Muscles of mastication and its role in prosthodontics

2. PRESENTED BY:
ARUSHI MAHAJAN
MDS FIRST PROF.
DEPARTMENT OF PROSTHODONTICS
DIRDS, FARIDKOT
GUIDED BY:
DR. PARDEEP BANSAL
DR. MANVEEN DHALIWAL

3. 1. INTRODUCTION
2. DEVELOPMENT
3. MUSCLES OF MASTICATION
A) MASSTER
B) TEMPORALIS
C) MEDIAL PTERYGOID
D) LATERAL PTERYGOID
E) ACCESSORY MUSCLES
Under the following subheadings :
i. Origin
ii. Insertion
iii. Action
iv. Palpation
v. Clinical consideration
vi. Role in Complete Denture Prosthesis

4. The four
principal
muscles of
mastication:

9. Mastication is the process of grinding and chewing food
into smaller pieces in the oral cavity turning it into a food
bolus.
This mass can then be swallowed with ease and further
digested as it passes along the alimentary canal.
Apart from the teeth and the tongue, certain muscles
known as the masticatory muscles take part in specific
movements of the temporomandibular joint (TMJ)
during this process to allow the initial stages of digestion
to occur.

10. Embryologically, the muscles of mastication develop from
the first pharyngeal arch.
Consequently, they are innervated by a branch of
the trigeminal nerve (CN V), the mandibular nerve

12. This is a quadrilateral muscle which covers the
lateral surface of ramus of mandible. Its fibers are
arranged in 3 layers.
The masseter is divided into two distinct sections:
•the 'superficial' and
•'deep' portions.
The superficial portion of the masseter is the thick and
tendon-like portion of the muscle that connects to the
cheekbone,
while the deep portion is the smaller and more muscular
portion of the muscle that connects to the mandible.

13. Superficial
layer
anterior 2/3rd
of lower
border of
zygomatic
arch
zygomatic
process of
maxilla.
Middle
layer
anterior 2/3rd
of deep
surface
1/3rd of lower
border of
zygomatic
arch
Deep layer
Deep layer
from deep
surface of
zygomatic
arch

15. Superficial
fiber
pass
downwards and
backwards at
an angle of 45°.
inserted into
lower part of the
lateral surface of
the ramus of the
mandible
Middle
fiber
pass vertically
downwards
inserted into the
middle part of
the ramus
Deep
fibers
pass vertically
downwards
Inserted into the
upper part of the
ramus and into
the coronoid
process

17. Masseteric nerve, a branch of the anterior division of the mandibular
nerve.

18. The muscle elevates the mandible to close the mouth and
clenches the teeth.

20. To perform an extraoral examination, stand behind the patient and visually
inspect and bilaterally palpate the muscle. Place the fingers of each hand
over the muscle and ask the patient to clench his or her teeth several times.

22. •The masseter muscle can become enlarged in
patients who habitually clench or grind
(with bruxism) their teeth and even in those who
constantly chew gum.
•This masseteric hypertrophy is asymptomatic
and soft; it is usually bilateral but can be
unilateral.
•Even if the hypertrophy is bilateral, asymmetry
of the face may still occur due to unequal
enlargement of the muscles.

25. •This extraoral enlargement may be confused with parotid
salivary gland disease, dental infections, and maxillofacial
neoplasms. However, no other signs are present.
•Most patients seek medical attention because of
comments about facial appearance, and this situation may
be associated with further pathology of
the temporomandibular joint.
•The muscle undergoes spasm with malignant
hyperthermia as do other skeletal muscles, but this one is
easily noted, since it is on the face

26. ANATOMICAL REGION:--
 In buccal vestibule
 Lateral to pear shaped pad
ROLE :---
It is large and powerful elevator, lies over the
buccinator muscle. This area of denture must be
carefully recorded because overextension causes
soreness, it is an elevator muscle that closes the
jaw so that denture cannot displaced, but it will
affect the retention of complete denture
prosthesis. Under extension, may result in a loss of
support and resistance, to distal displacement.

27. It is responsible for formation of masseteric
notch ( distobuccal to the pad i.e. outline of
distobuccal border)… it forms due to the
action of masseter over buccinator.
Depending on their action, massetric notch
can be categorized in:-------
concave- i.e. masseter muscle is active
Straight- i.e. masseter is moderate active
convex--i.e. inactive masseter.

28. HOW TO ACTIVATE IT
 Hold the tray with index finger and
thumb at lower border of mandible.
Instruct the patient to close his mouth
against the pressure exerted by the
finger of operator. This will result
masticatory muscle contract against
buccinator muscle.

30. The temporal muscle, also known as
the temporalis, is one of the muscles of mastication.
It is a broad, fan-shaped muscle on each side of the
head that fills the temporal fossa, superior to the
zygomatic arch so it covers much of the temporal
bone.
The temporal muscle is covered by the temporal
fascia, also known as the temporal aponeurosis.
This fascia is commonly used in tympanoplasty, or
surgical reconstruction of the eardrum.

31. a)Temporal fossa, excluding the zygomatic bone.
b) Temporal fascia.
a) Into the coronoid process.
b) Anterior border of ramus of mandible.
ORIGIN
INSERTION

33. Two deep temporal branches of anterior division of mandibular nerve.

34. •Elevates the mandible.
•Posterior fibers retract the protruded mandible.
•Helps in side to side grinding movements

38. •The temporalis is likely to be
involved in jaw pain and
headaches.
•Bruxism, the habitual grinding of
teeth typically while sleeping, and
clenching of the jaw while stressed
can lead to overwork of the
temporalis and results in pain.

39. •A myotendinous rupture of the temporalis can occur
during a seizure due to extreme clenching of the jaw.
•During a seizure the contralateral temporalis muscle
can enter spastic paralysis, this clenching in extreme
cases can lead to a rupture specifically on the
myotendinous insertion at the coronoid process of the
mandible.

40. ANATOMICAL REGION:-
 Anterior border of the ramus with tendon ending
on the alveolar bone distal to the pad area.
ROLE:-
 INDEPENDENTLY HAS NO SIGNIFICANT ROLE,
but associated with retromolar pad, is important
for obtaining support and peripheral seal.
HOW TO ACTIVATE IT:-
 SAME AS MASSETER,
 It help in obtaining pterygomandibular seal.

42. The lateral pterygoid muscle, also known
as pterygoideus externus or external pterygoid
muscle, is one of the muscles of mastication.
The lateral pterygoid is a short, thick muscle,
somewhat conical in form, which extends almost
horizontally, posteriorly and laterally between
the infratemporal fossa and the condyle of
the mandible.
It arises by two heads:
an upper (superior) and
a lower (inferior)

44. •Upper head is small. It arises from infratemporal surface and
crest of the greater wing of sphenoid.
•Lower head is larger and arises from lateral pterygoid plate
•Pterygoid fobea on anterior surface of neck of the
mandible.
•Anterior margin of articular disc and capsule of TMJ.
.

46. The lateral pterygoid nerve, Branch of anterior
division of mandibular nerve.

47. •Depresses mandible to open the mouth.
•Protrudes the mandible forward.

48. Palpation is done by 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

50. The medial pterygoid (or internal pterygoid
muscle), is a thick, quadrilateral muscle
of mastication.
It has a small superficial head and large deep
head which forms major part of muscle.

51. ORIGIN
Superficial
head
from the
tuberosity of
maxilla
Deep
head
from medial
surface of lateral
pterygoid and
adjoining part of
palatine bone

52. Fibers run
downwards and
backwards
inserted into
medial surface of
angle of mandible
mandible below
and behind
mandibular
foramen and
mylohyoid groove.

54. It is innervated by the main trunk of the mandibular
branch of the trigeminal nerve (V), before the division.

55. • Elevates mandible.
• Helps to protrude the mandible.

57. •Gently palpate them on the medial aspect of the jaw,
simultaneously from both inside and outside the mouth

58. MPDS
• Myofascial pain dysfunction syndrome is a most common
cause of temporomandibular pain.
• CAUSES: Tension, fatigue, and spasm of the masticatory
muscles results from nocturnal bruxism.
• Patients have pain and tenderness of the masticatory
muscles, painful limitation of jaw excursion, and sometimes
headache.
• Bedtime use of splints or mouth guards and a benzodiazepine
may help, along with non-opioid analgesics.

59.  Contraction of the medial pterygoid muscle can
causes a bulge in the wall of the Retromylohyoid
curtain.

60. Suprahyoid muscles
• Mylohyoid
• Geniohyoid
• Stylohyoid
• Digatric
Infrahyoid Muscles
• Sternohyoid
• Omohyoid
• Thyrohyoid
• Sternothyroid
Both groups of muscle are active in helping to
depress the mandible

61. Suprahyoid muscles

62. Infrahyoid muscles

64. ANATOMICAL REGION:--
 Alveolingual sulcus or middle or
mylohyoid vestibule..
ROLE:----
 It is very important to achieve
stability of lower denture by
acquiring adequate peripheral
seal in that area.
It can be determined by
 palpation.
 Skillful border moulding and
impression procedures.

65.  BOUCHER says that the denture flange must be
parallel to the mylohyoid muscle when it is
contracted.
DISADVANTAGES:---
 Of the impression is made with pressure on or
slightly over the ridge displacement of denture
resulting soreness from vertical and lateral stress.
 If the flange is shorter the mylohyoid ridge,
vertical forces will causes soreness and border seal
will be easily broken.

66.  WINKLER says that lingual flange of denture
border should be extend in between the
functional and rest position of mylohyoid muscle
i.e. slightly below the mylohyoid ridge.
 BLANCHARD gave standardization that average
mylohyoid border is around 4-6 mm and border
width should be 2-3mm.

67. • The lingual flange of the lower
denture should be concave and
face in and up, Because of the
shape of the mandible and
because of the functional
movement of the mucosal
reflection in the alveololingual
sulcus, this flange cannot
closely approximate the body of
the mandible below the
attachment of the mylohyoid.
 Consequently it’s greatest extension can be achieved by
turning it lingually under the lateral surface of the tongue .
this permits the tongue to direct the force inferiorly against
the flange.

68.  Opening / Depressor jaw muscles
 mylohyoid / digastric / lateral pterygoid
 Closing / elevator jaw muscles
 medial pterygoid / superficial masseter /
temporalis
 Protrusive &side to side movements
 Lateral & medial pterygoid
 Retraction movements
 Temporalis

69.  Text books on Anatomy- Gray’s
 Clinical Dental Prosthetics- Fenn
 Complete denture- Winkler
 Oral anatomy - Sicher and Dubrul`s
 www.wikipedia.com
 www.google.com