Characteristics of periodontal mechanoreceptors supplying cat canine teeth which have sustained orthodontic forces

The characteristics of these mechanoreceptors were investigated after orthodontic forces had been applied for either 3 days or 12 weeks, and also 8 weeks after the tooth had been moved into a new position and the tissues allowed to recover. Electrophysiological recordings were made from single mechanosensitive units dissected from the inferior alveolar nerve and each was characterized by applying forces to the tooth crown. The characteristics were compared with those of receptors innervating normal teeth. Three days after the onset of tooth movement, the periodontal mechanoreceptors had higher thresholds to forces applied at slow rates and lower discharge frequencies. Twelve weeks after the onset of tooth movement, the mechanoreceptors again had higher force thresholds and lower discharge frequencies but also responded to applied forces over a narrower range of directions and adapted more rapidly than the controls. After the tooth had been moved into a new position and the tissues allowed to recover, the mechanoreceptor characteristics were nearer to normal but they still had raised thresholds to forces applied at slow rates, lower discharge frequencies, and responded to applied forces over a narrower range of directions. It seems likely that the altered receptor characteristics would have resulted from a combination of disorganization of the collagen matrix and direct injury to the nerve terminals.