Muscles Of Mastication

Presentation describing the anatomy of muscles of mastication along with actions, functions, applied anatomy and conditions encountered in dental scenario along with treatment modalities

1. MUSCLES OF MASTICATION Dr. HRISHITA MDS- PART 1

2. CONTENTS INTRODUCTION BASIC PHYSIOLOGY OF MUSCLE CONTRACTION DEFINITION OF MASTICATION WHAT ARE MUSCLES OF MASTICATION DEVELOPMENT OF MUSCLES OF MASTICATION CLASSIFICATION PRIMARY MUSCLES OF MASTICATION ACCESORY MUSCLES OF MASTICATION SUMMARY OF ACTION OF MUSCLES OF MASTICATION MASTICATORY MUSCLE DISORDERS CONCLUSION REFERENCES

3. Muscles are contractile tissues that bring about movement Considered as motors of the body as they produce force and motion INTRODUCTION

4. Muscles in vertebrates are classified as- STRIATIONS CONTROL FUNCTION Striated Voluntary Skeletal Non Striated Involuntary Cardiac Smooth

5. The skeletal muscle is grossly divided into the following parts: PARTS FLESHY PART- BELLY FIBROUS PART- TENDON OR APONEUROSIS

6. ENDS ORIGIN INSERTION

7. BASIC PHYSIOLOGY OF MUSCLE CONTRACTION Ultrastructure of muscle shows the presence of 4 protein molecules MYOSIN ACTIN TROPONIN TROPOMYOSIN

8. An action potential arrives at the neuromuscular junction Acetyl Choline is released, binds to the receptors This opens sodium ion channels, leading to an action potential in sarcolemma The action potential travels along the T Tubules (transverse tubules) Calcium is released

9. Calcium binds to troponin , which moves the tropomyosin , exposing the myosin binding sites on the actin molecule Myosin binds to the myosin binding sites on the actin molecules and pulls the actin molecule (THE POWER STROKE )

10. Mastication is defined as the rhythmic opposition and separation of jaws with the involvement of teeth, lips, cheek and tongue for chewing of food in order to prepare it for swallowing and digestion DEFINITION OF MASTICATION

11. Three phases- Opening phase - Mouth opened, Mandible depressed Closing phase- Mandible raised to maxilla Occlusal/ Intercuspal phase- T eeth from upper and lower arches approximate PHASES OF MASTICATION

12. Muscles of mastication are the group of skeletal muscles that help in movement of the mandible during chewing and speech WHAT ARE THE MUSCLES OF MASTICATION?

13. FUNCTIONS OF MUSCLES OF MASTICATION To move mandible Secure and stabilize mandibular positions Determine directions of mandibular movements

14. The muscular system develops from the intra embryonic mesoderm They develop from the embryonic cells called myoblast 5 th -6 Th week Primitive cells form and differentiate DEVELOPMENT OF MUSCLES OF MASTICATION

15. 7 th week Mandibular arch mass enlarges Cells migrates to the areas of formation of the 4 major muscles of mastication 10 th week Muscle mass well organized Nerve mass gets incorporated

16. MUSCLES OF MASTICATION PHARYNGEAL ARCH NERVE Masseter, Medial Pterygoid, Lateral Pterygoid, Temporalis, Mylohyoid, Anterior Digastric 1 st Arch- Mandibular arch Mandibular Nerve (branch of Trigeminal Nerve) Posterior Belly Of Digastric 2 nd arch- Hyoid Arch Facial Nerve Geniohyoid Occipital Myotomes Hypoglossal Nerve

17. CLASSIFICATION PRIMARY MUSCLES ACCESSORY MUSCLES Masseter Digastric Temporalis Stylohyoid Lateral Pterygoid Mylohyoid Medial Pterygoid Geniohyoid

18. FUNCTIONAL CLASSIFICATION JAW ELEVATORS JAW DEPRESSORS Masseter Lateral Pterygoid Temporalis Digastric Medial Pterygoid Mylohoid Geniohyoid

19. PRIMARY MUSCLES OF MASTICATION

20. Quadrilateral muscle Partly fleshly, partly tendinous Covers the lateral part of ramus of mandible Multi- pentate arrangement of fibres MASSETER MUSCLE

21. LAYER ORIGIN INSERTION Superficial (Largest) From anterior 2/3 rd of lower border of zygomatic arch & adjoining zygomatic process of maxilla Into the lower part of lateral surface of ramus of mandible Middle From lower border of posterior 1/3 rd of zygomatic arch Into the central part of ramus of mandible Deep From deep surface of zygomatic arch Into rest of the ramus of the mandible Consists of 3 layers-

22. NERVE SUPPLY- Masseteric Nerve BLOOD SUPPLY- ARTERIAL - Masseteric branch of Maxillary artery VENOUS - Venous drainage through Masseteric vein

23. FUNCTIONS - Elevates the mandible to close the mouth & to occlude the teeth in mastication Small lateral movements Protrusion

24. SUPERFICIAL RELATIONS PAROTID GLAND & DUCT 4 BRANCHES OF FACIAL NERVE TRANSVERSE FACIAL ARTERY

25. DEEP RELATIONS THE INSERTION OF THE TEMPORALIS MUSCLE MASSETERIC NERVES AND VESSELS RAMUS OF THE MANDIBLE

26. ANTERIOR RELATIONS BUCCAL ARTERY BUCCAL NERVE BUCCINATOR MUSCLES BUCCAL PAD OF FAT

27. PALPATION Patient is asked to clench their teeth The practitioner uses both hands to palpate the masseter muscles on both sides extra orally Palpation is done along- Origin of masseter bilaterally along the zygomatic arch Continue to palpate down the body of the mandible to where the masseter is attached

28. APPLIED ANATOMY Most powerful muscle for the closure of the mandible Masseter is sometimes the target of plastic jaw reduction surgery This muscle commonly undergoes Hypertrophy in Bruxism

29. MASSETER REFLEX/ MANDIBULAR REFLEX/ JAW JERK REFLEX Neurological examination of jaw jerk reflex Examiner places index finger on chin of the patient and taps the finger with reflex hammer Normally, the masseter stretch provides upward movement of the mandible Indicative of a lesion of the Trigeminal nerve

30. TEMPORALIS MUSCLE Located in the temporal region Fan shaped Largest masticatory muscle

31. ORIGIN Temporal fossa- from the inferior temporal line INSERTION Margins & deep surface of the coronoid process Anterior border of the ramus

32. NERVE SUPPLY Two deep temporal branches BLOOD SUPPLY Deep temporal arteries branch of maxillary artery Superficial temporal vein & middle temporal vein

33. FUNCTIONS Anterior fibres- elevate the mandible Posterior fibres- retract the mandible Middle fibres - elevate and retract the mandible Posterior fibres draw the mandible backwards after it has been protruded Contributes side to side grinding movement

34. SUPERFICIAL RELATIONS SKIN SUPERFICIAL FASCIA AURICULARIS MUSCLE (ANTERIOR & SUPERIOR) TEMPORAL FASCIA SUPERFICIAL TEMPORAL VESSELS AURICULOTEMPORAL NERVE ZYGOMATIC ARCH MASSETER MUSCLE

35. DEEP RELATIONS MAXILLARY ARTERY BUCCAL NERVE & ARTERY DEEP TEMPORAL VESSELS & NERVE TEMPORAL FOSSA LATERAL & MEDIAL PTERYGOID BUCCINATOR PTERYGOID PLEXUS OF VEINS

36. PALPATION Divided into 3 parts that are palpated separately Patient is asked to clench The anterior region is palpated above the zygomatic arch, anterior to the TMJ The middle region is palpated directly above the TMJ & superior to the zygomatic arch The posterior region is palpated above and behind the ear ANTERIOR MIDDLE POSTERIOR

37. APPLIED ANATOMY The temporalis muscle is accessible on the temples and can be seen and felt contracting while the jaw is clenching and unclenching The temporal muscle is covered by temporal fascia, also known as temporal aponeurosis Sudden contraction of temporalis will result in coronoid fracture , which is rare

38. MEDIAL PTERYGOID Rhomboidal Muscle 2 heads- Superficial head Deep head

39. LAYER ORIGIN INSERTION Superficial Head From tuberosity of maxilla and adjoining bone Roughened area on the medial surface of angle and adjoining ramus of mandible, below and behind the mandibular foramen & mylohyoid groove Deep Head From medial surface of lateral pterygoid plate & adjoining process of palatine bone

40. NERVE SUPPLY Nerve to medial pterygoid

41. BLOOD SUPPLY Pterygoid branch of 2 nd part of Maxillary artery Lingual Vein

42. FUNCTIONS Elevates mandible Help protrude mandible Produce side to side movements

43. SUPERFICIAL RELATIONS UPPER PART OF MUSCLE SEPARATED FROM LATERAL PTERYGOID BY- Lateral Pterygoid Plate Lingual Nerve Inferior Alveolar Nerve UPPER PART OF MUSCLE SEPARATED FROM RAMUS OF MANDIBLE BY Lingual Nerve Inferior Alveolar Nerve Maxillary artery Sphenomandibular ligament

44. DEEP RELATIONS Tensor Veli Palitini Superior Constrictor muscle of Pharynx Styloglossus Muscle Stylopharyngeus Muscle

45. PALPATION Palpated by placing the finger on the lateral aspect of the pharyngeal wall of the throat This palpation is difficult and sometimes uncomfortable for the patient The muscle contracts as the teeth are coming in contact

46. APPLIED ANATOMY Is sometimes involved in MPDS Trismus following inferior alveolar nerve block is mostly due to involvement of medial pterygoid muscle When the medial pterygoid muscle is hypertonic , the patient is aware of a fullness in the throat and occasional pain on swallowing

47. LATERAL PTERYGOID Occupies primarily a horizontal position Thick, short, conical and triangular muscle 2 heads Superior head Inferior head

48. LAYER ORIGIN INSERTION SUPERFICIAL HEAD From infratemporal surface and crest of greater wing of sphenoid bone Pterygoid fovea on the anterior surface of neck of mandible INFERIOR HEAD From lateral surface of lateral pterygoid plate Anterior margin of articular disk and capsule of TMJ

49. NERVE SUPPLY Anterior branch of Mandibular nerve

50. BLOOD SUPPLY Pterygoid branches of Maxillary artery Ascending palatine artery of facial artery Lingual vein

51. FUNCTIONS TOGETHER - Protrude the mandible Depress the chin ALONE & ALTERNATING - Provide side-to-side movement of the mandible

52. SUPERFICIAL RELATIONS Masseter Ramus of Mandible Tendon of Temporalis Maxillary artery

53. DEEP RELATIONS Mandibular nerve Middle meningeal artery Sphenomandibular ligament Deep head of medial pterygoid

54. STRUCTURES EMERGING FROM UPPER BORDER: Deep Temporal Nerves Masseteric Nerve

55. STRUCTURES PASSING BETWEEN TWO HEADS : Maxillary Artery Buccal Branch Of Mandibular Nerve

56. STRUCTURES EMERGING FROM LOWER BORDER: Lingual nerve Inferior Alveolar Nerve Middle Meningeal Artery (passes upwards)

57. PALPATION Place the forefinger over the buccal area of the maxillary 3 rd molar region and exerting pressure in a posterior, superior and medial direction behind the maxillary tuberosity

58. APPLIED ANATOMY Most commonly involved in MPDS Unilateral failure- results in deviation of mandible towards the affected side on opening Bilateral failure- limited opening, loss of protrusion, loss of full lateral deviation In patients with occlusal interferences on the non working side , the lateral pterygoid on the opposite side of the interference becomes painful

59. ACCESORY MUSCLES

60. DIGASTRIC 2 muscles joined by intermediate tendon FUNCTION- Depression of the jaw Elevates the hyoid bone

61. MYLOHYOID Flat, triangular muscle Forms floor of the mouth FUNCTION - Helps in depression of the mandible Elevates the hyoid bone Elevates the floor of the mouth during deglutition

62. GENIOHYOID Short, narrow muscle Lies above mylohyoid FUNCTIONS Carry the hyoid bone & tongue upward during deglutition

63. STYLOHYOID Small muscle FUNCTION- Pulls hyoid bone upward and backwards

64. BUCCINATOR Muscle of the cheek FUNCTIONS- Flatten cheek against gums and teeth Prevent accumulation of food in the vestibule of the mouth Brings food to the occlusal table during mastication

65. ACTION PRIME MOVERS ANTAGONIST ELEVATION MASSETER MEDIAL PTERYGOID TEMPORALIS LATERAL PTERYGOID DEPRESSION LATERAL PTERYGOID DIGASTRIC GENIOHYOID MYLOHYOID ELEVATOR GROUP OF MUSCLES PROTRUSION LATERAL PTERYGOID MASSETER MEDIAL PTERYGOID DIGASTRIC POSTERIOR TEMPORAL FIBRES RETRUSION POSTERIOR & MEDIAL TEMPORAL FIBRES DIGASTRIC MASSETER LATERAL PTERYGOID SUMMARY OF ACTION OF MUSCLES OF MASTICATION

66. SUMMARY OF ACTION OF MUSCLES OF MASTICATION LATEROTRUSION- Lateral and Medial Pterygoids ELEVATION OF HYOID BONE- Posterior belly of Digastric, Mylohyoid, Geniohyoid .

67. MASTICATORY MUSCLE DISORDERS

68. TRISMUS Normal opening of mouth is restricted - Spasm of the muscles Masseter more commonly affected PROBLEMS- Difficulty in eating and swallowing Oral hygiene issues Joint immobilization TREATMENT- Removal of the cause Heat therapy Warm saline rinses NSAIDS Passive muscle stretching

69. BRUXISM Bruxism is the clenching or grinding of the teeth when the individual is not chewing or swallowing OCCURS AS- Brief rhythmic strong contractions of the jaw muscles in eccentric lateral jaw movements Maximum intercuspation - clenching Bruxism leads to tooth wear fracture of tooth and restoration muscle hypertrophy TREATMENT - Coronoplasty Stabilization appliance

70. MYOFACIAL PAIN DYSFUNCTION SYNDROME (MPDS)- It is a pain disorder in which unilateral pain is referred from trigger points in myofascial structures, to muscles of head and neck region No organic lesion clinically TRIGGER POINTS- Caused by stimuli - pressure on muscles creates trigger points Palpation of trigger points leads to POSITIVE JUMP SIGN

71. 4 CARDINAL SIGNS & SYMPTOMS- Pain and discomfort (especially morning hours) Muscle tenderness Clicking or popping in TMJ Limitation of mandibular movements unilaterally or bilaterally DIAGNOSIS When no clinically detectable organic lesion but with signs and symptoms

72. TREATMENT Mostly self-limiting Conservative management usually Patient education and self care practices Medications- NSAIDs Physical therapy Relaxation techniques-eliminating muscle spasms Psychological counselling

73. MYALGIA Muscle pain disorder SYMPTOMS- Localised pain Fatigue while chewing SIGNS- Tenderness on palpation Sometimes limited active vertical range

74. TREATMENT Rest of the muscle Pain Relievers Apply Ice- to reduce pain and inflammation

75. HYPERPLASIA/HYPERTROPHY Occurs rarely and mostly affects masseter & orbicularis oris Enlargement in size of the affected muscle, which shows an asymmetric facial pattern & stiffness in TMJ Associated with hypermobility of the muscles

76. ATROPHY Decrease in size ETIOLOGY - Disuse and fixation Aging and cachexia Denervation Muscular dystrophies Nutritional disturbances Infections and toxins Muscular hypotonias Vascular changes

77. Acquired autoimmune disorder clinically characterised by weakness of skeletal muscles and fatigability on exertion MYASTHENIA GRAVIS

78. CLINICAL FEATURES Rapidly developing weakness in voluntary muscles following minor activity Difficulty in mastication and deglutition , drooping of jaw. Speech slow and slurred Disturbance in taste sensation TREATMENT Physostigmine - intramuscularly. Immunosuppressants

79. Inflammation of muscles ETIOLOGY- Microbial, physical, chemical injuries ORAL MANIFESTATIONS- Masseter and temporalis more commonly affected Have difficulty in opening mouth MYOSITIS OSSIFICANS TREATMENT- Surgical excision of localised inflammatory tissue which is calcified Prognosis is good

80. Secondary spaces are associated with the muscles of mastication Namely- Masseteric, Pterygomandibular , Superficial, Infratemporal & Deep Temporal ETIOLOGY- Odontogenic infections, trauma, oral malignancies etc CLINICAL MANIFESTATIONS- Trismus Swelling Pyrexia & Malaise FASCIAL SPACE INFECTION

81. TREATMENT- Intraoral or Extraoral incision Antibiotic coverage Hospitalisation may be required in severe cases

82. The clinician should have a through knowledge about these muscles as they have a prime function in mastication and deglutition for providing nutrition to the body Pathologies in these muscles may affect the patient and the treatment plan we formulate for the patient CONCLUSION

83. BD Chaurasia , Human Anatomy (head, neck, face) part 3, 5 th Edition Shafer, Hine, Levy; Shafer’s textbook of Oral pathology, 7 th edition Nelson, Ash; Wheeler’s Dental Anatomy, Physiology and Occlusion, 9 th edition Inderbir Singh, G P Pal; Human Embryology, 9 th edition REFERENCES

84. THANK YOU