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PubMed1982

Changes in length and torque of the masticatory muscles produced by the activator appliance. A cephalometric study.

The purpose of this study was to measure cephalometrically the change in muscle length and torque of the masticatory muscles produced by an activator appliance. The study was based on 10 orthodontic cases with distoclusion. Muscle length and force arm (leverage) were measured on two lateral cephalometric roentgenograms of each subject, one with the teeth in centric occlusion and one with an activator between the teeth. The construction bite of the activator was taken with the mandible repositioned 2-3 mm below and 5-6 mm ahead of resting position. It was found that the temporal masseter and medial pterygoid muscles increased 5-15% in length whereas the lateral pterygoid decreased 25% in length with the activator in place. The effect on the force arm on the temporal muscle was small, a decrease of 3-6%, but that on the masseter was much more dramatic, a decrease of 21-22%. Thus, as far as the torque of the temporal muscle is concerned, the small decrease in force arm is well compensated for by the increased muscle tension due to the stretching by the activator. The clinical significance of the findings for obtaining the best construction bite of the activator is discussed.

Activator Appliances↗
PubMed2002

Effects of repeated + Gz forces on masticatory muscles.

OBJECTIVE: To study the effects of repeated + Gz forces on masticatory muscles. METHODS: 48 male Wistar rats were randomly divided into 4 groups. Group A was normally fed. Group B was only fixed with rat-kept devices for 5 minutes. Group C was borne + 1 Gz for 5 minutes. Group D was repeatedly exposed + 10 Gz (each for 30 s, onset rate about 0.5 G/s, 5 times/d with + 1 Gz 1 minute intervals, 4 d/wk, 3 weeks in total). The histological changes of the masseter, temporal and lateral pterygoid muscles were observed. RESULTS: No abnormal changes were observed in Group A, B and C. But pathological changes could be found in group D. The wrench and deformation of muscular fibers, the dissolution of partial myofibril, the swelling of mitochondria, the reduce of hepatin from the masseter and lateral pterygoid muscles could be found. CONCLUSIONS: Repeated + Gz stresses could induce the damage of masticatory muscles in different degrees.

Animals↗
PubMed1988

Masticatory muscle hyperactivity in temporomandibular disorders: is it an extrapyramidally expressed disorder?

Masticatory muscle hyperactivity appears to have an important role in temporomandibular disorders. A pathophysiological model for masticatory muscle hyperactivity is proposed that is centrally mediated, yet maintains support for present peripheral causes and therapies. In this hypothesis, masticatory muscle hyperactivity represents a mild extrapyramidal disorder distantly related to orofacial dyskinesias. Experimental evidence suggests a neurotransmitter imbalance in the basal ganglia, involving dopaminergic preponderance, or cholinergic and GABA-nergic hypofunction as the underlying cause.

Basal Ganglia Diseases↗
PubMed1991

Dental treatment of temporomandibular disorders and masticatory muscle pain.

The treatment of masticatory muscle and temporomandibular joint pain constitutes an important area in dentistry. Current information supports the use of reversible treatments for these disorders. Several recent references are discussed in relation to reversible treatment, the role of occlusion, and appliance therapy for internal derangement.

Facial Pain↗
PubMedDate not supplied

[Cardiovascular effects of isometric contraction of the masticatory muscles in humans].

The cardiovascular responses to static exercise do not include, until now, studies about masticatory muscles. In this work the cardiocirculatory effects of the isometric contraction of masticatory muscles were compared with those evoked by the handgrip exercise. Non invasive and, in one case, invasive (aortic catheterism) monitoring of arterial blood pressure was performed. The findings show that mean blood pressure and especially heart rate do not increase during static exercise of masticatory muscles as reported in the literature for other muscular groups: it is suggested that the peculiar architecture of masticatory muscles may explain the absence of significant cardiovascular response to their isometric contraction.

Blood Pressure↗
PubMed2005

[Changes of masticatory muscles after occlusal recovery in rats with unilateral chew].

PURPOSE: To study the effect of occlusal recovery on masticatory muscles in rats with unilateral chew. METHODS: 40 white rats were divided into two experimental groups and two control groups. The right upper and lower posterior teeth of all the rats were ground to the gingival level without occlusal contact. The rats of the first experimental and control group were killed 10 weeks late,those of the second groups were killed 16 weeks late. The pathological changes of masticatory muscles were studied. SPSS 10.0 software package was used for statistical analysis. RESULTS: There was significant correlation between the first experimental group and control group in the damage of masticatory muscles (Chi(2)=40, P<0.01). However,there was no significant correlation between the second experimental group and control group in the damage of masticatory muscles (Chi(2)=3.66, P>0.05). CONCLUSION: Early occlusal recovery can rehabilitate the damage of masticatory muscles in rats with unilateral chew.

Animals↗
PubMed2005

[The influence of botulinum toxin on the masticatory muscles of the temporomandibular joint osteoarthritis in rabbit].

PURPOSE: To study the influence of botulinum toxin on masticatory muscle activity in temporomandibular joint model osteoarthritis(TMJOA). METHODS: 30 adult rabbits were examined with EMG, and TMJOA was established by collagenase injection, then divided into experimental group and control group. EMG of masticatory muscles was recorded during postural position and clenching at the end of 4 weeks, 8 weeks and 12 weeks. Botulinum toxin was injected into the masseter muscle and temporal muscle in the experimental group. Those of the control group were only with TMJOA. All data were analyzed with group t test in SPSS 11.0. RESULTS: During postural position, EMG activity of masticatory muscles in the control group was significantly higher than that of the normal at each examination(P<0.05). EMG activity in th experimental group was lower than normal at the end of 4 weeks and 8 weeks(P<0.05), but at the end of 12 weeks, the two groups showed no difference(P>0.05). During clenching, EMG activity in the control group was lower than normal at each measurement(P<0.05), EMG activity in the experimental group was lower than normal at the end of 4 weeks and 8 weeks(P<0.05), but showed no difference at the end of 12 weeks. CONCLUSION: Botulinum toxin can change and improve masticatory muscle function of TMJOA in rabbit.

Animals↗
PubMed2002

Dento-skeletal adaptation after bite-raising in growing rats with different masticatory muscle capacities.

The aim of this study was to analyse the effects of normal and hypofunctional masticatory muscles on dento-skeletal adaptation to posterior bite blocks in growing rats. Fifty-two young male rats were divided into two groups, fed a hard and soft diet, respectively, to develop different functional capacities in the masticatory muscles. Bone markers were inserted in the mandible on day 0. After two weeks, an appliance that raised the bite by 2 mm was inserted in half of each group. Lateral radiographs were taken on day 0, 14, 28, and 42 of the experiment. Images of the mandible were superimposed on the bone markers. Differences in cephalometric measurements were analysed by two-way ANOVA. The reduced muscle capacity resulted in an upward growth of the snout and a shorter mandibular ramus with less bone apposition on its lower border. Bite blocks induced a more upward growth of the snout and a shorter mandibular ramus, and inhibited the eruption of the upper molars and intruded the lower molars. The rats with weaker masticatory muscles had less inhibitory effect of the posterior bite blocks on upper molar eruption and showed different bone apposition in the ramus, especially during the first two weeks. In conclusion, masticatory muscle capacity seems to influence the effect of the posterior bite blocks on both tooth eruption and skeletal adaptation. The results suggest that the characteristics of the masticatory muscles should be taken into account when predicting the efficiency of a functional appliance.

Adaptation, Physiological↗
PubMed2006

Masticatory muscle reaction in simulated low-velocity rear-end impacts.

AIMS: To evaluate the electromyographic (EMG) activity of masseter and temporalis muscles in relation to impact awareness, gender, impact magnitude, and kinematics of head movement in simulated low-velocity rear-end impacts. METHODS: Twenty-nine individuals (17 men and 12 women) were subjected in random order to 3 rear-end impacts: 2 unexpected impacts (chair accelerations of 4.5 m/s2 and 10.1 m/s2) and 1 expected impact (chair acceleration of 10.1 m/s2). The EMG activity of the deep and superficial masseter muscle was recorded bilaterally. EMG activity was also recorded for the left anterior temporalis muscle. Angular acceleration and angular displacement of the head were also recorded. The temporal relationship between onset of the masticatory muscle activity and maximum peak of the kinematics of head movement was determined. RESULTS: The magnitude of normalized masticatory EMG activity ranged from 1.4 to 1.8 times higher (P < .05) for fast unexpected impacts compared to slow unexpected impacts in all masticatory muscles. The magnitude of normalized anterior temporalis EMG peak response ranged from 1.8 to 2.5 times higher (P < .05) in female subjects than in male subjects for all impacts. No significant differences were identified for impact awareness in the magnitude of normalized EMG activity for any masticatory muscle. No significant differences were identified with respect to timing of masticatory muscle response (P > .05). CONCLUSION: EMG activity increased with increased impact magnitude. Temporal and amplitude awareness of a simulated impact did not produce a difference in the masticatory muscle response. Gender differences were identified in the anterior temporalis muscle response. The onset of the masticatory muscle response occurred after peak angular acceleration of the head but prior to peak angular displacement of the head.

Accidents, Traffic↗
PubMed1987

Familial hypertrophy of masticatory muscles.

Three familial cases of idiopathic hypertrophy of the masticatory muscles are reported. The muscular enlargement was noted in late childhood or early adult life, was bilateral, insidious, painless and non-progressive. Electrophysiological and laboratory findings were normal in one case. CT examination, performed in two cases, showed homogeneous bilateral enlargement of masseter muscle bulk consistent with true hypertrophy. Two patients also showed congenital malformations. A review of the literature showed that this disorder is very rare.

Adolescent↗
PubMed2000

Effect of unilateral posterior crossbite on the electromyographic activity of human masticatory muscles.

Studies dealing with the electromyographic activity of masticatory muscles in patients with unilateral posterior crossbite are infrequent. The purpose of this study was to assess the electromyographic pattern of masticatory muscles at rest position, during swallowing, and during mastication, in 30 subjects with right posterior crossbite and to compare them to 30 normocclusive subjects. The 2 groups were matched according to age, gender, skeletal Class I, and mesofacial growth pattern. Electromyographic activity of right and left anterior temporalis, posterior temporalis, masseter, and anterior digastric muscles was recorded at rest position, while swallowing water, and while chewing. Disposable bipolar surface electrodes were used in both groups. Data were compared between groups and between right and left sides within each group. The results revealed that the posterior temporalis of the non-crossbite side was more active than that of the same side in subjects with crossbite at rest position and during swallowing. The activity of both anterior digastrics was higher in the crossbite subjects during swallowing. During chewing the right masseter muscle was less active in the crossbite patients than in normocclusive subjects. The results obtained during chewing indicate a bilateral masticatory pattern in both groups.

Adolescent↗
PubMed2003

Influence of occlusal stabilization splint on the asymmetric activity of masticatory muscles in patients with temporomandibular dysfunction.

The aim of present study was to evaluate the symmetry of masticatory muscles' activity at various clenching levels in the intercuspal position in patients with functional disorders and in healthy subjects. The purpose was also to determine the effect of full-arch maxillary stabilization splint on the asymmetry of masticatory muscle activity in patients with temporomandibular dysfunction. In this study 6 TMD patients and 12 healthy subjects were investigated. Surface EMG recordings were obtained from left and right anterior temporal, left and right masseter and from the sub-mandibular group in the region of the anterior belly of the digastric muscle on the left and right side during clenching with the maximum 100% voluntary contraction (MVC) as well as during clenching at 50% and 25% of the maximum activity in the position of maximal intercuspation of teeth. In order to quantify asymmetrical masticatory muscle activity, the asymmetry index (AI) was calculated for each subject and for each muscle from the average anterior temporal, masseter and digastric potentials recorded during each test (100% MVC, 50% MVC and 25% MVC). In the group of patients EMG recordings were repeated during and after the splint therapy. The asymmetries of masticatory muscle activity was present in both groups, but in the group of TMD patients the asymmetry indices for anterior temporal muscle at 100% MVC (p = 0.049) and 50% MVC (p = 0.031) were significantly higher. Results have shown that the use of splint suppressed the asymmetry of all muscles, as during the splint therapy the asymmetry indices were lowered. After the therapy, the level of temporal muscle symmetry during submaximal clenching in the intercuspal position increased significantly (p = 0.046). This investigation points out that electromyography may be a valuable method of documenting that asymmetric activity of masticatory muscles improves after occlusal splint therapy in patients with TMD.

Adult↗
PubMed2004

Functional influence of masticatory muscles on the fibre characteristics and capillary distribution in growing ferrets (Mustela putonusfuro)--a histochemical analysis.

OBJECTIVE: Changes in the masticatory function of ferrets have been shown to cause alterations in their craniofacial morphology. The aim of the present study was to investigate how the functional changes influence the histochemical characteristics of fibres of the masticatory muscles of the animal. DESIGN: Forty five-week old male ferrets were divided into two groups: one group was fed a diet of hard pellets (HD group), and one group was fed the same diet but softened with water (SD group). After 6 months, specimens of temporalis, masseter and digastricus were taken from each ferret and prepared for enzyme histochemical analysis RESULTS: Type I muscle fibres constituted the majority of the temporalis and the masseter, while the digastricus mainly comprised type II muscle fibres. The fibre-type composition did not differ significantly between the two groups. The mean cross-sectional area of type I and type II fibres in the temporalis and the masseter, and type II fibres in the digastricus was significantly greater in the HD group than the SD group. Furthermore, the HD group had a significantly greater number of capillaries per fibre, but not per surface unit (mm2). CONCLUSIONS: The results suggest that the muscle fibre size and the number of capillaries per fibre of the masticatory muscles are readily adaptesd to the altered masticatory muscle functions.

Animals↗
PubMed1980

Ischaemic intermittent claudication of the masticatory muscles: two case reports.

Intermittent claudication of the masticatory muscles is an unusual symptom sometimes described in association with temporal arteritis. We describe here two cases where this symptom was due to insufficient blood supply to the masticatory muscles caused by atherosclerotic changes of carotid vessels. In one of our cases surgical revascularization was followed by the disappearance of this symptom.

Arterial Occlusive Diseases↗
PubMed1986

Gross anatomy of the mandibular joint and masticatory muscles in the domestic pig (Sus scrofa).

The mandibular joint (MJ) and masticatory muscles in 15 domestic pigs, aged 1 year, were investigated during and after dissection. The joint consisted of a fossa, disc and condyle surrounded by a ligamentous capsule. The fossa was almost flat, slightly convex antero-posteriorly and concave medio-laterally; the disc was biconcave and the condyle oval. The long axis of the condyles formed an anteriorly orientated angle to the frontal plane. The masticatory muscles were similar to human ones except for the pig zygomatico-mandibular muscle. The resemblance between the anatomy of the porcine and human joint and masticatory muscles makes the pig a useful animal for functional studies of the masticatory system.

Animals↗
PubMed2004

Precision and accuracy of CT-based measurements of masticatory muscles in patients with hemifacial microsomia.

OBJECTIVE: The objective of this study was to quantitatively assess masticatory muscle volumes in patients with hemifacial microsomia. Until recently, this congenital malformation was only studied in terms of restoring bony and skin morphologies. Study of the masticatory muscles, however, adds a new dimension. MATERIALS AND METHODS: Contiguous 1.5 mm CT scans were made using a Philips Tomoscan 350 in six patients with hemifacial microsomia and in one patient without asymmetry. These CT scans were processed by a Cemax 1500X 3D workstation. The volume of the masseter, temporal, and medial and lateral pterygoid muscles was measured from CT scans using three-dimensional (3D) segmentation followed by 3D imaging. The precision and accuracy of measurements of masticatory muscle volumes were investigated. The precision of 3D imaging was assessed by carrying out repeated measurements by two observers. The accuracy of the volume determination technique was assessed by scanning a piece of porcine muscle tissue with a known volume. RESULTS: Intraobserver repeatability was near perfect, with the lowest alpha being 0.96 (for the medial pterygoid muscle). All interobserver correlations were high (>0.99). The accuracy of the method of measurement demonstrated differences ranging from 2.3% to 4.4%. CONCLUSION: Craniofacial soft tissue measurements obtained from CT scans in patients with hemifacial microsomia were accurate and reproducible but time consuming.

Adolescent↗
PubMed1991

Demonstration of 'cardiac-specific' myosin heavy chain in masticatory muscles of human and rabbit.

Human and rabbit masticatory muscles were analyzed immuno- and enzyme-histochemically using antibodies specific to 'cardiac' alpha, slow and fast myosin heavy chain isoforms. In human masseter, temporalis, and lateral pterygoid muscle 'cardiac' alpha myosin heavy chain is found in fibres that contain either fast, or fast and slow myosin heavy chain. In rabbit masseter, temporalis and digastric muscles, fibres are present that express 'cardiac' alpha myosin heavy chain either exclusively, or concomitantly with slow myosin heavy chain or fast myosin heavy chain. Our results demonstrate a much broader distribution of 'cardiac' alpha myosin heavy chain than hitherto recognized and these might explain in part the specific characteristics of masticatory muscles. The 'cardiac' alpha myosin heavy chain is only found in skeletal muscles originating from the cranial part of the embryo (including the heart muscle), suggesting that its expression might be determined by the developmental history of these muscles.

Adult↗
PubMed1989

Electromyography of masticatory muscles in three jaw registration positions.

The purpose of this study was to investigate whether anteroposterior changes in mandibular position affect masticatory muscle activity. The electromyographic (EMG) activity of masticatory muscles during full and partial (10%) clenching in three mandibular bite registration positions--retruded contact position (RCP), intercuspal position (IP), and muscular position (MP)--was studied. Three groups of subjects with different ranges of anteroposterior positioning of the condyles were evaluated (normal occlusion, Class II, Division 2 malocclusion, and dual bite malocclusion). A posterior stabilizing splint for each registration position was made. EMG data were obtained from three bilateral muscles (masseter, anterior temporal, and posterior temporal). Clenching in the RCP elicited the lowest masseter muscle activity during full clenching, and the highest anterior temporal and posterior temporal muscle activity during partial clenching. If the relationships of the masticatory muscles are analyzed through a ratio that represents the interaction between biting and positioning muscles (masseter/posterior temporal muscle ratio), the RCP as compared with other positions had the lowest ratio. The RCP required more positioning muscle activity and permitted less biting muscle activity. There was no significant difference in the muscle activity between the IP and MP registrations. Small changes in jaw position (anterior to RCP) are not critical for the masticatory apparatus provided there is good intercuspation. The results of this investigation suggest that intercuspation in RCP is not the optimal position.

Adolescent↗