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At least 91 records · Page 5Linked to original sources
PubMed2001

Application of principal component analysis to the elucidation of perioral soft tissue movements during mastication.

We considered that elucidation of the movements of perioral soft tissue during mastication would be useful in evaluating masticatory movements. However, the evaluation of these movements is difficult because multivariable analysis is needed. In this study, we considered whether principal component analysis (PCA), a form of the multivariate analysis, can reduce the number of degrees of freedom (d.f.) of perioral skin movements (i.e. the time-series data with 45 d.f.). The subjects were 15 healthy persons with complete natural dentition. The chosen experimental food for this study was sufficiently softened chewing gum. Over 95% of the perioral soft tissue movements of healthy subjects with complete natural dentition during mastication could be expressed by PCA using the first three principal components (PCs). Therefore, perioral soft tissue movements in these subjects during mastication were considered to be spatially smooth. Moreover, time analysis of these movements was made possible by the application of proportion diagrams. The results of this study showed that the spatiostructural and temporal analyses of the movements of perioral soft tissue during mastication made possible by the application of PCA.

Adult↗
PubMed2002

Head movements in the occlusal phase of mastication.

It has been recognized that mandibular movements evoke head movements during jaw tapping. However there have been only a few studies that investigated the aspects of head movements during mastication. The objective of this study was to demonstrate the hypothesis that the head moves actively in mastication in order to achieve effective destruction of a food bolus. Head and mandibular movements during gum, gummi candies and kelp chewing among nine adult volunteers have been recorded as time series data with a three-dimensional motion capture system and the vertical components of the movements have been analyzed. To focus on occlusal phase of mastication, the following parameters have been examined: time lag of the head movements at the beginning of occlusal phase, perpendicular velocity of the head at the beginning of the phase of occlusion, and average velocity of the head during occlusal phase. The results showed that the head moved downward in mastication and the velocity of the head movements increased in the order of gum, gummi candies and kelp chewing. There is a possibility that the elasticity of a food bolus affects the activity of head movements, and the kinetic energy was increased to achieve effective destruction of a food bolus.

Adult↗
PubMed1998

Muscle pain modulates mastication: an experimental study in humans.

In this study, pain was induced in the masseter muscle by tonic infusion of hypertonic saline (5%) for up to 800 seconds in 12 healthy men. Subjects continuously scored the pain intensity on a 10-cm visual analogue scale. Mastication ipsilateral and contralateral to the infusion side was quantitatively assessed with the use of jaw-tracking and electromyograph recordings of jaw-closing muscles before, during, and after periods of constant muscle pain intensity. The maximum voluntary occlusal force (MVOF) during short static contractions also was monitored. Jaw movements and electromyographic data were divided into single masticatory cycles and analyzed on a cycle-by-cycle basis to account for intercycle variability. In all subjects, tonic infusion caused a deep localized pain at a clinically relevant intensity (mean VAS +/- SE, 4.6 +/- .3 cm). MVOF was significantly affected by muscle pain (P < .0005), with significantly lower MVOF during pain compared to prepain and postpain (P < .05). In a significant number of masticatory cycles, the averaged electromyograph activity of all jaw-closing muscles during their agonist function was decreased for both ipsilateral and contralateral painful mastication (P < .05). These electromyographic changes are probably a reflection of the natural bilateral recruitment pattern of jaw-closing muscles during mastication. Significant changes in jaw movements during painful mastication could not be detected with the present jaw-tracking device, but further studies with more accurate and sensitive devices are needed.

Adolescent↗
PubMed2004

Masticator space masses and pseudomasses.

We review the anatomy of the masticator space and the localization of masticator space lesions on cross-sectional imaging. The magnetic resonance imaging and computed tomography appearances of inflammatory, neoplastic, developmental and vascular masticator space lesions are discussed and illustrated. Benign processes and normal variations, which mimic masticator space pathology, are also considered.

Head and Neck Neoplasms↗
PubMed1997

Relationship between bone and muscles of mastication in hemifacial microsomia.

The relationship between the bone and muscles of mastication in hemifacial microsomia was studied using three-dimensional volumetric computed tomography scans and image processing techniques. High resolution head computed tomography scans were obtained from 31 patients with unilateral hemifacial microsomia and eight normal patients. Using three-dimensional volume renderings of bone, mandibular deformities in patients with hemifacial microsomia were classified using the Pruzansky system. For each patient, specific craniofacial bones (temporal bone, maxilla mandible) and the muscles of mastication (masseter, temporalis and lateral and medial pterygoid) were segmented bilaterally from the image volume for independent display and volume measurement. Volumes were expressed as the ratio of the affected: unaffected sides. For the masseter and temporalis, the relationship between muscular hypoplasia and osseous hypoplasia in its origin and insertion was studied by plotting affected:unaffected bone volume as a function of affected:unaffected muscle volume for each muscle, bone of origin, bone of insertion triplet. The volumes of the pterygoid muscles were compared with hemimandibular volumes. The precision of object segmentations was examined by repetitive definition tasks, whereas the accuracy of volume measurement was tested by scanning custom-made phantom objects and comparing digital to physical object volume measurements. Volume measurements performed using these techniques were both accurate and precise. In hemifacial microsomia, the extent of hypoplasia of specific muscles of mastication predicted the extent of dysplasia in their osseous origin and insertion. However, the reverse was not true. The extent of hypoplasia of the facial bones did not necessarily predict the extent of hypoplasia in the attached muscles of mastication. Pruzansky grade of the mandible described the degree of mandibular hypoplasia on the affected side, but was inconsistent in its prediction of volume decrease of the other facial bones.

Facial Asymmetry↗
PubMed1985

The masticator space: the influence of CT scanning on therapy.

The masticator space is an important suprahyoid tissue compartment bounded by the superficial layer of the deep cervical fascia, enclosing the ramus of the mandible plus the masseteric and pterygoid muscles. Pathology of this space has been clinically difficult to diagnose and treat. Twenty-five patients with either tumor or infection involving the masticator space who underwent CT scanning were evaluated retrospectively. Ten patients had infection and 15 had tumor. CT was influential in directing appropriate biopsies or therapy in 24 of 25 patients. It misguided therapy once. The gross anatomic and CT appearance of the normal and the diseased masticator space is described along with pictures of representative cases. A discussion is given of the advantages, disadvantages, and pitfalls of computerized tomography of the masticator space.

Abscess↗
PubMed2004

[Complete denture occlusion considered from occlusal contacts during mastication].

Few reports describe the functional superiority of full balanced occlusion to that of lingualized occlusion. Recently, a bilateral balanced scheme has been much more generally applied than a unilateral balanced scheme in lingualized occlusion as well as in full balanced occlusion. Occlusal contacts on the non-chewing side occur earlier than on the chewing side;in the order of second molar, first molar, and then premolars. The contact on the balancing side contributes to the prevention of denture dislocation and guidance from eccentric positions to the centric occlusal position during mastication. Therefore, bilateral balanced occlusion was shown to be effective for denture stability during mastication with complete dentures. Today's typical edentulous patients have greater mean age than in the past, and thus are seen with severe alveolar bone resorption, thin mucosa and sometimes abnormalities of the maxillomandibular relation. Their occlusal positions are often unstable and changeable after insertion of complete dentures. Because lingualized occlusion allows for easier accommodation and correction, lingualized occlusion is more suitable for such cases than full balanced occlusion, which requires a strict occlusal relationship. In light of the standard Japanese diet, there is some doubt about why lingualized occlusion might be suitable for Japanese edentulous patients in terms of the sense of mastication. A method of evaluating the sense of mastication needs to be established.

English Abstract↗
PubMed1992

Muscle force recruitment and biomechanical modeling: an analysis of masseter muscle function during mastication in Macaca fascicularis.

The main purpose of this study is to test the hypothesis that as subjects chew with increasing levels of force, the ratio of the working- to balancing-side jaw-muscle force (W/B) decreases and begins to approach 1.0. We did this by analyzing relative masseter force in Macaca fascicularis using both strain gage and surface electromyographic (EMG) techniques. In addition, we also analyzed: 1) the relationship between jaw position using cineradiographic techniques and relative masseter force, 2) the timing differences between relative masseter force from the working and balancing sides, and 3) the loading and unloading characteristics of the masseter muscle. Our findings indicate that when macaques increase the amount of overall masticatory force during chewing, the W/B ratio for masseter force frequently (but not always) decreases and begins to approach 1.0. Therefore, our working hypothesis is not completely supported because the W/B ratio does not decrease with increasing levels of force in all subjects. The data also demonstrate timing differences in masseter force. During apple-skin mastication, the average peak masseter force on the working side occurs immediately at or slightly after the initial occurrence of maximum intercuspation, whereas the average peak masseter force on the balancing side occurs well before maximum intercuspation. On average, we found that peak force from the balancing-side masseter precedes the working-side masseter by about 26 msec. The greater the asynchrony between working- and balancing-side masseter force, the greater the difference in the relative magnitude of these forces. For example, in the subject with the greatest asynchrony, the balancing-side masseter had already fallen to about one-half of peak force when the working-side masseter reached peak force. Our data also indicate that the loading and unloading characteristics of the masseter differ between the working and balancing sides. Loading (from 50 to 100% of peak force) and unloading (from 100 to 50% of peak force) for the balancing-side masseter tends to be rather symmetrical. In contrast, the working-side masseter takes much longer to load from 50 to 100% of peak force than it does to unload from 100 to 50% of peak force. Finally, it takes on average about 35 msec for the working-side zygoma and 42 msec for the balancing-side zygoma to unload from 100 to 50% of peak force during apple-skin mastication, indicating that the unloading characteristics of the macaque masseter during mastication closely approximates its relaxation characteristics (as determined by muscle stimulation).

Animals↗
PubMed2006

The challenge of mastication: preparing a bolus suitable for deglutition.

The main function of mastication is to transform a solid food into a bolus that can be swallowed safely. The bolus characteristics such as particles size or cohesiveness, are continuously sensed during mastication and they are important in initiating deglutition. This study examined the following question: What is the condition of the bolus just before swallowing? Ten subjects with normal dentition aged 37.5 +/- 3.7 years were asked to chew without swallowing six different foods (three nuts and three vegetables) while the number of cycles and the duration of the sequence were recorded. The particle size distribution shown by the expectorated food bolus just before swallowing was examined by image analysis. The results showed that, for a given food, the sizes of the bolus particles just before swallowing were comparable in all subjects. However, the number of cycles and duration of the sequence varied between subjects. Taken together these data strongly suggest that the granularity of the bolus before swallowing has to reach a predetermined state which is obtained by using an individual chewing strategy. This suggests that the bolus structure reflects a key factor for homeostasis and explains the large interindividual variability of the mastication physiologic parameters.

Adult↗
PubMed1989

Human jaw movement in mastication and speech.

The study of jaw movement in humans is a primary source of information about the relationship between voluntary movement and more primitive motor functions. This study focused on the geometric form of the velocity function, as measured by linear voltage displacement transducer. Movement amplitudes, maximum velocities and durations were greater in mastication than in speech. Nevertheless, there were detailed similarities in the shape of the normalized velocity functions. In jaw-closing movements, the normalized functions were similar in form over differences in rate, movement amplitude (speech movements) and the compliance of the bolus (mastication). In opening movements, the functions for mastication and speech were again similar over differences in amplitude and compliance. However, they differed in shape for fast and slow movements. Normalized acceleration and deceleration durations were approximately equal in rapid movements, whereas, for slower movements, deceleration took substantially longer than acceleration.

Biomechanical Phenomena↗
PubMed1993

Modelling relative masseter force from surface electromyograms during mastication in non-human primates.

The purpose was to analyse the relation between masseter electromyograms (EMGs) and relative masseter force during the power stroke of mastication. The electromyographic activity of the masseter was characterized by recording from bipolar surface electrodes placed over the superficial portion of the muscle; relative masseter force was estimated by characterizing surface bone strain along the lateral aspect of the zygomatic arch. The subjects were six adult macaques and one adult baboon. Masseter EMGs were quantified by r.m.s. analysis of the raw digitized EMG. The length of the time interval (the time constant) during which the r.m.s. values were calculated was repeatedly altered so as to determine which time constant was optimal for producing an EMG-derived waveform that best mimicked relative masseter force during the near-isometric phase of muscle contraction. The data indicate that between subjects this time constant varied from 35 to 72 ms, with an overall median of 42 ms and a grand mean of 49 ms. The use of a 42-ms time constant for all of the subjects resulted in an average latency between the masseter EMG waveform and relative masseter force of about 30 ms during the latter portion of the power stroke of mastication. This analysis provides, as a first approximation, an empirical basis for modelling relative jaw-muscle force using surface EMGs recorded during that portion of the power stroke of mastication when the jaw-closing muscles are contracting under near isometric conditions.

Animals↗
PubMed1987

The effects of cortical ablation on mastication in the rabbit.

To verify the hypothesis that the control of movement by the cortical masticatory area (CMA) is particularly important at the beginning of the mastication, we compared movements before and after bilateral CMA ablation. After ablation, the animal could not manipulate food placed in the front of the mouth for several days. With further recovery, the animals could masticate in a more normal way, but the times taken to manipulate the food and to chew to the point of swallowing were increased. However, the form and amplitude of the masticatory cycles were only slightly changed by loss of cortical control. The results indicate that CMA is of great importance at the beginning of mastication and probably also in terminating chewing and initiating swallowing.

Animals↗
PubMed2006

Oral physiology and mastication.

Mastication is a sensory-motor activity aimed at the preparation of food for swallowing. It is a complex process involving activities of the facial, the elevator and suprahyoidal muscles, and the tongue. These activities result in patterns of rhythmic mandibular movements, food manipulation and the crushing of food between the teeth. Saliva facilitates mastication, moistens the food particles, makes a bolus, and assists swallowing. The movement of the jaw, and thus the neuromuscular control of chewing, plays an important role in the comminution of the food. Characteristics of the food, e.g. water and fat percentage and hardness, are known to influence the masticatory process. Food hardness is sensed during mastication and affects masticatory force, jaw muscle activity, and mandibular jaw movements. When we chew for instance a crispy food, the jaw decelerates and accelerates as a result of resistance and breakage of food particles. The characteristic breakage behaviour of food is essential for the sensory sensation. This study presents a short review of the influence of oral physiology characteristics and food characteristics on the masticatory process.

Animals↗
PubMed1998

Effects on non-human primate mastication of reversible inactivation by cooling of the face primary somatosensory cortex.

Rhythmical jaw movements can be evoked by intracortical microstimulation within four physiologically defined regions, one of which is the primary face somatosensory cortex (face SI). It has been proposed that these regions may be involved in the selection and/or control of masticatory patterns generated at the brainstem level. The aim here was to determine if mastication is affected by reversible, cooling-induced inactivation of the face SI. Two cranial chambers were chronically implanted in two monkeys (Macaca fascicularis) to allow access bilaterally to the face SI. A thermode was placed on the dura or pia overlying each SI that had been shown with micro-electrode recordings to receive intraoral inputs. A hot or cold alcohol-water solution was pumped through the thermodes while the monkey chewed a small piece of apple or a sultana during precool (thermode temperature, 37 degree C), cool (2-4 degrees C), and postcool (37 degrees C) conditions. Electromyographic (EMG) activity was recorded intramuscularly from the masseter, genioglossus, and anterior digastric. Cooling of SI impaired rhythmical jaw and tongue movements and EMG activity associated with mastication in one monkey (H5), and modified the pattern of EMG activity in the other (H6). The total masticatory time (i.e., time taken for chewing and manipulation of the bolus before swallowing) was increased. This was due principally to an increase in the oral transport time (i.e., time taken for manipulation of bolus after chewing and before swallowing: monkey H6, control, 2.7 sec; cool, 5.2 sec, p < 0.05); the bolus was manipulated by the tongue during this period before swallowing. Within the chewing time (i.e., time during which chewing occurred), cooling resulted in a significant increase in anterior digastric muscle duration, a significant delay in the onset of masseter EMG activity, and a significant increase in the variance of genioglossus EMG duration. The data support the view that the face SI plays a part in modulating the central pattern generator for mastication.

Afferent Pathways↗
PubMed2003

Measurement of mechanical strain on mandibular surface with mastication robot: influence of muscle loading direction and magnitude.

OBJECTIVES: To investigate the mechanical effects of mastication on the mandible, we developed computational controlled mastication robot system with human dry skull and analyzed the strain distribution on the mandibular bone surface. DESIGN: In the mastication robot, the mandible was suspended by eight wires, which simulated masticatory muscles. A non-linear spring damper generated viscoelastic properties, and tension sensors for simulation of jaw reflection to avoid unusual biting force were applied as a biological feedback mechanism. By using this robot system, various patterns of muscle loading (change of wire direction and magnitude) were performed. RESULTS: From the results, significant differences in the amount of principal strain and its distribution were demonstrated in each condition (ANOVA, post hoc test, and p < 0.05). The value of maximum principal strain ranged from 79.66 x 10(-6) [at anterior border of ramus (Buccal side), 128 N] to -1.42 x 10(-6) [at foramen mentale (Buccal side), 32 N]. CONCLUSION: These results suggested that the muscle loading generated the mechanical strain on the mandibular bone surface and it was affected by the changes in loading direction and magnitude.

Analysis of Variance↗
PubMed2001

Controlled study of EMG activity of the jaw closers and openers during mastication in patients with myasthenia gravis.

Mastication was evaluated in patients with bulbar myasthenia gravis and compared with that of patients with ocular myasthenia gravis, patients in remission who previously suffered from bulbar symptoms, and healthy controls. Bulbar myasthenia gravis may impair mastication due to weakness of the masticatory muscles. The aim of the study was to objectively evaluate the influence of myasthenia gravis on mastication. The subjects chewed a piece of breakfast cake and chewed 1 min on a piece of chewing gum. Surface EMG of the masseter muscle, temporalis muscle and jaw opener muscles was recorded. Statistical analysis revealed that bulbar patients produced significantly less EMG activity in the closing phase of a chewing cycle in both experiments. The EMG of the masseter muscle expressed as percentage of the maximum EMG during maximal clenching showed significantly higher values in the bulbar group than in the other groups. This was not found for the temporalis muscle. It was suggested that bulbar patients use a strategy of limited effort to produce a bolus that can be swallowed. The ocular patients and the patients in remission showed no subclinical impairments in muscle function during chewing.

Adult↗
PubMed2001

Spaciostructural analyses of mandibular and perioral soft tissue movements during mastication.

We considered that elucidation of the movements of perioral soft tissues during mastication would be useful in evaluating masticatory movements. However, evaluation of movements specific to soft tissues is difficult because movements of the surface of the lower face during mastication include movements of the muscles of facial expression and mandibular movements. The aims of this study were to elucidate the influence of mandibular movements on perioral soft tissue movements during mastication using principal component analysis (PCA) and to abstract the component of movement specific to soft tissues in order to evaluate masticatory movements from the movements of perioral soft tissues. The subjects were 10 healthy persons with complete natural dentition. The experimental food used in this study was sufficiently softened chewing gum. The results of this study showed that the movements of mandibular and perioral soft tissue were closely related in the first and third PCs; in other words, the second PC was the component of movement specific to soft tissues. Thus, elucidation of the second PC is useful for evaluation of masticatory movements from movements of perioral soft tissues.

Adult↗
PubMed2003

Buccal and lingual activity during mastication and swallowing in typical adults.

A non-invasive protocol was developed to assess tongue and cheek movements during mastication and to evaluate the temporal relationship between mastication and the initiation of pharyngeal swallowing. Typical adults (three males and three females) were monitored during chewing. Miniature pressure transducers were bonded unilaterally to the buccal and lingual surfaces of the first mandibular molar and the buccal surface of the first maxillary molar on each subject's preferred chewing side. Surface electromyography of the ipsilateral masseter muscle was recorded as an indicator of jaw-closing activity. Pressure and electromyography (EMG) recordings were time-linked to simultaneous B-mode ultrasound imaging of the oral cavity using a submental, coronal view aligned with the first mandibular molar. The intervals between peak pressure recorded at each pressure transducer and peak jaw-closing activity for each masticatory cycle were not statistically different [analysis of variance (anova), P=0.9856] and displayed large statistical variation. These intervals were not different at the beginning of the trials (hard biscuit) than they were at the completion of mastication when the cookie had been broken down to a paste/puree consistency bolus. The interval between the last chewing stroke and the initiation of swallowing was 0.92 +/- 0.34 s). No significant difference existed among subjects for this time interval (anova, P=0.382).

Adult↗