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Tmj anatomy
CONTENTS
• Introduction
• Types of joint
•
•
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•
•
•
•
•
•
•
•
•

Development of TMJ
Mandibular fossa
Condyle
Articular disc
Histology of articular surfaces
Innervation of TMJ
Vascularization of TMJ
Ligaments
Muscles of mastication
Biomechanics
Conclusion
References
INTRODUCTION
• The Temporomandibular joint is that
which connects the mandible to the
skull and regulates mandibular
movement.
• It is a bicondylar joint in which the
condyles, located at the two ends of
the mandible, function at the same
time.
TYPES OF JOINT
A Joint is an articulation
between two bones.
1. Fibrous Joint: immovable
joint
–Suture - skull
–Gomphosis - teeth
–Syndesmosis – interosseous

2.Cartilaginous Joint:
limited movement
–Primary or synchondroses
• Hyaline cartilage at ends of long
bones
–Secondary or symphysis
• Bone-cartilage-fibrous tissuecartilage-bone; symphysis menti
3.Synovial Joint: permits free movement between two
bones; surrounded by capsule enclosing joint cavity
filled with synovial fluid. According to shape of
articulating surface:
– Ginglymoid
– Pivot
– Condyloid
– Ball-and-socket
Craniomandibular articulation – TMJ
Complex joint in the body
Hinging movement – ginglymoid joint
Gliding movements - arthrodial joint

ginglymoarthrodial joint
hence TMJ is a complex diarthrodial sliding-ginglymoid
synovial joint, which attaches the mandible to petrous
part of temporal bone of the cranium.
Seperating these two
bones from direct
articulation is the
Articular disc.
TMJ – Classified as
Compound joint
articular disc – serve as
non ossified bone that
permits complex
movements of the
joint.
Artricular
disc
interposed between the
condyle of the mandible
and the glenoid fossa of
the temporal bone.
The articular surface of
the temporal bone has a
posterior concave part –
mandibular fossa
Anterior convex part –
articular tubercle or
eminence
DEVELOPMENT OF TMJ
• The TMJ develops from
mesenchyme
lying
between the developing
mandibular condyle below
and the bone above,
which
develop
intramembranously.
• During the 12th week of IU
life ,2 clefts appear in the
mesenchyme –producing
the upper and lower joint
cavities.
• The remaining intervening mesenchyme becomes
the intra – articular disc.
• The joint capsule develops from a condensation of
mesenchyme surrounding the developing joint
• Mandibular fossa is flat at birth and there is no
articular eminence , this becomes prominent only
following the eruption of the decidous dentition.
MANDIBULAR FOSSA
Bounderies• Anterior aspect articular
eminence
• Posterior non articular
fossa Is a part of
temporal squama and is
formed by tympanic
plate which also forms
the anterior bony wall of
external auditory meatus
• As temporal squama and tympanic plate
converge medially on the spine of the sphenoid
bone – intersposed is the bony edge of the roof
of the tympanic cavity –tegmen tympani
• Squamotympannic fissure - fissure between the
temporal squama and tympannic bone
• It is divided medially into anterior part petrosquamous fissure and posterior part
petrotympannic fissure/glaserian fissure.
• Laterally petrotympannic fissure allows passage of
chorda tympani nerve.
• At the posterior border of the fossa – a tubercle or
cone shaped process present laterally between
tympanic bone and fossa.
• This prevents direct impingement of condyle on the
tympanic plate.
• the medial border of articular fossa also contains a
bony lip which extends into angular spine of
sphenoid bone .
• These two bone processes or lips limit condylar
displacement distally and laterally as well as
vertically.
A IKAI et al (ajodo 112;634:8)
• Studied the relationship between temporal
component of TMJ – mandibular fossa and articular
eminence) with facial bone structure.
• The angle between the line deepest point of the
fossa- the midpoint of the eminence and FH plane
(middle angle) was negatively correlated only with
ANB angle suggesting that a steeper middle angle of
eminence is related to retrusive maxilla or
protrussive mandible.
CONDYLE
Barrel shape –
measuring – 20mm –
mediolateral
10mm –
anteroposterior
• Perpendicular to
ascending ramus of
the mandible
• Oriented 10 – 30
degrees with frontal
plane.
Medial pole more
prominent than
lateral pole

Articular surface of
Posterior aspect >
anterior aspect
• In the frontal view – articular eminence often is
concave and fits roughly to superior surface of
condyle
• Bony surface of condyle and articular part of the
temporal bone – covered with dense fibrous
connective tissues with irregular cartilage like cells
• The number of cells increases with age and stress on
the joint.
ARTICULAR DISC
• Biconcave oval structure –
intersposed between the
condyle and the temporal
bone.
• Consists
of
dense
collagenous tissue that is
avascular , hyaline and
devoid of nerve tissues in
the central area but has
vessels and nerves in the
peripheral area.
• Divided into 3 regions
in the Saggital plane
• Intermediate zone
• Posterior
• Anterior

• Articular surface
situated in the
intermediate zone
Anterior view
– disc
thicker medially than
laterally

Shape
of
disc
–
determined
by
morphology of condyle
and mandibular fossa.
• During movement the disc is
flexible to some extent and
can adapt to the functional
demands of the articular
surfaces.
• The disc maintains its
morphology
unless
destructive
forces
or
structural changes occur in
the joint.
• If these changes occur , the
morphology of the disc can be
irreversibly altered producing
biomechanical changes during
function.
• ATTACHMENTS OF DISC • Retrodiscal tissue highly vascularized

posterior attachment

• Superior retrodiscal lamina – elastic fibres

• Inferior retrodiscal lamina - collagenous fibres.
• Remaining – large venous plexus which fills with
blood as condyle moves forward.
Tmj anatomy
Anteriorly–superior and inferior attachments of the
disc– capsular ligament
• Superior attachment –articular surface of temporal
bone
• Inferior attachment – articular surface of condyle
• Composed of collagen fibres
• Between the capsular ligament attachment – superior
lateral pterygoid muscles.
Capsular ligament
attachment
medially
and
laterally also –
dividing joint into 2
cavities.
Superior cavity –
mandibular fossa
and
superior
surface of disc.
Inferior cavity –
mandibular condyle
and inferior surface
of disc
• The internal surface of the cavities are surrounded by
specialized endothelial cells that form a synovial
lining.
• This lining along with a specialized synovial fringe
located at the anterior border of the retrodiscal
tissue produces synovial fluid which fills both the
joint cavities
• TMJ – synovial joint.
Synovial fluid serves 2 purposes
1. Medium for providing metabolic requirements to
the non vascular articular surface of the joint.
2. Lubricant between articular surfaces during
function.

2 mechanisms by which synovial fluid lubricates are
1. Boundary lubrication
2. Weeping lubrication
Boundary lubrication
• Occurs when joint is moved and synovial fluid is
forced from one area of cavity into another.
• The synovial fluid located in the border or recess
areas is forced on the articular surface thus providing
lubrication.
• Weeping lubrication
• Refers to the ability of articular surfaces to absorb a
small amount of synovial fluid
• During function of a joint , forces are created
between the articular surfaces
• These forces drive a small amount of synovial fluid in
and out of articular tissues.
• This is the mechanism by which metabolic exchange
occurs.
Under compressive forces therefore, a small
amount of synovial fluid is released.
This synovial fluid acts as a lubricant between
articular tissues to prevent sticking,
Weeping lubrication helps eliminate friction in
compressed but not a moving joint.
Only a small amount of friction is eliminated by
weeping lubrication.
Therefore prolonged compressive forces to the
articular surfaces will exhaust this supply.
HISTOLOGYOF
ARTICULAR
SURFACES
The
articular
surfaces
of
the
condyle and the
mandibular fossa are
composed of four
distinct layers or
zones.
• Articular zone
• Most superficial layer
• Found adjacent to the joint cavity and forms the
outermost functional surface.
• Made up of dense fibrous connective tissue .
• The collagen fibres are arranged in bundles and
oriented nearly parallel to the articular surface.
• The fibres are tightly packed and are able to
withstand the forces of movement.
• It is less susceptible to the effects of aging and
therefore is less likely to breakdown over time.
• It also has much better ability to repair than does
hyaline cartilage.
• The importance of these two factors is significant in
tmj function and dysfunction.
• Proliferative zone
• Undifferentiated mesenchymal tissue –
• This is responsible for the proliferation of articular
cartilage in response to the functional demands
placed on articular surfaces during loading.
• Fibrocartilagenous zone
• Collagen fibrils are arranged in bundles in a crossing
pattern.
• The fibrocartilage appears in a random orientation
,providing three dimensional network that offers
resistance against compressive and lateral forces.
• Calcified zone
• Made up of chondrocytes and chondroblasts
distributed throughout the articular cartilage.
• In this zone , the chondrocytes become hypertrophic,
die and have their cytoplasm evacuated , forming
bone cells from within the medullary cavity.
• The articular cartilage is composed of chondrocytes
and intercellular matrix.
• The chondrocytes produce collagen , proteoglycans ,
glycoproteins , and enzymes that form the matrix.
• Proteoglycans – complex molecule composed of a
protein core and glycosaminoglycan chains.
• The proteoglycans are connected to a hyaluronic acid
chain , forming proteoglycan aggregates that make
up a great protein of the matrix.
• These aggregates are very hydrophilic and are
intertwined throughout the collagen network .
• Since these aggregates tend to bind water ,the matrix
expands and the tension in the collagen fibrils
counteracts the sweeping pressure of the
proteoglycan aggregates.
• In this way the interstitial fluid contributes to
support joint loading .
• The external pressure resulting from joint loading is
in equilibrium with the internal pressure of the
articular cartilage.
• As joint loading increases , tissue fluid flows outward
until a new equilibrium is achieved.
• As loading is decreased , fluid is reabsorbed and the
tissue regains its original volume.
• Joint cartilage is nourished predominantly by
diffusion of synovial fluid, which depends on this
pumping action during normal activity.
• The pumping action is the basis for the weeping
lubrication, and this action is thought to be very
important in maintaining healthy articular cartilage.
Vincent .P. Willard Archieves of oral biology (2012) 599606
• Vincent concluded that although the TMJ disc and its
attachments form a seamless complex within the
joint ,a closer look at the biochemical constituents
reveals that these 2 components are distinct .
• While the disc and attachments both contain the
same major constituents ,the relative amounts of
these components vary based on functional
requirements of the tissue
• Disc region have more higher sulfated GAG and
collagen content than the attachment regions.
• In contrast attachment regions –contains more DNA
content than disc region.
INNERVATION OF TMJ
• Most innervation is provided
by the auriculotemporal nerve
as it leaves the mandibular
nerve behind the joint and
ascends laterally and
superiorly to wrap around the
posterior region of the joint
• Additional innervations by –
deep temporal and massetric
nerve.
VASCULARIZATION OF TMJ
•
•
•
•
•

Predominant vessels are
Superficial temporal artery - from the posterior
Middle meningeal artery - from the anterior
Internal maxillary artery – from the inferior
Other important arteries are – the deep auricular
,anterior tympanic and ascending pharyngeal
arteries.
• The condyle – through marrow spaces by way of the
inferior alveolar artery .
Superficial temporal artery
Middle meningeal artery
Maxillary artery
LIGAMENTS
• Ligaments play an important role in protecting the
structures
• The ligaments of the joints are made up of
collagenous connective tissue, which do not stretch.
• They do not enter actively into joint function but
instead act as a passive restraining devices to limit
and restrict border movements.
• 3 funtcional ligaments support the TMJ :
1. Collateral ligaments
2. Capsular ligament
3. TM ligament
2 accessory ligaments
1. Sphenomandibular ligament
2. Stylomandibular ligament
• Collateral (discal) ligaments
• Attach the medial and lateral
borders of the articular disc
to the poles of the condyle
• Commonely called as discal
ligaments – medial and
laterlal
• Medial discal ligament –
attaches the medial edge of
the disc to the medial pole of
the condyle.
• Lateral discal ligament –
attaches the lateral edge of
the disc to the lateral pole of
the condyle,
• These ligaments are responsible for dividing the joint
mediolaterally into the superior and inferior joint
cavities.
• The discal ligaments are true ligaments ,composed of
collagenous connective tissue fibres , therefore they
do not stretch.
• They allow the disc to move passively with the
condyle as it glides anteriorly and posteriorly on the
articular surface of the condyle
• Thus these ligaments are responsible for the hinging
movement of the TMJ , which occurs between the
condyle and the articular disc.
• These ligaments have a vascular supply and are
innervated .
• Strain on these ligaments produces pain.
Capsular ligament
• The entire TMJ is
surrounded
and
encompassed by the
capsular ligament .
• The fibres of the
capsular ligament are
attached superiorly to
the temporal bone
along the borders of the
articular surface of the
mandibular fossa and
articular eminence
• Inferiorly the fibers of the capsular ligament attach to
the neck of the condyle.
• The capsular ligament -resist any medial, lateral or
inferior forces that tend to separate or dislocate the
articular surfaces.
• 1 significant function – to encompass the joint thus
retaining the synovial fluid.
• Capsular ligament is well innervated and provides
proprioceptive feedback regarding position and
movement of joint.
• Temporomandibular
ligament
The lateral aspect of the
capsular ligament is
reinforced by strong ,
tight fibres – lateral
ligament
or
TM
ligament.
TM ligament has 2 parts
• Outer oblique portion
• Inner horizontal portion
• Outer portion – extends
from outer surface of the
articular tubercle and
zygomatic process
posteroinferiorly to the
outer surface of the
condylar neck.
• Inner horizontal portion –
extends from the outer
surface of the articular
tubercle and zygomatic
process posteriorly and
horizontally to the lateral
pole of the condyle and
posterior part of articular
disc.
• Oblique portion – resists excessive drooping of the
condyle – limiting the extent of mouth opening.
• During the initial phase of opening ,the condyle can
rotate around a fixed point until the TM ligament
becomes tight as its point of insertion on the neck of
the condyle is rotated posteriorly.
• When the ligament is taut , the neck of the condyle
cannot rotate further .
• If mouth were to be opened wider- the condyle has
to move downward and forward across the articular
eminence.
• Clinically tested by – closing the mouth and applying
mild posterior force to the chin-jaw easily rotates
until teeth are 20 – 25mm apart after which a
resistance is felt when the jaw is opened wider.
• This resistance is brought about by the tightening of
TM ligament.
This unique feature of TM ligament which limits
rotational opening is found only in humans.
• The inner horizontal portion of TM ligament limits
posterior movement of condyle and disc.
• When force applied to the mandible it displaces the
condyle posteriorly , this portion of ligament
becomes tight and prevents the condyle from
moving further into the posterior region of the
mandibular fossa.
• Hence it protects the retrodiscal tissues from trauma
created by posterior displacement of the condyle.
• Also protects the lateral pterygoid muscle from
overextension or overlengthening.
• The effectiveness of TM ligament is demonstrated
during cases of extreme trauma to the mandible.
• In such cases the neck of the condyle is seen to
fracture before the retrodiscal tissues are severed.
• Sphenomandibular ligament
• Accesory ligament of the TMJ
• Arises from the spine of the
sphenoid bone and extends
downwards to a small bone
prominence on the medial
surface of the ramus of the
mandible called the lingula.
• It does not have any
significant limiting effects on
mandibular movement.
• Stylomandibular ligament
• It arises from the styloid
process and extends
downwards and forward to the
angle and posterior border of
the ramus of the mandible.
• It becomes taut when the
mandible is protruded but is
most relaxed when the
mandible is opened.
• The stylomandibular ligament
therefore limits the excessive
protrusive movements of the
mandible.
MUSCLES OF MASTICATION
The skeletal components of the body are held
together and moved by the skeletal muscles.
• Muscles
fibers ranging between 10 – 80mm
subunits
According to amount of myoglobin
Muscles
slow/type1 muscle fibers
fast/type ll fibers.
• Slow muscle fibers• Deeper in red color due to higher concentration of
myoglobin,
• Capable of slow but sustained contraction
• Well developed aerobic metabolism therefore
resistant to fatigue.
• Fast muscle fibers –
• Whiter due to lower concentrations of myoglobin
• Have fewer mitochondria and rely more on
anaerobic activity for function.
• Capable of quick contraction but fatigue more
quickly
• All skeletal muscles contain a mixture of fast and slow
fibers in varying proportions, which reflect the function
of that muscle.
• Muscles that respond quickly – predominantly white
fibers
• Muscles for slow continuous activity –
higher concentration of slow fibers
• 4 pairs of muscles – muscles of mastication
1. Masseter
2. Temporal
3. Medial pterygoid
4. Lateral pterygoid
Masseter muscle
• Orgin -Rectangular muscle that originates from the
zygomatic arc and extends downward to the lateral
aspect of the lower border of the ramus of the
mandible.
• Insertion - extends from
the region of the second
molar in the mandible at
the inferior border
posteriorly to include the
angle.
• 2 portions –
• superficial portion (fibers
run downward and
slightly backward)
• Deep portion (fibers run
predominantly in vertical
direction)
Function – elevation of mandible and teeth brought
into contact
• Superficial portion – aid in protruding the mandible
• When the mandible is protruded and biting force is
applied ,the fibers of deep portion stabilize the
condyle against the articular eminence.
Acta Odontologica Scandinavica, 2008; 66: 2330
Studies concluded that there is a significant
association between the posterior-to-anterior facial
height ratio and the masseter muscle in children,
indicating that subjects with stronger masseter
muscles have an increased posterior facial height
for a given anterior facial height.
Girls show greater associations than boys between
the masseter muscle and vertical craniofacial
morphology.
Stavros Kiliaridis et al ,European Journal of
Orthodontics 25 (2003) 259–263
Studied the relationship between thickness of
masseter muscle and width of maxillary dental arch
and results showed that -

• Masseter muscle thickness was greater in older
individuals and in males.
• In the female group, maxillary intermolar width
showed a direct, significant association with
masseter thickness both during contraction and
relaxation i.e. females with thicker masseter muscles
had a wider maxillary dental arch.
• The findings of this study indicate that the functional
capacity of the masticatory muscles may be
considered as one of the factors influencing the
width of the maxillary dental arch.
• Temporal muscle
• Orgin-Large fan shaped
muscle that originates
from the temporal fossa
and lateral surface of
the skull.
• Divided into 3 distinct
areas according to fiber
direction and ultimate
function -anterior,
middle and posterior
portion
• Anterior portion –
vertically directed
fibers
• Middle portion obliquely across
lateral aspect of
the skull
• Posterior portion –
horizontally
alligned fibers
Function - elevates
mandible and
teeth brought into
contact
• Contraction of anterior portion – mandible raised
vertically
• Contraction of middle portion –elevates and retrudes
• Contraction of posterior portion – elevation and
slight retrusion
• Because the angulation of its muscle fibers varies ,
the temporal muscle is capable of co ordinating
closing movements. It thus is a significant
positioning muscle of mandible.
• Clinical examination:
• "Ask the patient to clench their teeth while you
palpate both masseter muscles above the angles of
the jaw and then while you palpate both temporalis
muscles over the temples."
• Medial pterygoid
muscle
• Origin - from the
pterygoid fossa and
extends
downward,
backward and outward
to insert along the
medial surface of the
mandibular angle.
• Along
with
the
masseter muscle ,it
forms a muscular sling
that
supports
the
mandible
at
the
mandibular angle.
Tmj anatomy
Function – mandible elevated and teeth brought into
contact
- also active in protruding the mandible.
- unilateral contraction brings about a
mediotrusive movement of the mandible
Lateral pterygoid muscle
• Divided into 2 –since their functions are nearly
opposite - inferior lateral pterygoid muscle
superior lateral pterygoid muscle
Inferior lateral pterygoid
muscle
• Origin- at the outer surface
of the lateral pterygoid
plate
and
extends
backward, upward and
outward to its insertion
primarily on the neck of the
condyle.
• function – when the
inferior right and left lateral
pterygoid muscle contracts
simultaneously –condyles
are pulled down their
articular eminences and
mandible is protruded.
• Superior lateral
pterygoid muscle
• Smaller than inferior
muscle
• Originat
infra
temporal surface of the
greater sphenoid wing ,
extending
almost
horizontally , backward
and outward to insert
on
the
articular
capsule, the disc and
the neck of the
condyle.
• While the inferior lateral pterygoid muscle is active
during opening ,the superior lateral pterygoid muscle
remains inactive ,becoming active only in
conjugation with the elevator muscles.
• Function -Superior lateral pterygoid muscle is
especially active during power stroke (movements
that invovle closure of mandible against resistance,
such as chewing or clenching the teeth together)
• Approximately 80% of the fibers that make up both
lateral pterygoid muscles are slow muscle fibers
/type I which suggest that these muscles are
relatively resistant to fatigue and may serve to brace
the condyle for long periods of time without
difficulty.
• Clinical examination of pterygoid muscles
• by forcefully opening the jaw against resistance
• with unilateral lateral pterygoid weakness the jaw
deviates to the ipsilateral side as it opens.
• As a person yawns ,the head is
brought back by contraction of
the posterior cervical muscles ,
which raises the maxillary teeth .
• This simple example shows that
normal functioning of the
masticatory system uses many
more muscles than those of
mastication.
• Muscles of mastication is only a
part of this complex system
Other accesory muscles are –
Digastric muscle
• Though not a masticatory
muscle-important influence
on the function of mandible.

• Divided into 2 –
posterior belly of digastric
anterior belly of digastric
Orgin• Posterior belly –originates from mastoid notch ,
medial to mastoid process – fibers run forward ,
downward and inward to intermediate tendon
attached to hyoid bone.

• Anterior belly - originates at a fossa on the lingual
surface of mandible ,close to the midline – fibers
run downward and backward to insert at the same
intermediate tendon as does the posterior belly.
• Function –
• When the right and left digastric muscle contract and
the hyoid bone fixed by suprahyoid and infrahyoid
muscles ,the mandible is depressed and pulled
backward and teeth are brought out of contact.
• When the mandible is stabilized the digastric muscles
with the suprahyoid and infra hyoid muscles elevate
the hyoid bone ,which is a necessary function for
swallowing.
• The digastric are one of the many muscles that
depress the mandible and raise the hyoid bone.
• STERNOCLEIDO MASTOID MUSCLE

• Large superficial muscles of the
neck that also play a role during
mastication
• Orgin –
• the sternal head is tendinous
and arises from the superolateral
part of the front of the
manibrium sterni
• The clavicular head is
musculotendinous and arises
from the medial one – third of
the superior surface of the
clavicle.
• It passes deep to the sternal head and the 2 heads
blend below the middle of the neck.
Function • When one muscle contracts it turns the chin to
opposite side .
• When both muscles contract together they draw the
head forwards as in eating and in lifting the head
from pillow.
Muscles of Mastication

Temporalis muscle
elevation
Medial Pterygoid
Lateral Pterygoid
protrusion

Medial Pterygoid
Temporalis muscle
retrusion

depression
Mylohyoid
Inferior belly
of diagastric

lateral movements
Medial Pterygoid
Lateral Pterygoid
BIOMECHANICS OF TMJ
• The TMJ is an extremely complex joint system -2 TMJ
connected to the same bone.
• TMJ structure can be divided into 2 systems1. Joint system – surrounds the inferior synovial cavity
– condyle and the articular disc(condyle –disc
complex)
Since disc is tightly bound to condyle by lateral and
medial discal ligaments, the only physiologic
movement that can occur between these surfaces
is rotation of on the articular surface of condyle .
This joint system responsible for rotational movement
in TMJ.
2 Second system is made up of the condyle – disc
complex functioning against the surface of the
mandibular fossa.
• Since the disc is not tightly attached to the
mandibular fossa , free sliding movement is
possible between these surfaces in the superior
cavity.
• This movement occurs when the mandible is moved
forward – transalation.
• Transalation – occurs between superior surface of
articular disc and mandibular fossa.
• Thus articular disc – non ossified bone – hence TMJ
classified as compound joint.
• The articular surfaces of the joint have no structural
attachment or union-yet contact must be maintained
for joint stability.
• Joint stability-maintained by constant activity of
muscles that pull across the joint.
• Even in resting state ,these muscles are in mild state
of contraction –tonus.
• as muscle activity increases –condyle forced against
disc and disc against mandibular fossa - resulting in
increase in interarticular pressure .
• In the absence of interarticular pressure- articular
surfaces separate and joint dislocates.
• Width of articular disc space varies with
interarticular pressure.
• When pressure is low- closed rest position – disc
space widens.
• When pressure is high – clenching of teeth – disc
space narrows.
• As interarticular pressure increases – condyle seats
itself on the intermediate zone
• When pressure is decreased –disc space widens and
thicker portion of disc is rotated to fill the space.
• Since anterior and posterior bands are thicker than
intermediate zone – disc rotates anteriorly or
posteriorly to accomplish the task.
• Disc attached posteriorly – retrodiscal tissues which
are highly elastic- hence condyle can move out of
fossa without creating damage to superior retrodiscal
lamina.
• During mandibular opening –condyle is pulled
forward down the articular eminence ,the superior
retrodiscal lamina becomes increasingly stretched ,
creating increased forces to retract the disc.
• The interarticular pressure and the morphology of
the disk prevent the disc from being overetracted
posteriorly.
• Superior retrdiscal lamina –only structure capable of
retracting the disc posteriorly on the condyle.
• Anterior border of articular disc attached to -superior
lateral pterygoid
• Constantly maintained in a mild state of contraction
or tonus –exerts slight anterior and medial force on
the disc.
• In the resting closed joint position thus anterior and
medial force will normally exceed that of
nonstretched Superior retrodiscal lamina.
• Therfore in the resting closed joint position when the
interarticular pressure is low and disc space widened
–disc will occupy most anterior rotary position on the
condyle and the condyle in contact with intermediate
and posterior zones of the disc.
• This disc relationship is maintained during minor
passive rotational and transalatory mandibular
movements.
• As condyle moves more forward – Superior
retrodiscal lamina gets stretched –greater force than
the superior lateral pterygoid – allows disc to be
rotated posteriorly to extent permitted by width of
articular disc space.
At rest condyle rests on posterior band; beginning of translation, it lies over the intermediate zone;
when mouth is fully open, it lies over the anterior band.
Power stroke –
• When resistance is met during mandibular closure
(biting hard food) – interarticular pressure on biting
side is decreased –because force of closure applied
to food not to joint .
• With condyle forward and disc space increased –
tension of Superior Retrodiscal lamina will tend to
retract the disc from a functional position-resulting
in separation of articular surfaces leading to
dislocation.
• To avoid this –superior lateral pterygoid becomes
active during power stroke rotating disc forward on
condyle so thicker posterior border of disc maintains
articular contact-therfore joint stability maintained.
• As teeth pass through the food and approach
intercuspation –interarticular pressure is increased –
disc space decreased – disc rotated posteriorly so
thinner intermediate zone fills the space.
• When the force of closure is discontinued the resting
closed joint position is once again assumed.
• Joseph H. Kronman et al (ajodo 1994;105:257-64.)
• Investigated the site of lateral pterygoid muscle
insertion into the TMJ disk, and the relationship
between that attachment and the disk.
• Results indicated a statistically significant
relationship between functional muscle attachment
and disk displacement.
• the SLP can maintain disk displacement only when it
inserts directly into the disk.
• In cases of normal disk arrangement and condylar
attachment, the muscle may not play a clinically
significant role in disk displacement because disk
attachment at the medial and lateral poles of the
condyle allows the disk to move freely with the
condyle.
• This movement of the condyle and the disk may
overcome the pull of the SLP when normal disk
attachment is maintained.
CONCLUSION
• It is impossible to comprehend the fine points of
occlusion without an in depth awareness of the
anatomy ,physiology ,and biomechanics of the TMJ.
• The first requirement for successful occlusal
treatment is stable, comfortable TMJ.
• The jaw joints must be able to accept maximum
loading by the elevator muscles with no signs of
discomfort.
• It is only through an understanding of how the
normal, healthy TMJ functions that we can make
sense out of what is wrong when it isn't functioning
comfortably.
• This understanding of TMJ is foundational to
diagnosis and treatment.
Tmj anatomy
References
1. Gray’s Anatomy
2. Fundamentals of occlusion and TMJ disorders
-- Okeson
3. Grant’s Atlas of Human Anatomy
4. Occlusion – Ash RamfJord
5. Orthodontics Principles and Practice
-- T.M.Graber
6. Joseph H. Kronman et al (ajodo 1994;105:257-64.)

7. Stavros Kiliaridis et al ,European Journal of
Orthodontics 25 (2003) 259–263
8. Acta Odontologica Scandinavica, 2008; 66: 2330
9. Vincent .P.Willard Archieves of oral biology (2012)
599- 606
10. A IKAI et al (ajodo 112;634:8)
Tmj anatomy

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Tmj anatomy

  • 2. CONTENTS • Introduction • Types of joint • • • • • • • • • • • • Development of TMJ Mandibular fossa Condyle Articular disc Histology of articular surfaces Innervation of TMJ Vascularization of TMJ Ligaments Muscles of mastication Biomechanics Conclusion References
  • 3. INTRODUCTION • The Temporomandibular joint is that which connects the mandible to the skull and regulates mandibular movement. • It is a bicondylar joint in which the condyles, located at the two ends of the mandible, function at the same time.
  • 4. TYPES OF JOINT A Joint is an articulation between two bones. 1. Fibrous Joint: immovable joint –Suture - skull –Gomphosis - teeth –Syndesmosis – interosseous 2.Cartilaginous Joint: limited movement –Primary or synchondroses • Hyaline cartilage at ends of long bones –Secondary or symphysis • Bone-cartilage-fibrous tissuecartilage-bone; symphysis menti
  • 5. 3.Synovial Joint: permits free movement between two bones; surrounded by capsule enclosing joint cavity filled with synovial fluid. According to shape of articulating surface: – Ginglymoid – Pivot – Condyloid – Ball-and-socket
  • 6. Craniomandibular articulation – TMJ Complex joint in the body Hinging movement – ginglymoid joint Gliding movements - arthrodial joint ginglymoarthrodial joint hence TMJ is a complex diarthrodial sliding-ginglymoid synovial joint, which attaches the mandible to petrous part of temporal bone of the cranium.
  • 7. Seperating these two bones from direct articulation is the Articular disc. TMJ – Classified as Compound joint articular disc – serve as non ossified bone that permits complex movements of the joint.
  • 8. Artricular disc interposed between the condyle of the mandible and the glenoid fossa of the temporal bone. The articular surface of the temporal bone has a posterior concave part – mandibular fossa Anterior convex part – articular tubercle or eminence
  • 9. DEVELOPMENT OF TMJ • The TMJ develops from mesenchyme lying between the developing mandibular condyle below and the bone above, which develop intramembranously. • During the 12th week of IU life ,2 clefts appear in the mesenchyme –producing the upper and lower joint cavities.
  • 10. • The remaining intervening mesenchyme becomes the intra – articular disc. • The joint capsule develops from a condensation of mesenchyme surrounding the developing joint • Mandibular fossa is flat at birth and there is no articular eminence , this becomes prominent only following the eruption of the decidous dentition.
  • 11. MANDIBULAR FOSSA Bounderies• Anterior aspect articular eminence • Posterior non articular fossa Is a part of temporal squama and is formed by tympanic plate which also forms the anterior bony wall of external auditory meatus
  • 12. • As temporal squama and tympanic plate converge medially on the spine of the sphenoid bone – intersposed is the bony edge of the roof of the tympanic cavity –tegmen tympani
  • 13. • Squamotympannic fissure - fissure between the temporal squama and tympannic bone • It is divided medially into anterior part petrosquamous fissure and posterior part petrotympannic fissure/glaserian fissure. • Laterally petrotympannic fissure allows passage of chorda tympani nerve. • At the posterior border of the fossa – a tubercle or cone shaped process present laterally between tympanic bone and fossa. • This prevents direct impingement of condyle on the tympanic plate.
  • 14. • the medial border of articular fossa also contains a bony lip which extends into angular spine of sphenoid bone . • These two bone processes or lips limit condylar displacement distally and laterally as well as vertically.
  • 15. A IKAI et al (ajodo 112;634:8) • Studied the relationship between temporal component of TMJ – mandibular fossa and articular eminence) with facial bone structure. • The angle between the line deepest point of the fossa- the midpoint of the eminence and FH plane (middle angle) was negatively correlated only with ANB angle suggesting that a steeper middle angle of eminence is related to retrusive maxilla or protrussive mandible.
  • 16. CONDYLE Barrel shape – measuring – 20mm – mediolateral 10mm – anteroposterior • Perpendicular to ascending ramus of the mandible • Oriented 10 – 30 degrees with frontal plane.
  • 17. Medial pole more prominent than lateral pole Articular surface of Posterior aspect > anterior aspect
  • 18. • In the frontal view – articular eminence often is concave and fits roughly to superior surface of condyle • Bony surface of condyle and articular part of the temporal bone – covered with dense fibrous connective tissues with irregular cartilage like cells • The number of cells increases with age and stress on the joint.
  • 19. ARTICULAR DISC • Biconcave oval structure – intersposed between the condyle and the temporal bone. • Consists of dense collagenous tissue that is avascular , hyaline and devoid of nerve tissues in the central area but has vessels and nerves in the peripheral area.
  • 20. • Divided into 3 regions in the Saggital plane • Intermediate zone • Posterior • Anterior • Articular surface situated in the intermediate zone
  • 21. Anterior view – disc thicker medially than laterally Shape of disc – determined by morphology of condyle and mandibular fossa.
  • 22. • During movement the disc is flexible to some extent and can adapt to the functional demands of the articular surfaces. • The disc maintains its morphology unless destructive forces or structural changes occur in the joint. • If these changes occur , the morphology of the disc can be irreversibly altered producing biomechanical changes during function.
  • 23. • ATTACHMENTS OF DISC • Retrodiscal tissue highly vascularized posterior attachment • Superior retrodiscal lamina – elastic fibres • Inferior retrodiscal lamina - collagenous fibres. • Remaining – large venous plexus which fills with blood as condyle moves forward.
  • 25. Anteriorly–superior and inferior attachments of the disc– capsular ligament • Superior attachment –articular surface of temporal bone • Inferior attachment – articular surface of condyle • Composed of collagen fibres • Between the capsular ligament attachment – superior lateral pterygoid muscles.
  • 26. Capsular ligament attachment medially and laterally also – dividing joint into 2 cavities. Superior cavity – mandibular fossa and superior surface of disc. Inferior cavity – mandibular condyle and inferior surface of disc
  • 27. • The internal surface of the cavities are surrounded by specialized endothelial cells that form a synovial lining. • This lining along with a specialized synovial fringe located at the anterior border of the retrodiscal tissue produces synovial fluid which fills both the joint cavities • TMJ – synovial joint.
  • 28. Synovial fluid serves 2 purposes 1. Medium for providing metabolic requirements to the non vascular articular surface of the joint. 2. Lubricant between articular surfaces during function. 2 mechanisms by which synovial fluid lubricates are 1. Boundary lubrication 2. Weeping lubrication
  • 29. Boundary lubrication • Occurs when joint is moved and synovial fluid is forced from one area of cavity into another. • The synovial fluid located in the border or recess areas is forced on the articular surface thus providing lubrication.
  • 30. • Weeping lubrication • Refers to the ability of articular surfaces to absorb a small amount of synovial fluid • During function of a joint , forces are created between the articular surfaces • These forces drive a small amount of synovial fluid in and out of articular tissues. • This is the mechanism by which metabolic exchange occurs.
  • 31. Under compressive forces therefore, a small amount of synovial fluid is released. This synovial fluid acts as a lubricant between articular tissues to prevent sticking, Weeping lubrication helps eliminate friction in compressed but not a moving joint. Only a small amount of friction is eliminated by weeping lubrication. Therefore prolonged compressive forces to the articular surfaces will exhaust this supply.
  • 33. • Articular zone • Most superficial layer • Found adjacent to the joint cavity and forms the outermost functional surface. • Made up of dense fibrous connective tissue . • The collagen fibres are arranged in bundles and oriented nearly parallel to the articular surface.
  • 34. • The fibres are tightly packed and are able to withstand the forces of movement. • It is less susceptible to the effects of aging and therefore is less likely to breakdown over time. • It also has much better ability to repair than does hyaline cartilage. • The importance of these two factors is significant in tmj function and dysfunction.
  • 35. • Proliferative zone • Undifferentiated mesenchymal tissue – • This is responsible for the proliferation of articular cartilage in response to the functional demands placed on articular surfaces during loading.
  • 36. • Fibrocartilagenous zone • Collagen fibrils are arranged in bundles in a crossing pattern. • The fibrocartilage appears in a random orientation ,providing three dimensional network that offers resistance against compressive and lateral forces.
  • 37. • Calcified zone • Made up of chondrocytes and chondroblasts distributed throughout the articular cartilage. • In this zone , the chondrocytes become hypertrophic, die and have their cytoplasm evacuated , forming bone cells from within the medullary cavity.
  • 38. • The articular cartilage is composed of chondrocytes and intercellular matrix. • The chondrocytes produce collagen , proteoglycans , glycoproteins , and enzymes that form the matrix. • Proteoglycans – complex molecule composed of a protein core and glycosaminoglycan chains.
  • 39. • The proteoglycans are connected to a hyaluronic acid chain , forming proteoglycan aggregates that make up a great protein of the matrix. • These aggregates are very hydrophilic and are intertwined throughout the collagen network . • Since these aggregates tend to bind water ,the matrix expands and the tension in the collagen fibrils counteracts the sweeping pressure of the proteoglycan aggregates.
  • 40. • In this way the interstitial fluid contributes to support joint loading . • The external pressure resulting from joint loading is in equilibrium with the internal pressure of the articular cartilage. • As joint loading increases , tissue fluid flows outward until a new equilibrium is achieved. • As loading is decreased , fluid is reabsorbed and the tissue regains its original volume.
  • 41. • Joint cartilage is nourished predominantly by diffusion of synovial fluid, which depends on this pumping action during normal activity. • The pumping action is the basis for the weeping lubrication, and this action is thought to be very important in maintaining healthy articular cartilage.
  • 42. Vincent .P. Willard Archieves of oral biology (2012) 599606 • Vincent concluded that although the TMJ disc and its attachments form a seamless complex within the joint ,a closer look at the biochemical constituents reveals that these 2 components are distinct . • While the disc and attachments both contain the same major constituents ,the relative amounts of these components vary based on functional requirements of the tissue • Disc region have more higher sulfated GAG and collagen content than the attachment regions. • In contrast attachment regions –contains more DNA content than disc region.
  • 43. INNERVATION OF TMJ • Most innervation is provided by the auriculotemporal nerve as it leaves the mandibular nerve behind the joint and ascends laterally and superiorly to wrap around the posterior region of the joint • Additional innervations by – deep temporal and massetric nerve.
  • 44. VASCULARIZATION OF TMJ • • • • • Predominant vessels are Superficial temporal artery - from the posterior Middle meningeal artery - from the anterior Internal maxillary artery – from the inferior Other important arteries are – the deep auricular ,anterior tympanic and ascending pharyngeal arteries. • The condyle – through marrow spaces by way of the inferior alveolar artery .
  • 45. Superficial temporal artery Middle meningeal artery Maxillary artery
  • 46. LIGAMENTS • Ligaments play an important role in protecting the structures • The ligaments of the joints are made up of collagenous connective tissue, which do not stretch. • They do not enter actively into joint function but instead act as a passive restraining devices to limit and restrict border movements.
  • 47. • 3 funtcional ligaments support the TMJ : 1. Collateral ligaments 2. Capsular ligament 3. TM ligament 2 accessory ligaments 1. Sphenomandibular ligament 2. Stylomandibular ligament
  • 48. • Collateral (discal) ligaments • Attach the medial and lateral borders of the articular disc to the poles of the condyle • Commonely called as discal ligaments – medial and laterlal • Medial discal ligament – attaches the medial edge of the disc to the medial pole of the condyle. • Lateral discal ligament – attaches the lateral edge of the disc to the lateral pole of the condyle,
  • 49. • These ligaments are responsible for dividing the joint mediolaterally into the superior and inferior joint cavities. • The discal ligaments are true ligaments ,composed of collagenous connective tissue fibres , therefore they do not stretch. • They allow the disc to move passively with the condyle as it glides anteriorly and posteriorly on the articular surface of the condyle
  • 50. • Thus these ligaments are responsible for the hinging movement of the TMJ , which occurs between the condyle and the articular disc. • These ligaments have a vascular supply and are innervated . • Strain on these ligaments produces pain.
  • 51. Capsular ligament • The entire TMJ is surrounded and encompassed by the capsular ligament . • The fibres of the capsular ligament are attached superiorly to the temporal bone along the borders of the articular surface of the mandibular fossa and articular eminence
  • 52. • Inferiorly the fibers of the capsular ligament attach to the neck of the condyle. • The capsular ligament -resist any medial, lateral or inferior forces that tend to separate or dislocate the articular surfaces. • 1 significant function – to encompass the joint thus retaining the synovial fluid. • Capsular ligament is well innervated and provides proprioceptive feedback regarding position and movement of joint.
  • 53. • Temporomandibular ligament The lateral aspect of the capsular ligament is reinforced by strong , tight fibres – lateral ligament or TM ligament. TM ligament has 2 parts • Outer oblique portion • Inner horizontal portion
  • 54. • Outer portion – extends from outer surface of the articular tubercle and zygomatic process posteroinferiorly to the outer surface of the condylar neck. • Inner horizontal portion – extends from the outer surface of the articular tubercle and zygomatic process posteriorly and horizontally to the lateral pole of the condyle and posterior part of articular disc.
  • 55. • Oblique portion – resists excessive drooping of the condyle – limiting the extent of mouth opening. • During the initial phase of opening ,the condyle can rotate around a fixed point until the TM ligament becomes tight as its point of insertion on the neck of the condyle is rotated posteriorly.
  • 56. • When the ligament is taut , the neck of the condyle cannot rotate further . • If mouth were to be opened wider- the condyle has to move downward and forward across the articular eminence. • Clinically tested by – closing the mouth and applying mild posterior force to the chin-jaw easily rotates until teeth are 20 – 25mm apart after which a resistance is felt when the jaw is opened wider. • This resistance is brought about by the tightening of TM ligament.
  • 57. This unique feature of TM ligament which limits rotational opening is found only in humans.
  • 58. • The inner horizontal portion of TM ligament limits posterior movement of condyle and disc. • When force applied to the mandible it displaces the condyle posteriorly , this portion of ligament becomes tight and prevents the condyle from moving further into the posterior region of the mandibular fossa.
  • 59. • Hence it protects the retrodiscal tissues from trauma created by posterior displacement of the condyle. • Also protects the lateral pterygoid muscle from overextension or overlengthening. • The effectiveness of TM ligament is demonstrated during cases of extreme trauma to the mandible. • In such cases the neck of the condyle is seen to fracture before the retrodiscal tissues are severed.
  • 60. • Sphenomandibular ligament • Accesory ligament of the TMJ • Arises from the spine of the sphenoid bone and extends downwards to a small bone prominence on the medial surface of the ramus of the mandible called the lingula. • It does not have any significant limiting effects on mandibular movement.
  • 61. • Stylomandibular ligament • It arises from the styloid process and extends downwards and forward to the angle and posterior border of the ramus of the mandible. • It becomes taut when the mandible is protruded but is most relaxed when the mandible is opened. • The stylomandibular ligament therefore limits the excessive protrusive movements of the mandible.
  • 62. MUSCLES OF MASTICATION The skeletal components of the body are held together and moved by the skeletal muscles. • Muscles fibers ranging between 10 – 80mm subunits According to amount of myoglobin Muscles slow/type1 muscle fibers fast/type ll fibers.
  • 63. • Slow muscle fibers• Deeper in red color due to higher concentration of myoglobin, • Capable of slow but sustained contraction • Well developed aerobic metabolism therefore resistant to fatigue. • Fast muscle fibers – • Whiter due to lower concentrations of myoglobin • Have fewer mitochondria and rely more on anaerobic activity for function. • Capable of quick contraction but fatigue more quickly
  • 64. • All skeletal muscles contain a mixture of fast and slow fibers in varying proportions, which reflect the function of that muscle. • Muscles that respond quickly – predominantly white fibers • Muscles for slow continuous activity – higher concentration of slow fibers
  • 65. • 4 pairs of muscles – muscles of mastication 1. Masseter 2. Temporal 3. Medial pterygoid 4. Lateral pterygoid Masseter muscle • Orgin -Rectangular muscle that originates from the zygomatic arc and extends downward to the lateral aspect of the lower border of the ramus of the mandible.
  • 66. • Insertion - extends from the region of the second molar in the mandible at the inferior border posteriorly to include the angle. • 2 portions – • superficial portion (fibers run downward and slightly backward) • Deep portion (fibers run predominantly in vertical direction)
  • 67. Function – elevation of mandible and teeth brought into contact • Superficial portion – aid in protruding the mandible • When the mandible is protruded and biting force is applied ,the fibers of deep portion stabilize the condyle against the articular eminence.
  • 68. Acta Odontologica Scandinavica, 2008; 66: 2330 Studies concluded that there is a significant association between the posterior-to-anterior facial height ratio and the masseter muscle in children, indicating that subjects with stronger masseter muscles have an increased posterior facial height for a given anterior facial height. Girls show greater associations than boys between the masseter muscle and vertical craniofacial morphology.
  • 69. Stavros Kiliaridis et al ,European Journal of Orthodontics 25 (2003) 259–263 Studied the relationship between thickness of masseter muscle and width of maxillary dental arch and results showed that - • Masseter muscle thickness was greater in older individuals and in males. • In the female group, maxillary intermolar width showed a direct, significant association with masseter thickness both during contraction and relaxation i.e. females with thicker masseter muscles had a wider maxillary dental arch.
  • 70. • The findings of this study indicate that the functional capacity of the masticatory muscles may be considered as one of the factors influencing the width of the maxillary dental arch.
  • 71. • Temporal muscle • Orgin-Large fan shaped muscle that originates from the temporal fossa and lateral surface of the skull. • Divided into 3 distinct areas according to fiber direction and ultimate function -anterior, middle and posterior portion
  • 72. • Anterior portion – vertically directed fibers • Middle portion obliquely across lateral aspect of the skull • Posterior portion – horizontally alligned fibers Function - elevates mandible and teeth brought into contact
  • 73. • Contraction of anterior portion – mandible raised vertically • Contraction of middle portion –elevates and retrudes • Contraction of posterior portion – elevation and slight retrusion • Because the angulation of its muscle fibers varies , the temporal muscle is capable of co ordinating closing movements. It thus is a significant positioning muscle of mandible.
  • 74. • Clinical examination: • "Ask the patient to clench their teeth while you palpate both masseter muscles above the angles of the jaw and then while you palpate both temporalis muscles over the temples."
  • 75. • Medial pterygoid muscle • Origin - from the pterygoid fossa and extends downward, backward and outward to insert along the medial surface of the mandibular angle. • Along with the masseter muscle ,it forms a muscular sling that supports the mandible at the mandibular angle.
  • 77. Function – mandible elevated and teeth brought into contact - also active in protruding the mandible. - unilateral contraction brings about a mediotrusive movement of the mandible
  • 78. Lateral pterygoid muscle • Divided into 2 –since their functions are nearly opposite - inferior lateral pterygoid muscle superior lateral pterygoid muscle
  • 79. Inferior lateral pterygoid muscle • Origin- at the outer surface of the lateral pterygoid plate and extends backward, upward and outward to its insertion primarily on the neck of the condyle. • function – when the inferior right and left lateral pterygoid muscle contracts simultaneously –condyles are pulled down their articular eminences and mandible is protruded.
  • 80. • Superior lateral pterygoid muscle • Smaller than inferior muscle • Originat infra temporal surface of the greater sphenoid wing , extending almost horizontally , backward and outward to insert on the articular capsule, the disc and the neck of the condyle.
  • 81. • While the inferior lateral pterygoid muscle is active during opening ,the superior lateral pterygoid muscle remains inactive ,becoming active only in conjugation with the elevator muscles. • Function -Superior lateral pterygoid muscle is especially active during power stroke (movements that invovle closure of mandible against resistance, such as chewing or clenching the teeth together)
  • 82. • Approximately 80% of the fibers that make up both lateral pterygoid muscles are slow muscle fibers /type I which suggest that these muscles are relatively resistant to fatigue and may serve to brace the condyle for long periods of time without difficulty. • Clinical examination of pterygoid muscles • by forcefully opening the jaw against resistance • with unilateral lateral pterygoid weakness the jaw deviates to the ipsilateral side as it opens.
  • 83. • As a person yawns ,the head is brought back by contraction of the posterior cervical muscles , which raises the maxillary teeth . • This simple example shows that normal functioning of the masticatory system uses many more muscles than those of mastication. • Muscles of mastication is only a part of this complex system
  • 84. Other accesory muscles are – Digastric muscle • Though not a masticatory muscle-important influence on the function of mandible. • Divided into 2 – posterior belly of digastric anterior belly of digastric
  • 85. Orgin• Posterior belly –originates from mastoid notch , medial to mastoid process – fibers run forward , downward and inward to intermediate tendon attached to hyoid bone. • Anterior belly - originates at a fossa on the lingual surface of mandible ,close to the midline – fibers run downward and backward to insert at the same intermediate tendon as does the posterior belly.
  • 86. • Function – • When the right and left digastric muscle contract and the hyoid bone fixed by suprahyoid and infrahyoid muscles ,the mandible is depressed and pulled backward and teeth are brought out of contact. • When the mandible is stabilized the digastric muscles with the suprahyoid and infra hyoid muscles elevate the hyoid bone ,which is a necessary function for swallowing. • The digastric are one of the many muscles that depress the mandible and raise the hyoid bone.
  • 87. • STERNOCLEIDO MASTOID MUSCLE • Large superficial muscles of the neck that also play a role during mastication • Orgin – • the sternal head is tendinous and arises from the superolateral part of the front of the manibrium sterni • The clavicular head is musculotendinous and arises from the medial one – third of the superior surface of the clavicle.
  • 88. • It passes deep to the sternal head and the 2 heads blend below the middle of the neck. Function • When one muscle contracts it turns the chin to opposite side . • When both muscles contract together they draw the head forwards as in eating and in lifting the head from pillow.
  • 89. Muscles of Mastication Temporalis muscle elevation Medial Pterygoid Lateral Pterygoid protrusion Medial Pterygoid Temporalis muscle retrusion depression Mylohyoid Inferior belly of diagastric lateral movements Medial Pterygoid Lateral Pterygoid
  • 90. BIOMECHANICS OF TMJ • The TMJ is an extremely complex joint system -2 TMJ connected to the same bone. • TMJ structure can be divided into 2 systems1. Joint system – surrounds the inferior synovial cavity – condyle and the articular disc(condyle –disc complex) Since disc is tightly bound to condyle by lateral and medial discal ligaments, the only physiologic movement that can occur between these surfaces is rotation of on the articular surface of condyle . This joint system responsible for rotational movement in TMJ.
  • 91. 2 Second system is made up of the condyle – disc complex functioning against the surface of the mandibular fossa. • Since the disc is not tightly attached to the mandibular fossa , free sliding movement is possible between these surfaces in the superior cavity. • This movement occurs when the mandible is moved forward – transalation. • Transalation – occurs between superior surface of articular disc and mandibular fossa. • Thus articular disc – non ossified bone – hence TMJ classified as compound joint.
  • 92. • The articular surfaces of the joint have no structural attachment or union-yet contact must be maintained for joint stability. • Joint stability-maintained by constant activity of muscles that pull across the joint. • Even in resting state ,these muscles are in mild state of contraction –tonus. • as muscle activity increases –condyle forced against disc and disc against mandibular fossa - resulting in increase in interarticular pressure . • In the absence of interarticular pressure- articular surfaces separate and joint dislocates.
  • 93. • Width of articular disc space varies with interarticular pressure. • When pressure is low- closed rest position – disc space widens. • When pressure is high – clenching of teeth – disc space narrows. • As interarticular pressure increases – condyle seats itself on the intermediate zone • When pressure is decreased –disc space widens and thicker portion of disc is rotated to fill the space. • Since anterior and posterior bands are thicker than intermediate zone – disc rotates anteriorly or posteriorly to accomplish the task.
  • 94. • Disc attached posteriorly – retrodiscal tissues which are highly elastic- hence condyle can move out of fossa without creating damage to superior retrodiscal lamina. • During mandibular opening –condyle is pulled forward down the articular eminence ,the superior retrodiscal lamina becomes increasingly stretched , creating increased forces to retract the disc. • The interarticular pressure and the morphology of the disk prevent the disc from being overetracted posteriorly. • Superior retrdiscal lamina –only structure capable of retracting the disc posteriorly on the condyle.
  • 95. • Anterior border of articular disc attached to -superior lateral pterygoid • Constantly maintained in a mild state of contraction or tonus –exerts slight anterior and medial force on the disc. • In the resting closed joint position thus anterior and medial force will normally exceed that of nonstretched Superior retrodiscal lamina.
  • 96. • Therfore in the resting closed joint position when the interarticular pressure is low and disc space widened –disc will occupy most anterior rotary position on the condyle and the condyle in contact with intermediate and posterior zones of the disc. • This disc relationship is maintained during minor passive rotational and transalatory mandibular movements. • As condyle moves more forward – Superior retrodiscal lamina gets stretched –greater force than the superior lateral pterygoid – allows disc to be rotated posteriorly to extent permitted by width of articular disc space.
  • 97. At rest condyle rests on posterior band; beginning of translation, it lies over the intermediate zone; when mouth is fully open, it lies over the anterior band.
  • 98. Power stroke – • When resistance is met during mandibular closure (biting hard food) – interarticular pressure on biting side is decreased –because force of closure applied to food not to joint . • With condyle forward and disc space increased – tension of Superior Retrodiscal lamina will tend to retract the disc from a functional position-resulting in separation of articular surfaces leading to dislocation.
  • 99. • To avoid this –superior lateral pterygoid becomes active during power stroke rotating disc forward on condyle so thicker posterior border of disc maintains articular contact-therfore joint stability maintained. • As teeth pass through the food and approach intercuspation –interarticular pressure is increased – disc space decreased – disc rotated posteriorly so thinner intermediate zone fills the space. • When the force of closure is discontinued the resting closed joint position is once again assumed.
  • 100. • Joseph H. Kronman et al (ajodo 1994;105:257-64.) • Investigated the site of lateral pterygoid muscle insertion into the TMJ disk, and the relationship between that attachment and the disk. • Results indicated a statistically significant relationship between functional muscle attachment and disk displacement. • the SLP can maintain disk displacement only when it inserts directly into the disk.
  • 101. • In cases of normal disk arrangement and condylar attachment, the muscle may not play a clinically significant role in disk displacement because disk attachment at the medial and lateral poles of the condyle allows the disk to move freely with the condyle. • This movement of the condyle and the disk may overcome the pull of the SLP when normal disk attachment is maintained.
  • 102. CONCLUSION • It is impossible to comprehend the fine points of occlusion without an in depth awareness of the anatomy ,physiology ,and biomechanics of the TMJ. • The first requirement for successful occlusal treatment is stable, comfortable TMJ. • The jaw joints must be able to accept maximum loading by the elevator muscles with no signs of discomfort.
  • 103. • It is only through an understanding of how the normal, healthy TMJ functions that we can make sense out of what is wrong when it isn't functioning comfortably. • This understanding of TMJ is foundational to diagnosis and treatment.
  • 105. References 1. Gray’s Anatomy 2. Fundamentals of occlusion and TMJ disorders -- Okeson 3. Grant’s Atlas of Human Anatomy 4. Occlusion – Ash RamfJord 5. Orthodontics Principles and Practice -- T.M.Graber 6. Joseph H. Kronman et al (ajodo 1994;105:257-64.) 7. Stavros Kiliaridis et al ,European Journal of Orthodontics 25 (2003) 259–263
  • 106. 8. Acta Odontologica Scandinavica, 2008; 66: 2330 9. Vincent .P.Willard Archieves of oral biology (2012) 599- 606 10. A IKAI et al (ajodo 112;634:8)