Unerupted human third molar crown segments were used to measure the change in the concentration of various substances which occurs when they move across dentin from pulpal to occlusal surfaces. The chemicals used were technetium-99m (99mTc), 45Ca, and [3H]-labeled tetracycline. When solutions of these isotopes were filtered across dentin at flow rates of 1 μl per min to 14 μl per min, 45Ca was almost completely removed, 99mTc showed no change in concentration, and 65 to 75% of the [3H]-labeled tetracycline was removed at a flow rate of 1 μl per min. This increased to a removal of 99% at 14 μl per min. 45Ca, 99mTc, or [3H]-labeled tetracycline were preloaded into dentinal tubules and eluted with nonradioactive substances or water. 45Ca was eluted with CaCl2 but not with water; 99mTc was rapidly removed with water; [3H]-labeled tetracycline was readily removed, but more slowly, with either tetracycline base or water. These data suggest that 45Ca ionically binds to dentin and 99mTc does not. The binding of 3H]-labeled tetracycline was flow rate dependent and it seemed to bind nonspecifically and reversibly.
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