Fluoroscopic evaluation of tongue and jaw movements during mastication in healthy humans.

When chewing solid food, part of the bolus is propelled into the oropharynx before swallowing; this is named stage II transport (St2Tr). However, the tongue movement patterns that comprise St2Tr remain unclear. We investigated coronal jaw and tongue movements using videofluorography. Fourteen healthy young adults ate 6 g each of banana, cookie, and meat (four trials per foodstuff). Small lead markers were glued to the teeth and tongue surface to track movements by videofluorography in the anteroposterior projection. Recordings were divided into jaw motion cycles of four types: stage I transport (St1Tr), chewing, St2Tr, and swallowing. The range of horizontal tongue motion was significantly larger during St1Tr and chewing than during St2Tr and swallowing, whereas vertical tongue movements were significantly larger during chewing and St2Tr than during swallowing. Tongue movements varied significantly with food consistency. We conclude that the small horizontal tongue marker movements during St2Tr and swallowing were consistent with a "squeeze-back" mechanism of bolus propulsion. The vertical dimension was large in chewing and St2Tr, perhaps because of food particle reduction and transport in chewing and St2Tr.