Sleep bruxism: a novel theoretical perspective through the lens of the free energy principle (FEP).

Sleep bruxism is a prevalent sleep-related motor phenomenon characterized by rhythmic masticatory muscle activity that ranges from physiological behavior to a condition with clinically significant craniofacial consequences. Existing models emphasize multifactorial risk factors and centrally mediated dysregulation but lack a unified mechanistic account linking neural regulation, autonomic physiology, airway function, craniofacial biomechanics, and the temporal organization of rhythmic masticatory muscle activity. In this Hypothesis and Theory article, we outline a Free Energy Principle (FEP) - informed framework in which sleep bruxism is interpreted as an expression of predictive regulation and active inference within nested craniofacial, autonomic, and respiratory systems, explicitly as a theoretical account rather than as an empirically established mechanism. Within this framework, we introduce the construct of homeostatic latency, defined conceptually as the temporally extended window over which polysomnographic and electromyographic indices of sleep bruxism frequency, intensity, and inter-episode intervals reflect the efficiency of recovering a quasi-stable equilibrium after arousal-related perturbations. From this, we derive testable hypotheses regarding: (i) clustering of rhythmic masticatory muscle activity around micro-arousals and respiratory events, (ii) characteristic autonomic signatures preceding episodes, (iii) homeostatic latency profiles derived from EMG timing measures, (iv) airway-related phenotypes and responses to mandibular advancement devices, and (v) differentiated profiles across stress-related, arousal-related, respiratory - airway protective, and neuromodulatory sleep bruxism endotypes. In addition, we briefly indicate how an FEP-informed ontological framework for SB could, in future work, be extended into a domain-specific, knowledge-graph - based representation to support integration of multimodal data and hypothesis-driven computational modeling, while emphasizing that such tools are not developed or validated in the present article. Overall, the framework aims to reconcile sleep bruxism as both behavior and condition, in line with contemporary consensus views, and to generate falsifiable predictions for future empirical studies.