Microradiographic and Polarized-Light Studies of Artificially Produced Lesions

¹ Eastman Dental Dispensary, Rochester, New York, and Forsyth Dental Infirmary, Boston, Massachusetts

1. Acid-etched lesions were produced by exposing enamel to acetate buffers at a pH of 4.0, 4.5, and 5.0 and a concentration of 0.1, 0.01, and 0.001 M.

2. Plane-parallel ground sections of the etched enamel, investigated by polarizing-light microscopy and microradiography, revealed that different types of lesions were produced, depending on the pH, the strength of the buffer, and the time of acid exposure.

3. Subsurface lesions similar to incipient carious lesions were produced by the weaker buffers at all pH levels.

4. Surface lesions simulating an advanced stage of carious lesions were produced by stronger buffers and at low pH's.

5. Polarized and microradiographic examination of the subsurface lesions revealed (a) partial decalcification of the external surface of the enamel; (b) variable decalcification in different areas of the same sections; (c) no indication of hypercalcification in different types of acid-etched lesions; and (d) progress of the lesion along the interprismatic substance and the striae of Retzius.