Role of Function in Malocclusion Etiology

Role of Function
In the
Etiology of
Malocclusion
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com

Contents
Introduction
Orthodontic equation
Classification
Moyers
Grabers
Respiration
Mechanics of respiration
Modification of respiration by sensory
feedback

Response of respiratory muscles to changes in
respiratory feedback
Clinical examination to assess mouth
breathing
Airflow measuring devices
Mouth breathing and malocclusion
Long face syndrome
Obstructive sleep apnea syndrome

Deglutition
Introduction
Review of literature
The swallowing pattern
Infantile swallow
Mature swallow
Tongue thrust
Simple tongue-thrust swallow
Complex tongue-thrust swallow
Retained infantile swallow

Mastication
The masticatory cycle
Speech

INTRODUCTION

Traditionally any deviation from an ideal
occlusion was termed as malocclusion.
Unfortunately there is no clear-cut definition
for an ideal occlusion. This is because it is
difficult to establish an individual norm
since function and physiologic adaptation
should be considered to determine an
individuals normal occlusion.

It is commonly accepted that the etiology of any
problem should be contained in the diagnosis.
Malocclusion is a developmental problem, not a
pathologic one, and although we can say that both
hereditary and environmental factors are important
influences on development, often we are not able
to ascertain which malocclusions are determined
largely on genetic basis and which result largely
from environmental factors and which are a
combination of both.

Classification of etiology of
Malocclusion
It is traditional to discuss the etiology of
malocclusion by beginning with a clinical
classification and working back to causes of
each problem.
It must be recognized at the outset that any
arbitrary division of causes is purely for the
sake of analysis.
The idea of studying etiology in terms of the
primary tissue site was first suggested by
Dockrell.

Dockrell’s Orthodontic equation

The primary etiologic sites are
 Neuromuscular system
 Bone
 Teeth
 Soft tissues
Malocclusions may involve four tissue systems: teeth,
bones,soft tissues, muscles and nerves. In some cases
only the teeth are irregular; jaw relationships may be
good and muscles and nerve functions normal. In
other cases teeth may be regular in their alignment,
but an abnormal jaw relationship may exist, so that
the teeth do not meet properly during function. Or
again, the malocclusion may involve all four systems,
with individual tooth malpositions, abnormal jaw
relationship and abnormal nerve and muscle function.

Moyers has classified the etiology of
malocclusion into seven groups as
1) Heredity
2) Developmental defects of unknown origin
3) Trauma
Prenatal trauma and birth injuries
Postnatal trauma
4) Physical agents
Premature extraction of primary
teeth.
Nature of food

5) Habits
Thumb sucking and finger sucking
Tongue thrusting
Lip sucking and lip biting
Posture
Nail-biting
Other habits

6) Disease
Systemic diseases
Endocrine disorders
Local diseases
Nasopharyngeal diseases and
disturbed respiratory function
Gingival and periodontal diseases
Tumors
Caries
7) Malnutrition

Graber has classified Etiology of
Malocclusion into the following
General factors
Heredity
Congenital defects
Environmental
Prenatal
Postnatal
Predisposing metabolic climate and disease
Endocrine imbalances
Metabolic imbalances
Infectious diseases
Dietary problems ( nutritional deficiency)www.indiandentalacademy.com

Abnormal pressure habits and functional aberrations
Abnormal suckling
Thumb and finger sucking
Tongue thrust and tongue sucking
Lip and nail biting
Abnormal swallowing habits
Speech defects
Respiratory abnormalities
Tonsils and adenoids
Psychogenic tics and bruxism
Posture
Trauma and accidents

Local factors
Anomalies of number
Supernumerary teeth
missing teeth
Anomalies of tooth size
Anomalies of tooth shape
Abnormal labial frenum; mucosal barriers
Premature loss
Prolonged retention
Delayed eruption of permanent teeth
Abnormal eruptive path
Ankylosis
Dental caries
Improper dental restorations

RESPIRATION

The effects of mouth breathing on the skeletal
morphology and malocclusion have long
been debated and are still unclear.
Mouth breathing has long been considered a
significant factor in the etiology of
malocclusion. Throughout the history of
orthodontics, there have been proponents of
this concept.
Equally, there have been opponents who
dispute the role of mouth breathing as a
clinically significant factor in orthodontics.

A major obstacle to resolving this issue lies in
the absence of a clearly stated definition of
"mouth breathing.
" Who s a mouth breather?
Is mouth breathing synonymous with an
absence of nasal respiration?
Is mouth breathing a combination of oral and
nasal breathing?
Is nasal obstruction (however measured) an
indisputable indicator of oral breathing?
Can nasal respiration exist with concurrent
partial nasal obstruction?

These are fundamental questions which need to
be addressed if clinically useful concepts are
to develop in this area.
It is obvious that, for survival, respiration must
continue throughout life. It is equally clear
that if the nasal passages are completely
blocked, survival depends on adaptation to
produce oral respiration.
However, complete obstruction of the nasal
airway is a relatively rare condition.
Even transient nasal congestion is considered
to be uncomfortable.

However, it does not follow that this
automatically results in oral breathing.
The preferred mode of respiration for human
beings is apparently nasal.
This is phylogenetically related to respiration
in the primates and other mammals who are
obligatory or near-obligatory nasal breathers.
It is entirely conceivable that in the human
being relatively high degrees of nasal
obstruction are overcome to maintain nasal
airflow if, indeed, nasal respiration is the
preferred mode of function.

The critical value of the nasal obstruction at
which this becomes impossible or too difficult
is not yet known. In the absence of data
which describe the physiologic and
aerodynamic variability of respiration in a
cross section of the population, one can only
speculate on the possible morphogenetic role
of this aspect of function.

MECHANICS OF RESPIRATION
Breathing is the movement of air into and out
of the lungs, results from contractions of the
respiratory muscles which produce changes
in the volume of the chest cage. The lungs
fill the thoracic cavity and its outer surface
(visceral pleura) is in intimate contact with
the inner surface of the thoracic cavity
(parietal pleura).

The two pleural layers are in apposition, separated
only by a thin film of fluid which enables the
lungs to slide freely within the cavity.
Whenever the chest enlarges, the lungs also
enlarge.
At the end of expiration when the respiratory
muscles are relaxed, pressure within the lungs
(pulmonary pressure) is atmospheric and there
is no airflow. This is the resting position.
Both the lungs and the chest wall contain
considerable elastic tissue, and at resting
position these pull with equal force but in the
opposite direction, creating a balance of elastic
forces.

Although the lungs and chest operate as a unit, the
two would have different resting positions if
separated.
That is, the lungs would collapse and the thoracic
cavity would expand.
When contraction of the diaphragm and the
intercostals muscles occur during inspiration, the
volume of the thoracic cage enlarges and the
elastic forces of the two units change.
When the diaphragm contracts, its dome moves
downwards into the abdomen, thus enlarging the
thoracic cavity. Simultaneously, the intercostals
muscles move the ribcage upwards and
outwards, also increasing the volume of the
thoracic cavity. www.indiandentalacademy.com

This enlarges the volume of air within the lungs, pressure
falls below atmospheric and air is drawn into the
expanding lungs.
While inspiration is an active process involving muscle
contraction, normal expiration is primarily, a passive
event.
The elasticity of stretched tissues and gravitational forces
tend to return the thorax to its resting position without
any further expenditure of energy.
Because the elements which have been stretched during
inspiration are elastic, they have a natural tendency to
return to their original position after relaxation of the
inspiratory muscles.

As the thorax and lungs spring back to their
original sizes, pulmonary air becomes
temporarily compressed so that its pressure
exceeds atmospheric pressure and air flows from
the lungs to the outside.
Most of the work in filling the lungs involves
overcoming the elastic recoil, and the energy
required to do this is stored during inspiration
and used during expiration. The compliance of
the respiratory system, or the degree of
distensibility which occurs with the application
of pressure, is an important factor in
determining the amount of energy required to
move air in and out of lungs.www.indiandentalacademy.com

The second factor determining the degree of work
required for breathing is the magnitude of airway
resistance. When the airway is open, the airflow is
mostly smooth (laminar) and resistance is low.
However, in disease states increased respiratory
secretions or obstructions can increase resistance
greatly. Airflow becomes turbulent and greater effort
is necessary to move air in and out of the lungs.
In order to understand the effects of oral respiration on
the craniofacial region, a concept of the underlying
principles of the neuromuscular function of the
primary and accessory respiratory muscles of the
trunk and neck is required.

The airflow through the respiratory tract is
subject to resistance at various levels.
Changes in the dimensions of the respiratory
tract will decrease airflow. When changes in
airway resistance modify airflow, respiratory
muscles must increase their work to produce
changes in the intrapulmonary pressure
sufficient for air to be moved in and out of the
alveoli.

Modification of respiration by
sensory feedback
In the initial adaptation to the partial obstruction
of the nasal airway, the respiratory system
increases its effort to compensate for the
increased nasal resistance.
The augmented effort in motor output is initiated
reflexively by alterations in sensory feedback.
Respiration is modified by input from sensory
receptors which are located within the
respiratory tract.

Receptors within the cardiovascular system include
baroreceptors which respond to changes in blood
pressure.
The baroreceptors are situated within the carotid and
aortic vessels, pulmonary veins and the right auricle of
the heart. Sensory receptors within the joints increase
pulmonary ventilation during exercise.
The respiratory system has receptors in the upper
respiratory tract responding to irritant
gases, liquids, and particles evoking a variety of
reflexive effects that alter respiration.
The alveolar wall and chest wall have pulmonary stretch
receptors that modify the respiratory phase and control
respiratory frequency.

. The first few inspirations following nasal
obstruction would be expected to be longer.
This would be due to a decreased tidal volume and a
resulting lack of stretch of the lungs which
normally assist in terminating the inspiratory
phase.
The sensory receptors which are most affected by
obstruction of the respiratory tract are
chemoreceptors that monitor the levels of oxygen
and carbon dioxide in the body.
These receptors are located in three regions: the
carotid bodies at the junction of external and
internal carotid arteries; the aortic bodies within
the wall of the large aortic vessel; and particular
sites on the ventral surface of the medulla in the
brain stem of the CNS.

The carotid bodies are the most sensitive to
changes in oxygen in the blood while the
medullary site is affected by levels of carbon
dioxide.
It is proposed that nasal obstruction leads to
transient hypoxia and hypercapnia and that
these states stimulate neural receptors which
modulate the respiratory system.

Response of respiratory muscles to
changes in respiratory feedback
The respiratory system increases its effort to
compensate for decreased airflow by using
the muscles of neck and trunk. This
increased effort is controlled by two
neuromuscular mechanisms.
One mechanism increases the tension
developed by the primary muscles.
The other recruits accessory respiratory
muscles which are normally not active in
quite respiration.

Both mechanisms assist in decreasing resistance of
the upper airway and increasing the forces during
inspiration and expiration.
The primary muscles are – diaphragm, Intercostals
muscles of upper two intercostals spaces, scalene
muscles, several of the intrinsic and extrinsic
laryngeal muscles.
In normal, quiet breathing, most of these muscles
contract during inspiration.
The laryngeal adductor muscles, the lateral
cricoarytenoid, and thyroarytenoid are active
during expiration.

The contraction of these primary respiratory
muscles enlarges the chest, lungs and
respiratory tract during inspiration, as well
as maintaining the larynx in a stable
position.
At the completion of the active inspiratory
phase, the tension of the expanded chest
and lungs is sufficient to cause their recoil
and expulsion of the air during quiet
expiration.
These primary respiratory muscles increase
their electromyographic activity and develop
more tension during partial obstruction of
the upper respiratory tract.www.indiandentalacademy.com

The accessory respiratory muscles are the
abdominal muscles which compress and
force the diaphragm upwards during
expiration.
The serratus anterior, trapezius and
sternomastoid muscles attach to the chest
wall at various points to assist in its
movement during increased pulmonary
ventilation.
The extrinsic laryngeal muscles assist in the
respiratory effort. Increased ventilation also
recruits the intercostals muscles in
descending interspaces.www.indiandentalacademy.com

At present the literature contains a volume of
confusing and conflicting views on the precise
details and mechanisms of respiratory mode and
the possible effect on dentofacial growth. Some of
this confusion may be attributed to the fact that in
most studies, assessment of respiratory mode (oral
or nasal breathing) has been made through rather
subjective means, such as clinical judgments by
orthodontists or otolaryngologists.

Patients have been classified as mouth breathers on
the basis of morphologic criteria, such as lips-apart
posture ("incompetent lips"), narrow facial
dimensions ("adenoidal
faces"), questionnaires, condensation on cold
mirrors, and visual inspection of the nasal airway
for obstruction both clinically and
radiographically.
On the basis of these observations, epidemiologic
surveys have been used for making comparisons
between mode of respiration and skeletal and
dental characteristics.

Clinical
Examination for
assessment of
mouth breathing

Dr. Bushey has given a six point clinical routine
examination designed to alert the orthodontist to a
significant morphologic and functional
characteristics of a mouth breathing patient.
Step 1: look for mouth gaping or lip incompetancy
when the patient is in a relaxed posture. A
short, flaccid and atrophic upper lip is typical of
adenoid faces.
Step 2: evaluation of nares and nasofacial angle. The
nares are narrow and pinched-together the entire
base of the nose is often tipped up.

Step 3: evaluation of the mode of respiration. Simple
techniques can be used such as, first asking the
patient to seal the lips for 1-2 minutes and assessing
the ease of nasal breathing. Then ask the patient to
seal the lips and alternately collapse each nostril to
evaluate nasal and/or pharyngeal obstruction. The
potential obstruction is amplified by having the
patient to hum through one nostril while other is
closed. A cold mirror test can also be used or a cotton
tuft can be held at the nostrils to check for nasal
breathing.
Also ask history of upper respiratory infections,
tonsillitis, respiratory allergies, middle ear infections
etc.

Step 4: determination of whether there is a teeth-
together or a tooth-apart swallow. The presence of
a simple or a complex tongue thrust can alert the
clinician to the potential complications caused by
an adaptive or active tongue habit.
Step 5: clinical assessment of frontal facial
morphology. The long, dolichofacial form is more
often associated with mouthbreathing.
Step 6: assessment of the most significant clinical
characteristics which are found within the oral
cavity. The first five are dental and the next five are
pharyngeal features.

Dental midlines significant deviations from rest o
occlusion are indicative of posterior constriction
leading to a functional shift.
Incisor overbite or openbite and axial inclination
should be noted. In mouth breathers there is an
openbite and an increase in interincisal angle.
Anterior crossbite or overjet should be noted as an
additional indication of a potential skeletal open
bite.
Posterior crossbite as evidenced by a unilateral or
bilateral narrowing of the maxillary segments.
Posterior arch width initiates questions of relative
and absolute size dimensions of maxillary and
mandibular arch.

Palatal vault the height and contour of palatal vault is
the first pharyngeal feature. It is determined in
order to decide whether to treat the case with
expansion procedure or not.
Palatine tonsils should be evaluated for degree of
enlargement. large and infected tonsils will often
meet at the midline, indicating a significant
potential for tongue displacement.
Gag reflex is the next factor. It is elicited by tongue
depression. Individuals extremely sensitive to
tongue depression are often found to have
inflamed tonsils which may not be enlarged. But it
still causes a lower and forward tongue posture
eliminating support for development of normal
maxillary arch width.

Adenoid tissue can be examined clinically by
moving the uvula to one side using a dental
mirror. The dental mirror is then tilted above
the posterior level of hard palate. But it is
best viewed in a lateral cephalograms which
are routinely used by orthodontists.
Soft palate if the soft palate is observed to have
a bifid uvula or a deep oropharynx or if there
is any indication of palatopharyngeal
insufficiency, adenoidectomy is
contraindicated.

Instruments used for measuring
Respiration
Instruments capable of precisely measuring the
respiratory parameters of breathing have been used
to assess upper airway structures.
Aerodynamic techniques are used routinely to
estimate the area of constrictions, resistance to
airflow and volume displacements.
Airflow measuring devices there are two types of
flowmeters used to measure airflow rate. The most
widely used instrument is the pneumotachograph,
the other less commonly used is the warm wire
anemometer.

The pneumotachograph consists of a flowmeter
and a differential pressure transducer and
operates on the principle that as air flows
across a resistance the pressure drop which
results is linearly related to the volume of rate
of airflow.
In most cases the resistance is provided by a wire
mesh screen that is heated to prevent
condensation. A pressure tap is situated on
each side of the screen, and both are connected
to a very sensitive differential pressure
transducer. www.indiandentalacademy.com

The pressure drop is converted to an electrical
voltage that is amplified and recorded either
on a magnetic tape or a chart recorder.
Pneumotachographs are accurate, reliable,
linear devices for measuring ingressive and
egressive airflow rates. They are also
inexpensive.

The warm wire anemometer uses a heated
wire as a sensing unit. The cooling effect of
airflow on the heated wire, through which an
electric current flows, alters its resistance.
The resultant change in voltage is amplified
and recorded. However, it has poor linearity
and does not sense the direction of airflow.
So it is less popular.

Pneumatograph

MOUTH BREATHING
AND
MALOCCLUSION

Effects on the Dentition
Upper incisors retroclination is seen in mouth
breathers. Studies have shown that with
resumption of nasal breathing in patients
who were treated with adenoidectomy, the
upper incisor position dramatically
improved.
In mouth breathers the lower incisors are also
retoclined. With adenoidectomy the lower
incisors procline to normal within the first
year, after which no change is seen.

Effect on Arch width
There is a decrease in the arch-width in mouth
breathers, in the upper jaw leading to a
crossbite and crowding because of a narrow
maxilla. There can be a deviated path of
closure for the teeth to occlude and it may
lead to skeletal asymmetery if not treated.
But, when the patient reverts to nose-
breathing, there is a yearly increase of
0.9mm growth in maxilla for the next 5 years
is observed.

Effect on Nasopharynx
The depth of the nasopharynx is decreased in
mouth breathers. It is the distance measured
from pterygomaxillary point to basion.
When they resume nasal breathing, the depth
is restored within the first I year.

Mandibular plane
In mouth breathers the mandibular plane
angle is severely increased which is a reason
for the long face or adenoid faces.
With the resumption of nasal breathing it is
shown that the mandibular plane starts
reducing in order to come towards
normalcy. Though the first year post
adenoidectomy values are not significant
statistically when compared to controls.

Head posture
One of the important functions of head
posture is to maintain an adequate
oronasopharyngeal airway. Therefore
patients with impeded nasal airflow will
have an extended head posture.

Long Face Syndrome
Extreme clockwise rotation, high angle type, adenoid
faces, idiopathic long face, total maxillary alveolar
hyperplasia, and vertical maxillary excess all have
excessive vertical growth of maxilla as their common
denominator.
The multiplicity of names describing this syndrome
partially arises from the difficulty in describing
vertical skeletal dysplasias by traditional antero-
posterior classifications and failure to direct enough
effort towards describing the frontal or full face
esthetic aspects of dentofacial deformities.

Clinical features
Frontal facial esthetics reveal :
Upper facial third is within normal limits.
Middle third of face reveals a narrow nose, narrow
alar bases, and depressed nasolabial areas.
Lower third of the face reveals excessive exposure of
maxillary anterior teeth, poor upper lip-to-tooth
relationship, large interlabial distance, long lower
third of face, and inordinate exposure of the
maxillary teeth and gingiva upon smiling.

In profile the upper third of the face is normal.
The middle third often reveals a somewhat
prominent nasal dorsum and recessed
nasolabial areas.
In assessment of the lower third of the
face, the nasolabial angle is essentially
normal; there is excessive exposure of
maxillary anterior teeth, large interlabial
distance and a retropositioned chin.

Occlusal analysis reveals most often a classII
malocclusion, with or without open-bite
deformity.
Consistently, there is a high palatal vault with
a large distance between the root apices and
the nasal floor.
All these are the general features of this
syndrome but, they variably manifest.

Cephalometrically following features are seen
The total anterior facial height is increased;
specifically the lower anterior facial height.
The increased facial height correlates with the excess
development of maxilla in the vertical direction.
Open-bite and non-open-bite are two variants of long
face syndrome – A normal ramus height is seen in
open-bite patients whereas an increased ramus
height is seen in non-open-bite cases.
A high mandibular plane is a characteristic feature.
A normal lip length and excessive maxillary incisor
exposure is seen.

Obstructive sleep apnea syndrome
Obstructive sleep apnea (OSA) syndrome is a
relatively common condition caused by
recurrent upper airway obstruction during
sleep. Patients complain of a range of
symptoms, particularly excessive daytime
sleepiness, and may develop physical
complications that include systemic
hypertension, right heart failure, and cardiac
arrhythmias.

The patency of the upper airway is a result of
many interrelated anatomic and physiologic
factors.
During inspiration a negative intrapharyngeal
pressure develops but airway collapse is
prevented by the action of the pharyngeal
abductor and dilator muscles.
These muscles are activated rhythmically
during daytime respiration but, in common
with other skeletal muscles, they become
hypotonic during sleep, and airway stability
becomes dependent upon pharyngeal size
and pharyngeal tissue compliance.

As yet, little is known about the compliance of
the pharyngeal tissues.
However, conditions that reduce airway
dimensions result in OSA.
There are reports of OSA in patients with
upper airway tumors, with adenotonsillar
hypertrophy, and with conditions associated
with macroglossia.
Airway size is also affected by craniofacial
morphology as reflected in the airway
narrowing and sleep apnea observed in
patients with significant retrognathia.

The Apnea index (Al) and body mass index (BMI) of
patients were studied to check for correlation.
The patients with a high Al and low BMI ratio had
retruded mandibles with high mandibular plane
angles and proclined lower incisors.
The patients with a low Al and high BMI ratio had
inferior hyoid bones and large soft palates.
In the patients with a high Al and low BMI ratio, a high
Al was related to a large skeletal anteroposterior
discrepancy, a steep manidbular plane, and an
inferoanterior position of the hyoid bone.

In the patients with a low Al and high BMI
ratio, a high Al was related to a large tongue
and a small upper airway. In both
groups, BMI was the major contributor to
Al.
These two groups represent distinct
subgroups of OSA patients and provide
some insight into the contribution of obesity
to the pathogenesis of OSA.
The patients with a high Al and low BMI ratio
have a skeletal mismatch, whereas the
patients with a low Al and high BMI have
atypical soft tissue structures.

DEGLUTITION

An average individual swallows about once a
minute.
During meals he swallows about 9 times in a
minute.
Children show an increased frequency of
swallowing.
The rate of swallowing also depends on
factors such as posture.
Nervous states also increase the deglutitional
frequency.

Patients having a class II div.1 and open bite
tendency also show an increased frequency
of deglutition.
It is obvious from the above data that the act
of swallowing, repeated so frequently, may
have a profound effect on the maxilla or
mandible, particularly if there is an
abnormal swallowing pattern.

REVIEW
OF
LITERATURE

One of the earliest writings is that of Lefoulon
published in 1839, in which it is obvious that he
appreciated that among the causes of irregularities
of teeth were "sounds of speech in which the
tongue strikes against the upper anterior teeth,
pushing them forward."
An article by Desirabode published in 1843, is the
first traceable reference to the fact that the lips on
the outside and the tongue on the inside of the
mouth constitute a balance of forces that may
retain the teeth in their position.

In 1859, Bridgeman introduced the "lateral
pressure theory" and described irregularities
of the teeth due to Visincrementi (external
muscle forces, as that of the lips and
cheeks), visextensionis (internal muscle
forces, as that of the tongue), and
visocclusionis (occlusal forces).
Kingsley in 1879 made a considerable study of
speech sounds but did not relate movements
of the soft tissues to dental arch form.

Angle (1907) recognized the problems of the
muscular environment of the dental arches
but would not accept the fact that in certain
cases they might form an insurmountable
difficulty in treatment. In the appendix to
the seventh edition of Malocclusion of the
Teeth, Angle states: "We are just beginning
to realize how common and varied are the
vicious habits of the lips and tongue, how
powerful and persistent they are to
overcome."

 Norman Bennett (1914) showed a clear
understanding of the problem when he wrote:
"The muscles of mastication produce conditions
of vertical and lateral stress, the use of the tongue
in mastication and speech reacts upon the teeth
internally, and the lips and cheeks in their every
movement, even of transient emotion, bring
pressure to bear externally. Many of these forces
are too slight and of insufficient duration to
produce any definite movement of the teeth, but
others are constantly acting; with the mouth shut
and the teeth closed the buccal cavity is
obliterated, and the teeth are compressed between
the tongue and the lips and cheeks.

Very little experience in the movement of teeth by
mechanical means is enough to show that even
quite a small force acting continuously will
produce a considerable movement, and it becomes
clear that the teeth in their arches are but passive
objects kept in a state of equilibrium under the
influence of the muscles that react on them directly
and indirectly."
Bennett discussed Sim Wallace's theory that tongue
size is dependent on tongue function and that this
is a dominant factor in determining the size of the
dental arches, but he rather dismissed the tongue
as an all-important factor in arch development.

Friel (1926) having studied muscle activity, was
convinced that it was static function, and not
dynamic function, which molded the dental arches
in their position of linguofacial balance and this, as
we shall see, has been reaffirmed.
Brash (1929) in his Dental Board lectures, did not
place emphasis on the effect of the soft tissues of
the tongue and lips on the dental arches, but he
went so far as to state: "The growth of the tongue
and the mandible are no doubt correlated, but it is
improbable that the tongue exercises any
important mechanical influence on the general
form and size of the mandible or in moulding the
form of the growing palate."

Van Thal (1935) was concerned with speech in
relation to malocclusion. She deduced that
malocclusion was not the cause of various types of
speech defect.
Froeschels (1937) found that lisping and open-bite
originated from the same abnormality of tongue
control.
Rogers (1939) was a strong exponent of
myofunctional exercises calculated to harness
muscle forces in order to treat malocclusions. This
scheme had a following, but it was based on the
concept of function dictating form and was not
widely accepted.

The papers which initiated intensive research
on problems of tongue behavior in the next
two decades were those of Rix (1946) and
Ballard and Gwynne-Evans (1947). Similar
observations were made on tongue behavior
and speech. Rix drew attention to tongue
activity which seemed to retain infantile
characteristics, with the tongue showing
great affinity for lower lip contact. He based
his thesis on the belief that this represented
a delay in maturation of behavior.

Ballard and Gwynne-Evans looked at the subject
from the genetic point of view, stressing the
familial patterns of behavior.
Brodie (1946) regarded the whole facial pattern from
the general morphologic point of view and was less
interested in the tongue and its behavior as a
single factor.
In the early 1950's many of the exponents of
multibanded techniques with excellent control of
tooth movement recognized that there were a few
cases in which the behavior of the tongue and lips
formed a pattern of activity that caused relapse.

Other authorities, such as Straub (1960) gave
the impression that tongue problems were
very extensive and that re-education of
orofacial behavior by trained speech
therapists was necessary for many
orthodontic procedures. Speech therapists
and speech pathologists became
increasingly involved.

 The confusion of thinking on the subject prompted
a poem by Professor Bloomer entitled "The
Inverted, Perverted, Reverted Swallow." In the
same paper Bloomer (1963) sums up the general
view when he states: “Some orthodontists and
speech therapists are happy in their common
endeavors in training patients to swallow. Others
from both professions look on with a measure of
disapproval. The concern represents not an
antithesis to cooperation but uneasiness about
prescribing 'cookbook' treatment programs for
problems in which the dynamics of cause and
effect are not yet understood. "

The infantile( visceral) swallow, an essential
function in the neonate, is closely associated
with suckling, and both are well developed
by about 32nd week of intrauterine life.
During the infantile swallow the tongue is
between the gum pads in close apposition
with the lips, and its contraction plus those
of the facial muscles help to stabilize the
mandible.
THE SWALLOWING PATTERN

The swallow is guided, and to a great extent
controlled by sensory interchange between
the lips and the tongue.
The mandibular elevators which play a
prominent role in normal mature swallow,
show minimal activity.

All occlusal functions are learned in stages as the
nervous system and the orofacial and jaw
musculature mature concomitantly with the
development of the dentition.
During the later half of the first year of life, several
maturational events occur that alter markedly the
functioning of the orofacial musculature.
The arrival of the incisors cues the more precise
opening and closing movements of the mandible,
compels a more retracted tongue posture, and
initiates learning of mastication.

As soon as bilateral posterior occlusion is
established, true chewing motions are seen
to start, and the learning of the mature
swallow begins.
Gradually, the fifth cranial nerve muscles
assume the role of mandibular stabilization
during the swallow, and the muscles of
facial expression abandon suckling and
infantile swallowing pattern and begin to
learn the delicate and complicated functions
of speech and facial expression.

The transition from infantile to mature
(somatic) swallow takes place over several
month, aided by maturation of
neuromuscular elements.
Most children achieve most characteristics of
a mature swallow at 12 to 15 months.

The characteristic features of a mature
(somatic) swallow are –
 teeth are together.
 the mandible is stabilized by contraction of
muscles of fifth cranial nerve.
 the tongue tip is held against the palate
above and behind the incisors.
 minimal contraction of the lips are seen
during the swallow.
Mature (somatic) swallow

The deglutitional cycle is divided into four
phases which are highly integrated and
synergestically coordinated.
The four phases are-
1. The preparatory phase
2. The oral phase
3. The pharyngeal phase
4. The oesophageal phase
The deglutiton cycle

The preparatory phase
The preparatory phase starts as soon as liquids
are taken in, or bolus has been masticated.
The liquid or bolus is then in a swallow-
preparatory position on the dorsum of the
tongue.
The oral cavity is sealed by the lip and the
tongue.

The oral phase
During the oral phase the soft palate moves
upward and the tongue drops downward and
backward.
At the same time the larynx and the hyoid
bone move upwards.
These combined movements create a smooth
path for the bolus as it is pushed from the
oral cavity by a wave-like rippling of the
tongue.

While solid food is pushed by the tongue,
liquid food flows ahead of the lingual
constrictions. The oral cavity, stabilized by
the muscles of mastication, maintains an
anterior and lateral seal during this phase.

The pharyngeal phase
The 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 off by
closure of the soft palate against the
posterior pharyngeal wall ( Pasavant’s
ridge).
The hyoid bone and the base of the tongue
move forward as both the pharynx and the
tongue continue their peristaltic-like
movement of the bolus of food.

The oesophageal phase
The 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 positions.

Tongue thrust
The tongue thrust pattern of the oral cavity
has been given many titles, some of which
are the following: perverted or deviate
swallow, reverse swallow, retained infantile
swallow, tooth apart swallow, and so forth.
Yet, because no single characteristic of tongue
thrust activity is constant, all such terms
become too restrictive.
Even the term “normal” versus “abnormal”
has been criticized.

There is no “norm” for the pattern of tongue
thrust.
Malocclusion may or may not be present.
Teeth may or may not be brought together.
Labial pressures may or may not be normal.
Speech defects may or may not be observed.
Even archform may or may not be affected, in
spite of all evidence that tongue force is
greater than opposing lip and cheek
pressure.

Simple tongue thrust swallow
The simple tongue thrust swallow typically
displays contractions of the lips, mentalis
muscle and mandibular elevators and the
teeth are in occlusion as the tongue
protrudes into an open bite.
There is a normal teeth-together swallow, but
a tongue-thrust is present to seal the open
bite.

The so called tongue thrust is simply an
adaptive mechanism to maintain an open
bite created by something else, usually
thumb-sucking.
The open bite in a simple tongue thrust is well
circumscribed; that is, if one studies the
teeth or the casts in occlusion, the open bite
has a definite beginning and ending.
When a patient is observed with a simple
tongue thrust, check carefully for any history
of chronic digital pacifier sucking, for that is
the most common primary etiologic factor.

A simple tongue thrust swallow may also be
found with hypertrophied tonsils which are
not enlarged and/or inflamed sufficiently to
prompt a tooth–apart swallow.
Problems in respiration are usually not
associated with a simple tongue-thrust.

When one fits together the dental casts of a
patient with a simple tongue-thrust, they
have a precise and secure intercuspation,
even though a malocclusion may be present,
because the occlusal position is continually
reinforced by the teeth-together swallow.
The incidence of simple tongue thrust
diminishes with increasing age, and its
treatment is simpler and prognosis more
certain than complex tongue thrust.

The complex tongue-thrust swallow is defined
as a tongue-thrust with a teeth-apart
swallow.
Patients with complex tongue-thrust combine
contraction of lips, facial and mentalis
muscle, lack of contraction of the
mandibular elevators, a tongue-thrust
between the teeth and a teeth-apart swallow.
Complex tongue-thrust swallow

The open bite associated with a complex tongue-
thrust usually is more diffuse and difficult to define
than that seen in simple tongue thrust.
On occasions there is no open bite at all.
Examination of the dental casts typically reveals a
poor occlusal fit and instability of intercuspation,
because the intercuspal position is not repeatedly
reinforced during the swallow.
Patients with complex tongue-thrust usually
demonstrate occlusal interferences in the retruded
contact position.

They are also far more likely to be mouth
breathers and to have a history of chronic
nasorespiratory disease or allergies.
The incidence of complex tongue-thrusting
does not diminish as much with age as does
the simple tongue-thrust.

Retained infantile swallow
Retained infantile swallowing behaviour is
defined as a predominant persistence of the
infantile swallowing reflex after the arrival of
permanent teeth.
Fortunately, a very few people have a true
retained infantile swallow.

Those who do, demonstrate a very strong contraction
of the lips and facial musculature, even a massive
grimace.
The tongue thrusts strongly between the teeth in
front and on both sides.
Particularly noticeable are the contractions of the
buccinator muscle.
Such patients have inexpressive faces, since the
seventh cranial nerve muscles are not being used
for the delicate purposes of facial expression but
rather for the massive effort of stabilizing the
mandible during the swallow.

Patients with a retained infantile swallow have
serious difficulties in mastication, for
ordinarily they occlude on only one molar in
each quadrant.
The gag threshold is typically low.
These patients may restrict themselves to a
soft diet and state frankly that they do not
enjoy eating.
Food often is placed on the dorsum of the
tongue and mastication occurs between the
tongue tip and palate because of the
inadequacy of occlusal contacts.

The prognosis for conditioning of such a
primitive reflex is poor.
True retained infantile swallow is fortunately
rare.
Excessive anterior facial height often produces
severe frontal open bites and extreme
adaptive swallowing behavior as the
neuromusculature attempts to cope with the
skeletal imbalance.
Such a strained adaptive swallowing behavior
must be carefully discriminated from
complex and retained infantile swallow.

Mastication

Human mastication has been examined by
several authors with a variety of methods
including cineradiography, light-emitting
diodes, magnetic devices, and photooptical
devices, to describe movements of the
mandible. Comprehensive error analysis of
these methods has seldom been
reported, although such analysis should
improve the value of the results, permitting
interpretation of those results in light of the
magnitude of the errors.

Mastication has most often been described in terms
of single cycles; researchers have not attempted to
treat the data from multiple cycles
statistically, because the variability of the chewing
cycles can make mean masticatory movements
difficult to assess. While variability in the chewing
pattern among individuals is the rule, rather than
the exception, these patterns seem to have clear
individual characteristics that are more or less
unique for the individual.

Mastication has most often been described in
terms of single cycles; researchers have not
attempted to treat the data from multiple
cycles statistically, because the variability of
the chewing cycles can make mean
masticatory movements difficult to assess.
While variability in the chewing pattern
among individuals is the rule, rather than
the exception, these patterns seem to have
clear individual characteristics that are more
or less unique for the individual.

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
gum 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.
After a portion of the bolus of food is
accomodated between the occlusal surfaces,
the amndible is forcibly closed, primarily by
temporal and masseter muscle activity.

The masticatory freqency 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 an individual and is
relatively constant.
The masticatory stroke in an adult can be
explained in six phases

1. The preparatory phase- during this phase
the food is ingested and positioned by the
tongue within the oral cavity, and the
mandible is moved toward the chewing side.
There is a slight, constant deviation to the
non-food side an instant before the
mastication stroke begins and this point is
used to identify the precise beginning of the
preparatory phase.

2.Food contact- this is characterized by a
momentary hesitation in movement. This is
interpreted to be a pause triggered by
sensory receptors concerning the apparent
viscosity of the food and probable
transarticular pressures incident to chewing.

3.The crushing phase- this starts with a high
velocity and then slows down as the food is
crushed and packed. When the central
incisor is approximately 0.24”from
closure, the jaw motion is stabilized at the
condyle on the working side and the final
closing stroke thereafter is guided by this
braced condyle.the first three or four strokes
in mastication typically emphasize the
crushing phase and they usually display
equal and synchronous activity on both
sides.

4.Tooth contact- it is accompanied by a slight
change in direction but no delay. All reflex
adjustments of the musculature for tooth
contact are completed in the crushing phase
before actual contact is made. There is a
distinct and discrete pause , consistently
elicited in the temporalis and masseter
muscle following tooth contact.

5. The grinding phase- this coincides with the
transgression of the mandibular molars
across their maxillary counterparts and is
therefore highly constant from cycle to cycle.
This phase is also called as the terminal
functional orbit.during this phase the
bilateral muscle discharge becomes unequal
and asynchronous, indicating that the
person is chewing unilaterally.

6. Centric occlusion- when the movement of
the teeth comes to a definite and distinct
stop at a single terminal point, from which
the preparatory phase of the next stroke
begins. It is also seen that the jaws of
subjects with normal occlusion stayed in this
position for a considerable time compared to
those with malocclusion.

There is no evidence suggesting the function
of mastication as an etiologic factor for
malocclusion. Although the function of
mastication itself can be affected by
malocclusions.
The functions of the masticatory muscles
though may be contributing factors in
malocclusion.

The mastication of food is a primary function
of the dentition in the process of digestion.
Masticatory efficiency is known to be
impaired with the loss of teeth, but almost
no difference has been reported between
subjects with excellent occlusion and those
with most types of malocclusion.21 Although
unmasticated food may leave undigested
residues,22 the degree of mastication
required for maximum absorption of foods is
seemingly readily attained by subjects with
inadequate dentitions.

Actually, little research has been done on
mastication, and no evidence exists that
malocclusion (excluding conditions that
cause severe functional impairment) affects
the digestive process and general health.
Nevertheless, the ease of chewing and
swallowing, freedom from interdental food
impaction, self-cleansing action, and the
enjoyment of taste are factors which cannot
be quantitated but which must be satisfied
according to individual requirements.

SPEECH

The function of speech is something unique only to
the human beings.
Unlike respiration, deglutition and
mastication, which are reflexive in nature, speech
is largely a learned activity dependant on the
maturation of the organism.
Speech is to be distinguished from the reflexive
sounds thatare associated with physiologic states.
Coming late in the evolutionary development of
man, speech makes use of muscles which have
many other functions.

Other than speech functions are
Innate automatic vegetative reactions such as
swallowing, gagging, vomiting and
suckling.
Learned automatic vegetative reactions such
as biting, chewing and sucking.
Learned automatic emotional reactions such
as grimaces, mannerisms, tics.
Innate automatic emotional reactions like
laughing, sobbing, smiling.

Learned nonautomatic discriminatory and
specially voluntary reactions like exploratory
movements of tongue, spreading of the lips,
kissing and blowing.
Learned automatic practical reactions like
whistling, humming a tune, playing a wind
instrument.

It is easy to see why a large number of muscles are
involved.
The muscles of the walls of the torso, the respiratory
tract, the pharynx, the soft palate, the tongue, the
lips, and face, and the nasal passages are all
concerned in the production of speech sounds.
Simultaneous breathing to provide a column of air is
essential to provide vibrations necessary for sound.
The lips and tongue and velopharyngeal
structures modify the outgoing breath stream to
produce variations in the sound.

Assuming the presence of normal structures,
speech production is dependant 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
speeech sounds are not possible, despite the
compensatory muscle activity.
Even though the mechanisms for producing
sound involve atleast parts of the same
systems used for mastication, respiration
and speech, actions used in producing
language differ considerably.

The speech mechanism acts on the breath stream in
a number of ways, controlling the air mechanism,
air direction, air flow, air release, air pressure,
general air path and lingual air path.
These actions involve muscle groups and call for
compensatory interaction if abnormality exists in
one area.
With respect to the tongue, which fills the oral cavity
at bith, only the extrinsic muscles which largely
control horizontal movement needed for the suckle
swallow are well-developed.

Those intrinsic muscles needed for speech are poorly
developed.
The transition from gross movements of the tongue
to precise and finely controlled ones extends over
the first several years of life, through the infantile
and transitional swallow periods into the mature
deglutitional pattern era.
The speech therapist is concerned over the residual
infantile tongue posture and function, since lisp,
open bite, anterior escape and substitute speech
sounds are possible sequelae to a retained infantile
swallowing habit.

The lips as well as the tongue undergo
maturational changes preparatory to speech.
In infants , suckling and rooting reflexes are
dominant. The first sounds actually make no
demand on the lips e.g. “aa.” the degree of
lip protrusion is considered significant in
varying the length of the vocal tract. with
reduction in purse-string suckle-swallow
activity, more delicate peripheral lip
movements are seen, coinciding with tongue
maturation.

Of particular importance to the dentist is the
velopharyngeal valve. In children with cleft
palate, inadequte valving seems to be the
rule, not the exeption.
Upward and backward movement of the soft
palate in such problems does not emulate
the normal pattern.
Normally, the third quadrant of the soft palate
contacts the pharyngeal wall with sounds
like “p”, “b”, “f” and “w”.

The general awareness that the teeth are involved in
the production of speech does not imply a causal
relationship between malocclusion and speech
problems.
The vocal tract functions as an integrated unit during
speech production.
Since the tract is flexible and modifiable, a deviation
in one portion can be minimized frequently by
modification of other portions of the tract.
Sounds can therefore be produced in a variety of
ways.
Most speakers compensate automatically for all but
the most severe structural deviations to maintain
intelligibility of the acoustic signal because of the
impelling need to communicate.

The adaptability and compensatory action of the
vocal tract to a wide variety of deviations do not
negate the fact that in individual instances
improvement in speech disability can be secured
by orthodontic treatment in conjunction with
speech therapy.
Moreover, the greater the number of structural
deviations, the greater the demands placed upon
compensatory adjustments and, consequently, the
greater the likelihood that defective speech and
particularly consonant production can be
remedied by correction of the malocclusion.

Conclusion

Among the four functions namely
respiration, deglutition, speech and
mastication that we discussed;
The first two can be contributiary factors to
the etiology of malocclusion. Though there
is lot of controversy in literature.
The last two namely mastication and
speech, by themselves are not shown to be
etiologic factors for a malocclusion, but
malocclusion may lead to an abnormality in
these functions.

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Role of Function in Malocclusion Etiology

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