The functional anatomy of the jaw is essential to understand dystonic movements of the jaw when a patient is eating or speaking. The chewing movements are extremely complex and I will detail only the main posture of the jaw, following dystonic spasms.
The jaw can move in a vertical plan, with opening or closing the mouth
The jaw can move in a saggital plan, the jaw going forward ( protrusion) or backward ( retrusion)
The jaw can move in a lateral plan, the jaw going side to side or going down and to one side, called deviation of the jaw.
The masticatory muscles, responsible of these movements are 4 pairs of muscles ( masseters, temporalis, median pterygoid and lateral pterygoid muscles) and the mouth floor muscles ( supra-hyoid muscles).
A combination of these movements is usually involved in the dystonic spams of the jaw. The video recording of a patient when chewing can be very helpful for analysing in details the dystonic spasms.
Dr MH Marion at the London BTX centre, is specialised in the treatment of dystonia, and injects under electromyogram guidance the masticatory muscles involved in oro-mandibular dystonia.