power point has a detailed description about muscles of mastication and mechanism of action of muscles and the important facts related to muscles of mastication as well as clinical importance, pathology related to all the muscles of mastication.

1. MUSCLES OF MASTICATION
• Dr. RAGHU D
• PG STUDENT
• DEPT. OF PAEDODONTICS AND
PREVENTIVE DENTISTRY
• SRI RAJIV GANDHI COLLEGE OF
DENTAL SCIENCES,
BANGALORE.

2. Contents
• Definitions
• Introduction
• Development of Muscles
• Classification of Muscles
• Anatomy of Skeletal Muscle
• Muscle Physiology
• Muscles of Mastication
• Primary Muscles
• Secondary Muscles
• Description of Each Muscles
• Actions
• Role of masticatory muscles in various mandibular
movements
• Pathology of Muscles
• Clinical importance
• Clinical considerations
• Modiolus
• Conclusion
• Reference

3. Definitions
• MUSCLE (Glossary of Prosthodontic terms 8):
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.
• MASTICATON (Glossary of Prosthodontic terms 8):
The process of chewing food for swallowing and digestion.

4. INTRODUCTION
• Muscle refer to a group of muscle fibers bound together by connective
tissue.
• Muscle generate force & movements used in the regulation of internal
environment.
• By controlling the activity of these muscles the human mind ultimately
expresses itself.

5. Development of Muscle
• Craniofacial muscles are derived from the seven somitomeres & the seven most-rostral
somites.
• Skeletal muscle may be derived from the somites, somitomeres and from lateral plate
Mesoderm.
• At these sites there are cells that are precursors of muscles.
• These cells undergo many divisions and finally differentiates into Myoblasts.
• Myoblasts synthesise the proteins Actin & Myocin.
• Myogenesis is the formation of muscular tissue, particularly during embryonic
development. Muscle fibers formed from the fusion of myoblasts into multi-nucleated
fibers called myotubes.

6. • Molecules of actin, myocin and other contractile proteins form myofibrils
that are arranged in definite orientation.
• Aggregation of fibrils pushes nuclei to the periphery. Muscle fibre thus
formed.
• Satellite cells present around muscle fibres can help in growth of fibres.

7. • Development of Striated Muscle
• Striated muscle is derived from somites, somitomeres and from mesenchyme of the region.
• Smooth muscle
• Almost all smooth muscle is derived from mesenchyme.
• Smooth muscles in the walls of viscera (e.g. the stomach) is formed from splanchnopleuric
mesoderm in relation to them.
• However muscles of the IRIS (spincter and dilator pupillae) and myoepithelial cells of the
sweat glands are derived from Ectoderm.

8. Cardiac muscle
• This is derived from splanchnopleuric
mesoderm in relation to the developing
heart tubes and pericardium.
Muscles of Mastication
• Muscles of Mastication are derived from
First or MANDIBULAR ARCH

9. Classification of Muscles
• Muscles of the body can be broadly
classified based on structure, contractile
properties, control mechanisms into
a) Skeletal muscle
b) Smooth Muscle
c) Cardiac Muscle

10. Skeletal muscle
• Constitutes about 40% of body mass. It is
attached to the skeleton by tendons. The
contraction of it is responsible for
supporting and moving the skeleton.
• It is also called voluntary muscle because it
contracts voluntarily when signal is sent to it
along the central nervous system.
• It is also called striated muscle because the
microscopic appearance shows cross
striations. Most of the orofacial region are
skeletal muscles.

11. Smooth muscle
• It is named so because it lacks the
cross striated banding pattern
found in skeletal muscle.
• It is also known as involuntary
muscle because it is not under
direct voluntary control instead
they are controlled by the
autonomic nervous
system(ANS).

12. Cardiac Muscle
• It is the muscle of the Heart and it
shows the features of both skeletal &
smooth muscle.
• It shows the characteristic striated
appearance of skeletal muscles &
involuntary in action like the smooth
muscle.
• Contraction of the cardiac muscle
propels the blood through the
circulatory system.

13. Muscle physiology

14. Action potential Motor Nerve Muscle fiber ending
Secretion of Acetyl choline
(small quantity) (neurotransmitter)
Acetyl choline gated channels
Sodium Ions flow
to interior of muscle fiber membrane
Action potential along Nerve
membrane
Release of Ca++ ions from
Myofibrils (Large quantity)
Contractile process
Pump back of Ca++ ions into
Sarcoplasmic reticulum
Travels deep to muscle fibers

15. MUSCLES OF MASTICATION
• These are the muscles that move the
mandible during mastication, speech
& deglutition.
• They move the mandible quickly &
precisely to enable different speech
sounds that are to be made in rapid
succession and they are also capable of
exerting enormous forces that are
required to break down tough foods.

16. PRIMARY MUSCLES OF MASTICATION
• MASSETER
• TEMPORALIS
• LATERAL PTERYGOID
• MEDIAL PTERYGOID

17. SECONDARY MUSCLES OF
MASTICATION
• Suprahyoid Muscles
• Infrahyoid muscles

18. Suprahyoid group
• DIGASTRIC
• MYLOHYOID
• GENIOHYOID
• STYLOHYOID (is another
suprahyoid muscle which doesn’t
takes part in mastication)

19. Infrahyoid Muscles
• STERNOTHYROID
• THYROHYOID
• OMOHYOID
STERNOCLEIDOMASTOID &
TRAPEZIUS

20. MASSETER
• It is a Quadrilateral muscle that
covers most of the lateral aspect of
the ramus. It consists of three
layers which bent anteriorly

21. • Superficial head : It is the largest and arises by a thick aponeurosis from the
maxillary process of zygomatic bone & from the anterior 2/3rd of the
inferior border of the zygomatic arch. Fibers pass downwards & backwards
at angle of 45 to Insert into angle and lower posterior half of the lateral
surface of the mandibular ramus.
• Middle head : Arises from medial aspect of anterior 2/3rd of the zygomatic
arch & from the lower border of the posterior 1/3rd of the zygomatic arch.
Fibers pass vertically downwards & Inserted into middle part of the ramus

22. • Deep head : Arises from the deep
surfaces of the zygomatic arch.
Fibers pass vertically downward
and Insert into superior border of
ramus as a triangular shaped
insertion field.

23. Nerve supply :
• It is supplied by massetric branch
from anterior division of
Mandibular nerve.

24. Vascular supply :
• It is supplied by a branch from 2nd
part of Maxillary artery

25. Actions
• It is a powerful elevator of the mandible & is very active during forceful
clenched (centric) occlusion.
• Deep head exerts primarily a vertical force on the mandible.
• Superficial head exerts vertical & anteriorly directed force.
• It also helps in Ipsilateral excursion

26. TEMPORALIS
• It is a fan shaped muscle that fills
the temporal fossa.
• Origin: The periphery of the fan is
attached to the inferior temporal
line & handle of the fan is attached
to the coronoid process below. It
takes origin from temporal fossa
except the zygomatic bone & from
the overlying temporal fascia.

27. • Insertion : Its Fibers converge to form a
tendon that descends downward & pass
through the gap between the side of the
skull and zygomatic arch.
• They get inserted into apex, medial
surface, anterior surface, & posterior
surface of the coronoid process.
• They also get inserted to the anterior
border of the ramus.

28. Blood supply:
• Deep temporal part of maxillary
artery.

29. Nerve supply:
• It is supplied by deep temporal
nerve which is a branch from
anterior division of Mandibular
nerve.

30. Actions
• Elevates the mandible, this movement requires both the upward pull of anterior
fibres and backward pull of posterior fibres.
• Posterior Fibres draw the mandible backwards after it has been protruded.
• It is also a contributor to side to side grinding movement.
• It maintains the normal mandibular rest position when the subject is an upright
position
• Posterior fibres are lie in an almost horizontal plane & therefore are in good
position to pull the protruded mandible back to centric occlusion.

31. • It also helps in Ipsilateral excursion. This is made possible by the fact that
the insertion of Temporalis is medial to the origin & therefore Temporalis
acts singly is capable of pulling the mandible to the same side or ipsilateral
side.

32. LATERAL PTERYGOID
• ORIGIN : It is a short thick muscle
with two parts or head
• Upper head arises from infratemporal
surface and infratemporal crest of
greater wing of sphenoid bone.
• Lower head arises from lateral surface
of the lateral pterygoid plate.

33. Insertion
• Its fibers pass backwards and
laterally to be inserted into a
depression (Pterygoid fovea) on
the front of the neck of the
mandible and into the articular
capsule and disc of the
temporomandibular articulation.

34. Blood Supply
• Pterygoid branch of 2nd part of
Maxillary artery.

35. Nerve Supply
• Branch of anterior division of the
Mandibular Nerve

36. Actions
• Inferior head : Both the inferior pterygoids acting together are the prime
protractors of the mandible. The fibers are in a perfect position hault the condyles
and articular disc forward in moving mandible into a protrusive position.
• Inferior heads of the both sides acting together depress the mandible by pulling
forward the condylar process of the mandible & articular disc while head of the
condyle rotates on the articular disc
• Inferior heads of each side acting singly brings about contralateral excursion.

37. • Superior head: They are inactive during opening.
• They are active however during mandibular elevation or closing along with
Temporalis, Masseter & Medial pterygoid
• Superior heads are active particularly when the teeth encounter resistance
such as bolus of food. Closure on resistance is termed as power stroke &
the superior lateral pterygoids play an active role in power stroke.

38. MEDIAL PTERYGOID
• Origin: It is a thick quadrilateral
muscle
• Attached to medial surface of
lateral pterygoid plate and grooved
surface of pyramidal process of the
palatine bone and tuberosity of
maxilla.

39. • Insertion: Its fibers pass downwards
laterally & backwards.
• Attached by a strong tendinous lamina,
to the postero-inferior part of
medial surface of the ramus and
angle of the mandible.
• It is attached as high as mandibular
foramen and as forward as the
mylohyoid groove.

40. Blood Supply :
• Pterygoid branch of 2nd part of
Maxillary artery.

41. Nerve supply :
• Branch of the main trunk of the
Mandibular Nerve,
i.e Nerve to medial pterygoid.

42. ACTIONS
• Assists in elevating the mandible
• Acting with the lateral pterygoid they protrude it.
• Acting with medial pterygoid of the same side advances the condyle, while
the jaw rotates through the opposite condyle
• When the medial and lateral pterygoid of two sides contract alternatively
to produce side to side movement of the mandible, eg: chewing

43. PALPATION OF MASTICATORY
MUSCLES :
• An accepted method of determining muscle tenderness or pain is to use the
fingers tips of middle & index finger to palpate specific anatomic sites.
• It has been proposed that 2 lb of digital pressure on extraoral muscles &
1 lb (453.59gms) pressure on intraoral areas held for 3 to 5 seconds are
appropriate.
• (Check for the tenderness)

44. SECONDARY MUSCLES

45. Digastric muscle
• The muscle has secondary role in
mastication as a depressor muscle
adding to the action of lateral
pterygoid muscle when mouth is to
be opened against resistance.
• It elevates the Hyoid bone.

46. Mylohyoid Muscle
• The secondary role of this muscle
is evident as a depressor seen in
action when mouth is to be opened
against resistance.
• It elevates the floor of mouth to
help in deglutition.

47. Geniohyoid muscle
• Geniohyoid elevates the hyoid
bone and draws it forward, thus
acting as a partial antagonist to
styloid muscle.
• When hyoid bone is fixed it
depresses the Mandible.

48. Sternohyoid muscle
• Function: Depress the hyoid bone.

49. Thyrohyoid muscle
• Depresses the hyoid bone and
elevates the larynx.

50. Omohyoid muscle
• Depresses the hyoid bone.

51. Sternocleidomastoid muscle
• The function of this muscle is to rotate
the head to the opposite side or obliquely
rotate the head.
• It also flexes the neck.
• When both sides of the muscle act
together, it flexes the neck and extends
the head.
• When one side acts alone, it causes the
head to rotate to the opposite side and
flexes laterally to the same side.
(ipsilaterally).

52. Trapezius muscle

53. Roles of muscles in various Mandibular
movements :
• A) Elevation :
Right & Left Temporalis Muscles ( anterior fibers)
Right & Left Masseter Muscle
Right & Left Medial pterygoid Muscle

54. • B) Depression:
Right & Left Inferior heads of Lateral pterygoids
Right & Left Suprahyoid and Infrahyoid muscles
Anterior belly of Digastric & Mylohyoid

55. • C) Protrusion :
Right & Left Inferior heads of Lateral Pterygoids
Right & Left Medial pterygoids
Right & Left superior heads of Masseter

56. • D) Retrusion :
Right & Left Posterior fibers of Temporalis
Right & Left Deep Heads of Masseter

57. • E) Right Lateral Excursion :
Right Masseter, Right Temporalis, Left Medial Pterygoid
& Left Lateral pterygoids.

58. • F) Left Lateral Excursion :
Left Masseter, Left Temporalis, Right Medial Pterygoid
& Right Lateral Pterygoids.

59. Pathology Related to Muscle of
Mastication

60. Myofacial Pain:
• Most commonly reported type of masticatory muscle Disorder.
• It is characterized by a dull regional ache that increases during function.
• Palpation reveals the tenderness of the muscles.

61. Myositis:
• It is primary inflamation of muscle resulting from infection/ trauma.
• It is characterized by constant acute pain in one or more masticatory muscles
usually accompanied by swelling, redness of overlying skin & increase in
temperature over the affected area.
• It results in jaw dysfunction & limited range of movement.

62. Myospasm/ Muscle cramp :
• Acute condition resulting from a sudden, involuntary & continuous tonic
contraction of muscle.
• It is characterized by localized acute pain & severely limited range of motion
of the mandible.
• These characteristics coupled with their sudden onset at rest allows the
clinician to differentiate myospasm from other other masticatory muscle
disorders.

63. Myofibrotic contracture:
• It involves a painless shortening of muscles as a result of fibrosis in &
around the remaining contractile muscle tissue.
• It follows the infectious process or trauma.
• There is limited mouth opening & unyielding resistance to passive jaw
muscle stretch.

64. Clinical importance
• Masseter :
• Masseter muscle can be palpated both intraorally and extraorally
• The masseter muscle is sometimes the target of plastic jaw reduction surgery.
• The muscle that commonly undergoes Hypertrophy in Bruxism is
Masseter.
• Because of the Multipennate arrangement of fibers, masseter is a very
powerful muscle.

65. • Temporalis :
• Sudden contraction of temporalis muscle will result in coronoid fracture,
which is rare.

66. • Medial Pterygoid
• Most commonly involved in MPDS (Myofacial pain dysfunction syndrome)
• Trismus following inferior alveolar nerve block is mostly due to involvement
of medial pterygoid muscle.

67. CLINICAL CONSIDERATION
• Tetanus
• Bruxism
• Myofacial pain dysfuncton syndrome
• Trismus

68. TETANUS(LOCK JAW)
• Caused by exotoxins of gram positive bacillus Clostridium tetani.
• Disease of the nervous system characterized by intense activity of motor
neuron and resulting in severe muscle spasm.
• CLINICAL FEATURES
• Pain and stiffness in the jaws and neck muscles ,with muscle rigidity
producing trismus and dysphagia.

69. • TREATMENT:
• All patients should receive antimicrobial drugs.
• Active and passive immunization.
• Surgical wound care.
• Anticonvulsant if indicated

70. BRUXISM
• Jaw clenching, with or without forcible excursive movements, where the
intensity of the clenching dictates the severity (or lack of) grinding.
• Clenching- It can occur as a brief rhythmic strong contractions of the jaw
muscles during eccentric lateral jaw movements, or in maximum
intercuspation.

71. Causes
• 1) Associated with stressful events.
• 2)Non stress related or heredity.
• Bruxism may lead to -tooth wear -fracture of the teeth or restoratrion -
uncosmetic muscle hypertrophy.
• TREATMENT
• Coronoplasty.
• Maxillary stabalization appliance.

72. MYOFACIAL PAIN DYSFUNCTION
SYNDROME
• Pain, Muscle tenderness, Clicking in the joint, Limitation in the mouth
opening.
• TREATMENT
• Physiotherapy and Myotherapeutic exercises
• Transcutaneous Electronic Nerve Stimulation
• Muscle relaxants
• surgery

73. Trismus
• Trismus after anaesthesia is usually caused by intramuscular injection of the
anaesthetics in the pterygomandibular space.
• It can occur even 2 – 5 days after inferior alveolar block anaesthesia.
• Affected muscles are usually either the lateral pterygoid muscle or the
temporal muscle.
• Anaesthetic solutions are usually cytotoxic and can cause inflammation inside
the affected muscle and trismus.

74. • Intramuscular injections can cause haematoma formation inside the muscle
and fibrosis, which lead to trismus
• Trismus can also follow multiple injections to the same area, by a large
haematoma or infection close to the area.
• Needle fracture in the muscles inserting to styloid process can cause a painful
and sever trismus.
• It usually disappears within a few days without the need for further
treatment.

75. Other common causes
• Infection
• Trauma
• Dental treatment
• Temporomandibular joint disorders
• Tumours and oral care
• Radiotherapy and chemotherapy
• Congenital problems
• Miscellaneous disorders.

76. Treatment in severe cases
• Heat therapy, analgesics, soft diet, muscle relaxants or physiotherapy should
be considered.
• Trismus caused by an infection always needs antibiotics or even a surgical
intervention to heal.
• Awareness of the anatomical landmarks and muscles, careful insertion of
the needle and bone contact before injecting are good methods for avoiding
the painful trismus.

77. IMPORTANT FACTS ABOUT
MASTICATION
• There are about 15 chews in a series from the time of food entry until
swallowing.
• Average jaw opening during chewing is between 16-20mm.
• Average lateral displacement on chewing is between 3 and 5mm.
• Men chew faster and have a shorter occlusal phase than women, it also
depends on the type of food

78. MODIOLUS
• It is a fibromuscular mass
formed by the convergence of
various muscles towards a focus
just lateral to the buccal angle.
• It can be palpated most
effectively by using opposed
thumb & index finger to
compress the mucosa & skin.

79. • It is formed by nine muscles.
• They are divided into two groups.
i. Cruciate modiolar muscles
ii. Transverse muscle

80. • Cruciate modular muscles :
i. Zygomaticus major
ii. Levator anguli oris
iii. Depressor anguli oris
iv. Platysma pars modiolaris

81. • Transverse muscles:
i. Buccinator
ii. Risorius
iii. Orbicularis oris
iv. Incisivus Superior & Inferior

82. Actions :
• The contraction of modiolus presses the corner of the mouth against the
premolars so that the occlusal table is closed in front.
• Food is crushed by the premolars & molars and it does not escape at its
corner of mouth unless Seventh nerve (Bell’s palsy) damage has occurred.

83. CONCLUSION
• The masticatory system is extremely complex, primarily made of bones,
muscles, ligaments and teeth.
• Precise movement of mandible by musculature is required to move the teeth
effectively across each other during function.
• The knowledge of the anatomy , physiology and mechanisms of these
muscles are basic to understand the movements.

84. REFERNCES
• B D Chourasia’s. Human Anatomy for Dental students, 2nd ed. 2012.
• Inderbir singh. G P Pal, Human Embryology, 9th ed. 2012
• Sperber. Craniofacial Development, 2001
• Wheeler’s. Dental Anatomy, Physiology and Occlusion, 9th ed. 2013
• Guyton and Hall. Textbook of Medical Physiology. 9th ed. 1996
• Dr. A P Krishna. Textbook Of Physiology, 7th ed. 2010
• Shafer’s. Textbook of oral pathology, 6th ed. 2009
• Glossary of prosthodontic terms(GPT 8), 8th ed. 2005
• Dhanrajani P.J. and Jonaidel O. Trismus: Aetiology, Differential Diagnosis and Treatment, Dent Update
2002; 29: 88–94

85. Thank You