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There is limited information of the normal function of the human medial pterygoid muscle (MPt). The aims were to determine whether (i) the MPt is active throughout horizontal jaw movements with the teeth apart and (ii) whether single motor units (SMUs) are active during horizontal and opening-closing jaw movements. Intramuscular electrodes were placed in the right MPt of 18 participants who performed five teeth-apart tasks: (i) postural position, (ii) ipsilateral (i.e. right) jaw movement, (iii) contralateral movement, (iv) protrusive movement and (v) opening-closing movement. Movement tasks were guided by a target and were divided into BEFORE, OUT, HOLDING, RETURN and AFTER phases according to the movement trajectories recorded by a jaw tracking system. Increased EMG activity was consistently found in the OUT, HOLDING and RETURN phases of the contralateral and protrusive movement tasks. An increased RETURN phase activity in the ipsilateral task indicates an important role for the MPt in the contralateral force vector. Of the 14 SMUs active in the opening-closing task, 64% were also active in at least one horizontal task. There were tonically active SMUs at the postural jaw position in 44% of participants. These new data point to an important role for the MPt in the fine control of low forces as required for stabilisation of vertical mandibular position not only to maintain postural position, but also throughout horizontal jaw movements with the teeth apart. These findings provide baseline information for future investigations of the possible role of this muscle in oro-facial pain conditions., (© 2017 John Wiley & Sons Ltd.)

Background: A leaf gauge and an anterior jig may be used to assist the recording of a reproducible jaw position for restorative and prosthodontic treatment. This study investigated possible condylar displacement using an opto-electronic jaw-tracking device and a leaf gauge or anterior jig. The effect of a leaf gauge and anterior jig on jaw muscle electromyography was also examined., Methods: Five healthy adults without symptoms of temporomandibular disorders were selected. Condylar displacement during clenching were recorded simultaneously with electromyographic activity of superior and inferior heads of the lateral pterygoid, anterior and posterior temporalis, masseter, and suprahyoid muscles. Subjects were trained to bite at maximum and half-maximum bite-force using an anterior jig incorporating a force transducer., Results: No consistent condylar displacement was observed in x, y and z axes between different bite-forces although there was a trend towards superior displacement. Comparison of maximum intercuspal clench and maximum clench on a leaf gauge and an anterior jig produced significant decrease in anterior temporalis activity (p < 0.05), whilst an anterior jig with maximum clench significantly decreased posterior temporalis muscle activity., Conclusion: Within the limits of this pilot study, no consistent change in condylar position was identified with these appliances.

Previous studies in man have relied only on electromyographic (EMG) activity patterns and anatomical landmarks to confirm electrode placement in the superior head of the lateral pterygoid. Computed tomography (CT) was used here to determine whether indwelling fine wires could be visualized in that muscle head in man and thus provide evidence for correct placement before EMG. Two imaging sessions were conducted in six individuals. First, a series of contiguous axial CT slices was obtained to calculate the trajectory of insertion of fine wire electrodes into the superior head. For each individual, the trajectories for the location of the fine wires in the approximate mediolateral and anteroposterior centre of the superior head were different. Further axial CT slices were taken after electrode insertion; in each case, these slices clearly showed the wire ends located within the muscle. It was concluded that fine wires in the lateral pterygoid can be imaged by CT. Furthermore, imaging is necessary to accommodate interindividual anatomical variations and to confirm the position of the electrodes within the muscle.