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PubMed1988

Morphological studies of the neuromuscular mechanism shifting from sucking to biting of mice.

In order to give a neuroanatomical evidence to the mechanism of shifting from sucking to biting, we investigated in prenatal, newborn and postnatal mice whether there is a time difference in the neurogenesis of the neurons relative to sucking and biting or in the histogenesis of their peripheral effector organs by the HRP labeling technique and electron microscopy. The results obtained are as follows. (1) At birth the facial motoneurons exceed the trigeminal motoneurons in cell area and development. (2) After birth, the trigeminal motoneurons grow rapidly and outstrip the growth of the facial motoneurons at the age of 6 days. (3) Thereafter, the cell area of both neuron types continues to increase gradually. (4) The initial sign of the alpha motor end plates is found in the orbicularis oris muscle innervated by the facial nerve in 17-day-old fetuses, while that of the trigeminal nerve is delayed in the masseter muscle of 18-day-old fetuses. (5) The initial sign of the muscle spindle appears with the sensory terminals in the masseter muscle of 17-day-old fetuses and the fundamental structure of the muscle spindle is formed in 4-day-old youngs. (6) Myelination of the facial nerve begins in 3-day-old youngs, while that of the trigeminal nerve becomes apparent in 4- or 5-day-old youngs. From these bases, it is obvious that the facial nerve elements related to sucking are firstly developed at birth and that the differentiation of the trigeminal nerve elements related to biting is rapidly accelerated after birth.

Animals↗

PubMed1989

[Evaluation of the degree of restoration of function with fixed molar bridges].

The purpose of this study was to determine the degree of restoration of masticatory function with fixed molar bridges. Evaluations were made of the deep temperature of the masseter muscle, masticatory performance and occlusal contacts (duration, force distribution, area and number of contacts). Criteria were established for the parameters above mention in 30 normal subjects. Fixed bridges were placed in 10 patients with missing only the mandibular first molar. Measurements were carried out both prior to and after placement of the prosthesis. The following results were obtained. 1. The deep temperature of the masseter muscle patients recovered in 30 days after prosthesis. 2. The total number of contact points and contact area increased after placement by 30 days. 3. The duration of occlusal contacts increased up to 30 days after placement. 4. The force distribution of occlusal contacts decreased for a time but recovered as the normal subjects after 30 days. 5. The masticatory performance was restored immediately after the placement and showed no change by 45 days.

Body Temperature↗

PubMed1985

On the bilateral innervation of masticatory muscles: a study with retrograde tracers.

Using horseradish peroxidase and fluorescent compounds as retrograde tracers, the myotopical arrangement and axon trajectories of the motoneurons innervating the supramandibular and the suprahyoidal muscles were studied in the rat. Only motoneurons ipsilateral to the injection site were labelled. In the trigeminal motor nucleus, motoneurons of the superficial masseter muscle were found laterally, of the anterior deep masseter muscle centrally, and of the temporalis muscle dorsally and medially. Motoneurons of the anterior and posterior digastric muscle were located in the accessory motor nucleus of the trigeminal and facial nerve respectively. Evidence is provided that jaw-opening muscles are innervated from a separate motor complex.

Animals↗

PubMed2001

Proliferation of masseter myocytes after distraction osteogenesis of the porcine mandible.

PURPOSE: Long-term success of distraction osteogenesis depends on the ability of the surrounding soft tissues to tolerate distraction forces and to adapt to the resulting increase in skeletal length and volume. The hypothesis tested in this study was that mandibular elongation by distraction induces myocyte proliferation. MATERIALS AND METHODS: Unilateral mandibular angle osteotomies were performed in 16 Yucatan minipigs. The hemimandibles were lengthened using semiburied distraction devices (Synthes Maxillofacial, Paoli, PA) with 0-day latency, 1, 2, or 4 mm/d distraction rates, and a neutral fixation period of twice the gap size in days. In 2 additional animals, the dissection and osteotomies were performed, and distraction devices were placed without activation (sham control). At the end of neutral fixation, tissues were taken from masseter muscle overlying the osteotomy and the equivalent region on the unoperated side (contralateral control). Proliferation of myocytes was estimated using immunohistochemical localization with antibodies against proliferating cell nuclear antigen (PCNA). RESULTS: Muscle overlying the distracted mandible showed 6-fold more PCNA-positive myocytes (16.8% +/- 11.3%) than the contralateral control side (2.8% +/- 1.1%, P < .0001). In the 2 sham-control animals, there was a low index of PCNA-positive myocytes on both the osteotomy (2%, 5%) and the contralateral sides (1%, 2%). CONCLUSIONS: The results of this study suggest that distraction of the porcine mandible by the protocol described induces myocyte proliferation in the masseter muscle. A proliferative response may contribute to improved long-term stability of mandibular expansion by distraction osteogenesis.

Animals↗

PubMed2004

Brainstem evaluation in children with primary nocturnal enuresis.

We investigated the brainstem integrity in children with primary nocturnal enuresis (PNE) using auditory brainstem responses (ABR), blink reflex and exteroceptive suppression of the masseter muscle. We examined 23 children with PNE (16 male, 7 female; mean age: 10.4 years) and 19 control subjects (11 male, 8 female; mean age: 11.8 years). ABR parameters such as wave latencies, amplitudes and interpeak latencies and blink reflex parameters such as R1 and R2 amplitude and latencies were not significantly different between the 2 groups. Although S2 parameters of the exteroceptive suppression of the masseter muscle were easily and completely obtained from the control subjects, in the PNE group S2 onset latency and duration were not recorded in 26% of the study children (n = 6) (P = 0.01). S2 duration time was significantly lowered in the enuretic group (left side: P = 0.001 and right side: P = 0.003). S2 duration time changes in the enuretic group supports a possible brainstem dysfunction in children with PNE.

Adolescent↗

PubMed1982

Clenched jaw jerks in children.

Masseter muscle silent periods were assessed in 24 children divided into three groups according to their stage of dental development (primary, mixed, and permanent). Surface electrode EMG data, timing code, and microphone input were recorded on magnetic tape. A visual record was obtained by playing the tape into an optical oscillograph; measurements were made from the photosensitive paper. The results indicate the latency and silent period durations of clenched jaw jerks were similar among the three groups. For the subjects in this study, the mean latency and silent period durations of the masseter muscle during clenched jaw jerks were 14.9 ms (milli-seconds) and 27.0 ms.

Adolescent↗

PubMed1980

Pain, tenderness and strength of human mandibular elevators.

In terms of the mean voltage during maximal bite in the intercuspal position we compared the strength of the temporal and masseter muscles of 39 patients with functional disorders of the chewing apparatus and 45 controls. Maximal electrical activity was significantly stronger in the controls than in the patients. Differences between the two samples with respect to sex, age, number of opposing teeth in contact and the presence of pain and tenderness tended to favor stronger activity in the controls. However, the different levels of electrical activity, especially in the case of the masseter muscles, could only be accounted for on the basis of a difference in maximal strength. We suggest that the weaker elevator muscles of the patients was a predisposing factor making these muscles less fit to endure hyperactivity induced psychologically or as a reflex response to occlusal interferences and functional disorders of the temporomandibular joints or other elements of the oral neuromuscular system. The sample of controls had much stronger elevators, less susceptible to such hyperactivity.

Adolescent↗

PubMed2000

Hemimasticatory spasm associated with localized scleroderma and facial hemiatrophy.

OBJECTIVES: To report a case and discuss the mechanism of hemimasticatory spasm. DESIGN: Case report. PATIENT: A 37-year-old woman had a 3-year history of involuntary spasms of the right masseter muscle in association with localized scleroderma and facial hemiatrophy. Electrophysiological studies revealed a normal blink reflex. However, the masseter reflex and silent period were absent on the affected side. Distal latency and compound muscle action potential of the masseter nerve were normal. Needle electromyography demonstrated irregular bursts of motor unit potentials similar to those described in hemifacial spasm. A magnetic resonance imaging scan of the head showed mild hypertrophy of the masseter muscle and atrophy of subcutaneous fatty tissues on the affected side. Local injection of botulinum toxin A into the masseter muscle resolved the patient's symptoms. CONCLUSION: On the basis of clinical and electrophysiological findings, focal demyelination of motor branches of the trigeminal nerve owing to deep tissue changes is suggested as the cause of abnormal excitatory electrical activities resulting in involuntary masticatory movement.

Action Potentials↗

PubMed1991

Effect of occlusal bite-raising splint on electromyogram, motor unit histochemistry and myoneuronal dimensions in rats.

Composite resin bite-raising splints were fabricated on both sides of the upper jaw in rats. EMG activity of the deep masseter muscle was monitored continuously for 24 h before and up to 4 weeks after treatment. Together with the EMG activity, measurements of the neuromuscular junction area and muscle fibre histochemistry were made. EMG activity showed great variability immediately after splint fabrication. Some of the animals showed increased EMG activity, while others exhibited less activity 48 h after splint application. Overall, the fluctuation lasted for about 4 days, and after approximately 7 days all the animals exhibited decreased EMG activity, followed by a gradual increase in activity towards baseline levels. The neuromuscular junction territory increased significantly 5-10 days after splint application. Histochemical characterization of the deep masseter muscle revealed that it contained the three main types of muscle fibre: slow oxidative (SO), fast-oxidative-glycolytic (FOG) and fast glycolytic (FG). The frequency distribution of fibre types did not change after bite-raising splint treatment. These findings indicated that splint treatment in rats is effective in reducing EMG activity, while the muscle type characteristics remain stable. The effect of lower activity on the motor end-plates suggested that the neuromuscular junctions are quite sensitive to functional changes.

Adenosine Triphosphatases↗

PubMed2002

Effects of a denture adhesive on masticatory functions for complete denture wearers--consideration for the condition of denture-bearing tissues--.

The purpose of this study was to examine effects of a denture adhesive on masticatory functions for complete denture wearers considering the condition of denture-bearing tissues. Sixteen edentulous subjects wearing well-fitting complete dentures volunteered to participate in this study. According to the condition of denture-bearing tissues, subjects were divided into two groups; "good group" and "poor group". Maximum biting forces, masticatory performance, and electromyography of the masseter muscle during mastication were recorded with and without a denture adhesive. Durations of chewing burst and cycle, and coefficients of variation for these variables were calculated using electromyography recordings. Data were analyzed by using two-way repeated-measured ANOVA and paired t-test in order to assess the effect of the use of a denture adhesive. The use of the denture adhesive increased maximum biting force and provided rhythmic masseter muscle activity during mastication for both groups. Masticatory performance was improved and duration of chewing burst was decreased only for "poor group". It was concluded that the effects of the denture adhesive on masticatory functions were observed overall for both groups, and more significant for denture wearers with poor denture-bearing tissues than with good denture-bearing tissues.

Adhesives↗

PubMed1993

End results of 114 extended "commando" operations for retromolar trigone carcinoma.

Retromolar trigone carcinomas invade the mandible and the pterygoid and/or masseter muscles in a large number of cases. There is also a significant risk of ipsilateral lymph node neck metastasis. The purpose of this retrospective study was to report the survival results of 114 consecutive patients who underwent an extended "commando" operation (retromolar operation) from 1960 to 1991. The technique is a variation of a composite resection. The operation consists of hemimandibulectomy with resection of the pterygoid and masseter muscles, with an ipsilateral neck dissection (radical classical, modified, or supraomohyoid). The oral cavity and oropharyngeal defects were closed primarily in 83 patients. In the remaining 31 patients (27.2%), it was reconstructed by a tongue flap (12 patients), pectoralis major myocutaneous flap (10 patients), and other flaps (9 patients). There were 104 men and 10 women, with a median age of 55 years. All patients had squamous cell carcinoma. Tumor stages were T1 (5 patients), T2 (44 patients), T3 (24 patients), T4 (28 patients), and Tx (13 patients). The metastases were predominantly in levels I and II. Only patients with positive nodes at levels I and/or II had histologically positive nodes at levels IV or V. Complications occurred in 51.8% of the patients (wound infection in 21 patients, 18.4%). Sixty-six patients underwent postoperative irradiation (4 to 70 Gy, median: 50 Gy). To date, 41 patients have presented with 50 tumor recurrences: 31 local, 9 in the dissected neck, 3 in the contralateral neck, and 7 distant. The 5-year actuarial overall survival rate was 80.0% in patients with T1 tumors, 57.8% in those with T2 tumors, 46.5% in those with T3 tumors, and 65.2% in those with T4 tumors. In conclusion, the retromolar operation can be performed with acceptable morbidity, and it is effective (5-year overall survival rate of 55.3%). The rate of local recurrences (27.2%) suggests that radiotherapy as an adjunctive modality should be indicated in patients in whom recurrences are likely.

Adult↗

PubMed1987

Arthrotic changes and deviation in form of the temporomandibular joint--an autopsy study.

An autopsy study was performed on 84 left human temporomandibular joints. Frequency and location of osteoarthrosis and deviation in form were registered in each joint component. Locations of disc perforations were registered with special emphasis on involvement of the bilaminar zone. The anatomical relationship between the deep masseter muscle and the TMJ capsule was investigated in part of the material. Deviation in form was most frequent in condyles (53%) compared with temporal components (40%) and discs (15%). The relative frequencies of the three joint components were opposite for osteoarthrosis; discs (32%), temporal components (26%) and condyles (21%). Higher frequency of arthrotic changes was found in edentulous specimens than in dentulous ones. Disc perforations were located within disc tissue except for one joint where it also included part of the bilaminar zone. No correlation between sex and arthrosis and/or deviation in form was found. Insertion of the posterior fibres of the deep masseter muscle into the anterior capsule was macroscopically observed in six of ten joints.

Adaptation, Physiological↗

PubMed1995

Mean power frequency shift during fatigue and recovery in patients with craniomandibular disorders.

EMG spectral shifts of anterior temporal and medial masseter muscles were evaluated. Mean power frequency (MPF) shift during fatigue and recovery of 46 healthy subjects and 46 patients with craniomandibular disorder were recorded at the beginning and the end of fatiguing clenching, then 3, 8, 13 and 18 min following the fatiguing clenching. The reference clenching force was 80% of each subject's maximal voluntary contraction (MVC). Recording was stopped when subjects felt pain or discomfort. Significance was found between the healthy group (N) and the diseases group (CMD) in the three following points: (i) the mean of MPF values of the masseter muscles at the end of fatiguing clenching; (ii) the recovery pattern of the temporal muscles; and (iii) MPF shift induced by fatiguing clenching. Our results therefore suggest that MPF reflects several aspects of craniomandibular disorders. Thus, measuring fatigue and recovery MPF could be useful in the screening of CMD.

Adult↗

PubMed1996

Differences in capillary supply between human oro-facial, masticatory and limb muscles.

In this report we show that immunostaining of the capillary basement membrane with an antibody directed against laminin is a useful alternative in detecting the capillaries in human muscle. Using this method, the capillary supply of three embryologically, morphologically and functionally different muscle groups, oro-facial, masticatory and limb muscles, were analysed. Significant differences in capillarization between muscles and muscle groups were found. The oro-facial and masseter muscles showed significantly higher density of capillaries than the limb muscles, taken in consideration the muscle cross-sectional area, with the masseter having the highest capillary density ever reported for human sedentary skeletal muscles. Judged from the number of capillaries per muscle fibre, the limb muscles showed the best capillarization. However, since the three muscle groups investigated differed with respect to fibre diameter, our evaluation of number of capillaries per muscle fibre was related also to fibre diameter. Thus, capillary constants were created which take fibre diameter into account. Based on these new parameters, the oro-facial and masseter muscles were found to be relatively better supplied by capillaries than the limb muscles. These results suggest differences in tasks and functional activity between muscles, and reflect a relatively higher need and demand for blood supply in the masticatory and oro-facial muscles than in limb muscles.

Adolescent↗

PubMed1992

Mosaic lectin and enzyme staining patterns in rat skeletal muscle.

We compared the localizations of lectin binding and activity for myosin ATPase and succinic dehydrogenase in sections of the gracilis, soleus, and masseter muscles from 10- and 60-day-old rats. In the 60-day-old rats, incubation of the muscle sections with the lectins ConA, GS-II, HPA, and jacalin gave rise to a mosaic staining pattern, especially in the gracilis muscle, in which the same fibers were strongly stained for ConA, GS-II, and HPA, whereas the staining with jacalin in these fibers was weak, and vice versa. There was no correspondence in the staining patterns for the enzymes and the lectins. In the masseter muscle only GS-II gave rise to distinct differences in the staining intensity between muscle fibers. In 10-day-old rats all fibers in the muscles were moderately stained with ConA, HPA, and jacalin, whereas a chessboard staining pattern could be observed after incubation with GS-II. In an extract of hindleg muscle from 60-day-old rats there was strong affinity for ConA and HPA and weak affinity for GS-II and jacalin, as shown by dot-blotting. After electrophoresis and blotting to nitrocellulose membranes, three muscle protein bands with apparent molecular weights of 100,000, 90,000, and 43,000 showed affinity for ConA, HPA, and GS-II, whereas no bands were jacalin positive. The complex lectin staining pattern in skeletal muscle might be related to development, specialization, and function of the muscles.

Animals↗

PubMed1980

Masseter myopathy following systemic corticosteroid administration: an experimental study.

Immature A/J mice were treated with a series of alternate (every 4 days) doses of triamcinolone hexacetonide, a long-acting synthetic analogue of cortisol, and their masseter muscles were studied ultrastructurally. Various degrees of degenerative changes were found in most myofibers of triamcinolone-treated animals. These changes ranged from local alterations in the configuration of the Z discs to a complete disarray of the myofibrilar architecture. Severely affected myofibers revealed areas with total disintegration of myofilaments, loss of mitochondria, and an almost total depletion of glycogen. In addition, some nuclei were centrally located and an obvious enhancement of collagen fibrillogenesis was found in the endomysial spaces. The latter comprised a mixture of banded collagen fibrils and slender filaments which lacked any specific orientation of organization. Endothelial cells of intramuscular capillaries were hypertrophic, thus evoking a marked occlusion of the vascular lumen. Ultrastructural changes were also noted in axon terminals and in the sole-plate sarcoplasm: loss of synaptic vesicles along with shrinkage of axon terminals, partial loss of postsynaptic folds, and a decrease in the number of mitochondria within the sole-plate sarcoplasm. It is proposed that triamcinolone, even if administered on an alternate schedule, promotes myopathic changes in the masseter muscles of immature mice which, in turn, might possibly contribute to the hormone-retardive effect upon the growth potential of the developing mandible.

Animals↗

PubMed2006

The influence of masseter activity on rat mandibular growth.

Many studies have shown that mandibular and condylar growth is affected by compressive forces on mandibular bone and the condyle. It has been reported that chondroblastic differentiation and proliferation in chondrocytes play important roles in condylar growth. However, the influence of reduced compressive force on chondroblastic proliferation and mandibular bone formation is not fully understood. Thirty-six 3-week-old male Wistar rats were used in this study. In the experimental group, the masseter muscles were bilaterally resected to evaluate the influence of masticatory force on mandibular and condylar bone morphology. Six weeks after the operation, while the rats were in the pubertal growth stage, lateral X-rays were taken to analyze the skeletal pattern of the mandible. The form of the condyle and the thickness of the chondroblastic layers were evaluated by toluidine blue staining. Chondroblastic proliferation was identified by insulin-like growth factor-1 receptor (IGF-1r) immunostaining and bone resorption of the condyle was assessed by measuring tartrate-resistant acid phosphatase (TRAP) activity. Lateral X-rays of the mandible showed that rats in the experimental group tended to have large mandibular plane angles. The chondroblastic layer in the condyles of the experimental group rats was thinner than in the control group. The expression of IGF-1r immunopositive cells in the experimental group was significantly lower than in the control chondrocytes, and the number of TRAP-positive cells was significantly higher in the condylar bone of the experimental group. We conclude that masseter muscle activity is closely related to mandibular morphology during growth.

Acid Phosphatase↗

PubMed1990

The facial artery of the common marmoset (Callithrix jacchus).

The facial artery and its ramifications in 7 adult common marmosets (Callithrix jacchus) were studied by the plastic injection method. The findings obtained are discussed in comparison with those for other primates. In the submandibular region, the facial artery arose from the external carotid artery at the height of the atlas via the linguofacial trunk on 10 of the total of 14 sides examined and independently on the other 4 sides. This common trunk always gave rise to the superior thyroid artery. The facial artery passed anterolaterally between the styloglossus muscle and the intermediate tendon of the digastricus muscle, giving off the styloglossal and the submandibular glandular branches, and anteroinferiorly medial to the pterygoideus medialis muscle. In a position anterior to this muscle, the submental artery and masseteric branch were derived. The submental artery gave off the medial pterygoid, the digastric, the cutaneous, the sublingual glandular and the mylohyoid branches, and then continued up to the median line, where it terminated to supply the genioglossus muscle. In the facial region, the facial artery passed anterosuperiorly along the anterior margin of the masseter muscle on 12 sides and away from it forwards on 2 sides, giving off the premasseteric branch in one of these 2 sides. It gave rise to the cutaneous, the buccal and the buccinator branches, the inferior labial artery and the communicating branch with the zygomatic artery. It terminated to divide into the superior labial and the naris lateral arteries, although the latter was lacking on 4 sides. The inferior labial artery gave off the mandibular marginal, the inferior labial marginal and the inferior labial glandular branches and terminated to anastomose with the mental artery. The superior labial artery divided into the superficial and deep branches, each of which continued as a nasal septal branch. The facial artery of the common marmoset usually ascended along the anterior margin of the masseter muscle and did not reach the medial angle of the eye.

Animals↗