[Show abstract][Hide abstract] ABSTRACT: During feeding, solid food is chewed and propelled to the oropharynx, where the bolus gradually aggregates while the larynx remains open and breathing continues. The aggregated bolus in the valleculae is exposed to respiratory airflow, yet aspiration is rare in healthy individuals. The mechanism for preventing aspiration during bolus aggregation is unclear. One possibility is that alterations in the pattern of respiration during feeding could help prevent inhalation of food from the pharynx. We hypothesized that respiration was inhibited during bolus aggregation in the valleculae. Videofluorography was performed on 10 healthy volunteers eating solid foods with barium. Respiration was monitored concurrently with plethysmography and nasal air pressure. The timing of events during mastication, food transport, pharyngeal bolus aggregation, and swallowing were measured in relation to respiration. Respiratory cycle duration decreased during chewing (P < 0.001) but increased with swallowing (P < 0.001). During 66 recordings of vallecular bolus aggregation, there was inspiration in 8%, expiration in 41%, a pause in breathing in 17%, and multiple phases (including inspiration) in 35%. Out of 98 swallows, 47% started in the expiratory phase and 50% started during a pause in breathing, irrespective of bolus aggregation in the valleculae. Plethysmography was better than nasal manometry for determining the end of active expiration during feeding and swallowing with solid food. The hypothesis is rejected in that respiration was not inhibited during bolus aggregation. These findings suggest that airflow through the pharynx does not have a role in preventing aspiration during bolus aggregation in the oropharynx.
[Show abstract][Hide abstract] ABSTRACT: When healthy individuals eat solid food, chewed food is usually transported to the oropharynx where it accumulates before swallowing (stage II transport). We tested the hypothesis that this transport process can be altered by volition. Eight healthy young subjects ate 8 g pieces of cookie with barium while movements were recorded with videofluorography. There were two trials for each subject, each with different instructions: 1) without command: to eat the cookie in his/her usual manner; 2) with command: to chew the cookie, give a signal when ready to swallow, and then swallow on command of the investigator. We measured the number of chewing cycles, the duration of each stage in the feeding sequence, and the position of the leading edge of the barium at time of command and at swallow onset. Sequence duration was longer with than without command (P=0.02), primarily because of an increase in the number of chewing cycles (P=0.02). The leading edge was typically higher in the foodway at the time of swallow onset with than without command (P=0.06). Under the command condition, stage II transport was delayed, and transport to the valleculae was inhibited. Volition alters swallow initiation in both the timing and location of the food bolus relative to the airway.
[Show abstract][Hide abstract] ABSTRACT: The influence of food texture on the feeding behavior was investigated. The postero-anterior projection of videofluorographic (VFG) studies recorded the vertical and medio-lateral movement. The feeding sequences were analyzed using the stope-frame, slow motion and variable speed controls on the VCR. Parts of feeding sequences showed a significant differences between soft and harder foods in the duration of processing and oropharyngeal accumulation time (OPAT). The results show that the texture dependent parts of the feeding sequences were those associated with food breakdown and OPAT.
[Show abstract][Hide abstract] ABSTRACT: 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.
Journal of Dental Research 02/2005; 84(1):39-42. DOI:10.1177/154405910508400106 · 4.14 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The position of the tongue relative to the upper and lower jaws is regulated in part by the position of the hyoid bone, which, with the anterior and posterior suprahyoid muscles, controls the angulation and length of the floor of the mouth on which the tongue body 'rides'. The instantaneous shape of the tongue is controlled by the 'extrinsic muscles' acting in concert with the 'intrinsic' muscles. Recent anatomical research in non-human mammals has shown that the intrinsic muscles can best be regarded as a 'laminated segmental system' with tightly packed layers of the 'transverse', 'longitudinal', and 'vertical' muscle fibers. Each segment receives separate innervation from branches of the hypoglosssal nerve. These new anatomical findings are contributing to the development of functional models of the tongue, many based on increasingly refined finite element modeling techniques. They also begin to explain the observed behavior of the jaw-hyoid-tongue complex, or the hyomandibular 'kinetic chain', in feeding and consecutive speech. Similarly, major efforts, involving many imaging techniques (cinefluorography, ultrasound, electro-palatography, NMRI, and others), have examined the spatial and temporal relationships of the tongue surface in sound production. The feeding literature shows localized tongue-surface change as the process progresses. The speech literature shows extensive change in tongue shape between classes of vowels and consonants. Although there is a fundamental dichotomy between the referential framework and the methodological approach to studies of the orofacial complex in feeding and speech, it is clear that many of the shapes adopted by the tongue in speaking are seen in feeding. It is suggested that the range of shapes used in feeding is the matrix for both behaviors.
Critical reviews in oral biology and medicine: an official publication of the American Association of Oral Biologists 02/2003; 14(6):413-29. DOI:10.1177/154411130301400604
[Show abstract][Hide abstract] ABSTRACT: Chewed solid food accumulates in the oropharynx prior to swallowing. The mechanism for preventing aspiration during this interval is unknown, but may be related to respiration. The purpose of this study was to determine how eating, especially bolus formation in the pharynx, affects respiration. We examined nasal air pressures, masseter electromyography (EMG), and videofluorography (VFG) of four normal young adults eating 8 g each of banana and cookie (two trials each food). Resting respiration was recorded for 30 s before eating. Respiratory cycles (RCs) were classified as prefeeding, feeding (excluding cycles with included swallows), and swallowing cycles. RC duration was greater for swallowing than for feeding and prefeeding RCs (P < 0.001). There were up to three swallows in a single RC, but the increase in swallowing RC duration was greater than swallow duration. Swallow apnea began before bolus transport through the hypopharynx and ended as the bolus tail entered the esophagus. There were semirhythmic perturbations in nasal air pressure associated with masseter activity during chewing, suggesting that there was oronasal airflow during jaw closing via the velopharyngeal isthmus. The most important finding was that bolus aggregation in the valleculae usually occurred during an extended plateau in nasal air pressure following active expiration. This suggests that aspiration during eating is prevented by inhibiting respiration during bolus formation in the oropharynx.
[Show abstract][Hide abstract] ABSTRACT: Feeding and speech depend on integrated movements of the jaws, tongue surface and tongue base–hyoid complex. Phylogenetically and ontogenetically, the movements of feeding antedate those required for speech. The hypothesis that speech movements would fall within the range used in feeding was tested.Lateral projection videofluorographic records were made for 10 subjects eating 8 g samples of three foods and reading a standard diagnostic speech text (Grandfather Passage). Radiopaque markers were glued to the upper and lower canines and tongue. Marker positions (Cartesian coordinates) for each video frame were plotted relative to the upper occlusal plane (X axis) and to a perpendicular dropped from that plane at the upper canine (Y axis). A plot of all coordinates per record gives the spatial domain (in the sagittal plane) within which a given marker moved. Tongue marker domains showed an extraordinary range of movement in feeding with extensive palatal contact. In speech, there was little palatal contact, and markers moved within a smaller sagittal domain. Although speech domains fell within the range for feeding, their centroids were highly statistically different, P P Our hypothesis is confirmed for the tongue surface markers but not for the hyoid. We conclude that patterns of hyoid movement in speech are a specific adaptation for speech. This research was supported by USPHS NIDCD Award 02123.
[Show abstract][Hide abstract] ABSTRACT: 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.
[Show abstract][Hide abstract] ABSTRACT: During swallowing, the hyoid bone is described as moving first upward, then forward, then returning to the starting position. This study examined hyoid motion during swallowing of chewed solids and liquids. Barium videofluorography (VFG) was performed on 12 healthy volunteers eating 8-cc portions of various solid foods and drinking liquid. Hyoid position was measured frame-by-frame for 88 swallows relative to the occlusal plane of the upper teeth. The hyoid bone moved both upward and forward during swallowing, but upward displacement was sometimes very small. There was no correlation between the amplitudes of hyoid upward and forward displacements. The amplitude of upward displacement was highly variable, smaller for liquids than for solid foods (p <0.001), and, for solid foods, larger for the first swallow than for the second swallow (p = 0.02). The amplitude of forward displacement did not differ significantly between liquids and solids or between first and second swallows. We conclude that upward displacement of the hyoid bone in swallowing is related primarily to events in the oral cavity, while its forward displacement is related to pharyngeal processes, especially the opening of the upper esophageal sphincter.
[Show abstract][Hide abstract] ABSTRACT: The human hyoid moves continuously in feeding, facilitating movements of the tongue surface and the processing and transport of food. The hypothesis that similar hyoid movements support tongue movements in speech was tested in 10 normal young adults of both sexes, who were recorded with lateral-projection videofluorography when feeding on hard and soft foods and when reading the 'Grandfather Passage', which includes the major vowel-consonant combinations in English. Recordings were made with and without tongue-markers. Images were analysed with a digital frame grabber and computer. Each participant served as his/her own control. The hyoid moved continuously during speech and feeding. In speech, hyoid motions were irregular and not linked to jaw movement, as they were for feeding. The centroids and variances of the domains for all reference points were compared for speech and feeding; the centroid represents the average position of a structure and variance its amount of motion. Gape and hyoid centroids were significantly different for feeding and speech (P<0.001), but differences for gape averaged <1mm while the difference for the hyoid centroid was >7mm. There were no significant differences in gape attributable to sex. Consistent with the known differences in hyolaryngeal position there were significant sex differences in hyoid centroid (P=0.031) but not variance. In speech, tongue-markers had a smaller spatial domain (P=0.001) condensed within the larger feeding domain. The small shift in the gape centroid does not explain the larger forward shift of the hyoid during speech. These findings raise questions about the neuromotor control of hyoid position in the two behaviours and the biomechanics of the supralaryngeal vocal tract.
[Show abstract][Hide abstract] ABSTRACT: 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.
[Show abstract][Hide abstract] ABSTRACT: 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.
[Show abstract][Hide abstract] ABSTRACT: 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.
Journal of Human Evolution 10/1998; 35(4-5):507-22. DOI:10.1006/jhev.1998.0238 · 3.87 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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.
[Show abstract][Hide abstract] ABSTRACT: 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.
Journal of Dental Research 01/1997; 76(1):552-60. DOI:10.1177/00220345970760010501 · 4.14 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Complete feeding sequences (bite to terminal swallow) were recorded in 11 individuals (Class I occlusions) feeding on apple, banana and biscuit (hard cookie) to establish whether jaw movements characteristic of the stage I transport, chewing, stage II transport and swallowing processes found in non-human mammals could be identified in man. All participants took large natural bites (known weight) of each food, but seven were supplied standard 6-g pieces of apple. Jaw movements (three axes) 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 number of chewing cycles before the first in-sequence swallow increased in 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 distinct stage II transport cycles could not be identified. Swallows occurred intermittently during chewing (79% of all sequences, n = 146) with cycle durations in excess of 1 s in contrast to the range for chewing (0.6-0.7 s). Almost all sequences ended with a period, clearance, of highly irregular jaw movements often including swallows. Clearance has not been described in other mammals. Food consistency affected feeding behaviour. The "chew/swallow' ratio (total number of chews/total number 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 was also affected by bite weight and food hardness. It is concluded that initial food consistency determines the number of chewing cycles before the first swallow and overall sequence duration. The change in the pattern of jaw movement in both the vertical and mediolateral directions cycle to cycle suggests continuous sensory modulation of the motor output to the mandibular musculature.
[Show abstract][Hide abstract] ABSTRACT: 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.
[Show abstract][Hide abstract] ABSTRACT: 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.
American Journal of Physical Anthropology 11/1989; 80(3):369-77. DOI:10.1002/ajpa.1330800310 · 2.51 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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 cercopi-thecins 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.
American Journal of Physical Anthropology 09/1986; 71(1):103 - 113. DOI:10.1002/ajpa.1330710113 · 2.51 Impact Factor