A MICRORADIOGRAPHIC AND POLARIZING MICROSCOPIC STUDY OF SOUND ENAMEL

¹ Eastman Dental Dispensary, Rochester, N. Y., and Forsyth Dental Infirmary and Harvard School of Dental Medicine, Boston, Mass.

1. The mineralization of fully calcified sound enamel was studied in plano parallel ground sections using polarized light and microradiographic procedures.

2. Different retardation values were obtained with the specimens imbibed in hydrophobic liquids and in solutions of iodide in water having the same refractive index as enamel. Retardation varied when iodide solutions of different refractive indices were used, suggesting the presence of minute spaces between the apatite crystals. The form birefringence associated with these spaces was eliminated by imbibition in iodide solution with refractive index 1.620, but it was not affected when hydrophobic liquids were employed.

3. There was a gradual decrease in intrinsic retardation measurements, from the external surface to the inner third of the enamel.

4. Microdensitometric tracings of the radiographs also showed a gradual decrease in radiodensity from the external surface to the dentinoenamel junction.

5. There was good correlation between the intrinsic retardation values, and the radiographic density of different areas in the same specimens.