Temporomandibular dysfunction (TMD) is a complicated and multifactorial condition that affects the temporomandibular joint (TMJ) and muscles of mastication, resulting in pain and disability in 5-12% of the population. The condition involves genetic, anatomic and hormonal factors and is propagated, in part, by trauma, habitual activity, psychosocial components and occlusal variation. Yet, the exact etiology of TMD is still unknown and the most strategic conservative management of the condition is still a topic of debate. The purpose of this paper, the first of a two part series, is to provide greater insight into the pathoanatomical factors associated with TMD. Consistent with Scully (2008, 2013), degenerative changes seem to disrupt the relationship between the TMJ capsule, articular disc and muscles of mastication. The resulting position of the articular disc coincides with three primary classifications of TMD: Type 1 (muscle disorders), Type 2a/b (disc displacement with and without reduction), and Type 3 (any joint pain). Given the association of the lateral pterygoid with both the joint capsule and articular disc, the superior and inferior head seem to play a key role in TMD. Both heads undergo biological changes associated with the vicious cycle, pain adaptation and integrated pain adaptation, making the muscle a key pain generator associated with TMD. Clinicians must understand the pathoanatomic features associated with TMD so as to choose appropriate treatment strategies, leading to optimal short and long-term outcomes. While the former is discussed in part 1 of this narrative review, the latter will be considered in part 2.
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