[Orofacial idiopathic pain: clinical signs, causes and mechanisms]

Atypical facial pain, stomatodynia, atypical odontalgia, masticatory muscle and some temporomandibular joint disorders are grouped together under the category of orofacial idiopathic pain as they reveal numerous common clinical features. For each of these entities, problems of definition and terminology are discussed. Epidemiological and demographic data and a semiological description are given. Proposed diagnostic criteria and some of the causes or mechanisms common to these entities are also described in this article. Firstly, the rôle of female hormones in the physiology and treatment of certain patients is suggested with regard to the marked prevalence of changes in oestrogen levels in patients with orofacial idiopathic pain. Postmenopausal osteoporosis and the hypothesis of neuralgia due to the presence of cavities of osteonecrosis are placed within the context of atypical facial pain. A neuropathic component is suggested for these pain entities. These latter may be linked to a phenomenon of central sensitisation that is induced and maintained by activity in the peripheral tissues. Clinical features of both atypical facial pain and atypical odontalgia have led several authors to advocate the existence of a sympathetic mechanism in the physiopathology of these entities. Moreover, some arguments emphasize similarities with Complex Regional Pain Syndromes of limbs. Lastly, psychosocial components are also considered as a common factor, but it is currently impossible to determine if the pain is the cause or the result of psychosocial problems. Currently, none of these mechanisms can be considered as a single established etiological factor. Indeed, each of these mechanisms can be observed in all types of orofacial idiopathic pain. This leads to the hypothesis that these different mechanisms may act on each target tissue but the details of interaction are still unknown.