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We have studied the effects of air drying of exposed, acid etched dentin on the sensory innervation of rat molars. In the acute series of experiments, trigeminal nerve fibers were labeled by axonal transport of radioactive protein prior to the dentin exposure and desiccation, the anesthetized rats were fixed by aldehyde perfusion 10 min later, and the teeth were prepared for autoradiography. The results confirmed the hydrodynamic theory by showing outward movement of labeled nerve material in response to dentinal drilling and desiccation. It also showed that some odontoblasts could be separated from the dentinal nerve fibers. In the chronic series, teeth were injured 25 h, 5-7 days, or 21 days prior to fixation and nerves were labeled during the last 24 hours; the surviving vital nerve fibers were evident because of their axonal transport of the radioactive label. In that series, sensory nerve fibers were found to have been lost from areas with newly-formed reparative dentin, or from dentinal tubules that had lost their odontoblasts. In the teeth injured 25 h, 5-7 days, or 21 days earlier, an abnormal nonneuronal labeling occurred 0.2-0.3 mm into injured dentin. Our results are discussed in relation to the hydrodynamic theory, nerve-odontoblast interactions, differences between shallow and deep cavity injuries, altered nerve location in response to pulpal or dentinal injury, and characteristics of the pulp-dentin border.

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