I recently wrote a research report for a pre-dental seminar, and I thought I'd share my findings on the forum as they relate to an ongoing discussion about water fluoridation and the health dangers of systemic fluoride. I tried my best to keep it unbiased and focused mainly on evidence gathered from the latest scientific literature as I could find it on PubMed and other databases. It's not the best written paper (it was for school), but this synthesis of the available data regarding enamel and dentin fluorosis may prove useful.
An Emerging Public Health Issue: Prevalence and Dangers of Dental Fluorosis
Since 1945, fluoride has been artificially added to water systems in communities across the United States as a public health measure for the control of dental caries, which is a common disease in children “caused by bacteria that colonize on tooth surfaces, where they ferment sugars and other carbohydrates, generating lactic acid and other acids that decay tooth enamel and form a cavity” [1]. A cavity that breaks into the dentin of the tooth can cause infection of the dental pulp and lead to such debilitating oral health issues as toothaches, abscess, destruction of bone, and eventually systemic infection [1]. Since 1950, the American Dental Association (ADA) along with the United States Public Health Service (USPHS) has “unreservedly endorsed the fluoridation of community water supplies as safe, effective, and necessary in preventing tooth decay” [2]. The Centers for Disease Control (CDC) has recognized “the fluoridation of drinking water to prevent dental decay as one of 10 great public health achievements of the 20th century” [2]. Despite such widespread support from most governmental and professional associations in the U.S., the practice of water fluoridation has been a subject of controversy since it began.
On August 9, 2007, over 600 health professionals joined with the Fluoride Action Network (FAN) to release a “Professionals’ Statement Calling for an End to Water Fluoridation” in the United States [3]. As of May 20, 2008, the number of signatures has grown to 1718, including 246 PhD’s, 226 dentists, and 216 medical doctors. The Statement calls for “a new Congressional Hearing on Fluoridation so that those in government agencies who continue to support the procedure be compelled to provide the scientific basis for their ongoing promotion of fluoridation” [3]. Why are these professionals going against the opinion of the ADA, the CDC, the USPHS, and many other governmental agencies and professional associations that promote public water fluoridation as a safe procedure to fight dental decay?
This question is what attracted me to explore this topic in the first place. I realized quickly, however, that the answer to this question is more complex than I would have liked. In fact, going through all of the points of what has been called “The Fluoridation Debate” would take an enormous effort, particularly because this topic is not only highly controversial but of great importance to the oral and general health of millions of people in the United States who drink fluoridated water on a daily basis. Also, to give this issue an unbiased and critical analysis would take months, if not years, of thorough research of all the literature available on the topic. A debate of this magnitude requires a thorough investigation by unbiased experts in the various scientific disciplines involved to resolve.
Unfortunately, the Fluoridation Debate has extended past the halls of academia where it could have been resolved in an objective manner a long time ago and into the halls of politics and even corporations. The issue of water fluoridation has become so crusted over on both sides of the debate with special interests, pseudo-science, profiteering, and dogmatic arguments that to hammer through it all so as to come to the foundation of the debate would be quite a feat; to venture into this dangerous land with an open mind is akin to opening the proverbial can of worms. What is so tragic about this is that most people involved in the Fluoridation Debate at various levels really do have the best of intentions in mind for following their particular course of action; they truly believe that their position is the right and moral one. One thing is clear: there is quite a bit of ignorance, unprofessionalism, and misinformation present on both sides of this debate, and, sadly, it is usually this noise that reaches the public ear first through the media.
After realizing all of the above, I decided that the best way to extract the real essence of the water fluoridation issue is to deal with it in parts. Taking one of the issues and analyzing it thoroughly so as to come to a good understanding of its objective significance is much better, in my opinion, than superficially glossing over the whole of such a large topic; this is particularly true in this case, where the Fluoridation Debate is so extensive and its superficial layer so often misleading.
I have chosen dental fluorosis as the main topic of this research paper for several reasons. First, of the eight recent events that the aforementioned Professionals’ Statement mentions to affirm a sense of urgency to calling for an end to water fluoridation, two deal with the detrimental effects of dental fluorosis [3]. Secondly, of the many issues being discussed in the Fluoridation Debate overall, dental fluorosis appears to have the most scientific studies done to date. Thirdly, there is no question that dental fluorosis occurs as a consequence of systemic fluoride, so the large and confusing part of the debate that questions whether this or that health issue relates to fluoride intake does not apply to this topic. And finally, dental fluorosis is for the most part an oral health phenomenon; since I am to start dental school soon and will be on my way to becoming a dental and oral health professional, knowing more about this emerging issue is beneficial towards my education and future career.
So, what exactly is dental fluorosis? Dental fluorosis can come in interrelated two forms: enamel and dentin fluorosis. I’ll focus first on enamel and then move on to dentin fluorosis later on in the paper.
Enamel is the hardest and outer-most layer of the tooth; it is calcified tissue that covers the dentin, which covers the soft and sensitive pulp. Enamel is formed by matrix-mediated biomineralization, where “crystallites of hydroxyapatite form a complex protein matrix that serves as a nucleation site” and which is mainly occupied by proteins (synthesized by secretory ameloblasts) called amelogenins [1]. Amelogenins function in a structural way by “establishing and maintaining the spacing between enamel crystallites,” and complete mineralization of enamel occurs only when amelogenin fragments are removed from the extracellular space [1]. The maintenance of a specific arrangement of enamel crystallites during enamel formation is crucial to the eventual structural integrity of the tooth.
Systemic fluoride at high enough concentrations present during enamel formation can have detrimental effects to this process; fluoride is thought to inhibit the function of matrix proteinases that are responsible for removing amelogenin fragments, “resulting in widening gaps in its crystalline structure, excessive retention of enamel proteins, and increased porosity” [1]. Systemic fluoride present during enamel biomineralization has high affinity for developing enamel because hydroxyapatite crystals can bind fluoride into their crystal lattice [1].
Mild forms of enamel fluorosis are clinically classified to be identifiable by “white horizontal striations on the tooth surface or opaque patches, usually located on the incisal edges of anterior teeth or cusp tips of posterior teeth” [1]. This visible discoloration is caused by improper mineralization of sub-surface enamel that is often covered by a well-mineralized and mostly smooth outer enamel surface. In moderate to severe enamel fluorosis, enamel porosity is more widespread and “lesions can extend toward the inner enamel” [1]. With inner enamel so porous, the tooth becomes structurally unsound and the healthy but thin outer surface of enamel may chip off during tooth eruption, thus exposing the rugged landscape of the mottled inner tooth. Here, debris can be easily trapped and bacteria can fester, thus making the afflicted patient more susceptible to infection [1]. Furthermore, pitting and gaps in the outer enamel surface makes the inner porous enamel regions of the tooth more susceptible to yellow staining and dark (brown to black) discoloration.
One of the first developed standard indexes for classifying the extent of clinical enamel fluorosis is called the Dean’s index; it is the most widely used measure in research literature [1]. The following table reproduces the Dean’s index and ought to make enamel fluorosis more discernable to the reader:
Diagnosis Criteria
Normal (0) The enamel represents the usually translucent semivitriform type of structure. The surface is smooth, glossy,
and usually a pale creamy white color.
Questionable (0.5) The enamel discloses slight aberrations from the translucency of normal enamel, ranging from a few white
flecks to occasional white spots. This classification is utilized when a definite diagnosis of the mildest form of
fluorosis is not warranted and a classification of “normal” is not justified.
Very mild (1) Small, opaque, paper white area scattered irregularly over the tooth but not involving as much as
approximately 25% of the tooth surface. Frequently included in this classification are teeth showing no more
than 1 to 2 mm of white opacity at the tip of the summit of the cusps of the bicuspids or second molars.
Mild (2) The white opaque areas in the enamel of the teeth are more extensive but do not involve as much as 50%
of the tooth.
Moderate (3) All enamel surfaces of the teeth are affected, and surfaces subject to attrition show marked wear. Brown
stain is frequently a disfiguring feature.
Severe (4) All enamel surfaces are affected and hypoplasia is so marked that the general form of the tooth may be
altered. The major diagnostic sign of this classification is the discrete or confluent pitting. Brown stains are
widespread and teeth often present a corroded appearance.
Source: [4]
Moderate to severe enamel fluorosis can be very detrimental to the oral and general well-being of afflicted people. However, most reports on enamel fluorosis by various agencies like the ADA published before 2006 didn’t consider enamel fluorosis in any of its stages to have adverse effects on health; they only considered it to be an “aesthetically displeasing” phenomenon [1]. The National Research Council of the National Academies (NRC) committee responsible for the compilation of the 2006 report entitled “Fluoride in Drinking Water: A Scientific Review of EPA's Standards” was one of the first to reverse this trend by stating the following as part of its findings:
One of the functions of tooth enamel is to protect the dentin and, ultimately, the pulp from decay and infection. Severe enamel fluorosis compromises this health-protective function by causing structural damage to the tooth. The damage to teeth caused by severe enamel fluorosis is a toxic effect that the majority of the committee judged to be consistent with prevailing risk assessment definitions of adverse health effects. This view is consistent with the clinical practice of filling enamel pits in patients with severe enamel fluorosis and restoring the affected teeth. [1]
The majority of the committee felt that there was ample scientific evidence that links moderate to severe enamel fluorosis to oral health defects. I wish to explore some of these links, particularly those that suggest that mottled teeth are more susceptible to dental caries.
Topical fluoride, i.e. that which is placed on the tooth as during brushing with fluoridated toothpaste, continues to prove itself as an excellent anti-caries agent, both in kids and adults [5]; a recent extensive literature review concluded: “The benefits of topical fluorides have been firmly established on a sizeable body of evidence from randomized controlled trials” [6]. The same cannot be said about the effectiveness of systemic fluoride, i.e. that which is ingested as when drinking fluoridated water. There is some evidence that mild to moderate enamel fluorosis makes the enamel more resistant to dental caries; this initial finding was actually the origin of the discovery by scientists in the early-to-mid 20th Century of fluoride’s positive contribution to decreasing dental decay, and it continues to be the basis of the main argument by which proponents of water fluoridation make their case [2].
However, a UK government sponsored “Systematic review of water fluoridation” (the first of its kind in terms of its extensive review of the available literature on the topic) published in 2000 couldn’t find a single study in its search of all scientific databases that fit the criteria of “evidence level A (high quality, bias unlikely)” in support of the benefits of systemic fluoride and water fluoridation [7]. The study concluded: “The evidence of a beneficial reduction in caries should be considered together with the increased prevalence of dental fluorosis” [7]. Nevertheless, the status quo at this point in most of academia is that systemic fluoride may reduce the risk of dental caries in enamel. Ironically, however, new research is beginning to uncover that systemic fluoride may have the opposite effect on dentin – that is, dentin fluorosis makes one more susceptible to dental caries and other oral health defects like tooth fracture.
Dentin is a “collagen-based mineralized tissue underlying tooth enamel” that separates the enamel from the vascular pulp [1]. It has been thoroughly established by various studies that dentin, like bone, is less resistant to fracture and is more likely to crack with age because of hypermineralization; however, unlike bone, dentin doesn’t undergo turnover [1]. Recent studies suggest that the presence of fluoride may result in fluorine-rich crystals that may “alter the mechanical properties of dentin” and make it more susceptible to fracture [1]. Writes the NRC in the aforementioned report:
Enamel fluorosis, which accompanies elevated intakes of fluoride during periods of tooth development, results not only in enamel changes but also in dentin changes. It has now been well established that fluoride is elevated in fluorotic dentin. Some preliminary studies show that fluoride in dentin can even exceed concentrations in bone and enamel. [1]
As recent studies show, systemic fluoride may not only make dentin more susceptible to fracture but to dental caries, as well.
A 2005 population study of the correlation between dental fluorosis and caries concluded that “severe dental fluorosis was associated with increased caries prevalence” [8]. One of the reasons for this emerging trend may be dentin fluorosis. One study on the effects of fluorosis on dentin concluded:
The hypermineralization response of the dentin in our samples suggests that the mechanism of the response should be taken into account in dental caries and other dental disorders associated with severe fluorosis. [9]
Dentin fluorosis has been found to distort the intertubular collagen network in dentin, thereby causing detrimental hypermineralization of the dentin followed by higher susceptibility to acid degradation [10]. A recent study reports:
In moderately fluorosed dentine, the peritubular dentine appeared to be dissolved forming irregular dentinal tubular orifices. The intertubular dentine had chipped off regions forming some depressed areas. This may be a result of change in the acid penetration routes due to changed morphology of the moderately fluorosed dentine in a much vigorous manner than the mild fluorosed dentine. [10]
The study concluded that “mild and moderately fluorosed human dentine was significantly caries susceptible in vitro” [10].
Given the emerging evidence of the negative aspects of dental fluorosis, of both the enamel and dentin kind, as just discussed, it would be helpful to know just how prevalent this condition is presently. Numerous studies have been performed in recent years and they all confirm the conclusion that dental fluorosis has been rising at a dangerous rate amongst all populations. An extensive 2005 study by the CDC concluded:
Between 1999 and 2004, approximately 41% of adolescents aged 12 to 15 and 36% aged 16 to 19 years had enamel fluorosis. Moderate and severe fluorosis was observed in less than 4% in both age groups. […] A nine percentage point increase in the prevalence of very mild or greater fluorosis was observed among children and adolescents aged 6-19 years when data from 1999-2002 were compared with those from the NIDR 1986-1987 survey of school children (from 22.8% in 1986-1987 to 32% in 1999-2002). [11]
A 2004 study suggests that “the prevalence of fluorosis in permanent teeth in areas with fluoridated water has increased from about 10-15% in the 1940s to as high as 70% in recent studies” [12]. A 1999 Canadian study concluded the following:
Current studies support the view that dental fluorosis has increased in both fluoridated and non-fluoridated communities. North American studies suggest rates of 20 to 75% in the former and 12 to 45% in the latter. [13]
Finally, an extensive 2005 study concluded: “This systematic review concurs with recent reports of an increase in fluorosis prevalence in fluoridated and non-fluoridated communities” [14]. These and other similar studies [15, 16] show a dangerous trend of increasing rates of dental fluorosis in the United States and Canada in all communities. It’s important to note that while moderate to severe dental fluorosis usually occurs with water fluoride levels above those established by the ADA to be optimal for caries prevention (0.8-1.2 ppm), dental fluorosis rates for all types of fluorosis are increasing rapidly in both fluoridated and non-fluoridated areas.
It’s possible that these statistics and other recent studies that suggest that infants are most susceptible to the detrimental effects of systemic fluoride [17] caused the ADA to issue its November 2006 advisory on the dangers of feeding infants with formula mixed with fluoridated water because of the risks of the infant developing dental fluorosis in later life [18]. As more scientific proof emerges about the negative health effects of dental fluorosis, I hope that the ADA will make similar recommendations to the general public so that we can be better informed of the risks associated with fluoride consumption.
In conclusion, it should be clear that there may be a serious problem emerging with the high prevalence of dental fluorosis in the United States. It’s obvious that this trend is propagated by the widespread practice of public water fluoridation in many communities across the country. Recent research is increasingly giving evidence to the detrimental effects of both enamel and dentin fluorosis on oral health. All of this taken together points to a dangerous trend and an emerging public health issue, and it will be up to the dental professionals of the future to address this potentially serious problem with an open mind.
References:
1. “Fluoride in Drinking Water: A Scientific Review of EPA's Standards” (2006). Board on Environmental Studies and Toxicology (BEST), Division on Earth and Life Studies. NATIONAL RESEARCH COUNCIL OF THE NATIONAL ACADEMIES. THE NATIONAL ACADEMIES PRESS. <http://books.nap.edu/catalog.php?record_id=11571>
2. “Fluoridation Facts” (2005). American Dental Association. <http://www.ada.org/public/topics/fluoride/facts/index.asp>
3. Fluoride Action Network. (2007) “Professionals' Statement Calling for an End to Water Fluoridation.” May 20, 2008. <http://www.fluoridealert.org/statement.august.2007.html>
4. Dean, HT. (1942) “The investigation of physiological effects by the epidemiological method.” Ed: FR Mouton. Fluorine and Dental Health, ed. AAAS No. 19. Washington, DC: American Association for the Advancement of Science.
5. Griffin SO, Regnier E, Griffin PM, Huntley V. (2007) “Effectiveness of fluoride in preventing caries in adults.” Evid Based Dent. 2007; 8(3): 72-3.
6. Marinho VC, Higgins JP, Logan S, Sheiham A. (2004) “Topical fluoride (toothpastes, mouthrinses, gels or varnishes) for preventing dental caries in children and adolescents.” Evid Based Dent. 2004; 5(2): 36-7.
7. McDonagh MS, et al. “Systematic review of water fluoridation.” Ed: Hausen. BMJ 2000;321:855-859.
8. Rojas-Sánchez F, et al. (2007) “Dentin in Severe Fluorosis: a Quantitative Histochemical Study.” J Dent Res 86(9): 857-861.
9. Cunha-Cruz J, Nadanovsky P. (2005) “Dental fluorosis increases caries risk.” Journal of Evidence Based Dental Practice Vol. 5(3): 170-171.
10. Waidyasekera PG, at al. (2007) “Caries susceptibility of human fluorosed enamel and dentine.” J Dent. 2007 Apr; 35(4): 343-9.
11. Beltran E, Centers for Disease Control and Prevention. (CDC, 2005) “Surveillance for dental caries, dental sealants, tooth retention, edentulism, and enamel fluorosis--United States, 1988-1994 and 1999-2002.” Morbidity and Mortality Weekly Report Surveillance Summaries 54: 1-43.
12. Marshall TA, et al. (2004). Associations between Intakes of Fluoride from Beverages during Infancy and Dental Fluorosis of Primary Teeth. Journal of the American College of Nutrition 23: 108-16.
13. Locker, D. (1999). “Benefits and Risks of Water Fluoridation. An Update of the 1996 Federal-Provincial Sub-committee Report.” Prepared for Ontario Ministry of Health and Long Term Care.
14. Khan A, Moola MH, Cleaton-Jones P. (2005) “Global trends in dental fluorosis from 1980 to 2000: a systematic review.” SADJ 2005 Nov; 60(10): 418-21.
15. Warren JJ, Levy SM. (2003) “Current and future role of fluoride in nutrition.” Dental Clinics of North America 47: 225-43.
16. Fomon SJ, Ekstrand J, Ziegler EE. (2000) “Fluoride intake and prevalence of dental fluorosis: trends in fluoride intake with special attention to infants.” Journal of Public Health Dentistry 60: 131-9.
17. Browne D, Whelton H, O'Mullane D. (2005) “Fluoride metabolism and fluorosis.” J Dent. 2005 Mar; 33(3): 177-86.
18. American Dental Association. (2007) “Infants, formula and fluoride.” J Am Dent Assoc, Vol 138(1): 132.
Note:
I use [1] as a reference for much of my research, because the NRC report itself is an
excellent compilation of many studies done thus far on this and other fluoride-related health issues. I highly recommend it for anyone interested in further reading about this subject. The entire report is available free online at the URL listed above.
