The Effects of Occlusal Interference on Brain Activation by fMRI

Objectives: Some recent reports suggest that occlusal dysfunction may have systemic effects by acting on brain function. Therefore, in this study, we fabricated a crown for the left mandibular first molar of experimental occlusal interference, and during a gum-chewing task, we used 3.0-Tesla MRI to investigate detailed changes in brain functional responses associated with changes in input of afferent information.
Methods: In 11 subjects with normal occlusion, a crown was made using an electroforming technique for the left mandibular first molar, and subjects performed a gum-chewing task with crown overlay (200 µm of occlusal interference) and without (control). Each subject quantified their subjective feeling of discomfort during chewing with a mark on the VAS, which ranged from 0 to 10 (0 = no discomfort, 10 = extreme discomfort). Participants also verbally expressed to an interviewer how they felt during chewing. Each subject performed a series of four cycles of gum-chewing, each cycle consisting of 32s and 32s of resting, and brain activation sites were evaluated using functional magnetic resonance imaging (fMRI). Results were considered statistically significant at p < 0.05.
Results: Sensory evaluation showed that unpleasant sensation during gum chewing was significantly greater in the interference group than the control group. On group analysis of fMRI, the somatosensory-motor cortex, supplementary motor area, the insula, and the cerebellum were activated in both groups. In the interference group, activation was significantly higher in the amygdala, anterior cingulate cortex, prefrontal area, and hypothalamus.
Conclusions: Our findings show that stimulation from occlusal dysfunction is rapidly relayed to the brain and is closely related to activation of emotions of discomfort. This may have an influence systemically as a stress response.