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PubMed1992

The effects of zygomatic complex fracture on masseteric muscle force.

The masseter muscle often has been implicated as a primary cause of postreduction displacement of the fractured zygomatic complex. However, this contention has never been proved. This study compared masseter muscle force in 10 male controls with that in 10 male patients who had sustained unilateral zygomaticomaxillary complex (ZMC) fractures. Calculation of muscle force was based on measured bite force, electromyogram, and radiographic determination of muscle vectors. It was found that the masseter muscle in patients with ZMC fractures developed significantly less force than masseter muscle in controls. Following fracture, the masseter force slowly increased, but at 4 weeks following surgery the majority of patients were still well below control levels. The results of this study cast uncertainty on the role of the masseter muscle in postreduction displacement of the fractured ZMC.

Adult↗
PubMed1995

Temporomandibular joint injury potential imposed by the low-velocity extension-flexion maneuver.

PURPOSE: It has been proposed that significant temporomandibular joint injury can occur as a result of rapid extension-flexion motion of the neck (whip-lash). This motion, which is experienced by passengers in vehicles that undergo rear-end collisions, has been described as causing rapid protrusion and opening of the mandible. It has been speculated that this relative motion between the mandible and the cranium produces forces at the temporomandibular joint (TMJ) that injure the articular elements. The objective of this study was to measure these forces by an experimental method. MATERIALS AND METHODS: Accelerometer sensor and high-speed cinematographic data were obtained from the kinematic responses of live human test subjects positioned as occupants in motor vehicles that underwent staged low-velocity rear-end collisions. Linear and moment forces generated at the TMJs were obtained from the resultant acceleration pulse at the craniomandibular complex, estimation of the mass properties of the mandible and its appended soft tissues, and the application of Newton's Second Law of motion. RESULTS: The maximum linear forces generated at the TMJ in a rear-end collision resulting in a velocity change of the test subject of 8 km/h (5 mph) were in the 7 to 10 N (1.6 to 2.2 lb) range. Moment forces at the joint peaked briefly at 0.55 N.m (4.81 lb-in). CONCLUSIONS: These force magnitudes generated at the TMJ constitute a minor fraction of the forces experienced at the joint during normal physiologic function. It is a conclusion of this study that injuries to the TMJ attributed to low-velocity "whiplash" cannot be accounted for by the joint forces produced by this maneuver.

Acceleration↗
PubMed2006

Functional significance of strain distribution in the human mandible under masticatory load: numerical predictions.

A common feature of studies of mandibular morphology is the assumption that there is some functional relation between the form of the lower jaw and masticatory stress. It was noted that the local variation in cortical bone thickness in the mandibular corpus appears to be stereotypical among anthropoids. This occurs at sections under the molars, where the lingual cortical plate is thinner than buccal one. In this study we investigate and contrast the strain pattern along buccal and lingual surfaces of the mandibular corpus during mastication using a numerical model of a human mandible. We show that strain distribution differs in alveolar and mid-corpus segments of the mandible and that the latter develops an alternate pattern between the buccal and lingual aspects of the working and balancing sides of the jaw. We then relate the magnitude of these strains to Frost's mechanostat. Our results suggest that the cortical asymmetry of the human mandible is in fact not related to strain patterns generated during mastication.

Adult↗
PubMed1999

Variations in human masseter and temporalis muscle activity related to food texture during free and side-imposed mastication.

Adjustments of mastication to food texture have been examined in various studies, but the notion of food texture is often ill defined and usually assessed in terms of hardness. The goal of this study was to examine the pattern of activity in masseter and temporalis muscles during mastication of different food samples with known textural properties and to determine the interindividual variability. Electromyograms were recorded from the right and left masseter and temporalis muscles in 36 young adults during 'free-style' and side-imposed mastication. Five different types of food with known rheological properties were used. Both temporalis and masseter activity increased with increased stress at maximum strain of the chewed samples. A power function optimally described the relation between muscle work per chew and the mechanical measurements of food; this confirmed that the masticatory process is adjusted to accommodate to food texture. Temporalis muscle activity was more influenced by food texture than was masseter muscle activity. Less muscle work was needed to prepare the food bolus for swallowing during free-style mastication. However, 25% of the participants showed no differences between unilateral side-imposed mastication and 'free-style', suggesting that they might have greater chewing efficiency on one side.

Adult↗
PubMed1995

The ultrasonic value of local muscle hypertrophy in patients with temporomandibular joint disorders.

Muscle pain and tenderness on palpation are two common symptoms in patients with temporomandibular joint disorders. Examination of the masticatory muscles is largely restricted to the use of electromyography. The technique of ultrasonography in the diagnosis of muscle hypertrophy in patients with temporomandibular joint disorders was investigated. The results of the study indicate that ultrasonography may be beneficial to locate affected muscles that do not exhibit symptoms of tenderness on palpation and thereby give hints for treatment planning.

Adult↗
PubMedDate not supplied

Botulinum-A toxin in the treatment of craniocervical muscle spasms: short- and long-term, local and systemic effects.

Botulinum toxin has become the initial treatment of choice for the management of essential blepharospasm, hemifacial spasm and other craniocervical dystonias. Numerous studies have confirmed a 90% to 95% response rate. Although a number of common side effects have been reported, the occurrence and incidence of rare local complications remains poorly understood. More importantly, the acute and chronic distant effects of botulinum toxin have not been clearly elucidated. A better understanding of such effects is essential if clinicians are to appropriately advise patients on the use of this therapeutic modality. This article is based on the Duke University experience in the management of over 500 patients with craniocervical spasm disorders, combined with a review of the published literature. These disorders include essential blepharospasm, oromandibular dystonia, hemifacial spasm, and torticollis. The incidence of side effects following more than 6000 treatments with botulinum toxin is presented. Pertinent research relating to the causes of these complications is also reviewed. The most common complications of treatment with botulinum toxin are related to acute local effects resulting from chemodenervation. The most important clinical effect in this group is weakening of the levator muscle resulting in ptosis, and the corneal consequences of lagophthalmos. The latter includes exposure keratitis, dry eyes, blurred vision, and hypersecretion epiphora. Less common local effects include facial numbness, diplopia, and ectropion. Some distant effects are being observed with increasing frequency. These include pruritus, dysphagia, nausea, and a flu-like syndrome. Most significant, however, are the rare reports of generalized weakness and the documentation of EMG abnormalities distant to the site of toxin injection. This has been seen with injections for both blepharospasm and torticollis. Until further studies on the long-term distant complications of botulinum toxin are available, it is recommended that patients receive as few life-time doses of toxin as possible, consistent with adequate management of their spasms. The practice of reinjecting patients routinely every three months, or at the first return of mild spasms should be discouraged.

Blepharospasm↗
PubMed2003

Treatment of migraine headache with botulinum toxin type A.

Migraine is a common headache disorder with profound implications on patients' quality of life and the overall health care system. Traditional treatment options have been less than optimal and many migraine patients lack confidence in over-the-counter and prescribed medications. BTX-A has shown promise as an efficacious, well-tolerated, long-lasting preventive therapy. Completed placebo-controlled trials showed that BTX-A injections for migraine resulted in fewer headaches, reduced headache severity and duration, reduced migraine-associated symptoms, and reduced use of migraine medications. Because the administration of BTX-A is nonsystemic, reported adverse events have been rare and mild. Larger trials are currently underway to further evaluate BTX-A efficacy and to determine optimal dosing and injection sites. Based on the collective experience of clinicians in neurology, facial plastic surgery, and otolaryngology, as well as supporting evidence from completed and ongoing clinical trials and theorized mechanism of action, an effective BTX-A approach for treatment of migraine is emerging. With further refinement to its use as prophylactic therapy, BTX-A can potentially be a primary option for candidate migraine sufferers and prescribing clinicians.

Botulinum Toxins, Type A↗
PubMed2004

Case report: Myxoma of the temporalis muscle.

Intramuscular myxomas of the head and neck are rare entities. Primarily found in the myocardium, these lesions also affect the bones and soft tissues. We present a case of an intramuscular myxoma of the temporalis muscle. After reviewing the literature, this case constitutes, to our knowledge, the second reported occurrence of a myxoma in this specific location. The patient was treated for this condition with an excisional biopsy after fine needle aspiration revealed a benign process. No recurrence was seen 18 months after the excision.

Adult↗
PubMed2000

Neuromuscular and skeletal adaptations following mandibular forward positioning induced by the Herbst appliance.

The purpose of this study was to examine neuromuscular and skeletal adaptations to changes in sagittal jaw relationships induced by the Herbst appliance. Six patients (age, 9 years and 5 months to 11 years and 2 months) with Angle Class II, division 1 malocclusions were studied longitudinally. The structural changes were determined by analyzing serial lateral cephalograms. Electromyographic recordings of specific masticatory muscles were used to evaluate neuromuscular adaptations. Similar cephalometric changes were observed in all patients. In all patients, lateral pterygoid muscle activity increased immediately after insertion of the appliance, but the activity decreased markedly after 4 to 6 months of treatment. In 4 of the 6 patients studied, however, the condyles were located in a slightly more downward and forward position. These findings indicate that the adaptation of muscular function occurs within a relatively short period and precedes the compensatory morphological changes produced through functional appliance therapy.

Adaptation, Physiological↗
PubMed2005

Modulation of masticatory muscle activity by tongue position.

The purpose of this study was to test whether the tongue position affects the electromyographic (EMG) activities of masticatory muscles. We recorded the EMG activities of the masseter and anterior temporalis muscles in 10 skeletal Class I adults. Tongue position was monitored by two pressure transducers embedded in the midpalatal region and the lingual flange of a custom-made acrylic monoblock. We instructed subjects to assume three different tongue positions: rest, superior, and anterior. Friedman's test and Sheffe's F-test were used to statistically examine differences in muscle activities induced by changes in tongue position. Significant differences were found in masseter muscle activity between the rest and anterior positions and in anterior temporalis muscle activity between the rest and both the anterior and the superior tongue positions. We concluded that masticatory muscle activity is affected by tongue position.

Adult↗
PubMed2003

Effects of interocclusal appliances on EMG activity during parafunctional tooth contact.

To test the hypothesis that a flat plane interocclusal appliance affects the electromyographic (EMG) activity of the temporalis and masseter muscles in pain-free individuals, maxillary splints were fabricated for 20 individuals who reported no history, signs or symptoms of myofascial pain or arthralgia as determined by two trained, independent examiners. Subjects were instructed to establish light tooth contact, maximum clenching, and moderate clenching with/without the splint in place (as determined by random assignment) while EMG data from the left and right temporalis and masseter muscles were recorded. A 5-min biofeedback training session to relax the masticatory muscles was followed by a repetition of the tooth contact/clenching tasks with/without the splint in place. With the splint in place, the activity of the temporalis muscles decreased for all tasks, significantly for the left and right temporalis under maximal clenching and for the right temporalis under moderate clenching. In contrast, the activity of the masseter muscles increased under light and moderate clenching (significantly for the left masseter under moderate clenching) and decreased slightly under maximal clenching. The effectiveness of interocclusal appliances may be due to mechanisms other than redistribution of adverse loading.

Bruxism↗
PubMed1992

Evaluation of pressure pain threshold in head and neck muscles by electronic algometer: intrarater and interrater reliability.

Using a new electronic algometer, the mean values and standard deviations of pressure pain threshold and the intrarater and interrater reliability were evaluated on 13 muscles of the human head and neck region. The subjects were 40 healthy individuals, 21 females and 19 males. A comparison with data obtained from contralateral muscles failed to demonstrate significant differences. Statistically significant correlation coefficients were obtained from the values of intra-examiners and inter-examiners in all muscles except the medial pterygoid and middle sternocleidomastoid muscle in male subjects (p < 0.05). This study showed that the electronic algometer could be recommended for evaluation of the pressure pain threshold of human head and neck muscles in clinical and experimental studies.

Adult↗
PubMed1980

Some subjective-experiential parameters of experimental tooth clenching in children.

Twelve children, aged 9--14 years, exercised maximal voluntary tooth clenching until facial pains were experienced and could no longer be endured. The pains were localized in the masseter and temporalis muscles and, occasionally, in the supra-orbital region. After onset of clenching pains appeared, on average, in 49 s (pain threshold) and they could, on average, be endured for 118 s (pain tolerance). The pain threshold varied significantly between individuals, but not within individuals. The number of pain sites, and the number of teeth in contact during clenching, did not determine the moment of onset of pains, nor the ability to endure pains. The pain tolerance did not seem to be influenced by the pain threshold.

Adolescent↗