Role of function

Role of FunctionRole of Function
In theIn the
Etiology ofEtiology of
MalocclusionMalocclusion
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ContentsContents
IntroductionIntroduction
Orthodontic equationOrthodontic equation
ClassificationClassification
MoyersMoyers
GrabersGrabers
RespirationRespiration
Mechanics of respirationMechanics of respiration
Modification of respiration by sensoryModification of respiration by sensory
feedbackfeedback

Response of respiratory muscles to changes inResponse of respiratory muscles to changes in
respiratory feedbackrespiratory feedback
Clinical examination to assess mouthClinical examination to assess mouth
breathingbreathing
Airflow measuring devicesAirflow measuring devices
Mouth breathing and malocclusionMouth breathing and malocclusion
Long face syndromeLong face syndrome
Obstructive sleep apnea syndromeObstructive sleep apnea syndrome

DeglutitionDeglutition
IntroductionIntroduction
Review of literatureReview of literature
The swallowing patternThe swallowing pattern
Infantile swallowInfantile swallow
Mature swallowMature swallow
Tongue thrustTongue thrust
Simple tongue-thrust swallowSimple tongue-thrust swallow
Complex tongue-thrust swallowComplex tongue-thrust swallow
Retained infantile swallowRetained infantile swallow

MasticationMastication
The masticatory cycleThe masticatory cycle
SpeechSpeech

INTRODUCTIONINTRODUCTION

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

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

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

Dockrell’s Orthodontic equationDockrell’s Orthodontic equation

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

Moyers has classified the etiology ofMoyers has classified the etiology of
malocclusion into seven groups asmalocclusion into seven groups as
1) Heredity1) Heredity
2) Developmental defects of unknown origin2) Developmental defects of unknown origin
3) Trauma3) Trauma
Prenatal trauma and birth injuriesPrenatal trauma and birth injuries
Postnatal traumaPostnatal trauma
4) Physical agents4) Physical agents
Premature extraction of primaryPremature extraction of primary
teeth.teeth.
Nature of foodNature of food

5) Habits5) Habits
Thumb sucking and finger suckingThumb sucking and finger sucking
Tongue thrustingTongue thrusting
Lip sucking and lip bitingLip sucking and lip biting
PosturePosture
Nail-bitingNail-biting
Other habitsOther habits

6) Disease6) Disease
Systemic diseasesSystemic diseases
Endocrine disordersEndocrine disorders
Local diseasesLocal diseases
Nasopharyngeal diseases andNasopharyngeal diseases and
disturbed respiratory functiondisturbed respiratory function
Gingival and periodontal diseasesGingival and periodontal diseases
TumorsTumors
CariesCaries
7) Malnutrition7) Malnutrition

Graber has classified Etiology ofGraber has classified Etiology of
Malocclusion into the followingMalocclusion into the following
General factorsGeneral factors
HeredityHeredity
Congenital defectsCongenital defects
EnvironmentalEnvironmental
PrenatalPrenatal
PostnatalPostnatal
Predisposing metabolic climate and diseasePredisposing metabolic climate and disease
Endocrine imbalancesEndocrine imbalances
Metabolic imbalancesMetabolic imbalances
Infectious diseasesInfectious diseases
Dietary problems ( nutritional deficiency)Dietary problems ( nutritional deficiency)www.indiandentalacademy.com

Abnormal pressure habits and functional aberrationsAbnormal pressure habits and functional aberrations
Abnormal sucklingAbnormal suckling
Thumb and finger suckingThumb and finger sucking
Tongue thrust and tongue suckingTongue thrust and tongue sucking
Lip and nail bitingLip and nail biting
Abnormal swallowing habitsAbnormal swallowing habits
Speech defectsSpeech defects
Respiratory abnormalitiesRespiratory abnormalities
Tonsils and adenoidsTonsils and adenoids
Psychogenic tics and bruxismPsychogenic tics and bruxism
PosturePosture
Trauma and accidentsTrauma and accidents

Local factorsLocal factors
Anomalies of numberAnomalies of number
Supernumerary teethSupernumerary teeth
missing teethmissing teeth
Anomalies of tooth sizeAnomalies of tooth size
Anomalies of tooth shapeAnomalies of tooth shape
Abnormal labial frenum; mucosal barriersAbnormal labial frenum; mucosal barriers
Premature lossPremature loss
Prolonged retentionProlonged retention
Delayed eruption of permanent teethDelayed eruption of permanent teeth
Abnormal eruptive pathAbnormal eruptive path
AnkylosisAnkylosis
Dental cariesDental caries
Improper dental restorationsImproper dental restorationswww.indiandentalacademy.com

RESPIRATIONRESPIRATION

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

ClinicalClinical
Examination forExamination for
assessment ofassessment of
mouth breathingmouth breathing

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

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

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

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

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

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

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

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

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

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

Pneumatograph

MOUTH BREATHINGMOUTH BREATHING
ANDAND
MALOCCLUSIONMALOCCLUSION

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

Effect on Arch widthEffect on Arch width
There is a decrease in the arch-width in mouthThere is a decrease in the arch-width in mouth
breathers, in the upper jaw leading to abreathers, in the upper jaw leading to a
crossbite and crowding because of a narrowcrossbite and crowding because of a narrow
maxilla. There can be a deviated path ofmaxilla. There can be a deviated path of
closure for the teeth to occlude and it mayclosure for the teeth to occlude and it may
lead to skeletal asymmetery if not treated.lead to skeletal asymmetery if not treated.
But, when the patient reverts to nose-But, when the patient reverts to nose-
breathing, there is a yearly increase ofbreathing, there is a yearly increase of
0.9mm growth in maxilla for the next 5 years0.9mm growth in maxilla for the next 5 years
is observed.is observed.

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

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

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

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

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

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

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

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

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

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

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

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

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

DEGLUTITIONDEGLUTITION

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

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

REVIEWREVIEW
OFOF
LITERATURELITERATURE

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

The deglutitional cycle is divided into fourThe deglutitional cycle is divided into four
phases which are highly integrated andphases which are highly integrated and
synergestically coordinated.synergestically coordinated.
The four phases are-The four phases are-
1.1. The preparatory phaseThe preparatory phase
2.2. The oral phaseThe oral phase
3.3. The pharyngeal phaseThe pharyngeal phase
4.4. The oesophageal phaseThe oesophageal phase
The deglutiton cycleThe deglutiton cycle

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

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

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

The pharyngeal phaseThe pharyngeal phase
The pharyngeal phase of swallowing begins asThe pharyngeal phase of swallowing begins as
the bolus passes through the fauces.the bolus passes through the fauces.
The pharyngeal tube is raised upwardsThe pharyngeal tube is raised upwards enen
massemasse, and the nasopharynx is sealed off by, and the nasopharynx is sealed off by
closure of the soft palate against theclosure of the soft palate against the
posterior pharyngeal wall ( Pasavant’sposterior pharyngeal wall ( Pasavant’s
ridge).ridge).
The hyoid bone and the base of the tongueThe hyoid bone and the base of the tongue
move forward as both the pharynx and themove forward as both the pharynx and the
tongue continue their peristaltic-liketongue continue their peristaltic-like
movement of the bolus of food.movement of the bolus of food.

The oesophageal phaseThe oesophageal phase
The oesophageal phase of swallowingThe oesophageal phase of swallowing
commences as the food passes thecommences as the food passes the
cricopharyngeal sphincter.cricopharyngeal sphincter.
While the peristaltic movement carries theWhile the peristaltic movement carries the
food through the oesophagus, the hyoidfood through the oesophagus, the hyoid
bone, palate and tongue return to theirbone, palate and tongue return to their
original positions.original positions.

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

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

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

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

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

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

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

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

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

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

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

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

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

MasticationMastication

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

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

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

In the infant, as the bolus takes up the saliva it isIn the infant, as the bolus takes up the saliva it is
forced between the gum pads or the occlusalforced between the gum pads or the occlusal
surfaces of the erupting teeth.surfaces of the erupting teeth.
At the same time, the rhythmic action of the musclesAt the same time, the rhythmic action of the muscles
of the cheek serves to force the food back towardsof the cheek serves to force the food back towards
the tongue, which mashes the bolus of foodthe tongue, which mashes the bolus of food
against the hard palate.against the hard palate.
To permit the bolus of food to interpose between theTo permit the bolus of food to interpose between the
gum pads or teeth, the mandible is depressed bygum pads or teeth, the mandible is depressed by
gravity and the hyoid, and lateral pterygoidgravity and the hyoid, and lateral pterygoid
muscles, with a simultaneous deflection towardsmuscles, with a simultaneous deflection towards
the working side.the working side.

The lateral shift of the mandible is moreThe lateral shift of the mandible is more
apparent in hard-to-chew foods.apparent in hard-to-chew foods.
After a portion of the bolus of food isAfter a portion of the bolus of food is
accomodated between the occlusal surfaces,accomodated between the occlusal surfaces,
the amndible is forcibly closed, primarily bythe amndible is forcibly closed, primarily by
temporal and masseter muscle activity.temporal and masseter muscle activity.

The masticatory freqency is variable, butThe masticatory freqency is variable, but
appears to be one to two strokes perappears to be one to two strokes per
second with a normal bolus of food.second with a normal bolus of food.
The number of masticatory strokesThe number of masticatory strokes
before swallowing seems to bebefore swallowing seems to be
characteristic of an individual and ischaracteristic of an individual and is
relatively constant.relatively constant.
The masticatory stroke in an adult can beThe masticatory stroke in an adult can be
explained in six phasesexplained in six phases

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

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

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

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

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

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

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

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

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

SPEECHSPEECH

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

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

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

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