THE LABORATORY EVALUATION OF PROPHYLACTIC DENTIFRICES 489 REFERENCES (1) Fosdick, L. S., J. Arner. Dent. Ass., 40 133 (1950). (2) Mansbridge, J. N. Brit. Dent. J., 109 848 (1960). (3) Manly, R. S. and I-lodge, H. C. J. Dent. Res., 18 138 (1989). (4) Manly, R. S. and Bibby, B. G. J. Dent. Res., 9.8 160 (1949). (5) U.S. Pat: No. 3,105,798. (6) Gray, J. A. J. Dent. Res.. 41 633 (1962). (7) Gray, J. A. J. Dent. Res., 44 493 (1965). (8) Gray, J. A., Schweizer, H. C., Rosevear, F. B. and Broge, R. W. J. Dent. Res., 87 638 (19S8). (9) Jenkins, C. N. and Spelts, R. L. J. Physiol., 19.1 21 (1953). (10) Brudevold, F., Gardner, D. E. and Smith, F. A. J. Dent. Res., 815 420 (1956). (11) Isaac, S., Brudevold, F., Smith, F. A. and Gardner, D. E. J. Dent. Res., 87 318 (1958). (12) Spiers, R. L. Brit. Dent. J., 107 209 (1959). (13) Weatherell, J. A. and Hargreaves, J. A. J. Dent. Res., 48 958 (1964). (14) Weatherell, J. A. and Hargreaves, J. A. Advances in fluorine research and dental caries prevention, 4 181 (1966). (15) MiJhlemann, H. R., Schutt, A. and K6nig, B[. G. Helv. Odont. Acta., 8 147 (1964). (16) Wharton, H. W. Anal. Chem., 34 1296 (1962). (17) Brudevold, F., Chilton, N. W. and Wellock, W. D. J. Oral Therapeutics and Pharrnacol. 1 1 (1964). (18) Walter, H. G. Helv. Odont. Acta., 9. 40 (1958). (19) MiJhlemann, H. R. and Wolgensinger, F. Helv. Odont. Acta., Ii 35 (1959). (20) Holmes, A. W. and Middleton, J. D. Brit. Dent. J., 113 380 (1962). (21) Morley, C .W. and Holems, A. W. Brit. Dent. J., 115 71 (1965). (22) Herd, J. K. and Overell, B. G. Brit. Dent. J., 117 286 (1964•. (23) Brudevold, F., McCann, H. G. and Gordon, P. Caries-Resistant Teeth. Ciba Foundation Symposium (1965). Churchill, London. (24) Jenkins, G. N. Brit. Dent. J., 119 535 (1965). (25) Von der Fehr, F. Acta. Odont. Scan&, 19 431 (1961). (26) Pigman, W:., Elliott, H. C. and Laffre, R. O. J. Dent. Res., 31 627 (1952). (27) Pigman, W. and .Newbrun, E. J. Dent. Res., 41 1304' (1962). (28) Francis, M.D. and Meckel, A. H., Arch. Oral Biol., 8 1 (1963). DISCUSSION MR. N.J. VAN ABBI•: You mentioned that you use pH measurements rather than phosphate determinations to assess in vivo tooth solubility. I wonder how far the spread of results that you have, which seemed to be unaccountable, was due to trying to measure pH values accurately on small quantities of weak acids. THE LECTURER: We are fairly satisfied that, with attention to detail, we can achieve a good degree of reproducibility in determining pH values. We do, of course, rely on our statistician to show that the differences reported are statistically significant. MR. N.J. VAN ABBr.: One has seen an occasional statement that the case hardening effect due to fluoridation makes it more difficult to recognise a cavity with the probe. Is there any suggestion that this can be true in the case of a fluoride toothpaste? THE LECTURER: The recognition of what is a carious lesion is a vexed one in the context of clinical trials and has been the subject of much learned discussion. The phenomenon of 'reversals' in clinical trials shows that the development and recording of lesions is not a simple matter. If the suggestion were true then the apparent benefit derived from fluoride toothpastes would be inflated.

490 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS MRs. H. BUT•.ER: You were suggesting that fluoride in water prevented dental caries. I wondered if you were referring to work that has been done since the war in areas in this country where fluoride has been added to water or whether you were basing it upon areas known to have natural calcium fluoride in the water. T•E LECTURER: My understanding of the position is that if fluoride is present at the right concentration in the water supply irrespective of whether it occurs natrually or is added, then a reduction caries incidence will be obtained in that area. MRs. H. BU•LER: I should like to counter by saying that before the war in areas in this country where fluoride occurred at more than 5 ppm there was evidence of very bad dental caries in the children, and that it might be a bad thing to perpetuate this fiction. I should like to know what positive results have been obtained in areas where 1 ppm has been put into the water. TI•E I.EC•URER: A fairly high incidence of mottling of tooth enamel would be expected with 5 ppm of fluoride in the water supply. I have not read reports which suggest that this would lead to the high level of caries you mentioned. A British mission studied several areas in the U.S.A. where fluoride occurred naturally or was added to the water supply. They found no health hazard associated with the presence of about 1 ppm of fluoride in water while the caries rate in teeth which had developed in this environment was much less than in non-fluoride areas. The Ministry of Health report on the five year studies conducted in this country records a marked improve- ment in the condition of teeth which had developed during these experiments and confirms that 1 ppm of fluoride, whether natural or added, is nothing but beneficial. MR. R. C•.Am•: Extensive data has been collected in the U.S.A. in epidemiological studies where fluoride occurs naturally. The results are very significant and show that where 1 ppm or thereabouts of fluoride occurs in water, the incidence of caries is some 60% less than that where fluoride falls to about 0.2 ppm. This has been confirmed by extensive studies, again in America, where fluoride has been added artificially to water previously low in fluoride. When you have a high level of fluoride in the water supply you get tooth mottling and things like that but this is not the intention of those who want to fluoridate water. The evidence is incontrovertible. DR. K. H. R. WRmH•: Do you have any evidence of improved mechanical proper- ties of an enamel surface after treatment with a fluoride toothpaste ? THE LECTURER: I have no results of my own on this topic but there are references in the literature to the remineralisation of enamel which can occur, or rather which is accelerated, in the presence of fluoride. This has been shown by hardness measure- ments on partly demineralised enamel. The hardness increased after exposure to fluoride solutions. DR. K. H. P•. WRIGHT: How much more effective is a toothpaste than a simple mouthwash? THE LECTURER: I have no knowledge of in vivo tests which would answer this. In in vitro tests, fluoride is more effective in a simple solution in reducing enamel solu- bility than when mixed with other ingredients, e.g. toothpaste constituents. MR. J. M. B•.AI•EW•¾: Have electron microscopic studies been made on the effect of monofluorophosphate on enamel on the same basis as for stannous fluoride and sodium fluoride?