Hemimasticatory Spasm Treated With Muscle Afferent Block Therapy and Occlusal Splint

Hemimasticatory spasm: a series of 17 cases and a comprehensive review of the literature

“…However, data regarding BoNT therapy for HMS are insufficient, and the author believes that the dose should be adjusted according to oromandibular dystonia ( 61 ). Repeated BoNT injections are likely to cause apparent facial hemiatrophy due to masseter muscle atrophy and masticatory disturbance owing to a markedly decreased bite force ( 56 ). During BoNT therapy on the jaw-closing muscles, the author always measures the occlusal force on the bilateral molars using an occlusal force meter (GM10, Nagano Keiki Co.; Tokyo, Japan) and is careful not to cause excessive reduction of the occlusal force ( 61 ).…”

“…The jaw-closing muscles are rich in muscle spindles; therefore, MAB of the masseter muscle will be useful for patients with HMS. For patients who do not wish to undergo surgery and for whom expensive BoNT therapy is not feasible, a combination of MAB therapy and splinting, which improves muscle pain but does not cause muscle atrophy, has also been reported as an alternative ( 56 ).…”

“…Opening the mouth may stretch the jaw-closing muscles, thereby affecting signals from the muscle spindles. Some cases in which dental splints resulted in a slight to moderate relief of HMS symptoms have been reported ( 18 , 26 , 56 ). Increasing the occlusal vertical dimension with a splint may slightly stretch the jaw-closing muscles, making spasms less likely to occur.…”

“…Hemimasticatory spasm (HMS) is characterized by intermittent paroxysmal contractions of the unilateral jaw-closing muscles, resulting in brief twitches and/or prolonged spasms ( 1 – 56 ). Involuntary movements can cause muscle pain, tongue or buccal mucosa biting ( 9 , 18 , 21 , 25 , 34 , 35 , 55 ), and temporomandibular joint dislocation ( 6 , 18 , 54 ), resulting in masticatory disturbances or dysarthria.…”