in Acid? J Can Dent Assoc 69, 722-724.

    Loskill, P., Zeitz, C., Grandthyll, S., Thewes, N., Müller, F., Bischoff, M., Herrmann, M., Jacobs, K., 2013. Reduced Adhesion of Oral Bacteria on Hydroxyapatite by Fluoride

    Treatment. Langmuir 29, 5528-5533.

    Staines, M., Robinson, W.H., Hood, J.A.A., 1981. Spherical indentation of tooth enamel. Journal of Materials Science 16, 2551-2556.

  8. I really like this topic. I’m feeling so much more educated about my teeth and drinking water now! Do you know how much fluoride actually stays in the mouth versus being swallowed? How much water do you think you’d have to drink to see a positive effect on teeth?

  9. I’m looking forward to hearing more about the controversy over fluoride supplementation. I just did a quick google search and looked at some of the anti-fluoride websites – it is a bit overwhelming. Some did quote the maximum recommended levels of fluoride as evidence that fluoride was “bad” – so there seems to be an issue with risk perception where only the risks are being considered and the benefits not recognized. To me this seems to somewhat parallel the anti-vaccine movement which is becoming a big issue in terms of public health. However, that said, I have to admit I have pretty much accepted the paradigm that water fluoridation prevents cavities without evaluating whether there is sound evidence to back this up, so I am interested to find out more about the relative risks and benefits.

  10. Last week we discussed the physiological and chemical processes driving the beneficial effects of fluoride as a cavity-prevention treatment. Groups opposing to water fluoridation, often refer to fluoride as “poison”. Certainly, as claimed by these groups, exposure to fluoride, like any other substance, can lead to toxic effects in humans when it happens at high enough concentrations.

    Determining what is this critical concentration, if any, at which exposure to fluoride does not induce health effects is the first step on the development of a risk assessment that would help us elucidate whether these claims are founded or not.

    As mentioned on the first week, fluoride is a naturally occurring element, sometimes present in water supplies at concentrations above 10mg / L, with the highest natural level reported being 2800mg/L (WHO, 2011). It is this natural occurrence, as opposed to deliberate water fluoridation (usually yielding fluoride concentrations between 0.5-1mg/L) that has driven most of the research on health effects.

    For the next couple of weeks, we are going to explore the pharmacokinetics and metabolism of fluoride in humans as well as relevant studies on the effects of fluoride in laboratory animals and humans, both from an experimental, and epidemiological perspectives.

    After oral uptake, water-soluble fluorides are rapidly and almost completely absorbed in the gastrointestinal tract with the exception of certain mineral forms and certain aluminium, phosphorus, magnesium or calcium complexes (IPCS, 2002; WHO, 2004). If fluoride intake remains constant, (and assuming only water exposure) concentrations in blood and water will eventually reach equilibrium (up to 10 mg/litre)(WHO, 2004).

    Absorption of gaseous and particulate fluorides from the respiratory tract partial to complete, depending on the solubility of the fluoride form and particle size (IPCS, 2002).

    Fluoride has the ability to cross the placental barrier. Approximately 99% of the total body burden of fluoride is retained in bones and teeth; the remaining is eliminated primarily in the urine, with these percentages varying with urinary flow and pH.

    In the past, systemic as well as topic fluoride exposure were believed to have complementary effects on caries prevention. Despite fluoride accumulation on teeth structures via systemic exposure, in recent years evidence is accumulating pointing to the topical mode of action of fluoride being the main source of caries protection via its influence on de- and remineralisation kinetics of dental hard tissues in the mouth cavity (CDC, 2001; Hellwig and Lennon, 2004; Pizzo et al., 2007).

    As it is usually the case with metabolic and physiological processes, the rates at which absorption, distribution and excretion of fluoride take place will depend on factors such as age, sex and even the pre-existence of previous conditions (Fawell J et al., 2006). This uncertainty will need to be addressed when performing a proper hazard assessment.

    References

    CDC, 2001. Recommendations for using fluoride to prevent and control dental caries in the United States. Center for Disease Control and Prevention. Morb Mortal Wkly Rep, 50, 1-42.

    Fawell J, Bailey K, Chilton J, Dahi E, Fewtrell L, Magara Y, 2006. Fluoride in Drinking-water. World Health Organization / IWA Pub.,, Geneve.

    Hellwig, E., Lennon, Á.M., 2004. Systemic versus Topical Fluoride. Caries Research 38, 258-262.

    IPCS, 2002. Environmental Health Criteria 227 – Fluorides. International Programme on Chemical Safety, World Health Organization, Geneva.

    Pizzo, G., Piscopo, M., Pizzo, I., Giuliana, G., 2007. Community water fluoridation and caries prevention: a critical review. Clin Oral Invest 11, 189-193.

    WHO, 2004. Fluoride in Drinking-water. Background document for development of WHO Guidelines for Drinking-water Quality (WHO/SDE/WSH/03.04/96). World Health Organization, Genava.

    WHO, 2011. Guidelines for Drinking-water Quality. World Health Organization, Geneva.

  11. I mentioned to a friend that I took Human Health Risk Assessment the first question he asked was if I knew anything about fluoride in water and thanks to you I said I did know a bit. He asked what the benefit of having fluoride in the water was and I was able to say that it was to help in preventing tooth decay. Then he said he had heard that toothpaste in water was sufficient to counter the effects of tooth decay and that adding fluoride to water was unnecessary. I didn’t have the information on me at the time to investigate this but since then I have looked into it a bit.

    I was able to search for a case study that found that two communities (one with water fluoridation and one without) had similar fluoride levels which they attributed to toothpaste containing fluoride ingestion in both communities1. Additionally, they found that children in the fluoridated communities ingested similar amounts of fluoride from toothpaste and beverages. They didn’t look at tooth decay rates in the communities. Based on this couldn’t the problem be solved by governments providing fluoride toothpaste to citizens which presumably provides similar fluoride levels and would also give them the choice of whether or not they want to ingest fluoride at all and at what levels.

    Rojas-Sanchez F., Kelly S.A., Drake K.M., Eckert G.J., Stookey G.K., Dunipace A.J. (2007). Fluoride intake from foods, beverages and dentifrice by young children in communities with negligibly and optimally fluoridated water: a pilot study. Com. Dent. Oral Epi. 27: 288-297

  12. I like this topic too. I have the feeling that most anti-fluoride folks would likely opt out of toothpaste containing fluoride as well regardless of the fact that you wouldn’t be consuming it. I am intrigued by the idea of government supplied toothpaste. In a similar way to government provided toothpaste, I recall the ‘swish and spit’ fluoride treatments from my elementary school days. I always looked forward to them because I loved the bubble gum flavoured fluoride treatment. At the time, I lived in the NWT and I am pretty sure we were not receiving fluoridated water through the drinking water distribution. Obviously, I was cool with it.

    Much like 2,4-D and uranium, it is evident that people form strong associations or perceptions of fluoride and its health benefits or costs. In fact, those perceptions are so strong that they can result in the successful removal of fluoride from the public distribution system. Have a read of this McLean’s article (Manisha 2013) to see just how easy it is for a small group of people to support change against the advice of scientists. I am not too concerned about the level of fluoride in Saskatoon’s drinking water and if fluoride wasn’t there then I would ensure that it was in my toothpaste. Call it nostalgia but I personally would welcome the return of ‘swish and spit’ if a non-consumptive treatment of fluoride was preferred.

    Looking forward to your future posts!

    Krishnan, Manisha. “Something in the water: Windsor is the latest city to cave to anti-fluoride activists. It won’t be the last.” Maclean’s 18 Feb. 2013: 21. Expanded Academic ASAP. Web. 1 Oct. 2013.

  13. Do you know if there is any evidence for salivary secretion of fluoride after ingestion in drinking water as a possible mechanism for a protective topical effect of fluoride ingested via drinking water?

    The information about systemic vs topical effects of fluoride are interesting and came as a surprise to me (like I said, I’ve made a lot of assuptions about the use of fluoride personally!). Lorelei brought up the “swish and spit” use of fluoride and felt compelled to search about the efficacy of a “single” presumably high dose of fluoride administered this way – it seems to me that such intermittent administration of fluoride would be of minimal value compared to sustained treatments. The best I could find was a recent article (ten Cate, 2013) that recommended that use of fluoride is most efficient when used multiple times a day. The reason I am interested as I cringe at the thought of the “swish and spit” because my dentist recommends this as following routine yearly hygiene visits and I dutifully comply, even though I feel quite ill afterwards. I think I am now sufficiently armed to argue against agreeing to this treatment on my next visit (i.e. as a regular user of fluoride toothpaste, fluoridated tap water drinker and at a low risk for cavities, will a fluoride rinse do much for me other than make me feel ill?).

    The idea of government-issued toothpaste is definitely interesting, but to play devil’s advocated I might argue from a public health perspective that in the utility of providing toothpaste is limited by its actual uptake especially by those most at risk, and by the cost of delivering such a program on an ongoing basis. The CDC argues that fluoridation provides benefits without requiring change in personal habits (at least among those who consume tap water) and especially benefits lower socioeconomic strata who lack access to dental care. Economically, adding fluoride to drinking water is also considered extremely cost effective as a public health intervention, whereas providing other treatments would likely be more costly.

  14. I’d like to add to the point about single use efficacy of the “swish-and-spit” type treatment. I decided to look for some alternatives and found this study by

    Bonner et al 2008 that looked at the use of slowly dissolving glass beads that release flouride in children as a means to prevent decay. This study seemed to be somewhat inconclusive but I was wondering if perhaps a long term “chronic” exposure through something like these beads could become problematic? After our discussion in class regarding dental amalgams and the fact that they aren’t really studied/tested before they become widely used has made me extra cautious of dental implements. Have the flouride treatments well-studied?

  15. Author –
    My intention this week was to enter the hazard assessment section of my reflection with some animal studies. However given the number of comments that I received over the last week in relation to acute (toothpaste or swish and spit) or chronic (fluoridated water or slow release fluoride beads) fluoride treatments, I thought I would expand a bit more on fluoride absorption, distribution and mode of action.

    Let me begin by coming back to my first posts about the issues of caries formation and the preventive role of Fluoride. The original studies on fluoride’s effect on teeth and its relationship with caries from the 40’s (Dean et al., 1942), initiated the believe that the protective role of fluoride was higher when the element was introduced on the dental structures during their development. This remained the predominant belief for almost forty years until new, more scientifically rigours, research in the 80s started looking at the processes involved in more detailed (Aoba and Fejerskov, 2002; Hellwig and Lennon, 2004). These more recent studies started comparing acute and chronic exposures during and after development. Sometimes these studies where carried out in animals (Aoba and Fejerskov, 2002), sometimes as clinical trials and in other cases via epidemiological studies, where additional care was taken to attempt to separate the co-related effect of variables that had not been take into account in the past. This was the case for example with the problem separating the systemic effect of fluoride in water during teeth development from the effect the same water had as a topical treatment after teeth eruption.

    As mentioned in previous posts, teeth enamel is made of a mixture of hydroxyapatite and carbonated apatite. Teeth enamel, after development is not irrigated and does not regenerate with the exception of potential re-mineralization processes occurring in the oral cavity. It was explained before, as well, that after ingestion of a fermentable sugar, bacterial communities in the dental plaque tend to decrease the pH of the solution surrounding the teeth via the production of organic acids. The buffering action of saliva, eventually brings the pH back to normal levels within 20-30 min (in a healthy individual)(figure 1)(Featherstone, 1999). It is during these 20-30 minutes that the risk for teeth de-mineralization is the greatest, with the carbonated apatite dissolving first followed by the Hydroxyapatite. Fluoroapatite, presents a much lower pH-dependent solubility, just outside the levels usually reached in the oral fluid during these peaks (figure 2).

    It has been reported that fluoride levels in the structural inner section of the teeth of individuals exposed to fluoride during development ranges around 20-100ppm. On the other hand the outer layer can reach levels of 1000-2000 ppm. This, on its own gives an estimate of the differential rate of incorporation of fluoride from systemic sources (during development) and topical sources (post eruption). However even teeth presenting fluoride concentrations on the higher end (1000-2000ppm) have been shown in experimental studies to still be susceptible to acid dissolution (Featherstone, 1999).

    So what is actually driving the protective effect of fluoride if not acid-resistance due to fluoroapatite in the dental structure? The latest studies point into the high reactivity of fluoride and its direct effect on the de/re-mineralization process as the actual culprit for the protection. Some of these studies show that in the acidic environment of the plaque fluid, fluoride is able to take advantage of the de-mineralization process, to substitute the –OH groups in the Hydroxyapatite and re-mineralize the Calcium ions. Such is the speed of these processes that it has been shown that because of its direct effect on the re-mineralization processes, as little as 1 ppm of fluoride in the acid solution reduced the dissolution rate of carbonated apatite to that equivalent to hydroxyapatite (Featherstone, 1999).

    The summary of theses studies give us a relative easy answer to the questions induced by the last post.

    Systemic (swallowed and incorporated on the bloodstream) fluoride only has a signifficant effect on teeth structure and chemistry during teeth development, when it is incorporated to the teeth structure. However, even the presence of fluoroapatite in the dental structures does not seem to be able to significantly protect enamel from acid dilution. At the same time, and we will discuss the issue further when we reach the hazard assessment section, dental fluorosis, induced by the presence of fluoride during development is one of the main effects of fluoride exposure in humans.

    Once the dental structures have erupted (adults) systemic fluoride has little effect on dental structure due to the lack of blood irrigation in the enamel.

    Salivary re-exposure, as for Lianne’s comment, has been reported. Studies show that saliva fluoride levels follow those of plasma by about a 65%. A study by Oliveby et al. (1989) showed that after 2h, the amount of fluoride recovered from the saliva of subjects that had ingested a 1mg NaF pill was between 0.05 and 0.09% of the initial dose. This path could potentially be a source of protection from systemic exposure, but details on half-life of the fluorides in blood/saliva as well as the concentrations reached in the oral cavity should be clearly accounted for.

    As for the effect of fluoridated toothpaste and the use swish and spit method, the literature seems to suggest that their effectiveness would be determined by the timing of the application. As presented in this entry, fluoride’s protective effect peaks during the de/re-mineralization processes that occur during the 20-30minutes following the decrease in pH induce by the intake of sugars. Unless these products are applied to the oral cavity within that 20-30min gap, the protective effects would be minimal.

    After all the stated facts, it would be easy to see how, from a behavioural point of view, addition of fluoride to water would be the best way of getting that fluoride to the areas where it is needed at the times when it is needed. After all, I always get thirsty after my doughnut!

    References

    Aoba, T., Fejerskov, O., 2002. Dental Fluorosis: Chemistry and Biology. Critical Reviews in Oral Biology & Medicine 13, 155-170.

    Dean, H.T., Arnold, F.A., Jr., Elvove, E., 1942. Domestic Water and Dental Caries: V. Additional Studies of the Relation of Fluoride Domestic Waters to Dental Caries Experience in 4,425 White Children, Aged 12 to 14 Years, of 13 Cities in 4 States. Public Health Reports (1896-1970) 57, 1155-1179.

    Featherstone, J.D., 1999. Prevention and reversal of dental caries: role of low level fluoride. Community dentistry and oral epidemiology 27, 31-40.

    Hellwig, E., Lennon, Á.M., 2004. Systemic versus Topical Fluoride. Caries Research 38, 258-262.

    Oliveby, A., Lagerlof, F., Ekstrand, J., Dawes, C., 1989. Studies on fluoride excretion in human whole saliva and its relation to flow rate and plasma fluoride levels. Caries Res 23, 243-246.

  16. I find it interesting that dental disease has been associated with coronary heart disease (Humphrey et al. 2008; De Stefano et al. 1993). Therefore, reduction in dental decay due to fluorination of drinking water may reduce the risk of coronary heart disease. I wonder if the reduction in heart disease should be accounted for when considering the risk of fluorination to human health?

    Humphrey et al. 2008. Periodontal disease and coronary heart disease incidence: a systematic review and meta-analysis. Journal of General Internal Medicine, 23:2079-2086.

    De Stefano et al. 1993. Dental disease and risk of coronary heart disease and mortality. British Medical Journal, 306:688-691.

  17. think your topic has been quite interesting and I really enjoyed your last post. I had previously read articles that described when best to clean your teeth (e.g. Timing Your Teeth Brushing) but hadn’t paid attention to the timing of fluoride treatments. The article covers similar information to that in your post but also says that rinsing your mouth after acidic foods/drinks is likely better than brushing. If fluoride deposition is best done during this period immediately after eating or drinking then don’t you think it would be better to brush your teeth so you can more efficiently fluoridate your teeth?

    I continued to read a little more about caries and human health in an effort to get some perspective on health risks due to caries versus health risks due to fluoride exposure to prevent caries. What I found is that developing countries have major public health problems as a result of increased caries due to diet and insufficient exposure to fluoride (Petersen and Lennon 2004). Furthermore, Petersen and Lennon (2004) support the use of fluoridated toothpaste and water while suggesting alternative fluoridation strategies including its addition to salt and milk may provide good options!

    Lastly, I found an article by Hale (2003) that looks at the risks associated with caries in young children. It seems to me, from the limited reading I have done, the risk of having low concentrations of fluoride in drinking water appears to be much lower than the risk of caries, especially for children. As mentioned earlier in discussion, it may be the less fortunate in society that would benefit the most from water fluoridation; however, and this may be a huge assumption on my part, I doubt it is the impoverished that are fighting to have it removed from their drinking water.

    Hale, K.J. 2003. Oral health risk assessment timing and establishment of the dental home. Pediatrics. 111(5-1):1113-1116

    Petersen, P.E. and M.A. Lennon. 2004. Effective use of fluorides for the prevention of dental caries in the 21st century: the WHO approach. Community Dentistry and Oral Epidemiology. 32(5):319-321

    The Wall Street Journal. 2013. Timing Your Teeth Brushing. Written by Heidi Mitchell http://online.wsj.com/article/SB10001424127887323623304579059222363886720.html (accessed Oct. 9, 2013).

  18. Thanks for answering my question. I never knew that about fluoride in toothpaste. I did a few literary searches to look at fluoride use and the decline in tooth decay worldwide. In my search I found an article that stated that in the most recent decades tooth decay has begun to increase in several countries whereas in the past there was global decline in the rate of tooth decay1. The report found increases in tooth decay in the U.S., Philippines, Mexico, China, Taiwan, Norway, Armenia, U.K., Brazil and Argentina. In some cases, the increases in dental tooth caries occurred in areas with water fluoridation. They said that the prevalence of tooth decay was higher in lower socioeconomic groups and that it was due to immigration both between countries and emigration from rural to urban areas that result in altered health and diet and movement to areas that lack preventative measures (including oral health support and water fluoridation). The article also cited use of bottled water over tap water as a reason that could be contributing to a higher dental caries rate. Do you think water fluoridation alone can prevent tooth decay or are there other steps that need to be taken concurrently with it in order to prevent tooth decay? If so, how would this affect the risk-benefit analysis?

    Bagramian R., Garcia-godoy F., Volpe A.R. (2009). The global increase in dental caries. A pending public health crisis. Americ. Jour. Dent. 21: 3-8

  19. Author –
    For the last 4 weeks I have been trying to present the scientific reasons for the use of fluoride as a treatment for dental decay prevention as well as the physiological basis of its interaction with different body structures. The difference between the protective effect of fluoride and its potential cosmetic or toxic effects lays on the concentration to which people are being exposed. On this, my last entry on the issue, I will try to briefly summarize the current knowledge on the toxicology of fluoride, its negative effects and the level sat which this happen. I will follow by summarizing the levels at which people are being exposed to the element whether it is natural exposure, or anthropogenic in the way of water fluoridation or fluoride treatment through other products such as toothpaste. A comparison of hazard and exposure will lead us to a decision on whether water fluoridation does pose a risk for those populations where the method is being applied.

    Finally, I will briefly evaluate the global trends on dental cavity incidence and try to draw a few conclusions about the effectiveness of water fluoridation in today’s world.

    Hazard assessment

    According to Health Canada (Health Canada, 2011), adult acute LD100 for fluoride have been estimated in the range of 32–64 mg/kg bw (as sodium fluoride). Acute negative effects, such as nausea has been observed at minimum doses of 5 mg fluoride/kg bw. Assuming a 2L/day water intake and a 70kg adult, fluoride levels in water would need to be 1120 mg/L for lethal levels and 175mg/L for initial acute negative effects.

    From a chronic exposure point of view, Studies mainly usually differentiate the following types of effects: Dental effects (dental fluorosis), Musculoskeletal effects (Skeletal fluorosis), Carcinogenic, Mutagenic/genotoxic effects, reproductive/developmental effects, as well as Neurobehavioral effects.

    On previous weeks we discussed how fluoride could be incorporated on dental structures as floroapatite. Increased fluoride concentration on the external enamel layers provided the teeth with the dissolution protection needed to prevent dental cavities, however, when incorporated on the dental structure during development, fluoride on the crystal lattice could result on apparent teeth staining (due to different reflective properties of the different minerals and increased enamel porosity) and if present in high concentrations it presence could even make teeth more brittle and lead to potential teeth fragmentation.

    The original studies by Dean et al. (1942) showed that children consuming drinking water containing 1.6 mg fluoride/L experienced low rates of very mild (22%) and mild (4%) dental fluorosis, but no moderate or severe dental fluorosis (the ones that would lead to more brittle teeth). More recent review panels have analysed this aspect more recently, but in many cases they come back to those studies from the 40’s as in most of the modern day epidemiological studies it is hard to distinguish the effect of water fluoridation from that of other fluoridated products.

    As mentioned on previous entries, fluoroapatite incorporation and fluoride effect on dental structure formation can only occur during teeth development. Small children during dental development with their high water intake and low weigh dilution are the most susceptible age group; however, the effects will be present for the life of the individual. Cumulative fluoride exposure during dental development phase has been shown to be the dominant factor behind the development of dental fluorosis.

    Skeletal fluorosis, like its dental relative consists on fluoroapatite accumulation on the apatite bone structures. Differently from dental fluorosis, skeletal fluorosis can occur at any stage, as bone structures are constantly being regenerated. In the same manner as with teeth, skeletal fluorosis makes bones become brittle and more likely to break, although it can appear in earlier stages in the form of pain, stiffness of joints, and osteosclerosis of the pelvis and spine. Calcification of ligaments and other crippling effects can also appear as concentrations of fluoride increase in the bone matter. The most advances stages have been rarely documented and have been associated with grown water consumption with concentration above 10mg/l (Health Canada, 2008, 2011). Based on clinical, and epidemiological studies the US NRC reached the conclusion that a lifetime exposure to fluoride at drinking water concentrations of 4 mg/L or higher is likely to increase fracture rates in the population, compared with exposure to 1 mg/L, particularly in some demographic subgroups that are prone to accumulate fluoride in their bones (e.g., people with renal disease) (NRC, 2006).

    In relation to carcinogenicity potential, according to Health Canada (Health Canada, 2008, 2011), the weight of scientific evidence does not support a link between fluoride and cancer. A number of studies have evaluated the potential genotoxic effect of fluoride; however the results are contradictory and not highly significant at the concentrations we are dealing with in this case.

    As for other effects, Health Canada (Health Canada, 2008, 2011) reports the weight of evidence does not support a link between fluoride and IQ and the US NRC (USNRC, 2006) states that the number of available studies on the link between human developmental/reproductive effects and fluoride in drinking water are few and have some significant shortcomings in design and power, thus, limiting their impact.

    In summary, and based on a secondary endpoint such a moderate dental fluorosis, we can depart from the NOAEL presented on Dean et al. (1942). This value is 1600 μg/L. If we assume the 1 to 4 year-old age group, with an ingestion rate of 0.8 L/day and a body weight of 13 kg, the fluoride intake that represents no onset of dental fluorosis would be 98.5 μg/kg/day.

    Exposure assessment

    As mentioned on my opening entry, fluoride is a natural element ubiquitous in the environment. Exposure to fluoride mainly comes from water, food and fluoridated dental products. Dermal/ingestion soil exposures as well as inhalation are usually considered minor routes.

    Concentrations of fluoride in non-fluoridated drinking water in Canada range from <50 μg/L (detection limit) to 210 μg/L., being those elevated levels relatively infrequent in Canada. Locations in Quebec, Saskatchewan, and Alberta have, however, recorded concentrations as high as 2520–4350 μg/L (Health Canada, 2011)

    According to Health Canada (Health Canada, 2011) the mean estimated dose of fluoride ingested from fluoridated dentifrice varies from 0.02 to 0.03 mg/kg bw/day for 6–12 months old and from 0.02 to 0.04 mg/kg bw/day for 12 months to 4 years old (48 months) children. Adult ingestion is estimated to be 1.14 μg/kgbw per day, based on a mean concentration of inorganic fluoride in toothpaste of 1000 μg/g and an estimated intake of toothpaste of 0.08 g/day.

    It is important to notice that these values are highly variable, especially those calculated for children.

    Food exposure has proven to be, however, the most variable value, as it depends on the preparation method, the composition of the food, the geographic location of the production facility and whether this facility is supplied with fluoridated or non-fluoridated water.

    As a summary, estimates of daily fluoride intake by children in Canada range from <0.01 mg to 2.1 mg and from 2.2 to 4.1 mg for adults. In the case of individuals living in certain geographical areas rich in natural fluoride, daily intakes can be as high as 27 mg (IPCS, 2002).

    There is an intrinsic uncertainty associated to these levels. One of the main problems is that these estimates usually do not take into account its bioavailability which can vary significantly depending on the nature of the exposure. This information is highly valuable when trying to detect effects from the different exposure routes on epidemiological studies.

    Risk at current levels

    Based on the available data (USNRC, 2006), the US EPA decided to reduce their Maximum Contaminant Level (MCL) from 4 mg/L to 2 mg/L. As presented above on the short hazard assessment, this value should prevent all adverse health effects with the exception of very minimal dental fluorosis.

    The most recent studies still support the idea of a strong link between increasing water fluoride Level and a strong association with lower cavity occurrence, however, little decline in caries Levels has been observed between above 0.7mg/L. Those communities in wich water fluoridation is taking place usually do so at this optimal level of 0.7mg/L.

    Based on the presented data and the analysis performed by the US EPA, Health Canada and the World Health Organization (USNRC, 2006; Health Canada, 2008, 2011; WHO, 2011), water levels below 2mg/L are considered not to induce negative health effects. Water fluoridation at 0.7 mg/L. applying the same calculations as before, a 1-4 year old child would be exposed to 43 μg/kg/day, or about half of the dental fluorosis NOAEL based on Dean’s study. Even when accounting from exposure from other routes the values would only lead to fluoride exposures below those considered to induce moderate dental fluorosis, while protecting against dental cavity development.

    Summary

    As of 2007, 45.1% of the Canadian population had access to fluoridated water supplies (Rabb-Waytowich D, 2009). Based on the data presented on this reflection, we could easily conclude that water fluoridation does not pose a risk to human health, even when considering the uncertainty sorunding exposure and effects.

    Mild and moderate cases of dental fluorosis can still be detected on individuals living in areas with fluoridated water supply, but the question is whether this minor cosmetic effect is worth taking when considering the alternative. As mentioned on the first entry, the Centre For Disease control and prevention (Centers for Disease Control, 1999) named water fluoridation one of the great public health achievements of the century. The effectiveness of water fluoridation since its introduction in the 40s has been historically proven, however in recent years, a number of studies have been looking at whether the protection provided by the method is still relevant in today’s world (Ripa, 1993; Pizzo et al., 2007; Rabb-Waytowich D, 2009). Number of dental caries has been decreasing steadily since the 1940s, however, the latest research shows that this is also the case for those developed countries in which water fluoridation was never implemented, or it was implemented and stopped.

    These studies would suggest that fluoride exposure from other sources such as toothpaste and other dental treatments in communities with good dental hygiene could lead to equivalent protection to that of water fluoridation. Many voices, point however to the importance that water fluoridation could have in developing countries as well as areas where dental hygiene or access to proper dental care is limited.

    Despite the increasingly better understanding of the safety of water fluoridation treatments, the questions about the relevance of the method in the current society and wether the costs associated with the treatment should be better alocated will most likely ensure the survival of the controversy on the near future.

    References

    Centers for Disease Control, 1999. Achievements in Public Health, 1990-1999: fluoridation of drinking water to prevent dental caries. Morbidity and Mortality Weekly Reports, 933-940.

    Dean, H.T., Arnold, F.A., Jr., Elvove, E., 1942. Domestic Water and Dental Caries: V. Additional Studies of the Relation of Fluoride Domestic Waters to Dental Caries Experience in 4,425 White Children, Aged 12 to 14 Years, of 13 Cities in 4 States. Public Health Reports (1896-1970) 57, 1155-1179.

    Health Canada, 2008. Findings and Recommendations of the Fluoride Expert Panel (January 2007). In: Environment, F.-P.-T.C.o.D.W.o.t.F.-P.-T.C.o.H.a.t. (Ed.). Health Canada, Ottawa, ON.

    Health Canada, 2011. Guidelines for Canadian Drinking Water Quality: Guideline Technical Document – Fluoride. In: Environment, F.-P.-T.C.o.D.W.o.t.F.-P.-T.C.o.H.a.t. (Ed.). Health Canada, Ottawa, ON.

    IPCS, 2002. Environmental Health Criteria 227 – Fluorides. International Programme on Chemical Safety, World Health Organization, Geneva.

    Pizzo, G., Piscopo, M., Pizzo, I., Giuliana, G., 2007. Community water fluoridation and caries prevention: a critical review. Clin Oral Invest 11, 189-193.

    Rabb-Waytowich D, 2009. Water Fluoridation in Canada: Past and Present. Journal of the Canadian Dental Association 75, 451-454.

    Ripa, L.W., 1993. A half-century of community water fluoridation in the United States: review and commentary. Journal of public health dentistry 53, 17-44.

    USNRC, 2006. Fluoride in Drinking Water: A Scientific Review of EPA's Standards. United States National Research Council, The National Academies Press.

    WHO, 2011. Guidelines for Drinking-water Quality. World Health Organization, Geneva.

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