Characterization of food physical properties by the mastication parameters measured by electromyography of the jaw-closing muscles and mandibular kinematics in young adults

The relationship between the physical properties of solid food and the masticatory parameters is clarified. Eight solid foods of varying physical properties were chosen. Electromyography of the jaw-closing muscles and mandibular kinematics in eleven young subjects were recorded. The masticatory parameters were derived from the recorded data for the entire mastication process, for the first bite, and in the early, middle, and late stages of mastication. After calculating values relative to the mean value for each subject, nine parameters representing each group were chosen through a cluster analysis. Three principal components were extracted, each of them related to the masticatory time and cycle, minimum jaw opening at the early stage of mastication, and masticatory force. The principal component scores for each food were different, except for one combination in which the physical properties under large and extra-large deformations were similar, despite different breaking properties or small deformation properties. The masticatory parameters did not correlate with the physical properties of food measured for small deformation.     

Role of physical bolus properties as sensory inputs in the trigger of swallowing

Background

Swallowing is triggered when a food bolus being prepared by mastication has reached a defined state. However, although this view is consensual and well supported, the physical properties of the swallowable bolus have been under-researched. We tested the hypothesis that measuring bolus physical changes during the masticatory sequence to deglutition would reveal the bolus properties potentially involved in swallowing initiation.

Methods

Twenty normo-dentate young adults were instructed to chew portions of cereal and spit out the boluses at different times in the masticatory sequence. The mechanical properties of the collected boluses were measured by a texture profile analysis test currently used in food science. The median particle size of the boluses was evaluated by sieving. In a simultaneous sensory study, twenty-five other subjects expressed their perception of bolus texture dominating at any mastication time.

Findings

Several physical changes appeared in the food bolus as it was formed during mastication: (1) in rheological terms, bolus hardness rapidly decreased as the masticatory sequence progressed, (2) by contrast, adhesiveness, springiness and cohesiveness regularly increased until the time of swallowing, (3) median particle size, indicating the bolus particle size distribution, decreased mostly during the first third of the masticatory sequence, (4) except for hardness, the rheological changes still appeared in the boluses collected just before swallowing, and (5) physical changes occurred, with sensory stickiness being described by the subjects as a dominant perception of the bolus at the end of mastication.

Conclusions

Although these physical and sensory changes progressed in the course of mastication, those observed just before swallowing seem to be involved in swallowing initiation. They can be considered as strong candidates for sensory inputs from the bolus that are probably crucially involved in the triggering of swallowing, since they appeared in boluses prepared in various mastication strategies by different subjects.     

Differentiation of the dormouse Eliomys quercinus (Linnaeus 1766) fro the murid Mus caroli (Bonhote 1902) based on the masticatory muscles

Investigated were the masticatory musculature of the murid, Mus caroli, and the glirid, Eliomys quercinus. Differences between both species could be found, which includes different mastication. Mus caroli eats mixed food. The masticatory musculature admits mainly antero-posterior mandibular movements with a minimal transverse component. The food of Eliomys quercinus exists of mainly insects. The masticatory muscles, in particular the M. pterygoideus internus and the well developed M. zygomaticomandibularis, pars posterior, include high frequency of lateral movements between mastication.     

Mechanical properties of foods used in experimental studies of primate masticatory function

In vivo studies of jaw-muscle behavior have been integral factors in the development of our current understanding of the primate masticatory apparatus. However, even though it has been shown that food textures and mechanical properties influence jaw-muscle activity during mastication, very little effort has been made to quantify the relationship between the elicited masticatory responses of the subject and the mechanical properties of the foods that are eaten. Recent work on human mastication highlights the importance of two mechanical properties-toughness and elastic modulus (i.e., stiffness)-for food breakdown during mastication. Here we provide data on the toughness and elastic modulus of the majority of foods used in experimental studies of the nonhuman primate masticatory apparatus. Food toughness ranges from approximately 56.97 Jm(-2) (apple pulp) to 4355.45 Jm(-2) (prune pit). The elastic modulus of the experimental foods ranges from 0.07 MPa for gummy bears to 346 MPa for popcorn kernels. These data can help researchers studying primate mastication select among several potential foods with broadly similar mechanical properties. Moreover, they provide a framework for understanding how jaw-muscle activity varies with food mechanical properties in these studies.     

Influence of thickeners on the fragmentation of fish meat sausage by mastication

The influence of food thickeners (potato starch, guar gum, and xanthan gum and deionized water) on the breakdown of solid food was numerically analyzed, and an investigation was made into the cumulative size distribution of food fragments, textural properties, sensory evaluation and maximum transit velocity of a bolus in the pharynx.The results suggest that evaluating the breakability into small pieces was easily influenced by the addition ratio of the dispersion medium. However, in respect of the destruction process for the solid body, each sample was more strongly affected by the type of the dispersion medium than by the addition ratio of this medium.The destruction process was strongly influenced by the history of the breakdown caused by mastication when a liquid dispersion medium was added to the solid. However, when a high-viscosity sol was added to the solid, the destruction process was random and not affected by any history.     

Influence of Thickeners on the Fragmentation of Fish Meat Sausage by Mastication

The influence of food thickeners (potato starch, guar gum, and xanthan gum and deionized water) on the breakdown of solid food was numerically analyzed, and an investigation was made into the cumulative size distribution of food fragments, textural properties, sensory evaluation and maximum transit velocity of a bolus in the pharynx.

The results suggest that evaluating the breakability into small pieces was easily influenced by the addition ratio of the dispersion medium. However, in respect of the destruction process for the solid body, each sample was more strongly affected by the type of the dispersion medium than by the addition ratio of this medium.

The destruction process was strongly influenced by the history of the breakdown caused by mastication when a liquid dispersion medium was added to the solid. However, when a high-viscosity sol was added to the solid, the destruction process was random and not affected by any history.     

Masticatory-stress hypotheses and the supraorbital region of primates

The purpose of this study is to test various masticatory-stress hypotheses about the evolution and function of well-developed browridges of higher primates. This was done by measuring and analyzing patterns of in vivo bone strain recorded from three-element rosette strain gages bonded to the supraorbital region and to other portions of the bony face of Macaca fascicularis and Papio anubis during mastication and incision. The magnitude and direction of the principal strains recorded support Endo's hypothesis that the supraorbital region during mastication and incision is bent in the frontal plane (Endo, 1966). Our data do not, however, support his hypothesis that the supraorbital region is bent more during incision than during mastication. The data also demonstrate that overall levels of supraorbital strain are not larger in more prognathic subjects. Most importantly, the data indicate that the supraorbital region of nonhuman catarrhines is strained very little during mastication and incision. This indicates that there is much more supraorbital bone than is necessary both to counter masticatory loads and to provide an adequate safety factor to failure for these loads. This in turn suggests that the macaque and baboon browridges can be considerably reduced in size and still maintain these required structural characteristics. Thus, our experiments provide no support whatsoever for those hypotheses that directly link browridge morphology to masticatory stress (cf. Endo, 1966; Russell, 1983, 1985). A recent review of Endo's original work indicates that this latter statement is also true for humans (Picq and Hylander, 1989). We conclude, therefore, that there is no good reason to believe that enlarged browridges in living and/or fossil primates are structural adaptations to counter intense masticatory forces. The evolution of browridge morphology in primates is best explained on the basis of factors related to the position of the brain relative to the orbits (Moss and Young, 1960). When these structures are widely separated, as in gorillas, the large intervening space must be bridged with bone. In addition, enough bone must be present within the supraorbital and bridged regions to prevent structural failure due to non-masticatory external forces associated with highly active primates (e.g., accidental traumatic forces applied to the orbits and neurocranium). This requirement results in both pronounced browridges and in much more supraorbital bone than is necessary to counter routine cyclical stress during mastication and incision. This in turn explains why bone strains recorded from the supraorbital region are extremely small relative to other portions of the primate face during mastication and incision.     

Cortical control for mastication in cats: changes in masticatory movements following lesions in the masticatory cortex

In a previous paper (Hiraba and Sato 2004) we reported that an accurate mastication might be executed by the cortical processing in bilateral masticatory area (MA)and motor cortices. The aim of this study was to determine if cats with lesion of either unilateral or bilateral MA showed changes in mastication. After exploring mechanoreceptive fields and motor effects of mastication-related neurons (MRNs) in MA using the single unit recording and intracortical microstimulation methods, we made various lesions in MAs with injections of kainic acid (0.1%, 2.0 microl). Since the MA was divided into facial (F) and intraoral (I) projection areas as reported in the previous paper, cats with the unilateral lesion in F or I, and with the bilateral lesion in F and F, I and I or F and I (F on one side and I on other side) were prepared. Cats with unilateral lesion in F or I and with bilateral lesion in F and I showed no changes in mastication except for prolongation of the food intake and masticatory periods. Cats with bilateral lesion into F and F, or I and I showed wider jaw-opening during mastication. Particularly, the latter group showed enormous jaw-opening, delay in the start of mastication and difficulty in manipulating food on the tongue. In all cats with lesions of each type, masticatory and swallowing rhythms remained normal. These findings suggest that accurate mastication is executed by the close integration between F and F and I and I of the bilateral MA.     

Cortical control for mastication in cats: Changes in masticatory movements following lesions in the masticatory cortex

In a previous paper (Hiraba and Sato ) we reported that an accurate mastication might be executed by the cortical processing in bilateral masticatory area (MA)and motor cortices. The aim of this study was to determine if cats with lesion of either unilateral or bilateral MA showed changes in mastication. After exploring mechanoreceptive fields and motor effects of mastication-related neurons (MRNs) in MA using the single unit recording and intracortical microstimulation methods, we made various lesions in MAs with injections of kainic acid (0.1%, 2.0?µl). Since the MA was divided into facial (F) and intraoral (I) projection areas as reported in the previous paper, cats with the unilateral lesion in F or I, and with the bilateral lesion in F & F, I & I or F & I (F on one side and I on other side) were prepared. Cats with unilateral lesion in F or I and with bilateral lesion in F & I showed no changes in mastication except for prolongation of the food intake and masticatory periods. Cats with bilateral lesion into F & F, or I & I showed wider jaw-opening during mastication. Particularly, the latter group showed enormous jaw-opening, delay in the start of mastication and difficulty in manipulating food on the tongue. In all cats with lesions of each type, masticatory and swallowing rhythms remained normal. These findings suggest that accurate mastication is executed by the close integration between F & F and I & I of the bilateral MA.     

Development and validation of a mastication simulator

More and more research are being done on food bolus formation during mastication. However, the process of bolus formation in the mouth is difficult to observe. A mastication simulator, the Artificial Masticatory Advanced Machine (AM2) was developed to overcome this difficulty and is described here. Different variables can be set such as the number of masticatory cycles, the amplitude of the mechanical movements simulating the vertical and lateral movements of the human lower jaw, the masticatory force, the temperature of the mastication chamber and the injection and the composition of saliva. The median sizes of the particles collected from the food boluses made by the AM2 were compared with those of human boluses obtained with peanuts and carrots as test foods. Our results showed that AM2 mimicked human masticatory behavior, producing a food bolus with similar granulometric characteristics.     

Mastication effort estimated by electromyography for cooked rice of differing water content

The objective of this study was to quantify the mastication effort for cooked rice. We analyzed mastication patterns while normal subjects ate a spoonful of cooked rice that had been prepared by cooking with different amounts of water (1.5, 2.0, 3.0, and 4.0 times the water to rice weight). The rice samples were served with the same weight, same volume and same solid content, and electromyography (EMG) of the masticatory muscles was measured. The texture of the four cooked rice samples was instrumentally analyzed by the two-bite method. The number of chews, masticatory time, and jaw-closing muscle activities per chew evaluated by EMG were higher in the rice sample cooked with least water, which exhibited a high firmness value in the instrumental test. Rice cooked with 4.0 times the amount of water exhibited the longest jaw-opening duration, which was related to the adhesiveness value in the instrumental test. The ratio of jaw-opening muscle activity to the preceding jaw-closing muscle activity was lower for the rice containing least water, this corresponding to the area ratio (balance degree) in the instrumental test. Softer rice containing more water reduced the total mastication effort until swallowing because it required a shorter mastication time. It was not difficult for the softer rice with high density to be ingested in greater weight, decreasing the mastication effort for a certain amount.     

Time analysis of hard and soft bolus processing

Objective: Clinical observations and mathematical models show that dental implants are influenced by the magnitude of loading. Therefore, the knowledge of mandible movement during mastication is important to assess occlusal and masticatory force vectors. The purpose of this study was to detect the path of movement of the lower jaw and to distinguish stages of mastication, duration of bolus processing and peak amplitude of mastication. Method: Motion analysis was used to record three-dimensional mandible movements. Individualized sensors were rigidly attached to the mandible of 51 study participants. At the beginning of the measurement, all subjects were asked to move the mandible in extreme positions (maximal opening and maximal lateral movements). Then, each subject masticated a bite of hard and soft food. Duration of bolus mastication and peak amplitude of mastication movement in mesio-distal, cranio-caudal and vestibulo-oral axes related to peak amplitude of marginal movements were evaluated for each subject. The chewing record of each subject was divided into three phases (chopping, grinding and swallowing), and the duration of mastication and number of closing movements were evaluated. Results: The findings of this pilot study suggest that masticatory movements vary in individuals. Bolus character influences the process duration, but not the frequency of closing movements. Neither gender nor age had any influence on either the time or frequency of bolus processing. Conclusion: Relationships to directions and magnitudes of acting chewing force should be more precisely examined since transversally acted forces during grinding are important factors in tooth/implant overloading.     

Mandibular function in Galago crassicaudatus and Macaca fascicularis: an in vivo approach to stress analysis of the mandible.

Single-element and/or rosette strain gages were bonded to mandibular cortical bone in Galago crassicaudatus and Macaca fascicularis. Five galago and eleven macaque bone strain experiments were performed and analyzed. In vivo bone strain was recorded from the lateral surface of the mandibular corpus below the postcanine tooth row during transducer biting and during mastication and ingestion of food objects. In macaques and galagos, the mandibular corpus on the balancing side is primarily bent in the sagittal plane during mastication and is both twisted about its long axis and bent in the sagittal plane during transducer biting. On the working side, it is primarily twisted about its long axis and directly sheared perpendicular to its long axis, and portions of it are bent in the sagittal plane during mastication and molar transducer biting. In macaques, the mandibular corpus on each side is primarily bent in the sagittal plane and twisted during incisal transducer biting and ingestion of food objects, and it is transversely bent and slightly twisted during jaw opening. Since galagos usually refused to bite the transducer or food objects with their incisors, an adequate characterization of mandibular stress patterns during these behaviors was not possible. In galagos the mandibular corpus experiences very little transverse bending stress during jaw opening, perhaps in part due to its unfused mandibular symphysis. Marked differences in the patterns of mandibular bone strain were present between galagos and macaques during the masticatory power stroke and during transducer biting. Galagos consistently had much more strain on the working side of the mandibular corpus than on the balancing side. These experiments support the hypothesis that galagos, in contrast to macaques, employ a larger amount of working-side muscle force relative to the balancing-side muscle force during unilateral biting and mastication, and that the fused mandibular symphysis is an adaption to use a maximal amount of balancing-side muscle force during unilateral biting and mastication. These experiments also demonstrate the effects that rosette position, bite force magnitudes, and types of food eaten have on recorded mandibular strain patterns.     

Cortical control of mastication in cats. 2. Deficits of masticatory movements following a lesion in the motor cortex

Our previous study suggested that area P in the lateral wall of the presylvian sulcus and MA (masticatory cortex) in the rostral part of the orbital gyrus play an important role in execution of mastication. The aim of this present study is to examine if changes in orofacial behaviors and masticatory movements occur in cats with lesions of area P. First, we explored the locations in area P through the use of single unit recording and ICMS (intracortical microstimulation). Since mastication related neurons (MRNs) with the mechanical receptive field (RF) in facial or intraoral region were intermingled in area P, we performed either a partial or entire lesion in area P by injections of 2 microl or 4 microl of 0.1% kainic acid. Cats with the entire lesion in area P showed a decrease of food intake rates associated with abnormal tongue protrusion and wide jaw-opening, fluctuation of masticatory start, and prolongation of masticatory and food intake periods. Abnormal movements of tongue and jaw did not recover, although their prolongation and fluctuation returned to normal levels in one month. On the other hand, all deficits evoked by cats with the partial lesion recovered in about one month. In cats with the partial and entire lesions, masticatory rhythm remained normal. These findings suggest that area P may regulate accurate and suitable tongue and jaw movements during mastication depending on cortical processing.     

Masticatory function in patients with xerostomia

The effects of reduced salivary output in patients suffering from xerostomia on masticatory function has not been previously studied. This study compares masticatory performance and kinematic activity of patients suffering from xerostomia with age-, sex-, and number of occluding pairs-matched healthy controls. Masticatory function was evaluated by assessment of chewing motion and muscle activity during chewing an artificial food (CutterSil®), chewing gum and swallowing a bolus of almond. Chewing motion was recorded with the Optotrak® computer system. Bilateral muscle activity of both masseter and anterior temporalis was recorded using surface electrodes. Results of this study revealed significant differences between patients and controls in their ability to process food and masticatory muscle activity. The majority of patients could not break down the artificial food, others had a larger median particle size than the controls. A significant difference was also observed in the number of chewing cycles required to swallow almonds, the patients required more than twice as many chews as the controls, P<0.001. The right masseter muscle displayed significantly less activity for the patient than the controls. These findings suggest that patients with xerostomia exhibit reduced ability to process food. The observed decline in masticatory performance is probably due to reduced activity of the muscles of mastication.     

The modulation of sensory transmission through the medullary dorsal horn during cortically driven mastication

During mastication, reflexes are modulated and sensory transmission is altered in interneurons and ascending pathways of the rostral trigeminal sensory complex. The current experiment examines the modulation of sensory transmission through the most caudal part of the trigeminal sensory system, the medullary dorsal horn, during fictive mastication produced by cortical stimulation. Extracellular single unit activity was recorded from the medullary dorsal horn, and multiple unit activity was recorded from the trigeminal motor nucleus in anesthetized, paralyzed rabbits. The masticatory area of sensorimotor cortex was stimulated to produce rhythmic activity in the trigeminal motor nucleus (fictive mastication). Activity in the dorsal horn was compared in the presence and absence of cortical stimulation. Fifty-two percent of neurons classified as low threshold and 83% of neurons receiving noxious inputs were influenced by cortical stimulation. The cortical effects were mainly inhibitory, but 21% of wide dynamic range and 6% of low threshold cells were excited by cortical stimulation. The modulation produced by cortical stimulation, whether inhibitory or excitatory, was not phasically related to the masticatory cycle. It is likely that, when masticatory movements are commanded by the sensorimotor cortex, the program includes tonic changes in sensory transmission through the medullary dorsal horn.     

The function of sensory information from the first somatosensory cortex for facial movements during ingestion in cats

The aim of the present study was to investigate the relationship between the facial region of the first somatosensory cortex (facial SI) and facial region of the motor cortex (facial MI), as the basis of orofacial behaviors during ingestion of fish paste. Area M in the ventral cortex of the cruciate sulcus that was defined as part of the facial MI by and, showed various facial twitches evoked by intracortical microstimulation (ICMS) and recorded many mastication-related neurons (MRNs). Many MRNs in area M had receptive fields (RFs) in lingual, perioral and mandibular regions. The 60% value of activity patterns of MRNs (n = 124) recorded in area M of normal cats, were the pre-SB type (the sustained and pre-movement type) that showed increased firing prior to the start of mastication and then tonic activity during the masticatory period. MRNs recorded in area M of cats with the facial SI lesion, showed a noticeable decrease in MRNs with RFs in the perioral and mandibular regions and with activity of the pre-SB type. These results strongly suggest that blocking facial SI sensory inputs evoked by mastication interferes with the relay of important facial sensory information to area M required for the appropriate manipulation of food during mastication.     

Pharyngeal mastication and food transport in the carp (Cyprinus carpio L.): A cineradiographic and electromyographic study

Cyprinids constitute the largest fish family and are characterized by their pharyngeal teeth. The masticatory mechanism is still poorly understood. The complex of structures that determine the movements of pharyngeal teeth and chewing pad in the carp (Cyprinus carpio L.) is analyzed. Activities in 16 head muscles of a free-swimming carp were recorded. X-ray cinerecordings, synchronized with electromyograms, were made of the intake, transport, mastication, and deglutition of radiopaque food pellets. Metal markers allowed a detailed movement analysis. Masticatory cycles are bilaterally synchronous and show distinct crushing and grinding patterns. Direct masticatory muscles that suspend and connect the pharyngeal bones steer and stabilize the masticatory movements. Baudelot's ligament, between skull and pectoral girdle, is applied as fulcrum, effects a crucial shift of the rotation axis of the pharyngeal jaw, and transforms crushing into grinding; simultaneous abduction lengthens the grinding stroke. Body muscles supply indirectly the power for mastication; they also appear to be regulated more distantly. The epaxial muscles lift the skull and thereby the levators of the pharyngeal bones, thus transmitting high forces to the teeth. They also stretch the levator of the bone as soon as occlusion is reached and thus optimize its production of forces during grinding. The hypaxial muscles retract the pharyngeal bones indirectly during grinding and power the teeth in sliding. The chewing pad, previously assumed to be motionless, rotates rostroventrad with the skull and intensifies grinding. Respiration and mastication are mutually related. The extensive movements of the pharyngeal bones are permitted only by the simultaneous expansion of the buccopharynx and a slide-coupling in the branchial floor. Muscular pads that line the pharynx are shown to transport food toward the teeth. The constrictor pharyngis effects deglutition. Natural food, intestinal contents, and feces of the carp were analyzed with respect to the capacity for distinct masticatory operations. During the experiments pellets, barley, and worms were fed. The carp is specialized for polyphagy and this appears to be based on the profiles of the heterodont teeth rather than on drastic changes in the two preprogrammed activity patterns. Comparison of the pharyngeal jaw system in the carp and higher teleosts emphasizes the structural design for the application of large forces in this cyprinid.     

Telemetry System for Assessing Jaw-Muscle Function in Free-ranging Primates

In vivo laboratory-based studies describing jaw-muscle activity and mandibular bone strain during mastication provide the empirical basis for most evolutionary hypotheses linking primate masticatory apparatus form to diet. However, the laboratory data pose a potential problem for testing predictions of these hypotheses because estimates of masticatory function and performance recorded in the laboratory may lack the appropriate ecological context for understanding adaptation and evolution. For example, in laboratory studies researchers elicit rhythmic chewing using foods that may differ significantly from the diets of wild primates. Because the textural and mechanical properties of foods influence jaw-muscle activity and the resulting strains, chewing behaviors studied in the laboratory may not adequately reflect chewing behaviors of primates feeding in their natural habitats. To circumvent this limitation of laboratory-based studies of primate mastication, we developed a system for recording jaw-muscle electromyograms (EMGs) from free-ranging primates so that researchers can conduct studies of primate jaw-muscle function in vivo in the field. We used the system to record jaw-muscle EMGs from mantled howlers (Alouatta palliata) at Hacienda La Pacifica, Costa Rica. These are the first EMGs recorded from a noncaptive primate feeding in its natural habitat. Further refinements of the system will allow long-term EMG data collection so that researchers can correlate jaw-muscle function with food mechanical properties and behavioral observations. In addition to furthering understanding of primate feeding biology, our work will foster improved adaptive hypotheses explaining the evolution of primate jaw form.     

Deformation of nasal septal cartilage during mastication

The cartilaginous nasal septum plays a major role in structural integrity and growth of the face, but its internal location has made physiologic study difficult. By surgically implanting transducers in 10 miniature pigs (Sus scrofa), we recorded in vivo strains generated in the nasal septum during mastication and masseter stimulation. The goals were (1) to determine whether the cartilage should be considered as a vertical strut supporting the nasal cavity and preventing its collapse, or as a damper of stresses generated during mastication and (2) to shed light on the overall pattern of snout deformation during mastication. Strains were recorded simultaneously at the septo‐ethmoid junction and nasofrontal suture during mastication. A third location in the anterior part of the cartilage was added during masseter stimulation and manipulation. Contraction of jaw closing muscles during mastication was accompanied by anteroposterior compressive strains (around ?1,000 με) in the septo‐ethmoid junction. Both the orientation and the magnitude of the strain suggest that the septum does not act as a vertical strut but may act in absorbing loads generated during mastication. The results from masseter stimulation and manipulation further suggest that the masticatory strain pattern arises from a combination of dorsal bending and/or shearing and anteroposterior compression of the snout. J. Morphol., 2009. © 2009 Wiley‐Liss, Inc.