Muscle of mastication and muscle of facial expression

It's slide about muscle of mastication and facial expression. this slide will help all medical student to study and elaborate about it.

1. Muscles of mastication
Muscles of facial expression

2. CONTENTS
INTODUCTION
DEVELOPEMENT
MUSCLES OF MASTICATION
CLINICAL EXAMINATION
CLINICAL CONSIDERATION
MUSCLES OF FACIAL EXPRESSION
APPLIED ASPECTS
CONCLUSION
REFERENCES

3. “MOTION IS THE CAUSE OF
ALL LIFE”
LEONARDO DA VINCI


INTRODUCTION

4. DEVELOPEMENT
SKETCH OF 20 WEEK FETUS SHOWING MUSCLES
DERIVED FROM BRANCHIAL ARCHES

5. Classically the muscles of mastication are
Masseter
Medial Pterygoid
Lateral Pterygoid
Temporalis
Accessory muscles of mastication
Anterior belly of digastric
Mylohyoid muscle
Geniohyiod muscle
Buccinator

6. MasseterMasseter
ORIGIN
A) Superficial layer
Largest
From anterior 2/3 of
the lower border of
zygomatic arch and adjoining
zygomatic process of maxilla
B) Middle Layer
From anterior 2/3 of the
deep surface and posterior
1/3 of the lower border of
zygomatic arch
C) Deep layer
From the deep surface of
the zygomatic arch

7. Insertion
A) superficial layer
It passes downward and
backwards at 45 degree
and inserts into lower part
of lateral surface of ramus
of the mandible
B) Middle layer
It passes vertically
downward into the middle
part of the ramus
C) Deep layer
Into upper part of the ramus
and coronoid process of
the mandible
Its insertion on the mandible
extends from the 2nd molar
region at the inferior border
posteriorly to include the angle

8. ACTION
Elevation of
mandible to
close the
mouth
Forceful jaw
closing
Assist in
protrusion of
mandible

9. Temporalis
Fan shaped muscle
Fills the temporal fossa
Bipennate muscle
FIBRES
Converge and pass
through gap deep
to zygomatic arch

10. ORIGIN
Temporal fossa excluding
zygomatic bone
INSERTION
Margins and deep surface of
coronoid process
Anterior border of
ramus of mandible

11. FIBRESAnterior fibers are directed
vertically
Middle ones run obliquely
across the lateral aspect of
the skull
Posterior fibers are aligned
almost horizontal,coming
forward above the ear to
join the other fibers as they
pass under the zygomatic
arch

12. Actions
Elevation of the
mandible..
Retrusion of mandible
No activity when mandible
is elevated very slowly.

13. Lateral pterygoid
Short
Conical
Has upper and lower head
ORIGIN
A) upper head (small)
From infra temporal surface
and crest of greater wing
of sphenoid bone
B) lower head (larger)
From lateral surface
of lateral pterygoid plate

14. INSERTION
Pterygoid fovea on the
anterior surface of neck
of mandible
Anterior margin of
articular disc and capsule
of temperomandibular joint

15. ACTION
S
Assists in opening the mouth with
suprahyoid muscle.
The combinded efforts of the Digastrics and Lateral Pterygoids
provide for natural jaw opening.

16. SIDE TO SIDE GRINDING
MOVEMENT
medial and lateral
pterygoid of the two
sides contract
alternatively to produce
side to side movements
of mandible eg
chewing).

17. When the medial and lateral pterygoids of two
sides act together they protrude the mandible so
that the lower incisors project in front of the
other.

18. Medial pterygoid
Quadrilateral
Has a small superficial
and a large deep head
ORIGIN
Superficial head
From Tuberosity of maxilla and adjoining bone
Deep head
From medial surface of lateral pterygoid plate and
adjoining process of palatine bone

19. Fibres
Run downward
backward 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

20. ACTION
Elevates mandible
Helps protrude
mandible
Right medial pterygoid
with left lateral
pterygoid
turn the chin to left side

21. Anterior belly of digastric
It attaches to the lingual aspect of
mandible at the parasymphysis
and courses backward to insert in
the hyoid bone
ACTION
Contraction of this muscle
produces a depression and
retro positioning of the
mandible

22. Mylohyoid
ORIGIN
Flat triangular sheet of muscle,
Originates from mylohyoid line of
mandible
INSERTION
Posterior fibres are inserted into
the body of the hyoid bone,
anterior fibres are inserted into
the fibrous raphe

23. ACTION
Support the tongue and the floor of the mouth
Stabilises the hyoid bone during mandibular
movement
Assists in depressing the mandible and opening
the mouth

24. GENIOHYOID
ORIGIN
From the inferior mental spine
behind the symphysis menti of the
mandible
INSERTION
Inserted into the anterior surface of
the body of hyoid bone
ACTION
Retrusion of the mandible

25. Buccinator
It attaches inferiorly
along the facial
surface of the mandible
behind the mental
foramen
Superiorly attaches on the alveolar surfaces
behind the zygomatic processes
Fibres are arranged horizontally
Helps position the cheek during chewing
movements of the mandible

28. Protrudes: Medial & Lateral pterygoid
Retractors: Posterior fibers of Temporalis,
Diagastric & Geniohyoid
Elevators: Superficial & deep fibers of Medial
pterygoid & Masseter. Anterior & middle fibers of
Temporalis
Depressors: Lateral pterygoid, Diagastric &
Mylohyoid
Lateral movers: Medial & Lateral pterygoid on each
side

29. CLINICAL EXAMINATION

30. MASSETER

31. TEMPORALIS

33. FUNCTIONAL
MANIPULATION

34. Clinical consideration
Myofacial pain
Trismus
Muscle spasm
Muscle hypertrophy
Bruxisum
Ankylosis of TMJ
Trauma
Acute space infections
OSMF

35. Muscles of facial expression

36. Subcutaneous muscles
Develops from the mesoderm of second branchial arch
All of them are inserted into the skin
Need support from teeth for proper function

38. Orbicularis oris
Lip muscle
Two parts
-intrinsic,deepest stratum,very thin
sheet
-extrinsic,two strata,formed by
converging muscles
Origin
-intrinsic part
Superior incisivus,from maxilla
inferior incisivus from mandible
-extrinsic part
thickest middle part from buccinator
thick superficial strata from elevators and depressors of lips
and their angles

39. Insertion
-intrisic part in angle of mouth
-extrinsic part in the lips and angle of mouth

40. The muscles that merge into orbicularis oris
zygomaticus,
quadratus labii superioris,
caninus(levator anguli oris),
triangularis(depressor anguli oris)
quadratus labii inferioris,
mentalis,
buccinator and
risorius.

43. MODIOLUS
The insertion of the
group of muscles
about the oral cavity,
both superficial and
deep, partly into the
skin and partly into
the mucous
membrane of the lips
and immediate vicinity
situated slightly
lateral and above
the corner of the
mouth is called
modiolus

44. Except in instances of excessive ridge
resorption,the origins of most of these muscles
are removed from the denture bearing area to
the extent that their influence on the denture
except at the modiolus is negligible.
These muscles can be relaxed with the jaws
open while introducing the tray or the imp
material in the mouth.
When the lips are tense, a stretching action
often results in lacerations at corners of mouth
and/or distorted imp material

45. The labial flanges of the maxillary denture
frequently need to be reduced lateromedially
in the area of modiolus
If the muscles are not properly supported,
none of the facial expressions appear
normal.
 Incorrectly positioned teeth or an incorrectly
contoured denture base will destroy the
normal tonicity of the muscles

46. Lack of support allows sagging; stretching
retards the normal contracture of the muscle
and results in the loss of tonus.
When the muscles are stretched during mouth
opening ,the vestibular space between the
bundle in the cheek and the slopes of the
residual alveolar ridge are restricted. Reducing
the bulk of the flange to accommodate this
muscle action helps to prevent dislodgement of
the denture when the mouth is opened

47. With loss of teeth the action is impaired.
But when they are correctly supported by
complete dentures, the memory pattern
developed within the neuromuscular system
when the teeth were present, is restored so the
patient’s original appearance is maintained

48. Three factors affect the face in repositioning
the Orbicularis oris with Complete denture
1. thickness of labial flanges of both dentures
2. anteroposterior position of anteriors
3.amount of separation between the jaws
If the jaws are closed too far and the dental
arch located too posteriorly,the upward and
backward positioning of Orbicularis oris
complex will move the insertions of these
muscles near to its origin and result in sagging
when at rest and to be less effective when
contracting.

49. Many old patients want the nasolabial sulcus to be
obliterated because it appears as a wrinkle or skin
folds.The sulcus is normal and should not be
eliminated.
Repositioning the anterior teeth by protruding or retro
positioning to improve appearance is a mistake.
The physiologic length of muscles is determined
early.
In fact the muscles of lips,cheeks,tongue,face helped
align the teeth
Bring the entire upper arch forward to its original
position and maintain the normal arch form of the
natural teeth and their supporting structures,

50. The orbicularis oris and attached muscles
contract and force saliva and small particles of
food from the vestibule into the oral cavity and
seal off the space distal to last molar .The teeth
arrangement should allow for this movement to
occur
The correct width of the maxillary denture
borders play a great part in supporting the
muscles and lengthening the distance they
must extend to reach their insertion.
If the mouth had been edentulous for long with
considerable ridge loss,the borders need to
thick to restore the position of these muscles

51. Buccal frenum in maxilla needs to be relieved
coz it has attachments of the following muscles
Levator anguli oris---attaches beneath the
frenum
Orbicularis oris—pulls the frenum forward
buccinator—pulls it in backward

52. The maxillary labial frenum contains
insicivus and Orbicularis oris
Protrusion of the tongue helps in
recording the movements of mylohyoid
muscle.
The action of superior constrictor is
recorded by protruding the tongue.
That of medial pterygoid by asking the
patient to close forcefully against
resistance

53. Contraction of mentalis renders the vestibule
shallow hence capable of dislodging the
mandibular denture specially when the ridge is
non existent.
The mylohyoid constitutes the floor of the
mouth in the anterior part.
If the denture flange extends below and under
the mylohyoid line, it will impinge the muscle
and affects its action adversely during
swallowing, or the action of the muscle will
unseat the denture.
 Because the fibers are directed downwards
the flange can extend below but not under the
mylohyoid line.

54. It is not always possible to accentuate the
flange over the upper molars because the
attachment of the buccinator to the hamular
process sometimes brings the muscle very
close to tuberosity
Action of buccinator does not dislodge the
denture because the fibers are parallel to
occlusal plane. But again these fibers are
perpendicular to masseter, hence when the
masseter is activated it pushes the buccinator
medial against the border in the area of
retromolar pad area. This is a dislodging force
and the denture needs to be contoured
(massetric notch)

55. Failure to provide adequate interocclusal
distance produces excessive interarch distance
when the teeth are in occlusion. This position
does not allow the elevators to complete their
action, muscles will continue to exert force to
overcome this obstacle, and as a result
supporting tissues will be resorbed
Excessive interocclusal distance results in a
reduced interarch distance when in occlusion.
Facial distortion appears more noticeable with
over closure than with slightly opened closure,
the commisure turns down, and the lips lose
their fullness.

56. The proper contouring of occlusal rims for lip and
cheek support allows the muscles of facial
expression to act in a normal manner.
The rims should be designed to be within the neutral
zone
The best anatomic guides to proper contouring of the
anterior section of rims are the nasolabial sulcus,
mentolabial sulcus, philtrum and commisures.When
support is absent the sulci become more
deep,philtrum flattened and commisures droop.
When over supported the sulci become distorted and
shllow, philtrum partially or totally obliterated, and
commisures distorted laterally

57. NEUTRAL ZONE

58. While eating the stability of upper denture depends
upon the pressure of the tongue against the palate.
This presses the palate upwards and outwards, but
the cheeks and the lips balance the outward
component and the resulting upwards pressure is the
main stabilizing factor. This can only be achieved if the
teeth are in their correct facio lingual relationship to
tongue, cheeks and lips

59. There is no occlusal scheme that can stabilize
teeth if they are in an unbalanced relationship
with muscular forces against them

60. The lower dentures will be unstable,
1. If the premolars were set outside the
ridge so that the denture is lifted by the
corners of the mouth(modiolus),
2. If the buccal and lingual surfaces of
the denture in the molar region were
parallel so that tongue and buccinator
could not grip the plate and hold it down ,
3. If the edges were not muscle trimmed
in the incisor and premolar region and
correctly adapted to the muscles in the
posterior lingual and buccal regions

61. If the arch is wide at the lower premolar
region ,it will be squeezed in the v shaped
muscle band of zygomaticus and caninus and
will shoot up out of place. Therefore there
should be a sudden narrowing to escape a
collision with the modiolus
A little extra width is required in upper premolar
region as it will enable the modiolus to grasp
the upper denture by the outer cusp of the
premolars and hold it up.
Inner cusp of lower premolar can and indeed
should be cut off otherwise it will interfere with
the movements of the tongue and unstabilise
the denture.

62. The stabilizing or unstabilising force which depends
on the polished surface for its application to the
denture is the muscular power of the tongue,
buccinators, orbicularis oris and other muscles of
cheek and lips. It is the shape of this complex
surface as a whole, far more than the outline of the
muscle trimmed edge of the denture, which
determines whether muscle movements will dislodge
the piece; while on the other hand if the polished
surface is properly modeled so that the tongue,
cheeks and lips have complete freedom of
movement, the grip which the buccinators and the
tongue can exert on the plates will make them
wearable long after resorption has occurred and they
have ceased to fit the impression surface in the
ordinary sense of the term

63. PTERYGOMANDIBULAR RAPHE

64. CO-ORDINATED MUSCLE FUNCTION

65. Occlusal interferences which require
displacement of the TMJs to achieve
maximum intercuspation of teeth can
cause inco-ordination of all the
masticatory neuromusculature.This is
called occluso-muscle pain

66. When an occlusal interference is introduced in
mouth,it typically evokes a response of
hyperactivity and incoordinated contraction in all
the muscles that are prevented from functioning
in a coordinated pattern of contraction versus
release of opposing muscles .

67. IMPORTANCE OF OCCLUSAL
HARMONY
When closing muscle pull mandible
without interference it is stopped by bone
at medial pole
If tooth inclines interfere lateral pterygoid is
forced to position the mandible to accommodate
to the teeth
There are many variations of timing and degree
of muscle contraction to position the mandible
for maximum intercuspation of the teeth.
Pattern of deviation is reinforced every time
contact is made
Important facet of propioceptive memory is that
it fades if reinforcement of pattern ceases.

68. Elimination of interfering
contacts permit an almost
immediate return to normal
muscle function
posterior tooth interference
caused hyperactivity of
elevator muscle
But if the anterior guidance
was allowed to disclude all
posterior teeth from any
contact other than CR,
elevator muscle stopped
active contraction or reduced
it.

69. The reason muscle changes jaw position in the
presence of interferences is to protect the
interfereing tooth or teeth from absorbing entire
occlusal force
Muscles become patterned to the devious
closure ,such memorized patterns of muscle
activity are called ENGRAMS
Because of engrams it is easy to be fooled by
freely hinging jaw that appears to be in correct
CR.

71. When we create an occlusion in centric
relation,and disclusion when there is deviation
from centric,the anterior teeth (anterior
guidance) along with the condylar path take the
responsibility of separating the posteriors during
all excursions

72. 3 beneficial effects of this are
-greatly reduces the horizontal forces against
the anterior teeth,which are the only teeth in
contact during excursion
-reduces compressive loading forces on TMJs
-makes it impossible to overload or wear the
posterior teeth, even if the patient bruxes

We cannot keep teeth in a stable position where
muscle does not want them to be.
Muscle is the dominant determinant of both the
horizontal and vertical position of teeth

73. CURVE OF SPEE

74. It aligns each tooth for maximum resistance
to functional loading
 To prevent increase muscle loading of the
teeth and the joints during protrusive
movement.
If there is any tooth contact posterior to
canine during excursion the elevator
muscles are triggered into hypercontraction

75. CURVE OF WILSON
Results from inward inclination of
posterior teeth
In maxillary arch reverse is there because
of outward inclination of posterior teeth.
There are two reasons for this inclination of
posterior teeth
1) one has to do with resistance to
loading
2)second has to do with masticatory
function

76. Axial alignment of all
posterior teeth is nearly
parallel with the strong
inward pull of the medial
pterygoid muscle
Aligning both upper and
lower posterior teeth with
the principal direction of
muscle contraction
produce the greatest
resistance to masticatory
forces, and forms curve
of wilson

77. tongue and
buccinator must place
food onto occlusal
table
there must be easy
access for the food to
get to the occlusal
table
The inward inclination
of the lower occlusal
table allows for direct
access from lingual

78. The outward inclination of
the upper occlusal table
provides access from the
buccal for the food
When the curve of wilson
is made too flat ease of
masticatory function may
be impaired because of
increased activity
required to get the food
onto the occlusal table

79. Normal function versus parafunction

The image to the left is demonstrating
normal reciprocal functioning of the Lateral
Pterygoids and
Masseters/Med.Pteygoids/Temporalis'.
The Lateral Pterygoids advance the
condyles, thereby opening the mouth
(depressing the mandible), with the
assistance of the Digastric
The oblique orientation of the Masseters
and Medial Pterygoids create a sling. The
non-working side Medial Pterygoid
contracts simultaneously with the opposite
side working Masseter.
It is this oblique orientation of the
Med.Pterygoids and Masseters that create
the functional "shift" of the mandible, not an
unilateral contraction of a Lateral Pterygoid
.

80. In the event the
Temporalis' do not cease
their active contractions,
scenarios of varying
degrees of parafunction
result, as the Lateral
Pterygoids encounter
resistance to their
attempts at condylar
advancement, thereby
increasing their intensity
of contraction and strain
on their origins and
insertions: the pterygoid
plates of the sphenoid
bone, and the condylar
neck and disc.

81. The degree of
frequency, duration
and intensity of the
contractions of a
Lateral Pterygoid is
a function of the
resistance
provided by the
parafunction
ipsilateral and/or
contralateral
Temporalis.

82. The maximum clenching intensity occurs in the
musculoskeletally stable position
The mandibular position
of the temporalis' most
intense contraction is not
when the teeth are
together, but when they
are a particular distance
apart, and separated by
an object (such as a
splint, or food).

84. REFERENCES
Clinical Anatomy. 7
th
ed
Richard S Snell,

BD Chaurasia’s ,Human Anatomy volume 3 - 4
th
edition
Grays Anatomy -36
th
ed

 Clinically Oriented Anatomy -4th ed
Keith L.Moore,

Grants atlas of anatomy -10
th
ed
Atlas of human anatomy-4
th
ed
Netter
Principels of anatomy and physiology-11
th
ed
Tortora,Derrickson
Human embrology-6
th
ed
Inderbir Singh

85. Functional occlusion-from TMJ to smile design
Peter E Dawson
Clinical Periodontology -8th ed
Fermin A Carranza,Micheal G
Newman
Wheeler’s Dental anatomy physiology and occlusion,6
th
ed
Management of temporomandibular disorders and occlusion-
5
TH
ed
Okeson
Oral medicine diagnosis and treatment,10
th
ed
Burket

86. Syllabus of complete dentures-4
th
ed
Heartwell and Rahn
Essentials of complete denture prosthodontics- 2nd ed
Sheldon Winkler
Prosthodontic Treatment for Edentulous Patients-12
th
ed
George A.Zarb,Charles L Bolender