Toxic Paste



JADA 24:3-7-309 (1937)

In an earlier report, the Council called attention to the granting of patents for dental articles after what appeared to the Council to be inadequate scientific study (J.A.D.A., 21:1494 [Aug.] 1934). More recently, a patent has been issued by the U. S. Patent office for a dentifrice which is stated to contain, as one of the important ingredients, sodium fluoride. Claims that it will whiten teeth by virtue of the fluoride content are permitted. These allowed claims were investigated at the request of the Council by a qualified collaborator in the laboratory of a member of the Council, because (1) a patent for an essentially toxic substance in a dentifrice was issued, and (2) it was believed that the attention of the profession should be called to the presence of potentially toxic substances which appear in dentifrices from time to time. The Council accepted the report of its collaborator with a note of appreciation for the careful manner in which the work was carried out, and authorized its publication.


The object of this report is to present results on growth rate and the incisors of the albino rat from feeding a tooth paste (U. S. Pat. No.1,943,856) as evidence of toxic potentialities of fluoride, said to be a constituent of the product. Roy Cross, Kansas City, Mo., assignor to Silica Products Company, Kansas City, has secured U. S. Patent No. 1,943,856 on a dental preparation with the following composition:

  • Bentonite. .....................50 parts
    Magnesium oxide...........50 parts
    Sodium fluoride..............1 part
    Sodium phosphate..........5 parts (acid or basic?)
    Soap powder.................5 parts
    Oil of eucalyptus............1 part
    Gum camphor................ 1 part
    Tincture of benzoin..........5 parts

Water in sufficient quantity to give a paste of the right consistency. Samples of Cross' product were not available for toxic tests and, therefore, a mixture was prepared according to the composition as stated. PROCEDURE In compounding this mixture, the sodium fluoride, bentonite, magnesium oxide and soap powder were thoroughly mixed. The camphor, eucalyptol and tincture of benzoin were thoroughly dissolved. The two mixtures were then combined and well mixed in a mechanical mixer.

For the purposes of the experimental tests to be described, the water was omitted from the formula. The inventor does not state whether acid sodium phosphate or disodium phosphate should be used. Since the resultant mixture is alkaline in reaction, acid sodium phosphate would be converted to disodium phosphate. The use of acidsodium phosphate would put more phosphate into the mixture and in the belief that the inventor would have no objection to using the maximum amount of the bone building phosphate for rubbing on the gums, the acid salt was used. It will be seen that the foregoing formula contains about 0.8 per cent sodium fluoride before water is added to form a paste. The proposal to apply such a concentration of sodium fluoride to the mouth one or more times daily is not to be considered lightly, in view of the known toxic actions of fluorine. Hence, this investigation of the possibility of chronic fluorine poisoning was undertaken. That fluorine can cause chronic poisoning has been amply demonstrated [1]. One part of fluorine in 1,000,000 parts of water has been shown to be sufficient to cause mottling of the teeth in children. Fourteen parts of fluorine in 1,000,000 parts of food has been shown [2] to produce bleaching of rat incisors. The possibility of deleterious effects from fluorine in the above-mentioned tooth paste formula was tested by feeding female albino rats well-balanced diets to which definite concentrations of the tooth powder were added. The growth curves of the rats were determined and compared with the growth curve of normal female albino rats.

At the same time, bleaching of the incisor teeth was watched for, since this effect is a delicate criterion of fluorine toxicity. Details of the experiments on the lower dosage levels will not be discussed, since the results were surprisingly negative. Only the two highest dosage levels need be considered. RESULTS Starting with a weight of approximately 50 gm., control female rats gained about 100 gm. during the first two months, about 20 gm. in the second two-month period and about 10 gm. in the third two-month period. Female rats on the same diet, to which tooth powder had been added, so that 96 parts of fluorine per million parts of food were present, grew at a somewhat slower rate. The effect on growth was too small to be significant. Pregnancies took place; whereas, addition of the same concentration of sodium fluoride to the diet in the absence of the other ingredients permitted very few, if any, pregnancies. Evidently, the fluorine of the tooth powder was not absorbed. Fourteen parts of fluorine per million parts of food will cause bleaching of the incisor teeth in young growing rats, but 96 parts of fluorine, as an ingredient in the above-mentioned tooth powder, failed to show bleaching during two months of feeding. Double the dose, or 192 parts of
fluorine per million parts of food, did produce a detectable bleaching by the end of the next month. This quantity of fluorine is 14 times the quantity necessary to produce bleaching of rat incisors. Since the proposed tooth paste is alkaline in reaction and contains magnesium oxide, magnesium fluoride may be formed, and this salt may actually be present in the dentifrice because of its low solubility product. The low solubility of 0.0087 per cent at 18 C., and the alkaline reaction of the digestive tract, may account for an extremely low absorption of fluoride and thus for the negative results obtained.

COMMENT In spite of the failure to produce bleaching of rat incisors with reasonable amounts of the poisoned tooth powder in the diet, the inclusion of sodium fluoride in the formula is irrational and should be discouraged. The claims that sodium fluoride in the preparation bleaches the teeth is based on false premises. Bleaching of human teeth by fluoride occurs only in children prior to eruption of the permanent teeth. The mechanism depends on an internal physiologic action. No effect is produced on the enamel of permanent teeth subsequent to eruption. Ammonium fluoride is used in dental practice to whiten teeth, but this action on external application to the teeth depends on an etching effect of the ammonium fluoride, which is acid in reaction. Such an action would not occur with sodium fluoride added to a tooth paste which is alkaline in reaction. As shown by the investigation of Sharpless and McCollum [3], fluorine is not an essential element in tooth structure, and even if it were essential, it could not be supplied by rubbing on the tooth surface. A rational scientific basis for the use of sodium fluoride in tooth paste does not exist. Despite the fact that the results as to toxicity of this commercial product were essentially negative, it does not follow that the product is necessarily innocuous or at least free from toxic potentialities under all possible dental conditions. For example, local absorption of the fluoride might be promoted by massage of the gums with the aid of a toothbrush, and by the presence of pathologic conditions, such as ulcers, inflammatory states, pus pockets and the like. In other words, uncontrolled usage of the product by the laity might still result in undesirable systemic reactions, especially in children.


1. The fact that a patented fluoride dentifrice was not demonstrably toxic when tested for typical fluoride toxicity in feeding experiments on rats does not mean that this dentiifrice is not potentially toxic under all dental conditions.

2. Conditions of dental usage and pathologic states in the mouth might promote absorption of fluoride and toxicity.

3. The use of fluoride in dentifrices is unscientific and irrational, and therefore should not he permitted.

[1]. DeEds, Floyd: Chronic Fluorine Intoxication (A Review), Medicine, 12 (Feb.) 1933). DeEds, Floyd, and Thomas, J. 0.: Comparative Chronic Toxicities of Fluorine Compounds, Proc. Soc. Exper. Biol. & Med., 31:824-825, 1934.mith, Margaret C.; Lantz, E. M., and Smith. H. V.: Univ. Arizona Col. Agr. Tech. Bull. 32, 1931.

[2]. Footnote [1], first reference. [3]. Sharpless, G. R., and McCollum, E. V.: Is Fluorine an Indispensable Element in Diet? J. Nutrition, 6:163-178, 1933. J.A.D.A. 24 (1937) 307-9

Cross Patent :