Dental Muscles and Their Importance in Prosthodontics

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

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•Myology – study of muscles.
•Muscle is a soft tissue made up of a
large number of fibers bound together by
connective tissue into bundles, or
fascicles.
• These bundles are surrounded by
connective tissue sheaths and grouped
together into still larger bundles.

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• The whole muscle is enveloped by a
connective tissue sheath, the epimysium.
• Blood vessels enter a muscle and branch
into smaller vessels that course through
these connective tissues to reach the
individual muscle fibers, which are also
muscle cells.

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• Muscles can be Voluntary (skeletal) or
invouluntary (smooth or cardiac).
• The muscles that are intimately
involved with Prosthodontics are
skeletal muscles.

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• In the majority of skeletal muscles, the
origins and insertions are in bone.
• However, many of the skeletal muscles
involved in complete denture construction
have a bony origin but insert into an
aponeurosis, a raphe, or another muscle
with one exception, the muscles of
mastication have their origins and
insertions in bone.

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• The orbicularis oris has no bony origin or
insertions, and its primary function is to
close the oral orifice (sphincter).
• When the origin and insertion of a muscle
are in bone, there is a limitation to the
positions and action of the muscles.
• When an attachment is in an aponeurosis,
a raphe, or another muscle, a more flexible
situation exists.

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• Knowledge of this relationship is used
in making jaw relation records,
particularly centric relation or centric
position. Centric relation is a bone-to-
bone relation controlled by the
attached musculature, the tissue-lined
bony fossae, the ligaments, and the
articular disk.www.indiandentalacademy.com

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• The muscles of facial expression, the
muscles of the tongue, the suprahyoid
muscles, the muscles of the soft palate, and
the pharyngeal muscles do not have both
origins and insertions in bone.
• These are the muscles primarily involved
with determining the extent of the denture
borders, the contour of the denture bases,
and the positions of the teeth.

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• The nonbony attachments of these
muscles account for the various
contours, borders, and positions of
teeth that are seen in dentures.
Impression techniques are influenced
by these attachments. The muscles
should not be stretched or left
unsupported during an impression.www.indiandentalacademy.com

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• The teeth, not the denture borders,
support the muscles of facial
expression.
• The available vestibular spaces should
be used to their fullest extent but
should not be overfilled.

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MUSCLES OF MASTICATION
• TEMPORALIS
• Origin:
• The temporalis arises from the temporal
fossa on the lateral aspect of the skull. The
area is bounded above by the temporal line,
and below by the zygomatic arch. It
includes parts of the frontal, parietal, and
squarnous temporal and of the greater wing
of the sphenoid bone.

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• The anterior fibres of the muscle run
vertically downwards; the posterior fibres
run horizontally forwards; while the
intermediate fibres run obliquely to
converge in a tendon. The tendon passes
deep to the zygomatic arch.

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• Insertion:
• The muscle is inserted into the
coronoid process of the mandible. The
region of insertion covers the entire
medial aspect of the coronoid process
(including its apex, anterior and
posterior borders). Some fibres are
inserted into the anterior border of the
ramus

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• Actions:
• The temporalis helps to close the mouth by
elevating the mandible.
• The movements of elevation and depression
of the mandible have two components.
• Firstly, there is a hinge like movement
between the condyle of the mandible and the
inferior surface of the articular disc of the
temporomandibular joint. The second
component is a gliding movement of the disc

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• MASSETER
• The masseter is a quadrilateral muscle placed
superficial to the ramus of the mandible
• Origin:
• The muscle arises from the Zygomatic arch
• The more superficial muscle fibres arise
from the anterior two thirds of the lower
border of the arch; whereas the deeper fibres
arise from its deep surface, and from the
posterior one third of its lower border. The
most anterior fibres arise from the zygomatic
process of the maxilla.

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• Insertion:
• The muscle is inserted into the lateral
surface of and angle of the mandible.
• Actions:
• The masseter elevates the mandible to
close the rr Its anterior fibres help in
protraction (forward in of the jaw.

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• LATERAL PTERYGOID:
• It is seen that the muscle has two heads
upper and lower
• Upper head arises from:
• infratemporal surface, and (ii) the
infratemporal crest of the greater wing of
the sphenoid bone.
• The lower head arises from the lateral
surface of the lateral pterygoid plate.

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• Insertion:
• The fibres of both heads run backwards and
laterally to be inserted into a depression
(pterygoid fovea) on the anterior aspect of
the neck of the mandible. Some fibres are
inserted into the intra articular disc and‑
some into the capsule of the
temporo mandibular joint.‑

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• MEDIAL PTERYGOID
• Origin:
• The medial pterygoid muscle takes origin
from:
(a) the medial surface of the lateral pterygoid
plate and
(b) the adjoining part of the palatine bone
(pyramidal process).

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(c) A superficial slip arises from the lateral
aspect of the pyramidal process of the
palatine bone and from the maxillary
tuberosity
• Insertion:
• The fibres of the muscle pass downwards,
backwards and laterally to be inserted into
the medial surface of the angle of the
mandible and the adjoining part of its
ramus.

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• Actions of Pterygoid Muscles:
• The fibres of the lateral pterygoid , pull
the mandible forwards (protraction)
and medially.
• . The fibres of the medial pterygoid
also perform the same actions in
addition elevate the mandible.

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• (a) The medial and lateral pterygoids of
both sides acting together protract the
mandible.
• (b) The medial and lateral pterygoids of one
side acting together pull the mandibular
condyle of that side forwards (and
medially). As a result the chin moves
forwards and to the opposite side. Alternate
action of the muscles of the two sides
results in side to side chewing movements.

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• (c) The two pterygoid muscles have
opposite actions as far as opening and
closing of the mouth is concerned. The
medial pterygoid elevates the jaw. The
lateral pterygoid helps in opening the
mouth by pulling the head of the
mandible forwards along with the
intra articular disc‑ www.indiandentalacademy.com

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MUSCLES OF THE TONGUE
• The extrinsic muscles of the tongue
enter it from outside. They are the
styloglossus, the palatogloss
genioglossus, and the hyoglossus.
• The intrinsic muscles lie within the
substance of the tongue.

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• Styloglossus
• The styloglossus arises from the anterior
and lateral aspects of the styloid process,
and from the upper part of the
stylomandibular ligament .It runs
downwards and forwards to merge with
the side of the tongue.

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• Palatoglossus
• The palatoglossus muscle arises from the
anterior side of the palatine aponeurosis (a
sheet of fibrous in the soft palate). The
muscle passes do nw forwards to be
inserted into the side of the tongue. with
the mucous membrane covering it, it for
palatoglossal arch, which lies anterior to
the tonsil

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• Genioglossus
• The genioglossus lies next to the median
plane. It arises from the upper genial
tubercles on the posterior of the symphysis
menti.
• The fibres spread to be inserted into the
whole length of the ventral of the tongue.
The lowest fibres muscle are attached to
the body of the hyoid bone.

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• Hyoglossus
• The hyoglossus muscle arises from
the hyoid bone. The area of origin
includes :
a. The greater cornu, and b. the lateral
part of the body.
b. The fibre pass outwards to enter the
side of the tongue.www.indiandentalacademy.com

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• Actions:
• The muscles of the tongue move the tongue
and alter its shape for movements
concerned with speech, mastication and
swallowing.
• Hyoglossus –depress the tongue
• Styloglossus – pulls it upwards and
backwards.

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• Genioglossus – protrudes the tongue.
• Palatoglossus – both sides act together
to bring the palatoglossal arches
together, thus shutting the oral cavity
from the oropharynx.
• Intrinsic muscles – alter the shape of
the tongue.

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MUSCLES OF FACIAL
EXPRESSION
• The zygomaticus major, zygomaticus
minor, levator labii superioris, levator labii
superioris alaeque nasi, levator anguli oris,
mentalis, depressor labii inferioris,
depressor anguli oris, risorius, platysma,
incisivus superioris, incisivus inferioris,
orbicularis oris, and buccinator muscles are
responsible for the expressions seen in the
lower half of the face.www.indiandentalacademy.com

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• The actions of these muscles are
responsible for various facial
expressions including smiling,
laughing, and frowning. When these
muscles are relaxed, the face lacks
expression. The actions of these
muscles often reflect the mood and
emotional status of an individual.www.indiandentalacademy.com

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• MUSCLES OF THE SOFT PALATE
• The tensor veli palatini, levator veli
palatini, musculus uvulae, palatoglossus,
and palatopharyngeus are the muscles of
the soft palate, which is a movable curtain
extending downward and backward into the
pharynx.
• During deglutition, it is raised and helps to
seal off the nasopharynx: above from the
oropharynx below.

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• The Tensor veli palatini is a thin, flat
triangular muscle that arises from the
scaphoid fossa of the pterygoid plates,
spine of the sphenoid bone, and the lateral
wall of the auditory tube.
• Inferiorly, it becomes a slender tendon that
turns around the pterygoid hamulus to enter
the palate where it joins the palatine
aponeurosis.

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• The levator veli palatini is a thick, rounded
muscle that arises from the petrous portion
of the temporal bone and the medial aspect
of the auditory tube.
• It courses downward and medially toward
the midline of the soft palate, where it
interlaces with the same muscle from the
opposite side.
• The sling that is formed by the joining of
these two muscles causes the soft palate to
be elevated during contractionwww.indiandentalacademy.com

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• The palatoglossus muscle and the mucous
membrane covering it form the
palatoglossal arch that extends from the
soft palate to the side of the tongue.
• When the two palatoglossi contract, they
draw the tongue and soft palate toward
each other. This assists in closing the
isthmus faucium during deglutition.

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• SUPRAHYOID MUSCLES
• The functions of the suprahyoid
muscles include elevation of the hyoid
bone and the larynx and depression of
the mandible.
• The digastric, stylohyoid, mylohyoid,
and geniohyoid muscles compose this
group of muscles.www.indiandentalacademy.com

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• The mylohyoid and the geniohyoid
muscles may influence the borders of
the mandibular denture.
• The mylohyoid muscle is a thin sheet
that arises from the whole length of the
mylohyoid line. The posterior fibers
are inserted into the body of the hyoid
bone. www.indiandentalacademy.com

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• The geniohyoid muscle arises from the
inferior mental spine (genial tubercle),
which is located on the inner aspect of
the symphysis menti just above the
anterior attachment of the mylohyoid
muscle.
• This muscle presents no problem in
complete denture construction unless
there is extensive loss of the residual
ridge.

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• INFRAHYOID MUSCLES:
• The origin and insertion of this group of
muscles, which consists of the stemohyoid,
omohyoid, sternothyroid, and thyrohyoid,
have no particular significance in complete
denture prosthodontics with respect to any
influence on the denture borders.
• However, the actions of these muscles are
important to the prosthodontist, for they are
a part of the kinetic chain of the mandibular
movement.

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• Their action is to fix the hyoid bone, as it
were, to the trunk. It is from this fixed
position that the suprahyoid muscles can
act on the mandible.
• In contrast, these muscles can relax and
allow the hyoid bone to be pulled upward
by the suprabyoid muscles during
deglutition.

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• PHARYNGEAL MUSCLES
• Of the several pharyngeal muscles, the
superior constrictor is the one of most
interest in complete denture construction.
• The superior constrictor has four sites of
origin: the posterior border of the medial
pterygoidplate and pterygoid hamulus, the
pterygomandibular raphe, the posterior end
of the mylohyoid line, and the side of the
tongue.

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The muscles that hold move or stabilize the
mandible do so because they receive
impulses from the central nervous system.
Mandibular motion at conscious level
results in voluntary movement where as at
subconscious level due to stimulation of
oral or muscle receptors cause involuntary
movement.

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Receptors in the oral mucous
membrane are stimulated by touch
pain thermal changes or pain and
pressure where as other receptors are
principally located in the periodontal
ligaments, mandibular muscles and
ligaments provide information as to the
location of mandible in space and thus
called PROPRIOCEPTORS

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• Impulses form oral receptors
Trigeminal nuclei
• From proprioceptors
Mesencephalic nuclei of the brain
From these 2 receptors
Cerebral cortex

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• From the cerebral cortex
It comes though three ways
Via the thalamus to the sensoriomotor cortex
(conscious level) to produce voluntary change in
the position of the mandible
By way of a reflex arc to the motor nuclei of the
Trigeminal nerve to cause involuntary movement
By combination of the these two ways through the
subcortical areas as the hypothalamus, basal
ganglion.

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In edentulous patients the periodontal ligament
are lost thus the source of control in the
positioning of the mandible are lost thus to
compensate this centric occlusion must be in
harmony with the centric relation and meet
evenly in the normal range of functional activity
and these impulses can be generated by
voluntary thought which are transmitted
through the motor nuclei and from there to the
muscle of mastication so the mandible performs
the desired activity

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Mastication is a programmed event
residing in a chewing centre located in
the brain stem (in the reticular
formation of the pons )
The cyclic nature of mastication (jaw
opening and closure ,tongue protrusion
and retrusion) is a result of of action of
this central pattern generation.

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The alteration of the chewing pattern
or character (rate, force,
duration)are related to the
consistency of the bolus of the food.
The relatively continuous flow of
impulses through the specific
pathway form the receptors to the
CNS and back to the musculature
establishes a memory pattern for
mandibular movements.

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Thus when natural teeth are present
a individual sub consciously develops
these memory patterns
But these patterns are disturbed
when the teeth are lost or a new
restoration is placed with an
occlusion which is not in harmony
with mandibular movement leads to
pain ,pathosis and mental stress

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• Basically the muscles concerned with a
prostheses can be simply dealt as :
• A. muscles associated with the
borders of the prostheses and its
importance
• B. muscles associated with surfaces
of the denture and its importance.

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• A. Muscles associated with the borders
of the prostheses and its importance
• The insertions of the various muscles
around the oral cavity, both superficial and
deep, are important. These muscles insert
partly into the connective tissues of the
skin and partly into the mucous membrane
of the lips.

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• The origins of several of the muscles of
facial expression are near enough to the
denture-bearing areas that their actions
must be considered as definitely
influencing the denture borders.
• Their influence is in proportion to the
contour and quantity of residual ridge
present in a vertical direction. The higher
the residual ridge, the less influence these
muscle attachments will exert.

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MAXILLARY DENTURE
• The posterior extension of the
maxillary denture base rests on the soft
palate. The mucous membrane in this
area overlies the palatine aponeurosis.
• This tendinous sheet lies in the anterior
two thirds of the soft palate and is
attached to the crest the lower surface
of the hard palate near its posterior
end.

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• Near the hard palate,muscle fibers are very
scanty, and the aponeurosis is thick and
strong at the junction; the anterior part of
the soft palate is therefore more horizontal
and less movable than the posterior part.

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• The characteristics of the aponeurosis
and the overlying mucosa, the activity
of the palatine muscles, and the
contour of the soft palate determine the
extent and the contour of the posterior
palatal seal. The seal should be in the
soft palate and not over the palatine
bones.

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• The placing of the posterior palatal seal
is the responsibility of the dentist. The
extent, depth, and slope of the
extension into the soft palate is
determined by visual examination and
by palpation.
• As a general rule, the more acute the
angle of attachment between the
aponeurosis and the bone, the more
active the reflection.

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• The more active the reflection, the less
the denture base can extend on to the
soft palate distally, and the more it
must extend vertically into the soft
tissues.

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• The tensor veli palatini inferiorly,
becomes a slender tendon that turns
around the pterygoid hamulus to enter
the palate where it joins the palatine
aponeurosis.
• This slender tendon, when taut, can
influence the denture contour in the
hamular notch area.

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• The levator veli palatini medially toward
the midline of the soft palate, interlaces
with the same muscle from the opposite
side.
• The sling that is formed by the joining of
these two muscles causes the soft palate to
be elevated during contraction.

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• The action of this muscle bilaterally is
critical in closing off the oropharynx
from the nasopharynx during
swallowing, as well as in determining
the position of the vibrating line when
developing a posterior palatal seal for a
maxillary denture.

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MANDIBULAR DENTURE
• The mandibular labial frenum contains
a band of fibrous connective that helps
attach the orbicularis oris muscle.
• Therefore frenum is quite sensitive and
active and the border has to be given a
relief in this area.

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• The mentalis muscle elevates the skin of
the chin and turns the lower lip outward.
• Because its origin extends to a level higher
than that of the fornix of the vestibule, the
mentalis muscle renders the lower vestibule
more shallow when it contracts.

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• The contraction of this muscle is capable
of dislodging a mandibular denture,
particularly when the residual ridge in the
anterior region is the same height as the
fornix of the vestibule.
• Therefore, the mentalis muscle attachment
to the alveolar ridge can dictate the level
of extension of the labial flange of the
mandibular denture below the crest of the
ridge.

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• The incisivus labii superioris and inferioris
muscles arise from the maxillary and
mandibular alveolar processes, respectively,
and then course laterally to blend with the
orbicularis oris muscle.
• Their actions on the vestibular fornix are
similar to that of the mentalis muscles.
• They are small muscles, and it is doubtful that
their action alone would dislodge a denture.
However, their presence beneath the mucous
membrane might present problems associated
with flange extension and denture retention.

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• The extent of the Buccal border is influenced
by the Buccinator muscle, which extends
from the modiolus antreriorly to the
pterygomandibular raphae postrerioly and
has its lower fibres attached to the buccal
shelf and the external oblique ridge.
• Denture covers completely the buccal shelf,
though it rests on fibres of the buccinator
because the fibers run parallel to the base
and hence its pull cannot displace the
denture.

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• The distobuccal border at the end of the
buccal vestibule must converge rapidly to
avoid displacement by the contracting
masseter.
• Distal extension is limited by the ramus of
the mandible, by the buccinator and the
superior constrictor of pharynx.
• If denture extends onto the ramus –
buccinator function is limited, also
soreness develops

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• The denture should extend
approximately one half to two thirds
over the retromolar pad as extra
pressure on the terminal portion may
limit the functions of buccinator,
superior constrictor of pharynx fibers
and tendons of temporalis which are
attached here.

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• Lingual borders should not extend below
the mylohyoid ridge as it interferes with the
function when it contracts and displaces the
denturs causing soreness.
• The flange must be made parallel to the
mylohyoid muscle but posteriorly the
border can go beyond the muscle
attachment to the mandible because the
mucolongual fold is not in this area.

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• The palatoglossus muscle and the
mucous membrane covering it form the
palatoglossal arch assist in closing the
isthmus faucium during deglutition.
• This action also exerts lateral pressure
on the lingual extension of a
mandibular denture

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• The action of the superior constrictor
of pharynx exerts pressure against the
distal extremity of the mandibular
denture.
• Overextension in this area is very
painful to the patient, as the denture
will perforate the tissue and create a
painful lesion.

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• B. Muscles associated with surfaces
of the denture and its importance
• When muscles of facial expression are
relaxed, the face lacks expression. The
actions of these muscles often reflect
the mood and emotional status of an
individual.

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• The perioral muscles of facial
expression generally do not insert
into bone and need support from
the teeth for proper function. If the
muscles of facial expression are
not properly supported, either by
the natural teeth or by the artificial
substitutes, none of the facial
expressions appears normal.

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• The nasolabial sulcus, the philtrum,
the commissures of the lips, and the
mentolabial sulcus will not have
their normal contours.
• Incorrectly positioned teeth or an
incorrectly contoured denture base
can affect the normal tonicity of
these muscles and can affect facial
expressions adversely.

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• Lack of support allows sagging of the
soft tissues of the face, while
stretching inhibits the normal
contraction of the facial muscles and
results in changes in muscle tone.

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• In an area situated laterally and
slightly above the corner of the
mouth is a concentration of the many
fibers of this muscle group.
• This concentration is known as the
muscular node, or modiolus and
represents thearea where extrinsic
perioral muscles decussate to join the
intrinsic fibers of the orbicularis oris
muscle.

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• Any muscle that inserts into the mucous
membrane of the lips is influenced by the
position of the teeth and the contours of
the denture bases.
• . Except in instances of excessive loss of
residual ridge, the origins of most of the
perioral facial muscles are removed from
the denture-bearing area to the extent that
their influence on the denture, except at
the modiolus, is negligible.

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• The labial flanges of the maxillary
denture frequently need to be reduced
in thickness in the area of the
modiolus. When the perioral muscles
are stretched during mouth opening,
the vestibular space between the
muscles in the cheek and the slopes of
the residual alveolar ridges is
restricted.

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• Reduction of the bulk of the flange to
accommodate this muscle action helps
to prevent the denture from being
dislodged when the mouth is opened.
• At times, the labial flanges of the
mandibular denture base is affected
similarly and should be reduced in
thickness.

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• The buccinator muscle provides support
and mobility for the soft tissues of the
cheek. It is a wide, muscle that arises from
a horseshoeshaped line along the outer
surfaces of the maxillary and mandibular
alveolar processes in the area of the molar
teeth.
• In addition, the buccinator originates from
the pterygornandibular raphe or ligament.
The ligament serves as the junction
between the buccinator muscle and the
superior constrictor muscle of the pharynx.www.indiandentalacademy.com

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• . A major function of this muscle is to
keep the cheeks taut. If this were not
so, when the jaws close, the cheeks
would collapse and be caught between
the teeth.
• Another very important function of
this muscle is its participation in
deglutition.

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• It is important to know at this point
that the proper external or the polished
surface is obtained by the functional
influence of buccinator, tongue and
lips to provide adequate stability for
the denture base.
• The polished surface occupies a
position of equilibrium among these
group of muscles and is referred to as
“Neutral zone”

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• Its importance is best explained by
Fish “ if there is not much ridge, the
impression and occlusal surfaces
cannot resist lateral displacement.
Therefore the only hope lies in the
third or polished surface. It must be
fashioned to fit the lips, cheeks, and
tongue, both at rest and in function.

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•The oral cavity is surrounded by muscles.
Jaw and soft tissue movements are the
products of muscle activity.
• If the muscles are strong and their activity
well coordinated, they will help the patient
use a correctly designed denture.
• Conversely, poor denture design, weak
muscles, and poor muscle coordination all
detract from denture stability and retention.

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DIAGNOSIS
• Muscle Tonus
• The tone of the facial tissue is critical
to several steps of denture construction.
• Tissue tone that is either too strong or too
weak is unfavorable.
• As a result, completing clinical
procedures may require more than the
usual amount of time.

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• If the muscles are too tense, cheek and lip
manipulations will be difficult; if too slack,
the lips and cheeks may be displaced easily
by impression materials.
• Patients may take more time than usual to
learn to use the dentures.
• Optimum functioning of the postural and
facial expression muscles requires correct
support from the natural teeth and ridges or
from correctly designed and built
prostheses.

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• Neuromuscular Coordination
• Good muscular control and coordination are
essential to the effective use of complete
dentures. They also are helpful in denture
construction.
• For example, when tongue movements are
used for border molding the lingual flanges of a
mandibular impression, the timing, direction,
and amount of movement are critical to the
success of the molding.
• Similarly, coordination of jaw movements is
important during denture construction and use.

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• On the whole as a part of physiologic
changes of aging muscle activity lacks
coordination and the muscle loose tonus.
• The cheeks sag, the mandible when it rest
appears to drop lightly more in a
protruded position. The conduction of
nerve impulses also diminishes slightly.

104
• A patient lacking ability to move the
mandible to the right place at the right time
reveals the potential for problems in
making jaw relation records before they are
attempted.
• To make an observation of muscular
control, the dentist can ask the patient to
open the mouth about halfway and move
the lower jaw from left to right, then to put
the tongue into the right cheek and into the
left cheek, to stick it out and to put it up
and back inside the mouth.

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• The ability, or lack of ability, to do these
movements on demand will be apparent.
The treatment schedule can be modified
accordingly.
• If the dentist feels the problems are
significant, the patient can be asked to
practice jaw movements at home.

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• Emphasis can be placed on deliberate
border movements ending in centric
relation.
• Practicing in front of a mirror will allow
the patient to visually coordinate the
movements.

107
• Patients with one or more of the following
symptoms usually are considered to have a
temporomandibular disorder (TMD).
• The symptoms include (1) pain and
tenderness in the muscles of mastication
and the TMJs, (2) sounds during condylar
movements, and (3) limitations of
mandibular movement.
• Quite logically, the TMJs should be
healthy before new dentures are made.

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• Unhealthy TMJs complicate the
registration of jaw relation records.
• If it is to be functional position, centric
relation depends on the structural and
functional harmony of osseous structures,
the intra articular tissue, and the capsular
ligaments.

109
• . If these specifications cannot be fulfilled,
the patient will not be able to position the
mandible in correct centric relation or, for
that matter, provide the dentist with a
repeatable one.
• Thus the importance of the routine
evaluation of a patient’s
temporomandibular function as an integral
part of complete denture treatment.

110
• Tongue
• Apart from the example of tongue
movement coordination during impression
making, tongue position and coordination
are significant in complete denture
functioning.
• A retruded tongue position deprives the
patient of a border seal of the lingual flange
in the sublingual crescent and also may
produce dislodging forces on the distal
regions of the lingual flanges.

111
• Normally, the tongue should be expected
to rest in a relaxed position on the lingual
flanges, which, if properly contoured,
will allow the tongue to help retain the
denture.
• A tongue thrust tends to dislodge a lower
complete denture by raising the floor of
the month and, in so doing, lifting the
lingual flanges and by exerting pressure
on the anterior teeth.

112
• Cheeks and Lips
• The external form of the cheeks and lips
is dependent on their internal structure
and their underlying support. This
support may be natural teeth and ridges
or denture teeth and bases.
• The muscles in the cheeks and lips have a
critical function in successful use of
dentures.

113
• The denture flanges must be properly shaped
to aid in maintaining the dentures in place
without conscious effort by the patient.
• This involves the development of the correct
arch from and tooth positions, as well as the
shape of the polished surfaces and the
thickness of the denture borders.
• The amount of denture space must be
considered carefully if fixed implant-
supported prosthesis is planned because it
does not usually provide a tissue-supporting
base.

114
• Patients with very thick cheeks may
present technical problems during some
clinical steps.
• Thick cheeks often do not allow easy
manipulation for border molding of
impression materials.

115
• Various characteristics of the lips not
only are significant for denture retention
but also are prominent in considerations
of esthetics and phonetics.
• The tissue around the mouth has wrinkles
and the rest of the face does not, lack of
lip support can be suspected and
significant improvement can be expected.

116
• Patients with thin lips present special
problems.
• Any slight change in the labio lingual tooth
position makes and immediate change in
the lip contour.
• The evaluation of anterior tooth position is
complicated by short or incompetent lips.
• Long lips tend to hide the teeth, Short teeth
may expose all the upper anterior teeth.

117
IMPRESSION MAKING
• The insertion of the muscle of facial
expression distal to corners of the mouth
at the modiolus and the position and
action of the orbicularis oris have a
definite influence in impression making.
• These muscles can be relaxed with the
jaws open, and this relaxation is desirable
when introducing the impression tray or
impression material.

118
• The patient should be trained to open the
jaws and relax the lips and cheeks to
avoid interference from a pair of tense
lips.
• When the lips are tense, a stretching
action often results in lacerations at the
corners of the mouth and/or distorted
impression material.

119
• The buccinator muscle joins the superior
constrictor at the pterygomandibular
raphe distal to the retromolar pad area.
• It is buccal to this area that the action of
the masseter muscle pushes the
buccinator muscle toward the retromolar
pad.

120
• The impression will be reflected
superiorly and medially forming a groove
called the masseter groove
• If the distobuccal flange of the
mandibular denture base is not contoured
to allow freedom for this action, the
denture will be displaced.

121
JAW RELATION RECORDS
• The muscles that move that mandible are
under voluntary control.
• These muscles can be directed to move
the mandible in various directions.
• At the first consultation appointment,
patients can be given a training exercise
that will prepare them for the time of jaw
relation records.

122
• This exercise is accomplished at home, in
a relaxed atmosphere, three times daily
facing a large mirror.
• The mandible is relaxed and with the
jaws separated slightly more than rest
position, not a wide separation, the chin is
brought forward (protruded) until it stops.
• From this position, the jaw is carried
backward (retruded) until the condyles
are felt to stop in the fossae.

123
• This exercise is continued during the
construction phase, but make certain that
patients are fully aware of when the
condyles stop in the fossae.
• At the time of recording the jaw relations,
patients are first rehearsed, and then with
the recording records in place, are directed
to protrude, retrude until they feel the
condyles stop, and then close on the back
teeth (recording media) until the anterior
teeth touch. www.indiandentalacademy.com

124
• With exercise, muscle can alter its shape
and size.
• This property of muscle provides a
method of improving the shape and size
of a tongue that is abnormal in size,
position, and/or function.

125
• If a muscle contracts too slowly or too
rapidly, the efficiency to do work is
decreased.
• Maximum efficiency is developed when
the velocity of contraction is about 30%
of maximum.
• If a muscle is in a highly contracted
state, it may contract more strongly than
normal.

126
• When an agonist muscle contacts under
physiologic conditions, the antagonist
muscle relaxes.
• Under abnormal conditions, however, the
antagonist muscle can become activated,
and the result will be change in the
agonist muscle.

127
• If a muscle is already shortened before
it is stimulated to contract, the force of
contraction is less than normal.
• If it is stretched beyond the optimum
length before contraction, the force will
also be less normal.
• These and other physiologic muscle
interactions are important in recording
the jaw relations and also in educating
patients in denture use.

128
• When a load is placed on a muscle, the
muscle elongates, and within limits the
greater the load the greater the stretch.
• When the load is released, the muscle
shortens almost to its original length. If
the load is excessive the muscle relaxes
reflexly to keep from injuring the muscle.
• The property of extensibility should be
considered when jaw relations are
recorded under manual guidance.

129
• A muscle contraction is so well graded by
the nerves system that almost many
degree of contraction can be called forth
from a muscle.
• The phenomenon of muscle is one of the
reason that a reaction of the denture
supporting tissues in one individual
varies from that of another because the
degree of muscle contraction in a given
situation can vary from person to person.

130
• Another interesting property of muscle is
its power to undergo physical contracture.
• For e.g., If a patient receives complete
upper and lower denture with an excessive
interocclusal distance, the fibers of the
elevator muscles actually shorten and
reestablish new muscle lengths
approximately equal to the maximum
length of the lever system itself, thus
reestablishing to produce optimum force of
contraction.

131
• . In contrast, over stretching the muscle makes
its normal contraction impossible and will
cause a reduction in a force of contraction.
• Muscle do not act alone. When one muscle
contracts in synergist also contracts but its
antagonist must relax. When one muscle is
short its antagonist is stretched.
• This type of interaction among muscle
agonist, synergist and antagonist must be a
coordinated effort to ensure efficient
physiology activity. When this is lost muscle
dysfunction results.

132
• When a muscle are addressed a certain
amount of tone usually remains – Muscle
Tone.
• Blocking of muscle spindle impulses
causes lots of muscle tone and the muscle
becomes almost flaccid.
• Prolonged and strong contraction of a
muscle leads to fatigue

133
• For fatigue muscle contraction becomes
weaker and weaker.
• If an individuals mandible is protruded and
allowed to remain until fatigue occurs the
antagonist action of the retractor and
elevator muscle will be weakened.
• It would be possible to retrude and elevate
the mandible to the centric position against
very little or no opposing action from the
lateral pterygoid.

134
• When the artificial teeth are placed in
positions that do not support the muscles
of facial expression in the manner of the
natural teeth or if for other reasons the
muscles lose tone, the facial expressions
change.
• Another problem is cheek biting when the
denture teeth are placed in the positions
formerly occupied by the natural posterior
teeth. With patient training and a return of
muscle tone, the problem is minimized.

135
CONCLUSION
• A good sound prosthodontic service
cannot be accomplished without
accurate impressions and records
which in turn depend on
neuromuscular co-ordination.

136
CONCLUSION
• Muscle function in general affects:
• Impression
• Occlusal plane
• Arch arrangement
• Jaw registration
• Esthetics
• Polished surface contour
• Neuromuscular skills

137
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Dental Muscles and Their Importance in Prosthodontics

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