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- Teeth 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
 5th-6Th week
• Primitive cells form and
differentiate
DEVELOPMENT OF MUSCLES OF MASTICATION

15.  7th week
• Mandibular arch mass
enlarges
• Cells migrates to the areas of
formation of the 4 major
muscles of mastication
 10th 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
1st Arch-
Mandibular
arch
Mandibular
Nerve (branch of
Trigeminal
Nerve)
Posterior Belly Of
Digastric
2nd 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 2/3rd
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 1/3rd 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 2nd 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 3rd 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, 5th Edition
Shafer, Hine, Levy; Shafer’s textbook of Oral
pathology, 7th edition
Nelson, Ash; Wheeler’s Dental Anatomy,
Physiology and Occlusion, 9th edition
Inderbir Singh, G P Pal; Human Embryology,
9th edition
REFERENCES

84. THANK YOU