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PubMed1997

[Sternocleidomastoid-mandibular interaction and the rest position].

BACKGROUND: The aim of this study was to evaluate the functional role of the interaction between the sternocleidomastoid muscles and the mandibular corners (ISM) in the context of the stomatognathic apparatus. METHODS: Registrations were effected about opening and closing movements of the mandible from the rest position with two different postures of the head. For the evaluations four volunteer subjects unaffected by functional anomalies of stomatognathic apparatus were selected. RESULTS: The resulting graphics allowed the elaboration of a theory about the way of setting up the mandibular rest position. The interactions between the sternocleidomastoid muscles and mandibular corners might be the supports where the strengths, which work on the mandible to avoid any stresses to masticatory muscles, are spread. The knowledge of determining factors for the rest position is considered basic for both diagnosis and rehabilitation purposes. CONCLUSIONS: Furthermore this study allows us to explain the already known relationships between the stomatognathic apparatus and cervical rachis with a new method.

Adolescent↗
PubMed2004

Dynamic reconstruction of eye closure by muscle transposition or functional muscle transplantation in facial palsy.

For patients with facial palsy, lagophthalmus is often a more serious problem than the inability to smile. Dynamic reconstruction of eye closure by muscle transposition or by free functional muscle transplantation offers a good solution for regaining near-normal eye protection without the need for implants. This is the first quantitative study of three-dimensional preoperative and postoperative lid movements in patients treated for facial paralysis. Between February of 1998 and April of 2002, 44 patients were treated for facial palsy, including reconstruction of eye closure. Temporalis muscle transposition to the eye was used in 34 cases, and a regionally differentiated part of a free gracilis muscle transplant after double cross-face nerve grafting was used in 10 cases. Patients' facial movements were documented by a three-dimensional video analysis system preoperatively and 6, 12, 18, and 24 months postoperatively. For this comparative study, only the data of patients with preoperative and 12-month postoperative measurements were included. In the 27 patients with a final result after temporalis muscle transposition for eye closure, the distance between the upper and lower eyelid points during eye closing (as for sleep) was reduced from 10.33 +/- 2.43 mm (mean +/- SD) preoperatively to 5.84 +/- 4.34 mm postoperatively on the paralyzed side, compared with 0.0 +/- 0.0 mm preoperatively and postoperatively on the contralateral healthy side. In the resting position, preoperative values for the paralyzed side changed from 15.11 +/- 1.92 mm preoperatively to 13.46 +/- 1.94 mm postoperatively, compared with 12.17 +/- 2.02 mm preoperatively and 12.05 +/- 1.95 mm postoperatively on the healthy side. In the nine patients with a final result after surgery using a part of the free gracilis muscle transplant reinnervated by a zygomatic branch of the contralateral healthy side through a cross-face nerve graft, eyelid closure changed from 10.21 +/- 2.72 mm to 1.68 +/- 1.35 mm, compared with 13.70 +/- 1.56 mm to 6.63 +/- 1.51 mm preoperatively. The average closure for the healthy side was from 11.20 +/- 3.11 mm to 0.0 +/- 0.0 mm preoperatively and from 12.70 +/- 1.95 mm to 0.0 +/- 0.0 mm postoperatively. In three cases, the resting tonus of the part of the gracilis muscle transplant around the eye had increased to an extent that muscle weakening became necessary. Temporalis muscle transposition and free functional muscle transplantation for reanimation of the eye and mouth at the same time are reliable methods for reconstructing eye closure, with clinically adequate results. Detailed analysis of the resulting facial movements led to an important improvement of the authors' operative techniques within the last few years. Thus, the number of secondary operative corrections could be significantly reduced. These qualitative and quantitative studies of the reconstructed lid movements by three-dimensional video analysis support the authors' clinical concept of temporalis muscle transposition being the first-choice method in adult patients with facial palsy. In children, free muscle transplantation is preferred for eye closure, so as not to interfere with the growth of the face by transposition of a masticatory muscle. In addition, a higher degree of central plasticity in children might be expected.

Adolescent↗
PubMed2002

Reperfusion response changes induced by repeated, sustained contractions in normal human masseter muscle.

The purpose was to evaluate the intramuscular reperfusion response characteristics associated with repeated isometric contractions in normal human masseter. Intramuscular blood volume was quantified with a near-infrared spectroscopic device that measured the total haemoglobin (Hb) concentration in the muscle. Electromyographic (EMG) activity from the masseter and total bite forces were also recorded. Sixteen healthy volunteers, eight females and eight males, without masticatory muscle pain participated. They were asked first to clench their teeth for as long as possible at 50% of their maximum voluntary contraction (MVC). This was followed by a 60s rest and then immediately by a standard clenching task (50% MVC for 30s) and a 60s recovery period, immediately after which they were asked to repeat exactly the same procedure, with a final 5 min recovery period after the second 30s contraction. Bite force, EMG and Hb concentration were measured continuously and the duration of the two endurance tasks and the amplitudes of all recorded signals were compared (first trial versus second trial). Specifically, the difference between the lowest Hb (trough) seen during the standardised 30s contractions and the highest (peak) seen just after them was assessed. The trough-to-peak difference in Hb concentration of the second standard contraction task was significantly smaller than that of the first standard task (P<0.05, paired t-test). These data show that with sustained effort the post-contraction vasodilatory reperfusion responses of the human masseter are diminished, suggesting a progressive desensitisation of the vasodilatory system.

Adult↗
PubMed1998

Neurotrophin-3 and trkC in muscle are non-essential for the development of mouse muscle spindles.

Neurotrophin-3 (NT3) or TrkC null mutant mice were examined for the presence of muscle spindles. Muscles of mastication, but not limbs, contained spindles in newborn and adolescent mutants. The intramuscular distribution and morphological properties of spindles in mutant masticatory muscles were indistinguishable from those of wild-type spindles. Intrafusal fibers of NT3- or trkC-deficient spindles-expressed the slow-tonic isoform of myosin heavy chains, characteristic of wild-type spindles. Sensory nerve endings were observed in spindles of mutants by electron microscopy. Thus, NT3 or trkC, which is expressed in wild-type spindles, may serve functions other than those related to spindle assembly. Presumably, proprioceptive neurons innervating jaw muscles are dependent on factors other than NT3 for survival and maintenance.

Animals↗
PubMed1980

An electromyographic study of masticatory and lip muscle function in patients with complete dentures.

The activity of the anterior and posterior portions of the temporal muscle, of the masseter muscle, and of the upper and lower lips was studied with electromyography in 10 individuals with complete dentures. Recordings were made when the patients had old, ill-fitting dentures and 6 months after these were replaced with new dentures. The muscle activity was studied in the postural position of the mandible, during chewing and swallowing of three test foods, and during maximal biting. The maximal tooth tapping rate was also recorded. The postural muscle activity was the same with old and new dentures and comparable with that in patients with natural teeth. The muscle activity during maximal biting was markedly lower than in patients with natural teeth and lower with new than with old dentures. There was no difference in muscle activity between chewing with old and new dentures, but the activity was lower than in patients with natural teeth. This was not compensated for by a longer duration of chewing. The lips were not especially active during chewing in the complete denture wearers.

Aged↗
PubMed2003

Temporal relationship of muscle weakness and pain reduction in subjects treated with botulinum toxin A.

Botulinum toxin A has demonstrated efficacy in relieving pain in spastic and nonspastic muscle conditions. This analgesic property has generally been attributed to muscular relaxation. This study demonstrates initial muscular relaxation and concomitant pain relief in a masticatory muscle model. However, as muscle power returns to normal, pain relief is still very evident. This result suggests that the analgesic effect attributed to botulinum toxin is more complex than simple muscular relaxation.

Adolescent↗
PubMed1993

Histochemical characterization of pig masseter muscle: an animal model.

Masseter muscle autopsies were obtained from six different areas of six pigs. The autopsies were stained for the demonstration of myosin ATPase activity by means of a conventional histochemical technique. As compared with human masseter, the pig masseter muscle contained more type II fibers. But, like the human masseter, the pig muscle had a varying distribution of fiber types in the different autopsy areas, a distribution which might be the result of an adaptation to carry out special functions such as chewing, swallowing, and jaw posture. The fiber type distribution in the pig masseter also varied among individuals, probably reflecting various levels of utilization of the muscles besides different genetic influences. Moreover, pig masseter contained fibers of intermediate staining intensity (IM fibers), a fiber type rarely seen except in human masticatory muscles. In conclusion, we consider the pig masseter to be a useful animal model to study muscular adaptations to altered function in the orofacial region.

Adenosine Triphosphatases↗
PubMed2003

Activation of peripheral NMDA receptors contributes to human pain and rat afferent discharges evoked by injection of glutamate into the masseter muscle.

Peripheral N-methyl-d-aspartate (NMDA) receptors are found in deep tissues and may play a role in deep tissue pain. Injection of the endogenous NMDA receptor agonist glutamate into the masseter muscle excites deep craniofacial afferent fibers in rats and evokes pain in human subjects. It is not clear whether peripheral NMDA receptors play a role in these effects of glutamate. Accordingly, the effect of NMDA on afferent activity as well as the effect of locally administered NMDA receptor antagonists on glutamate-evoked afferent discharges in acutely anesthetized rats and muscle pain in human subjects was examined. Injection of NMDA into the masseter muscle evoked afferent discharges in a concentration-related manner. It was found that the NMDA receptor antagonists 2-amino-5-phosphonvalerate (APV, 10 mM), ketamine (10 mM), and dextromethorphan (40 mM) significantly decreased glutamate-evoked afferent discharges. The effects of APV and ketamine, but not dextromethorphan, were selective for glutamate-evoked afferent discharges and did not affect hypertonic saline-evoked afferent discharges. In human experiments, it was found that 10 mM ketamine decreased glutamate-evoked muscle pain but had no effect on hypertonic saline-evoked muscle pain. These results indicate that injection of glutamate into the masseter muscle evokes afferent discharges in rats and muscle pain in humans in part through activation of peripheral NMDA receptors. It is conceivable that activation of peripheral NMDA receptors may contribute to masticatory muscle pain and that peripherally acting NMDA receptor antagonists could prove to be effective analgesics for this type of pain.

Adult↗
PubMed1998

[Botulinum toxin treatment of neurogenic dislocation of the temporomandibular joint].

Botulinum toxin leads to paresis of the skeletal muscle lasting 2-4 months via an inhibition of acetylcholine release at the neuromuscular junction. Since 1995, botulinum toxin injections have been used in the treatment of recurrent dislocation of the temporomandibular joint (TMJ). The chemical denervation of the external pterygoid muscle restricts the angle of mouth opening, thus helping to prevent dislocation. TMJ dislocations that occur as a result of increased tone in the protracted masticatory muscles were recently defined as neurogenic dislocations of the TMJ. We conducted a clinical study to investigate the efficacy of botulinum toxin injections into the external pterygoid muscle in five patients with recurrent neurogenic dislocations of the TMJ. In the 3 months prior to the first treatment, the patients had suffered a total of 19 dislocations. In the 3-month period following the initial treatment, only one woman experienced a dislocation. We performed the treatment a total of 25 times. Five dislocations occurred during the 6- to 36-month observation period. In the meantime, two patients remain recurrence-free 1 year after receiving treatment. All the patients had a restricted ability to open their mouths as a side effect of the weakening of the external pterygoid muscle that was completely reversible over the course of 3-4 months. All other side effects were equally well-tolerated by the patients and fully reversible after 3 weeks at the most. In the two patients who remain recurrence-free without any further treatment, the increased tone of the muscles serving the jaw normalised spontaneously over the course of the underlying neurological disease. Our results show that, in the treatment of recurrent neurogenic dislocations of the TMJ, botulinum toxin injections represent a therapeutic alternative that has few side effects.

Adult↗
PubMed2003

The effect of unilateral partial edentulism to muscle thickness.

OBJECTIVE: Teeth and muscles play a very important role for occlusal equilibrium and function. When tooth loss begins, it may also affect the function of the muscle tissues. METHODS: The thickness of the masseter and anterior temporalis muscles were measured bilaterally in 30 healthy fully dentate adults and in 30 unilateral edentulous patients by using ultrasonographic imaging. All scans were carried out by the same radiologist to eliminate the inter-observer difference, using a real time scanner (Toshiba SSA- 270 A Japan). A 7.5 MHz linear transducer was used. The transducer was held against the cheek with light pressure. The effect of age, sex, duration of the partial edentulism, unilateral chewing habits of the individuals to the muscle thickness were also evaluated. In all subjects, facial proportion index was also determined. RESULTS: No study has been found in the literature concerning the masticatory muscle thickness in unilateral partial edentulous patients. Therefore, the main purpose of this study was to compare and establish the differences of the muscle thicknesses between dentate and edentulous sides in unilateral partial edentulous patients with ultrasonography and to test whether the variation in the thickness of the muscle is related to the variation in the facial morphology using the facial proportional indices in the study groups. In the present study, ultrasonography revealed a large variation in the thicknesses of the masseter and temporalis muscles in experimental and control groups, during both relaxed and contracted conditions. The thicknesses of the muscles in females during both relaxed and contracted conditions were less than those in males in both control and experimental groups. In experimental group, a high negative correlation was found between the thickness of the masseter muscle and Facial proportion Index (FPI) in females, however, the statistical analysis showed no significant difference in males. Also, a high negative correlation was found in control group, especially in females. There was no statistically significant relationship between thicknesses of the muscles and age of the subjects in both groups. There was no statistically significant relationship between unilateral chewing habits and muscle thickness. In this study, the duration of partial edentulism did not affect the thickness of the muscles. CONCLUSION: Further research is required to study muscular atrophy for comparison with total edentulism.

Adult↗
PubMed2002

Ultrastructural abnormalities of muscle spindles in the rat masseter muscle with malocclusion-induced damage.

Human temporomandibular disorders due to disturbed occlusal mechanics are characterized by sensory, motor and autonomic symptoms, possibly related to muscle overwork and fatigue. Our previous study in rats with experimentally-induced malocclusion due to unilateral molar cusp amputation showed that the ipsilateral masseter muscles undergo morphological and biochemical changes consistent with muscle hypercontraction and ischemia. In the present study, the masseter muscle spindles of the same malocclusion-bearing rats were examined by electron microscopy. Sham-operated rats were used as controls. In the treated rats, clear-cut alterations of the muscle spindles were observed 26 days after surgery, when the extrafusal muscle showed the more severe damage. The fusal alterations affected predominantly capsular cells, intrafusal muscle fibers and sensory nerve endings. These results suggest that in the malocclusion-bearing rats, an abnormal reflex regulation of the motor activity of the masticatory muscles may take place. They also allow us to hypothesize that muscle spindle alterations might be involved in the pathogenesis of human temporomandibular disorders.

Animals↗
PubMed1997

Motor activity in sleep bruxism with concomitant jaw muscle pain. A retrospective pilot study.

In a controlled polysomnographic (PSG) study that we recently performed in our laboratory, we noticed that some patients with a chief complaint of sleep bruxism reported concomitant non-myofascial pain in their masticatory muscles. To study the influence of such pain on the pattern of bruxism motor activity, we re-assessed the 2nd out of 2 consecutive PSG and masseter electromyographic (EMG) recordings of 7 bruxers without pain and 6 bruxers with concomitant jaw muscle pain. Among others, the selection of these patients was based on reports of current jaw muscle pain intensity, using 100-mm visual analogue scales. In our sample of bruxism patients with pain, levels of pain intensity did not differ significantly between bedtime and awakening in the morning. Although there were no significant differences between both subgroups of bruxers in the number of bruxism bursts per episode and the root-mean-squared EMG level per bruxism burst, bruxers with pain had 40% less bruxism episodes per hour of sleep. This suggests that non-myofascial jaw muscle pain decreases the number of initiations of bruxism episodes, but leaves their contents unaffected.

Adult↗
PubMedDate not supplied

Congenital ocular aberrant innervation--new concepts.

BACKGROUND: We have the impression that congenital aberrant innervations are more common than previously reported. Many varieties exist and typically involve the sixth nerve. The most common ocular miswirings are Duane's syndrome and Marcus Gunn jaw-winking ptosis. The second most common miswiring involves lateral rectus activation in upgaze causing a "Y" pattern exotropia (pseudo inferior oblique overaction). This commonly is confused with inferior oblique overaction but surgery on the obliques does not cure the condition. Lateral rectus recession and elevation are required. METHODS: We selected demonstrative cases from our practices to illustrate a variety of congenital aberrant innervations. A literature search for previous reported cases of aberrant innervations was performed. This report is an eclectic collection of observations of individual selected cases. RESULTS: We found aberrant innervations of unusual varieties. These miswirings involve simultaneous firing of the lateral rectus with other muscles, including: the ipsilateral superior rectus, causing "pseudo inferior oblique overaction"; the contralateral lateral rectus, causing synergistic divergence; the ipsilateral superior rectus, in upward saccades only; and the masticatory muscles, causing exotropia with sucking. The third nerve by itself rarely is involved in congenital miswirings, but commonly shows aberrant regeneration after traumatic injuries. We know of no cases of aberrant innervation involving the fourth nerve. SUMMARY: We present cases describing these congenital aberrant innervations and discuss a unifying hypothesis as to their typical involvement of the sixth nerve.

Blepharoptosis↗
PubMed2002

Inflammatory myopathies.

Inflammatory myopathies are the result of infiltration of inflammatory cells into striated muscle, with or without an association with an underlying cause. Two broad classifications are IIMs and secondary inflammatory myopathies associated with other diseases. Standard diagnostic criteria for inflammatory myopathy include the presence of weakness or loss of specific muscle group function, an increase in CK, EMG changes associated with muscle membrane instability, and histologic evidence of inflammation. Not all these criteria, however, must be present. Fresh-frozen biopsy from two proximal muscles is recommended for biopsy confirmation. IIM can either focally affect head or neck muscles or be more diffuse. MMM is an immune-mediated disease characterized by a humoral antibody produced against the unique type IIM and type I variant mvofibers of masticatory muscles of dogs, which causes inflammation and loss of function of the muscles of mastication. Idiopathic polymyositis can affect focal muscle groups (extraocular, laryngeal) or present as multifocal or diffuse involvement of skeletal muscle in the cat and dog. Familial canine DM is an inflammatory disease of the striated muscle, skin, and vasculature in young Collies, Shetland Sheepdogs (Shelties), and, rarely, Collie-crossbred dogs. Immunosuppressive therapy is the key to successful treatment. Protozoal parasitic myopathies are the most common cause of clinically relevant secondary inflammatory myopathies. The degree of systemic involvement is often the limiting factor to successful treatment. Early recognition of the clinical signs for proper diagnostic testing and institution of appropriate therapy can result in a rewarding outcome in treating inflammatory myopathies in the cat and dog.

Animals↗
PubMed2002

[Maximal isometric bite force and sports. Preliminary study].

INTRODUCTION: The evaluation of the bite forces coupled with EMG activity of masseter muscles allows to point out temporo-mandibular joint disorders. The intense practice of sports induces stress which may affect the mandibular statics, due to an hyperfunction of the elevator masticatory muscles, especially the masseter muscles. This concept has led us to compare the maximum isometric bite forces of sedentary and physically trained subjects. MATERIAL AND METHODS: The aim of this experimentation is to study the maximum isometric bite forces of the premolars, with a force transducer, for two groups of physically trained and sedentary volunteers (25 subjects), with distinction between male and female subjects. Subjects with normal denture and no temporo-mandibular joint disorder were retained. EMG and force recording were synchronized and recorded during 10 seconds of maximal contraction. RESULTS: The male subjects developed a maximal bite-force significantly higher (p < 0.05) compared to the female subjects. There is no significant difference between subjects practising a sport (at least 6 hours a week) and sedentary ones. The evolution of force during the contraction is different between sexes. EMG activity allowed to control that subjects developed a maximal force and an increase in muscular fatigability of physically active females compared to sedentary ones was noticed. DISCUSSION: The difference of maximal force between men and women is similar to the one found for the locomotor muscles. The analysis of the evolution of the force according to the contraction duration, might be linked to a different distribution of muscular fibers according to the sex. The practice of a sport might increase the fatigability of the masseter muscles and might be a factor inducing a muscular imbalance of the mandibular posture. But the relatively low number of subjects and the absence of well defined distinctions between different kinds of sport limit our conclusions.

Adult↗