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PubMed2006

Insights into the bilateral cortical control of human masticatory muscles revealed by transcranial magnetic stimulation.

In this brief review I describe details of the functional organisation of the bilateral corticobulbar projections to the trigeminally innervated masticatory muscles, as revealed by transcranial magnetic stimulation of the human brain. The motor cortices of both hemispheres are involved in control of trigeminal motoneurons, however the contralateral hemisphere has the greater excitatory influence. Corticomotoneuronal cells in each hemisphere project to jaw-closer and jaw-opener motoneurons. Less is known about cortically mediated inhibitory effects in the trigeminal motor system, but the available evidence suggests that drive to jaw muscles on each side is affected similarly by intracortical inhibitory processes activated in one hemisphere. Functional studies reveal that the two hemispheres play distinct roles in control of ipsilateral and contralateral muscles, particularly for jaw-closers. Masseter and digastric motor units recruited during low-force contractions do not receive uniform inputs from each hemisphere; the majority of masseter motor units are excited only from the contralateral hemisphere, and while digastric motor units are usually excited from both hemispheres the direct CM cell influence appears to be augmented on the contralateral side by corticobulbar activation of segmental excitatory interneurons. Differences in bilateral cortical control of jaw-closer and jaw-opener muscles may contribute to the more independent control of jaw-closers on each side during functional tasks. Corticobulbar control of the trigeminal muscles during natural tasks such as chewing and speech remains to be investigated with TMS.

Humans↗
PubMed2005

Effects of masticatory muscle fatigue without and with experimental pain on jaw-stretch reflexes in healthy men and women.

OBJECTIVE: To examine the effects of experimentally evoked masticatory muscle fatigue, without and with experimental muscle pain, on the short-latency jaw-stretch reflex, using a randomised crossover design. METHODS: Reflexes were evoked in both the masseter and temporalis muscles in 15 men and 13 women. The study was performed in two blocks, both containing 3 experimental conditions (before, directly after, and 15 min after provocation). Provocation consisted of a fatiguing chewing test, followed by an intramuscular injection of either isotonic saline (IS; non-painful) or hypertonic saline (HS; painful). RESULTS: No significant effects of the experimental condition 'fatigue+IS' were found for any of the reflex outcome variables. For each muscle, the 'fatigue+HS' condition yielded significantly higher normalized reflex amplitudes than the other conditions. Several muscles displayed gender differences regarding both onset latency and normalized reflex amplitude. CONCLUSIONS: Experimentally evoked mild-to-moderate muscle fatigue does not modulate the human jaw-stretch reflex. On the other hand, experimental muscle pain, evoked after the performance of a fatiguing chewing test, does yield a facilitation of this reflex. The gender differences found in both onset latency and peak-to-peak amplitude stress the need to take gender into consideration in future jaw reflex studies. SIGNIFICANCE: The sensitivity of the human jaw-stretch reflex can be modulated by HS-induced muscle pain; not by muscle fatigue that is provoked by intense chewing.

Adult↗
PubMed1994

Effect of a fatigue test and chewing training on masticatory muscles.

The effects of fatigue induced by 30 min of intense chewing before and after 4 weeks of 1 h daily chewing training on masticatory muscles were studied in 15 healthy subjects while eight subjects served as controls. EMG measurements in the postural position and during maximal clenching in the intercuspal position and clinical examination of the stomatognathic system were performed. Marked clinical signs of dysfunction were recorded after the first fatigue test. The severity of dysfunction diminished during the 4-week training period and was back at the baseline level at the end of it. In the second fatigue test, after the training period, the subjects developed less dysfunction. In the control group, a mainly stable pattern was found during the observation period. There was a great variation in EMG activity during the experimental period and there were no statistically significant changes observed between any of the recordings in any of the groups.

Adult↗
PubMed1997

Sex difference of electromyogram of masticatory muscles and mandibular movement during chewing of food.

The aim of this study was to investigate whether there were sex differences in the electromyograms (EMG) of the masticatory muscles and in the mandibular movement of young adults when chewing food. Twenty subjects with normal dentitions were selected. The 11 test foods selected were all easily available in Japan. The results showed firstly that although there were no significant differences of chewing frequency between males and females, females chew food more slowly with less masticatory force and narrower mouth opening width than males; and secondly it appears that the chewing function in females is lower than in males.

Adult↗
PubMed1998

[The correlations between the echographic aspect of the perioral and masticatory muscles and dento-skeletal characteristics].

INTRODUCTION: US of some muscular components of the stomatognathic system (orbicularis oris and masseter muscles) has proved to provide important information about their morphologic features. The purpose of this study is to explore the US features of the perioral and masticatory muscles in patients affected with any type of malocclusion and to analyze the correlations between dento-skeletal characteristics and muscle changes. MATERIAL AND METHODS: We examined 26 untreated patients (10 men and 16 women); we measured their cephalometric parameters on lateral skull teleradiographs and then we measured with US both the masseter and orbicular muscles dimensions. The US images were acquired with 5 MHz and 7.5 MHz probes, measuring the masseter muscle with transversal and longitudinal scans, and the two parts of the orbicularis oris with longitudinal scans. The cephalometric measures were calculated with: angular parameters useful to determine the sagittal relationships, both angular and linear parameters to define the vertical relationships and angular measures that define the incisor position. We applied the Spearman test to assess if there was a relationship between the US dimensions of the orbicularis oris and the masseter, and the dento-skeletal characteristics of these 26 patients. RESULTS: Our results show that there is a strong correlation between mandibular morphology, the palatal plane, respectively, and the masseter length. There is a direct correlation with the masseter dimension for the palatal plane obliquity, and an inverse correlation for the mandibular morphology. The incisor position is influenced by the orbicular oris muscle dimension and by the asymmetric position of the superior and inferior incisors. CONCLUSIONS: This noninvasive diagnostic examination is a useful aid to the clinical examination of the muscles, especially in orthodontic diagnosis, together with MRI and CT, respectively more expensive and unhealthier.

Adolescent↗
PubMed1995

Effect of masticatory muscle fatigue on cranio-vertical head posture and rest position of the mandible.

The aim of this study was to investigate whether induced fatigue of the masticatory muscles had any influence on the head posture, and whether this influence is related to the rest position and the movement characteristics of the mandible. The sample consisted of 13 female individuals, aged 23-34 yr. For the evaluation of possible changes in the natural cranio-vertical head posture, standardized facial profile photographs were used. Photographs were also used for the study of the facial characteristics. The freeway space and the opening and closing velocity of the mandibular displacement, as well as the duration of the masticatory cycles, were monitored with an optoelectronic method. A controlled dynamic fatigue was induced by a specially constructed spring-loaded device placed in the premolar region. No significant changes in the mean cranio-vertical postural position of the head were found during the various recording stages, while the freeway space was found to increase significantly after the fatigue test. No significant differences were observed concerning the average values of the mandibular movement characteristics. The analysis of the association between the individual changes showed an increase in the freeway space after the fatigue test in the subjects which exhibited an increase in the duration of the masticatory cycle in that period. No significant associations could be found between the changes in the head posture and the mandibular movement characteristics. Also, no significant correlation could be found between the facial type of the subjects and the variables studied.

Adult↗
PubMed1985

Electrophoretic comparison of myosins from masticatory muscles and selected limb muscles in the dog.

Myosins from canine limb muscles (triceps brachii [medial and long heads], anconeus, and extensor carpi radialis) were compared biochemically with myosins from canine masticatory muscles (temporalis and masseter). Compared with the limb muscles, the temporalis and masseter muscles had: a unique myosin isoform pattern as determined by nondenaturing pyrophosphate gel electrophoresis; unique light chains as determined by 1-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis, 2-dimensional gel electrophoresis, and peptide mapping; and a unique heavy chain as determined by peptide mapping.

Animals↗
PubMed2002

A comparison between masticatory muscle pain patients and intracapsular pain patients on behavioral and psychosocial domains.

AIMS: To identify differences between 2 groups of patients with temporomandibular disorders (TMD), those with masticatory muscle pain (MMP) versus intracapsular pain (ICP), and to compare these differences on behavioral and psychosocial domains. METHODS: There were 435 patients in the MMP group and 139 patients in the ICP group. The overall sample was 88.2% female and had an average age of 36.1 years (SD = 11.7). Patients completed measures of psychological symptoms (SCL-90), pain severity (MPI), sleep (PSQI), activity (MBI), and life stressors (PCL). Heart rate and blood pressure were also measured, and a complete medical/dental history was taken for each patients. RESULTS: Results indicated no significant difference in pain severity or duration between the 2 groups (P > 05). The ICP group, however, reported fewer affective symptoms of pain than the MMP group (t = 6.8, P = .01). The ICP group had twice as many adaptive copers as dysfunctional patients (chi 2 = 7.84, P < .01), while there was no significant difference between these 2 categories for the MMP group (P > .05). Finally, the ICP group reported fewer psychological symptoms (P < .05), better sleep quality (F = 7.54, P = .01), and fewer life stressors (F = 7.00, P = .01) than the MMP group. CONCLUSION: In contrast to many previous studies, the data set in this study showed no differences in pain severity and duration between the MMP and the ICP groups. Even though pain severity levels were equivalent, the MMP diagnostic group of chronic TMD patients demonstrated more dysfunctional behavioral profiles and significantly higher psychological distress than the ICP subgroup.

Adaptation, Psychological↗
PubMed2007

The effect of mandibular advancement appliances on awake upper airway and masticatory muscle activity in patients with obstructive sleep apnoea.

BACKGROUND: There is little understanding of how dental appliances, designed to posture the mandible forwards, act on pharyngeal airway dilatory and masticatory muscles in patients with obstructive sleep apnoea (OSA). This study evaluates, in a prospective cohort design, the effect of mandibular advancement splints (MAS) on awake genioglossus (GG), geniohyoid (GH) and masseter (M) muscle activity. METHODS: Fifty OSA patients received a custom-made removable Herbst MAS appliance, adjusted for maximum therapeutic benefit, as judged by subjective improvement. Awake electromyographic (EMG) activity was recorded at baseline and with the MAS in situ, by using bipolar surface electrodes in patients seated upright and in the natural head position. The lower splint was modified to facilitate the placement of the intra-oral bipolar surface electrodes used to record GG EMG activity. RESULTS: Significant increases in GG (P = 0.041), GH (P<0.001) and M (P<0.001) muscle activity accompanied placement of the MAS. CONCLUSIONS: These findings support the contention of a physiological role, which may act to augment the anatomical action of MAS.

Cohort Studies↗
PubMed2001

The Krox-20 null mutation differentially affects the development of masticatory muscles.

The Krox-20 null mutation results in a loss of rhombomeres 3 and 5, which give rise to neurons that are essential to oral motor behaviors. Thus, the Krox-20 null mutant is an excellent model to investigate the development of oral motor circuitry. Our morphological examination of embryonic and neonatal Krox-20 null mutants revealed that a significant reduction of anterior digastric and mylohyoid muscles, the primary jaw openers, occurs between embryonic days 15 and 19. There are no gross morphological alterations in other masticatory muscles. These findings demonstrate that Krox-20 expression is critical for the normal development of the primary jaw opener musculature and they help explain previous studies documenting a reduction in jaw opening in Krox-20 null mutants. Since jaw opening is the power stroke of suckling behavior, our data help explain the reduction of colostrum/milk ingestion in Krox-20 null mutant neonates.

Animals↗
PubMed1985

Malocclusion, masticatory muscle, and temporomandibular joint tenderness.

The Angle classification of occlusion, as well as occlusal contacts determined at retrusion, mediotrusion, laterotrusion, and protrusion were recorded from 298 dental students. Various masticatory muscles and the TM joints were palpated simultaneously for tenderness. No significant relationships were observed between (1) tenderness and Angle class or (2) tenderness and any occlusal contact. In relation to a slide between retruded contact position and intercuspal position: measurements for (a) vertical and (b) horizontal displacements, but not (c) lateral deflection, were greater in Class I students without tenderness than in Class I students with tenderness.

Adult↗
PubMed1990

Analysis of jaw movements and masticatory muscle activity.

This paper describes software developed to analyze the temporal and spatial aspects of jaw movements, the speed, direction and magnitude of these movements in three dimensions, and the associated electromyograms (EMGs) of the masticatory muscles. Data from a subject chewing gum illustrates the software application. Manipulations of the stored digitized data are described. Temporal aspects of each chewing cycle are defined by specified delimiters for the beginning and ending of jaw opening and closing; spatial aspects are quantified by measurements derived from movement trajectories; and peak and mean velocities are derived from the velocity profiles. EMGs are digitized, rectified, averaged and referenced to jaw movement. Onset latencies, burst durations, rise times to peak activity, time of occurrence of peak activity, and amplitudes of peak and mean activities are measured from the EMGs. This detailed kinematic/EMG analysis provides previously inaccessible information about jaw muscles and the movements they control.

Electromyography↗
PubMed2003

Regional alterations in fiber type distribution, capillary density, and blood flow after lower jaw sagittal advancement in pig masticatory muscles.

Muscular remodeling is known to be a prerequisite for permanent correction of mandibular-maxillary malocclusion. The objective of this study was to clarify if an increase in type I fiber number is accompanied by an increased capillary density and improved muscular blood flow. Juvenile pigs received build-ups on the molars, which induced a protrusion of 7.6 + 1.5 mm. After 4 weeks of treatment, chronic lower jaw protrusion induced a marked muscle blood flow increase in the anterior and medial regions of the superficial part of the masseter and in the medial pterygoid muscle (P < 0.05). Furthermore, an increase in capillary density and in the amount of type I fibers was found in all regions of masticatory muscles with an increased muscle blood flow (P < 0.05). Finally, the capillary-to-fiber ratio increased (P < 0.05). Muscle blood flow and capillary density showed a strong linear correlation (r = 0.89, P < 0.01). These changes suggest a complex muscle adaptation for long-term, fatigue-resistant activity during the early corrective period of mandibular-maxillary malocclusion treatment.

Animals↗
PubMed1985

Migration of craniofacial periosteum in guinea-pigs with unilateral masticatory muscle paralysis.

The amount and direction of movement of the fibrous periosteum of the nasal, frontal, and parietal bones in the guinea-pig have been documented after experimentally induced unilateral paralysis of the masticatory muscles. Marked craniofacial asymmetries and muscle atrophy were observed after electrolytic lesions of the trigeminal motor nucleus were made. The induced muscle paralysis had only a small effect on the periosteal migration. The direction of migration was slightly less medial on the operated as compared to the non-operated side. The periosteal migration of the non-operated side closely paralleled the direction of movements observed in the control animals studied previously. There was an increase of bone apposition at the coronal sutural margins on the operated side and an associated convexity of the midline toward the operated side. Additional research on the dynamic relationship of the muscle-periosteum-bone interface is necessary in order to understand better the morphogenetic controls of craniofacial growth.

Animals↗
PubMedDate not supplied

[Comparative characteristics of masticatory muscle tonus in children with orthognathic and prognathic deep bites before and after orthodontic treatment].

In 99 orthognathic children 7 to 15 years and 83 age-matched children with deep prognathism the masticatory muscles stiffness was measured in a relatively resting state and maximal voluntary contraction. In children with anomalous occlusion the stiffness of relaxed muscles was increased as related to normal values, and their contractility was reduced. After the orthodontic treatment the indices of muscular tonus improved.

Adolescent↗