CALCIUM EXCHANGE IN ENAMEL AND DENTIN AS SHOWN BY CALCIUM

¹ The Division of Pharmacology and Toxicology, Department of Radiation Biology, The University of Rochester School of Medicine and Dentistry, Rochester, N. Y.

1. The adsorption of Ca⁴⁵ by powdered dentin and enamel from aqueous calcium solutions (1.25 x 10-², x 10-³, and x 10-⁴ M.) has been measured in vitro.

2. On glycol-ashed dentin, the rapid phase of calcium adsorption is an exchange reaction in which as much as 1/5 of the total calcium atoms of the dentin may ultimately take part. In fresh dentin, a slower but even more extensive exchange may occur. On enamel, only 2 per cent of the calcium atoms appear to exchange.

3. The adsorption probably takes place on the surfaces of the ultramicro-extensive exchange may occur. On enamel, only 2 per cent of the calcium atoms scopic hydroxylapatite crystals. These crystals are much larger in enamel (10-⁴ cm. in length) than in dentin (10-⁶ cm.).