NITROGEN CONTENT OF ZONES DISTINGUISHED BY REFLECTED LIGHT IN ENAMEL SECTIONS FROM UNERUPTED THIRD MOLARS

¹ U. S. Naval Dental School, National Naval Medical Center, Bethesda, Md.

1. Undemineralized tooth slices, 200 µ thick, were obtained from unerupted third molars of young adults, and fragments of enamel were sectioned according to their opacity to reflected light.

2. Selected samples weighing from 0.4 to 7.3 mg. were analyzed for phosphorus and nitrogen. (A modified ultramicro-Kjeldahl technic was adapted for the nitrogen determinations.)

3. The average nitrogen content of clear enamel for all teeth was 0.07 per cent; of cloudy white enamel 0.17 per cent; and of opaque yellow enamel 0.43 per cent. (Air-dried dentin contained about 2.5 per cent nitrogen.)

4. Comparison of the nitrogen content and of the phosphorus-nitrogen ratios of different areas of enamel from the same tooth revealed that, on the average, cloudy white enamel contained about 3 times as much nitrogen, and opaque yellow enamel about 10 times as much nitrogen, as clear enamel.