Tmj /certified fixed orthodontic courses by Indian dental academy

T M J Functional Anatomy

Function must be understood before
dysfunction can have any meaning.

INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com

12th May 2004 -Seminar


CLASSIFICATION OF JOINTS
•

BASED ON ANATOMICAL
CHARACTERISTICS
(Structural classification)

•

BASED ON FUNCTIONAL
CLASSIFICATION:
( type of movement)



STRUCTURAL CLASSIFICATION:
Based on presence or absence of joint cavity:
FIBROUS JOINT:
CARTILAGENOUS JOINT:
SYNOVIAL JOINT
FUNCTIONAL CLASSIFICATION:
SYNARTHROSIS: Immovable joints
AMPHIARTHROSES: Slightly movable joints
DIARTHROSIS: Freely movable joints:



SYNARTHROSIS: Immovable joints
SUTURE: sutura = seam
Fibrous joint composed of thin layer of dense fibrous
connective tissue that unites bones of the skull
GOMPHOSIS: to bolt together
Cone shaped peg fits into a socket eg tooth into alveolar bone
through periodontal ligament
SYNCHRONDROSIS: syn= together , chondros=cartilage
Cartilaginous joint in which connective material is hyaline
cartilage eg epiphyseal plate


AMPHIARTHROSES:
SYNDESMOSIS:band /ligament
fibrous joint in which there is considerably more fibrous
connective tissue than in a suture. The fit of the bones is not so
tight. Some amount of flexible movement. EG distal articulation
between fibula and tibia
SYMPHYSIS:growing together
Cartilaginous joint in which connecting material is broad flat disc of
fibro cartilage EG intervertebral discs.pubic symphysis



DIARTHROSIS: Also known as synovial joints. Presence of
Synovial cavity and articular cartilage a characteristic feature.
Based on types of movement:
GLIDING : eg intercarpal joint
HINGE eg: elbow joint/ ankle
CONDYLOID eg: joint between
radius and carpals
PIVOT eg: joint between atlas and
axis
SADDLE eg : joint between
carpus and thumb
BALL AND SOCKET: eg :
shoulder/ hip joint


BILATERAL SYNOVIAL
GINGLYMOID (DIARTHRODIAL )
COMPOUND JOINT



SYNOVIAL JOINT:
Specialized endothelial cells form a synovial lining and forms the
synovial fluid which fills both joint cavities and performs two functions:
 Medium for metabolic exchange: as the articular surfaces are avascular
Lubricant during function:
Two mechanisms by which lubrication occurs:
BOUNDARY LUBRICATION:
primary mechanism;synovial fluid forced from one region to
another by movement of the joint itself.
WEEPING LUBRICATION:
The articular surfaces itself absorb some amount of synovial
fluid which due to the pressure during function is forced in and out of the
articular tissues and provided the medium for metabolic exchange. This
occurs only during compression but not all other movements.



COMPONENTS OF THE TMJ
CONDYLAR HEAD
GLENOID FOSSA
ARTICULAR EMINENCE
MUSCLES OF THE TMJ:
MUSCLES OF MASTICATION
SOFT TISSUE COMPONENTS:
ARTICULAR DISC
JOINT CAPSULE
LIGAMENTS
ARTERIAL AND NERVE SUPPLY TO THE JOINT



CONDYLAR HEAD
• The oval condylar head is shaped like a rugby ball
• The lateral pole is slightly at a a lower level to the medial pole
• The long axis makes a line of 140 degrees with the line joining
the external acoustic meatus
The cartilage layer is thicker
laterally and posteriorly
suggesting the growth
direction is more active in
these areas.
Anteromedially the cartilage
becomes thin early and bone
forms in this region of
attachment of the lateral
pterygoid


The glenoid fossa
Shallow oval depression in the infratemporal area
Bone of the deepest part is quite thin and shows that this part
of the joint is not designed to play an active functional role in
the joint.

The articular
eminence
The two slopes of the
articular eminence are
considered to be a
functional part of the
joint.
The posterior slope
resorbs with
edentulism



Muscles of mastication
mastication is a a harmonious and skillful activity which requires the
presence and co ordination of not only the muscles of mastication but
also the supra infrahyoid muscles, and the facial muscles



The strongest of the
masticatory muscles

The temporalis

Divided into three parts
Well developed in
carnivores and animals
requiring a strong bite
force

Temporalis
muscle
tendon

It elevates the mandible
when it contracts.
Contraction of the
anterior part raises the
mandible
Contraction of the middle
part elevates and retrudes
the mandible



Powerful elevator muscle

The masseter

Superficial muscle helps in
protruding the mandible
Deep portion helps in
stabilizing the condyle against
the articular eminence when
biting in a protruded position.
Unilateral movement helps in
lateral movement of the
mandible
Well developed in ruminants
Deep portion

Superficial portion



The medial pterygoid muscle
Originates from the
pterygoid fossa and extends
downwards backwards and
outwards to insert in the
medial side of the ramus of
the mandible forming a
sling along with the
masseter at the angle of the
mandible.

It assists in closing of the jaw and
contraction of the muscle also causes
protrusion.


The lateral pterygoid muscle
Superior lateral pterygoid muscle
Originates form the infratemporal
surface of the greater wing of the
sphenoid, extends almost
horizontally backward and outward
to insert on the articular capsule the
disc and the neck of the condyle.
60 to 70% of the fibres attach to the
condyle and the rest to the disc.
Plays an active role not during
opening but during closing (power
stroke)



Originates at the outer surface of
the lateral pterygoid plate and
extends backward upward and
outward to insert into the neck of
the condyle.
When there is bilateral contraction
the condyles are pulled down the
articular eminences and the
mandible is protruded.
Unilateral contraction causes a
mediotrusive movement of that
condyle and lateral movement of
the mandible to the other side
. The inferior lateral pterygoid is
active during opening in contrast
to the superior part.



Soft tissue components of the TMJ

Articular disc, capsule, ligaments and muscles


Articular Disc
Articular disc
Superior head of the
lateral pterygoid

Inferior head of the
lateral pterygoid


ARTICULAR DISC
Divides the joint into two compartments
According to Rees divided into 4 parts:
Anterior band –thickened
Intermediate band- narrow and thin
Posterior band – again thick
Bilaminar zoneupper part having ELASTIC fibres and
attaching to the posterior margin of the glenoid
fossa and the tympano squamous fissure,
forms the posterior border of the upper
compartment.
lower part: mainly collagen fibres and attached
to neck of condyle.
Posterior border of the lower compartment.



Articular disc
Joint capsule

Lateral ligament of the
TMJ
Articular disc has the shape of a laterally wide ovoid.
In frontal section the disc is wedge shaped thicker medially
and thinner laterally


Articular disc

Joint capsule

The intermediate band: It is the functional zone of the disc
Blood vessels are rarely found here in the intermediate part of
the disc


Unlike other synovial joints the TMJ
condyle and temporal bone do not fit
together in the absence of the disc.
The disc fills the wedge like gap and
stabilizes the join during rotation and
translation.
Normally there is no space between the disc and the
articulating bones except the antero- superior and inferior
recesses and the postero -superior and inferior recesses.
These recesses are filled with synovial fluid and movement of
the joint squeezes them into the other recesses so a thin film of
lubricant is obtained on the moving parts.
The disc also acts as a shock absorber.


LIGAMENTS:

They are made up of collagenous connective tissue which do
not stretch and do not actively participate in the normal function
They act as guide wires restricting certain movements while
permitting certain others.
They restrict movement mechanically as well as through neuro
muscular reflex activity.
Ligaments do not stretch. They can be elongated by traction
forces but once they have been elongated joint activity is usually
compromised.


Functional ligaments which support the TMJ :

• The collateral ligaments (discal)
• Capsular ligament
• TM ligament

Accessory ligaments:
Stylomandibular ligament.
Sphenomandibular ligament



The collateral ligaments (discal)
Attach the medial and lateral poles of the articular disc to the
poles of the condyle. They are two in number:- medial and
lateral .
They function in allowing the disc to move passively with the
condyle as it glides anteriorly and posteriorly.
They also allow the disc to be rotated anteriorly and
posteriorly on the articular surface of the condyle..
Thus these ligaments are responsible for the hinging
movements of the condyle which occurs in the lower
compartment.



Capsular ligament
The capsular ligament encompasses the joint retaining the
synovial fluid. It is fibroelastic, very well vascularised and
well innervated and provides proprioceptive feedback
regarding the position and movement of the joint.
.

Capsular ligament
Lateral ligament



TM ligament
It has two parts outer oblique and an inner horizontal.
The outer part extends from the articular tubercle to the neck of the
condyle
The outer oblique part has the following functions:
 It restricts excessive dropping of the condyle and therefore
limits the normal opening of the mandible.
Secondly during opening of the mouth, the condyle rotates
till this ligament becomes tight as its point of insertion is
rotated posteriorly. When it becomes taut the neck cannot
rotate any further.
This unique feature is found only in humans preventing excessive
rotation for the mandible from impinging on the vital mandibular
and retromandibular structures behind the jaw.


the inner horizontal part extends backwards from the
articular tubercle to insert into to the lateral pole of the
condyle and posterior part of the articular disc.
Function:
The inner horizontal portion protects the posterior
retrodiscal tissues from trauma and also prevents the lateral
pterygoid muscle from over lengthening.



Accessory ligaments:

Sphenomandibular ligament
Stylomandibular ligament.
It becomes taut
when the mandible is protruded
and thus limits the excessive
protrusive movements of the
mandible.



Vascular supply:
Superficial temporal artery
Middle meningeal artery
Maxillary artery
Innervation:
Auriculotemporal nerve
Deep temporal and
masseteric nerve

VASCULAR SUPPLY
AND INNERVATION
OF THE JOINT

Others : deep auricular ,
anterior tympanic,
ascending pharyngeal


JAW MOVEMENTS AND JOINT MECHANICS



The border area of the movement of the mandibular
incisor point is known as Posselt’s figure



MOVEMENTS IN THE MANDIBLE:
Two types of movement occur in the
mandible:
Rotational
Translational
Rotation is the movement of a body around
its axis
The mandible can rotate in all three reference
planes
Horizontal/Frontal/Sagittal
Translation movement:
It is defined as a movement in which every
part of the moving body has the same
direction and velocity of movement.
Translation occurs in the superior cavity of
the joint while rotation occurs in the inferior
cavity of the joint.


SAGITTAL PLANE BORDER MOVEMENTS
AND FUNCTIONAL MOVEMENTS:
Mandibular motion in the sagittal direction has 4
distinct movement components:

*posterior opening border movement
*anterior opening border movement
*superior contact border movement
*functional movements



EFFECT OF POSTURE ON FUNCTIONAL MOVEMENT:

NORMAL

DIRECTED 45
degrees
UPWARD

ALERT
FEEDING
POSTURE


HORIZONTAL PLANE BORDER AND FUNCTIONAL
MOVEMENTS
The horizontal plane border movements are traced by the
gothic arch tracing.
The mandibular movements are in a rhomboid pattern with 4 distinct
movement components.
Left lateral border
Continued left lateral border with protrusion
Right lateral border
Continued right lateral border with protrusion.


Functional movements:
Centric relation
Intercuspal position
Area used just before swallowing
Area used in early stage of mastication
End to end position of anterior teeth

During chewing the range of jaw movements begins some
distance from the maximum Intercuspal position but as the food
is broken down into smaller particle sizes the jaw action comes
closer to the ICP . The exact position of the mandible during
chewing is dictated by the occlusal configuration


FRONTAL BORDER (VERTICAL) AND
FUNCTIONAL MOVEMENTS:

The border movement has a shield
shaped movement along with the
functional movement.
Left lateral superior border
Left lateral opening border
Right lateral superior border
Right lateral opening border



ENVELOPE OF MOTION:
By combining the
mandibular border movements
in the three planes a three
dimensional envelope of
motion can be produced that
represents the maximum range
of movement of the mandible.
Although it has a
characteristic shape it varies
from person to person.



In normal intercuspal position, the force generated by the
masticatory muscles is concentrated on the teeth thus the joint
receives only a small amount of the force.


8
7 1
2
6

3
5

4

The work of GIBBS is well know in the field of masticatory movements.
Gibbs classified one masticatory cycle into 8 steps:12th May 2004 -Seminar


CLENCHING IN THE
INCISOR REGION

Superficial portion of the masseter and the medial and
lateral pterygoid work during this.
Lateral pterygoid is especially active
In an individual without molars and premolars the same
muscles work with the exception of the temporalis.


UNILATERAL
CLENCHING IN THE
MOLARS

The temporalis on the working side is active whereas the
one on the balancing side is not. In contrast the lateral
pterygoid on the working side is inactive while the one on
the balancing side is active.
The masseter contracts powerfully on the working side
while slightly but firmly on the balancing side.


CLENCHING IN THE
INTER CUSPAL POSITION

All the muscles of mastication work except the lateral
pterygoids on both sides



MASTICATORY
MOVEMENT

The temporalis works through all stages of the cycle.
On the working side all the muscles are in action except the
lateral pterygoid.
On the balancing side the temporalis and the medial pterygoid
work strongly while the lateral pterygoid works slightly


Thus the workings of the masticatory system are extremely complex.
It is a remarkable phenomenon that in most instances it functions
without complication in a person’s lifetime.
When the breakdown does happen however a situation is produced
which is as complicated as the system itself.
Therefore without a sound understanding of normal function
dysfunction cannot be comprehended…



Thank you
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www.indiandentalacademy.com


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