1. 1
Dr. Mohammed Alruby
Muscles
Part 2
Prepared by:
Dr. Mohammed Alruby

2. 2
Dr. Mohammed Alruby
Muscle function and malocclusion
Muscle development and skull form in relation to function
Facial balance, muscle balance, and orthodontic therapy
EMG response of muscles
Myofunctional therapy
Basic concepts of neuromuscular physiology

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Dr. Mohammed Alruby
Muscle function and malocclusion
Muscle function is a factor in shaping the dental arches and is important in maintaining the
stability of the teeth following orthodontic treatment
Muscle fibers contract in response to change in electrical potential of its investing membrane,
proprioceptors located in the muscles and the periodontal membrane make possible a high degree
of accuracy in bringing the teeth in contact
Class II malocclusion:
The muscle function is usually normal in class I malocclusion with the exception of class I Openbite
In class I cases, the teeth are in state of balance with environmental force, although the actual
measurements of tongue and lip forces showed that, they are not equal at any area during
particular function
Class I openbite:
= Usually caused by thumb sucking, retained infantile tongue swallowing or both, the child begins
with finger habits of sufficient intensity and duration to deform the maxillary anterior segment
forcing the incisors labially and allowing the tongue to move farther in forward direction
= the tongue continues to thrust instead of entering the transitional phase, a large part of this
activity may be compensatory or adaptive to produce anterior seal with lower lip during
swallowing
=such activity accentuates the openbite, prevent complete eruption of incisors and increase the
overjet to the extent that the lower lip may cushion behind the maxillary incisors during rest and
functional movements
- The upper lip become more hypotonic
- The lower lip become hyperactive
- Chin puckering can see with each swallowing
= the hyperactive mentalis muscle, retroclined, imprecate and flatten the mandibular anterior
segment
= the tongue drop downward and mouth breathing become a dominate pattern, as the tongue thrust
forward, it elongates in shape thus alter the balance with buccinator mechanism resulting in:
- Collapse of posterior segment
- V-shaped palate
- Buccal cross bite
This occurs also as a result of molding effect of the tongue upon the hard palate
Mouth breathing:
Is the good explain for these changes a result of underdeveloped nasopharyngeal structures and
subsequently maxillary deficiency
Class II division 1 malocclusion:
= In contrast to class I class II div 1 involve an abnormal muscle function from beginning
= As abnormal muscle function in class II div 1 is a compensatory or adaptive and is secondary to
skeletal relationship
= Because of large overjet, there is lack of the lip seal during rest and various functions so, mouth
breathing is developed
= Some individuals translate the mandible forward to effect lip seal and to improve the facial
profile, so the condyles become outside the fossa (Sunday bite) and the persons being as who
wearing activator
= the lower lip cushion to the lingual surface of maxillary incisors in both rest and during function

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Dr. Mohammed Alruby
= lower lip sucking may develop and lip become hypertrophied
= the upper incisors move farther forward resisted by the hypotonic and relatively functionless
upper lip
The lower anterior teeth are flattened by continuous pressure of mentalis muscle, the curve of spee
increased
Class II division 2 malocclusion:
The precise role of musculature in class II div 2 is more difficult to establish, Activity of cheek and
lip muscles are normal in contrast to div 1. Some authors have suggested that the tongue behavior
tend to exaggerate the curve of spee by occupying the intra-occlusal space and interfering with
eruption of posterior teeth so that, the inter-occlusal space in class II div 2 is large
= the lingual inclination of maxillary incisors combined with excessive inter-occlusal space may
produce a functional guidance in the mandibular closure and forced retrusion of the mandible
By EMG: studies have shown an increased activity of masseter and posterior fibers of temporalis
from the point of initial contact to the position of habitual occlusion
== some authors related the type of malocclusion to the hyperactivity of the mandibular elevator
muscles which permit adequate eruption of posterior teeth and may also contribute to relapse after
retention
Class III malocclusion:
There is a strong hereditary pattern in class III malocclusion and it is thought that abnormal
muscular activity in this class is adaptive one
The upper lip is relatively short but not necessarily hypotonic. The lower lip is hypertrophied and
appear passive during deglutition cycle
Muscle development and skull form in relation to function
The relation of Muscle function to the structure and form of the skull can be summarized as follow:
1- Certain internal elements of the skull, especially in the base of the cranium, are entirely
independent of muscle growth and function
2- Some of the structure and form of the skull is related to muscle function through polygenetic
development and appear to be independent to some degree of the development or function
of the individual muscles
3- The degree of muscle function generally determines much of the quantity, quality, structure
and form of the face
4- Muscles can change their location and extent through change their attachment or through
change in position due to new attachments and new function which can produced also
change in the morphology of the facial skeleton
5- The masseter, temporalis, temporal bone ridges and zygomatic arches show strong
developmental increase.
6- The pterygoid plate grow wider and the tuberosity become well developed
7- The mandible shows an everted border and bi-gonial width show an increase

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Dr. Mohammed Alruby
Facial balance, muscle balance and orthodontic therapy
Facial balance in orthodontic refers to the orthognathic appearance of the face as evidenced in
the soft tissue profile, since the force exerted by:
- Tongue
- Circum-oral musculature
- The buccinator
- The muscles of mastication
Is not equal in amount, it indicates that there are other factors in addition to muscle balance
responsible for the stability of the dentition
Regardless to orthodontic therapy, the following factors are important in establishing facial
muscle posture:
1- Axial position of the teeth
2- Kinesthetic of the dentition which are developed by the proprioceptors
3- Quantity and quality of the functional force exerted in the movement of the mandible
4- Atmospheric pressure
5- Pressure developed in breathing and swallowing
= muscle posture and functional balance of mimetic and masticatory muscles are important in
maintaining the stability of orthodontically obtained results
Presence or absence of muscle balance is an important reason why orthodontic therapy is
successful in some cases but is followed by relapse in other similar
Scott studied fetal muscle and bone configuration, and found that muscles can adapt to new
functional pattern and growth changes.
The ability of muscles to change their insertion is recognized as being responsible for dento-facial
morphologic change brought about by orthodontic therapy
Under retention, the muscles can adapt themselves to the changes functional pattern brought about
by change in the occlusion of the teeth
If muscle balance is not achieved because of insufficient retention, orthodontic therapy is followed
by relapse
Early treatment in young children is advantageous for stability of orthodontic results because the
muscles are in state of active growth, during which their origins and insertions are changing and
can be more easily influenced in a direction favorable to the achievement of state of balance
N: B:
There is a compensatory changes occur in:
- Functional pattern
- Muscle behavior
- Actual extent and manner of muscle insertion
- Change in periodontal ligament
- Change in the inter-dental fibers
Some if not all of these changes take longer for their adjustment than it takes to move the tooth into
their new position. Therefore, retention of moved teeth is required until equilibrium is stablished

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Dr. Mohammed Alruby
EMG response of muscles
EMG: a method of studying the physiologic basis of mastication, deglutition and speech.
In patient with normal occlusion (Perry and Harris) found by EMG tests that the temporal muscles
and masseter act in synchronized manner, although the temporal muscles become active before the
masseter muscles
In class II div 1 malocclusion they found electrical activity to appear in masseter muscle before
temporal muscles, the temporal muscle is rapid in action and relatively weaker than the masseter
muscle in power
= According to Moyers the external pterygoid proceeds the digastric muscle action in mandibular
depression
= Ralston, states that at present: EMG is capable of assessing:
- time only,
- duration,
- phasic relationship of muscle contraction,
but not measuring such function as:
- Force
- Speed of contraction
- Work produced
At rest position:
- There is an equilibrium between all the forces operating on the mandible
- The elevator and depressor muscle of mandible exhibit their minimal electrical activity
Shpuntoff, found that:
- General posture
- Pain
- Fatigue
- central nervous system excitation
were major factors affecting the constancy of the physiologic rest position
Myofunctional therapy
1935 – 1951 – Rogers, related the normal development of the face, jaw and dentition to the
normal functional balance of the facial muscles.
Rogers suggested, that muscle exercise be used as an adjunct to mechanical correction of
malocclusion
He also was careful to point out that although muscle exercise elsewhere in the body generally
used to increase the size or strength of the muscles in the circumoral region
He proposed certain exercise to establish proper tonicity and function of facial muscles
Purpose: myotherapy is used to:
1- guide the development of the occlusion
2- give the growth pattern an optimal chance to express itself
3- provide the best retention possible for mechanically treated cases

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Dr. Mohammed Alruby
limitations:
= muscle exercise will not greatly alter the bony growth pattern or perform heronic tooth
movements
= clinician have that myofunctional appliances are generally more useful than exercise alone
Principles:
1- study the possible role of muscle dysfunction in the etiology and maintenance of the
malocclusion
2- remove, if possible such etiologic factor as deleterious habits (tonsils and adenoids)
3- remove by occlusal equilibration any interference in the primary dentition
4- establish early with minimal mechanotherapy, the proper arch form and occlusal
relationship
5- begin appropriate myofunctional therapy
6- be certain of occlusal functional harmony during reflex activities before ceasing appliance
therapy
Types of muscle exercise therapy:
1- Pterygoid muscle exercise:
indicated for the treatment of disto-occlusion as the weakness of this muscle can be responsible for
this type of malocclusion
= bringing the mandible in forward position so that, the mandibular incisors are held anterior to
the maxillary one, provided the maxillary incisors are in normal position
= then the patient is instructing to relax the pterygoid muscle and allow the mandible to recede to
the point where the dental arch is in their relatively mesiodistal relationship
= when the maxillary incisors are in extreme protrusion, the mandibular incisors should be
protruded to the limit forward direction but not anterior to the maxillary incisors
This exercise accomplishes the followings:
a- Enhance the ability of the patient to maintain correct mesiodistal relationship of the dental
arches without strain when an inclined plane is employed
b- The habit of keeping the mandible in the correct position in gradually developed
= when the dental arches are brought to correct form and normal mesiodistal relationship, the
patient is provided with an appliance as activator or inclined plane to ensure the maintenance of
the position of mechanical advantages
2- Masseter, temporalis muscles exercises:
= they assist in the correction of infra-occlusion and disto-occlusion
= this exercise should not be performed if the patient is unable to place the mandible in its correct
position
= the exercise consists of the contraction and relaxation of the masseter group of muscles with the
mandible in normal position
= the patient should be instructed when learning this exercise to place the tip of the forefinger over
the masseter muscles near the angle of the mandible to enable him to feel the contracting and
relaxing movements

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Dr. Mohammed Alruby
3- Tongue exercise:
= is an adjunct to the masseter temporalis exercise
= the patient is instructing to place the tongue against the mucous membrane directly behind the
mandibular incisors with each contraction of the masseter- temporal group of muscles to press the
tongue against the anterior section
= at the same time, by widening the tongue to force it against the lateral sides of the alveolar
process
= this exercise trains the tongue to remain in its proper position and has a tendency to prevent the
narrowing of the mandibular arch, facilitating the earlier removal of retentive appliance
4- Mentalis muscle exercise:
= include the development of the orbicularis oris and the associated muscles
= the exercises should be started as soon as the protrusion has been reduced to the extent, that it
is possible for the patient to close the lips without stretching them
Three exercises are recommended:
a- Exercise developed for the upper lip:
Developed by L, S, Lourie:
- Grape the chin firmly between the thumb and index finger with the lip relaxed
- Hold the lower lip down
- Close the lips
- Relax and repeat from 10 to 50 times at a specified time, as before meals
Note: when the lower lip is held down as the lips are closed, the upper lip must come down to meet
the lower lip
b- The exercise for enunciation of the letter P:
- The sound should be made forcibly
- It should be made in front of mirror
- The patient should be instructing how to make the sound
- Whether the mentalis muscle show excessive muscular activity at the beginning of the sound
must be noted
- Two exercises periods of 5 to 10 minutes each must be observed daily
c- Whistling:
= is an exceptionally fine exercise for orbicularis oris muscle, mentalis and the associated muscles
= the muscular activity is much more vigorous and powerful than that used in making the sound
P, the higher the note, the greater the muscular activity
= closer the lips in the presence of an overdeveloped mentalis muscle usually is accomplished by
an upward movement of the lower lip but slight, if any downward movement of the upper lip
= when the lips are closed, there is usually dimpling in the chin and tautness of mentalis muscle S
5- Orbicularis oris and facial muscle exercise:
a- Orbicularis oris exercise:
Is best performed with the aid of an exerciser designer, so that it is difficult to keep it within the
mouth (oral orifice) unless the orbicularis oris muscle is contracted properly
= the exercise is made of:
- Two curved bars of acrylic or stainless steel and united near their center by joint to which
handle at right angle is attached
- There are notches at one end of the bar, to which the elastic bands are attached so that,
there is a resistance to approximate the free ends of the bars
- The free ends are shaped to engage the angle of the mouth

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- This exercise is continued with one elastics during the 18th
week or two, and contraction
are increased daily until reach 50 to 60 a day
b- General tonic exercise:
Influenced not only the orbicularis oris, but also the muscles which work with the orbicularis oris
= it consists in taking a generous mouthful of warm saline solution, at a temperature which is
breakable to the mucous membrane of the mouth
= teeth held in firm occlusion
= the solution is forced through:
- Interproximal space
- Buccal cavity
- Lingual space
= the exercise is performed morning and night
= the exercise is continued until muscle fatigue is occur
= it is good for: tonic activity, mouth hygiene

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Dr. Mohammed Alruby
Basic concept of neuromuscular physiology
Introduction:
When the muscle is stretched the tension within the muscle is increase
Active tension: tension result from contraction of muscle tissue. All the mandibular elevator
muscles possess spindle so it has stretch reflexes but the facial muscles possess no spindle so the
stretching of this muscles not elicit stretched reflexes
Passive tension: tension result from the physical properties of the tissue. In many muscles,
elongation will result in an increase in both active and passive tension, and the sum of the tension
called total tension
1- Physiology of skeletal musculature:
= When the muscle is stimulated, it contracts usually causing its origin and insertion to approach
each other
= Muscle are not contractile but also are elastic, after repeated contraction or stretching, they
return to their original or resting length and maintain this length without further contraction
= Impulses run continually from the spindle of the muscles to the midbrain where connection is
made with motor pathways and the muscles are kept in a constant state of reflex determined
contraction called tonus. Tonus serve to maintain body posture
= when muscles are completely relaxed, there is no electro-myographic evidence of motor unit
activity
 Clem Mensen: has suggested that resting muscle tone is due to passive elastic tension within
the muscle that is quite independent of the reflex stimulation through a motor nerve
 Josef et al: have shown that the muscles of mastication nerve completely rest, due to the
continuing force of gravity
When the motor nerve to muscle is cut, the muscles undergoes atrophy when the muscle is
not used, disuse atrophy is set in. the process of atrophy is slower than the atrophy result
from nerve section.
2- Reflexes:
The basic unit of all integrated neural activity is the reflex arc. Each reflex arc has:
= receptor = afferent neuron = efferent neuron
= effector organ = one or more synapse
In both monosynaptic and polysynaptic reflexes but specially in polysynaptic reflexes activity is
modified by facilitation and inhibition
a- Conditioned reflexes: is an automatic response to stimulus that previously did not elicit the
response. The reflex is acquired by repeatedly pairing the neutral stimulus with another
stimulus that normally does produce the response
Example: in Pavlov’s classic experiments, there are two stimuli in dog brain, surrounding
bell and meat. It is possible to produce salivation by surrounding bell alone
b- Unconditioned reflexes: at the time of birth, the neonate’s central nervous system has
already matured sufficiently to perform many integrative processes
= the baby has appropriate integrative centers in the medulla sufficiently matured to control
reflex: blood pressure, respiration, protective reflex of cough and sneezing
As the child grows, the nervous system continuous to developed anatomically and to mature
physiologically

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Dr. Mohammed Alruby
3- Muscle learning:
= During fetal life, motor performance capability appears before sensory control, gradually, the
primitive motor system comes under sensory control of basic functions that must be operable before
birth
= Muscle learning is largely a process of acquiring new conditioned reflexes, in this manner, the
various pathways through the brain are gradually developed and imprinted as the body grows
through infancy, childhood into adulthood
= These pathways constitute muscle memory thoughts themselves are the result of complex reflex
in the central nervous system
= The brain gradually accumulates memory traces from both thought and motor activity as a part
of learning process
= any time a person decides to master a new motor skill; the learning process involves the three
important stages:
a- The brain must have a clear mental image of the task to be mastered
b- New pathways must be established and the conditioned reflex reinforced by repeated
practice of the new skill
c- Control of execution of the new skill must pass, the great extent from the higher centers of
the brain to the: midbrain, brain stem, and spinal cord.
4- Classes of neuro-muscular activities:
a- Unconditioned reflexes:
Unconditioned reflexes are present at birth, having appeared as normal part of the prenatal
maturation of the neuromuscular system
A process that does not involve any conditioning or learning. If such maturation has not occurred
by birth, the infant may not survive
Among the unconditioned reflexes operable in the oro-pharyngeal region of the neonate, are those
of: respiration, infantile swallow, suckling, cough, sneezing
Vomiting, gagging, tongue posture, mandibular posture
Unconditioned reflex requires minimal reinforcement and are very difficult to alter or change by
usual conditioning procedure
b- Conditioning reflex:
Include all reflexes that have been learned, including unwanted bad habits: tongue thrust, thumb
sucking.
c- Voluntary effort:
Willful acts are under cortical control rather than the lower centers, which reflexes activities are
integrated
The infantile swallow of the neonate is an example of an unconditioned reflex, the mature teeth
together swallow, which appear during the first year of life is an example of reflex appearing with
normal growth and development.
The learned teeth together a part swallow caused by painful tooth is an example of conditioned
reflex swallow, and of course, voluntary swallows as possible as well
d- Reflexes appearing with normal growth and development:
Obviously, no conditioned is capable of being learned until all the necessary units in the central
nervous system and musculature have matured sufficiently to make possible that learning
a- Mastication:

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Mastication is a complex pattern of jaw movements which are used to prepare the food for
swallowing. Pre-masticatory movements of the jaw can be seen before eruption of the teeth
= These movements are at first mainly in the vertical plane (simple hinge axis movements):
- Protrusive movements become evident with eruption of deciduous canines
- Lateral movements become evident with the eruption of deciduous molars
= The pattern of chewing become well defined by the end of the 1st
year, the chewing pattern
become comparatively mature
= Masticatory function is influenced by the eruption of primary teeth. the muscles controlling
mandibular position are stimulated by the fits occlusal contact of newly erupted incisors
= the sensory guidance of masticatory movements is provided by receptors present in TMJ, tongue,
muscles, oral mucosa
The lips become elongated and more selectively the tongue mobility is developed in various
movements independent of the lips and mandibular movements, the lips form anterior seal during
mastication, so that, the foods are not lost
b- Mature swallowing:
= As the deciduous teeth erupt, the mouth become divided into the oral cavity proper and the oral
vestibules. The alveolar bone and teeth now form the anterior and lateral rigid support to the
tongue during swallowing.
= Rix and Whillis have suggested, that, the significance difference between infant and adult
swallowing is the firm occlusion of the teeth at the moment of transfer of foods into the oropharynx.
The transition from infantile to mature swallowing takes place over several months aided by:
- Complete eruption of primary teeth
- Stabilization of the mandible
- Neuro-muscular regulation
- Appearance of upright head posture
N: B: change to achieve mature swallowing between 12 and 15 months
Swallowing can be divided into three phases:
1- Intra-oral phase: (voluntary)
= This phase includes mechanisms by which the food is transferred from anterior to posterior part
of tongue, in this phase, the food is taken into the mouth by the tongue and present in the depression
of the central portion of the tongue, the groove is obliterated from backward by contraction of
transverse group of muscles, (intrinsic muscles of tongue)
= As the result of that, the bolus of food is moved backward to the posterior aspect of the dorsal
surface of the tongue, then inter the 2nd
stage
2- Second or mylohyoid phase: (voluntary):
= the teeth are brought into firm occlusion to fix the mandible allowing a firm contraction of
mylohyoid muscle to evaluate the floor of the mouth and tongue
= the tongue is compressed against the hard palate
= the lips and cheek play no actual part
= with semisolid foods, there is definite grooving and squirting actions of the tongue as described
in swallowing fluids.
3- Third phase:
= this phase includes the movements of bolus of food down to esophagus
= as the food enter the pharynx, the muscular activity is no longer under voluntary control
= two protective mechanisms come into play:

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1- Nasopharyngeal closure by contraction of the pharyngeal musculature and elevation of the
soft palate
2- Closing the larynx by epiglottis
Characteristic features of mature swallowing:
a- The teeth are brought together into centric occlusion with the exception of swallowing
liquids from a cup
b- The mandible is elevated and stabilized by the mandibular elevators
c- The tongue tip is held against the rouge area of the hard palate just behind the maxillary
incisors
d- Minimal role of the buccinator and lips
e- No contraction of muscles of facial expression
c- Speech:
Speech is a conditioned reflex which performed on background of stabilized and learned position
of the mandible, pharynx and tongue. Speech consists of four parts:
- Language
- Voice: produced by air passed between the vibrating vocal cords of the larynx
- Articulation: the movement of speech organs: lips, teeth, palate, tongue, mandible, to
produce sounds
- Rhythm: variation in the quality, length, timing and stress of sound if no disturbance in
hearing or oral sensation
The child will learn to speck by imitation
All speech function takes place within border movement of the mandible
d- Facial expression:
In the new born infant, the facial musculatures, particularly that of the middle third of the face are
rather flaccid
Only the lower lip is active
The lips may either together or slightly parted at this time and this is not related to their future
posture
The initial expression of the child face may be in the form of discomfort or displeasure, and time,
the facial expression become meaningful
Facial expression depends on:
- The morphology and configuration of soft tissue covering the face
- Neuro-muscular maturation
- Type of external stimuli
Facial expression is a conditioned reflex which can be learned by imitation