Lip closing pressure and spoon management in passive spoon feeding

To determine the sources of lip closing pressure (P(LC) ) generation during passive spoon feeding, we used a fine pressure transducer glued into a wooden spoon, as well as electromyography (EMG) of the upper and lower lips and the submental muscle complex, in normal adult volunteers (average age 24·5 years). An assistant fed a seated subject 0·6 mL of yogurt and then withdrew the spoon from the subject's closed mouth. The spoon was held at an angle of 0° (i.e. in the naso-auricular plane) during serving and at either 0° or 60° during withdrawal. We detected simultaneous increases in P(LC) and in EMG activity in the lips and the submental muscle complex. The maximum P(LC) was significantly higher at 60° [65 ± 11 g cm(-2) (mean ± s.e.m)] than at 0° (42 ± 8 g cm(-2)). The former was correlated with the maximum EMG amplitude, which was analysed by using the mean of the root-mean-square EMG and presented as a percentage of the maximum EMG obtained in the lower lip region and the submental muscle complex during subsequent swallowing in each subject. In conclusion, in healthy adult subjects, perioral muscles of the lower lip region and the submental muscle complex participate in P(LC) generation, particularly at a steep spoon withdrawal angle. The results suggest that a steep withdrawal angle not only increases P(LC) but also promotes these muscles' activities in passive spoon feeding.