Imaging Brain Networks: Insights into Mechanisms of Temporomandibular Disorders

Temporomandibular disorders are a group of craniomaxillofacial disorders mainly characterized by pain and motor dysfunction of the temporomandibular joints and surrounding masticatory muscles. Clinically, patients with temporomandibular disorders often display central nervous system dysfunction, such as negative mood disorders, but the underlying cause remains unclear. Recent developments in neuroimaging techniques have facilitated new understanding. Notably, the triple network model consisting of the default mode network, the central executive network, and the salience network is of particular interest in this regard and may provide new insights into brain network alterations. Specifically, we observed that patients with temporomandibular disorders have abnormal activation of attention-related brain regions in the default mode network, which may be related to pain rumination. In addition, cortical atrophy and altered functional connectivity were found in regions related to the regulation of emotion and pain. In the central executive network, decreased activity and metabolism were seen in pain regulation regions, while abnormal activation occurred in regions associated with negative emotions. The salience network showed aberrant activation and metabolic changes in pain perception regions, and negative emotions were associated with an abnormal activation pattern. Potentially treatment-induced changes included a return to normal activity in attention and emotion regulation regions, suggesting that assessing activity in these networks may be used to evaluate treatment efficacy. Finally, this review highlights current dilemmas and future opportunities for the field in terms of research cohorts, methods, scope, and analytical techniques. Further exploration is necessary to realize a better understanding of the neuropathophysiology of temporomandibular disorders and ultimately more effective treatments.