Muscles of mastication and mandibular movements/dental courses

MUSCLES OF MASTICATION
AND
MANDIBULAR MOVEMENTS.
INDIAN DENTAL ACADEMYINDIAN DENTAL ACADEMY
Leader in continuing Dental EducationLeader in continuing Dental Education
www.indiandentalacademy.com

TABLE OF CONTENTS
• INTRODUCTION
• REVIEW OF LITERATURE
• DEVELOPMENT OF MUSCLES OF
MASTICATION
• ANATOMY OF MUSCLES
• GENERAL MECHANISM OF MUSCLE
CONTRACTION
• MUSCLES OF MASTICATION
• TEMPOROMANDIBULAR JOINT
• TYPES OF MANDIBULAR MOVEMENTSwww.indiandentalacademy.com

• ROTATION ALONG:
-TRANSVERSE AXIS
-SAGITTAL AXIS
-VERTICAL AXIS
• PROTRUSIVE MOVEMENTS
• RETRUSIVE MOVEMENTS
• LATERAL MOVEMENTS –BENNETT
MOVEMENT
• BORDER MOVEMENTS
• FUNCTIONAL MOVEMENTS
• MASTICATION
• SWALLOWING
• SPEECH

• OCCLUSAL MORPHOLOGY AND
MANDIBULAR MOVEMENTS
• NEUROMUSCULAR REGULATION
• CLINICAL SIGNIFICANCE
• SUMMARY
• CONCLUSION
• REFERENCES

INTRODUCTION
One of the functions of the masticatory system
is to prepare food for swallowing by crushing
it into small pieces to be moistened with
saliva. The degree of fragmentation of the
food particles depends on factors like the
chewing force generated by the closer
muscles, the jaw movement, and the
morphological aspects of the teeth. The jaw
movement is the result of a precise
neuromuscular control of the various chewing
muscles.

• The primary muscles of mastication
include the paired masseter, temporalis,
medial and lateral pterygoids.

– MUSCLE (GPT 8): An organ that by
contraction produces movements of an
animal; a tissue composed of contractile
cells or fibres that effect movement of an
organ or part of the body.
– MASTICATION (GPT 8): the process of
chewing food for swallowing and digestion.

- MASTICATORY MUSCLE (GPT 8):
Muscles that elevate the mandible to close
the mouth (temporalis m., superficial and
deep masseter m., medial pterygoid m.)
– MANDIBULAR MOVEMENTS (GPT 8): any
movement in lower jaw

• BORDER MOVEMENT (GPT 8) –
mandibular movement at the limits
dictated by anatomic structures, as
viewed in a given plane

REVIEW OF LITERATURE

Joseph R. Jarabak
J Prosthet Dent (1956)
Muscular behavior in mandibular movements
in subjects wearing dentures were studied
electromyographically.

• It was found that correct vertical dimension of
occlusion coupled with an adequate
interocclusal distance between the teeth of
upper and lower denture is essential to
maintain the muscles of mastication at there
most efficient functional length.
• when vertical over closure was obtained,
there was loss of muscle tension which
frequently caused spontaneous hyperactivity.
When vertical dimension was excessive
muscle tension increased.

Woelfel et al
• They investigated the function of External
Pterygoid muscle during mandibular hinge
axis opening by means of EMG. It was found
that the electrical activity of external pterygoid
muscle does not increase during the hinge
opening movement.
• The suprahyoid muscles aided by the post.
fibers of temporalis muscle maintain the
retruded position of the mandible.www.indiandentalacademy.com

Hickey et al
• In this study 3 identical dentures were
constructed and various food stuffs
masticated by the patient while
electromyographic tracings were made.

• It was concluded that ext. pterygoid and
suprahyoid muscles were responsible for
uncontrolled opening movement while
masseter and temporal muscles for closing
movement
• Both external pterygoid muscles were
responsible for the protrusion of mandible

Bennett
• It was stated that there is no one centre of
rotation for the mandibular movement, but the
centre is constantly shifting .
• It starts at a point behind and below the
condyle , travels backwards and downwards
then forwards finally upwards and forwards,
finishing at a point little below the condyle
path.

Garnick et al
• This study evaluated electro -myographically
some elevator and depressor group of
muscles in relation to conventional rest
position and to test electromyographically the
concept of a well defined rest position
associated with minimal activity of muscles.
• It was concluded that a resting range rather
than a well defined mandibular rest position
existed.

• Average combined and concurrent resting
range for temporal masseter and anterior part
of the digastric was 11.1 mm.
• Resting activity of the jaw muscles or tonus is
not entirely dependent on stretch reflex of the
muscle. This activity is also dependent upon
gamma efferent system as influenced by
CNS and peripheral impulses from, for
instances, occlusal disharmony of the teeth.

Brill et al
• One complete upper and two complete lower
dentures, one of which accommodated
maximal occlusion with mandible in the
muscular position, and other accommodated
maximal occlusion with the mandible in a
protruded position .

• It was shown that the movement pattern of
mandible can change to accommodate the
protruded occlusal position.

Shanahan and Leff
J Prosthet Dent (1963 )
• The theory that the mandible rotates about
vertical axis in the region of condyles during
lateral movements was investigated using
central bearing plates .

• They concluded that use of a central bearing
point produces unnatural influences upon the
lateral movements of the mandible.
• The direction and character of lateral
movements made with a central bearing point
in mouth are entirely different from those
movements made under normal conditions
such as lateral movements made with the
teeth in contact.

Atwood
J Prosthet Dent (1966 )
• He supported the concept that the postural
position of mandible is not a single absolute
position but a range of positions.

Gibbs et al
• They studied jaw motion and maxillo-
mandibular relation during chewing.
• Starting from the closed position ,a typical
motion of mandible was summarized as
follows

• Both condyles begin the opening immediately
downward and forward .
• Early in the closing stroke ,the entire
mandible moves laterally.
• The working side condyle moves upward and
rearward and reaches its terminal position at
the most vertical rearward position before the
teeth approach each other far enough to
intercuspate.

• The working side condyle appears to be
nearly stationary in the sagittal view for the
remaining part of the closing stroke , which is
termed the Working Functional Movement .
During WFM ,the working side condyle moves
medially to its closing position ,while the
nonworking side condyle goes upward and
laterally to its closed position .

D. C. McNamara et al
• A cephalometric- elecromyographic method
was used to analyze the tooth contacts in
centric occlusion and at terminal hinge
contact and to correlate the neuromuscular
activity of masseter and temporalis muscles
at these positions.

• They found that a positional difference
between the centric occlusion and centric
relation was present in all subjects.
• However, the masseter and temporalis
muscle activity during maximal isometric
contraction did not differ significantly at these
two positions.

Gibbs et al
• They studied mandibular border movements
to determine the average movement pathway
of 163 subjects. It was found Bennett
movement of 2.5 to 3.5 mm caused a
dramatic flattening of lateral movement
pathways of molar cusp as seen in frontal
plane.

• When viewed in horizontal plane excessive
Bennett movement contributed to the greatest
potential for collision of molar cusps during
lateral movements. This was more
pronounced on non working side.

Tupac
• 136 dentulous were divided in 3 groups for
the purpose of quantitative pantographic
comparison of voluntary and induced Bennett
movements.

• Conclusion was-
Inducing Bennett movements has a greater
effect on immediate side shift component
than it has on the progressive side shift
component.
• For older individuals the amount and direction
of induced immediate side shift is greater
than for younger patients.

Arturo Manns et al
• The relation between EMG activity, bite force,
and muscular elongation was studied in 8
subjects with complete natural dentition
during isometric contractions of the masseter
muscle, measured from 7mm to almost max.
jaw opening.

• The results showed that for each subject, a
physiologically optimum muscular elongation
of major efficiency, where the masseter
develops highest muscular force with least
EMG activity, was present.

Ingervall B et al
• An electromyographic study was done to
determine the difference in muscle activity of
patients with complete dentures and those
with natural dentition.

• They found that the postural muscle activity
was the same with old and new dentures and
comparable with that in patients in natural
dentition.
• The muscle activity during max. biting was
markedly lower than in patients with natural
dentition.

Mahan et al
• Did a study to record simultaneous EMG
activity in the right SLP and ILP and to
determine the response of each belly of the
muscle during clenching of the teeth and at
basic mandibular positions.

• They found that EMG activities of superior
and inferior lateral pterygoid were nearly
reciprocal during vertical and horizontal
movements of mandible and when the teeth
were clenched in retruded contacts.

Williamson E.H. et al
• The purpose of this study was to determine
the effect of two occlusal schemes on the
temporal and masseter muscles.

• They found that only when posterior
disclusion was obtained by an appropriate
anterior guidance could the elevating activity
of masseter muscles be reduced.
• Further elimination of posterior contacts
decreases the activity of the elevator
muscles.

Gibbs et al
• They described the activities of SLP and ILP
in relation to masseter, temporalis, anterior
belly of digastric and medial pterygoid
muscles during some basic jaw movements
and positions.

• They found that anterior fibers of temporal
muscles are active in elevating the
mandibular condyles and mandible during
clenching .
• Anterior belly of digastric muscle depresses
and retrudes the mandible. Activity of the
elevating superficial fibers of the masseter
and medial pterygoid muscles is greatly
reduced in retruded contact position.

Kapur K.K. et al
• Did a study to determine the influence of
muscle activity on masticatory performance
and salivary secretion rates by comparing the
masseter muscle activity of denture wearers
with that of subjects with natural dentition.

• They found that the reduced muscle force
applied by denture wearers is an important
factor contributing to the diminished chewing
ability.
• Mucosal stimulation of dentures compensates
for decreased muscle activity.

William w wood
• In this study EMG activity of medial pterygoid,
masseter, anterior and posterior muscles
were recorded simultaneously with 3
dimensional incisor point movement of the
mandible.

• Patterns of medial pterygoid muscle activity
were consistent for ipsilateral chewing and
demonstrated activity of the muscle on the
chewing side that peaked near the onset of
intercuspation.
• The muscle on the contra lateral side was
active at the onset of intercuspation for
subjects with a chopping stroke and inactive
for those with a more lateral stroke guided in
to intercuspation on cuspal inclines.

• Activity in the early part of the closing phase
was associated with a marked jaw movement
towards the chewing cycle.

U. C.BELSER et al
• Did a study to describe the functional
behavior in the deep fibers of the masseter
muscle and to define any differences in its
behavior from that of the superficial fibers.
• During chewing, activity in the deep fibers
was distributed evenly bilaterally, and in
superficial fibers was biased significantly
toward the chewing side.

William W Wood
According to this article-
• Elevator muscles demonstrate maximum
activity when even bilateral occlusal contacts
occur during clenching in the intercuspal
position.

• The elevator muscles are activated together
in the intercuspal zone of the tooth contact
during chewing when the occlusal contacts
are balanced bilaterally in this intercuspal
position .
• Increasing the number of eccentric tooth
contacts increases the muscle activity in both
during chewing and clenching.

• Action of medial pterygoid is enhanced during
laterally directed chewing actions of the
mandible.
• Inferior head of lateral pterygoid has
reciprocal role with the medial pterygoid
muscle during chewing and contributes to
forward and lateral bracing of the condyle of
the mandible.

T. M. Wilkinson
• Did a study to assess the nature of the
insertion of both heads of the lateral pterygoid
muscle and nature of the attachment of the
inferior surface of the anterior part of the disk
to superior head of this muscle.

• The major insertion of the superior head of
the lateral pterygoid is to the condyle at the
pterygoid fovea.
• The anterior part of the disk blends with the
capsule and provides a mechanism by which
the foot is attached to the roof of the superior
head of the lateral pterygoid muscle

M.Th.Verkindere, J.Ph.Lodter
• Did a study to compare the silent period
duration in patients with natural dentitions
and in partial denture wearers.

• Concluded that the duration of the silent
period is the same for prosthesis- wearing
patients and with natural dentition.
• Suggested that wearing a prosthesis does not
change the normal activity of the masticatory
muscles.

Goldenberg et al
• In study it was concluded that loss of
occlusion has no effect on the increase in the
amount of mandibular immediate side shift.

Kang et al
• They measured range of mandibular
movements in frontal sagittal and horizontal
planes. Deviation of movements and angles
between planes and path of movements were
also measured.

• They suggested that the mandibular
movement could be evaluated more
comprehensively with these additional
measurements

Thomas R. Katona
• Study showed that mandibular rotation during
protrusion was the function of incisior and
condylar guidance, initial mandibular
angulation, mandibular size and the extent of
excursion.

Ferrario et al
Int J Prosthodont (1992)
• They found that males have a significantly
greater mean value of vertical rest position
than do females. There is no gender
difference in mean value of maximum
opening.

• Occlusal position during swallowing coincides
with or was very near to the intercuspal
position in most subjects.

Theusner
• In this study, tracings displayed in sagittal
and frontal planes were measured to evaluate
biomechanics of TMJ in between
symptomatic and asymptomatic groups.

• The symptomatic group had a significantly
longer condylar path and a smaller Bennett
angle compared with asymptomatic group.

Neal R. Garrett et al
• Did a study to test the null hypothesis that the
masseter muscle activity and biting forces
exerted during chewing do not differ between
denture wearers with superior and poor
masticatory performance.

• Concluded that application of more equivalent
force by the right and left masseter muscles
during unilateral chewing is consistent with
improved chewing ability in denture wearers.

Kazuya yoshida
J Prosthet Dent 1998
• Did a study to examine the effect of the
device on sleep apnea, and masticatory and
tongue muscles.
• Concluded that the apnea appliance activated
masticatory and tongue muscles during sleep
and prevented the upper airway from
collapsing.

Udo stratmann et al
• Did a study to assess the feasibility of the ILP
muscle palpation by a simulated clinical
setting.
• Concluded that it is nearly impossible to
palpate the ILP muscle anatomically.

• High frequency of false- positive results was
presumed to be due to palpation of the
medial pterygoid muscle.

Wilson et al
J Prosthet Dent ( 2000)
• They estimated the posterior displacement
that takes place at the mandibular condyles
and occlusal surfaces when the mandible is
moved from maximal intercuspal position to
the most retruded mandibular position.

• They concluded that when the mandible is
moved from maximal intercuspal position to
retruded condyle position any shift at occlusal
surface or the condyles is very small if
interfering contacts on the retruded path of
closure have been eliminated.

Ferrario V.F.
Clin Oral Implants Res (2004)
• Did a study to compare the
electromyographic characteristics of
masticatory muscles in patients with fixed
implant-supported prostheses and implant
overdentures.

• CONCLUDED that surface EMG analysis of
clenching and chewing showed that fixed
implant-supported prostheses and implant
overdentures were functionally equivalent.
• Neuromuscular coordination during
chewing was inferior to that found in
subjects with natural dentition.

Alajbeg IZ et al
J Oral Rehabil (2006)
• Did a study to determine the muscle activity
at various mandibular positions is affected by
age and dental status.

• There was a significant differences in muscle
activity in dentate subjects of different age
were found in protrusion for depressor
muscle and in lateral excursive positions for
the working side temporal and non-working
side masseter and depressor muscle.
• There was a significant effect regarding the
presence of natural teeth or complete
dentures in protrusion and maximal
protrusion for all muscles.

DEVEOPMENT OF MUSCLES OF
MASTICATION
• The muscular system develops from intra
embryonic mesoderm
• Muscle tissues develop from embryonic cells
called myoblast.
• Muscular component of Branchial arch form
many striated muscles in the head and neck
region.
• Muscles of mastication are derived from first
brachial arch that is the MANDIBULAR ARCH.

LATERAL VIEW OF A FOUR WEEK EMBRYO SHOWING
MUSCLES DERIVED FROM BRANCHIAL ARCHES

TYPES OF MUSCLES
• Muscle cells are mainly of two types
1. STRIATED MUSCLE
a. SKELETAL OR VOLUNTARY
b. CARDIAC MUSCLE
2. NON-STRIATED, SMOOTH OR
INVOLUNTARY

• Units of skeletal muscle are the muscle
fibers, each of which act as a single cell
having hundreds of nuclei (syncytial
striated myocytes).
• Fibers are arranged in bundles of various
sizes and pattern called fasciculi.
• Connective tissue fills the spaces between
muscle fibres within a fasciculus where it is
known as the endomyscium.
SKELETAL MUSCLE

• Each fasciculus is also surrounded by a strong
connective tissue sheath or perimysciun.
• Surrounding the whole muscle lies epimyscium.
• Cell membrane of muscle fibre is known as
sarcolemma while their cytoplasm is called
sarcoplasm.
• Sarcoplasm is divided into longitudinal threads or
myofibrils each of 1 µm in diameter.
• Each muscle fiber consists of several hundred to
several thousand myofibrilswww.indiandentalacademy.com

GENERAL MECHANISM OF
MUSCLE CONTRACTION
SLIDING FILAMENT MECHANISM.
• Caused by interaction of cross bridges from myosin
filament with the actin filament.
• Action potential causes sarcoplasmic reticulum to
causes release of calcium ion.
• Calcium ion combines with troponin c of troponin
tropomyosin complex causing a confirmational
change. And it moves deeper between two actin
strands.

• This uncovers the active sites of actin allowing
these to attract the myosin head and cause
contraction to proceed.

Interaction Between The ‘Activated’ Actin
Filament And the Myosin Bridges-The ‘Walk
Along Theory’ of contraction
• When myosin head attaches to a active site,
it causes the head to tilt towards the arm
and drag the actin filament along with it,
• This tilt of the head is called Power stroke.
• After tilting head automatically breaks away
from the active site
• Next, it returns to the perpendicular position
and combines with a new active site farther
down along the actin filament.
• Thus the heads of myosin filament bend
back and forth and walk along the actin
filament.

ACTIN AND MYOSIN
FILAMENT

MUSCLE FUNCTION
The motor unit can carry only one action i.e.
contraction or shortening, the entire
muscle, however has three potential
function.

A) ISOTONIC CONTRACTION
• When the muscle shorten and moves a
load, the contraction is isotonic. Hence
the load remains constant and equal to
the muscle tension throughout the most
of the period of contraction. It occurs in
the masseter, when the mandible is
elevated forcing the teeth through a
bolus of food.

B) ISOMETRIC CONTRACTION
• When a muscle does not shorter and
length remains same (iso- same, metry-
length), but develops tension, the
contraction is isometric. Such type of
contraction occurs when muscle attempts
to move a load that is greater than the
tension developed in muscles, this occurs
in masseter when an object is held
between the teeth. eg. Pipe or pencil.

C) CONTRACTION RELAXATION
• When stimulation of the motor unit is
discontinued the fibres of motor unit relax
and return to their normal length. This is
seen in masseter when the mouth opens
to accept new bolus of food during
mastication.

PRIMARY MUSCLES OF
MASTICATION
• MASSETER
• TEMPORALIS
• MEDIAL PTERYGOID
• LATERAL PTERYGOIDS

SECONDARY MUSCLES OF
MASTICATION
1.The suprahyoid group of muscles being
used as secondary or supplementary
muscles they are
• Digastric
• Mylohyoid
• Geniohyoid
2. Buccinator

THE MASSETER
• Quadrilateral and consist
of three layers.
• Superficial Layer: Arises by
thick aponeurosis. From
zygomatic process of maxilla
and anterior 2/3 of lower
border of zygomatic arch, pass
downward and backwards at
an angle of 45degree and
inserted into lower part of
lateral surface of ramus of
mandible

• Middle layer: Arises from anterior
2/3 of the deep surface and
posterior 1/3 of the lower border
of the zygomatic arch, pass
vertically downwards and
inserted into middle part of
ramus.
• Deep layer: Arises from
deep surface of the zygomatic
arch, pass vertically
downwards and inserted
into the upper part of the
ramus and into the coronoid
process.

Nerve supply:
• MASSETRIC
NERVE, a branch of
anterior division of
mandibular nerve
(which is the 3rd part
of V cranial nerve-
trigeminal nerve).
Blood supply:
• Maxillary artery,
which is a branch of
external carotid artery.

ACTIONS OF MASSETER
• Elevates the mandible to close the mouth and
to occlude the teeth in mastication.
• Its activity in the resting position is minimal.
• It has a small effect in side-to-side
movement, protraction and retraction.

THE TEMPORALIS
• Fan shaped muscle
• Arises from whole of
temporal Fossa
• Fibers converge and
into a tendon .
• Attached to medial surface, apex, anterior and
posterior border of coronoid process and anterior
border of the ramus of the mandible as far as last
molar. www.indiandentalacademy.com

BLOOD SUPPLY :
• Deep temporal part of maxillary artery
NERVE SUPPLY :
• Temporalis is supplied by the deep
temporal branches of the anterior trunk
of mandibular nerve.

ACTIONS OF TEMPORALIS
• Elevates the mandible, this movement
requires both the upward pull of anterior
fibers and backward pull of the posterior
fibers.
• Posterior fibers draw the mandible backwards
after it has been protruded.
• It is also a contributor to side to side grinding
movement.

ELEVATION OF MANDIBLE

POSTERIOR FIBER DRAWS
MANDIBLE BACKWARDS

SIDE TO SIDE GRINDING
MOVEMENT

LATERAL PTERYGOID
ATTACHMENTS
It is a short thick muscle with
two parts or head
• UPPER head arise from infratemporal surface
and infratemporal crest of greater wing of
sphenoid bone
• LOWER head arise from lateral surface of
lateral pterygoid plate.www.indiandentalacademy.com

• Its fibers pass backwards and laterally to be
inserted into a depression(pterygoid fovea) on
the front of the neck of the mandible and into
the articular capsule and disc of the
temporomandibular articulation.

NERVE SUPPLY :
• The lateral pterygoid
is supplied by a
branch of anterior
division of the
mandibular nerve

BLOOD SUPPLY:
• Pterygoid branch of
2nd part of maxillary
artery

ACTIONS OF LATERAL
PTERYGOID
• Assists in opening the mouth with suprahyoid
muscle.
• Acting with medial pterygoid of same side
advances the condyle ,while the jaw rotates
through the opposite condyle (when the
medial and lateral pterygoid of the two sides
contract alternatively to produce side to side
movements of mandible eg chewing).

The combined efforts of the digastrics
and lateral pterygoids provide for
natural jaw opening.

Medial and lateral pterygoid act
together to protrude the mandible

MEDIAL PTERYGOID
• It is a thick quadrilateral muscle
• Attached to medial surface of lateral
pterygoid plate and grooved surface of
pyramidal process of the palatine bone.
• A more superficial slip from the lateral surface
of pyramidal process of the palatine bone and
tuberosity of maxilla
• Its fibers pass downwards laterally and
backwards www.indiandentalacademy.com

• Attached by a strong tendinous lamina ,to the
postero-inferior part of the medial surfaces of
the ramus and the angle of the mandible
• It is attached as high as mandibular foramen
and as far forward as the mylohyoid groove

NERVE SUPPLY :
• Branch of the main
trunk of the
mandibular nerve.
BLOOD SUPPLY :
• Pterygoid branch of
2nd part of maxillary
artery.

Actions of medial pterygoid
• Assits in elevating the mandible

Acting with the lateral pterygoid they protrude
the mandible.

• Acting with medial pterygoid of same side
advances the condyle ,while the jaw rotates
through the opposite condyle (when the
medial and lateral pterygoid of the two sides
contract alternatively to produce side to side
movements of mandible eg chewing)

SECONDARY MUSCLES TAKING
PART IN THE MASTICATION
The 4 primary muscles of mastication are in
turn supported or supplemented by few
secondary muscles
1. SUPRAHYOID GROUP of muscles that
include:
• DIGASTRIC
• MYLOHYOID
• GENIOHYOID
• STYLOHYOID (does not take part in
mastication)
2. BUCCINATOR

• It consists of 2 parts: anterior and posterior
connected by a round tendon.
• The posterior part arises from mastoid notch.
• The anterior part attaches to the lower border
of the mandible at the midline.
• The intermediate tendon is attached to the
hyoid bone.
DIGASTRIC

• NERVE SUPPLY:
Posterior part: branch of facial nerve
Anterior part: branch of mylohyoid n., branch of
mandibular division of trigeminal nerve.

Actions of digastric
• Both the parts of the muscle
are active during jaw opening
and demonstrate moderate to
marked activity during
protrusion, retrusion and
lateral movements.
• The muscle has secondary
role in mastication as a
depressor muscle adding to
the action of lateral pterygoid
muscle when mouth is to be
opened against resistance.
• Elevation of hyoid bone

MYLOHYOID
• Flat, triangular muscle lying deep to the
anterior belly of digastric.
• Forms the floor of the mouth.
• Arises from the mylohyoid line on the medial
aspect of the mandible. Runs medially and
downwards.

• Posterior fibres insert into body of hyoid bone.
Middle and anterior fibres insert into medial
raphae uniting the muscles of both sides.

• NERVE SUPPLY:
Mylohyoid nerve, branch of mandibular division
of trigeminal nerve.

Actions of mylohyoid
• The secondary role of this muscle is evident
as a depressor seen in action when mouth is
to be opened against resistance.
• It elevates the floor of mouth to help in
deglutition.

GENIOHYOID
• Short and narrow muscle lying above medial
part of mylohyoid.
• Arises from inferior medial spine (genial
tubercle) of the mandible.
• The fibres run back and down to inset into
anterior surface of the body of hyoid bone.

NERVE SUPPLY:
• First cranial nerve. The fibres pass through
the hypoglossal nerve.

Actions of geniohyoid
• Geniohyoid elevates the hyoid bone and
draws it forward, thus acting as a partial
antagonist
• Geniohyoid elevates the hyoid bone and
draws it forward, thus acting as a partial
antagonist to stylohyoid.
• When the hyoid bone is fixed, it depresses
the mandible
• When the hyoid bone is fixed, it depresses
the mandible

BUCCINATOR
• Primarily a muscle of facial expression
• Upper fibres arise from maxilla, opposite
molar teeth.
Middle fibres arise from pterygomandibular
raphae.
Lower fibres arise from mandible, opposite
molar teeth.

• The upper fibres insert into the upper lip.
The middle fibres decussate before passing
to the lip.
The lower fibres insert into the lower lip.

NERVE SUPPLY:
• Facial nerve.
ACTIONS:
• Flattens the cheek against gums and teeth
• Prevents food accumulation in the vestibule.

TEMPOROMANDIBULAR
JOINT
• The articulation between the temporal bone
and the mandible . It is bilateral diarthroidal ,
bilateral ginglymoid joint (GPT 8)

• The articulation of condylar process of the
mandible and the intra-articular disk with the
mandibular fossa of the squamous portion of
the temporal bone, a diarthroidal ,sliding
hinge (ginglymus) joint .
• Movement in the upper joint compartment is
mostly translational ,whereas that in the lower
joint compartment is mostly rotational. The
joint connects the mandibular condyle to the
articular fossa of the temporal bone with the
temporomandibular disk interposed.
• It is called ginglymoarthroidal joint which
means it has hinge and glide movements.

CONDYLE
• Barrel shaped with convex surface in the
frontal plane
• Anteroposterior dimension = 0.8-1.0 cm
• Mediolateral is about twice of A-P dimension

• Pterygoid fovea - a shallow concavity at
anteriomedial aspect of mandibular neck .
- gives attachment to superior
head of lateral pterygoid and inferior head of
lateral pterygoid.

• Long axis between the medial and lateral pole
of each condyle are generally perpendicular
to the plane of the ramus .
• This axis is not parallel to each other.

• Bony surface of condyle is made up of dense
cortical bone .
• Both condyle and articulating surface of
temporal bone are covered by dense fibrous
connective tissue with irregular cartilage like
cells.

MANDIBULAR FOSSA
• It is concave & triangular in shape .
• It is bounded
anteriorly by - posterior slope of articular
eminence
posteriorly by - postglenoid process or
tubercle .
medially by - narrow bony wall.

• Postglenoid process – is inferior extension of
temporal squama directly posterior to the
most lateral part of the fossa and anterior to
the opening into the external acoustic
meatus.
• It prevents the direct impingement of condyle
on the tympanic plate .
• The joint capsule is attached to its anterior
surface and a portion of retrodiscal pad is
interposed between it and condyle.

• The roof of the fossa is thin except the medial
portion which is reinforced with thick bone so
that it can resist the upward and inward
forces by lateral and medial pterygoid
muscle.

CAPSULE
• This is a thin ,relatively loose fibrous articular
capsule that surrounds the articular surface of
the condyle and blends with periosteum of
the mandibular neck.

• Attaches below the attachment of articular
disk at medial and lateral poles of the
condyle.
• It surrounds the eminence as well as anterior
to its crest .
• laterally – adhere to articular tubercle ,runs
along the lateral edge of eminence ,
mandibular fossa and postglenoid process

• anteromedially – some fibers of the superior
head of lateral pterygoid muscle attach to the
fused capsule and disk .
• Capsule consist of an internal synovial layer
and an outer fibrous layer containing veins,
nerves and collagen fibers.

ARTICULAR DISK
• Biconcave oval structure interposed between
condyle and the temporal bone .

• Divides the joint cavity into upper and lower
compartment consisting of dense collagenous
connective tissue that is avascular ,hyaline
and devoid of nerve tissue in the central area
but has vessels and nerves in the peripheral
area.
• Disk merges with the capsule at the periphery
and is firmly attached to the condyle at its
medial and lateral pole .

• Disk is not attached to temporal bone ,thus it
moves with the condyle as the latter
translates in relation to the articular
eminence.
• Posteriorly the disk is contiguous with the
loosely organised structure called the
retrodiscal pad .

• The central area of disk is thinner and is
called intermediate zone with thicker
peripheral

ARTICULAR EMINENCE
• It runs obliquely from the posterior root of the
zygomatic arch to the medial aspect of the
joint.
• During centric relation ,the condyle are
related anteriosuperiorly to the shapes of
articular eminence.

LIGAMENTS
• Ligaments play an important role in protecting
the structures.
• They are made up of collagenous connective
tissue , they do not stretch .if they stretch
over a prolonged period of time they get
elongated which can further compromise
their function .

• They do not actively enter into joint function
but have a passive restraining function to limit
and restrict border movements.

• Three functional ligaments which support the
TMJ are:
1.Collateral ligament
2.Capsular ligament
3.Temporomandibular ligament
• Two accessory ligament
1.Sphenomandibular ligament
2.Stylomandibular ligament

COLLATERAL LIGAMENT
• Commonly called discal ligament
• Attach the medial and lateral borders of the
articular disc to the poles of the condyle .

• Two types
1.Medial discal ligament
2.Lateral discal ligament

• These ligament divides the joint
mediolaterally into superior and inferior joint
cavities
• They restrict movement of disc away from
condyle
• They allow the disc to move passively with
condyles as it glides anteriorly and posteriorly

• They permit the disc to be rotated anteriorly
and posteriorly on the articular surface of the
condyles
• They are responsible for hinge movement
• They are well innervated , thus they give
information about position and movement .

CAPSULAR LIGAMENT
• Surrounds and encompasses the entire TMJ
• Superiorly attaches to temporal bone along
the borders of articular surface of mandibular
fossa and articular eminence
• Inferiorly to the neck of condyle

• Resist medial ,lateral, or inferior forces that
tend to separate or dislocate the articular
surfaces .
• Retains the synovial fluid .
• Well innervated so gives proprioceptive
feedback regarding position and movement of
the joint.

TEMPOROMANDIBULAR LIGAMENT
• This ligament composed of strong ,tight fibers
reinforce the lateral aspect of capsular
ligament .
• It is composed of
1.Outer oblique portion
2.Inner horizontal portion

• Outer oblique portion extend from outer
surface of articular tubercle and
zygomatic process posterioinferiorly to
the outer surface of condyle neck
• Inner horizontal portion extends from
the outer surface of the articular
tubercle and zygomatic process
posteriorly and horizontally to the lateral
pole of the condyle and posterior part of
the articular disk.

• Outer oblique portion extend from outer
surface of articular tubercle and zygomatic
process posterioinferiorly to the outer surface
of condyle neck
• Inner horizontal portion extends from the
outer surface of the articular tubercle and
zygomatic process posteriorly and
horizontally to the lateral pole of the condyle
and posterior part of the articular disk

• Outer oblique part limits the extent of mouth
opening
• Inner horizontal part limits the posterior
movement of disc & condyle.

ACCESSORY LIGAMENT
• Sphenomandibular Ligament
It is an accessory ligament which extends
between spine of sphenoid and lingula of
mandible.

• Stylomandibular Ligament
This ligament which extends between
styloid process, downward & forward to angle
of mandible. It limits excessive protrusive
movements of the mandible.

BIOMECHANICS
• TMJ is a compound joint . Its structure and
function can be divided into two distinct
system .
• stability of joint is maintained by the constant
activity of muscles mostly the elevating
muscles that pulls across the joint

• When the muscle activity increases , the
condyle is increasingly forced against the disc
and the disc against the fossa , resulting in
increasing interarticular pressure of these
joint structure .
• the width of the articular disc varies with
pressure . it widens when condyles are
closed and vice versa .

• as the interarticular pressure increases the
condyle seat against the thinner intermediate
zone of articular disc .when the pressure
decreases the disc spaces widens and
thicker portion rotates into the space .

• Lateral pterygoid is very important in
unilateral chewing. When jaw is closed, the
force is not applied to the joint but instead on
the food. The jaw is fulcrumed around the
hard food ,causing an increase in
interarticular pressure in contralateral joint
and sudden decrease in interarticular
pressure in ipsilateral joint .
• This leads to dislocation in the ipsilateral
joint .

• To prevent this this sup lateral pterygoid
becomes active during power stroke ,rotating
the disc forward on the condyle so the thicker
posterior border of the disc maintains articular
contact .
• The mandible works on class III lever
principle , as the muscle pull (force ) is
between the dentition (resistance) and
condyle (fulcrum ).

• More the force applied at 1st molar relative
to condyle and incisor .
• When resistance arm (tooth – TMJ distance)
increases relative to effort (muscle – TMJ
distance) will lead to increase load at the
fulcrum .

TYPE OF MOVEMENTS
• ROTATIONAL MOVEMENTS
• TRANSLATORY MOVEMENTS

ROTATIONAL MOVEMENT
• The process of turning around an axis
:movement of a body about its axis (Dorland’s
illustrated medical dictionary).
• Rotational movement occurs as movement
within the inferior cavity of the joint. It is thus
movement between the superior surface of
the condyle and the inferior surface of the
articular disc.

• Rotational movement of the mandible can
occur in all three reference planes; horizontal,
frontal (vertical), and sagittal. In each plane
occurs around a point, called the axis

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 the masticatory system it occurs when the
mandible moves forward, as in protrusion.
• The teeth, condyles, and rami all move in the
same direction and to the same degree..

• Translation occurs within the superior cavity
of the joint between the superior surface of
the articular disc and the inferior portion of
the articular surface

ROTATION
• around the transverse or the hinge axis .
• around the anteroposterior or sagittal axis
• around the vertical axis

TRANSVERSE OR THE ROTATION
AROUND THE HINGE AXIS
Kinematic axis (GPT 8)– the transverse
horizontal axis connecting the rotational
centers of the right and left condyles
• Mandibular movement around the horizontal
axis is an opening and closing motion .It is
referred to as a hinge movement

• This is a horizontal axis which passes from
the right to the left side of the mandible

ROTATION AROUND THE
SAGITTAL AXIS
• This axis runs around the mid sagittal
plane .The mandible shows slight rotation
around this axis. The condyle on one side
moves medially and downwards and on the
other side moves laterally and upwards

ROTATION AROUND THE
VERTICAL AXIS
• This axis runs through the condyle and
posterior border of the ramus of the mandible.
• This is seen during lateral movement .

• Occurs when one condyle moves anteriorly
out of the terminal hinge position with the
vertical axis of opposite condyle remaining in
the terminal hinge position

TRANSLATION
• Translation can be defined as the movement
in which every point of the moving object has
simultaneously the same velocity and
direction.
• This occurs in the protrusion, Bennett
movement ,here the mandible does not rotate
around any axis but it shifts en mass

• Hinge movement
• Protrusive movement
• Retrusive movement
• Lateral movement

HINGE MOVEMENT
• Purely rotational , around the horizontal axis
till the patient opens his mouth to about 20-
25m.This axis is called TERMINAL HINGE
AXIS

• The condyle rotates 10º-13º.This Occurs
while taking or crushing food .This is
produced by the lateral pterygoid and the
supra hyoid muscle aided by gravity .After
certain amount of opening the mandible
begins to glide .

PROTRUSIVE MOVEMENT.
• Occurs while incising and grasping food. This
movement occurs after the condyle rotates
about 13º in the TMJ. At this point the
transverse hinge axis shifts to the level of the
mandibular foramen
• The mandible moves forward and
downwards. This movement is complete
when the maxillary and the mandibular teeth
are edge to edge.

RETRUSIVE MOVEMENT
• Occurs when the mandible is forcefully
moved behind the centric relation. The patient
cannot voluntarily reproduce it.
• Brought about by the fibers of the temporalis,
digastric and the deep fibers of the masseter.
The magnitude is 0.5mm

LATERAL MOVEMENT
• Lateral rotation or laterotrusion
• Bennett movement

• Takes place on the left or the right side. Take
place while chewing food .If the condyle is
moving to the right side, the right side
condyle is called the “wo rking side ” o r the
late ro trusive side the condyle on the left is
called the “no n wo rking ” o r the m e dio trusive
side o r balancing co ndyle

BENNETT MOVEMENT
• It is defined as the bodily lateral movement or
lateral shift of the mandible resulting from the
movement of the condyle along the lateral
inclines along the mandibular fosse in lateral
jaw movements. (GPT)

• But according to GPT 8 mandibular lateral
translation is called bennett side shift and
laterotrusion is called bennett movement .
• Laterotrusion – condylar movement on the
working side in horizontal plane .
• Mandibular lateral translation – mandibular
translatory movement .

• This movement takes place due to restraining
influences of the temporomandibular ligament
on the working condyle and to some extent by
the medial wall of glenoid fossa on the non
working side.
• The average lateral movement is about 0.75
mm

• Bennett angle (GPT 4) – angle formed
between the sagittal plane and the average
path of the advancing condyle as viewed in
horizontal plane during lateral mandibular
movement.
• Angle is formed due to anterior and medial
movement of non working condyle .
• It varies from 2 to 44 degree with the mean
value of 16 degree.

• Timing of bennett movement: timing is the
amt of side shift.
It denotes the rate or amount of descent of
contralateral condyle and the rotation and
lateral shift of the ipsilateral condyle.

• GPT 8 recommends the term mandibular
lateral translation for side shift of mandible.
• Accordingly, two components are there for
this movement .
- Immediate side shift
- Progressive side shift

• Immediate mandibular lateral translation
• This occurs during mandibular lateral
movement when the orbiting condyle moves
from centric relation medially against the
medial and superior walls of the articular
fossa to a distance of approx. 1 mm (range
0.2 – 2.5
• Beyond this the condyle moves forward ,
downward and inward against the medial and
superior walls of fossa at a curved angle .
This component is the progressive side shift .

• Progressive mandibular lateral translation
This is the translatory portion of the lateral
movement that occurs at a rate or a amount
which is directly proportional to the forward
movement of orbiting condyle .
The progressive side shift determines the
value of bennett angle .

• Bennett angle – angle formed between the
sagittal plane and the average path of the
advancing condyle as viewed in horizontal
plane during lateral mandibular movement .
(GPT 4)
• Angle is formed due to anterior and medial
movement of non working condyle .

• It varies from 2 to 44 degree with
the mean value of 16 degree.

• When lateral movement is executed the
working condyle rotates and moves outward
while the other nonworking condyle translates
forward ,medially and downward orbiting
around the rotating working condyle .

• Fischer’s angle (GPT 8)
the angle formed by the intersection of the
protrusive and non working condylar path as
viewed in the sagittal plane.

BORDER MOVEMENTS
• Border movement (GPT 8) – mandibular
movement at the limits dictated by anatomic
structures, as viewed in a given plane.

• Mandibular movement is limited by the
ligaments and the articular surface of the
TMJs as well as by the morphology and
alignment of the teeth.
• When the mandible moves through the outer
range of motion ,reproducible describable
limits result, which are border movements .
• These movements can be described for each
reference plane .

• Centric relation (GPT 8)- the
maxillomandibular relationship in which the
condyles articulate with the thinnest avascular
portion of their respective disks with the
complex in the anterior superior position
against the shapes of the articular eminence.

• This position is independent of tooth contact.
This position is discernible when the
mandible is directed superior and anteriorly. It
is restricted to purely rotary movement about
the transverse horizontal axis .

• Maximum Intercuspal position (GPT 8)-
the complete intercuspation of the opposing
teeth independent of the condylar position
,sometime referred to as the best fit of the
teeth regardless of the condylar position

• Postural position (GPT 8)- any
mandibular relationship occurring during
minimal muscle contraction.

• Sagittal plane-
In this plane mandibular movements have
four distinct movement components
1.Posterior opening border
2.Anterior opening border
3.Superior contact border
4.Functional

POSTERIOR OPENING BORDER
• Occurs as a two stage hinging movements.
• Condyles are stabilized in their most superior
positions.-CR position
• In CR the mandible can be rotated around the
horizontal axis to distance of only 20-25mm,
• At this point tm ligaments tightens and after
which continued opening results in an ant,
and inf,translation of condyles.

• As the condyle translate the axis of rotation
shifts to ramus and second stage of post,
opening border movement starts.
• In this condyles are moving anteriorly
,inferiorly and anterior portion of the mandible
is moving posteriorly and inferiorly.
• Maximum opening is 40- 60mm

ANTERIOR OPENING BORDER
• With mandible maximally opened closure is
accompanied by contraction of the inferior
lateral pterygoids, will generate ant. Opening
border movement.
• If the condyles were stabilized in this anterior
position, a hinge movement can occur, while
the mandible is closing from the maximally
opened to maximum protruded position.

• When closure occurs, the tightening of the
ligaments produces a posterior movements of
the condyles.
• Condyle position is most anterior in max,
open but not max, protruded position.

SUPERIOR CONTACT BORDER
MOVEMENT
• Factor that influence the entire movement
1.The amt of variation between CR and
maximum intercuspation .
2.Steepness of the cuspal inclines of the
posterior teeth

3. Amt of vertical and horizontal overlap of the
anterior teeth .
4. Lingual morphology of the maxillary anterior
teeth .
5. General interarch relationship of the teeth.

• The slide from centric relation to intercuspal
position is present in approx 90% of the
population, and the average distance is 1.25
+ 1mm (posselt; 1957)

HORIZONTAL PLANE
BORDER
• Rhomboidal shape
• Components
1. Left lateral border
2.Continued left lateral border with protrusion
3.Right lateral border

• Continued right lateral border with protrusion .

LEFT LATERAL BORDER
MOVEMENT

CONTINUED LEFT LATERAL
BORDER MOVEMENT WITH
PROTRUSION

RIGHT LATERAL BORDER
MOVEMENT

CONTINUED RIGHT LATERAL
BORDER MOVEMENT WITH
PROTRUSION

FRONTAL (VERTICAL )
BORDER MOVEMENT
• Shield shape pattern
• Four distinct movements
1.Left lateral superior border
2.Left lateral opening border
3.Right lateral superior border
4.Right lateral opening border movement

LEFT LATERAL SUPERIOR
BORDER

LEFT LATERAL OPENING
BORDER

RIGHT LATERAL SUPERIOR
BORDER

RIGHT LATERAL OPENING
BORDER

FUNCTIONAL MOVEMENTS
• Functional movements (GPT 8)- all
normal ,proper, or characteristic movements
of the mandible made during speech
,mastication ,yawning ,swallowing, and other
associated movements

• These functional movements take place
within the border movements and therefore
are considered free movement.
• Most functional movements require maximum
intercuspation and therefore typically begin at
and below the intercuspal position.

•Physiologic rest position – the
mandibular position assumed when the head
is in an upright position and involved
muscles, particularly the elevator and
depressor groups , are in equilibrium in tonic
contraction .and the condyles are in neutral
,unstrained position .

• Rest position is located approximately 2 to 4
mm below the intercuspal position .
• The increased level of electromyographic
muscle activity in this position are indicative
of myotatic reflex .Because this is not a true
resting position ,the position in which the
mandible is maintained is more appropriately
termed the postural position .

POSTURAL EFFECT ON
FUNCTIONAL MOVEMENT
• When the head is positioned erect and
upright ,the postural position of the mandible
is located 2 to 4 mm below the intercuspal
position.

MASTICATION
• Mastication – defined as act of chewing foods
(Dorland’s medical dictionary ).
• Masticatory cycle (GPT 8 )- a three
dimensional representation of mandibular
movements produced during the chewing of
food.

• It is a functional activity that is generally
automatic and practically involuntary however
,when desired it can be readily brought under
voluntary control

CHEWING STROKE
• Mastication is made up of rhythmic and well
controlled separation and closure of the
maxillary and mandibular teeth.
• Tear drop shape movement pattern .

Divided into
• opening and
• closing movement.
- crushing phase .
- grinding phase .

• As with anterior movement , the lateral
movement of the mandible relates to the
stage of mastication .
• When food is initially introduced into the
mouth ,the amount of lateral movement is
great and then becomes less as the food is
broken down.

• The amt of lateral movement also
varies according to the consistency
of the food .
• Harder the food ,the more lateral
the closure stroke becomes .
(Lundeen and Gibbs ;1982)

• The chewing patterns of complete
denture wearers appear to be more
irregular on the average than those
in patients with natural dentition .
• This is likely a result of the
displacement of the mucosa on
which they rest ,as well as
preoccupation of tongue and
perioral muscles with denture base
retention.

• In denture wearers the jaw
movements are more vertical
• The form of the chewing cycle in
complete –denture wearers does
not seem to be influenced by the
cuspal inclinations (Drago,1981).

SWALLOWING
• Swallowing is a series of coordinate
muscular contraction that moves a
bolus of food from the oral cavity
through the esophagus to
stomach .
• During swallowing the lips are
closed sealing the oral cavity

• The teeth are brought up into their
maximum intercuspal position
,stabilizing the mandible .
• Stabilization of mandible is an
important part of swallowing .
• The normal adult swallow that uses
the teeth for mandibular stability is
called somatic swallow .

• The average tooth contact during
swallowing last about 686 msec.
this more than three times longer
than during mastication .
• When the mandible is braced , it is
brought into a somewhat posterior
or retruded position . If the teeth do
not fit together well in this position ,
an anterior slide occurs to the
intercuspal position .

SPEECH
Mandibular movements during
speech is variable according to the
syllables used, accent and the
speed .Definitive repeatable jaw
tracings are difficult to record
during speech.

Occlusal morphology and
mandibular movement
• The structures that control
mandibular movements are divided
into two types :
posterior controlling factor (TMJ)
anterior controlling factor (anterior
teeth)

• Posterior controlling factor
(Condylar guidance )
• As the condyle moves out the
centric relation position ,it descends
along the articular eminence of the
mandibular fossa.

• The angle at which the condyle
moves away from a horizontal
reference plane is referred to as the
condylar guidance angle.
• The condylar guidance is
considered to be a fixed factor .

• Anterior controlling factors
(anterior guidance )
• Defined as the influence of the
contacting surface of the
mandibular and the maxillary
anterior teeth during mandibular
movements .(GPT 8)

• As the mandible protrudes or
moves laterally ,the incisal
edges of the mandibular teeth
occlude with lingual surface of
the maxillary anterior teeth.
• The steepness of these lingual
surface determines the amount
of vertical movement of
mandible .

• The anterior guidance is
considered to be a variable
rather than a fixed factor .
• It can be altered by dental
procedures .

• The relationship of a posterior tooth
to the controlling factors influence
the precise movement of the tooth .
• The nearer the tooth is to TMJ
,more the joint anatomy will
influence its eccentric movement
and less the anatomy of the
anterior teeth will influence its
movement.

• The anterior controlling factor
and posterior controlling factor
are independent of each other
(Angle,1948;Rickett,1950;
Moffett,1962;)
• But they still function together in
dictating the mandibular
movements .

• Alteration of anterior controlling
factors can play an important
role in treatment of occlusal
disturbance in the masticatory
system .

• Occlusal contacts during
mandibular movement

• The term eccentric is used to
describe any movement of the
mandible from the intercuspal
position that result in tooth contact .
• The three basic eccentric
movement
• Protrusive
• Laterotrusive
• Retrusive

Protrusive mandibular
movement

Laterotrusive mandibular
movements

Retrusive mandibular
movements

Neuromuscular regulation
• Mastication is programmed in
“chewing center” residing in
brain stem (particularly in
reticular formation of the pons)
• Conscious effort may either
induce or terminate chewing .

• The sensory impulses from the
orofacial region may modify the
basic cyclic pattern of chewing
to achieve optimal function .
• The muscles that move, hold, or
stabilize the mandible do so
because they receive impulses
from the central nervous
system.

• Impulses may arise at conscious
level and subconscious level .
• Impulses from the subconscious
level including the reticular
activating system ,also regulate
muscle tone ,which play a primary
role in the physiological rest
position of mandible.

CLINICAL SIGNIFICANCE
• EFFECT OF CONDYLAR
GUIDANCE ON CUSP HEIGHT
• When the mandible is protruded
,the condyle descends along the
articular eminence . Its descend is
determined by the steepness of the
eminence .

• Steeper the eminence , the more
the condyle is forced to move
inferiorly as it shifts anteriorly .
• This results in greater vertical
movement of condyle ,mandible
and mandibular teeth.

Steeper condylar guidance allow for
steeper posterior teeth .

Effect of anterior guidance
on cuspal height
• by changing the vertical and
horizontal overlap of the anterior
teeth cause changes in the vertical
movement pattern of the mandible .
• More the vertical component to the
mandibular movement , steeper the
posterior cusps.

Effect of mandibular lateral translation
movement on the cuspal height .
1. Effect of the amount of lateral
translation movement on
cuspal height .
2. Effect of the direction of lateral
translation movement on
cuspal height .

Effect of timing of lateral
translation movement on cuspal
height .

Effect of the amount of lateral
translation movement on cuspal
height .
• As the lateral translation
movement increases, the bodily
shift of the mandible dictates
that the posterior cusps be
shorter to

• permit lateral translation without
creating contact between
maxillary and mandibular
posterior teeth .
• Greater must be the concavity
of anterior maxillary teeth .

Effect of the direction of lateral
translation movement on cuspal height
• Laterosuperior movement of the
rotating condyle will require
shorter posterior cusps
• Lateroinferior movement will
permit longer posterior cusp
tooth .

Effect of timing of lateral translation
movement on cuspal height .
• More immediate the side shift
,the shorter the posterior teeth

Effect of intercondylar distance on the
ridge and groove direction .
• If the intercondylar distance is
less ,the radius were shorter
,the arc of movement of
mandibular working side cusp
and fossae would occur in more
distal direction .

• More the intercondylar distance
– more distal must be the ridge
and balancing grooves on
mandibular teeth and more
mesial in maxillary teeth .

• Extension of distobuccal border at the end of
buccal vestibule is influenced by masseter
muscle activity.
• When the masseter contracts, it’s anterior
fibres alters the shape and size of the
distobuccal end of lower buccal vestibule by
pushing inward against the buccinator muscle
and suctorial pad of fat.

• More the intercondylar distance
– greater must be the lingual
concavity of maxillary teeth .

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