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PubMed2000

Formation of a full complement of cranial proprioceptors requires multiple neurotrophins.

Inactivation of neurotrophin-3 (NT3) completely blocks the development of limb proprioceptive neurons and their end organs, the muscle spindles. We examined whether cranial proprioceptive neurons of the trigeminal mesencephalic nucleus (TMN) require NT3, brain-derived neurotrophic factor (BDNF) or neurotrophin-4 (NT4) for their development. Complements of TMN neurons and masticatory muscle spindles were decreased by 62% in NT3 null mutants, 33% in BDNF null mutants, and 10% in NT4 null mutant mice at birth. The extent of proprioceptive deficiencies differed among different masticatory muscles, particularly in NT3 null mice. Masticatory muscles of embryonic mice heterozygous for the NT3(lacZneo) or BDNF(lacZ) reporter genes expressed both NT3 and BDNF, consistent with target-derived neurotrophin support of TMN neurons. Although more than 90% of TMN neurons expressed TrkB as well as TrkC receptor proteins by immunocytochemistry in wild-type newborns, TrkC or TrkB null mice exhibited only partial proprioceptive deficiencies similar to those present in NT3 or BDNF;NT4 null mice. Thus, in terms of the survival outcome, two main subpopulations of TMN neurons may exist during embryogenesis, one dependent on TrkC/NT3 functioning and the other utilizing TrkB/BDNF signaling. The differential dependence of TMN neurons on neurotrophins may reflect differential accessibility of the neurons to limiting amounts of NT3, BDNF, or NT4 in target tissues, especially if the tissue distribution or levels of BDNF, NT3, and NT4 were dynamically regulated both spatially and temporally.

Animals↗

PubMed1995

Craniomandibular disorders, edentulousness and the clinically estimated size of the masseter muscle.

A total of 355 postmenopausal women were classified according to the degree of edentulousness, and anamnestic information on masticatory dysfunction symptoms was recorded. Five masticatory muscles were palpated, and the subjects were classified according to size of the masseter muscle. This simple classification for the clinical inspection of the masseter muscle was tested. In agreement with previous reports, decreasing functional exercise of the jaws was found to diminish the size of the masticatory muscles making them more disposed to dysfunction symptoms. The three-level classification of size of the masseter muscle is useful in normal clinical practice for determining the condition of this muscle.

Chi-Square Distribution↗

PubMed1996

Is quantitative electromyography reliable?

The reliability of quantitative electromyography (EMG) of the masticatory muscles was investigated in 14 subjects without any signs or symptoms of temporomandibular disorders. Integrated EMG activity from the anterior temporalis and masseter muscles was recorded bilaterally by means of bipolar surface electrodes during chewing and biting activities. In the first experiment, the influence of electrode relocation was investigated. No influence of electrode relocation on the recorded EMG signal could be detected. In a second experiment, three sessions of EMG recordings during five different chewing and biting activities were performed in the morning (I); 1 hour later without intermediate removal of the electrodes (II); and in the afternoon, using new electrodes (III). The method errors for different time intervals (I-II and I-III errors) for each muscle and each function were calculated. Depending on the time interval between the EMG recordings, the muscles considered, and the function performed, the individual errors ranged from 5% to 63%. The method error increased significantly (P < .05 to P < .01) with the time interval between recordings. The error for the masseter (mean 27.2%) was higher than for the temporalis (mean 20.0%). The largest function error was found during maximal biting in intercuspal position (mean 23.1%). Based on the findings, quantitative electromyography of the masticatory muscles seems to have a limited value in diagnostics and in the evaluation of individual treatment results.

Adolescent↗

PubMed2000

Changes in pressure-pain thresholds of the jaw muscles during a natural stressful condition in a group of symptom-free subjects.

AIMS: To investigate the effects of a natural emotional stressor on pressure-pain thresholds (PPTs) of the masticatory muscles of symptom-free subjects. METHODS: Sixteen healthy dental students were selected before they undertook an academic examination. Sixteen gender-matched students who were not exposed to an examination served as controls. The 2 groups of students were monitored in parallel on 5 separate days over a 1-month period: 2 days before the examination (T1), on the day of the examination (T2), 2 days after (T3), 1 month after (T4), and again after another 2 days (T5). On the day of the examination (T2), the control students were only required to complete a brief, non-demanding questionnaire. On each day, the following parameters were assessed: PPTs of the masseter, the anterior temporalis, and the Achilles tendon; state anxiety; and present stress (measured on a visual analog scale [VAS]). Furthermore, in the students undergoing the examination, venous blood samples for assessment of beta-endorphin levels were obtained at T2 and T5. RESULTS: In the stressed students, the PPTs of the masticatory muscles and the Achilles tendon were significantly lower (analysis of variance [ANOVA], P < or = 0.02) on the day of the examination (T2) and on the days nearest the exam (T1, T3), and state anxiety and present stress were significantly higher (ANOVA, P < or = 0.003). No significant change was found in beta-endorphin plasma levels (P > 0.05). In the control group, PPTs, state anxiety, and present stress did not change significantly (ANOVA, P > 0.05). CONCLUSION: The results support a relationship between psychologic stress and pressure-pain sensitivity of the masticatory muscles.

Achilles Tendon↗

PubMed2004

Advantages of intraoral verticosagittal ramus osteotomy in skeletofacial deformity patients with temporomandibular joint disorders.

PURPOSE: This preliminary study was performed to clarify the usefulness of intraoral verticosagittal ramus osteotomy (IVSRO) in patients with temporomandibular joint (TMJ) disorders. PATIENTS AND METHODS: We examined 34 sides in 19 consecutive patients with dentofacial deformities with TMJ dysfunction undergoing IVSRO. Preoperatively, 15 patients had TMJ sounds bilaterally and 4 had sounds unilaterally. Five sides in 3 patients had pain in the TMJ, and 4 sides in 3 patients had masticatory muscle pain. The TMJ symptoms, including TMJ sounds, pain in the TMJ, and masticatory muscle pain in each patient, were assessed clinically before and approximately 12 months after IVSRO. Magnetic resonance imaging was also performed to determine joint status, including determination of the positions of the condyle and disc. RESULTS: The symptoms of the TMJ after 12 months of orthodontic treatment showed marked improvements, with the disappearance of the TMJ sounds in 94% of the sides examined. Pain in the TMJ improved in 4 of 5 sides, and pain of the masticatory muscle improved in 3 of 4 sides. With regard to the relative positions of the condyle and disc on magnetic resonance imaging, 6 of 8 joints and 5 of 7 joints showed improvement in anterior disc displacement with and without reduction, respectively. The direction and mean amount of movement in the distal segment were 8 mm in setback, 4 mm in advance, and 5 mm counterclockwise. CONCLUSION: IVSRO is potentially as useful for the treatment of TMJ disorders in orthognathic surgery patients as is intraoral vertical ramus osteotomy, and IVSRO can be used selectively in cases in which intraoral vertical ramus osteotomy is contraindicated.

Adolescent↗

PubMed2003

Muscle and temporomandibular joint forces associated with chincup loading predicted by numerical modeling.

Development of the components of the temporomandibular joint (TMJ) is thought to reflect joint loading. The aims of this project were to test 3 hypotheses: whether effective eminence morphology, masticatory muscle forces, and predicted TMJ forces during chincup loading of the mandible were consistent with the objectives of minimization of joint loads (MJL) or muscle effort (MME), or both. Regression relationships of MJL model-predicted versus measured eminence shapes in 9 subjects indicated a high degree of correlation (mean slope = 0.99, compared with perfect-match slope = 1.00). Model predictions of muscle output during chincup loading of the mandible were tested by comparison with data gathered in 6 subjects. Midsagittal plane chin loads were applied over a range of 60 degrees while bilateral masticatory muscle surface electromyography was quantified. The regression relationships of predicted versus measured masseter and anterior digastric muscle outputs indicated that model predictions were highly correlated (mean slope (masseter muscle) = 1.02; mean slope (digastric muscle) = 0.96). TMJ forces predicted by modeling showed intersubject differences of up to 34% for similar chincup loading conditions. Intrasubject variation in TMJ forces was as high as 57%, depending on chin load angle. The results demonstrated that TMJ eminence shape and masticatory muscle forces were consistent with objectives of both MJL and MME. Variation in TMJ forces depended on the subject and the direction of chincup loading.

Adolescent↗

PubMed1984

Masseter, digastric and omohyoidal responses from weak mechanical oral stimuli in the chewing rat.

In rats anesthetized with ketamine, effects of jaw jerks (rise time 5 ms, strength 70 mN) applied in the open direction were studied both in the quiescent preparation and during rhythmic jaw-opening and jaw-closing movements (induced by mechanical stimulation of the palate). The left masseter, posterior and anterior digastric and omohyoid muscles were fitted with electrodes for recording electromyographic responses. In the quiescent state a jaw jerk causes responses in all recorded muscles. In the rhythmic preparation masseter responses persisted but digastric and omohyoidal responses were suppressed. This suppression was most prominent when jerks were applied during closing. However, responses in digastrics and omohyoid persisted when masseter nerves and periodontal afferents of the lower incisors were blocked with xylocaine. The suppression of digastric and omohyoidal responses therefore originates--at least partly - from masseter and periodontal afferents. When the periodontal afferents alone were blocked with xylocaine only the response in the opening phase persisted. The suppression of digastric and omohyoidal responses during opening are therefore reflexes from periodontal receptors. These observations support the concept that oral activity is controlled by two relatively independent systems. The first program-oriented system generates the basic movements whereas the second, environment-oriented, system has access to the program for correcting perturbations. There is evidence that muscles poorly supplied with muscle spindles (digastrics and omohyoid) act as pure effectors. Modulation of their activity is prompted by exteroceptors and muscle receptors in the masticatory muscles.

Afferent Pathways↗

PubMed1995

Mandibular exercises to control bruxism and deviation problems.

A discussion of bruxism, mandibular deviation and hypermobility problems producing temporomandibular joint (TMJ) and masticatory muscle pathology is presented. The pathophysiology of painful masticatory muscle hyperactivity, TMJ dysfunction and chondromalacia are presented. The role that pain mediators play in the degradation of TMJ fibrocartilage, acute synovitis and joint and muscle pain is analyzed. Isokinetic and stretching exercises are described to assist in correcting or preventing pathology and dysfunction of these structures.

Bruxism↗

PubMed1996

Occlusal and functional conditions after surgical correction of anterior open bite deformities.

The dental occlusion and alterations in orofacial muscles were studied in 267 patients whose severe anterior open bite had been treated with a Le Fort 1 intrusion osteotomy with or without an advancement sagittal split osteotomy about 6 years ago. Only 17% of those patients showed anterior contact, and 20% had no vertical overlap of mandibular and maxillary central incisors at all. Tongue position, activity of masticatory muscles, lip competence, lip-incisor relationship, and breathing mode were assessed. Statistically significant correlations were found between tongue positions and occlusion in both the anterior and the posterior regions. In addition, the activity of the masticatory muscles, habitual mouth posture, and interlabial distance were each significantly correlated to overbite, open bite, and overjet. The interlabial distance was also significantly correlated with both breathing mode and mentalis muscle activity. The activity of the masticatory muscles was negatively correlated with tongue position.

Adaptation, Physiological↗

PubMed1982

Cysticercosis in cattle in Senegal.

The hearts of 51, and the masticatory muscles of another 51 cattle from the slaughter-house in Dakar, were examined by careful dissection. Cysticerci and/or cystic lesions were found in 13.7% of the hearts and in 25.5% of the masticatory muscles. The cystic lesions were examined histologically in an attempt to identify Taenia saginata cysticerci. A final infection rate of 5.8% in hearts and 15.7% in masticatory muscles was thus obtained. Lower percentages were recorded after inspecting 2088 slaughtered cattle by the routine meat inspection technique.

Abattoirs↗

PubMed1988

Intra-articular and skin surface temperature of the temporomandibular joint in patients with rheumatoid arthritis.

Intra-articular and skin surface temperatures of the temporomandibular joint (TMJ) were investigated in 34 patients with rheumatoid arthritis (RA). History was taken, and a clinical examination of the stomatognathic system was performed. The intra-articular temperature measurement was made with a thermocouple inserted through a needle, and the skin surface measurement was made with a thermocouple lateral to the condylar pole. The intra-articular temperature was lower for 37% and higher for 30% of the patients, whereas skin surface temperature was lower for 18% and higher for 6%, compared with normal individuals. Intra-articular and skin surface temperatures were positively correlated, and the average difference between skin surface and intra-articular temperatures was 1.6 degrees C. The intra-articular temperature was most strongly and positively correlated to the number of joint regions affected by RA and negatively correlated to the number of tender masticatory muscles, whereas skin surface temperature was most strongly and positively correlated to room temperature and negatively correlated to the number of tender masticatory muscles. These results indicate that pain and tenderness of masticatory muscles in RA are associated with hypothermia of the TMJ.

Adolescent↗

PubMed1983

Influence of central dopaminergic and oral sensory stimulation on the tone of the rat masseter muscle.

Dopamine neurons in the nigrostriatal subgroup of the basal ganglia are involved in the higher control of muscle tone and repetitive movements, possibly also in the masticatory muscles. For this reason, the effect of mechanical oral stimulation in combination with apomorphine-induced stimulation of dopamine receptors in the brain was experimentally studied in the rat. The masseter muscle tone during and after anesthesia was registered. A tachograph preamplifier and a bipolar electrode were used for the recording of summated potentials from the muscle. Dopaminergic stimulation increased the muscle tone. Oral sensory stimulation alone showed a tendency to increase the masseter tone, although the increase was not statistically significant. The increase of the tone with dopaminergic stimulation is presumably due to the fact that the dopaminergic system in the basal ganglia also controls the motor function of the masticatory muscles. Several pathological conditions of the mouth region, where a dopaminergic mechanism in the facilitation and inhibition of centrally coordinated jaw reflexes is obvious or possible, are discussed. Individual variation in neuronal dopamine synthesis, uptake, or receptor sensitivity may be one of the factors determining predisposition to masticatory disturbances both in experimental and clinical conditions.

Anesthesia, Dental↗

PubMed2000

Temporomandibular joint involvement in a patient with centronuclear myopathy.

We describe here the temporomandibular joint and masticatory muscle abnormalities disclosed by computed tomography and magnetic resonance imaging in a 25-year-old man with centronuclear myopathy (a congenital myopathy) who presented with marked limitation of jaw movements. We found an intense and general fatty replacement of the masticatory muscles, and magnetic resonance imaging signals indicated articular fibrosis. We conclude that in centronuclear myopathy, the presence of weakness and hypomotility of the masticatory muscles can induce chronic abnormalities of the temporomandibular joint.

Adipose Tissue↗

PubMed2003

Natural course of disc displacement with reduction of the temporomandibular joint: changes in clinical signs and symptoms.

PURPOSE: The goal of this study was to examine the natural course of disc displacement with reduction in the temporomandibular joint (TMJ). PATIENTS AND METHODS: This retrospective study involved 24 patients who had been diagnosed with disc displacement with reduction of the TMJ, but who had not undergone any treatment. The extent of maximal mouth opening, protrusion, lateral excursions, noise of the TMJ, pain of the TMJ, and tenderness of masticatory muscles were recorded monthly for a mean of 25.8 months. RESULTS: Maximal mouth opening, protrusion, and lateral excursions remained unchanged during follow-up. TMJ pain decreased by 15.7% (P >.05). Clicking decreased by 20.8% (P <.05), and tenderness of masticatory muscles decreased by 33.3% (P <.05). Reciprocal clicking remained unchanged in 19 patients (79.2%) and disappeared in 5 patients (23.8%). Four patients (16.7%) in whom clicking disappeared had a normal mouth opening, but locking developed in 1 patient (4.2%). CONCLUSIONS: In patients with disc displacement with reduction who do not undergo treatment, range of movement remains unchanged over time. Tenderness of masticatory muscles tended lessen, but reciprocal clicking and TMJ pain tended to remain. Clicking did not progress to locking in most patients.

Adolescent↗

PubMed2004

Ehlers-Danlos Syndrome (EDS) focusing on oral symptoms: a questionnaire study.

OBJECTIVES: To study the prevalence of oral problems reported among a large group of adults with Ehlers-Danlos Syndrome (EDS). Furthermore, to compare proportions of disorders and general psychological well-being with those in a cohort of randomized population-based controls. DESIGN: A questionnaire study. SETTING AND SAMPLE POPULATION: A total of 265 persons with EDS (response rate 77%) and 750 controls (response rate 63%) in a population-based cohort. Sixty persons were excluded from the EDS group (support members, children, undiagnosed EDS) leaving a final study group of 144 adults. The final control group consisted of 331 persons since many had sent back unanswered questionnaires. EXPERIMENTAL VARIABLES: Questions concerning general and oral symptoms, VAS scales for masticatory muscle pain ratings and General Health Questionnaire (GHQ12) questions were included. OUTCOME MEASURE: Proportions of affirmative answers in EDS group and controls were compared. Mean values for ratings on VAS scales. Proportions of GHQ12 scores with a threshold score of four or more. RESULTS: The proportions of affirmative answers for persons with EDS concerning general health problems, oral problems and masticatory muscle symptoms were significantly higher compared with controls. In the EDS group those who had daily pain in the masticatory muscles had significantly higher mean values on the VAS scales compared with those who had pain a few days per month. A GHQ12 score of four or more was significantly more common in the EDS group than in the controls, suggesting that a decline in psychological well-being was also more common in this group. CONCLUSION: It is important that dental practitioners should be aware of the oral problems associated with EDS and the impact the disease has on quality of life.

Adolescent↗

PubMed1988

The central projection of masticatory afferent fibers to the trigeminal sensory nuclear complex and upper cervical spinal cord.

Retrograde and anterograde transport of horseradish peroxidase-wheat germ agglutinin (HRP-WGA) conjugate was used to study the organization of primary afferent neurons innervating the masticatory muscles. HRP applied to the nerves of jaw-closing muscles--the deep temporal (DT), masseter (Ma), and medial pterygoid (MP)--labeled cells in the trigeminal ganglion and the mesencephalic trigeminal nucleus (Vmes), whereas HRP applied to nerves of the jaw-opening muscles--anterior digastric (AD) and mylohyoid (My)--labeled cells only in the trigeminal ganglion. Cell bodies innervating the jaw-closing muscles were found with greater frequency in the intermediate region of the mandibular subdivision, while somata supplying the jaw-opening muscles were predominant posterolaterally. The distribution of their somatic sizes was unimodal and limited to a subpopulation of smaller cells. Projections of the muscle afferents of ganglionic origin to the trigeminal sensory nuclear complex (TSNC) were confined primarily to the caudal half of pars interpolaris (Vi), and the medullary and upper cervical dorsal horns. In the Vi, Ma, MP, AD, and My nerves terminated in the lateral-most part of the nucleus with an extensive overlap in projections, save for the DT nerve, which projected to the interstitial nucleus or paratrigeminal nucleus. In the medullary and upper cervical dorsal horns, the main terminal fields of individual branches were confined to laminae I/V, but the density of the terminals in lamina V was very sparse. The rostrocaudal extent of the terminal field in lamina I differed among the muscle afferents of origin, whereas in the mediolateral or dorsoventral axis, a remarkable overlap in projections was noted between or among muscle afferents. The terminals of DT afferents were most broadly extended from the rostral level of the pars caudalis to the C3 segment, whereas the MP nerve showed limited projection to the middle one-third of the pars caudalis. Terminal fields of the Ma, AD, and My nerves appeared in the caudal two-thirds of the pars caudalis including the first two cervical segments, the caudal half of the pars caudalis and the C1 segment, and in the caudal part of the pars caudalis including the rostral C1 segment, respectively. This rostrocaudal arrangement in the projections of muscle nerves, which corresponds to the anteroposterior length of the muscles and their positions, indicates that representation of the masticatory muscles in lamina I reflects an onion-skin organization. These results suggest that primary muscle afferent neurons of ganglionic origin primarily mediate muscle pain.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗

PubMed1990

[A study of active induction of orthodontic therapy in TMJ dysfunction syndrome--from the data of patients with TMJ dysfunction in adolescents].

It seems that active orthodontic therapy using multi-bracket appliances presents effective assurance of a physiological stable occlusion for TMJ dysfunction syndrome in adolescents. The efficiency and problems concerning the progress of active orthodontic therapy after splint therapy were examined from the data of the change of occlusal conditions, and the function of masticatory muscles before and after therapy for TMJ dysfunction from four cases for which we performed orthodontic therapy activity. 1. All of the occurring symptoms of the TMJ dysfunction syndrome (limitation, pain, sound) in the progress of orthodontic therapy were concerned with using intermaxillary elastic. The symptom which occurred in process of using only intra-maxillary elastic was just a malaise of the TMJ. Also the sound of the TMJ relapsed in the process of using class III intermaxillary elastic and recurred after the multi-bracket appliance was removed. In this case, the condylar vertical position after orthodontic therapy changed from the lower position to the center position compared with the first visit. 2. Malocclusion was improved with orthodontic therapy in all four patients. 3. The function of the masticatory muscles after orthodontic therapy was improved in comparison with the first visit by evaluation of the masticatory muscles activity and the state of silent period.

Adolescent↗

PubMed1983

Surgical orthodontics and the temporomandibular joint. I. Superior repositioning of the maxilla.

Ten randomly selected adults who had undergone orthodontic treatment and isolated superior repositioning of the maxilla for vertical maxillary excess (VME) were evaluated clinically and radiographically (mean, 48.7 months postsurgery) for signs and symptoms of masticatory and temporomandibular joint dysfunction. The patients ranged from 18 years to 37 years of age (mean, 26.2 years) when evaluated. A three-part evaluation of the subjects was performed. This consisted of an anamnestic evaluation (previous medical history), a clinical examination, and a radiographic evaluation. The anamnestic evaluation revealed that, prior to surgery, facial pain was reported by one patient and was not present in any of the patients upon follow-up examination. We believed that the pain was not related to the masticatory musculature and/or the temporomandibular joint. No patients reported pain or sounds in their joints preoperatively, while 30 percent (3/10) of the patients related a history of temporomandibular joint sounds immediately after release of intermaxillary fixation, which subsequently was reported to have resolved in all instances without treatment. Clinical examination of the temporomandibular joints at the time of recall evaluated mandibular movements and the presence of pain or sounds during joint function. These examinations revealed that clinical measures of mandibular movements were somewhat reduced relative to normal. All patients were free of temporomandibular joint and masticatory muscle pain during function, upon contralateral masticatory loading, and upon palpation. Fifteen percent (3/20) of the joints examined demonstrated sounds (popping or crepitation) via auscultation. Masticatory loading in the contralateral premolar region did not induce noise in any of the joints examined. Cephalometric laminagraphic radiographs were obtained of each of the twenty temporomandibular joints with the mandible in three positions; maximum intercuspation, mandibular rest position, and maximal opening. Numerous anatomic relations were quantified from these radiographs. However, only three parameters (condylar position, movement, and evidence of arthrosis) were compared to normative data available in the literature. These comparative data suggested that persons who had undergone orthodontic treatment in conjunction with superior maxillary repositioning demonstrated (1) a relatively retropositional condyle within the fossa and (2) reduced condylar movement during maximal mandibular opening. Two of twenty temporomandibular joints demonstrated radiographic evidence of arthrosis; one condyle demonstrated articular surface erosions, and another exhibited articular surface sclerosis. The overall incidence of arthrosis was not much greater than normal, with 20 percent (4/20) of the joints demonstrating a reduced interarticular joint space. Overall, the clinical findings revealed a low incidence of pathologic masticatory muscle and temporomandibular joint symptoms and signs compared to normative data in the literature...

Adolescent↗