Chronic orofacial pain has a significant negative impact that influences individuals' quality of life and our society. The prevalence is around 11.2% to 33.2% and remains high in females. Currently, there are two main diagnostic classification systems that are used internationally for chronic pain: the International Classification of Diseases, 11th Revision (ICD-11), which was published by the World Health Organization (WHO) in 2018, and the International Classification of Orofacial Pain, which was published by the International Association for the Study of Pain (IASP) in 2020. Deficits in ascending and descending pain modulation pathways may be involved in the chronic pain pathophysiology. A newly described "trigeminal proprioceptive mesencephalic periaqueductal gray pathway" is considered to be the mechanism of action of occlusal appliance in managing orofacial pain. The genetic basis of chronic orofacial pain is not yet fully understood, but a genetic susceptibility involving multiple genes among the peripheral nerves, brainstem and higher brain regions to regulate and suppress the transmission of pain signals, thereby modulating the perception of pain, is likely.
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