A histologic and radioautographic study of migration patterns in the mandibular molars of normal and lathyritic mice

Abstract

Previous studies by Thomas (1965) and Michaeli, Pitaru, Zalicek and Weinreb (1975) revealed that a lathyritic disruption of the collagenous fibres of the periodontal ligament resulted in a retardation of tooth eruption. However, only incidental findings of the pattern of bone deposition and resorption have been reported in relation to tooth migration. The present study was undertaken to histologically and radioautographically compare the patterns of molar tooth migration in normal and lathyritic mice. The histologic examination determined a morphologic variation in the periodontal ligament fibres on either side of the alveolar septa of control mice. The relevance of this finding was compared with previous observations reported in the mouse (Dunstan, 1975) and in the human periodontal ligament (Edwards, 1977). Furthermore, no evidence could be found for the existence of transalveolar fibres as proposed by Cohn (1972a) and Johnson (1980). Radioautographic labe1ling confirmed the reliability of using Sharpey fibres as histologic indicators of bone deposition. Using both of these markers bone deposition in control animals was found on distal and buccal facing surfaces of alveolar bone as well as on the alveolar crest. Other alveolar bony surfaces showed evidence of resorption. As a consequence, the present study revealed that in addition to distal and occlusal drift in control mice there was also pronounced tooth migration in a buccal direction. The initiation of lathyrism by a dietary method produced a gradual and progressive change in the mouse periodontal structures. Disruption of the periodontal ligament was seen to commence in the apical region and extend coronally. Significantly however, after forty days, the supracrestal area remained seemingly unaffected. This was believed to reflect collagen turnover within the periodontal ligament. Concomittant with the lathyritic periodontal ligament disturbance an alteration appeared in alveolar bone activity. A direct relationship was evident between the development of the lathyritic lesion, a loss of Sharpey and principal fibre continuity, as well as a loss of radioautographic label. These findings indicated a cessation of the distal and buccal vectors of migration during lathyrism. However, occlusal drift was continuing. It was considered that the associated bony changes were a result of the inability of a weakened lathyritic periodontal ligament to support the tooth against occfusal load. The apparent continuation of tooth eruption therefore disagreed with the previous findings of Thomas (1965) and Michaeli et al (1975). Various explanations of this finding are discussed with the severity of the lathyritic induction cited as a likely contributing factor. Nevertheless, the collagen contraction theory of tooth eruption becomes untenable (Thomas, 1965¡ I976) . The intact nature of the transseptal fibres and the observed altered pattern of tooth migration contradicts the tenet of Picton and Moss (1973) who assign to this fibre system a principal role in approximal tooth drift. Since a disruption of either the transseptal or principal fibres alters the pattern of movement it was considered that the integrity of the entire periodontal ligament was essential for physiologic tooth migration . It has been noted that a force applied to lathyritic collagen, whether orthodontic or masticatory loading, produces contrasting periodontal effects. It was concluded that the behaviour of lathyritic collagen under stress was incompletely understood and an interesting area for further research.