c-fos expression in the trigeminal sensory complex and pontine parabrachial areas following experimental tooth movement.

Ortodontic tooth movement causes continuous pain. However, it does not appear immediately, usually appearing after the application of orthodontic force to the teeth. Mechanically induced inflammatory responses in the periodontal membrane are assumed to be related to the mechanism of the later pain sensation. In the present study, we investigated Fos-like immunoreactivity in the trigeminal sensory complex and pontine parabrachial areas 24 h after the commencement of experimental tooth movement. An orthodontic elastic module was unilaterally inserted between upper molars. Following experimental tooth movement, Fos-like immunoreactive neurons appeared ipsilaterally in the trigeminal subnucleus caudalis and bilaterally in the lateral parabrachial nucleus. These results indicate that experimental tooth movement evokes delayed and continuous nociception after application of orthodontic force to the teeth and that the nociceptive information would be conveyed to the ipsilateral trigeminal subnucleus caudalis and further processed, at least in part, to the lateral parabrachial nucleus.