An evolutionary perspective on craniomandibular dysfunctions

Craniomandibular dysfunctions (CMDs) are a set of clinical disorders primarily affecting the masticatory muscles and the temporomandibular joints manifesting as pain syndrome, functional limitations and hard and soft tissues degeneration. CMDs have a high impact on the patients’ quality of life as they limit important functions like chewing and deglutition, respiration, speech and social interaction, stress management and postural control. In industrialized societies, the incidence of adult CMD patients needing treatment is estimated to be about 5%, with females showing at least twice the prevalence of males. A review of the anthropological, clinical and biological evidence was carried out to elucidate adaptive aspects of the evolutionary origin of CMDs. The effects of modern lifestyle on the health and function of the stomatognathic system was evaluated and the hypothesis that CMDs should be considered diseases of civilization was tested within a theoretical framework. To prove this assumption, it must be shown that cultural and technological changes have affected the orofacial structures and that these changes have had negative functional effects that are causal to CMDs. Compared to pre-industrial populations, contemporary modern humans are characterized by smaller, retrognathic mandibles, with narrower dental arches and deeper palates and the presence of malocclusion. Anthropological and experimental animal research has shown that such changes are associated with a highly refined diet, typical of industrialized societies. The functional implications of these morphological changes can be derived from experimental and clinical studies. In the medical setting, CMDs’ etiological factors have long been discussed however, occlusion's role in the onset and maintenance of these disorders remains controversial. Yet, the interrelationship between the morphology of the masticatory structures and CMDs can be clarified by close examination and deductive reasoning applied to the available anthropological, clinical and biological evidence.