MICRORADIOGRAPHIC AND POLARIZED LIGHT STUDIES OF INITIAL CARIOUS LESIONS

¹ Eastman Dental Dispensary, Rochester, N. Y., and Forsyth Dental Infirmary, Boston, Mass.

1. Plano-parallel ground sections of initial carious lesions were studied by polarizing microscopy and microradiography.

2. Different polarizing colors were observed when the specimens were imbibed in oily media and in iodide solutions having the same refractive index. Form birefringence could not be completely eliminated with oily media because of failure of the liquids to penetrate the minute spaces in some areas of the lesion. The watery iodide solutions did effectively penetrate into the microspaces and imbibition of the specimens with a solution of refractive index 1.620 permitted quantitative measurements of intrinsic retardation in all areas of the lesions.

3. Measurement of intrinsic retardations suggested that the external layer of enamel was partially decalcified. The subsurface portion of the lesions varied in decalcification in different areas. No zones of hypercalcification were found within the lesions.

4. Microdensitometric tracings of radiographs of the lesions were carried out with a slit width of 16 by 16 µ. The tracings showed a decalcification pattern of the carious lesions, similar to that obtained with retardation measurements.