Trismus an overview
The word Trismus is Latin term derived from the Greek word “Trismos” which means grinding / rasping. In lay terms Trismus means limitation of mouth opening due to reduced mandible mobility. Two bones form the boundaries of oral cavity (maxilla and mandible). Out of these two maxilla is fixed and is not mobile, where as mandible is capable of upwards and downwards mobility with a limited forward and backward mobility too. The maximal interincisal opening (MIO) of at least 35mm 1 is used as a cutoff point to determine Trismus. Less than 5 mm of MIO indicates complete ankylosis. Roughly put the mouth opening should permit a minimum of three fingers when inserted sideways. Since the movement of the mandible occurs around Temporomandibular joint Kazanjian 2 classified ankylosis of TM joint into true and false types. True ankylosis of TM joint is usually caused due to pathology involving the joint while the term false ankylosis is used to describe restrictions of movement resulting from extra-articular joint abnormalities. It is this type of false ankylosis which clinicians commonly term as “Trismus”.
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