MASSETERS

From Big Medical Encyclopedia

MASSETERS — group of muscles which reduction displaces a mandible in the directions providing chewing. Topographical some muscles of the head (actually chewing, temporal, lateral and medial alate muscles — fig. 1) and the muscles of a neck which are above a hypoglossal bone (maxillary and hypoglossal, geniohypoid and biventral muscles) concern to this group of muscles.

Fig. 1. Masseters: and — temporal and actually chewing muscles; — alate muscles; 1 — a temporal muscle; 2 — actually a masseter: 3 — a lateral alate muscle; 4 — a medial alate muscle; 5 — krylonizhnechelyustny a seam; 6 — a buccal muscle.

Anatomy

Actually masseter (m. masseter) lies on an outer surface of a branch of a mandible; consists of three parts: superficial, intermediate and deep. A superficial part (pars superficialis) begins a sinew from bottom edge and an inner surface of a zygoma, goes down and is attached to chewing tuberosity of a mandible. An intermediate part (pars intermedia) begins from an inner surface of a zygoma and from a front slope of a joint hillock of a temporal bone, goes down and back, being attached to an outer surface of a branch of a mandible. A deep part (pars profunda) begins from an inner surface of a zygoma and a bone, being attached to a sinew of a temporal muscle. Function of a masseter: a superficial part pushes a mandible forward, intermediate and deep — lift it.

Temporal muscle (m. temporalis) lies in a temporal pole, fanlikely beginning from the platform of a bone, from the temporal surface of a big wing and an infratemporal crest of a wedge-shaped bone, from parietal, scales of a frontal and temporal surface malar bones and is attached by a powerful sinew to a coronal shoot and a branch of a mandible in the field of mandibular cutting and the slanting line. Function of a temporal muscle: front and average bunches lift a mandible, back — pull it back.

Lateral alate muscle (m. pterygoideus lat.) triangular shape lies in an infratemporal pole. Begins two heads: top and bottom. The upper head begins from the infratemporal surface and an infratemporal crest of a big wing of a wedge-shaped bone, goes back, being attached to a joint bag and a joint disk of a temporal and mandibular joint. The lower head begins from an outer surface of an alate shoot of a wedge-shaped bone, goes back and up, connects to an upper head and is attached to an alate pole on a neck of a mandible. Its function: at bilateral reduction pushes a mandible forward, at unilateral — displaces it to the opposite side.

Medial alate muscle (m. pterygoideus med.) a squared shape lies on an inner surface of a branch of a mandible. Begins tendinous and muscle fibers from an alate pole of an alate shoot of a wedge-shaped bone, goes back and down, being attached to alate tuberosity of a mandible. Function: at bilateral reduction lifts a mandible, at unilateral — displaces it to the opposite side.

Maxillary and hypoglossal muscle (m. mylohyoideus) is flat, a trapezoid form. Begins on an inner surface of a mandible on the maxillary and hypoglossal line. Fibers of a muscle go from top to down, outside inside and in front back to the centerline where form a tendinous seam. It is attached to a body of a hypoglossal bone.

Geniohypoid muscle (m. geniohyoideus) of triangular shape; begins from a mental awn of a mandible, goes down and kzad, being attached to a body of a hypoglossal bone.

Biventral muscle (m. digastricus) has two abdomens: back (venter post.) begins from mastoidal cutting of a temporal bone and front (venter ant.) — from a biventral pole of a mandible; they unite in one intermediate sinew which is attached to a big horn of a hypoglossal bone. Function maxillary and hypoglossal, geniohypoid and a front abdomen of a biventral muscle consists that at the fixed hypoglossal bone they lower a mandible.

Depending on function Zh. the m providing chewing (see), it is possible to subdivide into three groups: podnimatel, vydvigatel and opuskatel. To podnimatel actually chewing, temporal and alate muscles, belong to vydvigatel — lateral alate, to opuskatel — maxillary and hypoglossal, geniohypoid and biventral muscles. Blood supply — from branches of an infratemporal part of a maxillary artery, branches of facial and lingual arteries.

Innervation of masseters there is at the expense of the third branch of a trifacial (n. mandibularis) and a facial nerve (item facialis)

Pathology of masseters

Pathology of masseters can be shown in the form of dysfunction — paresis, paralyzes; e.g., at defeat of a trifacial or its kernel atrophic paralysis is observed. m. At hemilesion of a trifacial chewing though is complicated, but it is possible at the expense of the healthy party. At bilateral atrophic paralysis. chewing is impossible for m, the mandible droops. Such picture can be observed at a side amyotrophic sclerosis when pyramidal ways and kernels of motor cranial nerves are surprised. Defeat. the m can be also at a tick-borne encephalitis. Function Zh. the m is sharply broken also at lockjaw (see) — a tonic spasm. m which can be caused by inflammatory process in a mandible or in soft tissues, adjacent to area of an arrangement or attachment. m. Spasm. the m — a characteristic symptom at tetanus, can be observed at meningitis, in some cases — as hysterical reaction.

Fig. 2. True bilateral hypertrophy actually masseters.

Hypertrophy. the m is observed seldom, at the same time more often there is a unilateral hypertrophy of m. masseter. Distinguish so-called true and a pseudohypertrophy of m. masseter. The pseudohypertrophy is a development in the field of a masseter of an adenoid tissue or a vascular tumor. True hypertrophy. by m it is insufficiently studied. Occasionally it is observed at disturbance of a bite. It gipertrofiyaproyavlyatsya clinically only by disturbance of a configuration of the person (fig. 2), on the party of a hypertrophy the form of a corner of a mandible can be also changed. It is necessary to differentiate a true hypertrophy with high-quality new growths in the area Zh. m (lymphoma, lipoma).

. m are involved in patol, process at injuries of jaws, wounds of the person, specific inflammatory processes (actinomycosis), and also at malignant tumors on a face.

Treatment

Treatment patol, states. the m consists in treatment of a basic disease (an infectious disease of a nervous system, wound, a tumor); at a true hypertrophy of t. masseter — orthodontic treatment (see. Orthodontic methods of treatment ) for the purpose of elimination of anomalies of a bite; at sharply expressed hypertrophy attracting asymmetry of the person, perhaps partial surgical excision of a hypertrophied muscle; at detection of the tumor which is localized in the area Zh. m — the corresponding treatment.


Bibliography: Sparrows V. and Yasvoin G. Anatomiya, histology and embryology of an oral cavity and teeth, page 119, M., 1936; Gorenstein Ya. I. About a hypertrophy of masseters, Stomatology, No. 4, page 87, 1965; Ivanitsky M. F. Anthropotomy, t. 1, page 379, M., 1965; L of e r N of e r I. O. Hypertrophy of masseters, Stomatology, No. 2, page 40, 1960, bibliogr.; Limberg. A. A vascular tumor with multiple stones in the thickness of a masseter, in the same place, No. 4, page 90, 1965; Morphology of the maxillo-mandibular apparatus, Proc. symp. 9-th. Int. congr. Anat., Lpz., 1972; S i with h e r H. Oral anatomy, St Louis, 1965.

H. H. Mosolov, B. M. Bezrukov.

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