MANDIBULAR
MOVEMENTS
CONTENTS
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Introduction
Anatomy of TMJ
Muscles of Mastication
Mandibular Movements
Eccentric Mandibular Movements
Clinical Significance of Mandibular Movements
Methods Used For Recording Mandibular
Movements
• Conclusion
INTRODUCTION
• The masticatory system is extremely
complex.
• It is made up of three linked chains.
MUSCLES &
LIGAMENTS
MAXILLA &
MANDILBLE
TMJ
• During performance of various functions
there is a delicate balance between
various components.
• It is important to study mandibular
movements as it enables us to plan
arrangement of teeth & selection of
articulators so that artificial prosthesis is in
harmony with stomatognathic system.
ANATOMY OF TMJ
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TMJ is one of the most complex joints in the body.
It is called as GINGLYMOARTRODIAL JOINT.
COMPOUND JOINT.
TMJ consists of 4 main structures:– Condyle
– Temporal bone (Squamous part)
– Articular disc
– Ligaments
CONDYLE
• It is the portion of the mandible that articulates
with the cranium, around which movement occurs.
TEMPORAL BONE
• The mandibular condyles articulates at the base of the
cranium with the squamous portion of the temporal bone.
• ARTICULAR OR GLENOID FOSSA
• SQUAMOTYMPANIC FISSURE
• ARTICULAR EMINENCE.
ARTICULAR DISC
• Functionally – articular disc serves as a non
ossified bone that permits the complex
movements of the joint.
SAGITTAL PLANE
ANTERIOR VIEW
MUSCLES OF MASTICATION
• The skeletal muscles provide for the locomotion
necessary for the individual to survive.
• 4 muscles make up a group called Muscles of
Mastication
–
–
–
–
Masseter
Temporalis
Medial Pterygoid
Lateral Pterygoid
• Digastric also plays an important role in mandibular
function.
CLASSIFICATION:I) According to Sharry:a) According to direction - Opening and closing movements
Protrusion and retraction
Lateral gliding movements
b) According to tooth contact - Movements with tooth contact
Movements without tooth contact
c) Limitation by joint structure - Border movements
Intra border movements
d) Functions of masticatory system - Mastication
Deglutition
Speech
Respiration
e) CNS - Innate movements – breathing & swallowing
Learned movements – speech and chewing
II) According to the type of movement occurs in
TMJ:a) Rotational
b) Translation
III) According to the planes of border movements:a) Sagittal plane border movement
b) Horizontal plane border movements
c) Frontal plane border movements
MANDIBULAR MOVEMENTS
TYPES:• 2 types of movement occur in TMJ:– Rotational
– Translational
ROTATIONAL MOVEMENT:• Rotation – “movement of
a body about its axis.”
• In masticatory system,
rotation occurs when the
mouth opens and closes
around a fixed point or axis
within the condyles.
HORIZONTAL AXIS OF ROTATION:•
Mandibular movement around the horizontal axis is an
opening and closing motion, referred to as Hinge
Movement and horizontal axis around which it occurs is
therefore referred to as “HINGE AXIS”.
• The Hinge movement is the only
example of mandibular activity
in which a “pure” rotational
movement occurs.
• TERMINAL HINGE AXIS
When the condyles are in their most superior position in
the articular fossae and the mouth is purely rotated open,
the axis around which movement occurs is called the
‘Terminal Hinge Axis’.
FRONTAL (VERTICAL) AXIS OF
ROTATION:• Mandibular movement around the frontal axis
occurs when one condyle moves anteriorly out of
terminal hinge position with the vertical axis of
opposite condyle remaining in the terminal hinge
position.
SAGITTAL AXIS OF ROTATION:• Mandibular movement around the sagittal axis
occurs when one condyle moves inferiorly while
other remains in the terminal hinge position.
TRANSLATIONAL MOVEMENT:• Translation can be defined as a movement in which every
point of the moving object has simultaneously the same
velocity and direction.
• In masticatory system it occurs when the mandible moves
forward during protrusion. The teeth, condyles and rami all
move in the same direction and to the same degree.
• It occurs within the superior cavity
of the joint, between the superior
surface of the articular disc and
the inferior
surface of the articular fossa.
SINGLE-PLANE BORDER
MOVEMENTS:• When the mandible moves through the outer range of
motion, reproducible and describable limits result,
which are called BORDER MOVEMENTS.
Intra border functional movements
SAGITTAL PLANE BORDER &
FUNCTIONAL MOVEMENTS:• They have 4 distinct movement components:1) Posterior opening border:
determined by ligaments
& the morphology of
TMJ’s.
2) Anterior opening border
Superior contact border
determined by occlusal
& incisal surfaces of
teeth.
3) Functional
determined by
conditional responses of
neuromuscular system.
Posselt’s
Figure
Posselt’s Figure
MP
ICP
RCP
HA
MP = Maximal protrusion
ICP = Intercuspal position
RCP= Retruded Contact position
HA = Hinge axis
MO = Maximum opening
MO
Sagittal plane
Posterior Opening Border Movements:-
• Occurs as two stage hinging movements.
• 1st stage:– Condyles are stabilized in their
most superior positions in the
articular fossae.( i.e.terminal
hinge position).
– The mandible can be lowered
(i.e. mouth opening) in a pure
rotational movement without
translation of condyles.
– In CR, the mandible can be rotated
around the horizontal axis to a distance of
20-25 mm as measured between the
incisal edges of maxillary and mandibular
incisors.
– At this point of opening, the T.M.
ligaments tighten, after which continued
opening results in an anterior & inferior
translation of condyles.
• 2nd Stage:– As the condyle translates the axis of rotation of the
mandible shifts into the bodies of rami likely to be the
area of attachment of sphenomandibular ligament,
resulting in the second stage of the posterior opening
border movement.
– During this stage, the condyles move
anteriorly and inferiorly and the mandible
moves posteriorly and inferiorly.
– Maximum opening is reached when capsular
ligaments prevent further movement of the
condyles.
– Maximum opening range is 40-60 mm.
Anterior Opening Border Movements:• With the mandible maximally opened, closure
accompanied by contraction of inferior lateral
pterygoids (which keep the condyles positioned
anteriorly) will generate the
anterior border
movement.
• Because the maximum protrusive position is
determined in part by stylomandibular ligaments,
when closure occurs, tightening of ligaments
produces a posterior movement of the condyles.
• The posterior movement of the condyle from the
maximally open position to maximally protruded
position produces eccentricity in the anterior
border movement. Therefore, it is not a pure
hinge movement.
Superior Contact Border Movements:• Throughout this entire border movement tooth
contact is present.
• It depends on:– Amount of variation between centric relation and
maximum intercuspation.
– The steepness of the cuspal inclines of the posterior
teeth.
– Amount of vertical and horizontal overlap of anterior
teeth
– Lingual morphology of maxillary anterior teeth.
– General interarch relationships of the teeth.
• The initial tooth contact in
terminal hinge axis or centric
relation occurs between the
mesial inclines of maxillary
tooth & distal inclines of
mandibular tooth.
• When muscular force is
applied to the mandible,
a superoanterior movement
or shift will occur until the
intercuspal position is reached.
• The slide from CR to maximum intercuspation,
may have a lateral component.
Average distance is 1.25 ± 1 mm.
• In the intercuspal position, the opposing anterior
teeth usually contact.
• When the mandible is protruded,
from maximum intercuspation,
contact between the incisal
edges of the mandibular anterior
teeth & lingual inclines of
maxillary anterior teeth result
in an anteroinferior movement
of the mandible.
• This continues until the maxillary and mandibular
anterior teeth are in edge to edge relationship, at
which a horizontal movement continues until
incisal edges of mandibular teeth pass beyond the
edges of maxillary teeth.
• At this point mandible moves
in a superior direction until
the posterior teeth contact.
• The occlusal surfaces of
posterior teeth then dictate
the remaining pathway to
the maximum protrusive
movement, which joins
with the most superior portion
of the anterior opening border
movement.
Functional Movements:• Functional movement occurs during functional
activity of the mandible. They usually take place
within the border movements & therefore,
considered as free movements.
• Most functional movements require maximum
intercuspation & therefore typically begin at &
below the intercuspal position.
• When mandible is at rest, it is found to be located
approximately 2 to 4 mm below the intercuspal
position. This is called the Clinical Rest Position.
• Postural position – Since,
clinical rest position is not a
true resting position, the
position in which mandible
is maintained is termed as
‘postural position.’
• Chewing Stroke:- If it is examined in sagittal
plane, the movement will be seen to begin at the
intercuspal position & drop downward & slightly
forward to position of desired opening. It then
returns in a straighter pathway, slightly posterior
to the opening movement.
HORIZONTAL PLANE BORDER &
FUNCTIONAL MOVEMENTS:•
When mandibular movements are viewed in the
horizontal plane, a rhomboid-shaped pattern
can be seen that has a functional component, &
4 distinct movement components:1) Left lateral border
2) Continued left lateral border
with protrusion
3) Right lateral border
4) Continued right lateral border
with protrusion
Left Lateral Border Movements:• With the condyles in the centric relation position,
contraction of the right inferior lateral pterygoid move the
right condyle - anteriorly and medially.
• If left inferior pterygoid stays relaxed, with the left condyle
still in the CR & result will be left lateral border movement.
• Left condyle- working or rotatory
Right condyle- non-working or
orbiting
Continued Left Lateral Border
Movements With Protrusion:•
With the mandible in the left lateral border position,
contraction of the left inferior lateral pterygoid along with
continued contraction of right inferior lateral pterygoid will
cause the left condyle to move anteriorly to the right.
Right Lateral Border Movements:• Left condyle- orbiting
Right condyle- rotatory
Continued Right Lateral Border
Movements With Protrusion:-
Functional Movements:• As in the sagittal plane, functional movement in the
horizontal plane most often occur near the intercuspal
position.
• During chewing the range of jaw movements begins some
distance from maximum intercuspal position; but as the
food is broken down into smaller particles, jaw action
moves closer and closer to intercuspal position.
Horizontal plane
FRONTAL(VERTICAL) BORDER &
FUNCTIONAL MOVEMENTS:•
A shield-shaped pattern can be seen that has a
functional component, & four distinct movement
components:1. Left lateral superior border.
2. Left lateral opening border.
3. Right lateral superior border.
4. Right lateral opening border.
Left Lateral Superior Border
Movements:• With the mandible in maximum intercuspation,
lateral movement is made to the left.
• It depends upon morphology and interarch
relationships of maxillary and mandibular teeth.
• The maximum lateral extent of this movement is
determined by ligaments of the rotating joint.
Left Lateral Opening Border
Movements:• From the maximum left lateral superior border position, an
opening movement of the mandible produces a laterally
convex path. As maximum opening is approached,
ligaments tighten and produce a medially directed
movement that causes a shift back in the mandibular
midline to coincide with the midline of the face.
Right Lateral Superior Border
Movements:• Now, the mandible is returned to maximum
intercuspation. From this position a lateral
movement is made to right that is similar to the
left lateral superior border movement.
Right Lateral Opening Border
Movements:• From the maximum lateral border position an
opening movement of the mandible produces a
laterally convex path similar to that of left opening
movement.
Functional Movements:•
During chewing, the mandible
drops directly inferiorly until the
desired opening is achieved.
• It then shifts to the side on which
bolus is placed and rises up.
• As it approaches maximum
intercuspation, bolus is broken
down between the opposing
teeth.
• In the final closure, the
mandible quickly shifts back
to the intercuspal position.
Frontal plane
ENVELOPE OF MOTION:• Given by Posselt.
• By combining mandibular border
movements in all 3 planes, a 3-D
envelope of motion is produced.
• This represents maximum range
of movement of mandible.
ECCENTRIC MANDIBULAR
MOVEMENTS
•
Eccentric mandibular movement can be divided
into protrusive and lateral movements which
consists mainly of condylar translations:1) PROTRUSIVE MOVEMENT:- consists mainly of
condylar translations
a)Sagittal Protrusive Condylar Path:– It forms an angle with horizontal reference
plane known as sagittal inclination of
protrusive condylar path.
– Ranges from 5º- 55º.
Mean 30º.
b) Sagittal Protrusive Incisal Path:– The angle formed by the protrusive incisal path and the
horizontal reference plane is called “sagittal inclination
of protrusive incisal path” (incisal guidance angle) with
a range between 50-70 degrees.
2) LATERAL MOVEMENT:Sagittal Lateral Condylar Path:– When lateral movement is executed the working
condyle rotates & moves outward while, other non
working condyle translates forward, medially downward
orbiting around the rotating working condyle.
– The orbiting condylar path is
known as sagittal lateral
condylar path.
– Lateral condylar path is longer
& more steep than the protrusive
condylar path.
– Fischer Angle:- The angle formed
between the sagittal protrusive condylar
path & sagittal lateral condylar
path(approx 5º).
– The angle formed by the sagittal lateral
condylar path & horizontal reference
plane is known as “sagittal inclination of
lateral condylar path” with a range 11º 61º & mean 35º.
• Bennett in 1908, studied working condylar
path & called as BENNETT MOVEMENT.
• Bennett movement refers to condylar
movement on the working side &,
• Bennett Shift is the bodily side shift of the
mandible on working side in horizontal
direction.
• Bennett movement is consequent to the medial
movement of orbiting condyle & is regulated by:– Morphology of medial wall of mandibular fossa.
– Inner horizontal part of TM ligament which
attaches to the lateral pole of rotating condyle.
• Bennett movement has 3 components:– Amount
– Timing
– Direction
1) AMOUNT:– More medial the wall from the medial pole of the
orbiting condyle, closes the T.M. ligament attachment
of the rotating condyle the greater will be the Bennett
movement.
– When the Bennett movement occurs early, a shift is
seen before the condyle begins to translate from the
fossa. This is called as ‘IMMEDIATE SIDE SHIFT.’
– Beyond this the condyle moves forward, downward &
inward, this is known as ‘PROGRESSIVE SIDE SHIFT.’
2) TIMING:– Amount of immediate side shift and
progressive side shift. The rate or amount of
descent of contralateral condyle & the rotation
& lateral shift of working condyle.
– Immediate side shift – is the 1st movement the
mandible makes when initiating lateral
excursions. The non-working condyle moves
from centric position medially against the
medial & superior wall of the articular fossa to a
distance of approx. 1mm.(range 0-2.6mm).
– This is not an exact 90º or a right angled
medial move in horizontal plane.
– Progressive side shift:- Beyond the
immediate side shift the condyles move
forward, downward and inward. This
movement component is called progressive
side shift. Its value is 7.5 degrees.
– The combined amount of Bennet movement is
the Bennet Angle of the nonworking condyle.
(varies 2 º -44º mean 16º).
– The angle formed by lateral horizontal condylar
path & sagittal plane is called ‘BENNETT
ANGLE’ (varies 2º -44º mean 16º).
DIRECTION:– The direction of Bennett movement depends
primarily on the direction taken by the
rotating condyle during the bodily movement.
The direction of the shift of the rotating
condyle during Bennett movement is
determined by the TM joint undergoing
rotation
• PROTRUSIVE MOVEMENT:1) Condylar guidance and anterior guidance:
These are the two end controlling factors of the
mandibular movement when the movement of a solid body
is governed by contacting surfaces at either ends of that
body, the direction of movement of any point within the
body is determined by its location in rotation to two guiding
surfaces. Then,
a) Since a second molar is closer to the condylar
guidance than is a lateral incisor, the condylar guidance
has a greater effects on the direction of movement of
lower second molar than it does on lower lateral incisor.
b) Anterior guidance has a greater effect on the
direction of movements of the lower canine
than it does on the lower molar of the two,
anterior guidance has the greater effect of
direction of movement of tooth movement
during mandibular movement, as all of the
teeth are closer to anterior guidance than the
condylar guidance.
• Effects of condylar guidance and anterior
guidance on cusp height and fossa depth:
a) The lesser the condylar guidance angle, the
shorter the cusps must be.
b) The greater the condylar guidance angle, the
longer the cusps may be.
c) The greater the horizontal overlap of the
maxillary anterior teeth, the shorter the cusps
of the posterior teeth must be.
d)
e)
f)
The lesser the horizontal overlap the
longer the cusps of the posterior teeth
may be.
The lesser the vertical overlap, the
shorter the cusps of the posterior teeth
must be.
The greater the vertical overlap, the
longer the posterior cusps may be.
2) Bennet’s Movement:a)The bodily lateral movement or lateral shift of the
mandible during lateral jaw movement.
- Movement responsible for lateral chewing
stroke.
- Movement during which the greater lateral force
is exerted.
- It is extremely important that articulating
surfaces are is strict harmony with this side
shift.
METHODS USED FOR RECORDING
MANDIBULAR MOVEMENTS
• Graphic method record –
• STEREOGRAPHICS:• PANTOGRAPHS:• KINESIOGRAPH:• ELECTROMYOGRPAHY:
CONCLUSION
• “Nature has blessed us with a marvelously
dynamic masticatory system, allowing us
to function and therefore exist.”
• “ You cannot successfully treat dysfunction
unless you understand function.”