Distinguishing chronic pain from mechanical factors in chronic TMD: a narrative review

The International Classification of Diseases-11 (ICD-11) defines chronic pain conditions as those that lack identifiable underlying pathology at the site of pain. In parallel, the Diagnostic Criteria for Temporomandibular Disorders (DC/TMD) system was developed as a comprehensive framework for diagnosing and managing conditions previously classified under the broader category of temporomandibular disorders (TMD). While the DC/TMD system provides a structured and clinically useful approach, it does not fully distinguish between pain-related disorders and mechanical dysfunction associated with TMD. Specifically, mechanical temporomandibular joint (TMJ) conditions, as described in the DC/TMD, are distinct from chronic pain present in chronic TMD (cTMD). These mechanical issues may or may not involve chronic pain, and despite often coexisting with chronic facial pain, they represent separate diagnostic entities that necessitate individualised management strategies. This differentiation is essential for accurate diagnosis and effective treatment of chronic TMD patients. This review provides a comprehensive analysis of cTMD, synthesising evidence from genotyping studies, systemic inflammation, immune dysregulation, endocrine disturbances, advanced imaging, and the biopsychosocial model. By integrating these diverse perspectives, it explores the complex interplay between genetic predisposition, anatomical factors, systemic inflammation, immune and endocrine imbalances, and biopsychosocial influences in cTMD.