-Enosh Steward Nirmalkumar (20)
Submitted to department of orthodontics
Topics to be covered :-
Structures of stomatognathic system
Functions of stomatognathic system
Abnormal functions of stomatognathic system
Summary and conclusion.
When we want to check occlusion of teeth, we have the
patient close his mouth and we open the lips to see how
upper and lower teeth meet, or we carefully articulate the
plaster casts in fullest contact. This static analysis is
important, but equally important is a dynamic appreciation
of how these part functions.
It is becoming increasingly apparent that function can
influence the overall pattern and the very foundation of
stomatognathic system. We must know more about function
than just how mastication works. Equally important is the
full appreciation of, deglutition, respiration, speech and even
the maintenance of head in the constant postural position.
• STRUCTURES OF STOMATOGNATHIC SYSTEM
1) The jaw
The upper and lower jaws are the major part of
stomatognathic system. It helps in attachment of muscles,
supports the teeth.
Teeth are arranged in upper and lower jaw and are
supported by alveolar bone and periodontium. Teeth are
helpful for mastication and phonation.
The tongue is a highly muscular as well as adaptive organ. It
is made up of intrinsic as well as extrinsic muscles.
Intrinsic muscles are
- Superior longitudinal
- Inferior longitudinal
Extrinsic muscles of tongue are
Muscles are a potent force, whether they are in active
function or at rest. As we have seen resting muscle still
is performing a function that of maintaining posture
and a relationship of contagious parts.
The teeth and supporting structures are constantly
under the influence of the contagious musculature.
The integrity of dental arches and the relations of the
teeth to each other with opposing members are the
result of morphogenetic patterns, as modified by the
stabilizing and active functional forces of the muscles.
During mastication and deglutition, the tongue may
exert two or three times as much force on the dentition
as the lips and cheeks at any one time.
Buccinator mechanism is a continuous band of muscles
that encircle the dentition & is firmly anchored at the
pharyngeal tubercle of the occipital bone
Starts with decussating fibres of orbicularis oris joining
the right and left fibres of the lip which constitute the
anterior component of the buccinator mechanism
Runs laterally and posteriorly around corner of the
mouth, joining other fibres of the buccinator muscle
which gets inserted into pterygomandibular raphe.
Tongue acts opposite to buccinators mechanism
exerting an outward force
Muscles of mastication
• Lateral pterygoid
• Medial Pterygoid
• Origin- Bone of temporal fossa and temporal fascia
• Insertion- Coronoid process of mandible and anterior margin
• Nerve supply- Deep temporal nerves from anterior trunk of
• Function- Elevation and Retraction of mandible
•Origin: Upper head – infratemporal surface & crest of greater
wing of sphenoid bone; Lower head – lateral pterygoid plate
• Insertion :Pterygoid fovea on the anterior surface of neck of
mandible and Anterior margin of articular disc & capsule of TMJ
• Nerve Supply: Pterygoid branch of Trigeminal nerve
• Function: Depresses the mandible; Protrudes it forward for
opening of the jaw; Side Movements
• Origin- Medial surface of lateral plate of pterygoid process
and pyramidal process of palatine bone ; Superficial head-
tuberosity and pyramidal process of maxilla
• Insertion- Medial surface of mandible near angle
• Nerve supply- Nerve to medial pterygoid from the
• Function- Elevation and side to side movements of the
• Origin- Zygomatic arch and Maxillary process of zygomatic
• Insertion- Lateral surface of the ramus of the mandible
• Nerve supply-Masseteric nerve from the anterior trunk of the
• Function- Elevation of the mandible
WOLFF’s law of transformation of bone
In the year 1870, Julius Wolff gave the reason for the
arrangement of trabecular pattern
He attributed that the trabecular arrangement is due to the
“A change in the direction and magnitude of force could
produce a marked change in the intermal architecture and
external form of the bone”
Increase in function leads to increase in the density of bone
Trajectories of force/Benninghoff’s lines
The trajectorial theory states that the lines of orientation of
the bony trabeculae follow the pathways of maximal
pressure and tension
These lines of orientation of the bony trabeculae involve not
only the cancellous bone but also the compact bone
The stress trajectories respond to the demands of the
functional forces collectively as a unit and not as a single
Head is made up of only two functional units
1) Craniofacial unit
Physiologic rest position
Its defined as the position of the mandible when the muscles
of mastication are in a minimum tonus of contraction
Factors influencing rest position are
Body and head position, psychic factor, sleep, age, pain, tmj
Freeway space is the measured distance between the
occlusal surfaces of maxillary and mandibular dental arches.
Normal freeway space is 2-4mm
A large freeway space is related to excessive deep bite e.g.
Class II div 2
INITIAL CONTACT:-When the patient takes the mandible
from the rest position to occlusion, the position at which first
tooth contact occurs is called initial contact position.
CENTRIC RELATION:-Centric relation is the unstrained
neutral position of mandible in which the anteroposterior
surfaces of the mandibular condyles are in contact with the
concavities of the articular disc.
Bennett Movement:- Bodily side shift of the mandible
towards the working side during lateral excursion is called
Bennett movement is necessary to permit rotation of the
working condyle, because of the restraining influence of the
temporomandibular ligament on the working side, the walls
of the glenoid fossa
The working side condyle may either rotate, or rotate and
move laterally, and also upwards or downwards.
Stages of Bennett movement : Immediate shift or
progressive side shift
If the lateral component occurs early in the movement, it is
termed as immediate or early side shift
A gradual lateral component is termed as progressive side
Bennett angle:- When the working side condyle shifts laterally,
the non-working side condyle moves downwards, forwards and
Angle formed between the forward and inward movements of the
non-working condyle and a straightforward movement is known
as Bennett angle
Gothic arch:-The border movements of the mandible in the
horizontal plane are often described as a gothic arch when
observed in the incisal area
FUNCTION OF STOMATOGNATHIC SYSTEM
Mastication or chewing is the process by which food is
crushed and ground by teeth
In the infant food is taken in first by suckling. This is an
unlearned or autonomous reflex in homo sapiens.
The classic suckle swallow position in the new born, as
outlined by Bosma, shows the head extended, tongue
elongated and low in the floor of mouth, jaw apart and
lips pursed around the nipple.
As the infant learns to take the solid food, the intensity
of act of satisfying hunger is reduced, but most of
muscles of cheek, tongue and floor of mouth are
There is less activity of lips and less mandibular thrust.
The infant quickly learns to use his lips primarily to keep
the food from being forced out of mouth during the
peristaltic like action of the tongue and cheeks as the
bolus of food is forced back towards the pharynx. The
ingested food is mixed with saliva by active tongue
In the infant, as the bolus takes up the saliva it is forced
between gum pads or the occlusal surfaces of the
At the same time the rhythmic action of muscles of
cheek serves to force the food back toward the tongue,
which mashes the bolus of food against the hard palate.
After the bolus of food is accommodated between
occlusal surfaces, the mandible is forcibly closed,
primarily by temporal and masseter muscle activity.
Fletcher summarizes, recent work on masticatory stroke
in the adult, using the six phases outlined by Murphy.
a) The preparatory phase
In which food ingested and positioned by the
tongue with in the oral cavity and the mandible is
moved towards chewing side.
b) Food contact
It is characterized by a momentary hesitation in
movement. This Fletcher interpreted to be a pause
triggered by sensory receptors concerning the
apparent viscosity of the food and probable trans-
articulator pressures incident to chewing.
c) The crushing phase
If starts with high velocity then slows as the food is
crushed and packed.
d) Tooth contact
Accompanied by a slight change in direction but
not delay. According to Murphy all reflex
adjustments of the musculature for tooth contact
are completed in the crushing phase before actual
contact is made.
e) The grinding phase
Which coincides with transgression of the
mandibular molars across there maxillary
counterparts and is therefore highly constant from
cycle to cycle.
Messerman termed this phase the terminal
Ahelgren noted that during this phase the bilateral
musculature discharge becomes unequal and
asynchronous indicating that the person is chewing
f) Centric occlusion
When movement of the teeth comes to a
definite and distinct stop at a single terminal
point from which the preparatory phase of next
Masticatory frequency is variable but appears to
be one to two strokes per second with a normal
bolus of food. The number of masticatory
strokes before swallowing seems to be
characteristic of the individual and is relatively
It is defined as the mandibular position in which
there is maximum intercuspation of the teeth
2) Deglutition (swallowing)
a) Infantile (visceral) swallow
Moyers lists the characteristics of the infantile swallow as
1) The jaws are apart with the tongue between the gum pads.
2) The mandible is stabilized primarily by contraction of
muscles of VII cranial nerve and the interposed tongue.
3) The swallow is guided and to a great extend controlled by
sensory interchange between the lips and the tongue.
As stated above, the gum pads are not usually in contact
during the act of swallowing. With liquid food particularly a
„clucking‟ is frequently heard.
The intrinsic and rhythmic peristaltic like muscle activity
steers the liquid or bolus of food back into the pharynx by
the superior, middle and the inferior pharyngeal constrictors,
past the epiglottis into the esophagus.
The glottis closes off the pharynx as the posterior peripheral
portion are forced backward against the superior constrictor
b) Mature (somatic) swallow
With the change in semisolid and solid food and the eruption
of the teeth there is also a modification of swallowing act.
The tongue no longer is forced into the space between gum
pads or incisal surfaces of teeth, which actually contact
momentarily during the swallowing act.
Mandibular thrust diminishes during transitional period of 6-
12 months. The mandible closing muscles take over more of
the role of stabilizing the mandible as the cheek and lip
muscles reduce the strength of their contraction.
The tip of the tongue is no longer moving in and out
between anterior gum pads but assumes a position near the
incisive foramen at the moment of deglutition.
The change to the adult swallowing pattern occurs gradually
in what he has been called the transitional period.
Neuromuscular maturation, change in head posture
gravitational effect on mandible are conditioning factors.
Usually by 18 months of age, the mature swallow
characteristics listed by Moyers are –
1) The teeth are together
2) The mandible is stabilized by contraction of the
mandibular elevators, which are primarily V cranial nerve
3) The tongue tip is held against the palate, above and
behind the incisors.
4) There is minimal contraction of lips during the mature
Phases of deglutition
Fletcher divides the deglutition cycle in 4 phases, highly
integrated and synergistically coordinated.
2) Oral phase
3) Pharyngeal phase
4) Esophageal phase
Starts as soon as liquids are taken in, or after the bolus has
been masticated. The liquid or bolus is then in a swallow –
preparatory position on the dorsum of tongue. The position
on the dorsum of tongue. The oral cavity is sealed by lip and
2) Oral phase
During the oral phase the soft palate moves upward and
tongue drops downward and backward. At the same time
the larynx and hyoid bone move upward. The combined
movement create a smooth path for the bolus as it is pulsed
from the oral cavity by the wave-like ripping of the tongue.
While solid food is pushed by tongue, liquid food flows
ahead of the lingual constrictions. The oral cavity, stabilized
by the muscles of masticating maintains an anterior and
lateral seal during this phase.
3) The pharyngealphase
Begins as the bolus pulses through fauces. The pharyngeal
tube is raised upward and the nasopharynx is sealed off by
closure the soft palate against the posterior pharyngeal wall.
The hyoid bone and the base of the tongue move forward as
both the pharynx and the tongue continue these peristaltic
like movement of the bolus of food.
4) The esophageal phase
Swallowing commences as food passes the cricopharyngeal
sphincter. While peristaltic movement carries food through
the esophagus, the hyoid bone palate and tongue return to
their original positions.
The average individual swallows, about once/ twice a minute
between meals. Even during sleep the swallowing act is
performed at infrequent intervals.
These are various estimates of the frequency of deglutition,
which range as high as somatic and visceral swallows per
Respiration, like mastication and swallowing is an inherent
reflex activity. A wonder to behold is the fantastically
efficient split second opening and closing of the epiglottis,
keeping out the blood but permitting the entry of life giving
Bosma and his co-workers have analyzed respiration in the
infants and found that quiet respiration is typically carried
out through the nose, with the tongue in proximity to palate,
obstructing the oral passageway.
Both the pharynx and larynx are active during respiration
and it is in this area that the infant differentiates between
respiration and associated activities such as the cough cry or
sneeze. Posture also has a significant effect on respiration.
Respiration maintains the potency of the pharyngeal area,
since there is a collapse of pharynx in the tracheotomized
infant. Development of respiratory spaces and maintenance
of airway are significant factor in oro-facial growth i.e.
functional matrix theory.
The mechanism of crying is intimately tied up with
respiration, and the laryngeal and pharyngeal coordination
of muscles is seen quite early.
Speech like breathing, also makes no gross demands in the
perioral muscles. Although all mammals apparently
masticate, swallow and breathe speech is limited to the
Unlike mastication, deglutition and respiration, which are
reflexive in nature, speech is largely a learned activity
dependent on a maturation of organism.
The muscles of walls of the respiratory tract, the pharynx,
the soft palate, the tongue, the lips and face and the nasal
passages ways all are concerned in the production of speech
Simultaneous breathing to provide a column of air is
essential to produce vibrations necessary for sound. The lips
and tongue structures modify the outgoing breath stream to
produce variations in the sound.
Assuming the presence of normal structure, speech
production is dependent on the coordinated action and
precise activity of muscles that may be performing other
functions at the same time.
If the structures are not normal, as with cleft palate, normal
speech sounds may not be possible, despite the
compensatory muscle activity.
Even though the mechanisms for producing sounds involve
at least parts of the same system used for mastication,
respiration and speech, actions used in producing language
The speech mechanism acts on the breath streams in a
number of ways, controlling the air mechanism, air direction,
air flow, air release, air pressure, general air path and lingual
In cleft palate, with palatal insufficiency, the inability to
control the air path may elicit adaptive reaction elsewhere,
e.g. greater postpharyngeal wall activity, enlargement of
turbinates, mandibular postural position change, contraction
of the nares, enlargement of tonsils and adenoids.
With respect to the tongue, which fills the oral cavity at
birth, only the extrinsic muscles which largely control
horizontal movement needed for the suckle-swallow are well
Those intrinsic muscles needed for speech are poorly
developed. The transition from gross movements of tongue
to precise and finely controlled ones extends over the first
several years of life, through the infantile and transitional
swallowing periods, into the mature deglutitional pattern
ABNORMAL FUNCTIONS OF STOMATOGNATHIC
1) Mouth breathing
If the palate is high and narrow, the dorsum of tongue does
not fit against the palatal vault everywhere and a potential
away exist between tongue and palate.
If in addition, lips do not meet, the oral airway is complete
from open lips to the oro-pharynx. So air can be drawn in
and expired just as easily through mouth cavity as through
Mouth breathing is more commonly seen in children and
decreases with age. Also more common during sleeping.
Who have increased resistance to or a complete obstruction
of the normal flow of air thorough nasal passages. Because
of difficulty in inspiring and expiring air through nasal
passages the child is forced by sheer necessity to breathe
through his mouth.Seen in adenoid facies.
A child who continuously breathes through his mouth by
force of habit, although the abnormal obstruction has been
Whose shorter upper lip does not permit closure without
Effects of mouth breathing
• Tongue position is low and forward to keep oral airway
• Lips are flaccid, short upper lip, with lack of tonicity.
• Labial flaring of maxillary anterior teeth. Hyper trophy of
• Frequently marked overbite.
• Dryness of mouth
• Gingivitis and increased dental caries.
• Affected gingiva is demarked from unaffected gingiva, the
junction has been referred by „Worwick‟ as tension ridge.
1) Naso-pharyngeal obstruction
Obstruction may be due to
a) Nasal deformities – DNS
b) Irritation or thickening of mucosal membrane of nose
c) Bone pathology
d) Enlarged adenoids.
2) Mouth habits
Thumb sucking lip biting, finger or nail biting, tongue
3) Abnormal development
b) Short upper lip
4) Psychosomatic problems
May also show mouth breathing
Bruxism is a conscious or subconscious act performed by an
individual which overrides the protective neurologic mechanism
of masticatory system. In bruxism there is increase in tonic
activity in the jaw muscles.
Emotional or nervous tension, pain or discomfort and
occlusal interferences are the factors that can increase
muscle tone and lead to non-functional clenching.
• Tenderness of masticatory muscle
• Incisal wear, occlusal facets
• TMJ pain, headache or tiredness of masticatory muscles.
1) Psychic tension
Nervous children may develop bruxism
2) Occlusal discrepancies
Increased muscle tonus
Also seen in epilepsy, meningitis chorea.
3) Tongue Thrust
It is also known as perverted or deviated swallow, retained
infantile swallow, tooth apart swallow, tongue thrust
syndrome or abnormal swallow.
In the tongue thrust
The tip of the tongue is placed against or between the teeth
during swallowing. Then the mid portion of tongue does not
contact the hard palate and does not assure 450 angulations
relative to the past-pharyngeal wall as in normal swallowing.
Since in abnormal swallower the tongue is placed between
the teeth. Masseter muscle activity is prevented and as a
consequence these is no molar contact during deglutition.
Active mentalist muscle is noted.
Fletcher has collected a grouped patterns associated with or
characteristic of tongue thrust. They may include some or all
1) A thrusting movement of tongue against or between
2) Slight or no contraction of muscles of mastication.
3) Strong contraction lip musculature
4) Movement hyoid bone in oblique or forward direction
5) Distortion of speech sound
a) Anterior tongue upper and lower incision.
b) Lateral or posterior – premolar and molar region
a) Simple tongue thrust
This is localized posturing forward, of the tongue during rest
and active function with localized anterior openbite.
b) Complex tongue thrust
Forward tongue posture, tongue thrusting during swallowing,
contract of perioral muscles, excessive buccinator
hyperactivity. When all these symptoms present the pattern
is often called as complex tongue thrust.
Incidence and duration of tongue thrust
- High incidence in school going children and patients with
Fletcher associates reported following incidence
At age 6 years - 52.3%
8 years - 38.5%
9 years - 49.9%
10 years - 34%
Effects of tongue thrust
• Anterior openbite
• Lateral or posterior open bite
• Proclinated upper incisors
• Hypotonic upper lip which appear retracted or short
• Bilateral narrowing of maxillary arch
1) Bottle feeding due to rapid artificial with long feeding
nipple which may have enlarged opening.
The structure of the components of the face that is inherited,
rather than habit itself.
3) Oral habits – Thumb sucking, open bite.
4) Ankyloglossia or macroglossia may cause tongue thrust.
5) Tonsillar tissue – If tonsiller tissue enlarged, can create
destruction in oro-pharyngeal are a posterior to root of
tongue. As a consequence tongue may be boned to posture
6) CNS disorders – Neuromuscular problems can be severe
enough to prevent normal adult swallow. Recent
investigations has been accumulating demonstrate that so
called tongue thrust seems more likely to be the effect than
the cause of malformations. The tongue is a very adoptive
organ on an auxiliary function of the tongue to seal the
anterior gap when the lip mastication is too weak to produce
and oral seal.
Lisping and stammering
These are commonly occurring speech defects.
Speech defect create difficulty for the child while speaking.
Social adjustment is also affected because other children
laugh at his defect. The child may develop inferiority
complex. He develops a sense of insecurity.
This speech defect involves change of sound of letters and
Main cause is continuity of infantile mode of speech. If the
tongue is moved forward without mandible and lies on top of
lower incisors lisping may result.
Certain malocclusions like openbite, maxillary protrusion,
mandibular retrusion and mal-aligned tooth also cause
In stammering the child fails to produce any sound for
sometime. These create emotional tension and difficulty in
- Due to emotional tension
- Lack of balance among two hemispheres of the brain.
- Auditory amnesia
Before any treatment is started or during diagnosis, all
functions of stomatognathic system should be checked and if
not proper it can be primary etiologic factor in a
Many dysfunctions are acquired in the early stages of
Malocclusions that are acquired as a result of dysfunctions
can usually be treated simply by elimination of disturbing
environmental influences, which will foster normal
When the child is seated on dental chair, we should check for
breathing whether it is nasal or oro-nasal.
It is diagnosed by giving a sip of water to patient and ask to
keep it in mouth and by placing cotton in between nose and
The etiologic factors of mouth breath is first recognized and
then they are removed like correction of nasal obstruction.
Later on the restoration of oral health is done by giving
proper habit breaking appliances and also different exercises
like deep breathing, vigorous exercises, playing on blowing
type of musical instruments and lip exercises.
The masticatory apparatus contains teeth, muscles of
mastication, TMJ movement. The functioning should be
In case of bruxism there is presence of occlusal facets, or
occlusal interference, pain in TMJ or tenderness of muscles of
So the therapy includes elimination of triggering elements,
mainly discrepancies between centric relation and correction
by occlusal adjustment, by giving occlusal bite plate,
protective mouth guard or rubber splints.
Between 2 to 4 years of age mature swallow is seen in
normal developmental patterns.
A proper diagnosis of tongue thrust should be done on the
basis of clinical features or by checking the swallowing
patterns. Circumoral tension is being used as diagnostic
criteria by many clinicians.
After diagnosing a tongue thrust habit it should be properly
If the tongue thrust is present at 3 to 9 years of age no
appliance therapy is usually indicated only the dentist instruct
the patient how to swallow correctly.
On recall appointments if the openbite improves or remains
same, this approach is continued until 9 years of age.
If open bite continues to increase intraoral therapy is
If the tongue thrust present after 10 years of age then
dentist should consider using intraoral appliance when the
malocclusion is confirmed to an anterior open bite.
If tongue thrusting is associated with lisping, only a speech
therapist should be encouraged to correct the speech
problem using articulation therapy.
During diagnosis attention should be given towards speech
also. The etiology of speech problem should be recognized
and proper treatment should be given.
The presence of speech defects in childhood is due to lack of
sufficient training and maturity. As these factors are provided
the speech defects disappears.
The guardians and teachers should therefore encourage
children to pronounce correctly.
If defect continued till late age then they are removed by the
means of surgery.
SUMMARY AND CONCLUSION
Before the orthodontist appreciates abnormal functions of the
oro-facial muscles he must have a knowledge of their normal
development and maturation.
Abnormal functions or habits may be considered normal for a
certain stage of child‟s development. The abnormal functions
are particularly more at young age because of psychological
requirements and emotional adjustments in that period.
In young patients, new ideas are more easily learned and
more easily broken, so the treatment of habit should be
started as early as possible.
Its more difficult to break habit in an adult.
• Grays Anatomy for students 2nd
• Friedman MH, Wusberg I. Screening procedures for
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• Janda V. Some aspects of extracranial causes of facial pain.
J Prosthet Dent. 1981;56:484–7
• Orthodontics - Sridhar Premkumar