NATURAL BITES, FOOD CONSISTENCY AND FEEDING-BEHAVIOR IN MAN

Complete feeding sequences (bite to terminal swallow) were recorded in 11 individuals (Class I occlusions) feeding on apple, banana and bisc uit (hard cookie) to establish whether jaw movements characteristic of the stage I transport, chewing, stage II transport and swallowing pro cesses found in non-human mammals could be identified in man. All part icipants took large natural bites (known weight) of each food, but sev en were supplied standard 6-g pieces of apple. Jaw movements (three ax es) were recorded using a locally calibrated Sirognathograph. Discrete stage I transport movements (bite moved from incisors to postcanines) , were found in most records, but least frequently for banana. The num ber of chewing cycles before the first in-sequence swallow increased i n the order: banana, (=) apple without peel, apple with peel, biscuit. Chewing cycles showed subtle changes in gape profile but significant variation in mediolateral movement cycle to cycle. Morphologically dis tinct stage II transport cycles could not be identified. Swallows occu rred intermittently during chewing (79% of all sequences, n = 146) wit h cycle durations in excess of 1 s in contrast to the range for chewin g (0.6-0.7 s). Almost all sequences ended with a period, clearance, of highly irregular jaw movements often including swallows. Clearance ha s not been described in other mammals. Food consistency affected feedi ng behaviour. The 'chew/swallow' ratio (total number of chews/total nu mber of swallows) increased with food hardness. The number of chewing cycles before the first in-sequence swallow also increased. Food type significantly affected sequence duration. The duration of clearance wa s also affected by bite weight and food hardness. It is concluded that initial food consistency determines the number of chewing cycles befo re the first swallow and overall sequence duration. The change in the pattern of jaw movement in both the vertical and mediolateral directio ns cycle to cycle suggests continuous sensory modulation of the motor output to the mandibular musculature.