Abstract
Chronic orofacial pain conditions can be particularly difficult to diagnose and treat because of their complexity and limited understanding of the mechanisms underlying their aetiology and pathogenesis. Furthermore, there is considerable variability between individuals in their susceptibility to risk factors predisposing them to the development and maintenance of chronic pain as well as in their expression of chronic pain features such as allodynia, hyperalgesia and extraterritorial sensory spread. The variability suggests that genetic as well as environmental factors may contribute to the development and maintenance of chronic orofacial pain. This article reviews these features of chronic orofacial pain, and outlines findings from studies in animal models of the behavioural characteristics and underlying mechanisms related to the development and maintenance of chronic orofacial pain and trigeminal neuropathic pain in particular. The review also considers the role of environmental and especially genetic factors in these models, focussing on findings of differences between animal strains in the features and underlying mechanisms of chronic pain. These findings are not only relevant to understanding underlying mechanisms and the variability between patients in the development, expression and maintenance of chronic orofacial pain, but also underscore the importance for considering the strain of the animal to model and explore chronic orofacial pain processes.
Highlights
Orofacial pain conditions are very common and many that are chronic may be especially difficult to diagnose and treat because of their complexity and lack of clarity of the detailed mechanisms underlying their aetiology and pathogenesis [1,2,3,4,5,6]
The use of animal models of chronic orofacial pain has produced findings underpinning the general view that the peripheral changes and central nervous system (CNS) changes that can result from a peripheral injury or inflammation are involved to varying degrees in orofacial pain states, including the development of neuropathic pain conditions expressed in the orofacial region such as PTTN, BMS, trigeminal neuralgia, and trigeminal postherpetic neuralgia
The findings are consistent with earlier evidence of strain differences in spinal neuropathic pain models, and suggest that genetic factors influencing central sensitization may contribute to the variation between clinical cases in the development, expression and maintenance of trigeminal neuropathic pain and other chronic orofacial pain conditions in humans
Summary
Orofacial pain conditions are very common and many that are chronic may be especially difficult to diagnose and treat because of their complexity and lack of clarity of the detailed mechanisms underlying their aetiology and pathogenesis [1,2,3,4,5,6]. There can be sex differences in some pain conditions as well as considerable variability between pain patients of the same or different racial groups in their expression of these features of chronic pain, treatment response, and susceptibility to risk factors that may predispose them to develop or maintain chronic pain [3,4,12,13,14,15,16] These findings suggest that genetic as well as environmental factors may contribute to the development and maintenance of chronic pain and its expression in the orofacial region. Strain differences in these animal models will be described that provide insights into the role of genetic as well as environmental factors that are relevant to the variability between patients in the development, maintenance, and features of chronic orofacial pain and in responses to its treatment
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