Muscles of mastication/ orthodontics courses in india


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  • Lower head: the larger one in the lower position has its origin in the external surface of the lateral pterygoid lamina
  • Muscles of mastication/ orthodontics courses in india

    1. 1. Muscles ofMuscles of MasticationMastication Anatomy and Physiology.Anatomy and Physiology. INDIAN DENTAL ACADEMY Leader in continuing dental education
    2. 2. •Introduction •Terms - Origin - Insertion - Action •Development •Clinical examination •Masticatory muscles - masseter - temporalis - medial pterygoid - lateral pterygoid •Accessory muscles - suprahyoid - infrahyoid •Applied anatomy •Reference
    3. 3. Introduction • In general as one reads about muscles there are five terms that are constantly seen, they are Origin Insertion Action Nerve supply and Blood supply
    4. 4. Origin: it is generally considered to be the end of the muscle that is attached to the least movable structure. Insertion: it is the other end of the muscle, which is attached to the more movable structures. Action: it is the work that is accomplished when the muscle fibers contract. Terms
    5. 5. Masticatory muscles The muscles most immediately concerned with the movement of the mandible in mastication and speech are Masseter Temporalis Medial pterygoid and Lateral pterygoid
    6. 6. • There are four pairs of muscles attached to mandible, primarily responsible for • Elevating • Depressing • Protruding • Retruding • Lateral movement
    7. 7. Development • These muscles develop from first pharyngeal arch [mandibular] • Thus innervated by the nerve of the first arch, the fifth cranial nerve [trigeminal nerve]more specifically, by the third part of the fifth cranial nerve; mandibular division.
    8. 8. • Blood supply to all the muscles is by the maxillary artery, branch of external carotid artery.
    9. 9. Clinical examination • Masseter: • It can be palpated extra orally by placing fingers over the lateral surfaces of the ramus of mandible
    10. 10. • Temporalis: • Fingers are placed over the patients temples to feel the muscle.
    11. 11. • Medial pterygoid: • Index finger is used to touch the medial pterygoid muscle on the inner surface of the ramus.
    12. 12. • 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.
    13. 13. • The distance between maxillary and mandibular incisors is measured when the patient is instructed to open ‘all the way’. • Normal opening in an adult is about 35-50 mm. • Normal lateral movement is about 8-10 mm.
    14. 14. Masseter muscle: • Masseter means to chew. • It is a quadrilateral muscle in shape. • It is one of the outermost muscles in the skull. • The muscle consists of three layers, which blend anteriorly. They are. The superficial layer The middle layer The deep layer
    15. 15.
    16. 16. The superficial layer • It is the largest of the three layers. • Origin: by a thick aponeurosis from maxillary process of zygomatic bone and from the anterior 2/3’rd of the inferior border of the zygomatic arch. • Insertion: fibers pass downwards and backwards to insert into the angle and lower posterior half of the lateral surface of the ramus
    17. 17. The middle layer: • Origin: arises from the medial aspect of the anterior two thirds of the zygomatic arch and from the lower border of the posterior third. • Insertion: inserts into the central part of the mandibular ramus.
    18. 18. The deep layer • this layer is also called as ‘zygomaticomandibular muscle’. • Origin: from the deep surface of the zygomatic arch. • Insertion: these fibers travel downwards, into the upper part of the mandibular ramus and into its coronoid process.
    19. 19. • middle and deep layers ofmasseter referred to as ‘cruciate muscle’. • The superficial layer is covered externally by continuous tendinous tissue • During clinical palpation the most active region of the muscle is situated near the mandibular angle. • The fibers of deep and superficial layers diverge from each other at an angle of 50 degrees.
    20. 20. Actions: • Masseter is considered to supply ‘power’, rather than positioning. • It elevates the mandible to occlude the teeth in mastication. • It has small effect in side to side movements, protraction and retraction
    21. 21. Temporalis muscle: As it is close to temples,thus the name temporalis. It is characterized by its fan shape and fairly thin muscle It covers a great part of lateral area of the skull -the temporal fossa. -Narrow part of parietal bone -Great part of temporal bone -Sphenoid bone ‘Temporal fascia’ covers the temporalis muscle. Temporalis muscle:
    22. 22.
    23. 23. • Above: the fascia is single layered. it is attached to superior temporal line. • Below: the fascia is two layered. one attached to lateral side and the other to the mesial margin of the upper border of the zygomatic arch. • On the lateral portion of the skull, temporalis inserts at the level of the temporal line and divides into 3 parts. 1. The anterior bundle 2. The intermediate bundle 3. The posterior bundle
    24. 24. 1. The anterior bundle: • Origin: the upper extremity attaches to the temporal bone. • Insertion: the lower extremity inserts onto the apex of the coronoid process of the mandible and to the anterior border of the ramus.
    25. 25. • This group is active at the closing phase and inactive at the opening phase. • No activity is seen during mandibular depression, expect during maximum opening [or] opening against resistance. • This action prevents the accidental dislodgement of the condyles out of the articular fossa if the resistance is suddenly removed. • This bundle is more active in mandibular elevation, swallowing and rest position. • This bundle is frequently adapted to crush and chew food close to centric occlusion. No activity at normal protrusive movements
    26. 26. 2. The intermediate bundle. • Vigorous action of this bundle has been observed during protrusive movements.
    27. 27. 3. The posterior bundle. • Anatomically posterior bundle is oriented to elevate the mandible • They function primarily as mandibular retractors [or] positioners. • These remain inactive during mandibular depression and protrusion
    28. 28. Nerve supply: • It is supplied by the deep temporal branches of the anterior trunk of the mandibular nerve.
    29. 29. Action: • It elevates the mandible and thus closes the mouth and approximates the teeth. • Thus it acts as a postioner. • This movement requires the upward pull of the anterior fiber and backward pull of the posterior fibers. • Because the head of the condyles rests on the articular eminence when the mouth is open. • It is active in forcible elevation.
    30. 30. Medial pterygoid: • Pterygoid means wing like. • It is a thick, quadrilateral muscle. • It is located on the internal surface of the ramus. • It lies along the length of the masseter muscle. • It is less potent than masseter.
    31. 31.
    32. 32. Origin: • It originates from the medial surface of the lateral pterygoid plate and from the grooved surface of the pyramidal process of the palatine bone. • A more superficial slip arises from the lateral surface of the pyramidal process and maxillary tuberosity.
    33. 33. Insertion: • the fibers descend postero laterally and are attached by a strong tendinous lamina to postero inferior part of the medial surfaces of the ramus and angle as high as the mandibular foramen and almost as far forward as the mylohyoid groove.
    34. 34. Action: • It acts as elevator.
    35. 35. Lateral pterygoid: • It is a short, thick muscle. • It is also referred to as “sphenomeniscus muscle”. • It has two heads • Upper head- smaller. • Lower head- larger. • it is deeply located in the infratempoal fossa.
    36. 36.
    37. 37. Origin • Lower head: the larger one in the lower position has its origin in the external surface of the lateral pterygoid lamina. • Upper head: the smaller one in the upper position originates from the infratemporal surface of the sphenoid bone.
    38. 38. Insertion • The two separate bellies are oriented posterior where they fuse at the level of the temporomandibular joint. • The most superior fibers of the upper belly are directly connected to the anterior surface of the articular capsule. • Thus are indirectly attached to the anterior portion of the condylar neck.
    39. 39. Action • It assists in opening the mouth by pulling forward the condyles and the articular disk. • Slow elongation of the lateral pterygoid is seen during the closure of the mouth, backward gliding of articular disc and condyle. • Ipsilateral medial and lateral pterygoid advance the condyle of that side so that jaw rotates about a vertical axis through opposite condyle. • When both medial and lateral pterygoid act together they protrude the mandible, so that the lower incisors project in front of upper. • Upper head is involved mainly in chewing. • Lower head is involved in protrusion, but the primary function is to move the disk and condyle head forward. • No activity is seen during closing and swallowing. • The lower belly is synergistic with suprahyoid muscle during protrusive and opening movements of mandible. • It is antagonist to suprahyoid muscle during closure movement in mastication and tooth clenching. • This bundle acts as a antigravity muscle during certain swallowing movements. • This muscle is responsible for opening of mandible. • External pterygoid is active only at uncontrolled opening of mouth. • This is used to place the condyles in a favorable position as the mandible progresses in its depressing movement as this muscle is not essential for opening the mouth,stabalizing force of the external pterygoid is used necessary to prevent the dislodgement of the mandible during the masticatory function.
    41. 41. DIGASTRIC • Origin: There are muscle fibers at either end with a collagenous tendon at the middle. • One end: digastric notch just medial to the mastoid process behind the ear. • Other end: digastric fossa on the inferior surface of the mandible at the midline. • Action: is two fold. • By contracting, it can create a backward pull on the mandible. When the jaws are clenched. Contraction of the muscle elevates the hyoid bone, thus helps in the pulling the mandible downwards. • Nerve supply • Anterior belly by the trigeminal nerve. • Posterior belly by the facial nerve.
    42. 42. MYLOHYOID • The floor of the mouth is formed by the mylohyoid muscle. • Origin: from the mylohyoid line on the medial surface of the mandible. • Insertion: to the hyoid bone. • Nerve supply: mylohyoid branch of the trigeminal nerve. • Blood supply: branch of the inferior alveolar artery.
    43. 43. GENIHYOID • Origin: inferior genial tubercle or mental spine on the lingual surface of the mandible. • Insertion: hyoid bone. • Action: depresses the mandible. • Nerve supply: C1. • Blood supply: lingual artery.
    44. 44. INFRA HYOID GROUP • OMOHYOID • It has an inferior belly, common tendon and superior belly. • Arises from the inferior belly and inserted through superior belly. • Origin: upper border of the scapula. • Insertion: lower border of the body of hyoid bone lateral to sternohyoid. • Action: depresses hyoid bone ,fixes the hyoid in mandibular depression. • Nerve supply: C2 and C3. • Blood supply: superior thyroid arteries.
    45. 45. STERNOHYOID • Origin: posterior surface of the manubrium sterni. • Insertion: medial part of the lower border of the hyoid bone. • Nerve supply: C2 and C3. • Action: depresses the hyoid,fixes hyoid in mandibular depression.
    46. 46. STERNOTHYROID • Origin: posterior surface of the manubrium sterni. • Insertion: thyroid cartilage. • Action: depresses the larynx. • Nerve supply: C2 and C3. • Blood supply: superior thyroid artery.
    47. 47. THYROHYOID • Origin: oblique line of the thyroid cartilage. • Insertion: hyoid bone. • Action: depresses the hyoid and elevates the larynx. • Nerve supply: C1through hypoglossal. • Blood supply: superior thyroid artery.
    48. 48. BUCCINATOR • Origin: it is a wide muscle that arises from a horse shoe shaped line along the outer surfaces of the maxillary and mandibular alveolar processes in the area of the molar teeth. • It originates from pterygomandibular ligament. • Buccinator fibers arising from the mandible follow the external oblique line to the mesial aspect of the first molar and ascend slightly towards the corner of mouth.
    49. 49. Insertion • Some fibers insert into the mucous membrane of cheek and modiolus. • Remaining fibers enter the upper and lower lips to become a part of the orbicularis oris muscle.
    50. 50. Action • It pulls the corners of the mouth laterally and posteriorly. • Major function is to keep the cheeks taut. • If it were not so, when jaw closes, the cheeks collapse and be caught between the teeth. This is seen in senile patients or individuals with facial paralysis. • This muscle helps in deglutition. • Provides support and mobility for the soft tissues of cheek.
    52. 52. Masseter muscle: • The contraction of masseter muscle pushes the buccinator fibers against the denture border. For this reason, the borders must converge rapidly towards the retro-molar pad. • At the time of preliminary impression is made, while the compound on the borders of the impression tray in this region is still soft, considerable downward force should be exerted on the lower jaw by dentist. • Now the patient is attempting to counteract this downward pressure which will cause the masseter muscle to contract. • This forces the softened compound away from impingement in this region. • Thus the denture border can also be contoured to accommodate this action. If this is not done the muscle interaction will displace the mandibular denture and force it in an anterior direction
    53. 53. Temporalis muscle • Temporalis does not participate in biting force when the mandible is in protrusion. • Therefore the action of this muscle is sometimes used as a test to determine whether the patient is closing in centric relation. • When the mandible is in protrusion, no bulging can be felt with fingers on the side of the head. • This muscle is more sensitive to occlusal interferences than any muscle.
    54. 54. Mylohyoid muscle • It elevates the hyoid bone, the tongue and the membranous floor of the mouth during swallowing. • If the denture flange is extended below and under the mylohyoid line, it will impinge on the mylohyoid muscle and can affect its action adversely. • Thus the action of the muscle can unseat the denture. • As the fibers are directed downwards, the denture flange can extend below but not under the mylohyoid line. This places the inferior border of the denture in a compatible position with tongue.
    55. 55. Buccinator muscle • The action of buccinator muscle does not directly dislodge the denture because the muscle fibers contract in a line parallel to the plane of occlusion. • When masseter is activated, it pushes the buccinator medially against the denture border in the area of retro molar pad. • This is a dislodging force and the denture base should be contoured to accommodate this interaction between the buccinator and masseter. • This is termed as` masseter groove’. • The position of attachment of buccinator muscle in the upper jaw determines the vertical height of the disto buccal flange of the maxillary denture.
    56. 56. References • Gray’s anatomy - • Anatomy and physiology - Rod.R.Steley. • Anatomy of orofacial structures - Brand – 6th edition. • Occlusion - Major Ash. • Occlusion principles and concepts - José dos Santos - 2’nd edition. • Text book of complete dentures - Rahn. -5’Th edition. • Boucher’s prosthodontic treatment for edentulous patients – 10’Th edition. • Fundamentals fixed prosthodontics - H.T.Shillingburg.Jr
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