Effects of oral function on pupil response: a new view on bruxism pathophysiology

There is increasing evidence of the influence of the oropharyngeal stimulations on the autonomic nervous system and an easy approach to evaluate the balance between parasympathetic and sympathetic system is the measurement of the pupil diameter. The aim of this analytic observational study is to define the effects of clenching and swallowing on pupil diameter, and how an oral appliance can affect the outcome of these tasks, to establish their influence on the sympathetic-parasympathetic balance.

We measured the pupil diameter in 30 healthy subjects during clenching and swallowing, both with and without oral appliance. We compared the results with the mandibular rest position. The respective positions with and without oral appliance were also compared.

Pupillometry showed a mydriatic effect of swallowing (rest 6.94 mm, swallowing 7.26 mm, P=0.04) and oral appliance, more relevant in scotopic conditions. On the contrary, clenching seemed to enhance miosis, especially in intense brightness condition (rest 3.95 mm, clenching 3.83 mm, P=0.02).

Swallowing and oral appliance facilitate the sympathetic system, while clenching activates the parasympathetic branch. We argue that probably the locus coeruleus is the main hub. These results could have practical implications in bruxism physiology, because it could be an attempt to counteract the activation of the sympathetic system.