Craniofacial musculature /certified fixed orthodontic courses by Indian dental academy

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Craniofacial musculature

Presented by:- Dr.

Apurva k.Chitalia


Contents:introduction
Development of the muscles.
 classification of craniofacial musculature.
 the buccinator mechanism.
 the orbicularis oris.
 the muscles of mastication.
 accessory muscles of mastication
 The tongue.



Contents:The

temporo mandibular joint
Physiology of muscles.
Reflex of muscles
 myotactic reflex.
Methods to study muscles.
Emg
Is it the one of them?
The equilibrium theory

Contents:









Muscle and growth.
Muscle adaptation in malocclusion
Soft tissue environment of patients with
malocclusion.
Muscular adaptation after orthognathic surgery
Effects of orthodontic treatment on the
neuromuscular functions.
Muscles and its treatment modalities.
Conclusion

Introduction:A

Man to increase the strength of
skeleton has been blessed by 639
muscles which includes 6 million of
muscle fibers.
 Each fibers has 1000 fibrils
 Thus there is 6000 billion muscle fiber
working at one time.

 In

orthodontics and in real life we
judge / diagnose a individual when we
look at him.
 But here when we look at patient we
look at him in repose/rest and we try to
see the dentofacial complex and their
intimate relationship to each other





This is just the static analysis but important
is the dynamic appreciation on how they
function , as they function, how they affect
the growth and the relationships of parts ,
these constitutes the stomatoganthic
system.
Here musculature plays a very important
part.

 We

orthodontist try to achieve the
perfect equilibrium between the part of
stomatoganthic system which includes
the muscle.

 so

it is of definite importance that we
should know in and out about them.

Development of muscle.
During the 3rd week of I.U life the embryo undergoes gastrulation to
form a trilaminar disk i.e.
the cells from epiblast migrate to primitive streak and to primitive
node detach from the epiblast and they invaginated the hypoblast to
displace it and form the three layers.



Three germ layers derived from the epiblast



endoderm



mesoderm



ectoderm

Three germ layers derived
from the cells epiblast









The mesodermal layer is further divided
into:head
paraxial
intermediate
lateral
The mesoderm on either side of the notochordal
process thickens to form longitudinal columns of
tissue called the paraxial mesoderm.
These segments into paired blocks of tissue
called the somites. Of these the cranial ones are
called as somitomeres.

There are seven of somitomeres approx. In
register with that of the pharyngeal arches.
The skeletal muscles of the head and neck
develop from this somitomeres and the most
cranial somites.
The pharyngeal arches develop during the
4th wk. of the I.U life.
They significantly contribute to the
development of head, face neck and nasal
cavity, mouth and to some extent the larynx
and the pharynx.



The branchial arches have incomplete clefts
between the arches, the external ectodermal
branchial grooves and internal endodermal
pharyngeal pouches.



The branchial groove of the first branchial arch
persists as external acoustic meatus which is
covered by the tympanic membrane.



All the grooves disappear but they remain as
the tympanic cavity, auditory tube, tonsil,
thymus, parathyroid, and the thyroid gland.

Cartilage components derived from
pharyngeal arches are:


1.
2.


Arch I [mandibular arch]:- this is major contributor to
the development of the face.
The cartilage of the first arch is called as the meckels
cartilage.
The dorsal end of the meckels cartilage becomes ossified
to form 2 bones of the middle ear ossicle :malleus
Incus
The middle portion of the meckels cartilage regresses, but
its perichondrium forms the sphenomandibular ligament.



The ventral part of the meckels cartilage
forms a horse shaped structure in the shape
of the future mandible.



The mesenchymal tissue lateral to the
cartilage undergoes intra membranous
ossification to produce the mandible as the
original meckels cartilage disappears.

Arch II [hyoid arch]:- this cartilage is
called as the reicherts cartilage
 It dorsal end becomes ossified to produce
the other middle ear ossicle, the stapes, and
the styloid process of the temporal bone.
 A portion of the perichondrium of the
cartilage forms the stylohyoid ligament.
 This also contributes in the development of
the hyoid bone specially the lesser cornu,
and the superior portion of the body.





The cartilage of the 3rd arch gives rise to
the greater cornu and the inferior part of the
body of the hyoid bone.



The cartilage of the 4th and the 6th arches
fuses together to form the laryngeal
cartilage, including the thyroid, cricoids, and
arytenoids cartilage except the epiglottis.


Muscle components :

They are derived from the cranial
somites and the cells that migrate at
this region from the somitomeres.



Arch I: muscles derived are: the
muscles of mastication, anterior belly
of digastric, mylohyoid, tensor veli
palatine, tensor tympani.

Arch II: the muscles of facial expression.
These are relatively thinner and have
their origin and insertion in the skin and
are present throughout the face and the
neck.
 Arch III: it gives rise to stylopharyngeous
muscle.
 Arch IV and arch V: - muscles of the
pharynx and the larynx. Arch IV give rise
to cricothyroid and arch V to intrinsic
muscles of larynx.



Classification of
muscles:1.
2.




they can be primarily classified as:facial muscles
Muscles of mastication.
The facial muscles: they are related to the
orbital margins plus the eyelids, the
external nose & nostrils, the lips, cheeks,
mouth, the pinna, scalp and the cervical
skin.
These are also called as muscles of facial
expression as that is their function.

Muscles of mastication: they are chiefly
concerned with the movements of the
TMJ
 The division reflects the different
embryonic origins and innervations of the
two groups.
 But all the functions such as mastication,
deglutition, respiration, swallowing,
speech, communicative and emotional
expression, ocular, nasal and aural action
are the effect of close cooperation of two
groups.



According to moyers:1.
2.
3.

facial muscles
jaw muscles
Portal muscles.


Characteristics of the facial
muscles: The

primary function is expression of the emotions.
 The facial muscles are capable of performing 7000
expressions according to Coleman.
 They are also responsible for the maintenance of
the posture of the facial structures.
 Paresis of the orbicularis oculi leads to the
drooping of the lower eyelid.
 Paralysis of the orbicularis oris will lead to angular
cheliosis and the drooling.

The

facial muscle also contributes to
stabilization of the mandible during
the infantile swallowing and chewing
and swallowing in the occlusally
compromised adults.

It

is also important for the visual and
the spoken communications.


Characteristics of the jaw
muscles:




The mandible being maintained against the
gravity by the stretch reflex of the elevators.
EMG studies have shown of [postural position]
that the inframandibular groups of muscles are
more active than the levator.
Mandibular movement assisted by the levator
and the depressors can’t be considered just the
interplay between these 2 but is very much
thought as the intricate muscular web where the
teeth and the joints acts as the stops.









The head posture also affects the posture of the
mandible for e.g. when there is extension of the
head there is increase in the freeway space and
when there is flexion there is decrease in the
freeway space.
Changes in the head posture also results changes
in the anteroposterior positioning of the posture of
the mandible.
One of the most important factors is the posture of
the mandible affecting the development of the
jaws.
E.g. during the mouth breathing there is effect on
the growth of both maxilla as well as the mandible
due to alteration in position of the mandible, hyoid
and the tongue.

But in case where there is Sunday bite
there is no resultant correction probably
because the dorsal position of the
mandible during the functional activities
cancels the biologic signals to the joint
structures.
 Thus functional appliances work the best
as they are worn for the most hours of the
day .



Characteristics of the portal
muscles:Portal muscle is the word coined by
Bosma to denote the upper alimentary
tract and the respiratory tract.
 These muscles serve some functions of
our interest such as posture, respiration,
feeding.





The muscles include the muscles of
the tongue [both the intrinsic and the
extrinsic] the soft palate, the
pharyngeal pillars, the pharynx proper,
and the larynx.


According to grays:
1.
2.
3.
4.

they are broadly classifies as:
epicranial muscles
circumorbital muscles
the nasal musculature
the buccolabial musculature


The epicranial musculature

1.
2.

The epicranius consists of two main
parts
occipitofrontalis
Temporoparietalis.


The scalp:

1.
2.
3.
4.
5.

The scalp essentially consists of five
layers i.e.
superficial fascia
connective tissue
epicranial aponeurosis
loose aerolar tissue
pericranium

The superficial fascia in the scalp is firm and
fibro-adipose adherent to the skin and the
underlying epicranius and the aponeurosis,
the galea aponeurotica [epicranial
aponeurosis.]
 It is continuous with the superficial fascia of
the back of the neck; laterally, it is prolonged
to the temporal region where it losses its
texture.



The occipito frontalis
It is a broad, musculofibrous layer,
covers the dome of the skull, from the
nuchal lines to the eyebrows.
 It consists of 4 parts---- 2 occipital and
2 frontal connected by the epicranial
aponeurosis



 Occipital

part: - each of them are thin,
quadrilateral arises by tendinous fibers
from the lat. 2/3rd of the highest nuchal
lines of the occipital bone and the mastoid
part of the temporal bone. It ends in the
epicranial aponeurosis.
 Frontal part: - they are thin, quadrilateral,
and adherent to superficial fascia. It is
broader than the occipital part and its
fibers are longer and paler.



It has got no bony attachments. Its medial fibers are
contiguous with those of the procerus; its intermediate
fibers blend with the corrugator supercilli and the
orbicularis oculi; its lateral fibers are also blended with
the latter muscle over the zygomatic process of the
frontal bone.



From these attachments the fibers are directed upwards
to join the epicranial aponeurosis in front of the coronal
suture. The medial margins of the frontal slips are joined
together for some distance above the root of the nose;
but between the occipital bellies there is considerable,
but variable interval occupied by the epicranial
aponeurosis.

Galea aponeurotica:



It covers the upper part of the cranium and
along with the epicranius it forms the
continuous fibromuscular sheet extending
from the occipital to the eyebrows. Behind, in
the interval between the occipital parts of the
occipitofrontalis, it is attached on the
external protuberance or highest nuchal
lines of the occipital bone.
In front it splits to enclose the frontal parts
and sends a short narrow prolongation
between them.

It is united to the skin by firm, fibrous
superficial fascia; it is connected to the
pericranium by loose aerolar tissue
which allows its free movement. The
latter carrying it with the skin of the scalp
 Nerve supply: - the occipital part is
supplied by the posterior auricular
branch and the frontal part by the
temporal branches of the facial nerve.



Action:- the occipital slips draw the
scalp downward , the frontal slips
acting from above raise the eyebrows
and the skin of the root of the nose ;
acting from below they draw the scalp
forwards; throwing the integument of
the forehead into transverse wrinkles.
 They act in tandem in expression
like surprise, horror or fright etc.



The fourth layer of the scalp:
 it is made up of loose aerolar tissue. it
extends anteriorly to the eyelids; and
posteriorly to the highest nuchal lines
and on each side to the superior
temporal lines.
 The fifth layer is called as pericranium:-it
is loosely attached to the surface of the
bones, but is firmly adherent to their
sutures where the sutural ligaments bind
the pericranium to the endocranium.



Temporoparietalis:



It is variably developed sheet of muscle that
lies between the frontal part of the occipito
frontalis and the ant. And sup. Auricular
muscles.
A thin muscular slip, the transverse nuchae,
is present in about 25 percent of the people;
it arises from the external occipital
protuberance or from the superior nuchal
lines, present either sup. Or deep to
trapezius; it is frequently inserted with the
auricularis posterior, but may join the post.
Edge of the sterocleidomastoid.

Circumorbital and
palpeberal musculature.

1.
2.
3.

The muscle that come under this
heading are:orbicularis oculi
corrugator supercilli
levator palpebrae superioris


The orbicularis oculi:

it is a broad, flat, elliptical muscle that
occupies the eyelids, surrounds the
circumference of the orbit and spreads
on the temporal region and the cheek.
it consists of the orbital , palpebrae
and lacrimal parts.


The orbital part






it is reddish and thicker than the palpeberal
fasiculi
Origin:-arises from the nasal part of the frontal
bone, from the frontal process of the maxilla and
from the medial palpeberal ligament, which
interrupts the bony attachment.
It fibers form the complete ellipses without the
interruption on the lateral side, the upper ones
blending with the frontal part of the
occipitofrontalis and the corrugator.



Insertion:-some of the fibers are
inserted into the skin and the
subcutaneous tissue of the eyebrow.
They constitute the depressor
supercilli.


The palpeberal part


- it is thin and pale. It arises from the medial
palpeberal ligament chiefly from its superficial
but also from its deep parts, though not from
the lower margin, it arises also from the bone
immd. Above and below the ligament.



The fibers sweep across the eyelids in front of
the orbital septum and at the lateral
commissure and interlace to form the lateral
palpeberal raphe. A small group of the fine
fibers lies close to the margin of each eyelid,
behind the eyelashes; it is named as the ciliary
bundle.

The lacrimal part: 




it lies behind the lacrimal sac but separated
from it by the lacrimal fascia.
It is attached to lacrimal fascia, to the upper
part of the crest of the lacrimal bone, and
adjacent part of the lateral part of the lacrimal
bone.
Passing laterally behind the lacrimal sac the
muscle divides into upper and lower slips; some
fibers are inserted into the tarsi of the eyelids
close to the lacrimal canaliculi, but most
continue across in front of the tarsi and
interlace in the lateral palpeberal raphe.

The medial palpeberal ligament:- it is
about 4mm in the length and 2mm in the
breadth, is attached to the frontal
process of the maxilla in front of the
nasolacrimal groove. Crossing the
lacrimal sac it divides into 2 parts i.e.
upper and lower parts each one attached
to the medial end of the corresponding
tarsus.

It is separated from the lacrimal sac
by the fascia.





Nerve supply: - temporal and zygomatic
branch of the facial nerve.



Actions: - the orbicularis oculi: - it is the
sphincter muscle of the eyelids.



The palpeberal portion acts under
voluntary control closing the lids gently as
in sleep or blinking; the orbital portion is
more frequently under voluntary control




During the eye closure there is lowering of
the upper as well as elevation of the lower
eyelid. thus palpeberal part has depressor
and elevator fasicles.when the entire
muscle contracts than the skin of the
forehead , temple and cheek is drawn
towards the medial angle of the orbit, and
the eyelids are not only firmly closed but
they are moved in toto medially. The skin is
thrown in the folds on the lateral angle of
the eyelids due to this action which are
called as crow’s feet.









The lacrimal part of the muscle draws the eyelids
and the lacrimal papillae medially, and exerts
traction on the lacrimal fascia and it dilates the
lacrimal sac.
Thus the muscle has important action in tear
transport.
The muscle is also an important element in facial
expression and the ocular reflexes.
Partial closure of the palpeberal fissure together
with bunching and the protrusion of the eyebrows
diminish the entry of the light.



These action of the upper orbital fibers
and their peripheral extension cause
vertical furrowing above the bridge of the
nose. This is called as blink reflex and its
protective value is obvious.


The corrugator
supercilli:
it is a small pyramidal muscle, at the
medial end of the eyebrows, deep to the
frontal part of the occipitofrontalis and the
orbicularis oculi .
 From the medial end of the superciliary
arch its fibers pass slightly laterally and
slightly upwards to the deep surface of
the skin above the middle of the
supraorbital margin.



Nerve supply: - the temporal branches of
the facial nerve.
 Action: - draws the eyebrows medially
and downwards
 Together with the orbicularis oculi
causing vertical wrinkles of the forehead.
 It assists in drawing the eyebrows
downwards in the bright sunlight and is
also involved in frowning



The nasal musculature:

1.
2.
3.

This group comprises of three
muscles:the procerus
the nasalis
The depressor septi.


The procerus: it is a small pyramidal slip continuous with
the medial side of the frontal part of the
occipitofrontalis.
 Origin:-It arises from the fascia covering
the lower part of the nasal bone and the
upper part of the lateral nasal cartilage.
 Insertion:-it is inserted into the skin over
the lower part of the forehead between
the eyebrows.



Action: - it draws down the medial angle
of the eyebrow and incidentally produces
wrinkles over the bridge of the nose.
 It is active in frowning and concentration.
 It also aids in reducing the glare of the
sunlight.



The nasalis: it consists of transverse and alar parts
which may be continuous at the origin.
 The transverse part:-[compressor naris] –
it arises from the maxilla just lateral to the
nasal notch; its fibers proceed upwards
and medially and expand into a thin
aponeurosis, which is continuous on the
bridge of the nose with that of the muscle
of the opposite side, and with the
aponeurosis of the procerus.











The alar part [dilator naris]—it arises from the
maxilla, below and medial to the transverse part. It
is attached to the cartilaginous ala nasi.
Actions: - the transverse part: - it compresses the
nasal aperture at the junction of the vestibule with
the nasal cavity.
The alar part draws the ala downwards and
laterally and so assists in widening the ant. Nasal
aperture.
These actions are visible in deep respiration,
especially in its inspiratory phase, and they also
accompany certain emotional states.

The depressor septi: often regarded as the part of the
dilator nasi; is attached to maxilla
above the central incisor roots.
 Present immediately deep to the
mucous membrane of the upper lip.



Action: - it assists the alar part of the
nasalis in widening the nasal aperture
while deep inspiration.
 Nerve supply: - All the nasal musculature
supplied by superior buccal branches of
the facial nerve.



buccolabial musculature:

1.
2.
3.
4.
5.
6.

These are the muscle slips which control the
shape of buccal orifice and the posture of the
lips
They include: the retractors and elevators of
the upper lip viz:levator labii superioris alaeque nasi
levator labii superioris
the zygomaticus major
the zygomaticus minor
risorius
levator anguli oris

1.
2.
3.

the depressor and retractors of the
lower lip viz:depressor labii inferioris
depressor anguli oris
mentalis


The levator labii superioris alaeque
nasi

Origin:-it arises from the upper part of the
frontal process of the maxilla and, passing
obliquely downwards and laterally, divides
into medial and lateral slips.
 Insertion:-The medial slips is inserted into
greater alar cartilage and skin of the ala of
the nose.





the lateral slip is prolonged into the
lateral part of the upper lip, and blends
with the levator labii superioris and
orbicularis oris

Action: - the lateral slip raises and everts
the lip
 The medial slip acts as dilator of the
nostril.




Nerve supply: - it is supplied by the
buccal branches of the facial nerve.

The levator labii superioris: Origin:-it starts immediately above the
infra-orbital margin at the lower margin
of the orbital opening.
 It arises from the maxilla and the
zygomatic bone.












Insertion:-Its fibers converge into the muscular
substance of the upper lip between the lateral slip
of the levator labii superioris alaeque nasi and
levator anguli oris.
Action: - it raises and everts the upper lip.
Along with the zygomaticus major it forms the
nasolabial furrow, from the side of the nose to the
upper lip.
The furrow deepens while expressing sadness
and seriousness.
Nerve supply: - it is supplied by the buccal
branches of the facial nerve.

The zygomaticus minor: 





Origin:-arises from the lateral surface of the
zygomatic bone immediately behind the
zygomaticomaxillary suture.
Insertion:-it passes downward and medially
into the muscular substance of the upper lip.
It is separated from the levator labii
superioris by a short interval.




Action:-it elevates the upper lip and also
produces the nasolabial furrow.






When the levator labii superioris alaeque
nasi, the levator labii superioris and the
zygomaticus minor are in action together
they express contempt and disdain.

The levator anguli oris: Origin: it arises from the canine fossa,
just below the infra –orbital margin.
 Insertion:-it is inserted into the angle of
the mouth, intermingling with fibers of the
zygomaticus major, depressor anguli oris
and orbicularis oris...
 Between the levator anguli oris and the
levator labii superioris are the infra orbital
vessels and nerves.



Action: - it raises the angle of the
mouth
 It is instrumental in producing the
nasolabial furrow.






The zygomaticus major: Origin:-extends from the zygomatic bone
in front of the zygomaticotemporal suture.
 Insertion:-to the angle of the mouth,
where it blends with the fibers of the
levator anguli oris, orbicularis oris and the
depressor anguli oris.





Actions: - it draws the angle of the mouth
upward & laterally as in laughing.






The zygomaticus major and minor and the
levator labii superioris are sometimes
enclosed by thin sheet of muscle called
as musculus malaris and are continuous
with the orbicularis oculi. [Lightoller 1925]

The depressor labii inferioris:
Origin:-it is quadrilateral in shape and
arises from the oblique line of the
mandible between the mental foramen
and the symphysis menti. At its origin it is
continuous with the platysma.
 Insertion:-it passes upwards and medially
into the skin of the lower lip, blending with
its fellow and orbicularis oris.



Action - it draws the lower lip downward
and a little laterally in masticatory
activity
 It contributes to expression of irony.
 Nerve supply: - it receives supply from
the mandibular marginal branch of the
facial nerve.



The depressor anguli oris: Origin:-arise from the oblique line of the
mandible, below and lateral to the
depressor labii inferioris.
 Insertion:-it converges into the narrow
fasciculus blending with the other muscles
at the angle of the mouth.
 It is continuous with the platysma at its
origin and at its insertion with the
orbicularis oris and risorius;



Some of the fibers are directly continuous
with that of the levator anguli oris, and
others accidentally cross to the other side
these are called as the transversus menti.
 Action: - draws the angle of the mouth
downward and laterally while opening of
the mouth and during expression of the
sadness.
facial nerve.



The mentalis:
Origin:-it is a conical fasciculus at the
side of the frenulum of the lower lip. It
arises from the incisive fossa of the
mandible.
 Insertion:-it descends to be attached
to the skin of the chin.



Action:- it raises and protrude the lower lip
and at same time wrinkles the skin of the
chin.
 It helps in drinking and in expressing
disdain and doubt.
 There is continuous activity in the muscle
also during the sleep according to EMG
studies.
facial nerve.



The buccinator:
it is thin quadrilateral muscle occupying
the interval between the maxilla and the
mandible, in the cheek.
 It is attached to the outer surfaces of the
alveolar processes of the maxilla and the
mandible, opposite to molar region and
behind, the anterior border of the
pterygomandibular raphe, which
separates it from the superior constrictor
of the pharynx.



Between the maxillary tuberosity and the
upper end of the raphe a few fibers arise
from the tendinous band which bridge the
gap between the maxilla and the pterygoid
hamulus.
 The tendon of the tensor veli palatini on its
way to the soft plate pierces the pharyngeal
wall in the small gap which lies behind this
tendinous band.



The fibers of the buccinator converge
towards the angle of the mouth , where
the central fibers intersect each other,
those from below being continuous with
the upper segment of the orbicularis oris,
and those from above with the lower
segment of orbicularis oris.
 The lowest and the highest fibers are
continuous forward into the corresponding
lip without decussation.



Relations:it is covered by the buccopharyngeal
fascia and lies in the same plane as
that of the superior constrictor.
 Superiorly, posteriorly a large mass of
fat separates it from the ramus of the
mandible, masseter, and small portion
of the temporalis.this is called as the
suctorial pad.



Anteriorly, superficial surface of the muscle
is related to the zygomaticus major
risorius, levator and depressor anguli oris,
the parotid duct which pierces it opposite
to the 3rd molar tooth. the facial artery and
facial vein crosses it; the facial nerve and
the buccal nerves also cross it .
 The deep surface is related to the buccal
glands and the mucous membrane of the
mouth.



Nerve supply: - supplied by the lower
buccal branch of the facial nerve
 Action: - it compresses the cheek against
the teeth so helps in mastication as the
food is passed between them.
 It helps in blowing, hence the name
buccinator= the trumpeter.



The buccinator mechanism
There is a strong interdependence of
muscles and bone and the major factor
in this environmental balance is the
musculature. They are the potent force
whether in active state or at rest.
 The teeth and the supporting structure
are under constant pressure from the
contiguous musculature



The integrity of the dental arch and its
relation with the same arch and the
opposing arch is maintained by the
morphogenetic pattern, which is modified by
the stabilizing and active functional force of
muscles
 Environmental factors are the contact
relations and resistance afforded by the
buttressing effect of contiguous teeth,
occlusal interdigitation and the bone building
– resorption balance maintained in the
periodontal membrane.



Thus stability is dependent on the 1.
Genetic. 2. Environmental 3. Epigenetic
factors
4.
Morphologic
factors
5.
Physiologic.
 Acc. To Winders the tongue exerts two to
three times more pressure on the dentition
than the lips and the cheeks but the net
effect is maintained as the tonal contraction,
peripheral fiber recruitment of the buccal &
labial muscles and the atm. Pressure team
up to offset the momentarily greater
functional force of the tongue.





Acc. to Lear and Moorress the enigma
between the dental arch and the muscle
function remains as there are limitations such
as measuring equipment; hydraulic nature of
response, size and sample and even the
geometry of the dental arch which do not
permit definitive form- function conclusions.


The buccinator mechanism.
The orbicularis oris muscle decussating fibers joins the
right and left fibers in the lips. The buccinator mech.
Runs laterally and posteriorly around the corner of the
mouth, joining other fibers of the buccinator muscle
which insert into the pterygomandibular raphe just behind
the dentition. Here it intermingles with the fibers of the
sup. Constrictor muscle and continues posteriorly and
medially to anchor at the origin of the superior constrictor
muscles, the pharyngeal tubercle of the occipital bone.
The tongue pressure opposes the buccinator mech.

The pterygomandibular raphe:
It is the interlacing of the tendinous fibers
stretched from the hamulus of the medial
pterygoid plate to the posterior end of the
mylohyoid line of the mandible.
 Medially it is covered by the mucous
membrane of the mouth.



Laterally, it is separated from the
ramus of the mandible by quantity of
fat.
 Posteriorly, it gives attachment to the
superior constrictor of the pharynx.
 Anteriorly to the part of the
buccinator.



The orbicularis oris: Is made of the several strata which
surround the orifice of the mouth but
have different directions. It consists partly
of the fibers derived from the other facial
muscles which pass into the lips, partly of
fibers proper to them.
 Of the former there is no. of them derived
from buccinator, and from the deeper
stratum.



Some of the buccinator fibers viz: those
near the middle of the muscle- decussate at
the angle of the mouth; the uppermost and
the lowermost fibers pass across the lips
from side to side without decussation.
 Superficial to this is the second strata,
formed by the levator and the depressor
anguli oris, which cross each other at the
angle of the mouth; the fibers from the
levator pass to the lower lip and that from
the depressor into the upper lip. Along
which they run to reach the skin at the
anterior median line.







Fibers are also derived from the levator labii
superioris, zygomaticus major and minor, and
the depressor labii inferioris; these intermingle
with the transverse fibers described above, and
have principally an oblique direction.
Thus some eight or nine muscle thus converge
at the angle of the mouth and interlace here at a
palpable nodular mass , The modiulous. this can
be fixed in a given position by the combined
action of the depressor anguli oris , zygomaticus
major ,levator anguli oris.. This thus serves to fix
the attachments of the orbicularis oris and the
buccinator.

Within the lips the fibers of the orbicularis
oris are divisible into two fasiculi, the
marginal and the peripheral.
 These combine to form the labial bands
that are traceable to the modiulous
[lightoller 1925, burkitt and lightoller in
1926, 1927]
 The fibers of the lip are in oblique
direction, and pass from the deep surface
of the skin to the mucous membrane, thru
the thickness of the lip.



Finally there are fibers of the muscle bands
that are attached to the maxilla above and
mandible below.
 In the upper lip these constitute the incisive
labii superioris which arises from the
alveolar border of the maxilla, opposite to
the lateral incisor tooth, and arching laterally
which is continuous with the other muscles
at angle of the mouth.





The additional fibers of the lower lip
constitute a slip of incisive labii inferioris, on
each side; the slips arise from the mandible;
lateral to the mentalis, and mingles with the
other muscles at the angle of the mouth.



In a study on children on fetal lips [14-25
weeks] Latham and Deaton in 1976
conclude that orbicular oris fibers interlace
and cross the midline to their cutaneous
insertions, thus creating the ridges of the
philtrum of the upper lip.

Nerve supply: - it is supplied by the lower
buccal and the mandibular marginal branch
of the facial nerve.
 Actions: - its ordinary action is to effect
direct closure of the lips, by its deep and
oblique fibers it compresses the lips against
the teeth.
 The superficial part, consisting principally of
the decussating fibers , brings the lips
together and protrudes them. The
orbicularis oris and other muscles of the lips
play an important part in articulation, as well
as in mastication. [Duckworth 1947]



The risorius: Origin:-arises from the parotid fascia
 Insertion:-is inserted into the skin at the
angle of the mouth.
 It is a narrow bundle of fibers, broad at its
origin.
 It may vary much in its size and form; like
may arise from the zygomatic arch,
external ear or the fascia over the
mastoid process.



Nerve supply: - is supplied by the buccal
branches of the facial nerve.
 Action: - it retracts the angle of the mouth
and produces the sardonic expression.


Facial muscles also play an important role
in the speech and feeding and drinking.

Their importance in mastication has
always been a topic of EMG study.



Muscles of the
mastication:-





1.
2.
3.

These muscles immediately are
concerned with the movements of the
mandible [and speech],
These muscles are viz:Masseter
Temporalis
Pterygoid muscles.


The masseter: 

A strong layer of fascia derived from the deep cervical
fascia is named the parotid fascia; it covers the
masseter and is firmly connected with it. It is attached to
the lower border of the zygomatic arch and invests the
parotid gland.










It is quadrilateral in shape and consists of three
superimposed layers blending anteriorly.
The superficial layer, the largest arises by a thick
aponeurosis from the zygomatic process of the
maxilla and from the anterior 2/3rds of the lower
border of the zygomatic arch.
Its fibers pass downwards and backwards, to be
inserted into the angle and lower half of the lateral
surface of the ramus of the mandible.
Intramuscular septa in this region are responsible
for the ridge on the bone.


The middle layer: - it arises from the deep
surface of the anterior 2/3rd and the
posterior 1/3rd of the lower border
zygomatic arch.
 It is inserted in the middle of the ramus of
the mandible.
 The deep layer: - it arises from the deep
surface of the zygomatic arch and is
inserted into the upper part of the ramus of
the mandible and the coronoid process.



The middle and the deep layers constitute
to form a cruciate muscle. [Where the
fasiculi run in 2-3 directions]
 As it is close to the skin it can be palpated
when it is thrown into contraction
vigorously as in clenching of the teeth.
 Acc. To mcconnaill 1975 the most
superficial fibers are continuous thru their
attachment at the lower border of the
mandible, into the attachment of the medial
pterygoid muscle.



Nerve supply: - is supplied by the branch
of the anterior trunk of the mandibular
nerve
 Actions: - it elevates the mandible to
occlude the teeth in mastication. Its
activity in the resting position of the
mandible is minimal.
 In clenching of the teeth.
 It has little effect in side to side
movements, protraction and the retraction
of the mandible.



The temporal fascia:



It covers the temporalis muscle. It is a strong,
fibrous investment covered, laterally, by the
auricularis anterior and superior, the galea
aponeurotica and part of the orbicularis
oculi.The superficial temporal vessels and the
auriculotemporal nerve ascend over it.
Above it is a single layer attached to the whole
of the sup. Temporal line and below it is two
layers one attached to the lateral and the other
to the medial margin of the upper zygomatic
arch.

A small quantity of fat, the zygomatic
branch of the superficial temporal
artery, the zygomatico temporal
branch of the maxillary nerve lie
between these layers.
 The deep surface of the fascia affords
attachment to the superficial fibers of
the temporalis.



The temporalis: 

Origin:-It is a fan- shaped muscle. It arises from
the whole of the temporal fossa [except the part
formed by the zygomatic arch] and the deep
surface of the temporal fascia.




Insertion:-Its fibers converge and descend into a
tendon which passes thru the gap between the
zygomatic arch and the side of the skull, to be
attached to the medial surface, apex, anterior
and posterior borders of the coronoid process,
and the anterior border of the ramus of the
mandible nearly as far as the last molar tooth.



Nerve supply: - supplied by the deep temporal
branch of the ant. Trunk of the mandibular
nerve.
Actions: - it elevates the mandible i.e. closes the
mouth and approximates the teeth.
It is also contributor to the side to side grinding
movements.







About its action on the elevation of the
mandible there are lots of studies that
states the temporalis is active in the
forcible elevation but not involved in
the slow elevation without occlusion.
[Vitti and basmajian 1977]



It’s not easy to palpate but the
contraction of the temporalis muscle
can be felt.

The lateral pterygoid: 

It is a short and thick muscle with two
parts of the head:-


1.

2.


Upper from the infra temporal surface
and from the infra temporal crest of the
greater wing of sphenoid bone,
Lower head from the lateral surface of
the lateral pterygoid plate.
Insertion:-its fibers pass backwards and
laterally to be inserted in the depression
on the front of the neck of the mandible,
and into the articular capsule and disk
of the TMJ.

In the 3rd month of the I.U life the lateral
pterygoid muscle is inserted in the
mesenchyme condensed around the dev.
Condyle of the mandible but a part of its
tendon sweeps backwards above the
condyle and gains into the portion of the
meckels cartilage which later forms the
head of the malleus.
 Then gets inserted into the articular disk of
the TMJ and the attachment with the
malleus does not persist.



Nerve supply: - it is supplied by the br.
from the anterior trunk of the mandibular
nerve.
 Actions: - it assists in opening the mouth
by pulling forward the condylar process of
the mandible and the articular disk while
the head of the condyle rotates on the
articular disk. [Posselt 1952]



In the closure the backward gliding of the
articular disk and the condyle of the
mandible is controlled by the slow
elongation of the lateral pterygoid, while
the masseter and the temporalis restore
the jaw to the occlusal position
 Along with the medial pterygoid of the
same side the lateral pterygoid advances
the condyle of that side so that the jaw
rotates about the vertical axis.







When the medial and the lateral pterygoid act
together than the mandible protrudes so that the
lower incisors project in front of the upper and
they also produce the side to side movement as
in chewing when the two muscles contract
alternatetly.
According to [McNamara 1972—EMG study]
both the heads of the lateral pterygoid have
diff. actions i.e. the upper head is being involved
in the chewing and the lower head is in
protrusion.

The medial pterygoid: 





It is quadrilateral in shape and consists of two
heads
Deep head:-attaches to the medial surface of
the lateral pterygoid plate and the grooved
surface of the pyramidal process of the
palatine bone
superficial head:- from the lateral surfaces of
the pyramidal processes of the palatine bone
and the tuberosity of the maxilla.



Insertion:-its fibers pass downwards and
backwards and are attached to a strong
tendinous lamina, to the posterior-inferior
part of the medial surface of the ramus and
the angle of the mandible, as high as the
mandibular foramen and nearly as forward
as the mylohyoid groove.




Nerve supply:-it is supplied by the
branch of the mandibular nerve.



Acc. to a study done by Schumacher
et.Al on the ramifications of the
muscular nerve of the masticatory
muscles a very similar mode of
branching in all these muscles is
observed.



Actions: - it assists in elevating the
mandible. Acting with lateral pterygoid it
protrudes the mandible.



When the 2 pterygoid of one side are in
action the corresponding side is swung
forward and to the opposite side with slight
degree of rotation.


Palpation of muscles:





The muscles of mastication are palpated for
tenderness or pain during the screening
examination.
It is accomplished mainly by the palmar surface
of the middle finger, with the index finger and the
forefinger testing the adjacent areas.
Soft but firm pressure is applied to the
designated muscles, the fingers compresses the
adjacent tissues in a small circular motion.

A

single firm thrust of 1 or 2 seconds is
usually better than many light thrusts.
 During that the patient is asked for the
symptoms.
 The temporalis: - it has three functional
areas and each is independently palpated.
 Anterior region: - palpated above the
zygomatic arch and anterior to the TMJ.
 Middle region: - directly above TMJ and
superior to the zygomatic arch.









Posterior region: - palpated above and behind
the ear. Otherwise, the patient is asked to clench
the teeth so that the temporalis contracts and
this is felt with hands placed on the above
specified locations.
The masseter muscles are palpated bilaterally at
their superior and inferior attachments.
The fingers are placed on the zygomatic arches
and then dropped down slightly just anterior to
the tmj for palpating superior part.
Secondly, the fingers are placed on the inferior
border of the rami to palpate inferior attachment.

 Medial

pterygoid: - palpated at the
intersection of medial surfaces of
mandibular angles. Finger tips are placed
on the inferior border of the mandible at
the angles and are rolled medially and
superiorly. Ask the patient to clench the
teeth if it is difficult to locate the muscle.


 The

lateral pterygoid palpation is difficult.
 It is accomplished by placing the forefinger
behind the maxillary tuberosity, right above
the occlusal plane, with the palmar surface
of the finger directed medially toward the
pterygoid hamulus.
 If there is tenderness in the superior head of
the lateral pterygoid muscle than it indicates
abnormal functional loading of the joint.


 The

finding are classified into four
categories.1. Zero: - no tenderness or pain is reported
by the patient,
2. One: - patient’s response is recorded.
Here the palpations cause discomfort.
3. Two:-there is definite discomfort or pain.
4. Three: - patient shows evasive action
or verbally expresses desire not to
palpate.

The accessory muscles of
facial expression:The superficial and the lateral
cervical muscles:
1.
2.
3.

These include viz:The platysma
The trapezius
The sterocleidomastoid muscles

The platysma: 



Origin:-it is a broad sheet arising form the
fascia covering the upper part of the pectoralis
major and the deltoid.
Insertion:-it is inserted at the lower border of the
body of the mandible and the posterior fibers
cross the mandible and the lower anterior part
of masseter to be attached to the skin and the
subcutaneous tissue of the lower part of the
face. And many fibers blending at the angle and
the lower part of the mouth.



Action: - when the entire platysma is in
action it diminishes the concavity
between the jaw and the side of the
neck.




Its anterior portion i.e. the thickest part
helps in depressing the mandible



It also serves to draw down the lower lip
and the angle of the mouth as in
expression of horror or surprise.



The trapezius and the sterocleidomastoid
maintain the posture of the head.


The accessory muscles.


These are the muscle’s which when
involved assist the main group of
muscles in the function of
stomatoganthic function:

1.

The suprahyoid muscles

2.

The infra hyoid muscles

The suprahyoid muscles: 1.
2.
3.
4.

The digastric .
The stylohyoid.
The mylohyoid .
The geniohyoid.


The digastric: It has two bellies that are united by an
intermediate tendon. Hence the name.
 The posterior belly: - it s longer than the
anterior and is attached to the mastoid
notch of the temporal bone and passes
downwards and forwards.



The anterior belly: - it is attached to the
digastric fossa on the base of the mandible
close to the median plane and passes
downward and backwards.




Actions: - it depresses the mandible and can
elevate the hyoid bone.



On EMG studies it has been confirmed that
they always act together and 2ndary to the
lateral pterygoid for the depression the
mandible and are required only during the
maximal depression. [Moyers 1950]



The posterior belly is active during the
swallowing and the chewing.

The tongue:

The tongue begins its
activities even before
the birth when it
function the
swallowing of
amniotic fluid. It is
one of the best dev.
Muscle / structure in
the human body at
birth.





It is relatively larger than the contiguous
structure and assumes posture
interposed between the gum pads rather
than completely contained within them.
In infancy extrinsic muscles are attachés
to various osseous structures and are
largely responsible for the various
important movement of the tongue in the
horizontal plane like suckle and swallow.

The extrinsic muscles:1.
2.
3.
4.

Hyoglossus---- attached to the hyoid bone.
Styloglossus----- to the styloid process.
Genioglossus --------to the mandible.
Palatoglossus ------- to the palatine
aponeurosis.




As stated by kwamura that
protraction, retraction, and lateral
deviation to these muscles along with
the genioglossus involved mostly in
the suckle swallow function.


The intrinsic muscles








Four in number named acc to their fibers
position. i.e.
Superior longitudinal
Inferior Longitudinal
Vertical
Transverse.
Nerve supply: hypoglossal nerve {12th} except
Palatoglossus which is supplied by the
accessory nerve thru the pharyngeal plexus.

 The

tongue being anchored only at one
end so free to move and this freedom
permits the tongue to deform the dental
arch when the functn is abnormal.


Muscular attachments of
the TMJ.:





- It is by far the most complex joint in the body.
It provides for the hinging movement in one
plane hence called ginglymoid joint. And it also
provides for the gliding motion so called as
arthroidal joint.
Therefore it is sometime referred to as the
ginglymoarthrordial joint. Also called as synovial
joint.
It is a compound type of the joint.

Articular disc:

The articular disc is composed of dense fibrous
connective tissue devoid of any blood vessels or
nerve fibers.



The condyle lies in the intermediate zone.
The articular disc is related posteriorly to an
area of loose connective tissue that is highly
vascularized and innervated.
This is known as the retrodiscal tissue.






Synovial membrane: 

The capsule of the TMJ is lined on the inner side by a
synovial membrane. It consists of a cellular intima and
subintima. This membrane is formed of the synovial
lining.



This membrane produces the synovial fluid.



The synovial fluid acts as a medium for providing
metabolic requirements to these tissues as the articular
disk is non-vascular.



It also acts as a lubricant between the articular surfaces
during function.

Ligaments of the joint:








Collateral [discal] ligament: - they attach to the
medial and the lateral borders of the articular
disc to the poles of the condyle.
Function: - they restrict the movement of the
disc away from the condyle.
They permit the disc to be rotated anteriorly and
posteriorly on the articular surface of the
condyle.
They are responsible for the hinging
movements.

Capsular ligament: 





The entire TMJ is encompassed by the capsular
ligament.
They act to resist any medial, lateral, or inferior forces
that tend to separate or dislocate the articular surfaces.
It encompasses the joint thus retains the synovial fluid.


Tmj ligament:-[lateral ligament]
Functions: - it resists the excessive drooping of
the condyle and acts as a limit to the extent of
the mouth opening.
 It also influences the normal
opening movement of
the mandible.



Accessory ligaments:1.
2.

Sphenomandibular ligament.
Stylomandibular ligament.


Concept of orthopedic
stability.
 Orthodontic

correction has always been
the correct contact pattern and not the
orthopedic stabilization.
 Its time the clinician better understand the
need of orthopedic stability which to
appreciate the sound principles if the
occlusion and its role in function or
dysfunction of the masticatory system.



The TMJ consists of the articular disc which is
non vascular and does not elicit pain. But this
does not find the positional stability of the joint.



The positional stability is determined by the
muscles that pull across the joint and prevent
the dislocation of the articular surfaces.



The direction of forces of this muscle determine
the correct position.



The major muscles that stabilize the tmj are the
elevator muscle. The direction of the force
placed on the condyle by the masseter and the
medial pterygoid is superioanterior.

 The

temporal muscles also stabilize the
Tmj.They have some horizontal oriented
fibers.



The lateral pterygoid also plays some part.

 In

postural position, the muscle without any
influence from the occlusal condition place
the condyles in the superioanterior
direction. In the articular fossae and this
most stable position.



Thus it is defined as, the position in which the condyles
are in their most superioanterior position in the articular
fossae, resting against the posterior slopes of the
articular eminences with the articular disc properly
interposed.



This position is also the most musculoskeletally stable
position.



The teeth at this position should be in maximum
intercuspation to contribute in the orthopedic stability.


Physical properties of
muscles:
I)

They help in kinetic activity of the
muscles.
elasticity:-elasticity of a body is
related to:1. length
2.cross section
3. force exerted
4. a constant coefficient
5. deformation.




1.
2.
3.
4.


A relaxed muscle can withstand only a
certain amount of elongation. (about
6/10th of its natural length.)
This further depends on the:Type of the stress
Individual resistance
Age
Possible pathology
The process of the material returning to
its original shape after being stretched
illustrates elasticity.

Contractibility:





The ability of the muscle to shorten in length
under innervational impulse.
This occurs by:- muscle is stimulated by an
electric action potential causing a contraction.
Energy for the muscle is provided by the
breakdown of the high energy bonds in
atp( adenosine triphosphate)
Fatigue in muscle is produced when the lactic
acid an energy breakdown product collects in
tissue lowering the ph to a level at which the
muscle can no longer function efficiently.

 According

to sherrington—
Individual muscle fibers have no variable
contraction status but they are relaxed or
they are in maximum contraction only on
the basis of the stimulus.
This is termed as the “all or none” law.
 The strength of the muscle contraction
depends on the number of the muscle
fibers engaged in the activity. Even during
rest there are peripheral fibers under
stimulus to maintain the posture.



1.
2.
3.
4.
5.


Shortening of the muscle during the
contraction depends on:Striated or the smooth muscle
No. of the muscle
Cross section
Frequency of discharge
Muscle fiber length
E.g. temporalis muscle due to its
relatively longer fibers has a greater
contraction length than the masseter
muscle.

 The

greatest strength of the muscle
contraction is when the muscle
approximates its resting length and it
diminishes as muscle shortens in length
beyond the resting length.
 E.G. Mandible closing from physiologic
position to occlusion there is reduction in
the strength of the contraction if the
closure continues beyond occlusal
position there is rapid diminution of the
contractile muscles.

Types of contraction:1.

2.

Isometric contraction:-it occurs when a
muscle is resisting an external force
without actual shortening
Isotonic contraction:-it occurs during
flexing of biceps i.e. when there is actual
shortening of the muscles.


Tension on the muscles:
1.
2.


Tension: - two type viz:Active
Passive
When a muscle is stretched the
tension in the muscle increases and
this increase in tension may be the
result of reflex control contraction of
the muscle.



Active: - the tension resulting from the
contraction of the muscle tissue is active tension.



In this the result of the reflex activity can also be
increased by willed contraction of muscles as in
volitional clenching of the teeth.



Passive: - tension which results from the physical
properties alone of the tissues is called passive
tension.



In many muscles the elongation will increase
both active as well as the passive tension.



The sum of both the tension is called as the total
tension.

Different types of the muscles
are:

–
–


–
–


–
–
–

1.
2.
3.

According to the presence of the cross striation:Striated
Non-striated [plain or smooth muscles]

Acc. To the nature of the control

Voluntary [controlled by the volition]
Involuntary [ not controlled by volition]( wish)

Acc. To the distribution :Skeletal
Cardiac
Visceral

These classifications can be summarized in the
following way:
Skeletal- striated voluntary
Cardiac-striated involuntary
Visceral - non-striated [plain or smooth] involuntary.

Morphology of the skeletal
muscles:






Morphology: - the skeletal muscle is primarily made up
of myofibrils.
These are the characteristic feature and they consist of
the alternate light and dark bands [transverse striations]
and thick longitudinal strands.
On e.m it is revealed that longitudinal striation are due to
the presence of the myofibrils of the different thickness
whereas the transverse striations are due to the
presence of the dark and light segments of longitudinally
arranged segments.
The myofibrils are separated by sarcoplasmic areas
which are called as field of cohnheim.

Type of muscles fibers:
1.
2.



Slow muscles fibers
Fast muscles fibers

Buller 1969

Acc. To dubowitz 1969 and gaytheir
(1974)
–
–
–

type I
type II
type III[ rare in humans]








Slow muscles fibers:-[Tonic muscles]
This is a slow twitch lasting in mammals
about 75 msec. these are the muscle which
are redder in colour because of some
pigment protein myoglobin which has
properties similar to that of hemoglobin.
These are also called as the type I fibers.
E.g. Temporalis, the masseter, the anterior
medial pterygoid and the lateral pterygoid
are 75 % composed of type I fibers.
[Eriksson]











Fast muscles fibers: - it is a phasic type fiber
producing a twitch that last for about 25msec.
They are paler in colour
They are also considered as the type II muscle
fibers
Acc. To burke ET .al 1973type can be subdivided
into fibers which fatigue easily [type IIB] and the
other one which are resistant to fatigue [type II A].
Type IIA is found in 30 % only in digastric muscle.
Type IIB is found in 45 % in the superior
temporalis, posterior medial pterygoid, and anterior
digastric muscle. [Acc to Eriksson]

EMG :

It is the study of the action potential in
the human skeletal muscle. This
machine was designed to study the
bioelectric phenomenon of the active
muscle. Electric activity in the living
tissue is related to the existence of the
polarized membranes at the cellular
surfaces.



Basis:-as a part of the electrical currents
generated is transmitted to the outer surface of
the body. The changes in action potential can be
studied by either putting electrodes at the
surface of active muscle area or inserting them
directly into the muscle concerned. Electrode
can be selected according to the size of the
muscle i.e. A large portion has to be studied or
few motor units of the muscle are studied.



Surface electrodes are used for the larger group
of the muscles and needle electrodes fro the
smaller ones.







The resting electric charges are positive on the external
surface and negative on the internal surface. When
these are activated the charges are reversed i.e. There
is reversal of polarization at the tissue surface of which
produce the electric current.
These signals are then received. Amplified and recorded
by the EMG. The measurement can be done by
measuring either the height of the action potential or the
frequency of the individual action potential. Moyers was
the first one to study the orofacial muscles using the
EMG.
Or
The potential can be recorded by cathode ray
oscillograph.

 Significance:

In orthodontics this can be
used in the pre, mid and post to analyze
the appraisal of the muscle activity.
 The study has a great clinical value in the
diagnosis of different types of the
neuromuscular functional impairment in
which either the rate or the rhythm of nerve
impulse is influenced.


Reflexes of the muscles:
1.
2.

They can be in numerated as :Myotactic reflex( stretch).
Nociceptive (flexor) reflex.


Myotactic(stretch) reflex.
 It

is the only monosynaptic jaw reflex.
 When the afferent fibers stimulate the
efferent fibers directly in the CNS than it
is called as monosynaptic.
 When a skeletal muscle is quickly
stretched , this protective reflex is elicited
and it brings about the contraction of the
muscle.







Observed by the masseter when a sudden
downward force and is applied to the chin.
This force can be applied with a small rubber
hammer.
As the muscle spindles within the masseter
suddenly stretch afferent nerve activity is
generated from the spindles to reach the brain
stem at the trigeminal motor nucleus ,,here it
acts on the primary afferent cell bodies causing
synapse with the Alfa efferent motor neurons at
the extrafusal fibers of the masseter to cause
the muscle to contract









Clinically can be observed , by relaxing the jaw
muscles allowing the teeth to separate slightly.
A sudden downward tap on the chin will cause
the jaw to be reflexly elevated. The masseter
contracts resulting in the tooth contact.
Significance:- it occurs without the specific
response from the brain and is important in
determining resting position of the jaw.
It is principle determinant of the muscle tonus.


Nociceptive (flexor) reflex:



It is a polysynaptic reflex to noxious
stimuli and is thus considered
protective.
The afferent neuron stimulates one or
more interneuron's in the CNS which
in turn stimulate the efferent fibers.








In the masticatory system this reflex
becomes active when a hard object is
suddenly encountered during mastication.
As the tooth is forced down on the hard
object a noxious stimulus is received by the
tooth & the surrounding pdl structures.
The associated sensory receptors trigger
afferent nerve fibers
Interneuron's in the trigeminal
motor nucleus.






It is more complicated than the myotactic reflex
as not only the elevator muscles has to be
inhibited to prevent further jaw closure on the
hard object, but the jaw opening muscles must
be activated to bring the teeth away from the
potent damage.
The excitatory fibers interneuron's leads to
efferent fibers of the jaw opening muscles are
stimulated which causes muscle contraction






The efferent fibers stimulate inhibitory
interneuron's which have their effect on the jaw
elevating muscles and cause them to relax.
This produces the antagonistic inhibition and
the jaw drops quickly and the teeth are pulled
away from the object causing noxious stimuli.


Other reflexes are:




Simple orofacial reflexes:Facial reflexes: a perioral reflex, which can be
elicited by brief mechanical or electrical
stimulation of the lips. Has been said to play
role in voluntary lip motor control in speech .

Jaw reflexes:- simple jaw reflexes can
be divided into vertical[ jaw closing and
opening] and horizontal [anteroposterior and
lateral]







Tongue reflexes: - reflex control of the
tongue posture is essential for the
maintenance of the pharyngeal airway
and plays an important role in the
position of the teeth.
Complex orofacial reflex:Mastication:- Significant for the
orthodontic treatment is the magnitude
and the direction of the occlusal forces in
mastication and the extent to which
these forces contribute to the tooth
movement and the mobility.



Bruxism: This is a parafuctional activity
along with the tooth clenching. It results
from physiologic stress with or without
occlusal interference.



Swallowing:-The most significant feature f
swallowing is their role in occlusal and
tongue forces in establishing tooth
position. It is a protective reflex and is
initiated by mechanically stimulation by a
bolus in the pharynx.

Methods of the study:1.
2.
3.



Anatomic
Functional
Behavioral
Anatomic: - the types of the muscles.


Functional: 

1.
2.
3.

This assessment can be done under
the following heading i.e.
Movement
Force and pressure
Emg


Movement:





The study of the movement in the muscles is a
very old concept and is called as kinesiology.
The technology of the mapping can be adapted
to study of the face in repose.
Observing the movement of the shadow grid
projected onto the face during activity of the
facial musculature is an old technique which is
now updated using moiré fringe and computer
technique.






Movement of the facial structure can be explored
in the three dimensions by holography.
One of the oldest of the technique to study the
movement of the mandible is to record a moving
film on the movement of the ball from the lower
incisors. This has also been updated so that now a
small magnet is attached to the lower incisors
which are tracked by three magnetometers and
the movement is displayed in three planes of the
space with the oscilloscope or x-y recorder.
Movement of the condyle and the portal structures
can be visualized o the cineradiography,
landmarks are digitized and alteration in the
position and shape is quantified. This tool is very
much useful in understanding the movements
associated with the swallowing.

Force and pressure:





Pressure of the orofacial structure like the
tongue, lips and cheeks are measured by
investigators like profitt using strain gauges.
Masticatory, swallowing, and maximal biting
forces are recorded on the teeth by Graf et.al
Pressure transducers are an important tool in
studying the pressure gradients in the upper
alimentary tract during swallowing.

Behavioral: 







This is sometimes preferred ones as it is a non
invasive technique and examines the total
activity in the natural state.
Windle has explained it looking at complex
patterns of the behavior upon the analogy to a
tree
According to the concepts of the Windle.
Discrete reflexes become aggregated into
increasingly complicated patterns of behavior.



The branches and twigs are consolidated into
the trunks: - an alternative concept is that dev.
Of the behavior takes place in the human fetus,
and the gross behavior such as the flexure of
the head and the jaw opening precedes more
discrete behavior such as eyelid and the
tongue reflexes.



To the trunk of the tree are added the branches
and the twigs:Mastication can be visualized as the
consolidation of simple elements such as jaw
opening, jaw closing etc.




Muscle as the etiology:


1.

2.

Muscle dysfunction:The facial muscles can affect the growth of the
jaws in two ways:The formation of the bone at the point of
muscle attachment depends on the activity of
the muscles
The musculature is important part of the total
soft tissue matrix whose growth normally
carries the jaws downward and forward.







When there is birth injury that can result in the
loss of that part of the musculature which will
likely result damage to the motor nerve due to
which there will be underdeveloped. jaw on that
side.
Excessive muscle contraction can restrict the
growth. This effect is same as that of the
scarring after the injury.
This effect can be most clearly seen in torticollis
i.e. twisting of the head caused by excessive
tonic contraction of the neck muscles on one
side [primarily the sterocleidomastoid]-this
results in facial asymmetry because of the
growth direction on the affected side.

 If

the reverse happens i.e. there is
decrease in tonic muscles activity that
occurs in muscular dystrophy, this allows
the mandible to drop downward away
from the rest of the facial skeleton. This
results in increase of the anterior facial
height, distortion of facial proportions and
mandibular form, excessive eruption of
the posterior teeth, narrowing of the
maxillary arch and anterior open bite.


The equilibrium theory:



As it is applied in the field of engineering it
states that an object subjected to unequal
forces will be accelerated and thereby move to
different position in the space. If the force is
applied onto an object but if it remains in the
same space than the forces are said to be in
equilibrium or balanced.
The dentition is obviously in equilibrium since
the teeth are subjected to a variety of forces but
do not move to a new location under usual
conditions. Even when the teeth are moving the
movements are so slow that a static equilibrium
can be presumed to exist at any instant in time.

Equilibrium effects on the dentition: 



One might think that force multiplied by duration would
explain the effects, but this is not the case .The
duration of a force, because of the biologic response is
more important than its magnitude.
This point is made clear by examining the response to
the forces during the chewing. When heavy forces are
applied during the mastication to the teeth, the fluid
filled pdl acts as a shock absorber, this stabilizes the
tooth for an instance, the force than is transmitted to
the alveolar bone which bends and the tooth moves for
a short distance along with the bone.





Second contributor to the equilibrium that
governs the tooth position is pressure from the
lips, cheeks and tongue. These pressures are
much lighter from the masticatory forces but are
greater in duration. Studies have proved that
even the light force can produce tooth movement
if the duration is long these duration threshold is
6 hours. Since the pressure from the lips, cheeks
and the tongue is maintained most of the time
there is indeed tooth movement in conditions
when there is loss of equilibrium.
Example, in scarring or contracture of the soft
tissue of the lips the incisors in the vicinity will
move lingually as the lip tightens against them.







If the restraining pressure of the lips and the cheeks is
removed than due to the tongue pressure the teeth tends
to jet out. Even if there is alteration of the tongue
pressure and the lips and the cheeks are intact than too
the teeth tends to move outward as there is loss of
equilibrium.
In cases with the orthodontic appliances for e.g. If arch
expansion plate is given and after that the lips and
cheeks pressure tends to increase but there will be
balance of forces until the plate is there once that is
removed there is unbalance and the teeth would collapse
lingually until a new position of balance is achieved.
With a habit for e.g. Thumb sucking. If habit like these
creates pressure for more than 6hrs than teeth will move
but if more force is applied for less duration than there
will be no effect.

Effects on the jaw size and
shape:




The jaws, particularly the mandible, can be
thought as consisting of the core of bone to
which the functional processes are attached.
The functional processes of the bone are
altered if the function is lost or changed.
E.g. The alveolar process of the bone exist only
to support the teeth that means that if the tooth
is absent then the alveolar bone is absent and if
it is extracted than the alveolar bone resorbs
until it finally atrophies.







The position of the tooth not the functional load
determines the position of the alveolar ridge.
The same stands true for the muscular
processes: the location of the muscle
attachments is more important in determining
the shape of the bone than the mechanical
loading or degree of activity.
Growth of the muscle however determines the
position of the attachments, and so muscle
growth can produce a change in shape of the
jaw, particularly at the coronoid process and the
angle of the mandible.

 Since

the condylar process is considered
as the functional process serving to
articulate the mandible with the rest of the
facial skeleton then there is possibility that
altering the position of the position of the
mandible might alter the growth of the
mandible.
 The effect of the force duration is not clear
for the growth of the jaw s as that for the
teeth thus the same principle applies that
the magnitude of the force is less important
than its duration.

Muscle adaptation in malocclusion


In case of improper or abnormal
muscle function i.e. compensatory
muscle activities such as hyperactive
mentalis muscle activity, hypoactive
upper lip, increased buccinator
pressures and tongue thrust that occur
as a result of change in spatial
relationships of the jaws and the teeth.







When there is hereditary basal malrelationships
in class II div 1 malocclusion there require the
compensatory muscular adaptation.
thus to swallow the lower lip cushions the
maxillary incisors, the tongue thrusts forward to
close off to crate the anterior lip seal required for
the deglutition.
Even when there are normal jaw relationships
and no compensatory activity is required for the
mastication and deglutition {class I} individuals
elicit a synchronous contraction pattern of the
masticatory muscles.









According to moyers, motor impulses initiate
occlusal movements but are modified by
disorganized proprioceptive responses from the
TMJ.
Adaptive activity may induce aberrant patterns of
occlusal activity as a result enhancing the original
malocclusion.
These adaptive responses may alter the degree of
the total contraction under peripheral and CNS
stimuli. Usually this is a hypertonic response.
Thus even the perverted function of the muscle in
case of class II div 1 can lead to increase in
severity of overjet and overbite.

Soft tissue environment of patients with
malocclusion:

Patterns of muscular activity in patients with
class II div 1 malocclusion:-



These patients have a short hypotonic upper lip. In
addition to that the lower lip cushions against the palatal
surface of the upper incisors. Causing lip trap.



This abnormal contraction of the hyperactive mentalis
muscle increases the proclination of the upper incisors.



In addition there is lack of anterior lip seal due to short
upper lip.

Here is abnormal buccinator activity
leading to constricted, narrow upper arch
along with low tongue posture.
 Thus muscle aberration is produced by
hyperactive buccinator and the hyperactive
mentalis along with altered tongue posture.



Patterns of muscular activity in
patients with class II div 2
malocclusion: 

They have low occlusal plane angle.
These patients have increased
muscular activity of the temporalis and
masseter muscle.


Patterns of muscular activity in
patients with mandibular prognathism:

Here the anterior and the posterior
temporal muscle are found to be more
active than that of masseter muscle in
the interocclusalposition.


Patterns of muscular activity in patients with
anterior open bite: -



Here also the occlusal plane is the
related factor.
Here the plane is high and so the
muscular activity of the muscles is low.


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