Dr.Komal Sharma Periodontist

1. Muscles of mastication and its
physiology
By : Dr. Komal Sharma
Pg 1st year

2. Contents
 Introduction
 Development
 Muscles of mastication-Anatomy
 Physiology
 Periodontal consideration
 Conclusion
 References

3. INTRODUCTION
 Mastication:
 Rhythmic opposition & separation
of jaws with the involvement of
teeth, lips, cheeks, 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. Development of muscles of mastication:
 Muscles of mastication are derived
from first or mandibular arch (first
arch).
 The muscular system develops
from intra embryonic mesoderm
from embryonic cells called
myoblast.
Lateral view of a four week
embryo showing muscles derived
from branchial arches

5. Muscles of mastication
 Primary muscles of mastication:
 Masseter
 Temporalis
 Lateral pterygoid
 Medial pterygoid
 Secondary muscles of mastication:
The suprahyoid group of muscles being used as secondary or supplementary
muscles. They are:
 Digastric
 Mylohyoid
 Geniohyoid

6.  MASSETER:
 Quadrilateral, covers lateral surface
of ramus of mandible and consist of
three layers.

7. Three layers of masseter

8.  Superficial layer (largest):
 Origin:
From anterior 2/3 of lower border of
zygomatic arch and adjoining zygomatic
process of maxilla. Fibers pass
downward and backwards at an angle of
45 degree.
 Insertion:
Into lower part of lateral surface of
ramus of mandible

9.  Middle layer:
 Origin:
From anterior 2/3 of deep surface and posterior 1/3 of lower border of
zygomatic arch.
Middle and deep fibres pass vertically downwards.
 Insertion:
Into middle part of ramus.

10.  Deep layer:
 Origin:
From deep surface of zygomatic arch.
 Insertion:
Into upper part of ramus and coronoid process of mandible.
Three layers are separated posteroinferiorly by an artery and a nerve.
 Nerve supply:
Masseteric nerve, a branch of anterior division of mandibular nerve
 Blood supply:
Maxillary artery, which is a branch of external carotid artery.

11.  RELATIONS OF MASSETER SUPERFICIAL LAYER:
 Platysma
 Risorius
 Zygomaticus Major
 Parotid gland
 Parotid duct
 Branches of facial nerve
 DEEP SURFACE Overlies the:
 Insertion of temporalis and ramus of the mandible
 In front buccinator and the buccal nerve
 Massetric nerve and artery.

12.  ANTERIOR MARGIN:
Projects over the buccinator and is crossed below by the facial vein.
 POSTERIOR MARGIN:
Overlapped by the parotid gland.

13. Actions of masseter muscle
 The whole muscle elevates the mandible
to close the mouth to bite.
 The superficial fibers protract the
mandible.

14. TEMPORALIS MUSCLE:
 Fan shaped, fits the temporal fossa.

15. Temporal Fascia:
 Thick aponeurotic sheet - roofs over the temporal fossa & covers temporalis
muscle.
 Superiorly, fascia- single layered & attached to superior temporal line.
 Inferiorly, it splits into 2 layers which are attached to inner & outer lips of upper
border of the zygomatic arch.
 Small gap b/w 2 layers contains - fat, a branch from the superficial temporal
artery & the zygomatico-temporal nerve.

16.  Origin:
 Temporal fossa excluding zygomatic bone.
 Temporal fascia
 Fibres Converge and pass through gap deep to zygomatic arch.
 Insertion:
 Margins and deep surface of coronoid process.
 Anterior border of ramus of mandible.

17.  Nerve supply:
Two deep temporal branches from anterior division of mandibular nerve.
 Blood supply:
Deep temporal part of maxillary artery.

18.  RELATIONS OF TEMPORALIS SUPERFICIAL:
 Skin
 Auricularis anterior
 Temporal fascia
 Superficial temporal vessels
 Auriculotemporal nerve
 Temporal branch of facial nerve
 Zygomatic arch
 Masseter

19.  DEEP SURFACE:
 Temporal fossa
 Lateral pterygoid
 Superficial head of medial pterygoid
 Small part of buccinator
 Maxillary artery
 Deep temporal nerves
 Buccal vessels and nerves
 ANTERIOR BORDER:
 Separated from zygomatic bone by a mass of fat

20.  ACTIONS OF TEMPORALIS:
 Elevates mandible
 Posterior fibres retract the
protracted mandible
 Helps in side to side grinding
movement

21.  LATERAL PTERYGOID MUSCLE: SHORT, CONICAL, HAS UPPER
AND LOWER HEADS.

22.  ORIGIN:
 UPPER HEAD(small):
 From infratemporal surface and crest of greater wing of sphenoid bone.
 LOWER HEAD(larger):
 From lateral surface of lateral pterygoid plate.
 Fibers run backwards and laterally and converge
 INSERTION:
 PTERYGOID FOVEA
 On the anterior surface of neck of mandible
 Anterior margin of articular disc and capsule of temperomandibular
joint.Insertion is posterolateral and at a slightly higher level than origin.

23.  Nerve supply:
 A branch of anterior division of mandibular nerve
 Blood supply:
 Pterygoid branch of 2nd part of maxillary artery.

24. Relations of lateral pterygoid muscle

25.  ACTIONS OF LATERAL PTERYGOID MUSCLE:
 Depress mandible to open mouth, with suprahyoid muscle
 Protract mandible
 Left lateral pterygoid and right medial pterygoid turn the chin to left side as part
of grinding movements.

27.  MEDIAL PTERYGOID MUSCLE: Quadrilateral, has a smallsuperficial and
a large deep head.

28.  ORIGIN:
SUPERFICIAL HEAD (SMALL SLIP):
 From tuberosity of maxilla and adjoining bone.
DEEP HEAD (QUITE LARGE):
 From medial surface of lateral pterygoid plate and adjoining process of palatine
bone.
 Fibres run downwards,backwards and laterally.
 INSERTION:
 Roughened area on the medial surface of angle and adjoining ramus of
mandible, below and behind the mandibular foramen and mylohyoid groove.

29.  NERVE SUPPLY:
 Nerve to medial pterygoid, branch of main trunk of mandibular nerve.
 BLOOD SUPPLY:
 Pterygoid branch of 2nd part of maxillary artery.

30.  Relations of Medial Pterygoid:
 Superficial Relations
 The upper part of the muscle is separated from the lateral pterygoid
muscle by:
 The lateral pterygoid plate;
 The lingual nerve;
 The inferior alveolar nerve

31.  Deep Relations
 The relations are:
 Tensor veli palatini;
 Superior constrictor of pharynx;
 Styloglossus
 Stylopharyngeus attached to the styloid process

32.  ACTIONS OF MEDIAL
PTERYGOID:
 Elevates mandible
 Helps protraction of mandible
 Right medial pterygoid with left
lateral pterygoid turn the chin to
left side

33.  SECONDARY MUSCLES TAKING PART IN THE MASTICATION
 4 primary muscles of mastication are in turn supported or supplemented by few
secondary muscles known as SUPRAHYOID GROUP of muscles they are:
 Digastric
 Mylohyoid
 Geniohyoid

34.  DIAGASTRIC MUSCLE: Two
bellies united by tendon
 Origin –
 Anterior belly from diagastric
fossa of mandible. Posterior belly
from mastoid notch of temporal
bone.
 Insertion –Both meet at the
intermediate tendon and held by
the fibrous pulley.

35.  ACTIONS:
 Muscle - secondary role in mastication as depressor muscle + to action of
lateral pterygoid when mouth to be opened against resistance.
 Elevation of hyoid bone

36.  MYLOHYOID MUSLE: Flat
triangular
 Origin –Mylohyoid line of
mandible.
 Insertion – Middle & Anterior
fibers into median raphae. Posterior
fibers body of hyoid bone.

37.  ACTION:
 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

38.  GENIOHYOID: Short and narrow
muscle lies above mylohyoid
 Origin –Inferior mental spine
 Insertion – Anterior surface of
body of hyoid bone

39.  ACTIONS:
 Geniohyoid elevates the hyoid bone and draws it forward, thus acting as a
partial antagonist to stylohyoid.
 When the hyoid bone is fixed, it depresses the mandible

40. Physiology: Neuromuscular
transmission
 The function of masticatory
system is complex.
 A highly refined neurologic
control system regulates and co-
ordinates the activities of the
entire masticatory system.
 It consists primary of nerves and
muscles, hence the term neuro-
muscular system.

41.  Basic component - neuro-muscular system is motor unit consists of muscle
fibres - innervated by 1 motor neuron each neuron joins muscle fibres at motor
end plats- thick sarcolemma.
 Cell membrane of nerve terminal or “PRE-JUNCTIONAL MEMBRANE” and
muscle fibre (end) plated - “POST JUCTIONAL MEMBRANE”.
 Space b/w pre and post junctional membrane is called as “NEURO-
MUSCULAR CLEFT”.
 Cleft contains choline esterase enzyme (which destroys acetyl choline).

42.  Motor nerve terminal contains abundant mitochondria and vesicles containing
Ach (Acetylcholine).
 Receptors of Ach are present in post junctional membrane (motor and plate).
 SEQUENCE OF EVENTS IN NMT
 Nerve impulse (action potential)reaches presynaptic nerve ending .
 As it reaches presynaptic membrane it causes release, diffuses within few
hundred microsec. Across the very short distance to the post synaptic
membrane i.e. motor end plate.

43.  A-ch attaches to nicotinic A-ch receptors on motor end plate surface & ses
permeability of motor end plate to Na+ (mainly) & other positive ions .
 sed permeability of Na+ -- depolarization of post synaptic membrane--
generation of local potential ,called end plate potential
 Resting membrane potential in skeletal muscle membrane is -90 mV. when end
plate potential reaches a threshold of 30-40 mV, it depolarizes the surface
membrane of muscle & results in generation of action potential (magnitude 120-
130 mV)
 Spike potential thus sets up a propagated muscle action potential which can
travel in both directions along the muscle membrane.
 Once it reaches the muscle cell then the muscle gives mechanical response by
contraction.

44. Clinical importance of NM junction:
 Blocking of NM junction produces muscle relaxation, therefore:
 Helps in surgical operations by providing open fields.
 Reduces movements during electroconvulsive treatment of psychotic patients
 Blockage of NM junction can be achieved by two ways:
 By inhibiting release of A-ch from presynaptic membrane i.e. motor nerve
endings eg botulinum toxin
 Drugs whih antagonize the action of A-ch on the post –synaptic membrane i.e.
motor end plate.

45.  MUSCLE FUNCTION
 Motor unit can carry only one action i.e. contraction or shortening, entire
muscle, has 3 potential function.
 ISOTONIC CONTRACTION
 When muscle shortens & moves a load, the contraction is isotonic. Hence
load remains constant & equal to muscle tension throughout the most of the
period of contraction
 Occurs in the masseter, when the mandibular elevated forcing the teeth
through a bolus of food.

46.  ISOMETRIC CONTRACTION
 When a muscle does not shortern and length remains same (iso- same, metry-
length), but develops tension, the contraction is isometric.
 Such type of contraction occurs when muscle attempts to move a load that is
greater than the tension developed in muscles, this occurs in masseter when an
object is held between the teeth. eg. Pipe or pencil

48.  CONTRACTION RELAXATION
 Stimulation of motor unit discontinued ----the fibres of motor unit relax &
return to their normal length.
 Seen in masseter when mouth opens to accept new bolus of food during
mastication.

49. Periodontal consideration
 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,

50.  Bruxism is defined as diurnal or nocturnal parafunctional activity
including clenching, bracing, gnashing, & grinding of teeth.
Bruxism has potential to cause :
Tooth wear
Fracture
Periodontal & muscle pain
Major cause of mobility.

51.  Causes:
 Associated with stressful events
 Non stress related or hereditary
 Bruxism may lead to -tooth wear .
 Treatment -coronoplasty -maxillary stabilization appliance

52. Clinical consideration
 Masseter muscle hypertrophy is commonly seen in bruxism.
 Bruxism is also associated with an increased rate of implant failure.
 Many consider bruxism to be a contraindication to implant treatment.
 Protective measures for implant patient with bruxism :
 Creating narrow occlusal table with flat cusp angles
 protected occlusion
 regular use of occlusal guards.

53.  MYOFASCIAL PAIN DYSFUNCTION SYNDROME(MPDS)
 When muscle spasm develops , dysfunction as well as pain occurs and the condition
usually is designated as MPDS.
 It is initiated as spasm of one or more masticatory muscle.
 Most commonly involved muscles: lateral pterygoid and medial pterygoid muscle
 Etiology:
 Abnormal occlusion
 Prosthetic problems
 Malocclusion
 Emotional problems
 Hypermobility

54.  Clinical features:
 Age and sex distribution: Seen in middle age group with more predilections
for women.
 Onset: Occurs in episodes of several times a day, at times, with extended
symptom free intervals. Usually during increased emotional tension.
 Symptoms:
 Masticatory pain- due to myalgia or arthralgia
 Pain localized to preauricular area but radiate to temporal, frontal,& occipital
region.
 Difficulty in chewing and restriction of mandible excursion.
 Patient complains of noise on rubbing, grinding, clicking,and popping snapping
sounds on mandibular movement.

55.  Laskin’s cardinal criteria of MPDS

56. Fascial space infection
 Fascial spaces or compartments are generally "potential spaces" that become
opened or expanded by invading infection that intervenes between the structures
surrounding the space.
 Such spaces are of particular significance in the head and neck as they may
serve as pathways for the spread of infection from one region to another.

57. Buccal space
 Boundaries:
 Superiorly: zygomatic arch.
 Inferior: inferior border of mandible.
 Laterally: skin & subcutaneous tissue.
 Medially: buccinator muscle
,buccopharyngeal fascia.
 Posteriorly: anterior edge of masseter
muscle.
 Anteriorly: posterior border of
zygomaticus major & depressor anguli
oris.
Contents: Buccal fat pad, Stenson’s duct.
Facial artery.

58.  Etiology:
 Infected mandibular &
maxillary premolars & molars.
 Clinical Features:
 Obliteration of nasolabial fold.
 Angle of mouth shifted to
opposite side.
 Swelling in cheek extending to
corner of mouth.

59. Submental space
 Submental space:
 Boundaries:
 Roof: mylohyoid muscle.
 Inferior: deep cervical fascia,
platysma, superficial fascia & skin.
 Laterally: anterior belly of
digastric.
 Posteriorly: submandibular space.
Contents: Lymph nodes, anterior
jugular vein.

60.  Etiology:
 Infected mandibular incisors.
 Anterior extension of
submandibular space.
 Clinical Features
 Chin appears glossy & swollen.
 Pain & discomfort on swallowing

61. Submandibular Space
 Boundaries:
 Superiorly: mylohyoid muscle,
inferior border of mandible.
 Inferior: anterior & posterior belly of
digastric.
 Laterally: deep cervical fascia,
platysma, superficial fascia & skin.
 Medially: hyoglossus, styloglossus,
mylohyoid muscle.
 Posteriorly: to hyoid bone.
 Anteriorly: submental space.

62.  Contents:
 Submandibular salivary gland
 Proximal portion of Wharton’s duct
 Lingual & hypoglossal nerves
 Branches of facial artery- palatine, tonsillar, glandular, submental.

63.  Etiology:
 Infected mandibular 2nd & 3rd
molars.
 From submental, sublingual
spaces.
 Clinical Features:
 Indurated swelling in
submandibular region.
 Usually bulges over lower border
of mandible.

64. Pterygomandibular Space
 Boundaries:
 Superiorly: lower head of lateral
pterygoid muscle.
 Laterally: medial surface of ramus.
Medially: medial pterygoid muscle.
 Posteriorly: deep part of parotid.
 Anteriorly: pterygomandibular raphe.
Contents: Inferior alveolar
neurovascular bundle, Lingual &
auriculotemporal nerves, Mylohyoid
nerve & vessels.

65.  Etiology:
 Infected mandibular 3rd molars.
 Pericoronitis.
 Infected needles or contaminated LA
solution.
 Clinical Features:
 Absence of extra-oral swelling
 Severe trismus.
 Difficulty in swallowing.
 Anterior bulging of half of soft palate
& tonsillar pillars with deviation of
uvula to unaffected side.

66. Ludwig’s angina
 It is a rapidly swelling cellulitis of
the sublingual and submaxillary
spaces, often arising from infection
of the tooth roots that extent below
the mylohyoid line of the mandible.
 Involves submandibular, submental
and sublingual spaces bilaterally.
 Most commonly encountered neck
space infection.

67.  Fatal complications:
 Respiratory obstruction
 Generalized septicemia
 Erosion of carotid artery
 Cavernous sinus thrombosis
 Clinical features:
 Swelling is firm, painful & diffused
 Woody tongue
 Bull neck

68. Local anesthesia
 Inferior alveolar nerve block: Also known as Mandibular block
 Nerves anesthetised:
 Inferior alveolar nerve
 Incisive
 Mental
 Lingual
 Indication:
 Procedures on multiple mandibular teeth in one quadrant.
 Area anesthetized:
 Mandibular teeth,
 Body & ramus of mandible
 Buccal mucoperiosteum
 Anterior two third of tongue (lingual nerve).

69.  Procedure:
 Height of injection determined by imaginary line extend posteriorly from
coronoid notch to pterygomandibular raphe as it turns upwards towards maxilla.
 Anteroposterior site on injection: about three fourths the distance from anterior
border of ramus.
 Penetration depth: till bone is touched usually 20-25 mm.
 Complication:
 Trismus
 Transient facial palsy.
 Hematoma.

71. Trismus
 Trismus is a spasm of the muscles of mastication where opening of the mouth
becomes restricted.
 Most commonly seen following an IA nerve block. Since an IA nerve block
will almost always cause soreness because the needle is inserted through
through muscle, causing an injury to the tissue by the needle.
 Since an IA nerve block injures the muscles of mastication specifically the
medial pterygoid muscle, the patient constantly irritates the tissue when talking
and eating.
 Trismus is more common when dental professionals have difficulty getting an
IA nerve block and require multiple cartridges of local anesthesia to succeed.
 The tissues have been injured multiple times and larger volumes of fluid have
been deposited each time, stretching the tissue.

72.  Patient does not notice it while in the
dental chair due to numbness but when
the patient wakes up the following
morning after 6-8 hours of not using
the mastication muscles, the muscles
go into spasm.
 Gradually over the next day or so, the
patient becomes able to open his or
mouth a little more and eventually
maybe within 3 or 4 days, trismus is
gone.
Management includes using a warm,
moist compress on the area, but it just
takes time to go away.

73. PALPATION OF MASTICATORY
MUSCLES
 Digital palpation: Regional muscles are examined for the tenderness and trigger
points using the digital palpation.
 Temporalis muscle: Temporalis muscle can be seen and readily palpated
throughout entire length and breadth when the patient’s teeth are firmly
clenched.
 Masseter muscles: They are most effectively examined by simultaneously
pressing them from inside and outside the mouth in the process of bimanual
palpation.
 Lateral pterygoid muscle: The lateral pterygoid muscles are evaluated by
inserting a finger each behind the maxillary tuberosities.
 Medial pterygoid is checked by running a finger in an anteroposterior direction
along the medial aspect of the mandible in the floor of mouth.

74. Masseter muscle
Temporalis muscle

75. Lateral pterygoid
Medial pterygoid

76. References
 Carranza’s clinical periodontology.11th edition
 Human physiology for bds students. Prof AK jain.3rd edition
 Harrison’s principle of internal medicine.17h edition
 B.D Chaurasia’s human anatomy for bds students.5th ed
 Anil govindrao ghom.Textbook of oral medicine.2nd ed
 Flaviana Soares Rocha, Jonas Dantas Batista, Cláudia Jordão Silva,
Roberto Bernardino Júnior and Luis Henrique Araújo Raposo
.Considerations for the Spread of Odontogenic Infections — Diagnosis and
Treatment. ISBN 978-953-51-2035-3, Published: April 22, 2015

77.  Kamlapur G.M, Patil B.P, Joshi S., Shastri D. Pseudomalignant myositis
ossificans involving multiple masticatory muscles: Imaging evaluation.
indian journal of radiology and imaging.2014:24(1):75-79
 Young A.L, Khan J , Thomas D.C, Quek Y.P. Use of Masseteric and Deep
Temporal Nerve Blocks for Reduction of Mandibular Dislocation. Anesth
Prog. 2009:56(1): 9–13.
 Clarke M.A, Bueltmann K.W. Anatomical Considerations in Periodontal
Surgery. J. Periodont.1971:42:610-25