Eccentric movements of mandibular movements/prosthodontic courses

ECCENTRIC MANDIBULARECCENTRIC MANDIBULAR
MOVEMENTSMOVEMENTS
Eccentric mandibular movements can be
divided into protrusive and lateral
movements.
It consists mainly of condylar translation
instead of rotation.
Protrusive movementProtrusive movement:
The mandible translates in a forward and
downward direction during protrusive
movement.
INDIAN DENTAL ACADEMY
Leader in continuing Dental Education
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The right and left condyle –disk assemblies
also slide forward and downward;a total
movement of only about 10mm.
Theoretically, the mid point on inter
condylar axis and the incisal point move
within the same sagittal plane. The orbit
produced by the centers of the right and left
condyles during protrusive movement is a
called protrusive condylar path.
When is projected in sagittal plane , it is
called as sagittal protrusive condylar path.

 it is a s- shaped curve.
 this curve is more obvious in dentulous arches
than in edentulous arches; shape varies from
shallow curve to straight line.
 Sagittal inclination of protrusive condylar path- it
is the angle formed by protrusive condylar path
and horizontal reference plane.
 The average angle formed is 33 degrees when
CAMPER’S is used as horizontal reference plane
(GYSI-1910,GYSI.KOHLER-1929)

 The average angle formed when FRANK FORT’S
horizontal plane is used as reference plane’ the
angle is 35.6 degrees according to ISAACSON-
1959.
 45-50 degrees according to Lunden and
worth(1973).
 HOBO(1982) INVESTIGATED THE SAGITTAL
PROTRUSIVE CONDTLAR PATH IN
RELATION TO THE HORIZONTAL
REFERENCE PLANE AND FOUND IT
RANGED BETWEEN 5-55 DEGREES WITH A
MEAN 30.4 DEGREES

 sagittal protrusive incisal path:
During protrusive movement, the
mandibular anterior teeth protrude forward
and downward along the lingual concavities
of the maxillary anterior teeth discluding
posterior teeth.
 the orbit of incisal point varies from
maximum inter cuspation to edge to edge
bite is referred as protrusive incisal path.
The mean length of this path is 5mm with
variable paths in different individuals.

The angle formed by the protrusive incisal
path and horizontal reference is called the
sagittal inclination of protrusive incisal
path(incisal guide angle) with a range
between 50-70 degrees-GYSI-1910
Usually sagittal inclination of protrusive
incisal path is steeper than the sagittal
inclination of protrusive condylar path

Lateral movementLateral movement:
Lateral movement occurs when one condyle
rotates with in the temporo mandibular
fossa & the other condyle translates
forward, inward & downward.
Translating condyle is called NON
WORKING CONDYLE
Rotating condyle is called WORKING
CONDYLE.

When the orbit of the centre of non working
condyle is traced on the saggital plane it is
called SAGGITAL LATERAL CONDYLAR
PATH i.e. medial & downward movement
of non working condyle also called as
MEDIOTRUSIVE PATH.
This path is longer & usually steeper than
the saggital protrusive condylar path.
The angle formed between saggital
protrusive condylar path & saggital lateral
condylar path is called as FISHER
ANGLE,with a mean of 5degrees.

 Angle formed by the saggital lateral condylar
path & the horizontal refference plane is called
SAGGITAL INCLINATION OF LATERAL
CONDYLAR PATH.
 The angle between lateral condylar path &
frankfort horizontal plane is approximately 45-
50degrees.(LUNDEN,WIRTH-1973)
 The saggital inclination of lateral condylar path
ranges between 11-61degrees with a mean of 35
degrees when the anterior reference point is set at
43mm superior to the maxillary right central
incisor edge(HOBO –1982)

The sagittal inclination of lateral condylar
path on non working side have 5 different
patterns
Unique concave curve type
Concave curve type
Straight type
Convex curve type
Unique convex curve type

Horizontal lateral condylar path: when the
orbit of center of nonworking condyle is
traced on the horizontal plane.
Angle formed by horizontal lateral
condylar path and sagittal plane is called
BENNET angle –varies between 2-44
degrees with a mean value of 16 degrees.

Condylar movements in theCondylar movements in the
horizontal planehorizontal plane
– During the lateral movements of the mandible
,the non working condyle is drawn inward from
its centric position by the pterygoids &
translates in a forward,downward & moves
outward.
GPT-refers this movement of the condyle as
laterotrusion & it considers it synonymous
to Bennet`s movement.

Precisely, the orbiting condyle moves
medially & as a result of this, the rotating
condyle moves outward
The bodily shift of mandible during the
laterotrusion of the working condyle is
known as Bennet`s side shift .

 Terminology of the movements of the mandible &
condyle
 Working sideWorking side non working side/
 balancing side/idlingside
 Rotating side orbiting side
 (rotating condyle) (orbiting condyle)
 Ipsilateral side contralateral side
 (ipsilateral condyle) (contra lateral condyle)
 Laterotrusive side mediotrusive side
 (laterotrusive condyle) (mediotrusive condyle)
 Pivoting side swerving side
 (pivoting condyle) (translating condyle/advancing
c

 BENNET MOVEMENT:
 Bennet-1908 studied the working condylar path &
called it BENNET MOVEMENT,presently
it is referred to as laterotrusion.
Bennet movement refers to the condylar
movements on the working side.
BENNET SHIFT is the bodily side shift of
the mandible during the laterotrusion of the
working condyle in horizontal direction.

The glossary of occlusal terms by the
international academy of gnathology-1979
on the contrary equates BENNET
MOVEMENT with transtrusion(across
thrust) & the bodily side shift of the
mandible,which is regulated by the
anatomical configuration of glenoid
fossa,the slackness of capsular ligaments &
contraction of medial ptrerygoid on the non
working side.

The degree of inward movement of the
orbiting condyle is determined by 2 factors
Morphology of the medial wall of the
mandibular fossa .
Inner horizontal portion of the Tmligaments
which attaches to the lateral pole of the
rotating condyle.
If the Tm ligament of the rotating condyle is
very tight & the medial wall is close to
orbiting condyle & therefore no Bennet
movement occurs.such condition rarely
occurs.

 Bennet movement has 3 attributes I.e.
 Amount
 Timing
 Direction
 Amount:
 The more medial the wall from medial pole of the
orbiting condyle the greater will be the amount of
Bennet movement,looser Tm ligament attachment to
rotating condyle the greater will be the Bennet
movement.
 When the Bennet movement occurs early a shift is seen
before the condyle begins to translate from fossa,this is
called immediate side shift.
 If it occurs in conjunction with eccentric movement this
is known as progressive side shiftwww.indiandentalacademy.com

 Timing of Bennet movement-amount of immediate
side shift & progressive side shift .
 The rate or amount of descent of contra lateral
condyle & the rotation & lateral shift of the
ipsilateral condyle
 immediate side shift-this occurs in mandibular
lateral movements where the orbiting condyle
moves from centric position medially against the
medial & superior wall of articular fossa to a
distance of approximately 1mm(range from 0.2-
2.5mm) & beyond this condyle moves forward
downward & inward against the medial & superior
walls of the fossa at a curved angle

Progressive side shift- beyond the immediate
side shift the condyle moves forward
,downward& inward.GUICHET referred this
movement component as progressive side
shift. Its value is 7.8degrees.
Bennet angle- the combined amount of the
Bennet movement I.e. ISS+PSS is the bennet
angle of the orbiting condyle.
 Bennet angle is measured by the angle
formed by the horizontal lateral condylar path
& the saggital plane . It varies from 2-
44degrees, with a mean value of 16 degrees .www.indiandentalacademy.com

 Direction-the direction of Bennet 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 Bennet movement is determined by Tm
joint under going rotation. Therefore additions to
lateral movement the rotating condyle may also
move in –superior direction-laterosurtrusion
 Inferior direction-latero detrusion
 Lateral direction-laterotrution
 Anterior direction-latero protrution
 Posterior direction-lateroretrution
-

Role of musculature in mandibular
movement:
Lateral pterygoid:
It is a muscle which runs in a horizontal
direction . This location make it the chief
muscle for protrusion f mandible.
As it relaxes, the posterior fibers of
temporalis muscle pull the condyle back
toits centric position.
When it contracts it draws forward the
condyle along with the disc.

This muscle is responsible for the initial
opening of hinge movement.
If the external pterygoids on one side
contracts and the remains relaxed,then the
mandible will be moved laterally to the
other side.
External pterygoid is not a muscle used for
chewing.it only places the mandible to open
into any position forward so that incision of
food can be made with anterior teeth by
contraction of masseter and temporalis.

It can also place the mandible into lateral
position, so that the same muscles can
permit chewing at the molar and bicuspid
region.
It guides the mandible into lateral position
and keeps it steady when chewing takes
place in lateral position.
Functions of superior and inferior heads of
lateral pterygoid:

 harmonious contraction of both heads of
muscle:there is a synchronization of superior and
inferior head during protrusion thus
permitting condyle and disc assembly to move
forward. Simultaneous relaxation these two
heads of the muscle permit the condyle disc
assembly to go back to centric position.
Independent functions of the two heads of
muscle: the superior and inferior heads of
the muscle function as two different
muscles.the superior head is active only on
closing. It braces the disc against the
posterior slope of eminence .the inferior
head is active on mouth opening.

MEDIAL PTERYGOID:
It helps in lateral positioning of
mandible.The external pterygoids move the
condyles forward while internal pterygoid
on one side moves the body of mandible
laterally to the opposite side.It thus
contributes to Bennet movement.acting
together it elevates the mandible.Acting
alone it draws he mandible laterally
MASSETER:
The superficial portion of masseter elevates
the mandible.Deep fibers of the masseter
run more horizontal in direction and they
assist in retraction of mandible.www.indiandentalacademy.com

TEMPORALIS:
Since the posterior fibers are directed
forwards and towards the ascending ramus
when they contract,they retrude the jaw.The
middle fibers run almost vertical and their
contraction elevates the mandible.The
anterior fibres run backwards and their
contraction protrudes the mandible.When
all fibers of temporalis contract
simultaneously they close the mandible.

Temporalis and masseter muscles are closing
muscles of the mandible.They also retrude the
mandible and are partners in action.It is
interesting to observe that the temporalis is
attached to the upper part of the Ascending
ramus.while masseter is inserted down below
in the ramus.Further the temporalis is inserted
on the medial surface,while masseter is
inserted onto the outer surface of ramus of
mandible.As a result of this pattern of
insertion,simultaneous contraction of these
muscles helps to position the mandible
without un stabiliZing it during function.This
is a very significant observation.www.indiandentalacademy.com

Temporalis and lateral pterygoid are
antagonistic in their function.It should be
noticed that there is no muscle to oppose
the action of lateral pterygoid(protraction)to
retract the mandible from behind.There is
no muscle inserted into the posterior aspect
of condyle to retract the condyle or articular
disc.The function of retrusion is performed
by temporalis attached to coronoid
process.The simultaneous contraction of
middle and posterior fibers of temporalis
assisted by deep fibers of masseter and
poisterior belly of digastric retrude the
mandible.

MANDIBULAR RETRUSION
PROTOGONIST ANTAGONIST
(mover muscle)
Temporalis+digastric+ lateral pterygoid
Deep fibers of masseter
MANDIBULAR PROTRUSION
PROTOGONIST ANTAGONIST
(mover muscle)
Lateral pterygoid Temporalis+digastric+
deep fibers of
masseterwww.indiandentalacademy.com

HINGE CLOSURE
OPENING ON RETRUSIVE ARC-digastric,
geniohyoid
CLOSURE ON RETRUSIVE ARC-posterior
fibers of temporalis+deep fibers of masseter
exerting a backward pull
DEPRESSION LATERAL-elevation
BENNET SHIFT
Masseter on one side with contraction of
pterygoids of opposite side

Determinants of mandibular movements:
The major factors that determine or control
mandibular movement are:
Those that influence the movement of the
posterior portion of the mandible
Those that influence the anterior position of
the mandible.
Neuro muscular factors

Posterior controlling factor(condylar
guidance):
Condylar guidance can be defined as the
“mandibular guidance generated by the
condyle and articular disc traversing the
contour of the glenoid fossa-GPT7
It is nothing but the path of the movement
taken by the condyle in the glenoid fossa.
The glenoid fossa and condyle are the
articulating surfaces of the glenoid fossa.

Hence the surface of the glenoid fossa
determines the path of the condyle.
The shape of the glenoid fossa is not
straight, instead it is a s shaped.
Hence condyle also move along a s-shaped
path.
The shape of the glenoid fossa which
determines the path of movement of the
condyle is called as condylar guidance.

The rate at which the condyle moves away
from horizontal reference plane
(FRANKFORT’S HORIZONTAL
PLANE)is referred to as condylar guidance
angle.
Condylar guidance is considered to be fixed
factor,since in the healthy patient it is
unalterable.
It can be altered however under conditions
like trauma,pathosis and surgical
procedures.

Anterior controlling factors(anterior guidance
or incisal guidance)
Incisal guidance can be defined as the
influence of contacting surfaces of
mandibular and maxillary anterior teeth
during mandibular movements-GPT7
When the mandible is brought forward I.e
during protrusion, the incisal edge of lower
anteriors slide along the slope of the lingual
surface of upper anteriors before reaching to
edge to edge contact.

The slopes of lingual surface of the upper
anterior teeth determine path along which
the mandible moves during protrusive
movement.
In other words, the lingual surfaces of
maxillary anteriors guide the mandible
during protrusive movement and is called
incisal guidance.
The angle formed between the long axis of
the upper and lower anteriors is called
incisal guide angle.

Incisal guide angle defined as the angle
formed in horizontal plane by drawing a
line in the sagittal plane between the incisal
edges of maxillary and mandibular central
incisors when the teeth are in maximum
inter cuspation-GPT7
The incisal guidance is absent in completely
edentulous patient. It is reproduced in the
complete denture by arbitrarily setting the
anteriors using starting guide value and
modifying them to suit the patient during
aesthetic anterior try in.

The anterior guidance is variable factor.
It can be altered during dental procedures
such as restoration,orthodontia and
extractions.
It can also be altered by pathologic
conditions such as caries,habits and teeth
wear.

Neuro muscular factors:
The muscles of mastication are most
important determinants of mandibular
movements.
In a normal patient,the muscle function in a
co-ordinated smooth manner.
But when there is a hypertrophy or
dysfunction of one group muscles, the
movement of mandible is uncoordinated
and asymmetrical.

Similarly tone of the muscle also
determines the freedom of movement.
Muscle dysfunction should be evaluated
before performing jaw relation.

Eccentric movements of mandibular movements/prosthodontic courses

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