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OBJECTIVE: Calcification of degenerating tissues in the periodontal ligament (PDL) during tooth movement was investigated longitudinally. MATERIALS AND METHODS: Upper first molars of male Wistar rats were moved lingually for 1, 7 and 21 d, following which unfixed undecalcified sections of the lingual PDL (in the pressure zone) were examined histologically, histochemically (autoradiography and electron probe microanalysis). RESULTS: On d 1 of tooth movement, degenerating tissues, together with some calcified particles, were visible in the pressure zone of the lingual PDL. On d 7, substantial calcified aggregations were seen in the degenerating tissues, predominantly situated between the bone and root. This was confirmed by the 45Ca autoradiography. On d 21 of tooth movement, large calcified aggregations were still clearly evident between the bone and root. CONCLUSIONS: This calcification of the degenerating tissues is a self-defense response of the living body to prevent direct contact between alveolar bone and the tooth root during compression of the PDL, so preventing friction between them and the development of ankylosis.
Nakamura et al. (2003) studied this question.