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PubMed1990

Demonstration with [14C]2-deoxyglucose of brain structures involved in the masticatory activity of the hedgehog (Erinaceus europaeus).

The different brain structures activated during mastication in the hedgehog were revealed using Sokoloff's 2-deoxy-D-[1-14C]glucose technique. Brain sections of animals having received an injection of 2-deoxy-D-[1-14C]glucose during mastication were compared with those of animals treated during calm waking. Only brain structures that presented a 20% increase in glucose consumption were considered. The greatest increases were observed in the bulbar parvocellular reticulum and the trigeminal spinal nucleus (+80%), followed by structures also involved in mastication such as the trigeminal motor nucleus (+73%) and the hypoglossal nucleus (+64%). Other activated areas, not directly involved in mastication, were for example, the area postrema (55%), the olfactory (44%) and visual cortex (41%). This study emphasizes the importance of the bulbar parvocellular reticulum during mastication.

Animals↗

PubMed1979

Nonfunctional and functional occlusal contacts: a review of the literature.

A review of the literature on occlusal contacts emphasizes the following points. 1. Contacts in centric occlusion do not correspond to any ideal occlusal diagram. 2. Canine protection and group function appear to correspond to two successive states of the evolving dentition under the effect of abrasion. In most lateral occlusions, two maxillary teeth, of which one is the canine, are involved. 3. During mastication, tooth contacts exist. They occur most often during a sliding movement in which the direction and the origin are variable. This justifies the concept of an occlusal field of mastication. 4. During unilateral mastication, the chewing of the food is performed by working as well as nonworking contact. This imposes the distinction between the chewing and nonchewing sides (functional) and the working and nonworking sides (kinematic). 5. Centric occlusion is the occlusion most often used during mastication. It is also the occlusion for which the masticatory forces are the greatest. 6. The bibliographic data concerning occlusal contracts during swallowing are largely contradictory. It nevertheless seems that the occlusal contacts obey laws nearly the same as those governing the occlusal contact during mastication (sliding on an occlusal field of deglutition, and the importance of centric occlusion).

Deglutition↗

PubMed2006

Prospective randomized clinical trial comparing the effects of a masticatory bite wafer and avoidance of hard food on pain associated with initial orthodontic tooth movement.

INTRODUCTION: The purpose of this prospective, randomized clinical trial was to compare the use of masticatory bite wafers with the avoidance of mastication in reducing pain and discomfort associated with initial orthodontic tooth movement. METHODS: Eighty-four subjects (mean age, 14.1 years), randomly allocated to a bite-wafer group (BWG) or a reduced-mastication group (RMG), completed the study. In each subject, 1 arch was bonded and ligated with a round austenitic active 0.016-in nickel-titanium wire, and placebo instructions were given. The subjects in the BWG then performed immediate supervised mastication of the wafers for 10 minutes, and they were instructed thereafter to bite on the wafers to prevent pain for the next 7 days. The subjects in the RMG were instructed not to masticate for 3 hours after placement of the fixed appliance and to avoid masticating hard food for 7 days. Each patient's level of anxiety was assessed before treatment with standard psychometric questionnaires. Each patient recorded the level of pain immediately after archwire ligation on a 100-mm visual analogue scale (VAS) and used a pain diary with a verbal rating scale for the next 7 days. RESULTS: No statistically significant differences in the VAS immediately after ligation of the archwires were observed between the 2 groups. The median pain score for the BWG was higher for the first 4 days. The median peak difference was reached on the evening of the first day. At this maximum value, the median pain score of the BWG was higher and statistically significant (P = .006). CONCLUSIONS: Although the amount of pain and discomfort reported by the patients undergoing fixed orthodontic therapy varied, more pain was reported by those using bite wafers than by those who avoided masticatory activity after placement of fixed appliances.).

Adolescent↗

PubMed2006

Mandibular mechanics after osteotomy and distraction appliance placement I: Postoperative mobility of the osteotomy site.

PURPOSE: Fixation at the osteotomy site for mandibular distraction osteogenesis (DO) is probably not rigid, especially during mastication. Micromotion may affect the course of DO. This study aimed to measure the mobility of the fresh distractor-fixed osteotomy site in response to mastication and masticatory muscle stimulation. MATERIALS AND METHODS: Twenty-eight domestic pigs, 6 to 8 weeks old, underwent osteotomy of the right mandible and placement of a distractor appliance. Immediately after surgery, displacement at 3 different locations (superior-lateral, inferior-lateral, and inferior-medial) of the osteotomy site was assessed using ultrasound piezoelectric crystals or differential variable reluctance transducers (DVRTs). The amount of lengthening or shortening at each location was measured during mastication and muscle stimulation. Displacement was also measured for bilateral osteotomy during muscle stimulation from a subgroup of 12 pigs. RESULTS: The osteotomy site demonstrated significant mobility during power strokes of mastication with an average magnitude of 0.3 to 0.4 mm. Distinct patterns of displacement were associated with different locations, and the patterns varied between chewing sides. The most common pattern was lengthening at the superior-lateral and shortening at both inferior sites. Similar amounts of displacement were observed during the stimulation of jaw-closers (masseter and medial pterygoid), but the patterns produced by these muscles did not completely explain the masticatory pattern. Opening the osteotomy to 1.5 mm did not alter the displacements observed during muscle stimulation. Bilateral osteotomy tended to decrease displacement. CONCLUSIONS: The study demonstrates that during mastication and masticatory muscle stimulation, an acute mandibular osteotomy site is mobile despite fixation by a distractor appliance.

Analysis of Variance↗

PubMed1999

Changes in masticatory patterns after bilateral fracture of the mandibular condylar process.

PURPOSE: Because the morphology of the temporomandibular joint is thought to control movements of the mandible during mastication, bilateral fractures of the condylar process should disrupt masticatory patterns. The purposes of this study were 1) to document changes in masticatory patterns after such fractures, and 2) to determine whether and when normal masticatory patterns are recovered. PATIENTS AND METHODS: Twenty-two patients (15 men and 7 women) were examined at 6 weeks, 6 months, 1 year, 2 years, and 3 years after bilateral condylar process fractures. Patients were age and sex matched to a control sample. Incisor movements in three dimensions, along with muscle activity from the anterior temporalis, posterior temporalis, and superficial masseter, were recorded at 500 Hz during mastication of a gummy candy. RESULTS: Although the patients showed no reduction of interincisal opening during mastication, the opening was achieved with reduction of anterior translation of the condyles. Patients had significantly narrower chewing cycles, with significantly lower adductor muscular effort during the closing phases of mastication. Differences from controls were no longer detectable 1 year after the fractures. CONCLUSION: The amount of opening during mastication may appear clinically normal in patients with bilateral condylar process fractures. However, disruption of controlling structures and lateral pterygoid function appears to reduce the amount of anterior translation and lateral excursion during the chewing cycle. Reduced adductor muscle activity during the closing phases may reduce loads on the fractured condylar processes. In general, these patients recover normal masticatory cycles within 1 year.

Adolescent↗

PubMed1995

Gastric emptying of solid food in edentulous patients.

Whether mastication of food by teeth is a physiological contributor in the process of nutrient digestion remains a debatable issue. In this study we sought to determine whether mastication could influence the gastric emptying of solid food. In 8 edentulous patients, we measured the gastric emptying of a test meal ingested with or without their dental prostheses. Clinical dental evaluation and Helkimo chewing test were first performed to verify that the mastication deficiency was adequately corrected by the dental prostheses. A mixed meal containing ten cubes (1.5 cm) of beef liver labeled with 99mTc and mixed in a chicken stew was ingested by the subjects and followed by gamma camera external scintigraphy. The gastric emptying rate of the 99mTc-labeled liver was similar whether the meal was ingested with the denture properly inserted, allowing normal mastication of the liver cubes, or whether the food was swallowed unmasticated in the absence of functional prostheses (Tlag = 60 +/- 5 vs. 58 +/- 11 min, p = NS; T1/2 = 73 +/- 21 vs. 55 +/- 10 min, p = NS; Tlag+T1/2 = 133 +/- 19 vs. 114 +/- 17 min, p = NS). These results show that gastric trituration and emptying of solid food was not facilitated by prior mastication.

Dentures↗

PubMed1988

Loci and characteristics of EMG silent periods during masticatory mandibular movements in rats.

Frontal plane mandibular movements and the associated superficial masseter EMG signals of six 39-day-old rats were simultaneously recorded and digitized at a rate of 1 kHz by the optoelectronic method in order to investigate the loci and attributes of masseteric silent periods during mastication of hard (pellets) and soft (slurry) food items. The marked silent periods, defined as cessations of EMG activity during the slow-close (SC) phase of single chewing cycles, were analyzed for their (1) onset and offset durations relative to physiological centric occlusion (PCO), (2) frontal vertical (FV) and frontal horizontal (FH) loci relative to PCO, and (3) FV and FH velocities and accelerations of masticatory mandibular movements in relation to PCO. The start (SSP) and end (ESP) of silent period loci relative to PCO moved superiorly as sequences of pellet mastication progressed. All silent period attributes during slurry consumption were significantly different (p less than or equal to 0.01) from pellet attributes: Slurry SSP and ESP loci were closer to PCO than were pellet loci; durations of silent period loci during pellet mastication were more variable than were slurry durations. FV distance and velocity values for pellets were greater than with pellets. Although FV velocities during both pellet and slurry mastication decreased at ESP relative to SSP values, their FH velocities at ESP actually increased relative to SSP velocities. Loci attributes of EMG silent periods appeared largely dependent on the consistency of the food item being masticated.

Animals↗

PubMed2005

[Investigation of meals in health care service facility].

PURPOSE: Oral care and oral treatment are promoted in health care service facilities. However, disorders of eating, mastication and swallowing and care management of meal were get behind. This study investigated them in health care service facilities. METHODS: Doctors who work in facilities were screened for care management of meal using questionnaire. Inpatients were screened for age, meal menu, vertical stop, prosthetic treatment, satisfaction of mastication and difference of meal menu in the home and in the facility. RESULTS: Doctors and care workers have little understanding of mastication. Inpatients were satisfied to be able to eat rice in the home and in the facility. It is of paramount importance to have remaining teeth, to maintain vertical stop and to have prosthetic treatment. CONCLUSIONS: Education on the importance of mastication is needed. The research results show that new action and diagnosis method for deciding menus aiming at mastication of steamed rice need to be developed.

Aged↗

PubMed1982

Mandibular movement patterns relative to food types in common tree shrews (Tupaia glis).

Although common tree shrews have long been considered a model system for early eutherian mastication, little information on mandibular movement patterns relative to specific food types has been reported. Detailed analysis of mandibular movement patterns when related to resulting attrition facets may permit more accurate extrapolations regarding the dietary habits of primitive mammals. Marker beads were sewn to chins of five animals that were placed in a restraint system and filmed while they fully masticated mealworm larvae and standardized pieces of banana, almond, and commercial cat chow. These sequences were divided into early, middle, and late thirds of food reduction. Mandibular positions from both frontal and lateral perspectives were digitized frame by frame to yield plots of orbits in three dimensions as well as graphic display of displacements, velocities, and accelerations. Plot coordinates were averaged to generate composite orbital shapes. Significant (p less than 0.01) findings included: (1) shortest orbital durations and greatest peak closing velocities and accelerations in early third of reduction; (2) smallest maximum gape, smallest maximum lateral excursion from midline, and longest duration of powerstroke relative to orbital duration in late third of reduction: (3) shortest orbital durations and smallest maximum gape during mastication of chow; (4) greatest maximum lateral excursion during mastication of mealworm larvae; and (5) smallest peak closing accelerations during mastication of banana. Significant differences were also found among subjects for all parameters examined. Capacity for complex jaw movement may have been critical for allowing primitive molars to be used for trituration of a variety of food types, and may have preceded evolution of more specialized molar forms.

Animals↗

PubMed1988

Response patterns of craniomandibular muscles with and without alterations in sensory feedback.

1. Surface EMG recordings were made bilaterally from the anterior part of the temporal muscle, superficial masseter muscle, and the suprahyoid complex of muscles while tracking mandibular incisor movement in three planes. This was done in 20 normal subjects with 16 different responses. Some responses involved clenching whereas other responses occurred with actual mandibular movement. 2. Each muscle demonstrated a probability of recruitment dependent on the response that correlated with the intensity of recruitment. The higher the probability of recruitment, the greater the intensity of muscle activity. 3. The anterior temporal muscle demonstrated no statistically significant difference in any of the responses between the left and right muscles. The masseter muscle also demonstrated bilateral symmetry. 4. The anterior part of the temporal muscle was recruited in more than 60% of its trials (60% to 100%) in ipsilateral laterotrusion, retrusion, fast vertical raising, clenching on the ipsilateral or intercuspal position, and mastication. The temporal muscle was recruited in less than 60% of its trials in contralateral and incisor clenching, and less than 30% in contralateral laterotrusion, protrusion, and opening. 5. The superficial masseter muscle was recruited in more than 60% of its trials in protrusion, vertical raising, all clenches, and mastication. The masseter muscle was recruited less than 60% in retrusion, ipsilateral laterotrusion, and opening. 6. The suprahyoid group of muscles was recruited in more than 60% of its trials in protrusion, opening, and mastication. This group of muscles was recruited less than 60% of the time in clenching, lateral movements, and rapid vertical raising of the mandible. 7. Applying a maxillary splint to seven subjects significantly decreased the recruitment of the anterior temporal and masseter muscles during mastication. The splint also modified the use of the masseter muscle during protrusion so that it was less active, but increased its recruitment during contralateral clenching. The suprahyoid muscle group was unaffected by the maxillary splint. 8. These data support the concept that movement of the mandible from the intercuspal or rest position develops a coactivation pattern that will excite or inhibit a given muscle regardless of whether clenching with occlusal contacts or no occlusal contact is involved. 9. The data also demonstrate that the maxillary splint can alter the use of the jaw elevator muscles, predominantly in mastication.

Adult↗

PubMed1989

Changes in the physical properties of the Ultrafil low-temperature (70 degrees C) thermoplasticized gutta-percha system.

Three tests were used to obtain a basic understanding of the changes taking place in the physical properties of the Hygienic Ultrafil system. The materials studied were raw gutta-percha, gutta-percha points, and the two Ultrafil materials Blue (firm set) and White (regular set) gutta-percha. In the first test a differential scanning calorimeter was used to determine melting points; two crystalline forms were observed in the dental materials and only one crystalline form in the raw gutta-percha. In the second test a magnetic bearing torsional creep apparatus was used in which the rates of crystallization were observed. The differences seen in the induction times of the crystallization are related to the amount of mastication of the gutta-percha. Mastication in this usage is the manufacturers process of mixing the raw gutta-percha with its other components. The gutta-percha is masticated slightly in the points and considerably more in the Ultrafil material. Ultrafil exhibits longer periods of time required to induce nucleation at any specific temperature due to the increased mastication. Melting points were also decreased with increased mastication. In the third test a dilatometer was used to observe isothermal volumetric shrinkage of the materials during crystallization. When the Ultrafil material was compared with the gutta-percha points, the blue material had approximately the same amount of shrinkage, 2.6%; the white material shrank slightly less, 2.2%. The raw gutta-percha being 100% polymer had the greatest amount of shrinkage, 4.6%.

Calorimetry↗

PubMed1998

Mandibular corpus strain in primates: further evidence for a functional link between symphyseal fusion and jaw-adductor muscle force.

Previous work indicates that compared to adult thick-tailed galagos, adult long-tailed macaques have much more bone strain on the balancing-side mandibular corpus during unilateral isometric molar biting (Hylander [1979a] J. Morphol. 159:253-296). Recently we have confirmed in these same two species the presence of similar differences in bone-strain patterns during forceful mastication. Moreover, we have also recorded mandibular bone strain patterns in adult owl monkeys, which are slightly smaller than the galago subjects. The owl monkey data indicate the presence of a strain pattern very similar to that recorded for macaques, and quite unlike that recorded for galagos. We interpret these bone-strain pattern differences to be importantly related to differences in balancing-side jaw-adductor muscle force recruitment patterns. That is, compared to galagos, macaques and owl monkeys recruit relatively more balancing-side jaw-adductor muscle force during forceful mastication. Unlike an earlier study (Hylander [1979b] J. Morphol. 160:223-240), we are unable to estimate the actual amount of working-side muscle force relative to balancing-side muscle force (i.e., the W/B muscle force ratio) in these species because we have no reliable estimate of magnitude, direction, and precise location of the bite force during mastication. A comparison of the mastication data with the earlier data recorded during isometric molar biting, however, supports the hypothesis that the two anthropoids have a small W/B jaw-adductor muscle force ratio in comparison to thick-tailed galagos. These data also support the hypothesis that increased recruitment of balancing-side jaw-adductor muscle force in anthropoids is functionally linked to the evolution of symphyseal fusion or strengthening. Moreover, these data refute the hypothesis that the recruitment pattern differences between macaques and thick-tailed galagos are due to allometric factors. Finally, although the evolution of symphyseal fusion in primates may be linked to increased stress associated with increased balancing-side muscle force, it is currently unclear as to whether the increased force is predominately vertically directed, transversely directed, or is a near equal combination of these two force components (cf. Ravosa and Hylander [1994] In Fleagle and Kay [eds.]: Anthropoid Origins. New York: Plenum, pp. 447-468).

Animals↗

PubMed2005

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.

Animals↗

PubMed1979

The functional significance of primate mandibular form.

A stress analysis of the primate mandible suggests that vertically deep jaws in the molar region are usually an adaptation to counter increased sagittal bending stress about the balancing-side mandibular corpus during unilateral mastication. This increased bending stress about the balancing side is caused by an increase in the amount of balancing-side muscle force. Furthermore, this increased muscle force will also cause an increase in dorso-ventral shear stress along the mandibular symphysis. Since increased symphyseal stress can be countered by symphyseal fusion and as increased bending stress can be countered by a deeper jaw, deep jaws and symphyseal fusion are often part of the same functional pattern. In some primates (e.g., Cercocebus albigena), deep jaws are an adaptation to counter bending in the sagittal plane during powerful incisor biting, rather than during unilateral mastication. The stress analysis of the primate mandible also suggests that jaws which are transversely thick in the molar region are an adaptation to counter increased torsion about the long axis of the working-side mandibular corpus during unilateral mastication. Increased torsion of the mandibular corpus can be caused by an increase in masticatory muscle force, an increase in the transverse component of the postcanine bite force and/or an increase in premolar use during mastication. Patterns of masticatory muscle force were estimated for galagos and macaques, demonstrating that the ratio of working-side muscle force to balancing-side muscle force is approximately 1.5:1 in macaques and 3.5:1 in galagos during unilateral isometric molar biting. These data support the hypothesis that mandibular symphyseal fusion is an adaptative response to maximize unilateral molar bite force by utilizing a greater percentage of balancing-side muscle force.

Adaptation, Physiological↗

PubMed2003

Selection of food and chewing side for evaluating masticatory path stability.

In order to find the most suitable food and chewing side for evaluating the stability of masticatory movement, three types of food with varying textures, as well as both free chewing and unilateral chewing, were utilized in analyzing the masticatory path during mastication. A piece of chewing gum, one peanut, and a slice of crispy bread were used as test foods. For 20 healthy subjects, movement of the incisal point while masticating a test food for 10 s on the free side and the habitual side was recorded. Indicators representing movement path stability were calculated and compared among the foods and between the chewing sides. Masticatory movement was most stable when masticating chewing gum, and less stable for the peanut, and most unstable for the crispy bread. There was a statistically significant difference between each pair of foods for almost all of the indicators. The indicators for peanut were approximately 1.5 times larger than those for masticating chewing gum and the indicators for crispy bread were double those for the chewing gum. When comparing free chewing with unilateral chewing, the masticatory movement of unilateral chewing was significantly more stable than that of free chewing for all test foods. From these results it was suggested that, for evaluating masticatory movement path stability, the most suitable type of food was softened chewing gum and the most suitable chewing method was unilateral chewing on the habitual chewing side.

Adult↗

PubMed1993

Difference in chewing patterns between involved and opposite sides in patients with unilateral temporomandibular joint and myofascial pain-dysfunction.

Surface electromyograms (EMG) during maximal clenching and gum and peanut chewing were recorded from the temporal and masseter muscles of 30 patients with unilateral temporomandibular joint and myofascial pain-dysfunction (TMD). The gum-chewing integrated EMGs were transformed to a differential Lissajous EMG figure (DL-EMG) to facilitate comparison of mastication on the dysfunctional and opposite side. Variables, mainly those in the gum-chewing DL-EMG, were statistically analysed, and were compared with those of normal subjects. Patients were then classified into three types: (1) same side, (2) opposite side and (3) intermediate side. Same-side patients chewed peanuts on the dysfunctional side, although this side did not necessarily show abnormal behaviour during gum chewing. Opposite-side patients chewed peanuts by avoiding the dysfunctional side and showed excellent chewing activity on the side opposite the dysfunction. Intermediate-side patients had a chewing pattern that was a combination of the first two types. The relation between the pain side, the preferred or habitual mastication side, and the side showing better mastication in the EMG pattern was shown to be important in research on the origin of TMD syndromes. It was speculated that in the same-side patients, overwork on the side with the better dental condition for chewing was the main cause of the dysfunction, and that so-called hyperactivity on the dysfunctional side in TMD patients may result from habitual unilateral mastication.

Adolescent↗

PubMed1992

The effect of odours on stimulated parotid salivary flow in humans.

We have previously shown that smell has no effect on resting parotid salivary flow in humans. In this study we investigated the effect of two odours on unilateral parotid salivary flow stimulated by either mastication or mastication with gustation. Neither odour stimulated flow above that elicited by either mastication or mastication with gustation. Removing an odour by sealing the nares has been reported to reduce stimulated parotid salivary flow, suggesting that smell contributes to stimulated salivary flow. However, in the present study, sealing the nares with a nose clip caused a significant reduction in the saliva elicited by an odourless stimulus. Even placing the nose clip over the bridge of the nose without sealing the nares significantly reduced the salivary flow, suggesting that the nose clip itself causes a reduction in stimulated parotid salivary flow. In conclusion, smell has no effect on stimulated parotid salivary flow in humans.

Adult↗

PubMed1994

Masticatory performance, muscle activity, and occlusal force in preorthognathic surgery patients.

Previous studies have indicated that patients scheduled for orthognathic surgery tend to have lower maximum bite forces and exert lower forces during mastication. The effect of these deficits on masticatory performance have not been previously assessed. Masticatory performance was analyzed in four groups: male and female orthognathic surgery patients prior to presurgical orthodontics (n = 12 and 23), and male and female controls (n = 27 and 31). Mastication performance was analyzed by having the subjects chew 5-g pieces of carrot for 20 cycles and measuring the resulting median particle size with a standard sieve method. Masticatory performance showed the same trends as maximum bite force and masticatory forces: male controls had the best and patients the poorest masticatory performance. There was a weak correlation between masticatory performance and maximum bite force at the molar positions. Masticatory performance also weakly correlated to electromyographic signals during mastication of a constant bolus (gummy bears) for all muscles except the left posterior temporalis. Correlations were generally not present or were very weak between masticatory performance, estimated masticatory forces, and muscle efficiency, suggesting that muscle efficiency and forces generated during mastication are not the primary factors that determine masticatory performance. Other factors contributing to a person's ability to chew food might include occlusal relationships and mechanical advantage.

Adolescent↗