The properties of periodontal mechanoreceptors supplying lower canine teeth in cats have been investigated 12 wk after the crushing or sectioning of the inferior alveolar nerve. Forces were applied at right angles to the crown of the tooth and recordings made from filaments dissected from the nerve central to the injury site. Data obtained from 41 units after nerve crush and 65 units after nerve section were compared with those from a series of control animals. 2. The range of directions to which each receptor was sensitive was significantly smaller after both nerve crush and nerve section. There were significantly more rapidly adapting units after both nerve crush (37%) and nerve section (34%) than in the controls (19%). 3. Force thresholds measured at three rates of application (20 N/s, 2 N/s, and 0.25 N/s) were significantly higher after nerve section but not after nerve crush. The maximum frequency of discharge was significantly reduced after both nerve crush and nerve section. 4. Bone was removed from over the roots of the teeth to localize receptors in the underlying periodontal ligament. Seventeen receptors were localized in the nerve crush group and 23 in the nerve section group, and their distribution appeared similar to that found in controls. The conduction velocities of these units were significantly reduced after nerve section but not after nerve crush. One unit in the nerve section group appeared to have branched and innervated receptors in two locations.
