Physiology of the stomatognathic system /certified fixed orthodontic courses by Indian dental academy

PHYSIOLOGY OF THE
STOMATOGNATHIC
SYSTEM
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com


INTRODUCTION
 Stomatognathic- of or relating to the jaws
and the mouth :webstar’s medical dictionary
 As a dentist and especially as an orthodontist,it
is essential that we have a sound knowledge of
and understand the importance of the
stomatognathic system
 Until we know what is normal we will not be
able to recognise aberrancy

Functional Osteology
 Bone is one of the hardest tissues of the human body
 But it is most adaptive and responsive to functional
forces
 Meyer -1864:proposed the trajectory theory of bone
formation
 >the arrangement of the trabeculae in the spongiosa
followed a trajectory pattern
 1870:julius wolff>these trabecular arrangement was
due to functional forces
 Any change in direction or intensity of the forces would
change the internal archietecture

Contd.
 Was expresseds by a mechanical mathematical law=
law of orthogonality
 Now it is established that cartilagenous and
membranous bones react differently to forces
 Tajectories need not pass at right angles to each
other—even their course may be wavy
 Increased function increases bone density while
decreased function decreases itmuscles have a great
influence over bones and may even change their
shape
 Thus the timed manipulation of the musculature
may be beneficial to the orthodontist

Beninghoff’s trajectories
 Concluded that trajectories can be demonstrated in the
maxillo-facial area
 Lines pass through both the spongy and compact bone
 They obey no individual bone margins
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Maxilla:
Transfers the whole stress to the cranium
Has thin cortices that are interconnected by trabeculae
Stress trajectory:can be considered as the
craniofacial unit

 3 main pillars of
trajectories:
 All from the alveolar bones
an endin in the base of the
skull
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The canine pillar
The zygomatic pillar
The pterygoid pillar

 Curve around the
sinuses,nasal and orbital
opening
 The supra and infra orbital
ridges and the zygomatic
buttress reinforce these
pillars

 Mandible
 Absorbs all the stresses
 Thick cortices and more radially arranged
trabecuae
 Stress trajectories
 From beneath the teeth-join together in comman
pillar—ends at the condyle
 Mandibular canal and nerve are protected-unloading
of nerve

 Thick cortical layer at the base rovides esistance to
bending forces
 Trajectories from www.indiandentalacademy.com and coronoid
the symphysis,angle
process join this main pillar

myology


myology
 Property of muscles that are important fr help
in kinetic activity are
 Elasticity= the ability to return to oiginal lemgth and
shape after contraction or extension
 Normally relaxed muscle withstand only a certain
amount of elongation
 Contractility=the ability to contract forcefully when
stimulated by an action potential
 Energy for this is provided by high energy bonds of
ATP
 Lactic acid accumulation leads to fatigue

 Each fibre is either relaxed or in complete
contraction(all or none law)
 The state of the muscle depends on how many
such fibres are active
 Isometric contraction when muscle resists
external stress withot shortening-only the
tension increases
 Isotonic contraction when the tone or
tension remains the same but the length
decreases

 The greatest of contraction is seen when the muscle
approximates its resting position
 The strength reuces as the muscle shortens or lengthens beyond
this position

 Other principles of muscle physiology
 All or none law
 Intensity of contraction is independent of the strength of thr action
potential as long as the threshold is crossed
 Seen only when the muscle is not fatigued
 Muscle tonus
 State of slight constant tension
 Basis of reflex posture

 Resting length
 Rather constant
 Permits maintenance o postural relationship

 Reciprocal innervation and
inhibition
 Inhibition of contraction may be brought about
by excitation of the antagonist
 It is through this that movements are
coordinated

Buccinator mechanism
 there is strong inter relarionship between bone
an muscle
 Muscles are a potent force-at rest or when
active
 Teeth and supporting tissues are influenced by
the contiguous musculature
 The balance between the tongue and the perioral musculature influences the morphology of
the dental arches and the teeth

 The shape and size o the tooth root and the
periodontal spaces also helps in the final
adaptation
 During swallowing and mastication- tongue
exerts 2-3 times more force than the peri oral
muscles
 Counter acted by the tonal
contraction,atmospheric pressure,peripheral
recruitment from the buccal musculature

 Even though doubs still
eist about such a
balance o force-we must
admit that aberration of
muscles can an do lead
to
markedmalocclusion

 The continuous
band of muscle that
encircle the
dentition and attach
to the pharyngeal
tubercle comprises
the buccinator
mechanism

Mechanism contd.


Tongue
 Opposing the buccinator mechanismis a very
powerful structure- the tongue
 It has multiple functions
 Most developed in a new born
 In infancy extrinsic suspensory muscles attach
the tongue to the osseous structures
 Produces gross movement in the gorizontal
direction(suckle-swallow)

Contd.
 Attached only at the posterior end-can perform many
functions
 Abnormal functions cause deformation in the dental
arches
 May be caused by either deformed arches or visceral
swallow pattern
 Leads to proclination o the maxillary
incisors,constriction of buccal segment an may create
an open bite
 Compensating action of mentalis causes retraction of
the lower incisors

MUSCLES OF THE TONGUE

INTRINSIC

EXTRINSIC

Superior longitudinal

Genioglossus

Inferior longitudinal

Hyoglossus

Transverse

Styloglossus

Vertical

Palatoglossus


Muscles of the tongue


SUPERIOR LONGITUDINAL
MUSCLE
Shortens the tongue & makes the dorsum concave

INFERIOR LONGITIDINAL MUSCLE
Shortens the tongue & makes the dorsum convex

TRANSVERSE MUSCLE

Makes the tongue narrow & elongated

VERTICAL MUSCLES

Makes the tongue broad & flattened

jhg


EXTRINSIC MUSCLES

Genioglossus - Mandible
Hyoglossus

- Hyoid bone

Styloglossus

- Styloid process

Palatoglossus - Palate


Hyoglossus

– depresses the tongue

Styloglossus - pulls it upward & backward
Genioglossus – Protrudes the tongue out of the

mouth by pulling the posterior part forwards
Palatoglossus – brings the palatoglossal arches
together, thus shutting the oral cavity
from the oropharynx

TMJ


 Articulation between the mandibular condyle
and the inferiorsurface of the sqamous portion
of the temporal bone
 Compound –movable joint

 Meniscus-a fibrous connective tissue
wafer fills most of the space between the
condylar head and the articular fossa and
divides the joint cavities into 2
compartments.

normally occupies only half of the joint space,
with its posterior attachments filling the
posterior half. The disc and its posterior
attachments are generally referred to as the
soft tissue component of the TMJ.
all the above mentioned structures are enclosed
with in the capsular ligament
It is lined by synovial membrane

Head of the condyle is tubular or ellipsoidal
Unique feature of the joint is that there are
actually 2 joint spaces-seperated by the disc
Thus the joint is capable of dual funcion
Lower cavity—rotary/hinge movement
Upper cavity—gliding/translatory movement


 Activity only in the lower cavity till the mnible is
opened to the physiological rest position
 After tis even gliding motion takes place
 When opened in his manner the articular disc
glides over the articular eminence
 The condyle rotates against the inferior surface
of the disc
 Lateral pterygoid helps to move the disc
anteriorly

 In the lateral shift/bennet movement the
conyle on the working side rotates nd moves
laterally
 The condyle on the other ide noves forwards
and mesially in an arc
 There is no muscle which ertracts the discnothig opposite the action of the lateral
pterygoid
 Posterior limit formed by the squamo-tympanic
fissure—medially by the petro-tympanic fissure

 Due to overclosures-the isc is move forward
and the conyle rides over the posterior border
of the disc
 Impinges on the retrodiscal soft tissues-cicking
an discomfort to the patient-misdiagnosed as
arthritic changespain may be ue to impingment
or ue to pterygoid muscle spasm(mpd)
 The main reason fo the mpd is neurogenic or
psychological

 The tmj is beautifully engineerd to hanle
multiple tasks endowed to it
 To maintain it-proper occlusal management an
mainenance of vertical dimensions is essential


functional movements of
the mandible
 Mandible ah 13 muscles attached to it
 Due to limitations of morphology and structure
of the tmj-can be moved only in certain
directions
 Has postural stability along with primay
movements


Forced retrusion Posterior fibres of the
temporalis,masseter,suprahyoid muscles
opening

lateral pterygoid-main. Supra,infra hyoidgenio,mylo hyoids,digasric>stabilising
Temporalis,masseter,medial
pter.>controlled relaxation

closure

Temporalis, masseter >main action
medial ptery. >part action
Lateral ptery >cntrolled relaxation

protrusion

Lateral and medial pter.

Lateral
movement

Temporalis + lat. pter

COMPENSATORY MUSCLE FUNCTIONS
 While mastication may call for most potent
effort from the associated muscles, the most
frequent demands are made by deglutition,
respiration, speech and posture.
 At times two or more of these functions are
carried on simultaneously.
 where there is malocclusion or abnormal
morphologic relationship certain compensatory
or adaptive muscle functions may arise, either
to restrain the dental malocclusion or to
actually increase the discrepancy.

Positions of the mandible
 basic positions are
 Postural resting position (Physiologic
rest)
 Centric relation
 Initial contact
 Centric occlusion
 Most retruded position (terminal hinge
position)
 Most protruded position
 Habitual resting position
 Habitual occlusion position

POSTURAL RESTING POSITION

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It is one of the earliest posture positions to be
developed. Mandible is suspended from the cranial
base by the cradling musculature. Here the jaws are
separated by a constant distance. Factors
influencing the postural position are the following:
Body and head posture
Sleep
Psychic factors influencing muscle tonus
Age
Proprioception from the dentition and muscles
Occlusal changes such as attrition
Pain
Muscle disease and muscle spasm and
Temporomandibular joint disease.

CETRIC RELATION
 As far as muscle physiology is concerned,
centric relation may be defined as unstrained,
neutral position of the mandible in which the
anteriosuperior surfaces of mandibular
condyles - in contact with the concavities of the
articular disks as they approximate the
posteroinferior third of their respective
articular eminentia.
 This means that the mandible is deviating
neither to the right nor to the left and is neither
protruded no retruded.
 Such a relation can be the same as the
postural resting position, the point of initial
occlusal contact and centric occlusion.

INITIAL CONTACT
 As the mandible moves from physiologic rest or
the postural resting position toward occlusion of
teeth, if all is normal it maintains a centric relation
position as far as the articular fossae are
concerned.
 If there is normal occlusion the point of initial
contact produces no change in the function of
temporomandibular joint and all inclined planes
are brought together simultaneously in the
maxillary and mandibular teeth.
 Premature contacts are seen quite frequently,
they can initiate deflections in the mandibular path
of closure.
 This causes traumatic forces to be exerted on the
teeth and severe cases will produce
temporomandibular joint problems

CENTRIC OCCLUSION
 Centric occlusion is a static position
 It is harmonious with the centric relation
 Teeth brought into contact with unstrained
relation of the condyles
 Few patients can show centric occlusion
 Establishes the occlusal vertical dimension
 Not necessarily the maximum
intercuspation position

MOST RETRUDED POSITION
(Terminal Hinge Position)
 Reproducible retruded mandibular
position with the teeth in occlusion
 Normally starting point in occlusal
rehabilitation
 Some patients can easily retrude a few
mm. while others find it difficult
 Mandible should not be guided or forced
beyond the unstrained position of the
mandible-unbiological-would compress
the tissues. www.indiandentalacademy.com

MOST PROTRUDED
POSITION
 This position is variable from individual to
individual than the detruded position.
 Shows the range of movement of the
mandible
 Flacidity of capsular ligament allows
ondyle to over ride the anterior margin of
the eminence
 Condyle locked-muscles tetanisedfatigue

HABITUAL RESTING POSITION
 There are certain types of malocclusions that
prevent the patient from achieving a physiologic
resting position.
 Example in class II div 2 malocclusion with
maxillary incisors inclined lingually there is a
tendency to force the condyles posteriorly and
superiorly in the articular fossae
 the physiologic resting positions can be changed
due to mental disturbances, enlarged adenoids,
temporomandibular joint pathology, psychic
trauma, selective paralysis by poliomyelitis and
confirmed mouth breathing etc.

HABITUAL OCCLUSAL POSITION
 In normal occlusion the centric occlusion
and habitual occlusion should be the same.
But the occlusal relationship can be
changed when there is an environmental
imbalance induced by improper restoration,
tooth loss etc.
 It is vitally important that the dentist make
sure that the habitual occlusal position and
the centric occlusal position are the same
 they are in harmony with centric relation
and the postural resting position of the
mandible.

Functions of the system
 These are
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Deglutition
Mastication
Respiration
Speech


DEGLUTITION
Infantile swallow ( visceral swallow)

Mature swallow ( somatic swallow)

INFANTILE (VISCERAL) SWALLOW


CHARACTERISTICS OF INFANTILE
SWALLOW
The jaws are apart, with the tongue between the
gum pads
The mandible is stabilized by contraction of the
muscles of the 7th cranial nerve & the interposed
tongue.
The swallow is guided, & to a great extent
controlled by sensory interchange between the lips &
the tongue.

TRANSITION PERIOD
At about the 5 to 6th month of age, as the

incisors begin to erupt, certain proprioceptive
impulses come into play & the peripheral portions
of the tongue starts to spread laterally.
An average infant would show a dominant &
exclusive thrusting swallow for the first 6 months of

life,a transitional thrusting & lateral spread of
tongue during the next year & a dominant somatic

swallow thereafter. www.indiandentalacademy.com

MATURE ( SOMATIC)
SWALLOW


CHARACTERISTICS OF
MATURE SWALLOW
The teeth are together
The mandible is stabilized by contraction of the
mandibular elevators,which are primarily 5th cranial
nerve muscles
The tongue tip is held against the palate, above &
behind the incisors
There are minimal contractions of the lips during the
mature swallow.

DEGLUTITION CYCLE
FLETCHER gave 4 phases
1.Preparatory swallow
2.Oral phase of swallowing
3.Pharyngeal phase of swallowing
4.Esophageal phase of swallowing

PREPARATORY SWALLOW
 Starts as soon as liquids
are taken in, or after the
bolus has been
masticated
 The liquid or bolus is
then in a swallowpreparatory position on
the dorsum of the
tongue.
 The oral cavity is sealed
by lip & tongue.

Oral phase of swallowing
 Soft palate moves upward &
the tongue drops downward &
backward
 Larynx & hyoid bone move
upward
 Smooth path for the bolus as
it is pushed from the oral
cavity by the wave like
rippling of the tongue
 Oral cavity is stabilized by the
muscles of mastication, &
maintains the anterior &
lateral seal


Pharyngeal phase of
swallowing
 Begins as the bolus passes
through the fauces
 The pharyngeal tube is raised
upward en masse
 Nasopharynx is sealed off by
closure of the soft palate
against the posterior
pharyngeal wall
 Hyoid bone & base of tongue
move forward as the pharynx
& tongue continue their
peristaltic – like movement of
the bolus of the food


Esophageal phase of
swallowing
 Commences as the food
passes the
cricopharyngeal
sphincter
 While peristaltic
movement carries the
food through the
esophagus, the hyoid
bone , palate & tongue
return to their original
positions

Mastication
 In the infant food is taken by sucklingunlearned or automatic reflex
 Rythmic cving in of the cheeks,bobbing of the
hyoid bone,snake like movement of the
tongue,anterior movement o the ongue and
nodding movement of the head
 Mandible is protuded
 During deglutition rythmic contractionof the
tongue and facial musclesaids in stabilising the
mandible

Contd.
 Change to solid food-lesser action of the lips
and lesser thrust o the mandiblelteral thrust of
the mandible seen-more to the working side
 6 phases outlined by murphy
 1)preparatory phase=>food in mouth-tongue
positions it-mandible moves to working side
 2)food contact=>characterised by a pauseprobably to determine food consistency

Contd.
 3)crushing phase=>starts with high velocity
and slows down as food is crushed
 4)tooth contact=>takes place with skight
change in direction-muscles are already ready
for this
 5)grinding phase=>transgression of the
mandible across the maxillary teeth-most
patients chew unilaterally-cyclic event
 6)centric occlusion=>mandible back to terminal
position-next cycle begins

Respiration
 Inherent reflex activity
 Demand on muscles are more subtle and more difficult
to appreciate
 Posture has a significant effect on respiration
 Oral musculature is responsible for vital positional
relationships-maintains the airway
 In the infant-airway maintained by Mandible maintained anteroposteriorly
 Stability f the tongue and post. Pharyngeal wall
 Axial musculature around the vertebrae

Cont.
 All the learned jaw functions are built around
and accomodated to the tongue and
mandibular positions wich ake clear airway
possible
 Maintainance of the respiratory spaces and
airway is significant in facial growth
 Respiration in the chil helps keeping the
pharynx patent as well
 Important for development of speech as well

Speech
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Learned activity –depends on maturation of organism
Makes use of muscles that have other functions
According to WEST other than speech functions are::
A>innate,automatic,vegetativeswallowin,breathing,gagging etc.
B>learned,automatic,vegetative-biting,chewing,sucking
C>lerned,automati,emotional-grimaces,mannerisms
D>innate,automatic,emotional-laugh,smile.sob
E>learned,non automatic,discriminatory,voluntaryexplore with tongue,spreading lips,kissing,blowing

 F>learned,automatic practical reactionswhistling,playing instrument,humming

Muscles involved
Walls of the torso,the respiratory tract,the
pharyx,the soft palate,the tongue,the lips
and face and nasal passageways are
involvedsimultaneou
breathing is necessary to provide
vibrations for sound
Tongue,lips and velopharyngeal closure
moify utgoing stream to produce sound

 Normal structure is necessary for production of
sound-in cleft palate cases not possible even
with muscular compensation
 Speech mechanism changes air
direction,flow,release,pressure,general and
lingual air path
 Any aberrancy may lead to compensatory
morphological changes like enlarged
adenoids,compressed nares etc.

With respect to tongue

 In infancy-suckle reflex is active-only extrinsic
muscles are well developed-only later the
intrinsic muscles capable of speech develope

 The lips and the tongue undergo maturational
changes
 Degree of lip protrution varys the length of the
vocal tract
 With the reduction of suckle swallow-delicate
movements of the lips are noted.

Velopharyngeal closure

 Very important for the dentist-in conditions of
cleft palate-inadequate valving is seen-even in
rehabilitated cases
 Upward and backward movement to contact
the post pharyngeal wall is important for certain
sound production
 It is seen that compensatory lip and tongue
activity is present to ward over
malocclusions.

conclusion
 The study of the intra oral and peri oral
structures-their normal morphology and activity
is very important for us.
 Unless we know what is normal it is difficult to
recognise and correct abnormalities
 Also, the structures are all inter related ::follow
scientific principles and order in their
development.
 It becomes important to follow the functions of
the structures which ultimately leads to
changes in the morphology..

bibliography
 Orthodontics:principles and practicesT.M Graber
 Orthodontics:Graber and Vanarsdal
 Contemporary Orthodontics:
William.R.Proffit
 Handbook Of Facial Growth
:Donald.H.Enlow

Physiology of the stomatognathic system /certified fixed orthodontic courses by Indian dental academy

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