Location and structure of sensory nerve endings in the periodontium of the third premolar in Monodelphis domestica have been investigated by means of light and electron microscopy. The periodontal cleft of the tooth is apically enlarged. The number of nerve endings increases towards apex. Three types of sensory nerve endings have been observed: free nerve endings, Ruffini nerve endings and lamellated corpuscles. Free nerve endings could only be identified by electron microscopy. Ruffini nerve endings are only incompletely surrounded by lamellae of the terminal Schwann cell. Protrusions of nerve terminals of the Ruffini corpuscles are anchored between bundles of collagen fibers. Small lamellated corpuscles occur exclusively in the apical portion of the periodontium. Ruffini and lamellated corpuscles are considered as part of a masticatory reflex feedback control system. Ruffini corpuscles detect tension, rapidly adapting lamellated corpuscles detect pressure and vibration in the periodontium. Free nerve endings may function as thermoreceptor or nociceptor.
