404 Orthodontic Tooth Movement Influences Face Mechanical Sensitivity and Motor-Cortex

Thursday, March 22, 2012: 2 p.m. - 3:15 p.m.
Presentation Type: Poster Session
M. SOOD, Dept. of Orthodontics and Oral Physiology, University of Toronto, Toronto, ON, Canada, J.C. LEE, Dept. of Oral Physiology, University of Toronto, Toronto, ON, Canada, P. BHATT, McMaster University, Hamilton, ON, Canada, and B.J. SESSLE, Dept. of Oral Physiology and Neuroscience, University of Toronto, Toronto, ON, Canada
Objective: To determine if altering the rat's dental occlusion by an orthodontic appliance produces mechanical hypersensitivity and influences the intracortical micro-stimulation (ICMS)-defined face primary motor cortex (face-M1). 

Method: Sprague-Dawley rats had a closed-coil spring placed to mesialize the right maxillary molars. Electromyographic (EMG) wires were implanted in the anterior digastric (AD-jaw-opening), masseter (MAS-jaw-closing), genioglossus (GG-tongue-protrusion), and buccinator (BUC-cheek) muscles. ICMS (20, 40, 60µA) was applied in microelectrode transdural tracks to define the right and left face-M1 in different groups of rats on days 1 (n=5), 7 (n=6), and 28 (n=8) subsequent to spring attachment. Sham groups with springs with no activation for days 1 (n=5), 7 (n=5), and 28 (n=6) served as controls. The evoked EMG activities of the muscles were analyzed by a customized program developed in LabVIEW. A similar set of experimental and control groups were tested for thresholds of mechanical sensitivity to facial mechanical stimuli applied by von Frey monofilaments. Group data were compared using one-way ANOVA and post-hoc Tukey test.

Result: A significant reduction in the number of M1 sites from which AD and/or GG activity could be evoked occurred in the day 1 experimental group (67.6 ± 12.8) compared to sham (127.6 ± 10.5; p<0.001). The number of sites increased in the day 7 experimental group (135.2 ± 12.9) compared to sham (94.2 ± 6.5); p<0.001), and decreased in the day 28 experimental group (86.4 ± 13.6) compared to sham (127 ± 5.4; p<0.001). A significant decrease in mechanical thresholds was observed on day 1 and was maintained until day 5, but only in the experimental groups.

Conclusion: Orthodontic tooth movement is associated with short-lasting changes in facial mechanical sensitivity but longer-lasting neuroplastic changes in face-M1 that may reflect the initial mechanical hypersensitivity and subsequently the changes in the dental occlusion.

This abstract is based on research that was funded entirely or partially by an outside source: CIHR grant MOP-4918

Keywords: Motor systems, Occlusion, Orthodontics, Pain and Teeth
See more of: Orthodontic Outcomes
See more of: Craniofacial Biology
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