A correlative morphological study was carried out on physiologically located periodontal mechanoreceptors in anaesthetised cats. Three periodontal mechanoreceptors were electrophysiologically identified from functionally single fibres teased from the inferior alveolar nerve. One receptor was studied by recording in the mesencephalic nucleus. The four receptors were located by punctate stimuli in the labial aspect of the periodontal ligament of the left mandibular canine tooth in three cats. The receptors were within the intermediate to rapidly adapting part of the range of adaptation rates with conduction velocities of 39.6 ms-1 +/- 4.7 ms-1 and were typical of those recorded in previous studies. The receptor loci were marked and these regions were studied in silver-stained sections and ultrastructurally. Under each ink-marked region Ruffini terminals and smaller terminals resembling free nerve endings were observed. The Ruffini terminals were unencapsulated and the majority had diameters of 2-3 microns. The terminals were observed near the junction of the inner (cemental) and middle zones of the periodontal ligament with the axons running from the alveolar aspect. The results support the view that periodontal mechanoreceptors, even those with more rapidly adapting properties, are Ruffini terminals.
