The TMJ dysfunction could cause subtle alterations in middle-ear biomechanics, and hypothesised that these could be attributable to anatomical links between the TMJ and the middle ear, including the discomalleolar ligament, the anterior malleolar ligament and the tendon between the tensor tympani and tensor veli palatini muscles. Changes in tension on these structures in TMJ dysfunction could be transmitted to the malleus, thereby altering the stapes position. The latter could cause a pressure change in inner-ear fluids and alter the polarisation state of cochlear and vestibular hair cells, thereby contributing to symptoms of ear fullness, tinnitus, subjective hearing loss and vertigo. Subtle changes in inner-ear fluid pressure have been detected by multiple frequency tympanometry.
The cause of hearing loss associated with temporomandibular disorder can only be speculated upon. Recently, a hypothesis was proposed linking temporomandibular disorders, Eustachian tube dysfunction and inner-ear dysfunction. Irritation in the TMJ region was hypothesised to result in the release of inflammatory mediators in the Eustachian tube via an axon reflex, which could further activate the anterior cervical sympathetic system. The latter would enhance neurogenic inflammation in the Eustachian tube, resulting in reduced middle-ear ventilation. The imbalance between middle-ear and inner-ear pressure could alter the polarisation state of cochlear hair cells, thereby causing sensorineural hearing loss. In this context, another recent study reported multiple system dysregulation (especially affecting the sensory, autonomic and inflammatory domains) in patients with painful temporomandibular disorders. This hypothesis may help explain the various types of hearing loss observed in patients with various categories of temporomandibular disorder.
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