Muscles of mastication


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Muscles of mastication

  1. 1. MUSCLES OF MASTICATION Masseter Temporalis Lateral Pterygoid Medial Pterygoid
  2. 2. MASTICATORY SYSTEM The masticatory system is a functional unit composed of the teeth; their supporting structures, the jaws; the temporomandibular joints; the muscles involved directly or indirectly in mastication (including the muscles of the lips and tongue); and the vascular and nervous systems supplying these tissues. Functional and structural disturbances in any one of the components of the masticatory system may be reflected by functional or structural disorders in one or more of its other components
  3. 3. MASTICATORY FUNCTIONS Mastication is the action of breaking down of food, preparatory to deglutition. This breaking-down action is highly organized complex of neuromuscular and digestive activities that, in normal individuals, integrate the various components of the masticatory system, such as the teeth and their investing structures, the muscles, the temporomandibular joints, the lips, the cheeks, the palate, the tongue, and the salivary secretions.
  4. 4. MASTICATION- ORAL BEHAVIOUR Mastication is oral motor behavior reflecting central nervous system commands, and many peripheral sensory inputs to modulate the rhythmic jaw movements. The action of masticatory muscles during chewing varies between subjects in amplitude, onset timing, and duration of the chewing cycle. However, it is possible to recognize similarity between muscle actions. These wide variations (within and between individuals) can be explained by differences related to individual occlusal contact features and specific musculoskeletal morphology. Since tooth guidance has an enormous influence on muscle activity during chewing and swallowing, it is advisable to make restorations compatible with the functional movement patterns of the patient rather than expect the patterns of the mastication to adapt to the new made restorations
  5. 5. CHEWING CYCLE The masticatory sequence is the whole set of movements from ingestion to swallowing. It is made up of masticatory cycles that change in form as the food is gathered, moved backward to the molar teeth, then broken down and prepared for swallowing.
  6. 6. tooth bolus jaw opening stretch of elevator muscles jaw closing re-opening of jaw via stimulation of periodontal and soft tissue receptors NEUROLOGICAL CONTROL To create precise mandibular movements, inputs from various sensory receptors must be received by the central nervous system through afferent nerve fibers. The brain assimilates and organizes these inputs and elicits appropriate motor activities through the efferent nerve fibers. These motor activities involve the contraction of some muscle groups and the inhibition of others. Chewing is a subconscious activity, yet can be brought to conscious control at any time
  7. 7. MUSCLES OF MASTICATION The muscles of mastication help in mastication. All supplied by the mandibular division of the Trigeminal nerve. Additional muscles of mastication supplied by trigeminal nerve Anterior belly of digastric Mylohyoid Tensor tympani (attaches to the malleus - 1st arch bone - part of the reptilian jaw joint) Tensor palati
  8. 8. PAROTIDEOMASSETERIC FASCIA  Also referred to as the ‘Masseteric Fascia’.  A strong layer of fascia derived from the deep cervical fascia.  Above it, the lower border of zygomatic arch is attached.  Behind, it invests the parotid gland.
  9. 9. MASSETER
  10. 10.  Arises by thick, tendinous aponeurosis from zygomatic process of maxilla and 2/3 of lower border of zygoma.  Fibres pass downwards and backwards.  Inserted into the angle and lower half of lateral surface of ramus of mandible.  Arises from posterior 2/3 of lower border and whole of medial surface of zygomatic arch.  Fibres pass downwards and forwards.  Inserted into the upper half of ramus and lateral surface of coronoid process of mandible. Superficial Layer Deep Layer Deep layer is partly concealed in front by superficial layer and behind by parotid gland. A thick, quadrilateral muscle and it consists of two portions:
  11. 11. TEMPORAL FASCIA  Covers the temporalis muscle.  It is a strong, fibrous investment covered laterally by auricularis anterior and superiorly by galea aponeurotica and by part of orbicularis oculi.  It consist of two layers:-one of which is inserted into the lateral and other into medial border of the arch.  Between these two layers- a small quantity of fat, orbital branch of superficial temporal artery and a filament from zygomatic branch of zygomatic nerve are present.
  12. 12. TEMPORALIS
  13. 13.  Arises from whole of the temporal fossa and from deep surface of temporal fascia.  Fibres converge as they descend and end in a tendon which passes which passes deep to the zygomatic arch.  Inserted into the medial surface, apex and anterior border of coronoid process and anterior border of ramus of mandible nearly as far forward as last molar teeth. Broad, radiating muscle situated at the side of the head.
  15. 15.  Arises from lower part of lateral surface of greater wing of sphenoid and from infratemporal crest.  It is active during various jaw closing movements only.  Arises from lateral surface of lateral pterygoid plate.  It is active during jaw opening movements and protrusion only. Upper Head Lower Head Short, thick muscle, conical in form. Extends horizontally between infratemporalfossa and condyle of mandible. Arises by two heads:- upper and lower Fibres pass horizontally backwards and laterally. Inserted into a depression in front of neck of condyle of mandible, and into front margin of articular disc of temporomandibular articulation. Suited for Protraction, Depression and Contralateral Abduction.
  17. 17.  Arises from medial surface of lateral pterygoid plate and grooved surface of pyramidal process of palatine bone.  Fibres pass downward, lateral and backwards.  Inserted by strong tendinous lamina, into the lower and back part of medial surface of ramus and angle of mandible, as high as the mandibular foramen. Thick, quadrilateral muscle. Principle functions are elevation and lateral positioning of mandible.
  18. 18. ADDITIONAL MUSCLES WHICH ARE SUPPLIED BY TRIGEMINAL NERVE Digastric Geniohyoid Tensor tympani Tensor veli palitini
  19. 19. DIGASTRIC  Attachment is at or near lower border of mandible and near midline.  Anterior digastric muscle covered by platysma muscle, beneath lie the mylohyoid and geniohyoid muscle.  Mylohyoid branch of mandibular division of fifth nerve innervates anterior digastric.  Digastric branch of facial nerve innervates posterior digastric muscle.
  20. 20. GENIOHYOID  Lies superior to mylohyoid muscle and adjacent to the midline.  Arises from mental spine on posterior aspect of symphysis menti of mandible.  Inserts on anterior surface of hyoid bone.  Innervation is from C1 to C2 and hypoglossal nerve.
  21. 21. The tensor tympani, the larger of the two muscles of the tympanic cavity, is contained in the bony canal above the osseous portion of the auditory tube. Its role is to dampen sounds, such as those produced from chewing. When tensed, the action of the muscle is to pull the malleus medially, tensing the tympanic membrane, damping vibration in the ear ossicles and thereby reducing the amplitude of sounds. It arises from the cartilaginous portion of the auditory tube and the adjoining part of the great wing of the sphenoid, as well as from the osseous canal in which it is contained. Inserted into the handle (manubrium) of the malleus, near its root. Passing backward through the canal, it ends in a slender tendon which enters the tympanic cavity, makes a sharp bend around the extremity of the septum, known as the processus cochleariformis TENSOR TYMPANI
  22. 22. TENSOR VELI PALITINI The tensor veli palatini (tensor palati) is a broad, thin, ribbon-like muscle in the head that tenses the soft palate. It arises by a flat lamella from the scaphoid fossa at the base of the medial pterygoid plate, from the spina angularis of the sphenoid and from the lateral wall of the cartilage of the auditory tube. The tendon then passes medially and is inserted into the palatine aponeurosis and into the surface behind the transverse ridge on the horizontal part of the palatine bone. The tensor veli palatini is innervated by the medial pterygoid nerve, a branch of mandibular nerve, the third branch of the trigeminal nerve (CN V). The tensor veli palatini tenses the soft palate and by doing so, assists the levator veli palatini in elevating the palate to occlude and prevent entry of food into the nasopharynx during swallowing.
  24. 24. IMPORTANCE TO DENTISTS The knowledge of this system is important in removable prosthodontics. Information based on this system was used in the design and setting of articulators, and in the design of the dentures and denture teeth themselves. Today the importance of jaw movements has become apparent in fixed prosthodontics, periodontics, orthodontics, and in the diagnosis and treatment of pain disorders of the masticatory system. The most important reason why dentists maintain and replace missing teeth should be to provide patients with good masticatory abilities. Therefore, it is important that dentists know how mastication normally occurs.
  25. 25. CLINICAL SIGNIFICANCE  Horner's syndrome can be produced by lesions of the nasociliary nerve as it runs with the ophthalmic division.  Lesions of the ganglion: herpes zoster infection, primary and metastatic tumors.  Trigeminal root lesions: adjacent tumors and vascular malformations, especially acoustic neurinoma and cholesteatomas. These lesions are prone to produce facial pain that is often misdiagnosed as tic douloureux or tooth pain.  Clinically there is atrophy and flaccid paralysis of the muscles of mastication.