A STUDY OF THE DEVELOPMENT OF DENTAL ENAMEL IN DOGS

¹ University of London, University of Sheffield, National Institute for Medical Research (London) and National Physical Laboratories (Teddington), England

With a view to investigating the different stages in enamel development and the chemical and physical basis for the differences between good and defective (M-hypoplastic) enamel produced by different diets, the enamel of the developing teeth of dogs has been examined histologically, by chemical analysis and by x-rays. Prior to the present work, no investigation on developing enamel has been undertaken on the quantitative side either by chemical or x-ray analysis.

The investigation is a continuation of the work of Mellanby (1929), who differentiated, from the staining reactions of ground sections of developing teeth, 2 stages in enamel calcification, enamel in the "first stage" being soft and staining deeply and in the "second stage" being relatively hard and not readily stainable with carmine.

For the purpose of chemical analysis, enamel was divided into 3 grades (A, B and C), which were distinguished by differences in surface appearance and consistency. Grade A enamel was approximately at the second stage of calcification and B and C at the first.

The results of quantitative chemical and x-ray analysis indicate that the great differences in hardness observed in these grades can be attributed to differences in the concentration of mineral matter. The results also give quantitative support to the previously accepted view that, in the second stage of development, calcification proceeds from the tip downwards. Radiographic analysis also confirmed the finding that in the early stages of calcification a thin strip of enamel along the amelodentinal junction is more highly calcified than the rest.

The chemical results show that when the cod liver oil was included in the diet the calcification of the enamel was more advanced than in control animals receiving peanut oil, which is deficient in vitamins A and D.

In contrast to the beneficial effect of cod liver oil as a source of vitamins A and D₃, addition of vitamins A and D₂ together in relatively large amounts (2,500 I.U. vitamin D₂ and 15,000 and 30,000 vitamin A, including a little D₃) did not produce a greater degree of calcification than was found in the controls. When, however, these high doses of the vitamins were given separately, an increase in the degree of calcification occurred. It is felt that any deductions from the results which concern higher doses of vitamin A must be regarded as tentative pending further experiment.