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PubMed1982

Intraoral masseter muscle transposition: use with reconstruction of regional facial paralysis.

The treatment of regional facial paralysis of the lips and commissure by masseter muscle transposition is well accepted and usually accomplished by an external approach. The intraoral transfer demonstrates distinct advantages for the rehabilitation of midfacial regional paresis. The procedure is performed totally intraorally, which exposes the masseter muscle before transposing the anterior portion in a subcutaneous tunnel to the upper and lower lips. The effects of this transposition are direct support and immediate contraction, with eventual myoneurotization of the surrounding perioral musculature. The indications, operative considerations, and results in 22 cases are reported. This technique considerably advances the procedural approaches of the reconstructive surgeon and in used either in conjunction with other reconstructive modalities or as a primary procedure in selected cases.

Facial Paralysis↗
PubMed1984

Muscle transposition for facial reanimation. Indications and results.

The technique of transposing the temporalis and masseter muscles to reanimate the face following long-standing facial paralysis was introduced at the turn of the century. More recently it has been popularized by Rubin and Conley. The indications for performing this technique are outlined, and the results are analyzed.

Adolescent↗
PubMed1988

Surgery on the buccal fat pad in masseter transfer.

The buccal fat pad is an essential anatomic structure in the esthetic presentation of the face. It may become hypertrophied, with fullness of the cheek, or atrophic, with a sunken appearance, or become a plus or minus factor in reconstruction in this area. Lipoma of this pad is extremely rare, but it must also be differentiated. There are, therefore, certain circumstances where the presence or absence of the buccal fat pad can create a specific imbalance and asymmetry in the face. The correction of these conditions may require reduction or augmentation. The anatomy, the risks, the classification, and the various surgical techniques that are available to accomplish this are outlined and correlated to the masseter muscle transfer.

Adipose Tissue↗
PubMed1990

Stimulation variables in electroneurography of the facial nerve.

Electroneurography is an electrophysiologic measurement of compound action potentials elicited by the supramaximal stimulation of a peripheral nerve. The stimulus intensity-response function was examined in the cat facial nerve following stimulation over two different sites of the facial nerve: the main trunk and the buccal branches. Thresholds were achieved at lower current settings, the resultant compound action potential exhibited a greater amplitude, and masseter muscle excitation was more evident following stimulation over the buccal region. The use of concurrent facial- and masseter-evoked electromyographic monitoring allows more sensitive detection of masseter excitation and a more accurate determination of the current level necessary for supramaximal stimulation.

Action Potentials↗
PubMed1985

The phantom earache. Temporomandibular joint dysfunction in children.

Temporomandibular joint dysfunction is a benign, relatively uncommon childhood disorder and should be considered in children who have intermittent unilateral otalgia of three to four days' duration and whose audiographic, tympanometric, and clinical otologic examinations reveal normal findings. Most of the patients in our study had undergone orthodontic therapy during the year preceding the onset of temporomandibular joint dysfunction, and the vast majority of them had received orthodontic treatment within two weeks of each episode of otalgia. The diagnosis can be confirmed clinically by reproducing the pain associated with masticatory muscle spasm by palpation of the preauricular areas, intraotic manipulation, and palpation of the pterygoid muscles. Treatment consists of administering acetaminophen, applying hot compresses to the preauricular area, and opening and closing the mouth 30 to 40 times after each compress as an effort to interrupt the muscle spasm.

Adolescent↗
PubMed1996

Jaw muscles of Old World squirrels.

The jaw, suprahyoid, and extrinsic tongue muscles were studied in 11 genera, belonging to five tribes, of Old World squirrels. Significant variation in most of the adductor muscles is evident. The most primitive state of sciuromorphy is seen in the African tree squirrels Paraxerus and Funisciurus, especially as reflected in the anterior deep masseter. A derived state of sciuromorphy is found in five genera of Old World squirrels and perhaps evolved independently in each. Reduction of the temporalis muscle was observed in three genera, distantly related to one another. A unique arrangement of the superficial masseter is reported in the Asian giant tree squirrels, Ratufa. The arrangement of the masseter in the African pygmy squirrel, Myosciurus, is very similar to that of the South American pygmy squirrel, Sciurillus. We present hypotheses about the functional significance of these differences. In the derived state of sciuromorphy, which is found in three cases in squirrels that feed extensively on hard fruits, the anterior deep masseter is well positioned to increase the strength of the power stroke of the incisor bite. Among the pygmy squirrels, the position of the anterior deep masseter suggests that it plays a more significant role in molar chewing.

Anatomy, Artistic↗
PubMed1983

Proliferative myositis of the masseter muscle. A case report and a review of the literature.

A case of proliferative myositis of the masseter muscle in a 62-year-old woman is presented and pertinent literature is reviewed. This benign pseudosarcomatous proliferative lesion has not been previously reported in any of the muscles of mastication. Clinically the patient presented with pain and difficulty in opening of the mouth. On initial examination, a malignant salivary gland tumor was suspected. The proliferative myositis exhibits a disturbing microscopic appearance characterized by the presence of numerous hyperchromatic fibroblasts and oval or spindle-shaped giant cells which resemble malignant rhabdomyoblasts. These lesions have been often misdiagnosed as rhabdomyosarcoma and other types of sarcomas. Awareness of the microscopic characteristics of proliferative myositis and the possibility of its occurrence in the perioral soft tissues is important in avoiding misdiagnosis of this benign condition.

Cell Division↗
PubMed1983

The embryonic origins of avian cephalic and cervical muscles and associated connective tissues.

The objective of these experiments was to determine the embryonic origins of craniofacial and cervical voluntary muscles and associated connective tissues in the chick. To accomplish this, suspected primordia, including somitomeres 3-7, somites 1-7, and cephalic neural crest primordia have been transplanted from quail into chick embryos. Quail cells can be detected by the presence of a species-specific nuclear marker. The results are summarized as follows: (table; see text) These results indicate that muscles associated with branchial arch skeletal structures are derived from paraxial mesoderm, as are all other voluntary muscles in the vertebrate embryo. Thus, theories of vertebrate ontogeny and phylogeny based in part on proposed unique features of branchiomeric muscles must be critically reappraised. In addition, many of these cephalic muscles are composites of two separate primordia: the myogenic stem cells of mesodermal origin and the supporting and connective tissues derived from the neural crest or lateral plate mesoderm. Defining these embryonic origins is a necessary prerequisite to understanding how the mesenchymal primordia of cephalic muscles and connective tissues interact to form patterned, species-unique musculoskeletal systems.

Animals↗
PubMed1983

Growth of the masseter muscle in rhesus monkeys (Macaca mulatta).

The growth of the masseter muscle in eight infant, juvenile, and adolescent female rhesus monkeys (M. mulatta) was examined over a 2.5 year period using serial radiographic cephalometric techniques with the aid of radiopaque muscle markers. The radiopaque markers, which are composed of small pieces of root canal broach inserted into the muscle belly, make it possible to determine longitudinal masseter muscle growth as well as migration of the masseter muscle relative to the mandible. It was found that the masseter muscle increased in length by 64% during the total growth period, most of which occurred between 6 and 18 months of age. Relative to the cranium, the masseter muscle grew markedly inferiorly and only slightly posteriorly. Relative to the mandible, the masseter migrated in a posterior and slightly superior direction, keeping pace with the ramus and condyle as they grew posteriorly and posterosuperiorly throughout the study period. It was concluded that: 1) radiopaque muscle markers are a valuable tool for analysis of muscle growth and alteration of muscle location; 2) the masseter muscle in the rhesus monkey undergoes elongation, probably due to addition of sarcomeres at the fiber-tendon junctions; and 3) posterior migration of the masseter muscle relative to the corpus of the mandible, probably due to the nature of its periosteal attachment, results in a stability of the anteroposterior position of the masseter muscle despite the anterior displacement of the mandible.

Aging↗
PubMed1986

Correlations between the cross-sectional area of the jaw muscles and craniofacial size and shape.

In adult human subjects, the correlations were determined between the cross-sectional areas of the jaw muscles (measured in CT scans) and a number of facial angles and dimensions (measured from lateral radiographs). Multivariate statistical analysis of the skeletal variables in a group of 50 subjects led to the recognition of six independent factors determining facial shape, i.e., cranial base length, lower facial height, cranial base flexure and prognathism, facial width, mandibular length, and upper facial height. In 29 of these subjects, the cross-sectional areas of the jaw muscles were determined, and correlations between these areas and the scores on the above-mentioned factors were calculated. It appeared that the cross-sectional areas of temporalis and masseter muscles correlated positively with facial width, whereas the areas of masseter and both pterygoid muscles did so with mandibular length. It has been shown experimentally that a decrease in jaw muscle size in various animals likewise has an effect on facial width and mandibular length. Our results therefore support the hypothesis that in man too the jaw muscles affect facial growth and partly determine the final facial dimensions. They also hint that the role of each muscle is different.

Adult↗
PubMed1989

Endo's stress analysis of the primate skull and the functional significance of the supraorbital region.

A review of Endo's experimental and theoretical procedures and data indicates that the magnitude of the principal strains in the glabella region of both humans and gorillas are low as compared to other parts of the face. Therefore, his data do not provide support for the hypothesis that the glabella region is a highly stressed region during biting. In addition, increased levels of strain in the supraorbital region are directly related to increased levels of masticatory muscle and reaction forces, and not necessarily to anterior tooth loading as opposed to posterior tooth loading. His data also indicate that the supraorbital region in extant humans cannot be accurately modeled as a beam. These conclusions either differ from those of Endo or are not clearly presented or emphasized throughout any of Endo's papers. Therefore, we suggest that a number of investigators have made unsupported or erroneous conclusions based on Endo's work. This is particularly true for those studies that have emphasized the existence of powerful bending stress in the glabella region during incisor biting in both humans and non-human primates.

Animals↗
PubMed1989

Relationships between the size and spatial morphology of human masseter and medial pterygoid muscles, the craniofacial skeleton, and jaw biomechanics.

The relationship between human craniofacial morphology and the biomechanical efficiency of bite force generation in widely varying muscular and skeletal types is unknown. To address this problem, we selected 22 subjects with different facial morphologies and used magnetic resonance imaging, cephalometric radiography, and data from dental casts to reconstruct their craniofacial tissues in three dimensions. Conventional cephalometric analyses were carried out, and the cross-sectional sizes of the masseter and medial pterygoid muscles were measured from reconstituted sections. The potential abilities of the muscles to generate bite forces at the molar teeth and mandibular condyles were calculated according to static equilibrium theory using muscle, first molar, and condylar moment arms. On average, the masseter muscle was about 66% larger in cross section than the medial pterygoid and was inclined more anteriorly relative to the functional occlusal plane. There was a significant positive correlation (P less than 0.01) between the cross-sectional areas of the masseter and medial pterygoid muscles (r = 0.75) and between the bizygomatic arch width and masseter cross-sectional area (r = 0.56) and medial pterygoid cross-sectional area (r = 0.69). The masseter muscle was always a more efficient producer of vertically oriented bite force than the medial pterygoid. Putative bite force from the medial pterygoid muscle alone correlated positively with mandibular length and inversely with upper face height. When muscle and tooth moment arms were considered together, a system efficient at producing force on the first molar was statistically associated with a face having a large intergonial width, small intercondylar width, narrow dental arch, forward maxilla, and forward mandible. There was no significant correlation between muscle cross-sectional areas and their respective putative bite forces. This suggests that there is no simple relationship between the tension-generating capacity of the muscles and their mechanical efficiency as described by their spatial arrangement. The study shows that in a modern human population so many combinations of biomechanically relevant variables are possible that subjects cannot easily be placed into ideal or nonideal categories for producing molar force. Our findings also confirm the impression that similar bite-force efficiencies can be found in subjects with disparate facial features.

Adult↗
PubMed1992

Three-dimensional finite element stress analysis of the dentate human mandible.

The biomechanical events which accompany functional loading of the human mandible are not fully understood. The techniques normally used to record them are highly invasive. Computer modelling offers a promising alternative approach in this regard, with the additional ability to predict regional stresses and strains in inaccessible locations. In this study, we built two three-dimensional finite element (FE) models of a human mandible reconstructed from tomographs of a dry dentate jaw. The first model was used for a complete mechanical characterization of physical events. It also provided comparative data for the second model, which had an increased vertical corpus depth. In both cases, boundary conditions included rigid restraints at the first right molar and endosteal cortical surfaces of the articular eminences of temporal bones. Groups of parallel multiple vectors simulated individual masticatory muscle loads. The models were solved for displacements, stresses, strains, and forces. The simulated muscle loads in the first model deformed the mandible helically upward and toward its right (working) side. The highest principal stresses occurred at the bite point, anterior aspects of the coronoid processes, symphyseal region, and right and left sides of the mandibular corpus. In general, the observed principal stresses and strains were highest on the periosteal cortical surface and alveolar bone. At the symphyseal region, maximum principal stresses and strains were highest on the lower lingual mandibular aspect, whereas minimum principal stresses and strains were highest on its upper labial side. Subcondylar principal strains and condylar forces were higher on the left (balancing or nonbiting) side than on the right mandibular side, with condylar forces more concentrated on the anteromedial aspect of the working-side condyle and on the central and lateral aspects of the left. When compared with in vivo strain data from macaques during comparable biting events, the predictive strain values from the first model were qualitatively similar. In the second model, the reduced tensile stress on the working-side, and decreased shear stress bilaterally, confirmed that lower stresses occurred on the lower mandibular border with increased jaw depth. Our results suggested that although the mandible behaved in a beam-like manner, its corpus acted more like a combination of open and closed cross sections due to the presence of tooth sockets, at least for the task modelled.(ABSTRACT TRUNCATED AT 400 WORDS)

Computer Simulation↗
PubMed1980

Muscle sarcomere length following passive jaw opening in the rabbit.

Sarcomere lengths were measured microscopically in formalin-fixed jaw muscles of 14 rabbits divided into two groups; jaw open, and jaw closed. The measurements were compared by means of a nested analysis of variance. The sarcomeres of the jaw open group were longer in the masseter and temporalis muscles (jaw elevators) and shorter in the digastric muscle (jaw depressor) than were those of the jaw closed group. In the jaw closed position, sarcomeres in the deep portion of the masseter muscle become markedly shorter than those in the superficial part of the muscle. The values for sarcomere length in the masseter muscle of the jaw open group and the digastric of the jaw closed group are near the top of the ascending limb of isometric length-tension relation for the rabbit digastric muscle.

Analysis of Variance↗
PubMed1990

Variation in histochemical enzyme profile and diameter along human masseter intrafusal muscle fibers.

The histochemical enzyme profile of human masseter intrafusal muscle fibers was analyzed in consecutive serial cross sections along the individual fibers. Two hundred intrafusal fibers in 21 muscle spindles were classified. On the basis of equatorial nucleation, myosin ATPase-staining reactions after alkaline and acid preincubations and diameter, four different populations or types of intrafusal fiber were identified: large-diameter alkaline-stable and acid-stable fibers, bag2; two types of fiber with intermediate-diameter, alkaline-labile and acid-labile fibers corresponding to bag1 and alkaline-labile and acid-stable fibers designated as AS-bag1; and small-diameter alkaline-stable and acid-stable (pH 4.6)-acid-labile (pH 4.3) fibers called chain fibers. Regional variability in staining and diameter along the individual fibers was noted. In general, intrafusal fibers showed stronger oxidative reactions than did extrafusal fibers. The enzyme profile of the human masseter intrafusal fibers differed from that of extrafusal fibers in jaw, limb, and trunk muscles and also from that reported for spindles in limb and trunk muscles in man. The result suggests unique properties of human jaw muscle spindles and the jaw motor system.

Adult↗
PubMed2005

Neurotransmitter phenotypes of intermediate zone reticular formation projections to the motor trigeminal and hypoglossal nuclei in the rat.

Numerous studies suggest an essential role for the intermediate (IRt) and parvocellular (PCRt) reticular formation (RF) in consummatory ingestive responses. Although the IRt and PCRt contain a large proportion of neurons with projections to the oromotor nuclei, these areas of the RF are heterogeneous with respect to neurotransmitter phenotypes. Glutamatergic, GABAergic, cholinergic, and nitrergic neurons are all found in the PCRt and IRt, but the projections of neurons with these phenotypes to the motor trigeminal (mV) and hypoglossal nucleus (mXII) has not been fully evaluated. In the present study, after small injections of Fluorogold (FG) into mV and mXII, sections were processed immunohistochemically to detect retrogradely labeled FG neurons in combination with the synthetic enzymes for nitric oxide (nitric oxide synthase) or acetylcholine (choline acetyltransferase) or in situ hybridization for the synthetic enzyme for GABA (GAD65/67) or the brainstem vesicular transporter for glutamate (VGLUT2). In three additional cases, FG injections were made into one motor nucleus and cholera toxin (subunit b) injected in the other to determine the presence of dual projection neurons. Premotor neurons to mXII (pre-mXII) were highly concentrated in the IRt. In contrast, there were nearly equal proportions of premotor-trigeminal neurons (pre-mV) in the IRt and PCRt. A high proportion of pre-oromotor neurons were positive for VGLUT2 (pre-mXII: 68%; pre-mV: 53%) but GABAergic projections were differentially distributed with a greater projection to mV (25%) compared to mXII (8%). Significant populations of cholinergic and nitrergic neurons overlapped pre-oromotor neurons, but there was sparse double-labeling (<10%). The IRt also contained a high proportion of neurons that projected to both mV and MXII. These different classes of premotor neurons in the IRt and PCRt provide a substrate for the rhythmic activation of lingual and masticatory muscles.

Acetylcholine↗