Neuroplastic changes in the sensorimotor cortex associated with orthodontic tooth movement in rats

Orthodontic tooth movement (OTM) causes transient pain and changes in the dental occlusion that may lead to altered somatosensory inputs and patterns of mastication. This study used intracortical microstimulation (ICMS) and electromyographic (EMG) recordings to test whether neuroplastic changes occur in the ICMS-defined motor representations of left and right anterior digastric (LAD, RAD), masseter, buccinator, and genioglossus (GG) muscles within the rat's face primary motor cortex (face-M1) and adjacent face primary somatosensory cortex (face-S1) during OTM. Analyses included any changes in the number of ICMS sites representing these muscles and in the onset latencies of ICMS-evoked responses in the muscles. Sprague-Dawley rats were divided into experimental (E), sham (S), and naive (N) groups; OTM was induced in the E group. Statistical analyses involved a mixed model repeated-measures analysis of variance (MMRM ANOVA). OTM resulted in significant neuroplastic changes in the number of positive sites in the E group for LAD, RAD, and GG muscles in face-M1 and face-S1 at days 1, 7, and 28 of continuous orthodontic force application, and in the number of sites in face-M1 from which ICMS could simultaneously evoke EMG responses in different combinations of LAD, RAD, and GG muscles. However, the onset latencies of ICMS-evoked responses were not significantly different between groups or between face-M1 and face-S1. The neuroplastic changes documented in this study may reflect adaptive sensorimotor changes in response to the altered environment in the oral cavity induced by OTM. J. Comp. Neurol. 523:1548-1568, 2015. (c) 2015 Wiley Periodicals, Inc.