Mechanics of mandibular movement/ dental implant courses

Mandibular movementsMandibular movements
 Generally they can be categorized as:
 According to function(ONTARIO UNIVERSITY)
 Functional movements
 Mastication
 Speech
 respiration
 Facial expression
 Voluntary movements
 Non functional
INDIAN DENTAL ACADEMY
Leader in continuing Dental Educationwww.indiandentalacademy.com

ACCORDING TO SHARRY:
According to direction:
 opening and closing movements
 protrusion and retrusion
 lateral gliding movements
According to tooth contact:
 movements with contact between u/l
teeth
 movements without contact between u/l
teeth
www.indiandentalacademy.com

Limitation by joint structure:
 border movements
 intra border movements
Functions of masticatory system:
 mastication
 deglutition
 respiration
 slight aimless movements of
sucking,spitting

OKESON-according to types movements
occures in T.M.J
 rotational-horizontal axis of rotation
 -vertical axis of rotation
 -sagittal axis of rotation
Translation movements
Border movements-sagittal plane
 -horizontal plane
 -vertical plane
Intra border movements

According DR.E.G.R SOLOMON CONDYLAR
MOVEMENTS may be classified as
1. Rotation- sagittal plane
 horizontal plane
 vertical
2. Translation – condylar path
a) Sagittal plane-
 sagittal protrusive condylar path
 sagittal lateral condylar path
 Horizontal plane-
 working condylar path
 non working condylar path
 -immediate side shift
 -progressive side shift


Mechanics of mandibularMechanics of mandibular
movementmovement
Mandibular movement occurs as a
complex series of inter-related three
dimensional rotational and t
translational activities.
It is determined by the combined and
simultaneous activities of both t.m.j
Although TMJs cannot function entirely
independently of each other ,they also
rarely function with identical concurrent
movements.

To better understand the complexities of
mandibular movement ,it is beneficial first
to isolate the movements that occur within a
single Tmj
Types of movement:
Two types of movements occur in the tmj
Rotational movements
Translational movements

Rotational movementsRotational movements
Def:it is the process of turning around an
axis:movement of the body about its axis.
(Dorlands medical dictionary)
In the masticatory system,rotation occures
when the mouth opens and closes around a
fixed point or axis within the condyles.
In other words,the teeth can be separated
and occluded with no positional change of
the condyles.

In the Tmj, rotation occurs as a movement
between the superior surface of the condyle
and the inferior surface of the articular disc.
Rotational movement of mandible occurs in
all three reference planes around a point
called axis. They are:
Horizontal axis of rotation:
Mandibular movement around the
horizontal axis is an opening and closing
motion.

It is referred as hinge movement and the
horizontal axis around which it occurs is
therefore referred to as the hinge axis.
The hinge movement is probably the only
example of mandibular activity in which
“pure rotational movement occurs”
Where as in all other movements rotation
accompanied by translation of the axis.
When the condyles are in their most
superior position in the mandibular fossa
and the mouth is purely rotated open:the
axis around which movement occurs is
called the terminal hinge axis.

It is also called as horizontal or transverse
axis where a pure rotation of condyles takes
place prior to translation of condyles. The
left and right centers where condyle
exhibits pure rotation is known as hinge
axis points.
Pure rotation of condyle takes place in the
first 10-13 degrees arc of mandibular
opening and closing or during initial mouth
opening of 15-20 mm.
Hinge axis is stable,reproducible and
repeatable. www.indiandentalacademy.com

 Value of hinge axis:
 Allows the centric relation record in dentulous
situations to be accurately mounted on articulator
with the use of inter occlusal record.
 It is the starting point of lateral movements.
 Allows the transfer of the opening axis to the
articulator so that occlusion would be same arc of
closure as the lower jaw.
 Opening and closing movements of the mandible
are reproduced in the articulator because the
opening axis of articulator is coincident with the
hinge axis patient.therefore teeth contact each
other in the articulator exactly as they do in the
mouth.

Frontal(vertical) axis of rotation:
Mandibular movement around the frontal
axis occurs when one condyle moves
anteriorly out of the terminal hinge position
with the frontal axis of the opposite
condyle remaining in the terminal hinge
position.
Because of the inclination of articular
eminence,which dictates that the frontal
axis tilt as the moving or orbiting condyle
travels anteriorly, this type of isolated
movement does not occur naturally.

Sagittal axis of rotation:
Mandibular movement around the sagittal
axis occurs when one condyle moves
inferiorly while others remain in the
terminal hinge position.

 Translational movement:
 Def:it is a movement in which every point of the
moving object has simultaneously the same
velocity and direction.
 In the masticatory system,it cccurs when the
mandible moves forward as in protrusion.
 The teeth.condyles and rami in the same direction
and to same degree.
 It occurs within the superior cavity of the joint
between the superior surface of articular disc and
the inferior surface of the mandibular fossa.
(between the condyle-disc complex and the
mandibular fossa)

During most normal movements of the
mandible,both rotation and translation occur
simultaneously I.e while the mandible is
rotating around one or more of the axis
,each of the axis is translating.

Border movements:
Mandibular movements takes place within
the certain three dimensional limits.
The mandible move about 10mm
laterally,open about 50-60mm,protrude
approximately 9mm and retrude about
1mm.
It was these limits that POSSELT described
in 1952 which are called as border
movements.

Border movements are the most extreme
positions to which the jaw is able to move.
They can be defined as mandibular
movements at the limits dictated by
anatomic structures as viewed in the given
plane(GPT-7)
A tracing of these borders is made by
moving the mandible along its most
extreme range of positions.
These positions are generally considered to
be relatively stable and reproducible.

Mandibular movement is limited by the
ligaments and the articular surfaces of the
tmjs.as well as by the morphology and
alignment of the teeth.
Boder movements can be recorded and
described in 3 referrence planes,
Sagittal
Horizontal
frontal

 Sagittal plane border movements and functional
movements:
 In this plane a characteristic “beak tracing” is
formed while tracing.
 In sagittal plane the mandibular movements has
four components.
 Posterior opening border-determined by
ligaments.
 Anterior opening border-T.M.J morphology
 Superior contact border-occlusal and incisal
surface
 Functional-determined by neuromuscular system.

Posterior opening border movements:
It occurs as two stage hinging movements.
In the first stage the condyles are stabilized in
their most superior positions in the
mandibular fossae(terminal hinge position)
The most superior condylar position from
which a hinge axis movement can occur is the
centric relation position or retruded contact
position or terminal hinge axis.
The mandible can be lowered (mouth
opening) a pure rotational movement without
translation of the condyles.

In centric relation the mandible rotated
around the horizontal axis to a distance of
only 20-25 mm as measured between the
incisal edges of maxillary and mandibular
teeth.
At this point of opening the Tmligaments
tighten.after which continued opening
results in an anterior and inferior translation
of condyles.

As the condyles translate,the axis of
rotation of the mandible shifts to the bodies
of rami,and results in 2nd
stage of posterior
opening border.
The exact location of the axis of rotation in
the rami is likely to be the area of
attachment of spheno mandibuar ligaments.
During this stage,in which the mandible is
rotating around a horizontal axis passing
through the rami,the condyles are moving
anteriorly and inferiorly and anterior
portion of mandible is moving posterioly
and inferiorly.

Maximum opening is reached when the
capsular ligaments prevent further
movement at the condyles.
Maximum opening is in the range of 40-
60mm when measured between the incisal
edges of maxillary and mandibular teeth.

Anterior opening border movements:
When the mandible is maximally
opened,closure accompanied by contraction
of inferior lateral pterygoid muscles(which
keep the condyles positioned
anteriorly)generates the anterior opening
border movement.
Theoretically,if the condyles were stabilized
in this anterior position,a pure hinge
movement could occur while the mandible
was closing from maximally opened to the
maximally closed protruded position.

Since the maximum protrusive position is
determined in part by the stylomandibular
ligaments,tightening of the ligaments as
closure occurs produces a posterior
movement of the condyles.Condylar
position is most anterior in the maximally
opened position but not the maximally
protruded position.
The posterior movement of condyle from
the maximally open position to the
maximally protruded position produces
eccentricity in the anterior border
movement.

Superior contact border movements:
This entire movement is determined by
tooth contact.Throughout this entire
movement,tooth contact is present.Its
precise delineation depends upon
1.The amount of variation between centric
relation and maximum intercuspation
2.The steepness of cuspal inclines of
posterior teeth.
3.The amount of horizontal and vertical
overlap of anterior teeth.
4.The lingual morphology of anterior teeth.
5.General inter arch relationships of teeth.www.indiandentalacademy.com

In the centric relation position ,tooth
contacts are normally found on one or more
opposing pairs of posterior teeth.The initial
tooth contact in terminal hinge
closure(centric relation)occurs between the
mesial inclines of a maxillary tooth and the
distal inclines of a mandibular tooth.
When muscular force is applied to the
mandible,a superio-anterior movement or
shift results until the intercuspal position is
reached.
Additionally this centric-to-maximum
intercuspal position may have lateral
component. www.indiandentalacademy.com

This slide is seen in 90% populatin and
average distance is 1.25 -+
1mm
In intercuspal position the opposing anterior
teeth actually contact.
When the mandible is protruded from
maximum intercuspal position,contact
between the incisaledges of mandibular
anterior teeth and the lingual inclines of
maxillary anterior teeth results in an
anteroinferior movement of the
mandible.This continues as until the
maxillary and mandibular anterior teeth are
in edge-to-edge relationship at which
horizontal pathway is noted.

At this stage complete disocclusion or
separation of posterior teeth occurs.This
characteristic pattern of separation seen
during anterior protrusion is called
CHRISTENSON’S PHENOMENON
The horizontal movement continues until
the incisal edges of mandibular teeth pass
beyond incisal edges of maxillary teeth.
At this point the mandible moves in a
superior direction until the posterior teeth
contact.

At this stage the mandible moves in a
superior direction till 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 position of the
anterior opening border movements.
Since this border movement is solely tooth
determined,changes in the teeth will result
in changes in nature of border movement.

Functional movements:
They occur during functional activity of the
mandible.
They occur within the border movements
-therefore called as intra border movements
and also free movements.
Most functional activities require maximum
intercuspation and therefore typically begin
at and below the intercuspal position.
When the mandible is at rest,it is found to
be located approximately 2-4mm below the
intercuspal position which has been called
the clinical rest position –this position is
quite variable www.indiandentalacademy.com

At this point the force of gravity pulling the
mandible down is in equilibrium with the
elasticity and resistance to stretching of the
elevator muscles and other soft tissues
supporting the mandible.,Thus this position
is bet described as clinical rest position.
In this position teeth an be quickly and
effectively brought together for immediate
function.
Increased levels of EMG muscle activity in
this position are indicative of myotatic
reflex.Since this is not a true resting
position,the position in which the mandible
is maintained is more appropriately termed
‘postural position’.www.indiandentalacademy.com

If the chewing stroke is examined in the
capital plane,the movement is seen to begin
at the intercuspal position and deep
downward and slightly forward to the
position of desired opening.
Postural Effects on Functional Movement:
When the head is erect and the and in
upright position,-postural position of
mandible is located 2-4mm below ICP.
If elevator muscles contract,the
mandible is elevated directly into the
intercuspal position.www.indiandentalacademy.com

 If the face is directed 45o
upward-postural position
of mandible is altered to a slightly retruded
position.This change is related to the stretching
and elongation of other tissues that are attached to,
and support the jaw
 Tooth contact occurs posterior to intercuspal
position
 Assumed during drinking
 Normal head position during eating is with face
directed 30o
downward-called alert feeding
position
 Mandible shifts anterior to upright postural
position
 Path of closure is anterior to intercuspal position
 Significant in considering functional relationships
of teeth. www.indiandentalacademy.com

HORIZONTAL PLANE BORDER ANDHORIZONTAL PLANE BORDER AND
FUNCTIONAL MOVEMENTSFUNCTIONAL MOVEMENTS
Traditionally Gothic Arch Tracer(Gysi-
1910)is used to record mandibular
movement in horizontal plane.
It consists of a recording plate attached to
the maxillary teeth and recording stylus
attached to the mandibular teeth.
As mandible moves stylus generates a line
on the recording table that coincides with
the movement.
When mandibular movement is observed in
the horizontal plane,a rhomboid shaped
pattern can be seen.www.indiandentalacademy.com

It has four distinct components and a
functional component:
1.left lateral border
2.continued left lateral with protrusion
3.right lateral border
4.right lateral with protrusion

Left lateral border:
 With the condyles in centric relation, contraction
of the right inferior lateral pterygoid muscle
causes the right condyle to move anteriorly and
medially.(also inferiorly).If the left inferior lateral
pterygoid stays relaxed,the left condyle remains
situated in centric relation and the result is a left
lateral border movement(right condyle orbiting
around the frontal axis of left condyle)
 The left condyle is called rotating condyle(since
mandible is rotating around it)and also called
working condyle since it is on working side or
laterotrusive condyle

The right condyle is called orbiting condyle
since it is orbiting around the rotating
condyle.Also called as nonworking condyle
since it is located on nonworking side.Also
called balancing or mediotrusive condyle
During this movement,the stylus generates a
line on the recording side plate that
coincides with left bordre movement

Continued left lateral border movements with
protrusion:
With the mandible in the left lateral border
position,contraction of the left inferior
lateral pterygoid muscle along with
continued contraction of the right inferior
lateral pterygoid musclecauses left condyle
to move anteriorly and to the right.since the
right condyle is already in its maximum
anterior position,the movement of condyle
to its maximum anterior position causes a
shift in the mandibular midline back to
coincide with the midline of facewww.indiandentalacademy.com

Right lateral border movements
 Once the left lateral border movements have been
recorded on the tracing,mandible is returned to
centric relation and right lateral movements are
made.
 Contraction of the left inferior lateral pterygoid
muscle causes left condyle to move anteriorly and
medially (also inferiorly)
 If the right inferior lateral pterygoid stays
relaxed,the right condyle remains situated in
centric relation
 The resultant mandibular movement is a right
lateral border movement(eg. Left condyle orbiting
around frontal axis of right condyle)

Here-left condyle-orbiting codyle-
nonworking condyle
Right condyle-rotating condyle-working
condyle
During this movement the stylus generates a
line on the recording plate that coincides
with the right lateral movement

 Continued right lateral with protrusion:
 With the mandible in right lateral
position,contraction of the right inferior lateral
pterygoid muscle along with continued contraction
of the left inferior lateral pterygoid muscle causes
the right condyle to move anteriorlyand to left.
 Since the left condyle is already in its maximum
anterior position,the movement of right condyle to
its maximum anterior position causes ashift back
in the midline to coincide with the midline of the
face.
 This completes the mandibular movement in the
horizontal plane.

 Functional movements:
 As in the sagittal plane, functional movement in
the horizontal plane most often occur near the
inter cuspal position.
 During chewing the range of jaw movement
begins some distance from maximum inter cuspal
position,but as the food is broken into smaller
particle sizes,jaw action moves closer and closer
to the intercuspal postion.
 The exact position of the mandible during
chewing is dictated by the existing occlusal
configuration .

 Frontal border and functional movements:
 When the mandibular motion is viewed in the
frontal plane, a “shield –shaped ”pattern can be
seen that has four distinct movement component
along with functional component.
 Left lateral superior border
 Left lateral opening border
 Right lateral superior border
 Right lateral opening border
 The movements in this plane have not been
traditionally traced,an understanding of them is
useful in visualizing mandibular activity in thre
dimensionally.

Left lateral superior border movements:
With the mandible in maximum inter
cuspation, a lateral movement is made to
left.
A recording device discloses an inferiorly
concave path being generated.
The precise nature of this path is primarily
determined by the morphology and inter
arch relation ships of the maxillary and
mandibular teeth that are in contact during
this movement.

Secondary influence are the condyle-disc-
fossa relationships and morphology of the
T.M.Jon the working or rotating side.
The maximum lateral extent of this
movement is determined by the ligaments
of the rotating joint.

Left lateral opening border movement:
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 in the mandibular midline to coincide
with the midline of the face.

Right lateral superior border:
Once the left frontal border movements are
recorded,the mandible is returned to
maximum inter cuspation.
From this position,a lateral movement is
made to right that is similar to left lateral
superior border movement.

Right lateral opening border movements:
From the maximum right lateral border
position, an opening movement of the
mandible produces a laterally convex path
similar to that of the left opening
movement.
As maximum opening is
approached,ligaments tighten and produce a
medially directed movement that causes
shift back in midline to coincide with the
midline of the face to end this movement.

Functional movements:
As in the other planes,functional
movements in the frontal plane begin and
end at the inter cuspal position.
During chewing,the mandible drops directly
inferiorly until the desired opening is
achieved.
It then shifts to the side on which the bolus
is placed and rises up.
As it approaches the maximum inter
cuspation, bolus is broken down between
the opposing teeth.

Envelope of motion:
By combining mandibular border
movements in the three
planes(sagittal,horizontal and frontal), a
three dimensional envelope of motion can
be produced that represents the maximum
range of movement of the mandible.
It was first described by POSSELT in
1952.
Although the envelope has this
characteristic shape, differences are found
from person to person.

Superior surface of envelope is determined
by tooth contacts,where as other borders are
primarily determined by ligaments and joint
anatomy that restrict or limit movement.

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 action during protrusive
movement.

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 condyle
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.

 BENNET MOVEMENT:
 Bennet-1908 studied the working condylar path &
called it BENNET MOVEMENT, now
reffered as laterotrusion.
Bennet movement reffers 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(acroos
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.this
movement component is called 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 orbiting condylar path & the
saggital plane . It varies from 2-44degrees,
with a mean value of 16 degrees .

 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
-

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 protrusoive
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 arbitarily 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,orthodontiaand
extractions.
It can also be altered by pathologic
conditions such as caries,habits and teeth
wear.

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

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.

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.

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-post
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

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