MUSCLES OF MASTICATION

Hi, I am Dr Komal Ghiya, a pediatric dentist by profession and I am here to upload some of my own presentations regarding dentistry for educational purposed for all the dental students, both undergraduates and postgraduates as well as dentists. I hope you like the presentation. All the best!

1. MUSCLES OF MASTICATION BY DR. KOMAL GHIYA MDS PEDODONTICS AND PREVENTIVE DENTISTRY 1

2. INDEX PRIMARY MUSCLES OF MASTICATION : Masseter Temporalis Lateral Pterygoid Medial Pterygoid ACCESSORY MUSCLES OF MASTICATION : Digastric Mylohyoid Geniohyoid CLINIAL CONSIDERATIONS : 2

3. DEVELOPMENT OF MUSCLES OF MASTICATION The muscular system developes from intra-embryonic mesoderm from embryonic cells called “ myoblast “ Muscles of mastications are derived from first pharyngeal arch i.e mandibular arch ( first arch ) 3

4. MASSETER It is a quadrilateral muscle placed superficial to the ramus of the mandible. It has 3 layers Human anatomy- B.D.Chaurasia -volume 3 -4 th edition 4

5. ORIGIN Human anatomy- B.D.Chaurasia -volume 3 -4 th edition 5

6. INSERTION Human anatomy- B.D.Chaurasia -volume 3 -4 th edition 6

7. BLOOD SUPPLY – Masseteric branch of maxillary artery , facial artery , superficial temporal artery. NERVE SUPPLY – masseteric nerve (branch of anterior division of mandibular nerve. Human anatomy- B.D.Chaurasia -volume 3 -4 th edition 7

8. HOW TO PALPALTE THE MUSCLE Ask the patient to clench teeth and palpate extra-orally . The origin of muscle is palpated bilaterally along the zygomatic arch & continue to palpate down the body of the mandible , where masseter is attached Burket’s oral medicine – 11 th edition 8

9. ACTION OF MUSCLE Elevates the mandible to close the mouth to bite. While elevating it exerts presure on the teeth in molar region The deep portion of the muscle has a retracting component causing a combination of elevation and retraction Human anatomy- B.D.Chaurasia -volume 3 -4 th edition 9

10. APPLIED ANATOMY SUBMASSETERIC SPACE INFECTIONS : Sometimes infection around a mandibular 3 rd molar tooth tracks backwards, lateral to mandibular ramus & pus localizes deep to masseter Such an abscess lying deep to thick muscle produce little visible swelling , accompanied by profound muscle spasm & limitation of jaw opening 10

11. TEMPORALIS Fan shaped muscle Occupies the temporal fossa region between superior temporal line and zygomatic arch on side of head. It is a bipenate type of muscle Human anatomy- B.D.Chaurasia -volume 3 -4 th edition 11

12. ORIGIN AND INSERTION Origin – from temporal fossa excluding zygomatic arch and from temporal fascia Fibres – converge and pass deep to zygomatic arch Insertion – margins and deep surface of coronoid process and anterior border of ramus of mandible. Human anatomy- B.D.Chaurasia -volume 3 -4 th edition 12

13. TEMPORAL FOSSA AND FASCIA Temporal fossa – contains temporalis muscle, auriculotemporal nerve , superior temporal artery Temporal fascia – thick aponeurotic sheet that roofs the temporal fossa and covers temporalis muscle Contains – fat , superior temporal artery , zygomaticotemporal nerve gray”s anatomy -36 th edition 13

14. Vascular supply – form deep temporal branches of second part of maxillary artery Nerve supply – deep temporal branch of mandibular nerve Human anatomy- B.D.Chaurasia -volume 3 -4 th edition 14

15. ACTION OF MUSCLE Closes mouth – elevates mandible . This requires upward pull of anterior fibres and backward pull of posterior fibres because head of condyle rests n articular eminence when mouth is open. Side to side grlnding movement Posterior fibres retract protruded mandible Human anatomy- B.D.Chaurasia -volume 3 -4 th edition 15

16. HOW TO PALPATE THE MUSCLE First the patient is asked to clench teeth Fingers are placed over the patients temples to feel the muscle. Burket’s oral medicine – 11 th edition 16

17. APPLIED ANATOMY TEMPORAL TENDONITIS – chronic strain from temporalis muscle pulling on tendon that attaches to mandible leads to headache in temple region(at the side of eyes) Gray”s anatomy – 36 th edition 17

18. LATERAL PTERYGOID MUSCLE Short conical muscle Has 2 heads – upper and lower Unlike the other muscles of mastication , lateral pterygoid is NOT PENNATE , nor does it have significant no. of golgi tendon organs associated with its attachments. Human anatomy- B.D.Chaurasia -volume 3 -4 th edition 18

19. ORIGIN Gray”s anatomy – 36 th edition 19

20. INSERTION Fibres run backwards and laterally and converge for insertion. INSERTION – pterygoid fovea , on the anterior surface of neck of mandible Anterior margin of articular disc & capsule of of temporomandibular joint (TMJ) (INSERTION is posterolateral & slightly higher level than origin) Human anatomy- B.D.Chaurasia -volume 3 -4 th edition 20

21. VASCULAR SUPPLY – from pterygoid branches of maxillary artery NERVOUS SUPPLY – from nerve to lateral pterygoid (branch of anterior division of mandibular nerve) Human anatomy- B.D.Chaurasia -volume 3 -4 th edition 21

22. HOW TO PALPATE THE MUSCLE Placing the forefinger, or the little finger , over the buccal area of the maxillary 3 rd molar region & exerting pressure in a posterior , superior , & medial direction , just behind the maxillary tuberosity Burket’s oral medicine – 11 th edition 22

23. ACTION Depress mandible to open mouth with suprahyoid muscles Lateral & medial pterygoid protrude mandible Left lateral pterygoid & right medial pterygoid turn the chin to left side as a part of grinding movements (acting with medial pterygoid of same side it pulls neck of mandible forward with articular disc causing jaw to rotate around opposite condye as in chewing) Human anatomy- B.D.Chaurasia -volume 3 -4 th edition 23

24. Clinical Anatomy-Richard .S.Snell-7 th edition 24

25. APPLIED ANATOMY Most commonly involved muscle in MPDS . Unilateral failure of lateral pterygoid muscle to contract results in deviations of mandible towards the affected side on opening Bilateral failure results in, Limited jaw opening Loss of protrusion Loss of full lateral deviation Clinical Anatomy-Richard .S.Snell-7 th edition 25

26. MEDIAL PTERYGOID It is a quadrilateral muscle Has two heads : superficial and deep Clinical Anatomy-Richard .S.Snell-7 th edition 26

27. ORIGIN Human anatomy- B.D.Chaurasia -volume 3 -4 th edition 27

28. INSERTION Fibres run downwards , backwards and laterally Inserted into the posterior inferior part of the medial surfaces of the ramus and angle of the mandible, as high as mandibular foramen and nearly as far forward as the mylohyoid groove. Human anatomy- B.D.Chaurasia -volume 3 -4 th edition 28

29. VASCULAR SUPPLY – from pterygoid branches of maxillary artery NERVOUS SUPPLY – from nerve to medial pterygoid (branch of main trunk of mandibular nerve) Human anatomy- B.D.Chaurasia -volume 3 -4 th edition 29

30. HOW TO PALPATE THE MUSCLE Gently palpate the muscle on the medial aspect of the jaw. Simultaneously from both inside & outside the mouth Burket’s oral medicine – 11 th edition 30

31. ACTION To elevate the mandible To protrude the mandible with lateral pterygoid muscle Human anatomy- B.D.Chaurasia -volume 3 -4 th edition 31

32. APPLIED ANATOMY Most commonly involved in MPDS Trismus following inferior alveolar nerve block is mainly due to involvement of medial pterygoid muscle Clinical Anatomy-Richard .S.Snell-7 th edition 32

33. DIGASTRIC MUSCLE Clinical Anatomy-Richard .S.Snell-7 th edition 33

34. origin ANTERIOR BELLY- digastric fossa of mandible POSTERIOR BELLY-mastoid notch of the temporal bone INSERTION Intermediate tendon ( hyoid bone ) Human anatomy- B.D.Chaurasia -volume 3 -4 th edition 34

35. BLOOD SUPPLY : Anterior belly – submental branch of facial artery Posterior belly – occipital artery NERVE SUPPLY : Anterior belly – mylohyoid nerve , branch of mandibular division (V3) of trigeminal nerve (CN V) Posterior belly – branch of facial nerve (CN VII Human anatomy- B.D.Chaurasia -volume 3 -4 th edition 35

36. ACTIONS Pulls mandible back & down Retrusive and opening movements Elevation of hyoid bone Human anatomy- B.D.Chaurasia -volume 3 -4 th edition 36

37. MYLOHYOID MUSCLE Clinical Anatomy-Richard .S.Snell-7 th edition 37

38. ORIGIN It has 3 fibers- posterior, middle and anterior, which originates from the mylohyoid line of the mandible . Human anatomy- B.D.Chaurasia -volume 3 -4 th edition 38

39. INSERTION Posterior fibres pass medially and slightly downwards and are inserted into the body of the hyoid bone. Anterior and middle fibres from each side interesect in a medium fibrous raphe that unites right and left muscles to form floor of the mouth Human anatomy- B.D.Chaurasia -volume 3 -4 th edition 39

40. NERVE SUPPLY – mylohyoid nerve (branch of inferior alveolar nerve) BLOOD supply – inferior alveolar artery ( branch of maxillary artery) Human anatomy- B.D.Chaurasia -volume 3 -4 th edition 40

41. ACTIONS depresses the mandible (opening of mouth) Aids in swallowing by raising tongue and floor of mouh by elevating the hyoid bone Human anatomy- B.D.Chaurasia -volume 3 -4 th edition 41

42. GENIOHYOID MUSCLE Strap shaped muscle Origin – genial tubercle of mandible Insertion – anterior surface of body of hyoid bone Human anatomy- B.D.Chaurasia -volume 3 -4 th edition 42

43. Nerve supply – First cervical nerve , fibers pass through the hypoglossal nerve. Action of muscle – Elevates the hyoid bone Depress the mandible Human anatomy- B.D.Chaurasia -volume 3 -4 th edition 43

44. CLINICAL CO-RELATION HYPERTROPHY ATROPHY ANKYLOSIS MYASTHENIA GRAVIS TETANUS (LOCK JAW) BRUXISM MPDS MYOSITIS OSSIFICANS TRISMUS Oral pathology-Shafer-6 th edition 44

45. MYOSITIS OSSIFICANS Disease of unknown etiology affecting interstitial tissue of muscles as well as tendon,ligament . Often masseter muscle is involved leading to fixation of jaw. Muscle gradually replaced by connective tissue Then osteoid formation& subsequently ossification. Oral pathology-Shafer-6 th edition 45

46. Clinical features Masster and temporalis most commonly affected Leads to spasm of muscles and difficulty in jaw movements. Treatment – surgical excision Oral pathology-Shafer-6 th edition 46

47. MPDS ( Myofascial pain dysfunction syndrome) Pain disorder in which unilateral pain is referred from trigger points in myofascial structures to muscles of head and neck. Pain is constant and dull Oral pathology-Shafer-6 th edition 47

48. Symptoms Pain Limitation of motion of jaw Joint noises – clicking Tendernes to palpation of muscles of mastication Diagnosis Palpation Biting tests Radiographs TMJ arthrography CT,MRI Auriculotemporal nerve block Oral pathology-Shafer-6 th edition 48

49. Treatment Analgesics –aspirin(0.3-0.6gm/4 hrly – 2tabs) Muscle relaxants – diazepam(2-5mg for 10days) Heat application Cryotherapy Electrogalvanic stimulation TENS Stretch exercise and biofeeedback Intra- articular injections of hydrocortisone Oclussal splints Oral pathology-Shafer-6 th edition 49

50. MYASTHANIA GRAVIS Acquired autoimmune disorder due to antibodies directed towards acetylcholine receptor at neuromuscular junction of muscle Muscles of mastication and facial expression involved leading to weakness and fatigabiliy Oral pathology-Shafer-6 th edition 50

51. Features Difficulty in mastication Dropping of jaw Diplopia , ptosis,sorrowed appearance of face Exhaustion,loss of weight Treatment Physostigmine ( anticholinestererase ) Oral pathology-Shafer-6 th edition 51

52. TRISMUS It is a muscular involuntary protective reflex as a result of localized muscular irritation or inflammation ,which causes foreshortening of muscles of mastication (esp. temporalis & medial pterygoid ) Treatment- Heat therapy Warm saline rinses Analgesics and muscle relaxants Physiotherapy(jaw exercises) Oral pathology-Shafer-6 th edition 52

53. BRUXISM Habitual grinding or clenching of teeth either during sleep or as an unconscious habit during waking hours. Oral pathology-Shafer-6 th edition 53

54. TETANUS Acute infection of nervous system characterized by intense activity of motor neurons leading to muscle spasms(caused by clostridium tetani bacteria) Oral pathology-Shafer-6 th edition 54

55. References Human anatomy- B.D.Chaurasia -volume 3 -4 th edition Handbook of Local Anaesthesia-Stanley.F.Malamed-5 th edition Clinical Anatomy-Richard .S.Snell-7 th edition Oral pathology-Shafer-6 th edition Cunningham’s manual of practical anatomy- G.J.Romanes – volume 3 Textbook of clinical neuroanatomy – Vishram Singh 55

56. Grays anatomy-36 th edition Last’s anatomy-10 th edition Textbook of oral and maxillofacial surgery – Neelima Malik – 2 nd edition Burket’s oral medicine – 11 th edition 56