MICROSCOPY Vol.46▶No.4 2011
â– Feature Articles: Advances in Somatosensory Research

Morphological Basis on Sensory Receptors in the Periodontal Ligament with Special Reference to the Ruffini Endings

Takeyasu Maeda

Abstract: The periodontal ligament serving as tooth support or anchor has a rich sensory nerve supply to function as sensory input apparatus to mastication system. The periodontal ligament contains nociceptive free nerve endings and mechanoreceptors. Stimuli applied to teeth easily evoke various oral reflexes, which make smooth mastication possible via the periodontal mechanoreceptors. Morphological and physiological studies have revealed that Ruffini ending, categorized as low-threshold slowly adapting type II, is a primarily mechanoreceptor in the periodontal ligament. The periodontal Ruffini endings are characterized by expanded axon terminals with extensive ramifications and by an association with the terminal or lamellar Schwann cells. Their axon terminals expressed various kinds of proteins such as Ca-binding protein. The mechanical stimuli due to tooth eruption and occlusion might be a prerequisite for the final differentiation and maturation of the periodontal Ruffini endings. Many experimental studies have revealed that periodontal Ruffini endings have high potential for neuroplasticity. It appears that the development/regeneration/maturation of the periodontal Ruffini endings is controlled by multiple neurotrophins including BDNF, NT-4/5 and GDNF in a stage-specific manner.

Key words: periodontal ligament, Ruffini ending, ultrastructure, development/regeneration, neurotrophin