TMJ is not really limited to the lower jaw. Actually, as the name indicates it is generally associated with the temporomandibular joints which are located at the temples above the ears and near the outer corner of your eyes. The associated lower jaw pain can come from muscle fatigue, arthritis, misaligned or deviated or damaged condyles or malocclusion (poor bite). TMD (temprormandibular disorder) is probably a better term to use when the lower jaw is affected because for some, although the tm joints are ok, their tmj symptoms are due to a disorder or functioning of the jaw and facial muscles. TMJ is a widely used term to describe a very complex disorder which can be due to various reasons or components for each person.