A postero-anterior videofluorographic study of the intra-oral management of food in man.

Recent studies of the manipulation and reduction of food in the human mouth have used lateral-projection videofluorography (VFG) and so have concerned antero-posterior food movement. To determine the degree to which (a) food was chewed bilaterally as opposed to unilaterally, (b) the frequency of side changes, (c) the contribution of tongue and cheek activity to food manipulation, and (d) the effect of food consistency on these activities, nine young adults were recorded eating 7g cubes of four foods (banana, biscuit [cookie] and two types of meat: "tender" and "tough") in the postero-anterior projection. Videotapes recorded at 30 frames/s were acquired to disk; data were analysed as single frames and in slow-motion. As expected, the meat samples, being fibrous, required more chewing and manipulation, allowing details of the process to be established. Food was ingested in the midline; the tongue then positioned the cube on the occlusal plane of one side by a combination of pushing, tilting and twisting movements before any occlusal contact (stage I transport). During processing, food was kept on the occlusal surface by a combination of rhythmic tongue-pushing moving the food buccally (41% of cycles), and cheek-pushing (28% of cycles) returning it in the lingual direction. This reciprocating movement ensured that different parts of the food were subjected to occlusal force in successive cycles. Bilateral chewing was common and associated with either: (a) a near-symmetrical closing movement with tooth-food-tooth contact occurring almost simultaneously on both sides, or (b) an identifiable "active side" but a jaw movement extended medially to carry the lower molars through a power stroke on the "balancing" side. During the sequence, food requiring further chewing might be moved to the erstwhile balancing-side (balancing-side shift); or across the mouth to the tooth row or vestibule on the other side and "stored" for later reduction (segregation shift). Towards the end of the sequence, triturated material was moved to the midline (aggregation shift) for bolus formation and deglutition. While distinct patterns of mediolateral and vertical jaw movements seem to be associated with shift and transport cycles, these connections have not yet been established with sufficient robustness to support predictions of intra-oral events from jaw movement profiles alone.