WEAVER, ROBERT : London, England (June 3, 1938).


(1) ” Association between two conditions does not warrant any conclusion as to causal relationship, and that being so, it cannot be regarded as estab­lished that the original structure of a tooth is of importance in determining its liability to caries. (2) The hypothesis that there is a close association be­tween structure and caries in the case of permanent teeth appears to be in conflict with Mrs. Mellanby’s own results. (3) The findings in the Sheffield and Birmingham experiments are capable of an interpretation other than that given by Mrs. Mellanby. It has not been established that the resistance of a tooth to caries can be raised or lowered after eruption. (4) Mrs. Mellanby’s theory does not appear to be in harmony with the information available as to (a) the relative liability to caries of the different surfaces of the teeth; (b) the incidence of rickets; (c) the incidence of caries in New Zealand, Australia and South Africa; (d) the asymmetry of caries on opposite sides of the mouth; (e) the views held by dentists concerning the relative liability to caries of vital and pulpless teeth.”

” Until a decade or so ago, it was believed by most people that the incidence of caries could be explained almost entirely in terms of the environment of the


SUMMARIES ON CARIES                                     165

teeth. A theory based on this belief may for convenience be referred to as an environmental theory, as opposed to a nutritional theory, such as Mrs. Mellanby’s, which postulates that the explanation is to be found almost entirely in the teeth themselves. We are now invited to regard environment as a very minor factor not because of any direct evidence that it is of little significance, but because it is claimed that nutrition has been shown to be of paramount importance. There is one very good reason why a nutritional theory should not be adopted in place of an environmental theory before the latter has been conclusively proved to be wrong. An environmental theory says that, if the teeth are not subject to the action of acid in the mouth, they will not become carious—an argument which is easily under­stood. But so far the way in which minute structure may influence liability to caries has not been explained. How can a tooth, however well formed, resist an attack which is apparently primarily chemical ; what is there in the teeth which can prevent acid from dissolving the enamel of those teeth with which it remains in contact ? Is it conceivable that, as fast as the enamel is decalcified, the vitality or resistance’ of the tooth effects a recalcification? The idea that some unex­plained resistance may inhere in the tooth itself must not be ruled out just because of the difficulty of believing it. Quite apart from this difficulty, however, there are, as has been shown, many serious weaknesses in the newer theory.”

Reference: Brit. Den. J., 1935.

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