Discussion.

Mr. J. Ll. Saunders, in opening the discussion, referred to the very concise and yet comprehensive account given by Professor Walsh of the work done on dental caries. In his analysis of the work done to date Professor Walsh had reduced the problem to four variable factors. It was noted that all four were purely intra-oral factors. Would the essayist say that the concensus of opinion to-day tended to exclude the possibility of diet having any other than a purely environmental role in the etiology of dental caries? In a study made by the speaker, no correlation was found to exist between the incidence of rickets and that of dental caries, a finding which supported the environmental theory, but in another phase of the same study a significant difference was disclosed in the incidence of dental caries at different social levels. Allowing that economic status, knowledge and judgment in regard to choice of foods would have a bearing on this finding, it did seem that the environmental theory would not necessarily of itself account for the variation in incidence between the different social groups.

Turning to the recommendations with which Professor Walsh concluded his paper, it was noted that he suggested that there was a magnificent opportunity for both the State services and private practitioners to undertake full-scale operation of the known preventive measures outlined in the paper.

Mr. Saunders said that speaking as a representative of the State services, he was sure that these services and the profession as a whole would adopt preventive measures with enthusiasm as soon as it was felt that their efficacy was established. He thought, however, that as yet these measures had not passed beyond the experimental stage. It was clear, however, that the outlook was promising, and the profession, including the State services, should be prepared to adopt full-scale preventive measures as they became available for general use.

After hearing Professor Walsh's paper, said Mr. Saunders, one felt that the time was approaching when, as a result of the research that was being done, the whole character of dental practice would change, and the dentist of the future would become to an increasing extent a dental physician rather than a dental surgeon, with the dental surgery yielding pride of place to the dental consulting room.

Professor Walsh replied that in pregnancy deterioration in dental status was due essentially to alteration in dietetic habits rather than to any drain of calcium from the teeth of the mother to the child. He stated that women who took extra care of their teeth at those times were found to have an improved dental state at the end of pregnancy. The rate of exchange of calcium within the teeth was extremely slow, even perhaps a life time, whilst in bones the exchange was quite rapid.

Miss Cunningham referred to the work with “tagged ions” which showed the interchange of calcium within the body structures, agreeing that the rate of exchange of calcium in the teeth was infinitesimal compared with that of the bones, where this could well be demonstrated in three weeks. However, change in the calcium content of teeth took place from the surface, and where there was calcium change during pregnancy this was exchange and not removal.

Dr. Muriel Bell stated that there was still much confusion between the theory and practice in regard to dental caries. She pointed out that the Chinese in China in general had good teeth, but that the Chinese in Malaya generally had bad teeth. The chemist could show no difference between the carbohydrates of refined white flour and those of refined white rice, and yet there was considerable difference in their effects on teeth. The high-carbohydrate rice diet of the Chinese in China still left them with good teeth. She therefore declined to accept that civilisation, merely through increasing the carbohydrate in the diet, is responsible for our increase in dental caries. There was still need for greater knowledge of the causation.

Professor Walsh agreed with Dr. Muriel Bell that in regard to diet we have not as yet got very far. Some sticky foods, though carbohydrate, had a detergent effect, though the reason for this was unknown. The physical characteristics of foods, apart from their chemical content, still needed much more investigation.

Mr. Lane stated that 90 per cent, of the white flour in England was treated by a chemical “improver” which destroyed the vitamins, and suggested this might explain the difference between white flour and rice and its effect on the teeth.