Effects of mandibular deviation on brain activation during clenching: an fMRI preliminary study

Using functional magnetic resonance imaging (fMRI) in eight healthy human subjects, the present study measured blood oxygenation level-dependent (BOLD) signals during clenching in a malocclusion model, using a custom-made splint that forced the mandible to a retrusive position and a splint of no modification for control, and compared the results to the BOLD signals during the corresponding resting conditions. An individual visual analog scale (VAS) score was also examined during clenching to evaluate the interactions between fMRI data and psychiatric changes. During both clenchings, activations in four brain regions (premotor cortex, prefrontal cortex, sensorimotor cortex, and insula) were seen. However, clenching in the malocclusion model, with psychological discomfort, increased additionally BOLD signals in the anterior cingulate cortex and the amygdala. Furthermore, there was a parallel relationship between BOLD signal intensities and VAS scores in these two regions. The findings may suggest the involvement of clenching with malocclusal conditions in the emotion and/or pain-related neural processing in the brain.