J Orofac Pain
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Chronic orofacial pain represents a diagnostic and treatment challenge for the clinician. Some conditions, such as atypical facial pain, still lack proper diagnostic criteria, and their etiology is not known. The recent development of neurophysiological methods and quantitative sensory testing for the examination of the trigeminal somatosensory system offers several tools for diagnostic and etiological investigation of orofacial pain. ⋯ By combining different techniques for investigation of the trigeminal system, an accurate topographical diagnosis and profile of sensory fiber pathology can be determined. Neurophysiological and quantitative sensory tests have already highlighted some similarities among various orofacial pain conditions and have shown heterogeneity within clinical diagnostic categories. With the aid of neurophysiological recordings and quantitative sensory testing, it is possible to approach a mechanism-based classification of orofacial pain.
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Transmission of noxious-stimulus-evoked inputs in the spinal and trigeminal systems is mediated primarily through excitatory glutamatergic synapses using alpha amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA), kainate and N-methyl-D-aspartate (NMDA) subtypes of glutamate receptors. Glutamatergic synapses exhibit multiple forms of short-lasting and long-lasting synaptic plasticity. Persistent enhancement of nociceptive transmission, known as "central sensitization," is a form of lasting plasticity that is similar mechanistically to long-term potentiation of glutamatergic transmission in other regions of the central nervous system. ⋯ Central sensitization is thus an expression of increased synaptic gain at glutamatergic synapses in central nociceptive-transmission neurons and thereby contributes importantly to pain hypersensitivity. In addition, recent evidence has revealed a new player in the mechanisms underlying pain hypersensitivity following nerve injury--microglia. Understanding of the roles of microglia may lead to new strategies for the diagnosis and management of neuropathic pain.
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To examine the jaw-stretch reflex after injection of local anesthetic (LA) into painful temporomandibular joints (TMJs), since the functional role of jaw-stretch reflexes in patients with painful temporomandibular disorders is still not well understood. ⋯ These results do not support the notion of asymmetries in the jaw-stretch reflex in patients with TMJ pain, but they do suggest that the reflex sensitivity can be influenced by nociceptive activity from the TMJ area.
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This article provides a brief overview of the tools and methods that may be useful to assess neuropathic trigeminal pain. Pain is a complex multidimensional and biopsychosocial experience. While the assessment of neuropathic trigeminal pain is complex, there are several meaningful ways available for the systematic assessment of neuropathic pain and its effects and manifestations. ⋯ In addition to the psychophysical techniques, a number of laboratory tests for assessment of trigeminal pain have been developed and tested, although critical information on sensitivity, specificity, and predictive values is still scarce. There is also a need for common guidelines on classification, diagnostic procedures, and management. This will require concerted international, interdisciplinary action.
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Evaluating sensory nerve damage is a challenging and often frustrating process. Diagnosis and follow-up is usually based on the patient's history and gross physical evaluation in addition to simple sensory tests such as brushing or pin prick. ⋯ In this article specific clinical uses of QST are described and its clinical applicability is demonstrated. Future studies should be directed at exploring the use of QST in the diagnosis and classification of further nerve pathologies.