TIME STUDIES OF THE PENETRATION OF EXTRACTED HUMAN TEETH BY RADIOACTIVE NICOTINAMIDE, UREA, THIOUREA, AND ACETAMIDE

II. PENETRATION OF DENTIN FROM THE PULP CHAMBER

¹ Radiobiology Section, Los Alamos Scientific Laboratory of the University of California, and the Dental Clinic, Los Alamos Medical Center, Los Alamos, N. M.

1. Isotope-labeled solutions of nicotinamide, urea, thiourea, and acetamide were tested for their ability to penetrate dentin by placing them in the cleaned pulp chambers of extracted human teeth. Twenty-one unfixed and five formolfixed teeth were treated, stored in a humid atmosphere, and, after periods of six minutes to three days, were sectioned under oil and examined radioautographically.

2. C¹⁴-nicotinamide, C¹⁴-urea, S³⁵-thiourea, and C¹⁴-acetamide penetrated dentin rapidly. Each compound penetrated through approximately 3.5 mm. of dentin to reach the dentoenamel junction in about twenty minutes. Acetamide penetrated through the dentin (4.1 mm.) and faintly through the enamel (2.1 mm.) within twenty-two minutes at 37° C.