Tmj muscles &movements / fellowships in orthodontics

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

INTRODUCTIONINTRODUCTION

ANATOMY OF TMJ
• It is synovial joint of condylar variety
• It consists of two components
1. Osseous components
2. Soft Tissue components
Osseous components
- Glenoid Fossae
- Articular eminence
- Head of the mandible
- Condylar Process
- Neck
- The convex superior surface of the condyle articulates
with the concave inferior surface of the articular diskwww.indiandentalacademy.com

SOFT TISSUE COMPONENTS
• Articular disc :: Flat, circular or dense fibrous tissueFlat, circular or dense fibrous tissue
connective tissue plateconnective tissue plate
• Concavo convex superior surface and concaveConcavo convex superior surface and concave
inferior surface.inferior surface.
• Superior surface permits gliding movements andSuperior surface permits gliding movements and
inferior surface permits rotation and glidinginferior surface permits rotation and gliding
movementsmovements
• The presence of articular disc differentiates a TMJThe presence of articular disc differentiates a TMJ
from any other joint in the body making it a bonefrom any other joint in the body making it a bone
to tissue and tissue to bone articulation.to tissue and tissue to bone articulation.

ARTICULAR CAPSULE
• Loose thin, sack of fibrous connective tissue
• Attached to the border of articulating surface of
temporal bone and (neck) condyloid process
• Lateral surface of the capsule is strengthened by
temporomandibular ligament.
• Sphenomandibular ligament:
– Spine of sphenoid-inserts into mandibular
ligament
• Stylomandibular Ligament:
– Styloid process- mandibular angle
• Temporomandibular ligament :www.indiandentalacademy.com

MUSCLES OF TMJ
• Muscles involved in functioning and stabilizingMuscles involved in functioning and stabilizing
of the TMJ are:of the TMJ are:
1.1. Masticatory musclesMasticatory muscles
2.2. The suprahyoid musclesThe suprahyoid muscles
• Muscles of Mastication:
– MasseterMasseter
– TemporalisTemporalis
– PterygoidsPterygoids
– LateralLateral
– MedialMedialwww.indiandentalacademy.com

ROLE OF MASCULATURE IN
MANDIBULAR MOVEMENT
Lateral Pterygoid
• Consists of Superior head and Inferior head
• Muscle which runs in a horizontal direction
• Chief muscle for the protraction of mandible
• As it relaxes, the posterior fibres of temporalis
muscle pull the condyle back to its centric position
• When it contracts it draws forward the condyle
along with the disc.
• If this muscle contracts one side and remains
relaxed on other side then the mandible will be
moved laterally on other side

Superior head
• Superior head is active only on closing. It braces
the disc against the posterior slope of articular
eminence
Inferior head of the lateral
• Active only on opening movement
Harmonious Contraction
• When both the heads contracts there is
synchronization of superior and inferior head
during protraction thus permitting the condyle and
disc to move forward. Simultaneously when there
is relaxation of these two heads the muscle permit
the condyle disc assembly to go back to centric
position www.indiandentalacademy.com

MEDIAL PTERYGOIDMEDIAL PTERYGOID
• The external pterygoid moves the condyle forward
and the internal pterygoid on one side moves the
body of the mandible laterally to the opposite side.
• Acting together it elevates the mandible, acting
alone it draws the mandible laterally
Masseter:
• Superficial fibres- elevate mandible
• Deep fibres – horizontal in direction – assist in
retraction of mandible

TEMPORALISTEMPORALIS
• Posterior fibres are forward and towards the ascending
ramus when they contact, retrade the mandible
• Middle fibres – vertical elevate the mandible
• Anterior fibres- protrudes the mandible
• When all fibres contract simultaneously elevate the
mandible
Temporalis and Masseter
• Are closing muscles and also retrude mandible. It is
interesting to observe that the temporalis is attached to the
anterior upper part of ascending ramus and the masseter is
inserted down below on the outer surface of ramus. So this
pattern of insertion stabilizes mandible in position during
function. www.indiandentalacademy.com

SUPRAHYOID MUSCLESSUPRAHYOID MUSCLES
These muscles help the mandible to depress they are
Diagastric
Stylohyoid
Mylohyoid
Geniohyoid
Blood Supply::
Superficial temporal artery
Deep part of maxillary artery
Nerve supply:
Sensory – Auriculotemporal
Motor – Messentric nervewww.indiandentalacademy.com

MANDIBULAR MOVEMENTSMANDIBULAR MOVEMENTS
Significance of understanding mandibular movements
Knowledge of mandibular movements is essential to
develop
1. Tooth forms
2. Understanding occlusion
3. For arranging artificial teeth
4. Treating TMJ disturbances
5. Preserving periodontal health
6. Designing, selecting and adjustment of articulators

The major structures to be observed in the TMJ movement
are:
1. The fossa with articular tubercle
2. Articular disc
3. Mandibular condyle
The two basic movements
– Rotation
– Translation

• Rotation: Rotational movement is the one in which all
the points within a body describe concentric circles
around a common axis, i.e., the body changes its
position but not place.
• Translation: This is the one in which all the points
within a body are moving at the same velocity and in
same direction.

• The mandibular movements are related to three planes of
the skull – horizontal, frontal and Sagittal and are usually
described as three dimensional
• Dimension is defined as magnitude measured in a particular
direction or along a diameter or principle axis.

Schematic representation of TMJSchematic representation of TMJ
movementmovement
The line A – A represents
a line of reference drawn
vertically through the
tissues to changes in
position of the related
structures as they refer to
centric occlusion.

The tissues have been
changed in position as the
mandible separates teeth
from centric occlusion. There
has been essentially a
rotatory movement of the
condyle head

Represents purely
translatory movement

Mandible has been
extended beyond the
respiratory rest position.
Joint has a combination
of small degree of both
translatory and rotary
movement.

Marked translatory and
additional rotary
movements of all element
of the joint.

Axis of RotationAxis of Rotation
• Rotational movements of mandible are made
around three axis:
1. Transverse
2. Vertical
3. Sagittal

Transverse axisTransverse axis
• During opening and closing the mandible
moves in the Sagittal plane around a transverse
axis
• Passes through or near both the axis
•Transverse axis can be located when opening
and closing occur with the mandible in its most
position
• Transverse axis moves as the mandible is
moved in lateral, protrusive and latero protrusive
movement
• If the mandible is in a forward position and
opening and closing occurs, the rotation will still
take place about the same transversal axis,
however since the mandible cannot be fixed in
space in the forward position, the transverse axis
will be instantaneous for any given location and
will move & tilt the mandiblewww.indiandentalacademy.com

Vertical AxisVertical Axis
• In lateral excursion the mandible around a vertical
axis passing through or near the condyle on the
working side and condyle on the balancing side
moves forward and medially.

Sagittal AxisSagittal Axis
• During lateral mandibular movement, the condyle on the balancing
side that is moving forward and medially also moves downward
movement of the condyle on the balancing side causes the mandible
to rotate around a Sagittal axis passing through or near the condyle
on the working side
As the condyle on the working side rotates around the vertical
axis the Sagittal moves in a corresponding manner

Border movementsBorder movements
• Border movements of mandible in any direction in which it
moves
• The envelope of motion of the mandible in the border
positions has been recorded in three planes – Horizontal,
Frontal, and Sagittal
• Different types of border movements:
– Opening and closing
– Protrusion – retrusion
– Lateral shift
• The envelope id the locus of the ultimate intersections of a
series of curves or surfaces

Envelope of motion in SagittalEnvelope of motion in Sagittal
planeplane
• The mandibular movements tracings
were made with a head attached to
lower central incisors and the envelope
of motion was plotted
• The diagram shows the envelope of
motion I.e., maximum border
movements in the Sagittal plane.
• The tracing starts at P (most protruded
position). As the mandible is moved
posteriorly while tooth contact is
maintained, a dip in the top line of the
tracing occurs as the incisor pass across
one another
• Centric occlusion (Co0 is reached when
there is maximum interruption.
• When the mandible is further retruded,
posterior position of the mandible in the
Glenoid fossa is depicted by centric
relation (CR)www.indiandentalacademy.com

Envelope of motion in SagittalEnvelope of motion in Sagittal
plane (Contd.)plane (Contd.)
• As the teeth separate from CR the mandible
and the patient continue to open this
retruded, with no apparent condylar
translation to MHO (Maximum hinge
opening)
• CR + MHO Terminal hinge
movement
• As the patient further open the mouth the
mandibular condyle moves anteriorly in the
Glenoid fossa depicting translation till MO
(Maximum opening)
• At this point the condyle are in an near their
most anterior downward position in fossae
• The most forward line on the tracing,
running from MO to P, represents the
pathway of the mandible as it is moved
from its most opening position upward to
its most protruded position.

• Any mandibular movementAny mandibular movement
observed from the side will fallobserved from the side will fall
within this envelope of motionwithin this envelope of motion
since it represents all extremesince it represents all extreme
positionposition
• When the patient is relaxed andWhen the patient is relaxed and
the jaws in the resting position.the jaws in the resting position.
Rest position occursRest position occurs
somewhere downward slightlysomewhere downward slightly
forward of CR.forward of CR.

Envelope of motion in frontalEnvelope of motion in frontal
planeplane

Bennett MovementBennett Movement
• Bennett movement is the bodily side
shift of the mandible which when it
occurs may be recorded in the region
of the rotating condyle on the working
side
• Demonstrated by Bennett in 1908
• Bennett studied working condylar path
moved outwards during sideward
movement of mandible in frontal plane,
where as the non-working condyle
moved inward or medially
• The orbiting condylar path consists of
two components namely,
ISS
PSS
ISS: Occurs when non working
condyle moves from centric relation
straight inward mediallywww.indiandentalacademy.com

• PSS: Is translatory portion of lateral movement
– Cause of Bennett movement is connection of external
pterygoid muscle
Importance of Bennett Movement :
– Its direction and timing influence the freedom of
movement to and from centric and eccentric jaw
positions.
– Balanced gliding occlusion will be difficult to achieve if
the direction and timing of Bennett movement is not
recorded and transferred to articulator
Bennett Angle :
Angle formed by the horizontal lateral condylar path and
sagittal plane (mean value 160
)

Tmj muscles &movements / fellowships in orthodontics

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