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PubMed2005

Successful treatment of a postpolio tinnitus with type a botulinum toxin.

OBJECTIVES/HYPOTHESIS: Objective tinnitus is a symptom often observed in patients with chronic hyperactivity of masticatory muscles. METHODS: We report here the unusual case of a 63-year-old woman who developed a distressing tinnitus related to contractions of reinnervated masticatory muscles. This reinnervation process was caused by a postpolio syndrome that gave rise to an acoustic resonance phenomenon transmitted to the middle ear as an audible sound. RESULTS: The tinnitus was successfully treated with electromyography-guided intramuscular injections of type A botulinum toxin. CONCLUSION: The intramuscular injection of botulinum toxin was found to be effective in relieving severe and disabling postpolio tinnitus.

Botulinum Toxins, Type A↗
PubMed1996

Masseter muscle thickness in growing individuals and its relation to facial morphology.

It is widely accepted that an interaction exists between masticatory muscle function and craniofacial growth. In adults, correlations have been found between facial dimensions and jaw-muscle cross-sectional area, and between facial dimensions and masseter muscle thickness. Little is known about growth of the human masticatory muscles and its relation with facial dimensions at different ages. In 329 Greek individuals, aged 7-22 yr, masseter muscle thickness was measured by ultrasonography. Muscle thickness was related to age, stature and weight, and to facial dimensions, measured by means of anthropological calipers. Muscle thickness was statistically assessed by univariate analysis of variance, after the males and females had been divided into three age groups. Facial dimensions were assessed by multivariate analysis of variance, age being considered as a covariate. The relation between muscle thickness and facial dimensions was subjected to stepwise multiple regression analysis. Masseter muscle thickness increased with age in both sexes. No differences were found between the left- and right-hand side. For each age group (and corrected for stature and weight), males had significantly thicker masseters than females (p < 0.01). Variation in muscle size and facial dimensions mainly coincided with variation in age, stature and weight. Apart from these, muscle thickness showed a significantly negative relation with anterior facial height and mandibular length, and a significantly positive relation with intergonial width and bizygomatic facial width.

Adolescent↗
PubMed2006

Dietary consistency and plasticity of masseter fiber architecture in postweaning rabbits.

Dietary consistency has been shown to influence cross-sectional area and fiber type composition of the masticatory muscles. However, little is known about the effects of dietary consistency on masticatory muscle fiber architecture. In this study, we explore the effects of dietary consistency on the internal architecture of rabbit masseter muscle. Because activity patterns of the rabbit chewing muscles show inter- and intramuscular heterogeneity, we evaluate if alterations in fiber architecture are homogeneous across various portions of the superficial masseter muscle. We compared masseter muscle fiber architecture between two groups of weanling rabbits raised on different diets for 105 days. One group was raised on a diet of ground rabbit pellets to model underuse of the masticatory complex, while the other group was fed a diet of intact pellets and hay blocks to model an overuse diet. In all portions of the superficial masseter, physiological cross-sectional areas (PCSAs) are greater in the overuse compared to underuse diet rabbits. Thus, the mechanical demands for larger muscle and bite forces associated with early and prolonged exposure to a tough diet are met by an increase in PCSA of the superficial masseter. The larger PCSA is due entirely to increased muscle mass, as the two rabbit groups show no differences in either fiber length or angle of pinnation. Thus, increasing pinnation angle is not a necessary biomechanical solution to improving muscle and bite force during growth. The change in PCSA but not fiber length suggests that variation in dietary consistency has an impact on maximum force production but not necessarily on excursion or contraction velocity.

Adaptation, Physiological↗
PubMedDate not supplied

Correlation between interdental occlusal plane and plantar arches. An EMG study.

The Authors carried out an experimental study on a homogeneous group of young people to provide evidence of functional correlation among masticatory muscles and, indirectly, between changes to the interdental occlusal plane and modifications of the plantar arches due to talipes valgus and flat foot. In the two analysed conditions, the masticatory muscles undergo different functional alterations. This is due to the fact that the mechanoreceptors in the tendons of the muscles governing the plantar arch configuration are stimulated in different ways during the activation of long osteoarthromuscular chains. Dental specialists will have to take these correlation into account when diagnosing TMJ disorders.

Adult↗
PubMed2006

Mandibular mechanics after osteotomy and distraction appliance placement I: Postoperative mobility of the osteotomy site.

PURPOSE: Fixation at the osteotomy site for mandibular distraction osteogenesis (DO) is probably not rigid, especially during mastication. Micromotion may affect the course of DO. This study aimed to measure the mobility of the fresh distractor-fixed osteotomy site in response to mastication and masticatory muscle stimulation. MATERIALS AND METHODS: Twenty-eight domestic pigs, 6 to 8 weeks old, underwent osteotomy of the right mandible and placement of a distractor appliance. Immediately after surgery, displacement at 3 different locations (superior-lateral, inferior-lateral, and inferior-medial) of the osteotomy site was assessed using ultrasound piezoelectric crystals or differential variable reluctance transducers (DVRTs). The amount of lengthening or shortening at each location was measured during mastication and muscle stimulation. Displacement was also measured for bilateral osteotomy during muscle stimulation from a subgroup of 12 pigs. RESULTS: The osteotomy site demonstrated significant mobility during power strokes of mastication with an average magnitude of 0.3 to 0.4 mm. Distinct patterns of displacement were associated with different locations, and the patterns varied between chewing sides. The most common pattern was lengthening at the superior-lateral and shortening at both inferior sites. Similar amounts of displacement were observed during the stimulation of jaw-closers (masseter and medial pterygoid), but the patterns produced by these muscles did not completely explain the masticatory pattern. Opening the osteotomy to 1.5 mm did not alter the displacements observed during muscle stimulation. Bilateral osteotomy tended to decrease displacement. CONCLUSIONS: The study demonstrates that during mastication and masticatory muscle stimulation, an acute mandibular osteotomy site is mobile despite fixation by a distractor appliance.

Analysis of Variance↗
PubMed1990

Comparison of muscle weight and force ratios in New and Old World monkeys.

Thin mandibles and small incisors found in New World monkeys as compared with Old World monkeys suggest that there may be differences in craniofacial loading patterns between these two groups, particularly in levels of mandibular corpus twisting (Hylander, 1975, 1979a; Eaglen, 1984; Bouvier, 1986a,b). This study examined the hypothesis that changes in the relative force contributions of the masticatory muscles were responsible for lowering torsion on the mandibular corpus in New World monkeys. Muscle weight and physiological cross-sections were compared using data from the literature (Schumacher, 1960: Turnbull, 1970; Cachel, 1979) as well as new data on adult male Cebus apella and Macaca mulatta. Both age and sex had an effect on muscle ratios. Mixed samples such as those used by Schumacher and Turnbull probably are not appropriate for drawing conclusions concerning species or group differences in muscle ratios. In addition, biomechanical conclusions based on muscle weight ratios alone to estimate muscle force may be misleading because fiber length inversely affects the amount of force a muscle can exert. A comparison of ratios based on physiological cross-section as an estimator of muscle force in New and Old World monkeys does not support the hypothesis that alterations in force contribution by individual masticatory muscles are responsible for minimizing mandibular corpus twisting in New World monkeys. Therefore, if twisting has been minimized in New World monkeys as suggested by their thin corpora, other changes in the craniofacial musculoskeletal complex, such as different muscle recruitment or pinnation patterns, may be responsible.

Animals↗
PubMed1998

Automatic on-line one-channel recognition of masseter activity.

The etiology of myoarthropathies of the masticatory system (MAP) is not fully understood. For the hypothetical association between the myogenous pain of MAP patients and masticatory muscle overuse to be proved, functional and parafunctional behavior of the masticatory muscles should be analyzed in normal and diseased subjects. The aim of this study was to test on-line the validity and reliability of an algorithm, applied to the electromyographic signal, to recognize various oral activities. The surface electromyogram of the masseter muscle was recorded in 12 subjects (seven females and five males, from 18 to 32 years old) who performed a series of functional and parafunctional activities (chewing soft food, chewing hard food, swallowing, laughing, speaking, and tooth grinding and clenching), as well as no activity. During the computer training phase, intra-individual classification functions of a multivariate discriminant analysis were calculated while each subject performed the described activities. During the test phase, each subject repeated the same activities, and the computer continuously classified them on-line. The percentage of correctly recognized activities was calculated for each activity and for each subject. No activity, chewing hard food, swallowing, laughing, grinding, and clenching were recognized correctly > 99% of the time. Chewing soft food was recognized correctly 97% and speaking 86% of the time. The sensitivity values for the recognition rates of the complete oral activities were, with one exception, > 0.82; the specificity values were > 0.95, and the kappa-values > 0.80. These results show that the algorithm had high sensitivity, specificity, and reliability in the classification of different oral activities under laboratory conditions.

Adolescent↗
PubMed1995

Biomechanical analysis of jaw-closing movements.

This study concerns the complex interaction between active muscle forces and passive guiding structures during jaw-closing movements. It is generally accepted that the ligaments of the joint play a major role in condylar guidance during these movements. While these ligaments permit a wide range of motions, it was assumed that they are not primarily involved in force transmission in the joints. Therefore, it was hypothesized that muscle forces and movement constraints caused by the articular surfaces imply a necessary and sufficient condition to generate ordinary jaw-closing movements. This hypothesis was tested by biomechanical analysis. A dynamic six-degrees-of-freedom mathematical model of the human masticatory system has been developed for qualitative analysis of the contributions of the different masticatory muscles to jaw-closing movements, it was found that the normally observed movement, which includes a swing-slide condylar movement along the articular eminence, can be generated by various separate pairs of masticatory muscles, among which the different parts of the masseter as well as the medial pterygoid muscle appeared to be the most suitable to complete this action. The results seem to be in contrast to the general opinion that a muscle with a forward-directed force component may not be suitable for generating jaw movements in which the condyle moves backward. The results can be explained, however, by biomechanical analysis which includes not only muscle and joint forces as used in standard textbooks of anatomy, but also the torques generated by these forces.

Biomechanical Phenomena↗
PubMed2004

Developmental regulation of connexins 26, 32, 36, and 43 in trigeminal neurons.

The transition from sucking to chewing during postnatal development is accompanied by changes in masticatory muscle activity patterns. We previously demonstrated that changes in numerous parameters of chemical synapses among neurons, and intrinsic membrane properties of neurons, comprising brainstem oral-motor circuits are coincident with changes in masticatory muscle activity patterns. Considering recent findings that implicate a role for gap junctions in early locomotor and respiratory behaviors, our present study focuses on the developmental regulation of connexin proteins in trigeminal neurons as a first step in understanding a role for gap junctions in developing oral-motor circuits used for ingestive behaviors. We conducted immunohistochemistry studies to examine connexin (Cx) 26, 32, 36, and 43 expression in trigeminal motor and mesencephalic trigeminal nuclei during postnatal development at the light and electron microscopic levels. Postnatal days (P) 1, 6, 14, 21, and adult mice were used. Cx32, 36, and 43 expression was developmentally regulated in the trigeminal motor nucleus, while Cx26 expression remained high throughout postnatal development. In the mesencephalic trigeminal nucleus, Cx26, 32, and 43 expression was intense throughout development, with only Cx36 showing a developmental regulation. Ultrastructural examination of neonatal trigeminal motoneurons and mesencephalic trigeminal neurons revealed connexin expression in cell membranes, cytoplasm, and cell nuclei (Cx43, Cx32). Our results show that connexin proteins are differentially regulated between trigeminal motoneurons and mesencephalic trigeminal neurons during development, and suggest a possible role for gap junctions in the development of trigeminal neurons and the function and maturation of oral-motor circuits.

Animals↗
PubMed1987

The growth of the skull and jaw muscles and its functional consequences in the New Zealand rabbit (Oryctolagus cuniculus).

Between weaning and adulthood, the length and height of the facial skull of the New Zealand rabbit (Oryctolagus cuniculus) double, whereas much less growth occurs in the width of the face and in the neurocranium. There is a five-fold increase in mass of the masticatory muscles, caused mainly by growth in cross-sectional area. The share of the superficial masseter in the total mass increases at the cost of the jaw openers. There are changes in the direction of the working lines of a few muscles. A 3-dimensional mechanical model was used to predict bite forces at different mandibular positions. It shows that young rabbits are able to generate large bite forces at a wider range of mandibular positions than adults and that the forces are directed more vertically. In young and adult animals, the masticatory muscles differ from each other with respect to the degree of gape at which optimum sarcomere length is reached. Consequently, bite force can be maintained over a range of gapes, larger than predicted on basis of individual length-tension curves. Despite the considerable changes in skull shape and concurrent changes in the jaw muscles, the direction of the resultant force of the closing muscles and its mechanical advantage remain stable during growth. Observed phenomena suggest that during development the possibilities for generation of large bite forces are increased at the cost of a restriction of the range of jaw excursion.

Animals↗
PubMed1998

Effect of muscle relaxation splint therapy on the electromyographic activities of masseter and anterior temporalis muscles.

The purpose of this study was to compare the effectiveness of splint therapy on the electromyographic activity of masticatory muscles (anterior temporalis and masseter) before and after the application of a muscle relaxation splint. Electromyography recordings from the masseter and anterior temporalis muscles were analyzed quantitatively during maximal biting in the intercuspal position both before and after treatment without a splint. Fourteen patients whose chief complaint was masticatory muscle pain were selected for the study. After the initial evaluations muscle relaxation splints were applied, and the patients were instructed to use the splints for 6 weeks. Surface electromyographic recordings were taken from each patient before the beginning of clinical therapy and after 6 weeks of wearing the splints. The data obtained were analyzed through paired sample t tests and Wilcoxon's signed rank tests. The results of the study were as follows: (1) the electromyographic activity of the two muscles during maximal biting was not markedly changed after the muscle relaxation splint was used; and (2) the changes observed in electromyographic activity of the involved and noninvolved sides were insignificant as well.

Adult↗
PubMed1977

Differentiation of fibres in human masseter, temporal and biceps brachii muscles. A histochemical study.

Masseter, temporal and biceps brachii muscles were histochemically evaluated for fibre type differentiation on 19 aborted fetuses (gestational ages 15-23 weeks), in 2 premature infants of 34 and 36 weeks gestation and in 2 fullterm stillborn infants. There was no convincing evidence of fibre type differentiation in the masticatory muscles before 22 weeks' gestation while a fairly distinct differentiation was seen in biceps brachii specimens at 16 weeks' gestation with ATPase at pH 4.35. Around 22 weeks two types of fibre were found in all specimens with ATPase at pH 4.35. With regular ATPase (pH 9.4) there was a relatively weak difference in staining between different types of fibre in the masticatory muscles. In biceps brachii Type I and Type II were demonstrated. Neonatally 3 levels of staining were seen in biceps brachii with regular ATPase (pH 9.4); while ATPase pH 4.35 and 4.6 demonstrated the subtypes IIB and IIC. In the masticatory mucles only 2 levels were recognized with regular ATPase and all type II fibres had the characteristics of Type IIC as seen with with ATPase at pH 4.35.

Adenosine Triphosphatases↗
PubMed1999

Morphologic and biochemical changes of the masseter muscles induced by occlusal wear: studies in a rat model.

Occlusal alterations may result in changes in the functional performance of masticatory muscles. In this study, we set up an experimental model in rats to examine whether masticatory muscle abnormalities occur after a malocclusion is induced. Rats underwent unilateral amputation of the molar cusps to simulate an occlusal wear situation. The masseter muscles ipsilateral and contralateral to the amputated molars were excised at different experimental times. Sham-operated rats were used as controls. The tissue samples were studied by light and electron microscopy and morphometry. Tissue calcium content, a biochemical index of muscle injury, was also determined. The results show that occlusal dysfunction leads to microvessel constriction and clear-cut morphologic damage of muscular fibers and blood capillary endothelium, as well as to elevation of tissue calcium content, in the ipsilateral masseter muscle. These changes are likely related to muscle fatigue and ischemia. The early signs of injury do not involve the entire muscle but are mostly restricted to tissue areas rich in type I (slow) muscle fibers, which are characterized by a predominantly aerobic metabolism. The muscle damage becomes more extended and severe with time. On the other hand, the contralateral muscles show only slight alterations which are reversible with time, possibly due to an adaptive response.

Analysis of Variance↗
PubMed2001

Development of sucking behavior in infants with Down's syndrome.

UNLABELLED: The aim of this study was to gain a better understanding of the development of sucking behavior in infants with Down's syndrome. The sucking behavior of 14 infants with Down's syndrome was consecutively studied at 1, 4, 8 and 12 mo of age. They were free from complications that may cause sucking difficulty. The sucking pressure, expression pressure, frequency and duration were measured. In addition, an ultrasound study during sucking was performed in sagittal planes. Although levels of the sucking pressure and duration were in the normal range, significant development occurred with time. Ultrasonographic images showed deficiency in the smooth peristaltic tongue movement. CONCLUSION: The sucking deficiency in Down's syndrome may result from not only hypotonicity of the perioral muscles, lips and masticatory muscles, but also deficiency in the smooth tongue movement. This approach using the sucking pressure waveform and ultrasonography can help in the examination of the development of sucking behavior, intraoral movement and therapeutic effects.

Down Syndrome↗
PubMed1993

The Castillo-Morales approach to orofacial pathology in Down syndrome.

Infants with Down syndrome often present with a familiar orofacial disorder which exists at birth or becomes more pronounced by the end of the first year. The primary pathology includes hypotonicity of the perioral muscles, lips, and masticatory muscles and a protruding tongue, later followed by active tongue protrusion. This results in problems with sucking, swallowing, drooling and dentition. Early intervention methods employing the combination of Castillo-Morales Manual Orofacial Therapy and his specially designed palatal plate, can improve orofacial function, facial appearance and prevent secondary conditions like pseudoprognathism, dental diseases, malocclusions, open mouth habit and pseudomacroglossia. This retrospective study examines the outcome of therapy, as prescribed by Castillo-Morales, in 39 children with Down syndrome. Normally, the average age to begin oral therapy is between six to eight months. The children were treated with the Castillo-Morales Manual Orofacial Therapy and his palatal plate for an average of 17.9 months. In this study, clinical evaluations at the beginning and the end of therapy focused only on open mouth posture and tongue protrusion. In addition, the direct stimulating effect of the palatal plate on tongue protrusion was evaluated. Significant positive results were observed in all three areas.

Child, Preschool↗
PubMed1993

A novel stretch receptor in the jaw of the rat.

We report here an unusual type of stretch receptor found on each side of the rat jaw. This receptor has unique morphological features: it is quite long (24-28 mm), lies in connective tissue in between masticatory muscles, and extends between the medial pterygoid muscle-tendon on the maxilla and the masseter-tendon on the mandible through a zigzag course, forming a Greek capital letter sigma when viewed from the side. The receptor is neither in parallel nor in series with any masticatory muscles and receives multiple innervation. The receptor increases its length when the jaw closes and shortens when the jaw opens. Electron microscopy revealed axial structures composed of a central cellular core surrounded by tightly packed collagen bundles which are separated from the capsule by a wide capsular space. Most of the sensory endings are found among axial collagen bundles, some in between core cells. The core cells have many finger-like processes on their surface, being coupled by desmosomes. The origin and nature of these cells are unclear. The wide capsular space is filled with Alcian blue positive substrate, probably acid glycosaminoglycans. The structures of outer and inner capsules are similar to those of muscle spindles, the former being composed of three to ten layers of thin flattened cells. The response of the receptor was examined with in vivo as well as in vitro preparations. In in vivo experiments, impulse discharges from this receptor increased with the increase in jaw closing. When the jaw was fully opened the impulse discharge from this receptor disappeared.(ABSTRACT TRUNCATED AT 250 WORDS)

Alcian Blue↗
PubMed1983

A method of bite force measurement in primates.

A bite force transducer consisting of two differential strain beams with four strain gages in a full bridge configuration was modified for measuring occlusal forces in rhesus monkeys. A procedure of muscle stimulation (20-50 V, 60 Hz, and 0.8 ms duration) produced maximal unilateral masticatory muscle contraction when stimulating electrodes were placed in the masseter muscle. Tests of this procedure revealed reproducible results and a potential for use in studies of the force of isometric contraction of the masticatory muscles in normal and experimentally altered macaques and other primates.

Animals↗