Cyclic motion of the soft palate in feeding.

The soft palate moves rhythmically during feeding, but the timing and frequency of this motion are not known. We tested the hypothesis that cyclic soft palate motion is temporally linked to cyclic jaw movement. Nine healthy, asymptomatic human subjects with normal dentition ate solid food coated with barium. Videofluorographic recordings showed that rhythmic motions of the soft palate during mastication were linked temporally to jaw motion. Soft palate motion occurred in every recording but not in every jaw cycle. The soft palate moved upward as the jaw opened, but the nasopharynx was not sealed. During swallowing, however, the soft palate invariably elevated during the intercuspal phase of jaw motion, sealing the nasopharynx. The frequency of soft palate cycles was lowest early in a feeding sequence and gradually increased as the sequence progressed from ingestion to swallowing. We conclude that cyclic movement of the soft palate in feeding is temporally linked to jaw motion.

The effect of food consistency upon jaw movement in the macaque: a cineradiographic study.

Variation in the form of masticatory cycles in individuals is often assumed to be limited. The contrary hypothesis, that jaw cycles vary widely but systematically with food consistency, was tested in macaques fed similarsized pieces of monkey chow, apple, and banana. With the animals under general anesthesia, radiopaque markers were inserted into the jaw, tongue, and hyoid. Oral movements were recorded by cineradiography at 100 frames/sec in lateral projection synchronously with frontal view cinephotography (50 frames/sec). The films were examined for the events that subdivide each jaw movement cycle into its constituent phases (fast closing, slow closing, intercuspal, slow or early opening, final opening). The frame numbers at which these events occurred were used to define phase durations. The numbers of cycles preceding a swallow increased with the hardness of the ingested food item. Regardless of the test food, every feeding sequence (initial ingestion to final clearance of mouth) contained multiple swallows, each of which defined the end of a sub-sequences when the animals were feeding on chow, the sub-sequences were initially long (20 cycles or more), but when they were feeding on banana, the sub-sequences were short (10 cycles or fewer). Although the form of individual cycles (defined by phase durations) was often unrelated to that of neighboring cycles, the general cycle characteristics in a sub-sequence typified a particular food. Chow feeding cycles were characterized by slow-closing (SC) phases of long duration with slow-opening (SO) phases of short duration; the characteristics of banana feeding cycles were the reverse. SC duration correlated directly and SO duration correlated inversely with food hardness (p < 0.001). The evidence supports the view that the centrally generated pattern of movement is highly dependent upon intra-oral sensory feedback.

Tongue-jaw linkages in human feeding: a preliminary videofluorographic study.

Motions of the tongue and jaw are closely coupled during feeding in mammals, but this relation has not been studied in humans. A videofluorographic method for measuring tongue movement relative to jaw motion using small radiopaque markers affixed to the tongue with dental adhesive was developed and tested in five individuals. Sagittal movements of the anterior tongue marker (ATM) and the lower jaw were measured for complete feeding sequences with a computerized image-analysis system. The ATM and jaw moved in loosely linked, semirhythmic cycles. Vertical and horizontal maxima of ATM motion were determined for each motion cycle in relation to maximum and minimum gape (greatest jaw opening and closing, respectively). The amplitude of tongue movements and their timing differed between hard and soft foods (p < 0.001). For both food types, motions varied as the feeding sequence progressed from ingestion to terminal swallow (p < 0.001). A basic temporal sequence was found in 70% of the 224 cycles analysed. On average, the ATM reached its most inferior position just after maximum gape, its most posterior during jaw closing, its most superior just after minimum gape, and its most anterior during jaw opening (p < 0.001). This study confirms that tongue and jaw movements are linked during human feeding, as they are in other mammals.

Patterns of tongue and jaw movement in a cinefluorographic study of feeding in the macaque.

Tongue movements in three female Macaca fascicularis, with radio-opaque markers in the tongue, teeth and hyoid, feeding on apple, banana and monkey chow, were recorded using lateral projection cineradiography (+/- 100 f.p.s.) with synchronized frontal view cinephotography (50 f.p.s.). Marker positions were digitized and the resultant Cartesian coordinates manipulated: (a) to establish the gape time profile; (b) anteroposterior and dorsoventral movements of tongue and hyoid markers relative to an upper occlusal/palatal reference plane; and (c) expansion and contraction of tongue segments in selected sections of complete sequences. The relative timing of tongue and jaw movement events was established using interval analysis. In simple transport cycles (semisolid food), all parts of the tongue moved in synchrony, travelling forwards and expanding during early opening, and backwards and contracting during late opening and closing. In contrast, in simple chewing cycles with a power stroke (SC phase): (a) the tongue markers reached their most backward position before or at the beginning of the SC phase, travelling forwards until the teeth approached intercuspation, then paused until after the teeth had reached centric occlusion; (b) the markers moved asynchronously, so that the relation between each marker and jaw movement changed; (c) expansion and contraction was largely confined to the middle tongue segment. In complex chewing cycles, jaw movement in opening was linked to the behaviour of the anterior tongue segment: reversal from forward to backward movement of the anterior tongue marker occurred within 30 ms of the rate change at the SO (slow open)-FO (fast open) transition: the greater the amplitude of forward movement, the longer the SO phase/Hyoid (tongue base) movement occurred throughout masticatory sequences. A backward drift of the hyoid and posterior part of the tongue occurred in cycles preceding swallows. Linkages between tongue and jaw movements in feeding in macaques are more complex than those reported for non-primate mammals, as they change between successive jaw cycles. The changes observed during sequences, and between different foods, suggest that the effector systems involved are continuously modulated, and the jaw-movement profile during opening may be dependent on the pattern of tongue movement.

Ontogeny of postnatal hyoid and larynx descent in humans.

Postnatal descent of the hyoid and larynx relative to the palate and mandible, which occurs uniquely in humans, is an anatomical prerequisite for quantal speech. This study tested the hypothesis that spatial constraints related to deglutition impose greater restrictions on the rate and degree of hyo-laryngeal descent than do adaptations for vocalization. Ontogenetic data on changes in the size and shape of the pharynx, the vocal tract, and the spatial positions of the larynx, hyoid, mandible and hard palate relative to each other and to the oral cavity were obtained for 15 males and 13 females from a longitudinal series of lateral radiographs (the Denver Growth Study) taken between the ages of 1 month and 14 years. To establish growth patterns, nine linear dimensions of the pharynx and 15 different pharyngeal and vocal-tract proportions were regressed against percentage growth. The results demonstrate that certain aspects of vocal-tract shape change markedly during ontogeny, especially in the first postnatal year and during the adolescent growth spurt. The ratio of pharynx height to oral cavity length (which is important for speech) decreases significantly (P<0.001) from 1.5 to 1.0 between birth and 6-8 years, after which it remains stable. In contrast, regression analyses indicated that superoinferior spatial relations between the positions of the vocal folds, the hyoid body, the mandible and the hard palate do not change significantly throughout the entire postnatal growth period (P<0.05). Sexual dimorphism in pharyngeal shape and size before the age of 14 years is very limited. The results suggest that the descent of the hyoid and larynx relative to the mandible is constrained by muscle function related to deglutition, highlighting the different functional roles of the hyoid during speech and oral transport.

Mechanism of intra-oral transport in a herbivore, the hyrax (Procavia syriacus).

Movements in the jaw, tongue and hyoid during feeding behaviour were recorded with cine-X-ray. Food was moved through the mouth by anterior/posterior motion of the tongue surface relative to the hard palate. This was true for both stage I transport, from the front of the mouth to the molar tooth row and stage II transport, from the molar tooth row to the vallecular area of the oropharynx. During a series of chew cycles, processed food collected in the oropharynx prior to a swallow. Swallows occurred as discrete events punctuating chew sequences and were characterized by coordinated movements of tongue and soft palate. Similar mechanisms of transport have been observed in the opossum and the cat, indicating a common mammalian behaviour. Differences between this herbivore and anthropoid primates can be attributed to differences in anatomy of the oral apparatus.

Distribution of enamel on the incisors of Old World monkeys.

Longitudinal ground sections of 29 Old World monkey central lower incisors were studied histologically and metrically. Labiolingual incisor width tended to scale isometrically with body weight but with important deviations in relative incisor size, which appeared to be correlated with diet in accord with work by Hylander. Lower incisors of the predominantly folivorous colobine monkeys had a substantial layer of enamel on both lingual and labial aspects and consequently had blunt incisal edges. These teeth in both cercopithecins and papionins, which are omnivorous or frugivorous, had little or no enamel on the lingual aspect, resulting in sharp incisal edges. It is suggested that colobine incisors are used mainly in gripping and tearing leaves, whereas cercopithecine incisors are better adapted to cutting and scraping. Crown height showed a positive allometric relationship with overall incisor height, so that the tall incisors of papionins, especially Papio and Mandrillus, were more hypsodont than the shorter incisors of colobines and cercopithecins. This appears to be related to differences in the rates of incisor wear between the groups.

Food transport and bolus formation during complete feeding sequences on foods of different initial consistency.

Food movements during complete feeding sequences on soft and hard foods (8 g of chicken spread, banana, and hard cookie) were investigated in 10 normal subjects; 6 of these subjects also ate 8 g peanuts. Foods were coated with barium sulfate. Lateral projection videofluorographic tapes were analyzed, and jaw and hyoid movements were established after digitization of records for 6 subjects. Sequences were divided into phases, each involving different food management behaviors. After ingestion, the bite was moved to the postcanines by a pull-back tongue movement (Stage I transport) and processed for different times depending on initial consistency. Stage II transport of chewed food through the fauces to the oropharyngeal surface of the tongue occurred intermittently during jaw motion cycles. This movement, squeeze-back, depended on tongue-palate contact. The bolus accumulated on the oropharyngeal surface of the tongue distal to the fauces, below the soft palate, but was cycled upward and forward on the tongue surface, returning through the fauces into the oral cavity. The accumulating bolus spread into the valleculae. The total oropharyngeal accumulation time differed with initial food consistency but could be as long as 8-10 sec for the hard foods. There was no predictable tongue-palate contact at any time in the sequence. A new model for bolus formation and deglutition is proposed.

Food transport through the anterior oral cavity in macaques.

Intraoral transport, the movement of food or liquid through the oral cavity and oropharynx, is a major component of feeding behavior. Stage I transport, transport through the oral cavity prior to mastication, has been described for several mammals (Franks et al.: Arch. Oral Biol. 30:539, 1985; Hiiemae and Crompton: Hildebrand et al. (eds.): Functional Vertebrate Morphology, Cambridge, MA, Belknap Press, 1985). Previous work (Franks et al.: Am. J. Phys. Anthropol. 65:275, 1984) indicated that this was not a significant behavior in macaques in a laboratory setting, because food was ingested directly to the region of the cheek teeth. Although relatively infrequent in a captive situation, stage I transport does occur in long-tailed macaques through a mechanism similar to other mammals, but also subject to unique aspects of primate anatomy. Transport takes several cycles during which the food moves back and forth in an anterior/posterior direction, due to tongue movements. Because anthropoid primates lack the pronounced rugae that in other mammals prevent the anterior displacement of a bolus, stage I transport uses the rounded arch of the upper, anterior dentition to hold the food during the forward movement of the tongue. During the final cycle of transport, a pronounced twisting of the tongue, along a midline anteroposterior axis helps funnel the food item toward the postcanine teeth for subsequent mastication. This twisting, which was described in humans by Abd-El-Malek (J. Anat. 100:215, 1955) but not within the context of jaw movement, occurs prior to the closing phase of the jaw cycle.

Variations in molar enamel thickness among primates.

Because of its hardness, resistance to abrasion and its influence on crown morphology, molar enamel thickness is an important factor in adaptation of the dentition to the diet. Enamel thickness has also been discussed extensively in relation to the phylogenetic relationships among the hominoids. The aims of this study were: (1) to analyse enamel thickness/tooth size relationships among primates as a whole, and (2) to evaluate variations in enamel thickness among hominoids against the background of the other primates. We employed measures of tooth size, and of enamel thickness and quantity based on measurements of areas in longitudinal sections of 125 molars of 39 species. Among primates, there were two grades of enamel thickness, prosimians having thinner enamel for a given tooth size or body weight than anthropoids. The scaling of enamel thickness with tooth size and body weight tended to show positive allometry among anthropoids. Comparison of hominoid enamel thicknesses with that in anthropoids led to the conclusion that Hylobates has enamel of average thickness, Homo has thick enamel and Gorilla has thin enamel, while Pan and Pongo had average or thin enamel, depending on tooth type. These results may be relevant to considerations of hominoid evolution.