everything related to muscle of mastication

1. by
Dr Avisha Agrawal
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MUSCLES OF
MASTICATION

2. CONTENTS
1. Introduction
2. Types of muscle
3. development of muscle
4. Primary muscle of mastication
5. Secondary muscle of mastication
6. Clinical features
7. Conclusion
8. References

3. 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. TYPES OF MUSCLE
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CARDIACSTRIATED
SMOOTH

5. PRIMARY
❖ Temporalis muscle
❖ Masseter muscle
❖ Medial pterygoid muscle
❖ Lateral pterygoid muscle
SECONDARY
❖ Digastric muscle
❖ Mylohyoid muscle
❖ Geniohyoid muscle
2 groups of muscles of
mastication

6. DEVELOPMENT
The neck is formed by the elongation of the
region between the stomatodeum and the pericardium.
This is achieved partly, by a ‘descent’ of
the developing heart.
However this elongation is due mainly to the
appearance of a series of mesodermal thickenings
on the wall of the cranial most part of the foregut
These are called pharyngeal, or branchial arches

7. ❖ At this stage the endoderm wall is separated from ectoderm by a wall of
mesoderm.
❖ Soon, thereafter the mesoderm comes to be arranged in the form of six bars
that run dorso-ventrally in the side wall of the foregut
❖ Each of this bars grow ventrally the floor of the developing pharynx and fuses
with the corresponding bar of the opposite side to form a pharyngeal or
branchial arch
❖ In the interval between any two adjoining arches ,the endoderm extends
outwards in the form of a pouch(endodermal or pharyngeal pouch) to meet
the ectoderm which dips into this interval as an ectodermal cleft.

8. Arch Nerve of the arch Muscle of the arch
First Mandibular
Medial and lateral
pterygoids,masseter,temporalis mylohyoid
,anterior belly of digastric,digastric, tensor
tympani, tensor palate
Second Facial
Facial
muscles,occipitofrontalis,platysma,stylohyoid,
post belly of digastric,stapedius,auricular muscles
Third Glosso phayrngeal Stylopharngeus
Fourth Superior laryngeal Muscles of larynx and pharynx
Fifth Recurrent laryngeal

9. MASSETER MUSCLE
❖ Masseter muscle is quadrilateral in shape
❖ origin-zygomatic arch and maxillary
process of the zygomatic bone
❖ Superficial part-maxillary process of
zygomatic bone and the anterior 2/3rd of
zygomatic process of maxilla
❖ Deep part- medial aspect of the
zygomatic arch and posterior part of its
inferior margin.
❖ Fibres-
❖ superficial fibres- pass downwards and
backwards at 45 degree
❖ Deep fibers- pass vertically downwards
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10. ❖ insertion-
❖ Superficial part-into lower part of
lateral surface of ramus of mandible
❖ Deep layer-into rest of the ramus of
mandible
❖ Innervation- massetric nerve from the
anterior trunk of the mandibular nerve
❖ Nerve supply- massetric nerve
❖ Actions-elevation of mandible to close
the mouth
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11. TEMPORALIS
❖ This muscle is large fan shaped that fills
much of the temporal fossa.
❖ Origin- bone of temporal fossa and
temporal fascia.
❖ Fibres- Ant. Fibres run vertically,
middle obliquely, posterior horizontally.
All converge and pass through gap deep
to zygomatic arch
❖ Insertion- margin and deep surface of
coronoid process of mandible and
anterior margin of ramus of mandible
almost to last molar tooth.
❖ Innervation-deep temporal nerves from
the ant trunk of the mandibular nerve.
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12. ❖ Function- elevates mandible.
❖ Helps in side to side grinding
movement
❖ Posterior fibers retract the
protruded mandible.
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13. LATERAL PTERYGOID
❖ Short, conical has upper and lower
heads
❖ 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
❖ Origin is medial to insertion
❖ Fibres- run backwards and
laterally and converge for insertion
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14. ❖ Insertion -
❖ Pterygoid fovea-on anterior surface of neck of
mandible
❖ Ant margin of articular disc and capsule of TMJ
❖ Insertion is posterolateral and at a slightly
higher level than origin supply
❖ Nerve supply- branch from ant. Division of
mandibular nerve
❖ Actions-depresses mandible to open mouth
with supra hyoid muscles
❖ Lateral and medial pterygoid protrude mandible
❖ Right lateral ptergoid and right medial
pterygoid turn the chin to left side as a part of
grinding movement. Type to enter a caption.

15. MEDIAL PTERYGOID
❖ Quadrilateral, has a small
superficial and a large deep head
❖ Origin-
❖ Superficial head(small slip)-from
tuberosity of maxilla and
adjoining bone
❖ Deep head(quite large)-from
medial surface of lateral pterygoid
plate and adding process of
palatine bone.
❖ Fibres-run downwards,
backwards and laterally.
Type to enter a caption.

16. ❖ Insertion-roughened area on the medial
surface of angle and adjoining ramus of
mandible,mandible, below and behind
the mandibular foramen and mylohyoid
groove.
❖ Nerve supply-nerve to medial
pterygoid,branch of the main trunk of
mandibular nerve
❖ Actions-
❖ elevates mandible
❖ Help protrude mandible
❖ Right medial pterygoid with right lateral
pterygoid turn the chin to left side. Type to enter a caption.

17. MYLOHYOID
❖ Flat triangular muscle, two
mylohyoid forms floor of mouth
cavity, deep to digastric muscle
❖ Origin- mylohyoid line of mandible
❖ Fibres-run medially and slightly
downwards
❖ Insertion
❖ posterior fibres- body of hyoid
bone
❖ Middle and anterior fibres-fibres;
median raphe,between mandible
and hyoid bone
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18. ❖ Nerve supply-nerve to mylohyoid
❖ Actions-elevates floor of mouth in first stage of deglutition.
❖ Helps in depression of mandible, and elevation of hyoid bone

19. GENIOHYOID
❖ Short and narrow muscle lies
above medial part of mylohyoid
❖ Origin-inferior mental
spine(genial tubercle)
❖ Fibres-run backwards and
downwards
❖ insertion-Ant surface of body of
hyoid bone
❖ Nerve supply-C1 through
hypoglossal nerve Type to enter a caption.

20. ❖ Actions- elevates hyoid bone
❖ May depress mandible when hyoid is fixed
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21. HYOGLOSSUS
❖ It is a muscle of tongue.
❖ It forms important landmarks in
this region
❖ Origin-whole length of greater
cornea and lateral part of body of
hyoid bone
❖ Fibres-run upwards and forwards
❖ Insertion-side of tongue between
styloglossus and inf longitude;
muscles of tongue
❖ Nerve supply-hypoglossal nerve
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22. ❖ Actions- depresses tongue makes
dorm convex, retracts the
protruded tongue
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23. CLINICAL FEATURES

24. OKESONS CLASSIFICATION OF MASTICATORY
MUSCLE DISORDERS
A. Myalgia
1. Local myalgia
2. Myofascial pain
3. Myofascial pain with referral
B. Tendonitis
C. Myositis
D. Spasm
2. Contracture
3. Hypertrophy

25. 4. Neoplasm
5. Movement disorders
A. Orofacial dyskinesia
B. Oromandibular dystonia
6. Masticatory muscle pain attributed to systemic/central
pain disorders
A. Fibromyalgia/widespread pain

26. MYALGIA
❖ It is a pain originating from muscles of mastication and differs from TMJ
pain in several ways
❖ It is loosely correlated with jaw function, where as joint pain is a direct
function of joint movement.
❖ It is typically delayed in onset
❖ The muscle pain from myalgia is mostly diffuse and slowly waxes and wanes
over time.
❖ When asked to locate pain, TMJ pain is located in front of the ear, while
myalgia patient will place hands over the entire side of the face

27. ❖ Myalgia is diagnosed by clinical examination
❖ Pain can be provoked by digital palpation of the muscles.
❖ patient seek treatment primarily to relieve pain
❖ Causes
❖ Drug-Induced Myalgias
❖ Mycoplasm pneumonia and atypical pneumonia
❖ Disorders of skeletal muscle
❖ Cramps muscle stiffness and exercise intolerance

28. ❖ Treatment
❖ NSAIDS and muscle relaxant are the first line of treatment.
❖ Antidepressant therapy is very effective for many of these patients

29. MYOFACIAL PAIN DYSFUNCTION SYNDROME
❖ Myofascial pain (MP) is a widespread and universal cause of soft tissue pain.
❖ The central feature of MP syndrome (MPS) is the myofascial trigger point (MTrP), a very
small, localized area of muscle contraction that is hard to touch, and that is very tender.
❖ The MTrP is always located on a tight or taut band of muscle. An MTrP that causes
pain is always tender to palpation.
❖ When stimulated mechanically by palpation or by needling, it contracts sharply,
referred to as local twitch response (LTR).
❖ The taut band limits stretch of a muscle and produces weakness that is rapidly
reversed as the trigger point is inactivated.

30. ❖ It can activate autonomic activity, such as vasodilation or constriction,
goose bumps, or piloerection.
❖ The MTrP, like other physical sources of chronic pain, refers pain to
distant sites and leads to central nervous system sensitization.
❖ MTrPs can be spontaneously painful (so-called “active” MTrPs) or they
can be nascent or quiescent (so-called “latent” MTrPs), inactive until
physical activity converts them to active MTrPs.

31. Anterior
Supraorbital ridge and downward
to incisors teeth
Intermediate
Posterior
Mid temple area an downward to
maxillary teeth on the same side
backward and upward
Pain referred
Upper border of
zygomatic arch.
Above the ear.
Palpation

32. MANAGEMENT
Treatment Description
Education
Explanation of diagnosis and treatment
Reassurance about the generally good prognosis for recovery and natural course
Explanation of patients and doctors role in therapy
Information to enable patients to perform self care
Self care
Control parafunctional oral behaviours
Provide information on jaw care associated with daily activities
Physical therapy
Education regarding biomechanics of jaw,jaw, neck and head posture and integrated movement pattern
Passive modalities(heat and cold therapy, ultrasound,laser and TENS)for pain
passive stretching and range of motion exercises
Posture therapy to regain a neutral zone.
General exercise and conditioning program
intraoral appliance
therapy
Cover all the teeth on the arch the appliance is seated on
Adjust to achieve simultaneous contact against opposing teeth
Adjust to stable comfortable mandibular posture
Does not alter mandibular position
Use during sleep and rely on behavioural methods for waking hours

33. behavioral/relaxation
technique
Relaxation therapy
Hypnosis
Biofeedback
Cognitive behavioural therapy

34. MYOSITIS
❖ refers to any condition causing inflammation in muscles.
❖ Weakness, swelling, and pain are the most common myositis symptoms.
❖ Myositis causes include infection, injury, autoimmune conditions, and drug
side effects. Treatment of myositis varies according to the cause.
❖ Causes
❖ Inflammatory condition
❖ Infection
❖ Drugs
❖ Injury

35. Inflammatory conditions causing myositis may require treatment with drugs that suppress the
immune system, including:
• Prednisone
• Azathioprine (Imuran)
• Methotrexate

36. TRISMUS
❖ The word Trismus is Latin term derived from the Greek word “Trismos” which means
grinding / rasping.
❖ In lay terms Trismus means limitation of mouth opening due to reduced mandible mobility.
❖ Two bones form the boundaries of oral cavity (maxilla and mandible).
❖ Out of these two maxilla is fixed and is not mobile, where as mandible is capable of upwards
and downwards mobility with a limited forward and backward mobility too.
❖ The maximal interincisal opening (MIO) of at least 35mm is used as a cutoff point to
determine Trismus.
❖ Less than 5 mm of MIO indicates complete ankylosis.

37. ❖Roughly put the mouth opening should permit a minimum of three fingers when inserted sideways.
❖Since the movement of the mandible occurs around Temporomandibular joint Kazanjian classified anky
❖True ankylosis of TM joint is usually caused due to pathology involving the joint
❖while the term false ankylosis is used to describe restrictions of movement resulting from extra articula
❖It is this type of false ankylosis which clinicians commonly term as Trismus

38. Etiology of Trismus may be classified into:
1. Infection
2. Trauma
3. Dental treatment
4. TM joint disorders
5. Tumors and oral care include benign and
6. malignant lesions involving oral cavity
7. and submucous fibrosis
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39. 6. Drug induced
7. Radiotherapy and chemotherapy
8. Congenital disorders
9. Miscellaneous disorders include Hysteria, Lupus erythematosus

41. MANAGEMENTConservative medical management for acute trismus:
1. Heat therapy – By placing moist hot towels on the affected area for 10-20 minutes / hour.
2. Analgesics – Aspirin is adequate. Narcotic analgesic may be indicated if the discomfort is too
much.
3. Soft diet
4. Muscle relaxants – Benzodiazepines 11 2.5 – 5 mg three times a day may be indicated in
patients with excessive masticatory muscle spasm
5. Physiotherapy can be started after cessation of the acute phase. Antibiotics is indicated only
if trismus has been attributed to infection.

42. HYPERTROPHY
Hypertrophy of muscle refers to an increase in size of individual muscle fibres.
Masticatory muscle hypertrophy can
affect all the muscles of mastication,
several muscles or just one muscle.
It can occur either bilaterally or unilaterally,
and most commonly the masseter muscles
alone are affected.
The involved muscles, which are variably enlarged and can be up to three times the normal
size, are otherwise normal on all imaging studies.
Type to enter a caption.

43. ❖ Masseter muscle hypertrophy (MMH) may present as unilateral or bilateral, benign increase
in size of masseter muscle.
❖ Its aetiology remains unexplained.
❖ It is most commonly seen in late adolescence and early adulthood, affects both males and
female but has slight male predominance.
❖ Very little information concerning this entity has appeared in dental literature because MMH
in itself is only occasionally associated with dental problems such as attrition, periodontal
breakdown or temperomandibular joint problem.
❖ Unilateral or bilateral hypertrophy of the masseter muscle is
❖ characterised by an increase in the volume of the muscle mass.

44. ❖ Clinically, patient may present with the complaint of unaesthetic appearance due to facial
asymmetry or ‘square’ face appearance.
❖ Some patients complain of pain, headache, muscle stress, trismus and intermittent masticatory
claudication.
❖ The radiographic findings associated with MMH are the bone spurs at the angle of mandible6
or flaring of mandibular angle and hyperostosis of mandibular ramus.

45. ❖ CT and MRI scans provide useful diagnostic information regarding this condition.
❖ This entity must be carefully differentiated from unilateral compensatory hypertrophy (due
to hypertrophy or hyperplasia in the contralateral side), masseter tumour, salivary gland
disease, parotid tumour, parotid inflammatory disease, masseter muscle intrinsic myopathy,
lipoma, vascular tumours, benign and malignant mandible tumours and metabolic
disorders.

46. TREATMENT
A longer acting, more reliable method of obtaining masticatory muscle relaxation can be
achieved by injecting measured doses of botulinum toxin (BTX) into specific sites in the
major muscles of mastication.12–14.
These doses are sufficient to shut down
the efferent response from spindle cells
within the muscles that are implicated in
initiating and potentiating the
sympathetic dystonic cycle.
Type to enter a caption.

47. ❖ The effect of BTX is to act as a governor on sympathetically driven trigeminal innervation to
the masticatory muscles.The obvious treatment goal is to reduce spasm but not to interfere
with normal function.15 A reduction in dystonia and pain with optimization of function is
easily achievable with a site-specific and dose-specific BTX injection protocol.
❖ BTX, a natural protein, is one of the most potent biological substances known.
❖ The toxin inhibits the release of acetylcholine (ACH), a neurotransmitter responsible for the
activation of muscle contraction and glandular secretion.

48. ❖ BTX is synthesized as a large single-chain peptide.
❖ Activation requires a two-step modification in the tertiary structure of the protein.
❖ This process converts the single- chain neurotoxin to a di-chain neurotoxin comprising a
100,000-Da heavy chain (HC) linked by a disulfide bond to a 50,000-Da light chain (LC).
BTX acts at the neuromuscular junction where it exerts its effect by inhibiting the release of
ACH from the presynaptic nerve terminal.
❖ ACH is contained in vesicles, and several proteins (vesicle-associated membrane protein
[VAMP], synaptosome-associated protein 25 kDA [SNAP-25], and syntaxin) are required to
release these vesicles through the axon terminal membrane.

49. ❖ BTX binds to the presynap- tic terminal via the HC.
❖ The toxin is then internalized and the HC and LC are separated.
❖ The LC from BTX-A cleaves SNAP-25, the LCs from serotypes B and F cleave VAMP, and
that from serotype C cleaves syntaxin.23
❖ This disrupts ACH release and subsequent neuro- muscular transmission, resulting in
weakness of the injected muscle.

50. ORAL DYSKINESIA
❖ Oral dyskinesias are abnormal ,involuntary movements of the tongue, lips and jaw.
❖ The term tar dive dyskinesia was introduced in 1964 to describe a dyskinesia
associated with antipsychotic medication
❖ The prevalence of tar dive dyskinesia in patients treated chronically with
conventional antipsychotic medication is estimated to be approx 20%
❖ Oral dyskinesias may be a factor contributing to muscle stiffness, TMJ
degenerative changes, mucosal lesions, damage to teeth, and dental prostheses.
❖ Tar dive dyskinesia has been reported to cause facial pain
❖ Complete loss of teeth is considered to be one cause of oral dyskinesia
❖ Ill fitting dentures or lack of replacements may initiate dyskinesia.

51. ❖ Dyskinesias are characterised clinically by the observation of involuntary
muscles and the effects of these movements on the jaw muscles,TMJ,oral
mucosa,and teeth.
❖ Emphasis on mangement is prevention because no treatment is predictably
effective and safe
❖ Tardive dyskinesia may be persistent even after drug therapy is stopped
❖ Palliative treatment using tetrabenzaine, a central monoamine depleter,
clonazepam and baclofen has been tried.

52. OROMANDIBULAR DYSTONIA
❖ Oro mandibular dystonia produces involuntary and excessive contractions of
tongue, lip and jaw muscles.
❖ The etiology and pathophysiology are unknown.
❖ The proposed mechanism is related to defective inhibitory control of the basal
ganglia of the forebrain, thalamus and brain stem.
❖ Injection of botulinum toxin has been used in the cases of oromandibular
dystonia

53. BRUXISM
The term ‘la bruxomanie’ was first introduced
by Marie Pietkiewicz in 1907 [3].
It was latter adopted as ‘bruxism’ to describe
gnashing and grinding of the teeth occurring
without a functional purpose.
Type to enter a caption.

54. ❖ Glossary of Prosthodontic Terms (GPT-8) [4] defines bruxism as parafunctional
grinding of teeth or an oral habit consisting of involuntary rhythmic or spasmodic non
functional gnashing, grinding or clenching of teeth in other than chewing movements
of the mandible which may lead to occlusal trauma.
❖ Bruxism can occur during wakefulness or during sleep.

55. ❖ Bruxism during daytime is commonly a semivoluntary ‘clenching’ activity and is also
known as ‘Awake Bruxism’ (AB) or Diurnal Bruxism (DB).
❖ AB can be associated with life stress caused by familial responsibility or work pressure.
Bruxism during sleep either during daytime or during night is termed as ‘Sleep Bruxism’
(SB).
❖ SB is an oromandibular behavior that is defined as a stereotyped movement disorder
occurring during sleep and characterized by tooth grinding and/or clenching [5].
❖ Sleep bruxism was recently classified as sleep related movement disorder according to
recent classification of Sleep Disorders.

56. ❖ Prevalence rate of AB and SB is about 20 and 8–16% respectively in adult population.
❖ AB is found to occur predominantly among females while no such gender difference
is seen for sleep bruxism.
❖ Onset of SB is about 1 year of age soon after the eruption of deciduous incisors.
❖ The disorder is appearing more frequently in the younger population.
❖ The prevalence in children is between 14 to 20%.
❖ In adults aged above 60 years and over only 3% are being aware of frequent grinding.

57. Management
Bite plane Occlusal splints

58. MASTICATOR SPACE
❖ The masticator space contains the mastication muscles, ramus of the mandible, and mandibular nerve.
❖ Because clinical assessment of lesions in this space may be difficult, CT and MR imaging is important
for the characterisation and mapping of the pathology.
❖ Inflammatory conditions of the space are particularly common and are usually odontogenic in origin.
❖ Lymphovascular malformations are also common, particularly in children.
❖ Benign and malignant tumours may arise from the different contents of the space, and malignant
tumours may appear well defined and confined by the fascia, without signs of aggressiveness.
❖ Tumours of the pharynx and parotid gland may also invade the MS.
❖ PNS can also occur with malignancies arising within this space.

59. Type to enter a caption.
❖ Masticator spaces are paired supra-hyoid cervical spaces on each side of the face that extend from the angle of
the mandible to the parietal calvarium.
❖ Each space is delineated by a superficial layer of the deep cervical fascia (SLDCF).
❖ At the lower border of the mandible, the SLDCF splits into two layers: an inner layer that extends deep to the
medial pterygoid muscle and attaches to the skull base medial to the foramen ovale and an outer or superficial
layer that covers the masseter muscle, attaches to the zygomatic arch, and then continues superiorly to encase
the temporalis muscle.
❖ These two layers fuse along the anterior and posterior borders of the mandibular ramus, enveloping the space.
ANATOMY

60. PATHOLOGY
❖ odontogenic abscess
❖ osteomyelitis
❖ direct spread of squamous cell carcinoma
❖ lymphoma
❖ minor salivary gland tumours
❖ muscle sarcoma
❖ bone sarcoma
❖ osteoradionecrosis
❖ schwannoma
❖ neurofibroma
❖ benign masseteric hypertrophy
❖ accessory parotid tissue

61. CONCLUSION
Mastication is oral motor behavior reflecting central nervous system
commands, and many peripheral sensory inputs to modulate the rhythmic jaw
movements.
Since tooth guidance has an enormous influence on muscle activity during
chewing and swallowing, it is advisable to make restorations and replacements
as much compatible as possible, with the functional movement patterns of the
patient, rather than expect the patterns of the mastication to adapt to the new
made replacements.

62. REFERENCES
❖ Kamble V, Mitra K. A Rare Association of Bilateral and Unilateral Masseter
Hypertrophy with Hypertrophy of Pterygoids. Journal of clinical and diagnostic
research: JCDR. 2016 Feb;10(2):TJ03.
❖ B.D chaurasia-human anatomy pg 144-148
❖ Inderbir singh- human embryology tenth edition
❖ Grays’s Anatomical basis of clinical practice 39th
edition. Elsevier under the Churchill
Livingstone publication.
❖ Rispoli DN Benign masseter muscle hypertrophy. Rev Bras Otorrinolaringol
2008;74(5): 790-3.