The document discusses the muscles of mastication - the muscles involved in chewing. It describes the anatomy, development, functions and clinical significance of the main muscles - the masseter, temporalis, lateral and medial pterygoid muscles. Conditions involving the muscles like myofascial pain dysfunction syndrome, trismus and benign masseteric hypertrophy are also covered. The muscles of mastication are important for prosthodontists to consider during treatments like impression making and recording jaw relations.

1. MUSCLES OF MASTICATION
MD ADNAN SHAUKAT
1ST YEAR PG
DEPT OF PROSTHODONTIC

2. CONTENTS
• INTRODUCTION
• DEVELOPMENT
• ANATOMY
• ACTIONS
• INNERVATIONS AND VASCULATURE
• CLINICAL SIGNIFICANCE AND APPLIED ASPECTS
• CONCLUSION
• REFERENCES

3. INTRODUCTION
• Muscle - an organ that by contraction produces
movements of an animal; a tissue composed
of contractile cells or fibers that effect movement
of an organ or part of the body.
• Mastication - is defined as the process of chewing
food in preparation for swallowing and digestion.

4. Development
 Muscles of mastication develop from the
mesoderm of the first pharyngeal arch.
 They are innervated by the Mandibular
division of the trigeminal nerve. But the
posterior belly of digastric muscle
develops from second brachial arch and
supplied by facial nerve.

5. Functionally, the muscles
of mastication are classified as
Jaw elevators Jaw depressors
Masseter
Temporalis
Medial pterygoid
Lateral pterygoid
Anterior digastric
Geniohyoid
Mylohyoid

6. Traditionally four powerful muscles and are called as
muscles of mastication.
Masseter
Temporalis
Medial Pterygoid &
Lateral pterygoid

7. ACCESSORY MUSCLES
SUPRAHYOID MUSCLES
Mylohyoid
• Geniohyoid
• Stylohyoid
• Digastric
INFRAHYOID MUSCLES
• Sternothyroid
• Omohyoid
• Thyrohyoid
• Sternohyoid

11. Short rectangular muscle.
Has a superficial layer, middle layer and deep
layer.
Superficial fibres pass downwards and
backwards at 45 degrees
Deep fibres pass vertically downwards
MASSETER MUSCLE

12. Superficial layer
Origin : from anterior 2/3 rd of zygomatic arch
and adjoining zygomatic process of maxilla.
Insertion : angle and lower posterior half of
lateral surface of mandibular ramus.

13. Middle layer
• Origin : from medial aspect of anterior 2/3rds of
zygomatic arch and from the lower border of
posterior third.
• Insertion : into the centre part of the ramus of the
mandible.

14. Deep layer
Origin : from the whole length of deep surface of
the zygomatic arch.
Insertion : into upper part of mandibular ramus and
its coronoid process.

15. Relations
Superficial : skin , platysma , risorius ,
zygomaticus major , parotid gland .
Deep : temporalis and mandibular ramus ,
masseteric nerve and artery .
Posterior margin : overlapped by parotid
gland .
Anterior margin projects over buccinator and
crossed below by facial vein.

18. Actions
Elevates mandible to occlude teeth in
mastication .
lateral movements of the mandible for
efficient chewing and grinding of the food.
unilateral chewing.
Retraction of the mandible.

19. Nerve supply
Anterior trunk of mandibular nerve.
Blood supply
 Massetric artery

20. Palpation
The patient is asked to clench their teeth and,
using both hands, the practitioner palpates
the masseter muscles on both sides
extraorally, making sure that the patient
continues to clench during the procedure.
Palpate the origin of the masseter
bilaterally along the zygomatic arch
and continue to palpate down the body of
the mandible where the masseter is attached

22. Clinical Importance of Masseter
Muscle of Mastication
On Denture border
 An active masseter muscle will create a
concavity in the outline of the distobuccal border
and a less active muscle may result in a convex
border.
In this area the buccal flange must converge
medially to avoid displacement due to
contraction of the masseter muscle because the
muscle fibers in that area are vertical and
oblique.

23. Activation of massetric notch and
distal areas
• Instruct the patient to open wide and then to
close against the resting force of your finger.

24.  Opening wide activates the muscles
of pterygo-mandibular raphe by stretching,
which thereby defines the most distal
extension.
 Instructing the patient to close
against your fingers on the tray
handle causes masseter muscle to
contract and push against the
medially situated buccinator
muscle.

25. Temporalis
• Fan shaped muscle
• Begins lateral development in the 8th week
occupying the space anterior to otic capsule, as the
temporal bone begins to ossify in the 13th week ,
muscle attaches to it.

26. Arises from the whole of the temporal fossa and from
the deep surface of temporal fascia.

28. • Fibres converge and descend into a tendon which
passes through gap between zygomatic arch and side
of the skull and attaches to medial surface , apex ,
anterior and posterior borders of the coronoid
process and anterior border of the mandibular ramus
almost to the last molar teeth.

31. Relations
• Superficial : skin , auriculares anterior and
superior , temporal fascia , superficial temporal
vessels , auriculotemporal nerve , temporal
branches of facial nerve , zygomaticotemporal
nerve , epicranial aponeurosis, zygomatic arch
and masseter.
• Deep : temporal fossa , lateral pterygoid ,
superficial head of the medial pterygoid ,
buccinator , maxillary artery , deep temporal
nerves and buccal nerve and vessels.

33. Nerve supply
• Deep temporal branches of anterior trunk of
mandibular nerve .
Blood Supply
• Deep temporal artery

35. Actions
• Elevation of the mandible
• Retraction of the mandible.
• Crushing of food between the molars.
• Posterior fibers draw the
mandible backwards after it has been
protruded.
• It also contributes side to side grinding
movement.

36. Palpation
• To locate the muscle ,ask the patient to clench.
• Apply two pounds of pressure

37. • The anterior region is palpated above the zygomatic
arch and anterior to the TMJ
• The middle region is palpated directly above the
TMJ and superior to the zygomatic arch
• The posterior region is palpated above and behind
the ear.

38. Clinical Importance of Temporalis
Muscle:
• Sudden contraction of temporalis muscle will
result in coronoid fracture, which is rare.
• The patient is instructed to close and move his
mandible from side to side and then
immediately asked to open wide.
• The side to side motion records the activity
of the coronoid process in a closed
position whereas opening causes the coronoid
to sweep past the denture periphery.

39. LATERAL PTERYGOID
 Short thick muscle , 2heads.
Upper head – arises from infratemporal surface and
infratemporal crest of greater wing of sphenoid .
Lower head – lateral surface of lateral ptergyoid plate.

41. Insertion : Depression in the front of
neck of the mandible , articular
capsule and disc of TMJ.

42. Relations
• Superficial : mandibular ramus , maxillary
artery tendon of temporalis and masseter.
• Deep : upper part of medial pterygoid ,
sphenomandibular ligament , middle
meningeal artery and mandibular nerve.
• Upper border : temporal and massetric
branches of mandibular nerve
• Lower border : lingual ,inferior alveolar nerves
and middle meningeal artery

44. Structures passing through the gap between the 2 heads :
 Maxillary artery
 Buccal branch of mandibular nerve .

45. Nerve supply
Anterior trunk of mandibular nerve.
Blood supply
Pterygoid branch of Maxillary artery
Actions:
SUPERIOR HEAD
Active during power stroke; which is closure of mandible
against resistance such as chewing, clenching the teeth
together.
INFERIOR HEAD
Depresses the mandible to open mouth, with suprahyoid
and infrahyoid muscle.

46. PALPATION OF THE LATERAL
PTERYGOID
Placing the forefinger, or the little finger, over the
buccal area of the maxillary third molar region and
exerting pressure in a posterior, superior, and medial
direction behind the maxillary tuberosity.

47. Clinical Importance of Lateral Pterygoid Mus
 Most commonly involved muscle in MPDS
 Unilateral failure of lateral pterygoid muscle
to contract results in deviation of the
mandible toward the affected side on
opening.
 Bilateral failure results in limited opening, loss
of protrusion and loss of full lateral deviation.

48. Medial pterygoid muscle
 Thick quadrilateral muscle

49. Origin
• Superficial head: originates from the maxillary
tuberosity and the pyramidal process of palatine
bone.

50. Deep head originates from the medial surface of
the lateral pterygoid plate and pyramidal process
of palatine bone.

51. Insertion :Roughned area of the medial surface of
the angle and adjoining ramus of mandible, below
and behind the mandibular foramen and mylohyoid
groove.

52. Relations
• Lateral surface : mandibular ramus
sphenomandibular ligament , maxillary artery
, inferior alveolar vessels and nerve , lingual
nerve and parotid gland .
• Medial surface: tensor veli palitini ,
styloglossus , stylopharyngeus and areolar
tissue.

54. Nerve Supply
• Mandibular nerve
Blood supply
• Pterygoid branch of Maxillary artery
Actions
• Elevates the mandible,
• Helps in side to side movement

55. Palpation of medial pterygoid
• Gently palpate them on the medial aspect of t
he
jaw, simultaneously from both inside and outsi
de the mouth.

56. Clinical Importance of Medial
Pterygoid Muscle:
• Medial Pterygoid muscle can be palpated only
intra-orally.
• Most commonly involved in MPDS.
• Trismus following inferior alveolar nerve block
is mostly due to involvement of medial
pterygoid muscle.

63. APPLIED ASPECTS
• 1. MPDS
• 2. Muscle dysfunction
• 3. Trismus
• 4. Temporal tendonitis
• 6. Benign masseteric hypertrophy

64. MYOFACIAL PAIN DYSFUNCTION
SYNDROME
• Myofacial pain is a regional myogenous pain condition
characterized by local areas of firm, hypersensitive bands of
muscle tissue known as trigger points.
• First described by Travell and Rinzler in 1952.
• In 1969, Laskin described MPDS.
• Laskin’s cardinal signs:
1. Muscle tenderness
2. Pain
3. Clicking or propping noise in TMJ
4. Limited jaw movement.

65. Masseter muscle
• Trigger points in superficial layer of the muscle
refers to posterior mandibular and maxillary
teeth, the jaw, and the face.
• Deep portion refers to ear and TMJ
• Moderate restriction of opening assosiated
with ipsilateral deflection of the midline incisal
path observed.

66. Temporalis muscle
• Reference zone : maxillary teeth and upper portion of the
face.
• Headache and toothache are common complaints
Medial Pterygoid muscle
• Reference zone : posterior part of mouth and throat, TMJ and
infra auricular areas.
• Throat pain and infra auricular pain are common.
• Moderate restriction of mouth opening.
• Contralateral deflection of the midline incisal path.
• Pain source is accentuated by opening widley and biting
firmly.

67. Lateral pterygoid muscle
• INFERIOR LP
• Trigger points in the TMJ region.
• Slight acute malocclusion of ipsilateral posterior
teeth and premature occlusion of contralateral
anterior teeth.
• SUPERIOR LP
• Referred to zygomatic area
• Diffuse pain in the malar area

68. Treatment
• Pain control (salicylates)
• Tranquilizers ( Diazepam 2-5mg at bedtime)
• Anti depressents
• Sedatives and hypnotics
• Tongue exercise
• Mouth opening exercise
• Hot packs
• Electrical stimulation (TENS)
• Anesthesia
• Surgery : eminectomy, zygomectomy, menisectomy,
high condylectomy

69. Muscle dysfunction

70. TRISMUS
• Trismus is defined as the significant restriction in mouth
opening due to spasm of masticatory muscles.
• Also called as locked jaw.
• Kazanjian divided ankylosis into true and false ankylosis.
• True kind is attributed to the pathologic conditions of the
joint.
• False kinds is applied to restrictions of movement resulting
from extra articular joint abnormalities. This is referred to
as trismus.

71. • Normal mouth opening :
Males : 39-70mm
Females : 36-56mm
Lateral movement :8-12mm
Reduced mouth opening observed

72. CAUSES
• Masticatory space Infections
• Inflammation of muscles of mastication
• Acute Pericoronitis
• Peritonsillar abscess
• TMJ disorders
• OSMF
• Trauma
• Iatrogenic
• Radiotherapy and chemotherapy

73. Treatment
• Heat therapy : consists of placing moist hot towels on the
affected area for 15–20 minutes every hour.
• Analgesics
• Muscle relaxants :diazepam (10mg bid) or other
benzodiazepine may be prescribed for muscle relaxation.
• Mouth opening exercises
• If trismus is attributed to infections, appropriate antibiotics
need to be administered.

74. Temporal tendonitis
• Chronic strain from temporalis muscle pulling
on tendon that attaches to mandible.
• Causes sharp headaches in temple just to side
of eyes.

75. BENIGN MASSETERIC HYPERTROPHY
• Benign enlargement of muscles of mastication,
especially masseter muscle.
• Muscle enlarges upto three times its usual size.
• Increased bigonial angle
• May also be due to laterally placed ramus of the
mandible. It may not be a true form of BMH.
• Bruxism, TMJ dysfunction, unilateral chewing
maybe etiolgy of BMH.
• Non tender lateral facial mass that enlarges with
clenching of jaw.

76. Treatment
• Botulinum toxic A injection
• Surgery for cosmetic reasons
• Treat TMJ dysfunction

77. UNILATERAL ENLARGEMENT OF MASSETER
MUSCLE

78. TREATMENT DONE WITH BOTULINUM TOXIN

79. Conclusion
• The masticatory muscles include a vital part of the
orofacial structure and are important both
functionally and structurally.
• It can be influenced by a variety of factors many
of which are controlled by the practicing
prosthodontist:
• During functional impression making
• Accurate recording of various clinical parameters like
vertical dimension, centric relation.

80. References
 Grays Anatomy 37th edition and 38th edition.
 Bergman's Comprehensive Encyclopedia of
Human Anatomic Variation.
 Human anatomy A K Dutta.
 Burkits oral medicine diagnosis & treatment 10th
edition.
 Textbook of Complete dentures by Charles
M Heartwell.