1. Hardwick, J. L., Br. dent. J., 119, 304–311 (1965).
2. Rich, C. and Ensinck, J., Nature, 191, 184–185 (1961).
3. Jowsey, J., Rigs, B. L., Kelly, P. J., and Hoffman, D. L., Am. J. Med., 53, 43–49 (1972).
4. Forrest, J. R., Br. dent. J., 119, 316–319 (1965).
5. Hodge, H. C., and Smith, F. A., in Fluorine Chemistry (edit. by Simons, J. H.), 786 (Academic, New York, 1965).