Sodium fluoride (NaF) is. used for the treatment and prevention of dental caries. Its application to the teeth makes the dental enamel more resistant to acid. In some communities, it is added to the water if the geographical area lacks sufficient fluoride. Another method of preventing dental caries is the use of sodium fluoride topically on the teeth in solution or in toothpastes or gels. Other indications for sodium fluoride are as an insecticide and rodenticide. It has also been used orally to treat diseases in which osteoporosis is a major feature (1).

Very few reports have been published regarding reactions to the topical use of sodium fluoride. Some reactions presumed due to hypersensitivity have been reported as urticaria, reactivation of atopic dermatitis, exfoliative dermatitis, stomatitis and respiratory allergy. Nevertheless, true allergic reactions have not been demonstrated, though sodium fluoride is considered to be an irritant (2-4).

Case Report

An 8-year-old girl first attended our allergy department because of chronic rhinitis. Positive prick tests to Dermatophagoides pteronyssinus, and horse and dog dander were obtained. The IgE level was 696 IU/I. LTTs with salicylates and benzoates were negative. Because she mentioned episodes of urticaria on eating bananas, prick tests with foods were also done, with negative results. Prior to her next presentation, her teeth had been treated topically by her stomatologist with sodium fluoride on 3 occasions: the 1st, 1 year previously, the 2nd, 4 months previously and the 3rd, 1 month previously. 7 h after the 3rd application, a very severe disseminated acute urticaria and facial angioedema appeared, requiring hospital admission. The commercial product applied had been Duraphat®, composed of 50 mg sodium fluoride (22.6 mg fluorine) in an alcoholic solution of resins. The printed information with the product advises that occasionally some oedematous inflammation can occur on the gingivae or oral mucosa if the application spreads beyond the dental surface; it also states that in extremely rare cases, mainly in allergic people, bronchospasm and dyspnoea can occur. An extensive history clarified that the patient had been intolerant of certain fluoride toothpastes in the past.

Patch testing with a standard series, plastics, resins;and Duraphat® showed only mild ( +) erythema and oedema at 2 days to this commercial product. At 4 days, only a slight erythema persisted. In vitro tests were not performed. Patch tests with Duraphat® and sodium fluoride 1% aq. in 14 controls were negative. The patient’s family refused a further patch test with sodium fluoride.

Comment The clinical features and patch test results do not allow a distinction to be made between immunological and non-immunological contact urticaria. Nevertheless, the case confirms that, in some atopic patients, painting the teeth with sodium fluoride can lead to severe and potentially dangerous reactions.

References

1. Martindale. The Extra Pharmacopoeia, 29th edition. London: The Pharmaceutical Press, 1989: 1614-1616.

2. Shea J J, Gillespie S M, Waldbott G. Allergy to fluoride. Ann Allergy 1967: 25: 388-390.

3. Douglas T E. Fluoride dentifrice and stomatitis. Northwest Med 1957: 56: 1037-1039.

4. Fisher A A. Pustular patch test reactions. Arch Dermatol 1959: 80: 742-743.