Dental fluorosis in the Cape Verde Islands: prevalence of clinical findings in an isolated island population.

INTRODUCTION

Fluoride is of interest because of its toxic properties and its effect on dental enamel and bone. As natural fluoride is widely distributed in nature, the soils of different regions of the world vary greatly in their fluoride content, with higher fluoride concentrations being found in groundwater due to the presence of fluoride bearing minerals. (1) While fluoride can be absorbed from the gastrointestinal tract, via the pulmonary tree, or via the skin, the major site of absorption is via the gastrointestinal tract. As such, ingested fluoride acts locally on the intestinal mucosa, and can form hydrofluoric acid in the stomach, leading to gastrointestinal irritation and corrosive effects. As a result, signs and symptoms of acute fluoride toxicity by ingestion can occur within minutes of exposure. (2) Although fluoride can be detected in all organs and tissues, including the thyroid, aorta, and kidneys, fluoride is preponderantly deposited in the skeleton and teeth, and the degree of skeletal storage is related to intake and age. Following absorption, fluoride ions are promptly deposited in the skeleton and teeth where they become incorporated into the crystal lattice of hydroxyapatite, substituting for hydroxyl ions.

With regard to fluoride toxicity, this can be classified as acute or chronic. Fluorine and fluorides are cellular poisons which block the glycolytic degradation of glucose, and fluorides also can form an insoluble precipitate with calcium which causes hypocalcemia, with ingestion of 1 to 2 gm of sodium fluoride being potentially fatal. Acute fluoride toxicity usually results from accidental ingestion of insecticides or rodenticides which contain fluoride salts. In addition, one recent comprehensive review describes the biochemical and physiologic mechanisms involved with aluminum-fluoride complexes, and its effect on the development of fluorosis. (3)

In chronic fluoride toxicity, the major manifestation of chronic ingestion of excess amounts of fluoride can result in significant enamel defects known as dental fluorosis. Additionally, chronic fluoride toxicity can be characterized by osteosclerosis, weight loss, anemia, and joint pain. The bony changes demonstrated may include exostoses of the spine and genu valgum, and are usually seen only after prolonged high intake in adults. In its severest form chronic fluoride toxicity is a disabling disease, and has been referred to as crippling fluorosis.

The well-recognized and historically documented example of chemically induced enamel hypoplasia refers to the effects of chronic fluoride toxicity on the dentition, and although total fluoride intake will vary with total water consumption, fluoride-induced enamel hypoplasia, also referred to as fluoride mottling, is usually inconspicuous at levels below 1.0 ppm in the drinking water. Indeed, mottling of the enamel is one of the first visible clinical signs of an excessive intake of fluoride during childhood.

Aim of the present study is to present the clinical findings of dental fluorosis in the isolated population of Brava, the smallest island among the Cape Verde Islands.

MATERIALS AND METHODS

In October of 2005, a healthcare team consisting of dentists, dental hygienists, nurses, surgical technicians, and administrators functioning under the sponsorship of Healing The Children, Northeast, Inc. (219 Kent Road, Suite 2, New Milford, CT, 06776) traveled to the island of Brava, which is the smallest and most isolated island in the Cape Verde archipelago, which is situated approximately 300 miles west of the continent of Africa. The goal of this humanitarian mission was to provide basic dental evaluations and dental care to the indigenous people of this island. In addition, basic medical laboratory testing, which consisted of measurements of hematocrit and urinalysis, were performed. This was done in order to screen for any nutritional deficiencies which may have gone unnoticed, and which might possibly have correlated with poor dental health.

During the four days that the team was able to work, a total of 174 patients were evaluated dentally, out of a population of 266 screened people. The 174 screened persons underwent dental examinations and basic laboratory testing, which included analysis of hematocrit and a basic urinalysis. The screening process involved an initial interview and evaluation for the presence of any need for dental care, and the only patients who were turned away were those deemed to be in overall good health and who did not wish to undergo a dental examination. The treatments provided for the population group consisted of either oral hygiene procedures, extraction of teeth, or other dentoalveloar surgical procedures.

As basic dental care for the island population was minimally existent, is was inferred that most likely increased concentrations of natural fluoride in the drinking water of the island of Brava was responsible for the high incidence of enamel mottling demonstrated clinically in the subject population (see results). The enamel mottling which was observed varied from slight to severe, ranging from chalky-white patches, and progressing to brown staining and surface irregularities on the enamel surfaces of the involved teeth (see figure 1). These were serendipitous and unexpected findings, and as such, samples of water from the island were obtained and transported to the United States at the conclusion of the trip for evaluation of fluoride concentration.

Samples of drinking water from the island were obtained and transported to the United States with the healthcare team, and were subsequently tested for concentrations of fluoride. An Individual Fluoride Testing Kit manufactured by LaMotte Company (802 Washington Ave, Chestertown, MD, 21620) was utilized to test the samples of water from the island. This system utilizes an octet comparator with an axial reader, in such a manner that a red zirconium lake reacts with fluoride to form a colorless solution, which decreases the red color of the solution in proportion to concentration. The range and sensitivity of this testing system was from 0.2 to 1.6 ppm of the fluoride anion.

RESULTS

Of these 174 patients who underwent dental examination, a total of 73 (41.95%) demonstrated some degree of enamel mottling, which ranged from chalky-white patches on the enamel surfaces, to brown staining and surface irregularities. This was immediately presumed to be due to dental fluorosis as a result of probable excessively high levels of fluoride in the drinking water on the island of Brava.

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The resulting fluoride concentration was noted to be 1.4 ppm, which was indicative of a high level of natural fluoride level in the water samples obtained. These findings confirmed the initial clinical suspicions of a high percentage of fluoride-induced enamel hypoplasia (dental fluorosis) in the isolated island population of Brava.

DISCUSSION

Although contemporaneous clinical findings associated with dental fluorosis are observed infrequently in the United States, there are historical examples of note. In 1901, Dr. Frederick S. McKay suggested the association between this mottled enamel and an agent in the Colorado Springs, Colorado water supply during investigation of the Colorado brown stain seen in the teeth of many of his patients. In 1930, H.V. Churchill, a chemist in Bauxite, Arkansas who was employed by the Aluminum Company of America, discovered extremely high concentrations of fluoride (13.7 ppm) in the drinking water of patients affected in that community, and when these were correlated with high natural fluoride levels in water samples from the affected areas on Colorado, the puzzle was solved. In an interesting review from 1938, H. Trendley Dean provides a useful and interesting early discussion regarding three phases of chronic fluorosis, including dental anomalies, osteosclerosis, and an osteomalacia-like disease. (4) Interestingly, when it was observed that children born in Bauxite after a new water supply had been obtained demonstrated a much higher incidence of dental caries than those who had been exposed to the former fluoride-containing water, the impetus was provided to the United States Public Health Service to initiate a series of studies in order to ascertain whether the fluoridation of water could be employed as a practical measure to reduce the incidence of tooth decay.

Recent studies demonstrate the variability of natural fluoride concentrations worldwide. A recent study from the Erode district of India demonstrated highly variable fluoride concentrations in the drinking water, ranging between 0.5 and 8.2 ppm, and revealed that 80% of the water samples contained fluoride above the maximum permissible limit. (5) An interesting recent study of naturally occurring fluoride levels in Carroll County, Maryland, demonstrated variable concentrations of naturally occurring fluoride at differing well depths, and described how this information could be useful with regard to avoidance of incorrect fluoride prescribing behaviors. (6)

Augenstein et al presented an interesting review of 87 cases of accidental fluoride ingestion, which included ingestion of topical fluoride products, excessive topical fluoride application by dental practitioners, and ingestion of a sodium fluoride insecticide, analysis of which indicated that the majority of cases of fluoride toxicity in children of less than 12 years of age, in amounts up to 8.4 mg/kg of body weight, resulted in mostly mild and self-limiting symptoms, which were mostly gastrointestinal in nature. (7)

While the exact mechanism of action of how fluoride causes enamel mottling remains unknown, it is well-recognized that with increased amounts of fluoride concentrations in the drinking water, the resultant enamel hypoplasia becomes progressively evident, as increased fluoride levels interfere with ameloblastic function, which adversely affects both enamel matrix formation and enamel matrix calcification. As mottled enamel is the result of partial failure of ameloblasts to properly elaborate and lay down enamel, it is a developmental injury.

One recent study reminds us that the effects of fluoride on enamel formation causing dental fluorosis in man are cumulative, rather than requiring a specific threshold dose, depending upon the total fluoride intake from all sources and duration of fluoride exposure. (8) It has also been recently shown that since exposure to fluoride can inhibit protein synthesis, fluoride may therefore induce endoplasmic reticulum stress in ameloblasts responsible for dental enamel formation. (9)

The changes noted in the dentition range from chalky-white, irregularly distributed patches on the surface of the enamel, which become infiltrated by yellow or brown staining, progressing to enamel surface pitting with increased exposure to excessive levels of fluoride. In addition, it should be remembered that regardless of the degree of fluoride mottling, affected teeth are largely resistant to dental caries. Finally, it should also be noted that in warmer climates, water consumption may be increased, so that a fluoride concentration as found with the population at hand may produce a variable range of mottling of enamel, from slight to severe. Such was the case on the island of Brava, which is located close to the equator such that the climate is hot and humid on a year-round basis, requiring the residents of the island to ingest high volumes of fluids in order to maintain proper hydration.

This report describes an unexpected, yet clinically significant, unusually high incidence of varying degrees of the clinical finding of dental fluorosis, also referred to enamel mottling, in an isolated island population. This is significant in that further studies of such relatively isolated populations may provide further insight into to the pathogenesis and prevalence of this condition in such populations, and as such, may further our knowledge base as to proper fluoridation strategies in population centers in general. In addition, as chronic fluoride toxicity may cause systemic manifestations, then public health efforts in these isolated populations should be directed toward prevention and mitigations of clinical effects. Indeed, a case report from 1994 described the toxic effects of excess fluoride in one of two public water systems in a village in Alaska, demonstrating the need for monitoring of fluoride concentrations in public water systems in general in order to prevent episodes of fluoride poisoning. (10) In addition, it has been shown that acute fluoride poisoning may be caused by exposure to lower levels of fluoride than has been commonly suggested, so that the levels required for toxicity to fluoride should be re-evaluated. (11) As such, follow up evaluations of the extent of chronic fluoride toxicity, including the high incidence of dental fluorosis, in the island population of Brava, in the Cape Verde archipelago, will be considered and encouraged.

Likewise, similar studies should be considered and undertaken on the other islands of this archipelago, primarily in order to increase the size of the data without changing the social structure of the populations involved. This should be undertaken for two reasons:

1) to respect and preserve the existing cultural norms, and 2) to maintain consistency within the study by examining multiple populations which are similarly small and secluded. This is a model somewhat similar to the research done in the Erode district, India, which also examined the prevalence of dental mottling in a relatively isolated community.

Being able to fully and accurately describe the pathogenesis and progression of dental fluorosis is of great importance for reviewing the efficacy of current fluoride supplementation regimens, as well for the development of possible treatment modalities. This is of crucial interest for isolated communities such as that seen on the island of Brava, which does not have the infrastructure available for conventional water fluoridation regimens, such as those seen in the United States. The healthcare team involved in this study intends to return to the Cape Verde Islands, specifically to the island of Brava, not only to provide much needed dental care, but also to continue data collection relating to this most interesting phenomenon.

ACKNOWLEDGMENTS

The authors wish to acknowledge our grateful appreciation to the staff of Healing The Children, Northeast, including Steven A. Nargiso, President, Dana Buffin, Executive Director, and Missy Law, Medical Teams Abroad Director, for their assistance with the preparation of this article, as well as for their tireless efforts on behalf of the underprivileged of the emerging nations of the world. A special acknowledgement is extended to Steven A. Nargiso for his exemplary leadership as the Healing the Children Northeast Team Administrator for the humanitarian mission described in this manuscript.

Conflict of interest: None declared.

REFERENCES

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(2.) Nochimson G. Toxicity, Fluoride. eMedicine Specialties>Emergency Medicine> Toxicology> http://emedicine.medscape.com/article/814774-overview.Retrieved on 2008-12-28.

(3.) Li L. The biochemistry and physiology of metallic fluoride: action, mechanism, and implications, Crit. Rev. Oral Biol. Med. 2003, 14(2):100-14.

(4.) Dean HT. Fluorine intoxication (Letter to the Editor). Am J Public Health 1938:28:1008-1009.

(5.) Karthikeyan K, Nanthakumar K, Velmurugan P, Tamilarasi S, Lakshmanaperumalsamy P. Prevalence of certain inorganic constituents in groundwater samples of Erode district, Tamilnadu, India, with special emphasis on fluoride, fluorosis and its remedial measures. Environ Monit Assess 2008; DOI 10.1007/s10661-008-0664-0.

(6.) Osso D. Relationship of naturally occurring fluoride in Carroll County, Maryland to aquifiers, well depths, and fluoride supplementation prescribing behaviors. Journal of Dental Hygiene 2008;82(1).

(7.) Augenstein WL. Fluoride ingestion in children: a review of 87 cases. Pediatrics 1991;88(5):907-912.

(8.) Aoba T. Dental fluorosis: chemistry and biology. Critical Review in Oral Biology and Medicine 2002;13(2):155-170.

(9.) Kubota K. Fluoride induces endoplasmic reticulum stress in ameloblasts responsible for dental enamel formation. The Journal of Biological Chemistry 2005;280(24):23194-23202.

(10.) Gessner BD, Beller M, Middaugh JP, Whitford GM. Acute fluoride poisoning From a public water system. N Eng J Med 1994;330(2):95-9.

(11.) Akiniwa K. Re-examination of acute toxicity of fluoride. Fluoride 1997:30(2): 89-104.

Corresponding author: Daniel J. Traub, DDS Oral and Maxillofacial Surgeon 3900 Eubank Blvd. NE, Suite 12 Albuquerque, NM USA 87111 Tel: [phone] E-mail: [e-mail]

Daniel J. Traub, Bruce V. Gallup, Michael A. Traub, Tamara Donald

A study supported by Healing the Children Northeast, Inc. (http://www.htcne.org) New Milford, Connecticut ,USA