muscles of mastication

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Definition of muscle : 

Definition of muscle Muscle can be defined as an organ or tissue that by contraction produces movement of an animal. A tissue composed of contractile cells or fibers that affect the movement of an organ or part of the body

Classification of muscles : 

Classification of muscles Basis of classification- 1 Depending upon striations. a) striated b)non-striated 2 Depending upon control. a) voluntary b)involuntary muscles. 3 Depending upon the function. a) skeletal muscle b)cardiac muscle c)smooth muscle.

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Units of skeletal muscle are the muscle fibers, each of which act as a single cell having hundreds of nuclei (syncytial striated myocytes). Fibers are arranged in bundles of various sizes and pattern called fasciculi. Connective tissue fills the spaces between muscle fibres within a fasciculus where it is known as the endomyscium. SKELETAL MUSCLE

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Each fasciculus is also surrounded by a strong connective tissue sheath or perimysciun. Surrounding the whole muscle lies epimyscium. Cell membrane of muscle fibre is known as sarcolemma while their cytoplasm is called sarcoplasm. Sarcoplasm is divided into longitudinal threads or myofibrils each of 1 µm in diameter. Each muscle fiber consists of several hundred to several thousand myofibrils

Muscles of mastication : 

Muscles of mastication Primary muscles Masseter Temporalis Lateral pterygoid Medial pterygoid Secondary or accessory muscles Digastric Mylohyoid Geniohyoid Buccinator

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There are four pairs of muscles attached to mandible, primarily responsible for Elevating Depressing Protruding Retruding Lateral movement

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They are functionally classified as: Jaw elevators: Masseter Temporalis Medial pterygoid Upper head of lateral pterygoid Jaw depressors Lower head of lateral pterygoid Anterior digastric Geniohyoid Mylohyoid


DEVELOPMENT OF MUSCLES OF MASTICATION The muscular system develops from intra embryonic mesoderm Muscle tissues develop from embryonic cells called myoblast. Muscular component of Branchial arch form many striated muscles in the head and neck region. Muscles of mastication are derived from first brachial arch that is the MANDIBULAR ARCH.

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Lateral View Of A Four Week Embryo Showing Muscles Derived From Branchial Arches

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Clinical examination : 

Clinical examination Masseter: Fingers are placed over the patients Zygomatic arch,Angle of mandible and body to feel the muscle.

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Temporalis: Fingers are placed over the patients temples to feel the muscle.

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Medial pterygoid: Index finger is used to touch the medial pterygoid muscle on the inner surface of the ramus.

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Lateral pterygoid: The little finger is inserted facial to the maxillary teeth and around distal to the pterygomaxillary, [or] hamular notch, to palpate the muscle.





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Myofascial PainWhen the nerve that is connected to the muscle becomes irritated small nodules or contractures form causing the muscle to become tight and painful. These contractures are called trigger points. Trigger points will often refer pain into distant locations. For example it is very common for jaw muscles with myofascial pain to refer pain into the teeth or ears.

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In addition to pain, muscles with myofacial pain also fatigue more easily and have decreased strength and range of motion. Headaches in the temples are usually the result of myofacial pain within the temporalis muscle, which is a jaw closing muscle. This can occur when the jaw muscles are chronically strained such as in teeth clenching or poor posture, through an acute trauma, or with nerve injury or jaw joint dysfunction.

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Temporal TendonitisThis can occur when there is chronic strain from the temporalis muscle pulling on the tendon that attaches to the mandible.  This can cause sharp headaches in the temples, just to the sides of the eyes.

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Stylomandibular Ligament StrainThis is usually felt as a sharp to aching pain in the region behind the jaw bone and below the ear.  It can be a result of bad bite or from a traumatic injury

Trismus : 


Masseter Hypertrophy : 

Masseter Hypertrophy

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Figure 2. Intraoral view showing midline deviation during occlusion.

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Masseter muscle hypertrophy is an asymptomatic,benign enlargement of one or both masseter muscles. Etiology : Unclear, acc to several authors “emotional stress results in chronic forceful clenching of the jaws and bruxism, which cause a work hypertrophy of the muscle . “ Differential diagnosis: PAROTIDITIS, PAROTID TUMOR, LIPOMA, BENIGN OR MALIGNANT MUSCLE TUMORS, VASCULAR TUMORS, BENIGN AND MALIGNANT MANDIBLE TUMORS.



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TREATMENT: NON-SURGICALTREATMENT MODALITIES; Reassurance, Tranquilizers or muscle relaxants, Psychiatric care and Injection of very small doses of botulinum toxin type A. Dental restorations and occlusal adjustments to correct premature contacts and malocclusions are important. Parafunctional habits must be prevented. SURGICAL TREATMENT; Surgical removal of the hypetrophied muscle, Partial removal of the muscle by modified liposuction techn ique. Therapy needs to be specifically tailored for each patient, because the etiology of this condition is multifactorial



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Hemangiomas of skeletal muscle represent 0.8% of all benign vascular neoplasm . Of these 13.8% occur in the head and neck region , with the masseter muscle being the most common site, followed by the trapezius and sternocleidomastoid muscles respectively. ETIOLOGY: Trauma (2) Congenital (3) Hormonal factors.. TYPES Cavernous (2)Capillary (3) Mixed. The capillary type of hemangioma occurred more frequently in the head and neck region. The cavernous and mixed types occurred more frequently in the trunk and lower limbs. DIFFERENTIAL DIAGNOSIS: cysts, lymphangiomas, rhabdomyosarcomas, masseteric hypertrophy, and schwannomas.

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Many treatment modalities like cryotherapy, radiation therapy, steroid administration embolization have been advocated but the treatment of choice at present remains surgical excision



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This is a benign conditon which results in reactive heterotopic bone formation, usually producing limitation of opening of the jaws. CLINICAL FEATURES: Limited mouth opening(trismus) TYPES: MYOSITIS OSSIFICANS TRAUMATICA MYOSITIS OSSIFICANS PROGRESSIVA M O ASSOCIATED WITH PARAPLEGIA M O ASSOCIATED WITH POLIOMYELITIS ETIOPATHOLOGY: MOT; Trauma leads to intramuscular hemmorhage which results in reactive heterotrophic bone formation within the muscle. T/T : Surgical removal of the abnormal mass.

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Panoramic radiograph indicating dense radiopaque mass extending from zygomatic arch to body and ramus of the left mandible. CT scan indicating a calcified mass in the left masseter muscle.


CENTRONUCLEAR MYOPATHY Centronuclear myopathy (CNM) is a rare form of congenital myopathy characterized by a universal involvement of the skeletal musculature leading to weakness and atrophy.Facial, masticatory, and extraocular muscles are characteristically involved

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This leads to fatty infiltration in masticatory muscles which leads to decrease in muscle mass and tone. This can lead to fibrous ankylosis of TMJ which can further lead to true ankylosis. TRETAMENT: Mouth opening exersices and surgical interventions

References : 

References Sicher and Dubrull Oral anatomy 8th edition Snell anatomy, Clinical anoatomy by Regions 8th edition.. B. D. Chaurasia. Wikipedia. Edmar Zanoteli, MD,a Antônio S. Guimarães, DDS...Temporomandibular joint involvement in a patient with centronuclear myopathy ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY Volume 90, Number 1 Keith Da Silva, BSc,a and Louis Mandel, DDS,b ,Bilateral temporalis muscle hypertrophy: A case report OOO, Volume 102, Number 1 Eduardo Kazuo SANNOMIYA1 Marcelo GONÇALVES2 Marcelo Paraíso CAVALCANTI3Masseter Muscle Hypertrophy - Case Report, Braz Dent J (2006) 17(4): 347-350. C D Narayanan1*, Preeth Prakash2 and C K Dhanasekaran3, Intramuscular hemangioma of the masseter muscle: a case report,Cases journal.

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