Effects of occlusal rebalancing on cognitive performance

Trigeminal input to the ascending reticular activating system is important for the maintenance of arousal and may affect the discharge of the Locus Coeruleus (LC) noradrenergic neurons, whose activity influences both vigilance state and pupil size, inducing mydriasis. Pupil size evaluation is now considered as a proxy of LC activity. Trigeminal imbalance due to malocclusion may lead to imbalance in LC activity and, as a consequence, in the brain excitability. Such an imbalance might, in turn, lead to functional impairment of cognitive and motor functions. In healthy subjects, showing asymmetry in the electromyography activity of masseter muscles during clenching (> 24%), we evaluated whether malocclusion, modifying the symmetry of the trigeminal sensorimotoractivity 1) induces changes in the cognitive performance, in the task-related mydriasis and in the pupil asymmetry; 2) modifies the brain activation during a pure motor task as evaluated by fMRI, in order to disentangle the possible role of motor behaviour in the performance of the cognitive task which consist of both cognitive and motor components. It was found that occlusal correction (through the wearing of an appropriate orthotic interposed between the dental arches) modifies the trigeminal input asymmetry and positively affects cognitive performance by changing the task-induced LC activation and its resting imbalance. Moreover, occlusal correction leads to a reduction in the brain activation during a pure motor task, suggesting the motor contribution into the cognitive performance improvement. So, trigeminal unbalance associated to malocclusion leads to an asymmetry in pupil size, while occlusal correction reduces both trigeminal and pupil size asymmetry and boost performance in a cognitive sensorimotor task.