Soil, Dental Decay Linked

Press, Volume CIV, Issue 30835, 21 August 1965, Page 3

Soil, Dental Decay Linked

(Parliamentary Reporter) WELLINGTON, August 20. A relationship between soil conditions in New Zealand and the prevalence of dental caries was the most interesting finding from a study by Dr. R. E. T. Hewat, the Medical Research Council said in its annual report tabled in Parliament today.

Dr. Hewat conducted an extensive epidemiological study of the prevalence of dental caries in the child and young adult population. Detailed dental examinations were made of more than 14,000 Europeans and 7000 Maoris aged seven to 17. The soil-caries relationship was investigated in the North Island in four selected soil areas which Dr. Hewat’s results indicated were associated with high or low caries, said the report. The high caries prevalence associated with certain wet, strongly-leached soils in the Haurake district was confirmed, although differences were not as clearly defined as expected. About the same time, however, in connexion with a study of fluoridation at Hastings, it was found by Dr. T. G. Ludwig that Napier children had an unusually low incidence of dental decay. Intensive investigation in Napier, Hastings and Palmerston North related the lower caries experience of Napier children to the fact they lived on saline soils formed from the bed of a former salt water lagoon during the major Hawke’s Bay earthquake in 1931.

Since these soils probably exerted their effect through locally - grown those grown in Napier and Hastings markets and home gardens were analysed. It was found that Napier vegetables contained greater amounts of molybdenum (a metallic element occurring in combination or, when separated, a brittle, almost infusible silver-white metal, aluminium and titanium (a rare metal never found free in nature but obtainable as an iron-grey powder), and Hastings vegetables contained greater amounts of copper, manganese, barium and stroutium.

Animal-feeding experiments using the ash residues of these vegetables showed the ash of the Napier vegetables had a pronounced cariesreducing effect when fed to rats as a supplement to a caries-producing diet. A similar caries-reducing effect could be imparted to the ash of the Hastings vegetables by increasing its molybdenum content to a level equivalent to that found in the Napier vegetable ash. The results obtained in this study suggested that the caries-reducing factor in Napier was likely to be related to the greater availability of molybdenum in Napier soils. Support for this was given by analyses which indicated that the molybdenum levels of teeth from Napier children had increased.

The manner in which molybdenum might act was not yet known, although investigation of the shape, size and form of teeth from Napier children indicated that these teeth had several physical charactertistics common to those found in other children with an increased resistance to dental decay, said the report.

Further animal experiments had shown that molybdenum, acting alone, produced only slight reductions in caries scores. It did, however, have a powerful synergistic effect with fluoride, so that these two elements acting together reduced dental caries by more than 80 per cent.