Is the superior belly of the lateral pterygoid primarily a stabilizer? An EMG study

The aim of the present study was to compare the activity levels within the two bellies of the lateral pterygoid muscle between different jaw positions to test the hypothesis that the upper head is primarily a stabilizer. Elec tromyographic (EMG) recordings, using monopolar concentric needle electrode s, were made from 14 healthy subjects during mandibular rest position (RP), clenching in intercuspal position and jaw opening, first about 10 mm and t hen about 25 mm. Both bellies had very little activity during RP. The activ ity level of the superior belly was high during clenching and large opening (LO) with a dip during low opening degree. This pattern differed from that of the inferior belly where the activity was relatively low during clenchi ng and then gradually increased to its highest level during LO. The results support that the lower belly is primarily a jaw opener while the superior belly acts as a stabilizer keeping the disc and condyle in a functionally s table position during clenching and jaw movements.