Stomatognathic system

PRESENTED BY :
DR. PRANSHU MATHUR
JR 1
PHYSIOLOGY OF
STOMATOGNATHIC SYSTEM

CONTENTS
 Introduction
 Definitions
 Parts of Stomatognathic System
 Functional Osteology
 History
 Stress Trajectories
 Myology
 Elasticity
 Contractility
 Principles of Muscle Physiology
 Buccinator Muscle
 Buccinator Mechanism
 Role of Buccinator Mechanism
 Tongue
 Temporomandibular Joint
 Anatomy of TMJ
 Ligaments of TMJ
 Blood Supply of TMJ
 Nerve Supply of TMJ
 Functional Movements
 Positions of Mandible (Sagittal Plane)
 Functions of the stomatognathic system
 Mastication
 Masticatory strokes
 Deglutition
 Infantile Swallow
 Transition from infantile to mature
swallow
 Mature Swallow
 Deglutitional cycle
 Tongue Thrust Habit
 Respiration
 Speech
 Conclusion
 Refrences

INTRODUCTION
 The stomatognathic system is a functional unit
characterized by several structures: skeletal components,
the Temporomandibular joint and masticatory muscles.
 These structures act in harmony to perform different
functional tasks (to speak, to break food down into small
pieces, and to swallow).
 In particular, the Temporomandibular joint makes
muscular and ligamentary connections to the cervical
region, forming a functional complex called the “cranio-
cervico-mandibular system.”

DEFINITIONS
• According to Dorland’s medical dictionary
Stomatognathic - stomato (mouth) + gnathic (jaws) which
means mouth & the jaws collectively forms stomatognathic
system.
• According to Webstar’s medical dictionary
Stomatognathic- of or relating to the jaws and the mouth.

PARTS OF STOMATOGNATHIC SYSTEM
 Functional osteology
 Myology
 Temporomandibular joint
 Functions of stomatognathic system

FUNCTIONAL OSTEOLOGY
 Although bone is one of the hardest materials in the body, it is
one of the most plastic and responsive to functional forces.
 An orthodontist can establish a perfect occlusal relationship of
the teeth but unless he takes into consideration the effects of use
of these teeth and unless he allows for the manifold
environmental functional influences, the delicately responsive
bony structures are apt to change and the tooth positions will
change with them.
 Form and functions are intimately related.

HISTORY
 Since the 1830s, the architecture of cancellous tissue
and its relations to the mechanical function of bone
has been the object of study.
 Historically, the apparent effect of the functions on
bone was noted first in the femur.

Bourgery and Jacob (1832)
 In 1832 Bourgery published a huge work of anatomy
which were beautifully illustrated by Jacob.
 In the proximal end of the femur he assumes the
existence of a "compression line" along which the
cancellous trabeculae appear particularly dense and
strong whereas a lighter pattern of trabeculae is
formed outside the compression line.

• The details of Bourgery's description are often unclear and erroneous, as
is his representation of the position of the "compression line" in the
femur.
Traite complet de l'anatomie de l'homme par Bourgery. Avec planches lithographiees d'apre:s nature par Jacob.Paris 1832

Ward (1838)
 In his book on osteology (1838), Ward published a
schematic picture of the internal architecture of one
bony region, the proximal end of the femur, with a
short description of this architecture.
 The English author compares the proximal end of
the human femur with a crane, correctly up to a
certain point, and he mentions the compressive and
tensile stresses evoked in the bone by loading.

 When comparing the femur with a crane, Ward
erroneously involved the femoral head and neck
only.
Ward FO (1838) Outlines of human osteology. London, p 370

Jefferies Wyman (1849)
 Wyman described the cancellous architecture of the
vertebrae, proximal end of the femur, talus and calcaneus
more accurately than his predecessors.
 Instead of the three groups of trabeculae of Ward, he
distinguished three others areas-
a) one arising from the medial side
b) one from the lateral side
c) a third system of small transverse trabeculae connecting the
trabeculae of the first two groups.

Wyman (1857) On the cancellated structure of the bones of the human body. Boston Nat Hist: VI 125-140

Jefferies Wyman (1849)
 He correctly considered the first two systems as compression
and tension systems but he was mistaken as far as the "third
system" was concerned.
 The thin transverse trabeculae which, according to Wyman,
would constitute the third system, behave totally differently
from what the author thought and sketched.
 These trabeculae connect not only the two adjacent trabeculae
of the first two systems but also intersect each other
everywhere and constitute continuous curves which belong
either to system (a) or to system (b).

Engel (1851)
 In the German literature the architecture of cancellous bone
was described and drawn for the first time in 1851 by Engel, a
professor of anatomy in Prague (previously in Zurich).
 He wrote: "The bony trabeculae interlock each other with
surprising regularity and similarity during the building of the
skeleton in such away, for instance, that the bones of the skull
present a very delicate appearance soon after their formation.
Longitudinal or transverse cross sections through adult bones,
through the medullary cavity or through the cortex, show fine
and regular architecture which leaves nothing to be desired“.

Engel (1851)
 He also wrote “It is not without
purpose that the architecture appears
different in different bones.
Utilization of either pointed arches
or elliptical arches or circles or
perpendicular abutments or oblique
buttresses certainly has a significance
other than the pleasure of the eyes of
the anatomist enjoying this delicate
carving”.
Engel (1851);Ober die Gesetze der Knochenentwicklung". Sitzungsberichte der Wiener Academie der Wissenschaften 1851, VII, P 591, Tables 25-28

Engel (1851)
 Engel suspected the acute or elliptical arches, circles, etc., as
confirming his “growth law of animal cells”. According to
this law, the proportions of the different elements
constituting the bone could be calculated.
 For instance, it should be possible to determine “the
diameter of the medullary system from the diameter of one
medullary cavity” and “the width of the external wall and
diameter of a medullary cavity from the width of a cell
nucleus”.

Humphry (1858)
 Humphry in England (1858) explained the
mechanical arrangement of the bony structure. His
explanations result from careful observation and are
often correct.
 For instance, Humphry found that the ends of the
cancellous trabeculae are at right angles to the
articular surfaces. However, he failed to observe that
the intersections of the trabeculae are at right angles.

 He wrote: “It is interesting to
observe the manner, in which the
cancelli are arranged near the
extremities of the bones, so that
the direction of their plates is
chiefly perpendicular to the
articular surface and therefore in
the line of the pressure the bone
has to bear, thus affording the
most effective support”.
Humphry GM (1858) A treatise of the human skeleton. Cambridge

Hermann von Meyer and Culmann (1867)
 Hermann von Meyer in 1867 described the trajectories of the
cancellous trabeculae in most bones of the human skeleton and
discussed the meaning of these trajectories much more accurately
and correctly than any of his predecessors. He thus significantly
contributed to our knowledge of the internal architecture of bone.
 Professor Culmann , a mathematician from Zurich, discovered the
mathematical significance of this architecture.
 Examining the specimens of von Meyer, Culmann noticed that, in
many areas of the human body, the cancellous trabeculae were
orientated along lines which he had learnt to draw for bodies which
had the same shape and were subjected to the same forces as the
bones.

 Hermann von Meyer published the discovery of
Culmann in his first work on the architecture of
cancellous bone (1867). Based on this discovery
he claimed that the cortex of the bones must be
considered as a compaction of cancellous
trabeculae. He thus opened a new way to further
investigations on bone, the research of the
mathematical significance of the bony structure.
 In all pictures the trabeculae rising from the
medial side of the femur intersect in most places
those with rising from the lateral side at acute and
obtuse angles. The trabeculae also end in the
surface of the bone mostly at acute or obtuse
angles
Julius Wolff – The Law of Bone Remodelling. Springer-Verlag Berlin Heidelberg (1986)

 Meyer along with Culmann propounded
what was later to be called the “trajectorial
theory of bone formation”.
 He pointed out that the allignment of the
bony trabeculae in the spongiosa followed
definite engineering principles.
• If lines were drawn following discernable columns of oriented bony
elements, these lines showed a remarkably similar structures of the
trajectories seen in a crane.
• Many of these trajectories crossed at right angles – an excellent
arrangement to resist the manifold stresses on the condyle of the femur.

Julius Wolff (1870)
 Wolff used Fournier sections. The bones were sawn into as thin
slices as possible using a steam-engine devised for cutting ivory.
Here he attempted to display only one or a few longitudinal or
transverse layers of the cancellous area. The bony architecture thus
appeared more clearly than on a bone sawn through its centre. The
plates of cancellous bone appeared as trabeculae or columns. Their
correspondence to the mathematical lines then appears particularly
obvious.
 His method presented another advantage. The thin specimens
required for a thorough study can be cleared from marrow much
more completely than bones simply sawn through their centres. A
powerful jet of water from a nozzle quickly removed all the marrow
from the cavity of the Fournier sections without damaging the
delicate cancellous trabeculae.

The section was carried out on a
femur from a 15-year-old male
Coronal section through the upper end of
the tight femur of a 31 year-old man,
Julius Wolff – The Law of Bone Remodelling. Springer-Verlag Berlin Heidelberg (1986)

Julius Wolff (1870)
 Wolff claimed that the trabecular alignment was due
primarily to functional forces.
 A change in the intensity and direction of these
forces would produce a demonstrable change in the
internal architecture and external form of the bone.
 This is referred to as the “Law of orthogonality”.

Roux (1885)
 Roux and other introduced functional factors in the
development of the so called “Law of transformation
of bones”.
 In essence, the law stated that the stresses of tension
or pressure on bone stimulate bone formation.

• Subsequent researches has qualified the theories of these early bone
physiologists.
• Endochondral bone may respond differently at its growth centres than
membranous bone.
• It has been shown that both pressure and tension can produce a loss of
bone tissue that the trabeculae do not cross each other at right angles
but at varying angles and that they do not form predominantly straight
lines.
• Many of the so called trajectories are irregular and wavy, varying from
bone to bone depending on stress encountered.

• Changes in functional forces produce measurable
changes in bony architecture.
• Lack of function leads to reduction of the density
of bone tissue, or osteoporosis.
• Increased function produces a greater density of
bone in a particular area or osteosclerosis.
• An example is a condition called kyphosis, or
curvature of spine, in which some of the
vertebrae are stressed unevenly.

• Abnormal pressure on bone can cause actual change, as shown in
studies of patients with scoliosis who are being treated with Milwaukee
Brace.
• Constant pressure on mandible produces a marked effect on the vertical
dimension as well as on the teeth.
• It is important to note that the stimulating influences of muscles causes
bone to change. Adaptive changes occur in bone.

Muscles and soft tissue grow, of course but once the growth is complete, the
muscles cannot lengthen to accommodate an increase in bony bulk.
Thus, in pathological situation like acromegaly, there is a morphologic change in
the bone as it adapts to the length of the mature muscles which are not as
responsive to the same erratic endocrine stimulus.
Sicher H., du Brul E. L. : Oral Anatomy. C V Mosby Co., 1970

Benninghoff (1925)
 Made an exhaustive study of the architecture of the
cranial and facial skeleton and the stress trajectories,
similar to those seen in the head of the femur.
 He showed that these lines of stress or trajectories,
involve both the compact and the spongy bone.
 They exist in direct response to epigenetic and local
functional influences, not as manifestations of intrinsic
genetic potential.

Benninghoff (1925)
• Benninghoff showed that the stress trajectories
obeyed no individual bone limits, but rather the
demands of functional forces.
• Following the reasoning, the head is composed of
only two bones – the craniofacial skeletal units and
the mandible, the only movable bone.

MAXILLARY VERTICAL PILLARS OF
TRAJECTORIES
 There are 3 main vertical pillars of trajectories –
 Canine pillar
 Zygomatic pillar
 Pterygoid pillar

MANDIBULAR STRESS TRAJECTORIES
 The mandible, because it is a unit by itself
and a movable bone, has a different
trabecular alignment from that of the maxilla.
 Trabecular columns radiate from beneath the
teeth in the alveolar process and join together
in a common stress pillar or trajectory
system, that terminate in the mandibular
condyle.
 The mandibular canal and nerve are
protected at the same time by the
concentration of trabeculae, demonstrating
the “unloaded nerve” concept.

MANDIBULAR STRESS TRAJECTORIES
 The thick cortical layer of compact
bone along the lower border of the
mandible offers the greatest
resistance to the bending forces.
 Other trajectory patterns are seen
at the symphysis, gonial angle and
leading downwards from the
coronoid process into the ramus
and the body of mandible.

MYOLOGY
 To propel his skeleton, man has 639 muscles,
composed of 6 billions muscle fibres.
 Each fiber has 1000 fibrils, which means there are
6000 billion fibrils at work at one time or another.

 Certain basic laws govern the muscle activity.
 Muscles have two physiological properties that are
important in its kinetic energy.
 These are –
 Elasticity
 Contractility

ELASTICITY
 Normally inert elasticity of a body is related to its
length, to the cross section, to the force being exerted
and to a certain constant coefficient, which is
determined by the nature of the body.
 E =
𝐹 𝐴
𝐿 ∆𝑙

ELASTICITY
 The linear elastic range or extent of elasticity is
expressed as Hook’s Law –
 Hook’s Law states that the stress should be proportional to the
strain produced.
 Stress ∝ Strain
 Hook’s Law is also dependent on the nature of the
material involved

ELASTICITY
 With muscle, the Hook’s Law is valid and linear only
at the beginning of increase in length or load.
 Normal relaxed muscle withstands only a certain
amount of elongation (about 6/10th of its natural
length) before rupturing.

ELASTICITY
 This is only an approximation and is dependent on the
muscle involved, the type of stresses, the individual
resistance, age and possible pathologic conditions which
have produced fibrotic changes that would markedly
limit extensibility of the muscle.
 Extensibility within certain limits is quite easily
accomplished by an external force, but the muscle
returns to its exact original shape after being stretched,
illustrating the quality of elasticity.

CONTRACTILITY
 It is the ability of the muscle to shorten its length
under innervational impulse. Although the elasticity
of the muscle influences the contractility but the
phenomenon is quite different.

CONTRACTILITY
 A simplified electric current version indicates that the
muscle is stimulated by an electric action potential,
causing a contraction.
 Energy for the muscle is provided by breakdown of high
energy bonds in Adenosine Triphosphate (ATP).
 Fatigue in muscle is produced when lactic acid, an energy
breakdown by-product, collects in the tissues, lowering
the pH to a level at which the muscle can no longer
function efficiently.

CONTRACTILITY
 The strength of the contraction of a particular muscle
depends on the number of fibres engaged in this activity
at a particular time. Even during rest, a certain number
of peripheral fibres are being called on by the nerve
system for maintenance of posture.
 Maximum contractility of a muscle brings into action all
available muscle fibres.
 Each fiber that is active contracts with the same amount
of force, as long as the action potential is adequate to
start the contraction cycle.

CONTRACTILITY
 How much muscle will shorten during contraction again
depends on a number of factors (striated or smooth
muscle, number of fibres, cross section, frequency of
discharge, muscle fiber length, etc.). Some muscle may
contract as much as 50 -75% of their natural length.
 Temporalis muscle because of its relatively longer fibres,
has a greater contraction length than the masseter
muscle.

 The dentist must know that the greatest strength of
contraction is elicited when the muscle approximates
its resting length. The strength diminishes as muscle
shorten or lengthen beyond their optimal or resting
length.
CONTRACTILITY

PRINCIPLES OF MUSCLE PHYSIOLOGY
1. All or None Law (first established by the American
physiologist Henry Pickering Bowditch in 1871) –
 The all-or-none law is the principle that the strength by which
a nerve or muscle fibre responds to a stimulus is independent
of the strength of the stimulus. If that stimulus exceeds the
threshold potential, the nerve or muscle fibre will give a
complete response; otherwise, there is no response.
2. Muscle Tonus –
 It is a state of slight constant tension which is characteristic of
all healthy muscle and which serves to obviate the muscle
taking up slack when it enters upon contraction.
 It is the basis of reflex posture.

PRINCIPLES OF MUSCLE PHYSIOLOGY
3. Resting length –
 It is rather constant predeterminable relationship, permitting
maintenance of postural relations and dynamic equilibrium by
contraction of minimal number of fibres, consistent with the
demands of particular moment (muscle tonus).
4. Stretch or Myotactic reflexes –
 The reflex contraction of a healthy muscle results from a pull on its
tendon is called stretch or myotactic reflex
5. Reciprocal innervation or inhibition –
 Inhibition of tonus or contractility of muscle may be brought about
by the excitation of its antagonist.
 Without reciprocal innervation or inhibition, the myotactic or stretch
reflexes would make flexion and extension simultaneously.

 Muscles are a potential force whether they are at
rest or in active function.
 There is a strong interdependence on the bone and
muscle.
 Teeth and other supporting structures of the jaw
are under the control of muscles.
 The balance between the muscles is responsible for
the integrity of the dental arches and the relation
of the teeth in the dental arch.

BUCCINATOR MUSCLE
 Buccinator is a quadrilateral muscle between maxilla and
mandible and it forms the mobile and adaptive substance
of cheek.
 Origin –
 Arises from outer surface of alveolar process of
maxilla and mandible opposite third molar teeth
and posteriorly attached to pterygomandibular
raphe.
 Insertion –
 Anterior buccinator fibers converge towards the modiolus near the
buccal angle.
 The central fibers decussates so that it continues into the orbicularis
oris muscle.
 The highest and lowest fibers enter into the corresponding lips

BUCCINATOR MUSCLE
 Actions –
 It draws the corner of the mouth laterally pulling the lips
against the teeth and flattens the cheek.
 It aids in functions like swallowing , blowing, whistling etc.
 It keeps cheek in close contact with teeth so prevents pocketing
of food between teeth and the cheek .

BUCCINATOR MECHANISM
 Starting with the decussating fibres of the
orbicularis oris muscle, joining other right
and left fibres in the lips, the buccinator
mechanism running laterally and
posteriorly around the corner of the
mouth, joining others fibres of buccinator
which inserts into the pterygomandibular
raphe just behind the dentition.
 Here it mingles with the fibres of superior
constrictor muscle and continues
posteriorly and medially to anchor at the
origin of superior constrictor muscles, and
the pharyngeal tubercle of occipital bone.
Thus completely encircling the face.

ROLE OF BUCCINATOR MECHANISM
 Role of buccinator mechanism is in maintaining arch
form and teeth maintaining arch form and teeth
position.
 The integrity of dental arches and the relationship of
the teeth to each other within each arch and with
opposing members are result of morphogenetic
pattern as modified by stabilizing and active
functional forces of muscle the tongue on one side
and lips and cheek on other side.

TONGUE
 Opposing the buccinator mechanism is a very
powerful muscle – the tongue.
 The tongue begins its manifold activities even before
birth, when it functions in the swallowing of the
amniotic fluid.
 It is relatively one the best
developed structures of the
human body.

TONGUE
 Winders (1958) has shown that
during mastication and
deglutition, the tongue may exert
two to three times as much the
force on the dentition as the lips
and cheeks at one time; but the
net effect is counterbalanced by
the tonal contraction and the
peripheral fiber recruitment of the
buccal and labial muscles and the
atmospheric pressure team up to
offset the momentarily greater
functional force of the tongue.
Winders R. V. Forces exerted on the dentition by the perioral and lingual musculature during swallowing. Angle Orthodont., 28:226-235 1958

TONGUE
 Has amazing versatile functional abilities (mainly
due to the fact that it is anchored at only one end)
 Deforms the dental arches when function is
abnormal.
 Aside from the ability to maintain the integrity of
the dental arches, it also plays a huge role in infant
nursing particularly when the teeth are still absent.

 The balance between the muscles is responsible for the
integrity of the dental arches and the relation of the teeth in
the dental arch.
 Any imbalance in the buccinator mechanism leads to
malocclusion
 In pernicious oral habits like thumb sucking, tongue
thrusting, the equilibrium between the buccinator mechanism
is lost. This causes various changes in dentition like:
 Constricted maxillary arch
 Increased proclination
 Openbite

 Diagrammatic
representation to show
muscle groups concerned
with maintaining the balance
of the head on the vertebral
column.

 The head is balanced, the eyes
are open and the mandible is
suspended in postural rest
during waking hours.
Kahn F : Man in structure and function. Alfred A. Knopf, 1943

 Sleep or lack of
consciousness reduces
muscle activity to the
minimum, allowing the head,
mandible and eyelids to
drop.
Kahn F : Man in structure and function. Alfred A. Knopf, 1943

TEMPOROMANDIBULAR JOINT
 It is an articulation of the
condyle of the mandible and
the inferior surface of the
squamous surface of the
temporal bone (glenoid
fossa).
 It is also a synovial joint.

ANATOMY OF TMJ
 Interposed between the head of the condyle and the
articular eminence is the ARTICULAR DISC.

LIGAMENTS OF TMJ
Gray H. Grays Anatomy. 20th edition. Lea and
Febiger, Philadelphia and New York (1918)
Atlas of Human Anatomy, Sixth Edition- Frank H. Netter, M.D

 A rather unique feature of the
Temporomandibular articulation
is that it is really 2 joints.
 The attachment is made in such a
way that the articular disk
between the condyle and the
articular eminence serve to
separate the structures into 2
separate joint cavities.

 Each Temporomandibular
joint is classed as a
“GINGLYMOARTHRODIAL”
joint since it is both
a ginglymus (hinging joint)
and an arthroidal (sliding)
joint.

BLOOD SUPPLY OF TMJ
 Branches of the
 Superficial Temporal Artery
 Maxillary Artery
supply the
Temporomandibular joint.
 Veins follow the arteries.

NERVE SUPPLY OF TMJ
 Auriculotemporal Nerve
 Masseteric Nerve

FUNCTIONAL MOVEMENTS
 The mandible is the only movable bone in the head
and face and it can be only moved in certain
directions because of the limitations of morphology
and of the structures of the Temporomandibular
articulation.
 Mandibular movements are a complex phenomenon. All
the muscles that are attached to the mandible influence
the position and movements of the mandible and
maintain the head posture.

 Muscles primarily responsible for
mandibular movements are:
1. Anterior and posterior fibres of the
temporalis muscle
2. Lateral pterygoid muscle
3. Anterior, middle and posterior components
of masseter
4. Suprahyoid muscles
5. Infrahyoid muscles

OPENING OF MANDIBLE
 Starting with the teeth in occlusion, the
mandible is opened by the condyle being
brought downward and forward as the chin
point drops downward and backwards.
 Gravity and also the primary contraction of
the lateral pterygoid muscles are largely
responsible for the opening movement.
 Stabilizing and adjusting activity is seen in
the suprahyoid and infrahyoid groups, in
the geniohyoid, mylohyoid and digastric
muscles.
 The stylohyoid muscle changes in length.
 The hyoid bone itself moves downward and
backward with the opening movement of
the mandible.
Atlas of Human Anatomy, Sixth Edition-
Frank H. Netter, M.D

 The temporalis, masseter and medial pterygoid
muscles show a controlled relaxation as the
mandible opens.

OPENING OF MANDIBLE
 During opening movements of the
mandible, the articular disc is brought
forward by lateral pterygoid muscle and
intimately related capsular ligaments as
the condyle rotates against the inferior
surface of the disc and the disc itself
glides forward on the articular surface.
 This controlled relaxation serves to make
opening movements smooth.
 It has been shown that paralysis of one or
more of these basic mandibular closers
may make the opening jerky and
uncontrolled.

CLOSING OF MANDIBLE
 It is also a coordinated activity of closing
and opening muscles.
 More power is elicited on mandibular
closure due to bilateral activity of
masseter and temporalis muscles,
assisted by the smaller medial pterygoid
muscles.
 The hyoid bone moves upward and
forward during mandibular closure.
 The lateral pterygoid muscle, through
their controlled relaxation, helps effect a
smooth and uninterrupted activity.

LATERAL MOVEMENTS OF MANDIBLE
 To establish the “working bite”, the
mandible must be moved to the
right or left.
 This lateral movement is initiated
by the combined activity of the
lateral and medial pterygoid
muscle on one side and controlled
relaxation on the other side, and by
the contraction of temporalis
muscle on one side and controlled
relaxation on the opposite side.

BENNETT MOVEMENT
 In the lateral shift of the mandible, the articular disc moves
towards the side of the working bite. This is known as the
“Bennett Movement”.
 The condyle moves slightly laterally and rotates on the
working side.
 On the balancing side, the condyle and disc move downward
and forward on the articular eminence.

POSITIONS OF MANDIBLE
 Basic sagittal plane positions of the mandible are :
1. Postural Resting Positions (Physiologic Rest)
2. Centric Relation
3. Initial Contact
4. Centric Occlusion
5. Most Retruded Position (Terminal Hinge Position)
6. Most Protruded Position
7. Habitual Resting Position
8. Habitual Occlusal Postion

POSTURAL RESTING POSITIONS
 It is one of the earliest posture positions to be
developed.
 Mandible is literally suspended from the cranial base
by the cradling musculature.
 Here the jaws are separated by a constant distance
(Freeway Space 2-3 mm).
 Even though the muscles are not in active function, a
limited number of fibres are apparently still
contracting to maintain the relaxed position of the
mandible and posture of the head.

POSTURAL RESTING POSITIONS
 Posselt (1968) observed – the postural position can be
altered by conditions in the masticatory system as well as
by systemic factors.
 Various factors influencing postural positions are –
 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.

CENTRIC 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
are in contact with the concavities of the articular
disks as they approximate the posteroinferior
third of their respective articular eminences.
 This means that the mandible is deviated
neither to the right nor to the left side and is
neither protruded nor retruded.
 Such a relation can be the same to the
postural resting position, the point of initial
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 and can be easily
reproduced by having the patient bring the teeth together, if
there is no malocclusion or malformation present.
 Centric occlusion must be 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 RERUDED POSITION
 Also called as the “Terminal Hinge Axis 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 as it would
compress the tissues.

MOST PROTUDED POSITION
 This position is variable from individual to
individual than the retruded position. It is
reproducible within the same individual.
 Flaccidity of capsular ligament allows
condyle to over ride the anterior margin of
the eminence.
 When the condyles are locked anterior to the
articular eminence, the muscles go into
partial tetanic contraction and a fatigue
syndrome is set up.

HABITUAL RESTING POSITION
 There are certain types of malocclusions that prevent the
patient from achieving a physiologic resting position.
 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 and that they are in harmony with centric relation
and the postural resting position of the mandible.
 In malocclusion, there is asynchronous activity of the closing
muscles in habitual and working bite occlusions.

TRACING OF MANDIBULAR MOVEMENTS

FUNCTIONS OF STOMATOGNATHIC
SYSTEM
 The functions of stomatognathic system are equally
to discuss.
 They are –
 Mastication
 Deglutition
 Respiration
 Speech

 The orofacial musculature is relatively the most
sophisticated in the new born so that the patency of
the airway breathing and nutritional demands may
be met.
 Already present as unconditional reflexes (for there
is no time to learn these life saving activities) are
oropharyngeal reflexes for mandibular posture,
respiration, tongue position, deglutition, suckling,
gagging, coughing, vomiting and sneezing.
SYSTEM

 Tactile sensation is extremely well developed in the new
borns.
 In utero
o 14 weeks – stimulation of lips causes tongue to move,
stimulation of upper lips may cause mouth closure
and even deglutition.
o 18 ½ weeks – gag reflex starts
o 25 weeks – respiration is possible
o 29 weeks – suckle can be elicited
o 32 weeks – suckling and swallowing
 At birth, the mouth is almost the sole avenue of
communication with the outside world and the tactile acuity
of this continues as the child brings all objects to the mouth
first.
SYSTEM

MASTICATION
 It is the reduction of food in size, changing its consistency,
mixing it with saliva, and forming into a bolus suitable for
swallowing.
 In the infant, the food is taken in first by suckling. This is an
unlearned or automatic reflex in Homo sapiens.
 At no time of life are more muscles involved in intake of food
than in the new born.
 The classic suckle - swallow position in the newborn shows
–
 Head extended
 Tongue elongated and low in the floor of the mouth
 Jaws apart
 Lips pursed around the nipple.

MASTICATION
 As the infant learns to take solid food, the intensity of the act
of satisfying hunger is reduced, but most of the muscles of the
cheeks, tongue and floor of the mouth are involved. There is
less activity of the lips and less mandibular thrust.
 The infant quickly learns to use his lips primarily to keep the
food from being forced out of the mouth during the
peristaltic-like action of the tongue and cheeks as the bolus of
food is forced back towards the pharynx.
 In the infant, as the bolus takes up the saliva, it is forced
between the gum pads or the occlusal surfaces of the erupting
teeth.

 At the same time, the rhythmic action of the muscles of
the cheek serves to force the food back towards the
tongue, which mashes the bolus of food against the hard
palate.
 To permit the bolus of food to interpose between the
gums pads or teeth, the mandible is depressed by gravity
and the hyoid and lateral pterygoid muscles, with a
simultaneous deflection towards the working side.
 The lateral shift of the mandible is more apparent in
hard-to-chew foods.
MASTICATION

MASTICATORY STROKES
 Fletcher (1965) summarized his work on masticatory
stroke in the adult, using 6 phases outlined by
Murphy –
 The Preparatory Phase
 Food Contact
 The Crushing Phase
 Tooth Contact
 The Grinding Phase
 Centric Occlusion

MASTICATORY STROKES
1. The Preparatory Phase –
Food is ingested and positioned by the tongue in the oral
cavity and the mandible is moved towards the chewing
side.
It is assisted by the gravity and little muscular force is
involved.
2. Food Contact –
Characterized by a momentary hesitation in movement.
Interpreted to be a pause triggered by sensory receptors
concerning the apparent viscosity of the food and probable
transarticular pressures incident to chewing.

MASTICATORY STROKES
3. The Crushing Phase –
Starts with high velocity then slows as the food is crushed
and packed.
4. Tooth contact –
Accompanied by a slight change in direction but otherwise
by its constancy of position, there is no delay.
According to Murphy, all reflex adjustments of the
musculature for tooth contact are completed in the
crushing phase before actual contact is made.

MASTICATORY STROKES
5. The Grinding Phase –
Coincides with transgression of the mandibular molars
across their maxillary counterparts and is therefore
highly constant from cycle to cycle.
Also termed as Terminal functional orbit.
During this phase the bilateral muscular discharge
becomes unequal and asynchronous, indicating that
the person is chewing unilaterally.

MASTICATORY STROKES
6. Centric Occlusion –
When the movement of teeth comes to a definite and
distinct stop at a single terminal point, from which the
preparatory phase of the next stroke begins.
 Masticatory frequency is variable, but appears to be one
or 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 constant.

DEGLUTITION
 It is the process in the human or animal body that
makes something pass from the mouth, to the pharynx,
and into the oesophagus, while shutting the epiglottis.
 It is also be termed as the act of swallowing of food.
 In infants and the adults the mechanism of swallowing is
a complex procedure and is different in both of them.
 The average individual swallows about once in a minute
between meals and as frequently as 9 times a minute
during eating.

INFANTILE SWALLOW
 Infants swallow food by suckling. This is an
autonomic reflex in human beings.
 Development of swallowing begins around 12.5
weeks of intra uterine life. Full swallowing and
sucking is established by 32-36 weeks of IU life.
 Suckling and swallowing reflexes are present in full
term baby and their absence would suggest a
development defect.

INFANTILE SWALLOW
Characteristics of Infantile Swallow –
 The jaws are apart, with the tongue in between the
gum pads.
 The mandible is stabilized primarily by the
contraction of the muscles of the VIIth cranial nerve
and the interposed tongue.
 The swallow is guided, and to a great extent
controlled by sensory interchange between the lips
and the tongue.

TRANSITION FROM INFANT SWALLOW TO MATURE
SWALLOW
 With the change to semisolid and solid food and the
eruption of teeth there is also a modification of
swallowing act.
 The tongue no longer forced into the space between gum
pads or incisal surfaces of the teeth, which actually
contact momentarily during the swallowing act.
 Mandibular thrust diminishes during a transitional
period of 6 to 12 months.

TRANSITION FROM INFANT SWALLOW TO MATURE
SWALLOW
 The mandibular 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 spatula like portion of the tongue collects the food
and forces it posteriorly.
 The tip of the tongue is no longer moving in and out
between the anterior gum pads but assumes a position
near the incisive foramen at the moment of deglutition.

MATURE SWALLOW
Characteristics of Mature Swallow – (3 years of age)
 The teeth are together.
 The mandible is stabilized by the contraction of the
mandibular elevators, which are primarily Vth cranial
nerve muscles.
 The tip of the tongue is held against the palate, above
and behind the incisors.
 There are minimal contraction of the lips during the
mature swallow.

DEGLUTITIONAL CYCLE
 Fletcher divides the deglutitional cycle into four
phases –
 Preparatory Swallow
 Oral Phase of Swallowing
 Pharyngeal Phase of Swallowing
 Oesophageal Phase of swallowing

PREPARATORY SWALLOW
 Starts as soon as the liquid
is taken or after the bolus
has been masticated.
 The liquid or bolus is then
in a preparatory swallow
position on the dorsum of
the tongue.
 The oral cavity is sealed by
the lips and the tongue.

ORAL PHASE OF SWALLOWING
 During this phase, the soft palate
moves upwards and the tongue
drops downwards and backwards.
 At the same time the larynx and
hyoid bone move upwards.
 These combined movements
create a smooth path for the bolus
as it is pushed from the oral cavity
by the wave-like rippling of the
tongue.
 The oral cavity, stabilized by the
muscles of mastication, maintains
an anterior and lateral seal during
this phase.

PHARYNGEAL PHASE OF SWALLOWING
 Begins as the bolus passes
through the fauces.
 The pharyngeal tube is raised
upwards en masse, and the
nasopharynx is sealed by
closure of the soft palate against
the posterior pharyngeal wall
(Passavant’s Ridge).
 The hyoid bone and the base of
the tongue moves forwards as
both the tongue and the
pharynx continue their
peristaltic like movement of the
bolus of food.

OESOPHAGEAL PHASE OF SWALLOWING
 Commences as the food
passes the
cricopharyngeal sphincter.
 While the peristaltic
movement carries the
food through the
oesophagus, the hyoid
bone, palate and tongue
return to their original
position.

TONGUE THRUST HABIT
 The prolonged retention of infantile swallowing
mechanism can be a matter of concern and may well
contribute to the creation of malocclusion.
 Some clinicians have observed malocclusion in over 80%
of persons with abnormal swallowing patterns.
 Intraoral manifestation of tongue thrusting habit may
include –
 Anterior open bite
 Proclined anterior teeth
 Generalised spacing between teeth.

RESPIRATION
 Respiration, like mastication and swallowing, is also an
inherent reflex activity.
 Also referred to as ventilation where in there is entrance of
oxygen and release of carbon dioxide.
 The demands on musculature are subtle and more difficult
to observe.
 The fantastically efficient split-second opening and closing
of the epiglottis, keeps out the food but permits the entry of
the life-giving air.

RESPIRATION
 Bosma and his co-workers have analysed respiration in
infant and found that quiet respiration is typically carried
out through nose, with the tongue in proximity to the
palate, obturating the oral passageway.
 Both pharynx and larynx are active during respiration
and it is in this area that the infant differentiates between
respiration and associated activities, such as grunt,
cough, cry, or sneeze.
 Posture has a significant effect on respiration.

RESPIRATION
 Respiration maintains the patency of the pharyngeal
area, since there is collapse of the pharynx in the
tracheotomized infant.
 Development of respiratory spaces and maintenance
of airway are significant factors in orofacial growth.
 The mechanism of crying is intimately tied up with
respiration, and the laryngeal and pharyngeal
coordination od muscles is quite early seen.

RESPIRATION
Characteristics of Normal Respiration –
 Presence of normal seal
 Normal atmospheric pressure
 Normal TMJ
 Normal Occlusion
 Normal antero-posterior relationship of maxilla and
mandible
 Tongue is kept within the oral cavity
 Establishment of physiologic rest positionn

SPEECH
 Speech, like breathing, also makes no gross demands on
perioral muscles.
 Although all mammals apparently masticate, swallow
and breath, speech is limited only to the human beings.
 Unlike mastication, deglutition and respiration, which
are reflexive in nature, speech is largely a learned activity
dependent on the maturation of the organism.

SPEECH
 A large number of muscles are involved in the speech.
 The muscles of the wall of the torso, the respiratory tract,
the pharynx, the soft palate, the tongue, the lips and the
face, and the nasal passageways are all concerned in the
production of the speech sounds.
 Simultaneous breathing to provide a column of air is
essential to produce vibrations necessary for sound.

SPEECH
 The lips, tongue and the velopharyngeal structures
modify the outgoing breath stream to produce vibrations
in the sound.
 Assuming the presence of normal structures, speech
production is dependent on the coordinated action and
precise activity of muscle 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.

SPEECH
Process involved in speech production and organisation –
 Respiration - simultaneous breathing to have stream of air from
lungs is needed to produce vibrations.
 Phonation - actual production of speech sounds.
 Resonance – process by which sound is intensified or amplified.
 Articulation – breaking up of sound and modification of sounds
from lung. This involves the complex conditioning movements of –
 Lips
 Cheek
 Palate
 Tongue
 Posterior laryngeal walls

ARTICULATION OF SOUND
 By varying the
relationships of the lips
and tongue to the palate
and the teeth, a variety of
sounds can be produced.

SPEECH DIFFICULTIES RELATED TO
MALOCCLUSION
Speech Sounds Problem Related Malocclusion
/s/, /z/ (sibilants) Lisp Anterior Open Bite, Large
Gap between Incisors
/t/, /d/ (lingua-alveolar
stops)
Difficulty in production Irregular Incisors,
especially lingual position
of maxillary incisors
/f/, /v/ (labiodental
fricatives)
Distortion Skeletal Class III
th, sh, ch (linguodental
fricatives) [voiced or
voiceless]
Distortion Anterior Open Bite

CONCLUSION
 Anatomy of stomatognathic system is the basic pillar for any dental
clinician whose sound knowledge is very important; it helps in diagnosis
and treatment of many oral disorders.
 Its knowledge helps in orthodontic treatment in such a manner that the
finished result reflects a balance between the structural changes obtained
and functional forces acting on the teeth and investing tissue at that time.
 The orthodontist is challenged constantly with the task of providing each
patient with acceptable esthetics and masticatory function. Although
esthetics is often the patient’s immediate and primary goal, functional
outcomes are far more important over the lifetime of the patient.
 Developing a sound functional masticatory system needs to be the primary
goal of all orthodontic therapy. No other dental specialist routinely alters
the patient's occlusal condition as a part of the therapy.

REFERENCES
 Julius Wolff – The Law of Bone Remodelling. Springer- Verlag Berlin
Heidelberg (1986).
 Graber T. M. Orthodontics Principals and Practice. 3rd edition. W B
Saunders (2001).
 Traite complet de l'anatomie de l'homme par Bourgery. Avec planches
lithographiees d'apre:s nature par Jacob.Paris 1832
 Ward FO (1838) Outlines of human osteology. London, p 370
 Wyman (1857) On the cancellated structure of the bones of the human
body. Boston Nat Hist: VI 125-140
 Engel (1851);Ober die Gesetze der Knochenentwicklung".
Sitzungsberichte der Wiener Academie der Wissenschaften 1851, VII, P
591, Tables 25-28..

 Humphry GM. A treatise of the human skeleton. Cambridge (1858).
 Sicher H., du Brul E. L. : Oral Anatomy. C V Mosby Co., 1970
 Winders R. V. Forces exerted on the dentition by the perioral and
lingual musculature during swallowing. Angle Orthodonthics., 28:226-
235 1958
 Kahn F : Man in structure and function. Alfred A. Knopf, 1943
 Atlas of Human Anatomy, Sixth Edition- Frank H. Netter, M.D
 Gray H. Grays Anatomy. 20th edition. Lea and Febiger, Philadelphia
and New York(1918).
 B D Chaurasia’s Human Anatomy – Regional and Applied, Dissection
and Clinical. 5th edition. CBS(2010).
REFERENCES

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