Effect of head position and mouth opening on the ability of swallowing

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Thirteen subjects were asked to swallow 10 ml of water that was injected into the mouth in a single attempt. After swallowing, the residual intraoral water was suctioned and its volume was measured. An electromyogram (EMG) of the suprahyoid (SH) muscles was also recorded during the test. The duration of SH muscle activity and peak amplitude of SH EMG were examined. The water swallowing test was performed under 3 head positions (neutral, extended and flexed) and 4 mouth opening patterns (interincisal distances of 0 mm, 20 mm, 30 mm and 40 mm). The wider the subject opened the mouth, the more water remained in the mouth after swallowing. The residual volume of water was more in the extended position compared with that in the neutral and flexed positions. Peak amplitude of SH EMG decreased with mouth opening. Duration of SH muscle activity was longer in the extended position than in the neutral and flexed positions.