Recovery of Periodontal Ruffini Endings following Re-establishment of Occlusion

Objective: It is known that over-loading of occlusal force causes the abnormal sensation and the alteration in morphology of periodontal Ruffini endings. However, it is unknown whether the reduction of occlusal force causes such morphological changes in periodontal Ruffini endings. Moreover, there is no report that re-loading of occlusal force rescue the morphological alterations of the Ruffini ending. The present study was examined whether mechanical stimulation is required for morphological maintenance of periodontal Ruffini endings of rat incisors by immunohistochemistry for protein gene product 9.5 (PGP 9.5). Methods: Occlusal force to the periodontal ligament was reduced by grinding the tips of upper and lower incisors of adult rats unilaterally for 3, 5, 7, 14, 28 and 56 days. Some animals received the grinding of the tips for 14 days, and untreated for additional 14 days. The periodontal ligament of upper jaw was immunostained with antibody against PGP 9.5. Results: The periodontal Ruffini endings of adult rats were restricted in the alveolar half of the lingual ligament, and showed expanded terminal arborization with dot-like structures. After grinding, the terminal portions of the Ruffini endings showed smooth-surfaced outlines on the ground sides. Ultrastructurally, the axon terminals apparently decreased in size, and mitochondria within the terminal became smaller. The percentages of immunoreactive areas in the restricted portion on the ground sides significantly decreased compared to those of normal animals. When incisor occlusion was re-established, the terminal portions of the Ruffini endings returned the normal appearance, and the percentages of immunoreactive areas also recovered. Conclusions: The present results indicate that proper mechanical stimulation is an important factor for maintaining the morphology of mechanoreceptors. (Supported by Grant-in-Aid #16390526 and 21st COE Program)