The Instruction of Chewing Well Affects Masticatory Activity and Bolus Flow During Rice Chewing in Healthy Humans

Chewing well (CW) is widely recommended for general health.

The study aimed to consider what healthy participants associated with the instruction of 'CW' and to investigate the effects of CW on masticatory activity and bolus flow during rice chewing.

Twenty-six healthy participants ate 8, 12 and 16 g of steamed rice with barium sulphate under the following two instructions: chewing freely and CW. We investigated the masticatory muscle activity by electromyography (EMG) and the bolus flow by videofluoroscopy. A paired t-test or Wilcoxon signed-rank test was used to analyse data.

All participants associated the 'CW' instruction with 'chewing for a long time'. CW shortened the masseter (Mas) EMG burst duration per chewing cycle (p < 0.001). At 8 and 12 g, CW decreased the suprahyoid (Shy) EMG activity per chewing cycle (p < 0.05) and increased the ratio of valleculae and hypopharyngeal time (VHT) to chewing time (p < 0.01). CW increased the chewing rate in the VHT for 8 and 12 g (p < 0.05) and in the processing time for 16 g (p < 0.05) in the participants who reached the food bolus in the valleculae area during chewing.

CW decreased the Mas activity during chewing at all volumes, while its effects on the Shy activity and bolus flow during chewing depended on the mouthful volume. CW increased the chewing rate in the final stage for the small and medium volumes, and in the early stage for the large volume.