Muscles of mastication are the group of muscles that help in movement of the mandible as during chewing and speech. We need to study these muscles as they control the opening & closing the mouth & their role in the equilibrium created within the mouth. They also play a role in the configuration of face.

1. MUSCLES
OF
MASTICATION
PRESENTED BY:
Dr. Anshul Sahu
MDS 1ST Year

2. CONTENTS:
 Introduction
 Definitions
 Development
 Important facts about mastication
 Features of Masticatory muscle
 Classification
 Primary muscles
 Accessory muscles
 Mandibular movements and role played by muscles
 Masticatory muscle disorders
 Conclusion
 Reference

3.  INTRODUCTION:
To propel the skeleton, man has 639 muscles, composed of 6
billion muscle fibers. Each fiber has 1000 fibrils, which means
there are 6000 billion fibrils at work at one time or another.
Food is the main source of energy this energy is derived through
the complicated process of digestion. 1st step of digestion is
mastication.
Teeth, jaws, muscles of the jaws, tongue and the salivary glands
aid in mastication.
Rhythmic opposition and separation of jaws with the involvement
of teeth, lips ,cheeks and tongue for chewing of food in order to
prepare it for swallowing and digestion.
Main purpose of mastication is to reduce the size of food particles
to a size that is convenient for swallowing (bolus formation) with
the help of saliva.

4. Muscles of mastication are the group of muscles that help in
movement of the mandible as during chewing and speech. We need
to study these muscles as they control the opening & closing the
mouth & their role in the equilibrium created within the mouth. They
also play a role in the configuration of face.
Four pairs of the muscles in the mandible make chewing movement
possible.
These muscles along with accessory ones together are termed as
“MUSCLES OF MASTICATION”
Influence of these muscles in prosthetic dentistry, defines the borders
& peripheral extensions.
A good knowledge of masticatory system and functional efficiency is
basic requirement for good prosthodontist.

5.  DEFINITIONS:
GPT 8
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.

6.  DEVELOPMENT:
The muscular system develops from intra embryonic mesoderm
from embryonic cells called myoblast.
Muscles of mastication are derived from first brachial arch that is
mandibular arch.
5th- 6th week
 Primitive cells form and differentiate
 Get oriented to site of origin and insertion
7th week
 Mandibular arch mass enlarges
 Cell migrate to areas of formation of 4 major muscles
of mastication
 Cell differentiation occurs before formation of
facial arch.
10th week
 Muscle mass well organized
 Nerve masses get incorporated

7.  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
 Duration of masticatory cycle varies between 0.6 and 1 sec
 Men chew faster and have a shorter occlusal phase than women, it
also depends on the type of food
 Masticatory forces: The aver maximum sustainable biting force is
756N{170 pounds}.
 Molar region: Biting force range 400-890N
 Premolar region: Biting force range 222-445N
 Canine region: Biting force range 133-334N
 Incisor region: Biting force range 89-111N

8.  FEATURES OF MASTICATORY MUSCLE:
 Have shorter contraction times than most other body muscles
 Incorporate more of muscle spindles to monitor their activity
 Do not have Golgi tendon organs to monitor tension
 Do not get fatigued easily
 Psychological stress increases the activity of jaw closing muscles
 Occlusal interferences cause a hypertonic synchronous muscle activity
 Closing movement also determined by the height of the teeth

9.  CLASSIFICATION:
PRIMARY MUSCLES
 Masseter
 Temporalis
 Lateral Pterygoid
 Medial Pterygoid
ACCESSORY MUSCLES
 Digastric
 Stylohyoid
 Mylohyoid
 Geniohyoid

10. FUNCTIONALLY CLASSIFIED AS
JAW ELEVATORS
 Masseter
 Temporalis
 Medial pterygoid
 Upper head of lateral pterygoid
JAW DEPRESSORS
 Lower head of lateral pterygoid
 Anterior digastric
 Geniohyoid
 Mylohyoid

11. PRIMARY MUSCLES OF
MASTICATION

12. MASSETER MUSCLE

13.  Greek word “maseter”- a chewer
 It is one of the most powerful muscles involved in the power
stroke closure of the mandible
 This is a quadrilateral muscle, partly tendinous, partly fleshy
which covers the lateral part of ramus of mandible.
 It consists of 3 layers which blend anteriorly.
 Multiple arrangement of fibers:
 Superficial
 Middle
 Deep
Deep Superficial

14. ORIGIN:
 SUPERFICIAL LAYER (LARGEST)
 Maxillary process of zygomatic bone
 Anterior 2/3rd of inferior border of zygomatic arch
 MIDDLE LAYER:
 Medial aspect of anterior 2/3rd of zygomatic arch
 Lower border of posterior third of zygomatic arch
 DEEP LAYER:
 Deep surface of zygomatic arch

15. INSERTION:
 SUPERFICIAL LAYER (LARGEST)
 Angle of mandible
 Lower posterior half of lateral surface of mandibular
ramus
 MIDDLE LAYER:
 Middle part of the ramus of mandible
 DEEP LAYER:
 Upper part of mandibular ramus
 Coronoid process

16. NERVE SUPPLY:
 Supplied by masseteric nerve a branch of anterior division of
mandibular nerve
BLOOD SUPPLY:
 Supplied by masseteric artery branch of maxillary artery
 Venous drainage through masseteric vein

17. FUNCTION:
 Elevates the mandible to close the mouth and to occlude the
teeth in mastication.
 Its activity in the resting position is minimal.
 It has a small effect in side-to-side movement, protraction
and retraction.

18. PALPATION:
 The patient is asked to clench their teeth and, using both hands, the
practitioner palpates the masseter muscles on both sides extra orally,
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.
Anterior Superior Position Posterior Inferior Position

19. CLINICAL IMPORTANCE OF MASSETER:
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

20. EFFECT OF MASSETER MUSCLE ON THE
DISTOBUCCAL BORDER:
A. Moderate activity will create a straight line
B. An active muscle will create a concavity.
C. An inactive muscle will create a convexity.

21. TEMPORALIS MUSCLE

22.  Extensive fan-shaped muscle that covers the temporal
region. It is powerful masticatory muscle that can easily be
seen & felt during closure of mandible.
 Bulk and length of the fibers are larger than that of medial
pterygoid and masseter.
 It is the largest masticatory muscle but not considered to be
the most powerful muscle.

23. ORIGIN:
 Origin is from inferior temporal line, floor of the temporal
fossa and from the overlying temporal fascia
 Divided into 3 areas:
 Anterior temporal
 Middle temporal
 Posterior temporal
Anterior Middle
Posterior

24. INSERTION:
 Margins & deep surface of the coronoid
process
 Anterior border of ramus of mandible
NERVE SUPPLY:
 Deep temporal branches from anterior
division of mandibular nerve
BLOOD SUPPLY:
 Superficial temporal artery branch of maxillary artery
 superficial temporal vein & middle temporal vein

25. FUNCTION:
 Anterior fibers elevate the mandible
 Posterior fibers retract the mandible
 Crushing of food between the molars
 Posterior fibers draw the mandible backwards after it has
been protruded
 It is also a contribute side to side grinding movement

26. PALPATION:
 The muscle is divided into three functional areas and therefore each
area is independently palpated.
 To locate the muscle, have the patient clench.
 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.
Anterior Middle Posterior

27. 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.

28. LATERAL PTERYGOID
MUSCLE

29.  Also called as external pterygoid muscle.
 It is the muscle of mastication that occupy primarily a
horizontal position.
 It is a thick, short, conical and triangular muscle with two
heads:
 Superior head
 Inferior head
Inferior head
Superior headInfratemporal creast

30. ORIGIN:
 Superior head: Infratemporal surface &
infratemporal crest of the greater wing of the
sphenoid bone.
 Inferior head: Lateral surface of the lateral
pterygoid plate.
INSERTION:
 Fibers run backwards and laterally and
converge into the pterygoid fovea on anterior
surface of neck of mandible
 Into anterior margin of articular disc and capsule
of TMJ
Superior
Inferior

31. NERVE SUPPLY:
 Mandibular nerve via lateral pterygoid nerve from anterior
trunk
BLOOD SUPPLY:
 Maxillary artery
 Ascending palatine artery
FUNCTION:
 Acting together, these muscles protrude the mandible and
depress the chin.
 Acting alone & alternately, they produce side –to –side
movements of mandible

32. PALPATION:
 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.

33. CLINICAL IMPORTANCE OF LATERAL PTERYGOID
MUSCLE:
 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
 In patients with nonworking side interferences, the lateral pterygoid
muscle on the opposite of the interference is sometimes painful

34. MEDIAL PTERYGOID
MUSCLE

35.  It is also called as the internal pterygoid muscle.
 It is almost a mirror-like image of the masseter muscle.
 It is rhomboidal and runs practically in the same direction on
the inner surface of the mandible
 It consist of two heads which differ in origin:
 Superficial
 Deep

36. ORIGIN:
 Superficial head from maxillary tuberosity
 Deep head from medial surface of lateral
pterygoid plate and part of palatine bone
INSERTION:
 Fibers run backwards, downwards and
Laterally into the roughened area of medial
surface of the angle mandible
Origin
Insertion

37. NERVE SUPPLY:
 Branch of the main trunk of mandibular nerve
BLOOD SUPPLY:
 Pterygoid branch of 2nd part of maxillary artery
FUNCTION:
 It helps to elevate the mandible and closes the jaws .
 Acting together, they help to protrude the mandible.
 Acting alone, it protrudes the side of the jaw.
 Acting alternately, they produce a grinding motion

38. PALPATION:
 It can be 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.
 Functional manipulation is done when the muscle becomes
fatigued and symptomatic.
 The muscle contracts as the teeth are coming in contact.
 Also stretches when the mouth is open wide.

39. CLINICAL IMPORTANCE OF MEDIAL PTERYGOID
MUSCLE:
 Most commonly involved in MPDS
 Trismus following inferior alveolar nerve block is mostly due to
involvement of medial pterygoid muscle
 The medial pterygoid muscle is not usually involved in gnathic
dysfunctions but when they are hypertonic, the patient is usually
conscious of a feeling of fullness in the throat and an occasionally
pain on swallowing

40. ACCESSORY MUSCLES
OF MASTICATION

41. DIGASTRIC MUSCLE
Formed by 2 belly like masses of muscle tissue joined by an
intermediate tendon.
ORIGIN:
 Anterior belly from diagastric fossa of mandible, lateral to
mental symphysis.
 Posterior belly from mastoid notch of temporal bone.
INSERTION:
 Both meet at the intermediate tendon and held by the
fibrous pulley to the hyoid bone.

42. NERVE SUPPLY:
 Anterior belly by nerve to Mylohyoid
 Posterior belly by –facial nerve
FUNCTION:
 Depression of jaw, both sides contract simultaneously
 Provide antagonism to elevation of mandible
 Elevation of hyoid during swallowing

43. MYLOHYOID MUSCLE
 Flat, triangular muscle lying deep to the anterior
belly of digastric
 It forms the floor of the mouth.
 Flat triangular
ORIGIN:
 Mylohyoid line of mandible.
INSERTION:
 Middle and anterior fibers into median raphae.
 Posterior fibers body of hyoid bone.

44. NERVE SUPPLY:
 Nerve to Mylohyoid
FUNCTION:
 Helps in depression of mandible, elevation of hyoid bone
 It elevates the floor of mouth to help in deglutition.

45. CLINICAL IMPORTANCE OF MYLOHYOID
MUSCLE:
ON DENTURE BORDERS:
Mylohyoid area
 Instruct the patient to place the tip of his tongue into the
upper and lower vestibules on the right and left side.
 The area to be molded is reheated and the patient and is
instructed to swallow two or three times in rapid succession.
 The tongue movements raise the level of the floor of the
mouth through contraction of the mylohyoid muscle.

46. GENIOHYOID MUSCLE
Short and narrow muscle lies above Mylohyoid
ORIGIN:
 Inferior mental spine (genial tubercle)
INSERTION:
 Fibers run backwards, downwards to be inserted into the
anterior surface of the body of hyoid bone.

47. NERVE SUPPLY:
 1st Cranial nerve, the fibers pass through hypoglossal
nerve.
FUNCTION:
 Carry hyoid bone and the tongue upward
during deglutition.

48. CLINICAL IMPORTANCE OF GENIOHYOID
MUSCLE:
For mandibular impressions:
 On recording labial flange and labial frenum
 The lip is massaged from side to side to mold the compound to
desired functional extension.
 In order to activate the mentalis muscle the patient is asked to
pout or lick his lower lip.
For maxillary impressions in labial flange and labial frenum area:
 Manually mold the compound by externally moving the lip side
to side, simultaneously applying finger pressure to control the
width of the border
 Lift the patients upper lip and vertically place the frenum into the
softened compound and mold with your fingers using a side to
side external motion

49. STYLOHYOID MUSCLE
Small muscle that lies along the upper border of
the posterior belly of digastric muscle.
ORIGIN:
 From the lateral & inferior surface of the styloid
process of temporal bone.
INSERTION:
 Is inserted into the body of the hyoid bone, at its
junction with the greater cornu.
NERVE SUPPLY:
 Branch from facial nerve
FUNCTION:
 Pulls hyoid bone upwards and backwards

50. BUCCINATOR MUSCLE
It is an accessory muscle of mastication, occupying the gap
between mandible and maxilla forming important part of the
cheek.
Also known as muscle of cheek.
ORIGIN:
 Upper fibers: From maxilla opposite molar teeth
 Middle fibers: From pterygomandibular raphe
 Lower fibers: From mandible opposite molar
INSERTION:
 Upper fibers: Straight to the upper lip
 Middle fibers: Decussate before passing to the lips
 Lower fibers: Straight to the lower lip

51. NERVE SUPPLY:
 Buccal branch of facial nerve
FUNCTION:
 Flatten cheek against gums and teeth, prevent
accumulation of food in the vestibule of mouth and to bring
the food on to the occlusal table during mastication.

52. CLINICAL IMPORTANCE OF BUCCINATOR
MUSCLE:
ON DENTURE BORDER
For buccal flange area in mandibular impressions:
 The area is moulded by massaging the cheek in an anterior-
posterior direction using moderate manual pressure against the
compound.
 This moves the fibers of the buccinators muscle and the tissues
of the cheek in the direction of functional action of the
buccinators muscle.
In maxillary impressions:
 The cheek is manually molded in anterior-posterior direction
using slight finger pressure against the compound or the patient
is instructed to control the amount of movement by sucking
action.

53.  MANDIBULAR MOVEMENTS AND ROLE
PLAYED BY MUSCLES:
1. ELEVATION:
 Prime Movers: (a) Masseter
(b) Medial Pterygoid
(c) Temporalis
 Antagonist: (a) Superior Lateral Pterygoid
2. DEPRESSION:
 Prime movers: (a) Inferior lateral pterygoid
(b) Digastric
 Antagonist: (a) Elevator group muscles

54. 3. PROTRUSION:
 Prime Movers: (a) Inferior Lateral Pterygoid
(b) Masseter
(c) Medial Pterygoid
 Antagonist: (a) Digastric
(b) Posterior Temporal
4. RETRUSION:
 Prime movers: (a) Posterior & Middle Temporal
(b) Digastric
 Antagonist: (a) Inferior Lateral Pterygoid
5. LATERAL:
 Prime movers: (a) Working side of temporal muscle
 Antagonist: (a) Non working side of Pterygoid muscle

56.  MASTICATORY MUSCLE DISORDERS:
SOME OF THE COMMON MASTICATORY MUSCLE
DISORDERS INVOLVE:
 Trismus
 Bruxism
 Tetanus
 Congenital hyperplasia/ hypoplasia
 Hypermobility/ hypo mobility of the muscle
 Muscle pains
 MPDS
 Myositis ossificans etc.
 Temporal tendonitis

57. TRISMUS
 Due to prolonged tetanic spasm of the jaw muscles by which
normal opening of the mouth is restricted.
 Restricted jaw movements regardless of the etiology.
CAUSES:
Intracapsular: Arthritis
Condylar fracture
Pericapsular: Irradiation
Dislocation
Infection & inflammation
Muscular: TMJ dysfunction syndrome
Tetanus
Other: Oral sub mucous fibrosis
Systemic sclerosis
Fractures

58. PROBLEMS:
 Eating issues
 Oral hygiene issues
 Swallowing issues
 Joint immobilization
TREATMENT:
 Removal of the cause
 Heat therapy
 Warm saline rinses
 NSAIDs
 Passive muscle stretching exercises

59. BRUXISM
 Bruxism is the clenching or grinding of the teeth when
the individual is not chewing or swallowing
 It can occur as a brief rhythmic strong contractions of the
jaw muscles during eccentric lateral jaw movements, or
in maximum intercuspation, which is called clenching.
CAUSES: Associated with stressful events
Non stress related or hereditary
Bruxism may lead to: Tooth wear
Fracture of the teeth or restoration
Muscle hypertrophy

60. Increased muscle tension is directly related to stress activity
during the day.
TREATMENT:
 Coronoplasty
 Maxillary stabilization appliance

61. TETANUS (LOCK JAW)
 Tetanus is a disease of the nervous system characterized by
intense activity of motor neuron and resulting in severe muscle
spasm
 Caused by exotoxins of gram positive bacillus, clostridium
tetani.
CLINICAL FEATURES:
 Pain and stiffness in the jaws and neck muscles ,with muscle
rigidity producing trismus and dysphagia
 Rigidity of facial muscles
 Sometimes whole body becomes affected.
TREATMENT:
 All patients should receive antimicrobial drugs
 Active and passive immunization.
 Surgical wound care
 Anticonvulsant if indicated

62. MYOFACIAL PAIN DYSFUNCTION SYNDROME
(MPDS)
 Muscular disorders (myofacial pain disorders) are the most
common cause of TMJ pain associated with masticatory muscles.
 Common etiologies include:
1. Many patient with “high stress level”
2. Poor habits including gum chewing, bruxism, hard candy
chewing
3. Poor dentition
TREATMENT:
 Its treatment includes 4 phases of therapy which includes muscle
exercises and drugs involving NSAIDs and muscle relaxants.
 A bite appliance is also worn by the patient in the furthur stages
to ‘splint’ the muscle movement.

63. CONGENITAL HYPOPLASIA/ HYPERPLASIA
 It occurs very rarely, and is more common in masseter and
orbicularis oris.
 Its oral symptoms include enlargement or decreased size of
the affected muscle, which may show an asymmetric facial
pattern and stiffness in the temporo-mandibular joint.
 It may or may not be associated with hypermobility/ hypo
mobility of the muscles.

64. MUSCLE HYPERMOBILITY/ HYPOMOBILITY
 This disorder involves extreme or diminished activity of the
masticatory muscles.
 Its etiology includes various factors such as:
 Decreased/ increased threshold potential of neural activity.
 Parkinsonism
 Facial paralysis
 Nerve decompression
 Secondary involvement of systemic diseases.

65.  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
 Morphology of artificial tooth
 Maintenance of arch form
 The proper management and periodical self -examination
of the muscles may provide a greater chance of catching
the disease process at an early stage which may be
useful for its better prognosis.

66.  REFERENCES:
 Human anatomy by B.D. Chaurasia, 3rd ed.
 Human anatomy by dental students by M.K. Anand,
1st ed.
 Burkits oral medicine diagnosis & treatment 10th
edition
 Textbook of complete dentures by Charles M heartwell
 Complete denture prosthodontics by John J Sharry.