A. Long et al., A HISTOLOGICAL STUDY ON THE EFFECT OF DIFFERENT PERIODS OF ORTHODONTIC FORCE ON THE INNERVATION AND DIMENSIONS OF THE CAT PERIODONTAL-LIGAMENT, Archives of oral biology, 41(8-9), 1996, pp. 799-808
Using light microscopy, the numbers of myelinated axons in the periodo
ntal ligament of the cat mandibular canine were counted after orthodon
tic forces had been applied for either 3 days or 12 weeks, and also 8
weeks after removal of a force that had been-applied for the previous
12 weeks. After 3 days no significant changes in axon number were reco
rded, but after 12 weeks there were significantly fewer myelinated axo
ns in the periodontal ligament of the experimental teeth than in the c
ontrol teeth. This reduction was not reversed after an 8 week recovery
period. The width of the ligament was measured in an attempt to corre
late regions of nerve fibre degeneration with areas of compression or
tension, and the tooth root circumference was measured to assess the e
xtent of any root resorption. It appeared that axon degeneration occur
red both in areas of compression and tension. Root resorption had occu
rred after 12 weeks of applied force and there was no significant chan
ge after the 8 week recovery period. These findings support the view t
hat nerve injury occurs as a result of orthodontic force and may possi
bly be permanent. Copyright (C) 1996 Published by Elsevier Science Ltd
.