Kinematics of lateral tongue-pushing movement in coordination with masticatory jaw movement: An anteroposterior projection videofluorographic study

Abstract

Objective: During the mastication of solid food, the tongue pushes the bolus laterally to place it onto occlusal surfaces as the jaw is opened. This movement is referred to as tongue-pushing (TP). TP has an important role in efficient chewing, but its kinematic mechanisms remain unclear. The present study quantified the kinematics of TP and its coordination with masticatory jaw movements.

Methods: Videofluorography (VFG) in anteroposterior projection was recorded while 14 healthy young adults ate 6 g each of cookies and meat. Small lead markers were glued to the tongue surface (left, right, and anterior) and buccal tooth surfaces (upper molars and lower canines). The position of the tongue and lower canine markers relative to the upper occlusal plane was quantified with Cartesian coordinates, using the right upper molar as the origin. Jaw motion during chewing was divided into TP and Non-TP cycles, based on the lateral movement of the food and tongue markers. The side of the jaw that compressed food particles was defined as the working side, while the other side was termed the balancing side. Horizontal and vertical displacements of tongue and jaw markers were compared between TP and Non-TP cycles, as well as between food types.

Results: The mediolateral displacement of all tongue markers was significantly larger in TP than in Non-TP cycles. Vertical displacement was also significantly greater in TP than in Non-TP cycles for the anterior and working side tongue markers. TP cycles occurred more frequently with meat-chewing than with cookie-chewing.

Conclusion: TP is accomplished by rotation and lateral movements of the tongue surface on the working side and the anterior tongue blade, along with medial movement on the balancing side. These movements produce lateral shift and rotation of the tongue surface toward the working side in concert with jaw opening. Designing exercises to improve the strength of the lateral motion and rotation of the tongue body may be useful for individuals with impaired tongue function for eating and swallowing.

Keywords: Cookie; Mastication; Meat; Occlusal surfaces; Radiopaque markers; Tongue pushing.

Fig. 1.

Positions of the upper and lower jaw and tongue markers visualized in anteroposterior projection. Lead discs were attached to the buccal surfaces of the lower canines (WC and BC, working and balancing side canine marker, respectively), upper first molars, and dorsal tongue surface (ATM, anterior tongue marker; WTM and BTM, working and balancing side lateral tongue markers, respectively). The WTM and BTM are approximately 2 cm posterior to the ATM. Marker positions are expressed as X-Y coordinates relative to the upper occlusal plane. The X-axis passes through the markers on the bilateral upper molars and the Y-axis is a line perpendicular to the X-axis and passing through the right upper molar marker.

Fig. 2.

Tongue with 3 tongue surface markers. Anterior tongue marker placed on the midline of tongue 1cm posterior to the tongue tip, and two lateral markers placed on the tongue surface near the right and left lateral edge.

Fig. 3.

Tongue surface angle (TSA) was defined as the angle between a line connecting the canine marker on the working side (WC) to that on the balancing (BC) and a line connecting the tongue marker on the working side (WTM) to that on the balancing side (BTM). The maximum TSA (MaxTSA) was measured for each cycle.

Fig 4.

Schematic frontal images of tongue-pushing (TP) during jaw opening based on videofluorography image tracings during a TP cycle in an individual feeding on meat. Left side drawings show upper and lower third molars, the margin of the hard palate, the outline of the tongue surface, tongue markers, and the food bolus (shaded). The anterior tongue marker (ATM) is colored black. The left side of the drawings represents the working side and the right side indicates the balancing side. For comparison, A and A’ show simple jaw opening without TP. At the end of the occlusal phase, tongue markers are mildly displaced to the balancing side (B). During jaw opening, the working side and ATM move downward and toward the working side. Rotation is evident (C to D). Until the start of tooth-food-tooth contact, tongue markers move laterally toward the working side and the main part of the bolus is positioned on the occlusal surface (E). As tooth-food-tooth contact is initiated, the jaw is moved to the working side in coordination with the tongue movement. The tongue surface is displaced toward the working side (F). A’, C’, and F’ illustrate the overall movement of the tongue surface during TP and these images correspond to A, C, and F, respectively.

Fig. 5.

Representative measurements of horizontal and vertical movements of the anterior tongue markers (ATMX and ATMY, respectively), vertical jaw movement, and tongue surface angle (TSA) over time while meat is chewed. In Non-tongue-pushing (Non-TP) cycles, only slight horizontal displacement of the ATM is observed, but in TP cycles, the ATM moves right and left alternately for each jaw motion cycle. Vertical ATM movement is temporally linked to vertical jaw movement.

Fig. 6.

Example of rotation of the tongue surface (represented by a line from the working side tongue marker (WTM) to the balancing side tongue marker (BTM)) during a tongue-pushing (TP) cycle. Lines represent the changing position of the tongue surface relative to the lower jaw in one TP cycle, from maximum closing to maximum opening. The surface tilts toward the working side and moves superiorly and laterally relative to the lower jaw.

Fig. 7.

Box and whisker plots of the displacement of the lower canine and tongue markers in tongue-pushing (TP) and Non-TP cycles in the horizontal (A) and vertical (B) dimension. * indicates P < 0.05. ^¶ indicates P < 0.05 between TP and Non-TP cycles. A. Downward displacement of all markers was significantly larger in TP cycles than in Non-TP cycles. Among TP cycles, horizontal displacement was largest for the anterior tongue marker (ATM), followed by the balancing tongue marker (BTM). Among Non-TP cycles, horizontal displacement was higher for the working side tongue marker (WTM) than for the BTM. B. In TP cycles, downward displacement was larger for WTM and ATM than for BTM.

Fig. 8.

Comparison of the displacement of the lower canine and tongue markers between cookie- and meat-chewing in tongue-pushing (TP) and Non-TP cycles. Displacements are shown in box and whisker plots in the horizontal (A) and vertical (B) dimension. * indicates P < 0.05. A. In TP cycles, horizontal displacement for the anterior and balancing side tongue markers (ATM and BTM, respectively) was significantly larger with cookie-chewing than with meat-chewing. There were no significant differences between food types for the working side tongue marker (WTM) or lower canine markers. In Non-TP cycles, there was no significant difference in horizontal displacement between food types for any tongue or jaw marker, apart from the ATM. B. In TP cycles, downward displacement for both balancing and working side canine markers (BC and WC, respectively) and the ATM was significantly larger with meat-chewing than with cookie-chewing. Downward displacement for the WTM was significantly larger with cookie-chewing than with meat-chewing in TP cycles. There was no significant difference between foods for the BTM. In Non-TP cycles, there was no significant difference in vertical displacement between food types for any tongue or jaw marker, apart from the ATM.