Pain Mechanisms and Centralized Pain in Temporomandibular Disorders

Abstract

Until recently, most clinicians and scientists believed that the experience of pain is perceptually proportional to the amount of incoming peripheral nociceptive drive due to injury or inflammation in the area perceived to be painful. However, many cases of chronic pain have defied this logic, leaving clinicians perplexed as to how patients are experiencing pain with no obvious signs of injury in the periphery. Conversely, there are patients who have a peripheral injury and/or inflammation but little or no pain. What makes some individuals experience intense pain with minimal peripheral nociceptive stimulation and others experience minimal pain with serious injury? It is increasingly well accepted in the scientific community that pain can be generated and maintained or, through other mechanisms, suppressed by changes in the central nervous system, creating a complete mismatch between peripheral nociceptive drive and perceived pain. In fact, there is no known chronic pain condition where the observed extent of peripheral damage reproducibly engenders the same level of pain across individuals. Temporomandibular disorders (TMDs) are no exception. This review focuses on the idea that TMD patients range on a continuum-from those whose pain is generated peripherally to those whose pain is centralized (i.e., generated, exacerbated, and/or maintained by central nervous system mechanisms). This article uses other centralized chronic pain conditions as a guide, and it suggests that the mechanistic variability in TMD pain etiology has prevented us from adequately treating many individuals who are diagnosed with the condition. As the field moves forward, it will be imperative to understand each person's pain from its own mechanistic standpoint, which will enable clinicians to deliver personalized medicine to TMD patients and eventually provide relief in even the most recalcitrant cases.

Keywords: evidence-based dentistry/health care; multisensory perception; neuroscience/ neurobiology; orofacial pain/TMD; psychosocial factors; treatment planning.

Figure.

Mechanistic characterization of pain. Pain mechanisms can be categorized as peripheral nociceptive, peripheral neuropathic, and centralized. While this classification scheme overly simplifies the vast array of possible mechanisms within each category, it does provide a framework through which clinicians can narrow down treatment options based on each patient’s most prevalent signs and symptoms. Although some chronic pain diagnoses are thought to be more centralized (e.g., fibromyalgia) and others more peripheral (e.g., osteoarthritis), on average, the reality is that no chronic pain state falls neatly into a single mechanistic category. NSAID, nonsteroidal anti-inflammatory drugs; SNRI, serotonin-norepinephrine reuptake inhibitor; TMD, temporomandibular disorder.