Successful therapy for temporomandibular pain alters anterior insula and cerebellar representations of occlusion

Abstract

Craniomandibular disorders (CMD) are widespread, but we know little about the cerebral representations associated with this pain syndrome and nothing about changes in cerebral representations of occlusion induced by common therapy approaches. In a longitudinal therapy study, we applied functional magnetic resonance imaging (fMRI) in 14 patients with mild CMD during occlusal movements. fMRI, pain scoring, kinematic investigations of occlusal movements, and jaw muscle electromyography (EMG) were measured before and after two weeks of therapy with an individually optimized Michigan splint. The patients' subjective pain ratings decreased, and the symmetry of condylar movements increased over the period of therapy. After therapy, EMG of the jaw muscles demonstrated more relaxed resting conditions and increased activity during maximal occlusion. fMRI during occlusion showed an activation decrease in the right anterior insula and right cerebellum over the course of therapy. Correlation analysis between pain score and fMRI activation decreases identified right anterior insula, left posterior insula and left cerebellar hemisphere. Left cerebellar and right primary motor activation magnitude was negatively associated with symmetry of the condylar movements. Our findings highlight the impact of the anterior insula for the internal monitoring and the anticipation of temporomandibular joint (TMJ) pain. In addition, an increase of symmetry of condylar movements after therapy has been associated with a decrease of activation magnitude in primary motor and cerebellar regions.