1. 1
Dr. Mohammed Alruby
Muscles
Part 3
Prepared by
DR. Mohammed Alruby

2. 2
Dr. Mohammed Alruby
Development of oropharyngeal function
Neuromuscular regulation of jaw positions and functions
Muscles controlling mandibular postures
- Muscles of mastication
- Submandibular muscles
- Extensor and flexor muscles of neck
Positions of mandible
Some clinical implications
Development of oropharyngeal function

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Dr. Mohammed Alruby
1- Prenatal maturation:
= During prenatal life, the neuromuscular system does not mature evenly, it is not accidentally
that the orofacial region matures a head of limb region
= In human fetus, by about the 8 week, generalized uniform reflex movement of entire body can be
elicited by tactile stimulation
Diffuse spontaneous movements in response to as yet unidentified stimuli have been observed as
early as 9.5 weeks
Localized specific and more peripheral responses cannot be produced before 11 weeks, and at this
time, stimulation of the nose-mouth region causes lateral body flexion
By 14 weeks, the movements have become much more individualized. Stimulation of the mouth
area, the general bodily movements no longer are seen but instead facial and orbicular muscle
response are produced
Stimulation of the upper lip causes the mouth to close and often deglutition occurs
Respiratory movements of the chest and abdomen are seen first at about 16 week
The gag reflex has been demonstrated in human fetus of 18.5 weeks. By 25v weeks, respiration is
shallow but may support life for few hours
Stimulation of the mouth at 29 weeks’ menstrual age has elicited sucking through complete
suckling and swallowing is not thought to be developed until at least 32 week
2- Neonatal oral functions:
a- The mouth as sensory instrument:
= At birth, the orofacial region is a very active perceptual system, the infant finds the mouth nipple
= more tactile than the visual sensation
At birth, the tactile sense already is more highly developed in the lips and mouth than in the fingers
= The neonate’s slobbers, drools, chew his toe, sucks his thumb and discovers the gurgling sounds
can be made with his mouth
= oral function of the neonate is guided primarily by local tactile stimuli, particularly those from
the lips and anterior part of the tongue
= the posture’s of neonate’s tongue is between the gum pads and often for enough forward to rest
between the lips, where it can perform its role of sensory guidance more easily
= the mouth of infant is used for many purpose, the perceptual functions of the tongue, lips, and
facial skin are mingled with the sensory function of taste, smell and jaw position.
= the sensitivity of tongue and lips is greater than other area of the body and the sensory guidance
for oral functioning, including jaw movements is from remarkably large area
b- Infant suckling and swallowing:
= Infant suckling and swallowing have been the subjects of much research due to the effectiveness
of these activities is a good indication of the neurologic maturation of premature infants
= the infant finds the mother’s breast and places the lips around the nipple, effecting a tight seal.
The neck of teat is first compressed between the upper gum and tip of the tongue covering the lower
gum with a general elevation of the jaw and tongue
= as the tongue is applied against the bulb of the teat from before, backward, indenting the teat
and expressing some of its content
= while the milk is being expressed from the breast, supplementary mechanisms within the mouth
create a suction. The milk now lies in a small reservoir on the dorsum of the tongue but is sealed
posterior by the opposed soft palate until sufficient increments of milk trigger the next step of suckle

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Dr. Mohammed Alruby
= EMG studies have confirmed visual reported in England that is, while the mandibular
movements are carried out by muscles of mastication (Vth cranial nerve), the mandible is primarily
stabilized during the actual act of swallowing by concomitant contraction of:
- Infra-mandibular muscles
- Tongue muscles
- Facial muscles
= during the actual time of infantile swallow, the tongue lies between the gum pads and is in close
position in the lingual surface of the lip.
Characteristic of infantile swallow:
1- The jaws are a part, with the tongue between the gum pads
2- Tongue thrust both anteriorly and laterally
3- The cheek muscles contract to meet the lateral spread spreading of the tongue
4- The mandible is stabilized by the infra-mandibular muscles
5- Extrinsic muscles of swallowing are not involved
6- Oro-facial musculature is involved in this t musculature is involved in this type of swallow
c- Maintenance of the airway:
= breathing is spontaneously evoked at birth, if the infant to be survived, the posture of mandible
and hyoid bone must be established to ensure that the airway is maintained
= the new born is essentially nasal breather, the lips may be together or slightly parted, the upper
lip and facial musculatures are rather flaccid and relatively immobile when compared with the
more active lower lip
= the laryngeal skeleton lies in high position in the neck, probably to allow normal nasal breathing
during suckling
In addition: there is a relationship between the dorsum of the tongue, soft palate and epiglottis in
such a manner that makes oral breathing is difficult
= as the child grows, the laryngeal skeleton descends in the neck, the tongue remains in contact
with soft palate, the oro-facial, prevertebral musculature, submandibular, postvertebral
musculatures are responsible for maintaining an adequate oro-pharyngeal airway
= when the infant is resting a uniform diameter of the airway is provided by:
- Mandibular posture mechanism: maintain the mandibular position anterior posterior
- Head postural mechanism
- Stabilizing tongue and posterior pharyngeal relationship
d- Infant cry:
The involvement of the orofacial and jaw musculatures in infant crying has been reported in classic
studies by Bosma and his workers.
When the aroused baby is crying, the oral region is unresponsive to local stimulation:
- The mouth is held wide open
- The tongue is separated from the lower lip and palate
e- Gagging:
= Gagging is the reflex refusal to swallow or accept foreign objects in the throat, it is an
exaggerated of the protective guarding the airway and alimentary tract
= gagging characterized by retching throat spasm, non-productive vomiting or reflex throat to
vomit
The lowest threshold for gagging in man are found in:

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Dr. Mohammed Alruby
a- The faucial pillars
b- Base of the tongue
c- Lateral aspect of the soft palate
d- The posterior pharyngeal wall
= therefore the nerve involved are the second and third division of the Vth, IXth and XII th cranial
nerves may be involved. inhibitory fibers for gagging found in the Xth cranial nerve
3- Early postnatal development of oral functions:
A- Mastication:
= mandibular growth downward and forward is greater in neonatal life than the midface growth,
giving rise to an increase in oral volume. Mandibular growth carries the tongue away from the
palate and help provide:
- differential enlargement of the pharynx
- maintaining patency airway
the soft palate and the tongue commonly are held in apposition, but as the tongue no longer is
lowered by mandibular growth, its functional relationship with the lips are altered- an alteration
is aided by the vertical development of alveolar process
= at rest, however the tongue no longer is entirely in generalized apposition with the lips, buccal
wall and soft palate
The lips elongate and become more selectively mobile and the tongue develops discrete movements
separate from the lip and mandibular movement and by time, the labial valve mechanism is
maintained during rest and feeding, so that is not lost
= The development of speech and mastication as well as facial expression requires:
- Furthering of the independent mobility of the separate parts
- Development of new motor pattern as well as greater autonomy of the motor elements
= one of the most important factors in the maturation of mastication is the sensory aspect of the
newly arriving teeth, the muscles controlling mandibular position are guided by the first occlusal
contacts of the antagonistic incisors
= serial EMG studies at very frequent interval during the arrival of incisors, have demonstrated
that the very instant the maxillary and mandibular incisors accidentally touch one another, the jaw
musculatures begins to learn to function in accommodation to the arrival of the teeth
= thus the closure pattern becomes more precise anterior posterior (since incisor arrive first)
before it does medio-laterally
= all occlusal functions are learned in stages as the central nervous system and orofacial and jaw
musculatures mature concomitantly with the development of dentition.
The earliest chewing movements are irregular and poorly coordinated like those during the early
stages of learning any motor skill
As the primary dentition is completed, the chewing cycle becomes more stabilized, using more
efficiently the individual’s occlusal pattern of intercuspation
In young child, sensory guidance for masticatory movements are provided by the receptors in:
- Temporomandibular articulations—Tongue --Oral mucosa –Muscle --Periodontal ligament
Thus the: cuspal height, incisal guidance, cuspal angle, play role in the
establishment of chewing patterns in the infant (which usually minimal in primary dentition)

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Dr. Mohammed Alruby
In young child, at the time of completion of the primary dentition, masticatory relationship is
optimal, since all of muscles, bone, teeth, still show the lability of development and thus highly
adaptive
Cusp height and overbite in the primary dentition are:
- more shallow
- Bone growth more rapid
- Adaptive and neuromuscular learning more easily to be obtained
B- 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
C- Speech:
Purposeful speech is different from infant cry:
Infant cry:
= Associated with irregular tongue and mandibular posture related to sporadic inspiration and
expiration during crying
= usually is a simple displacement of parts accompanied by a single explosive emission
= sporadic
= primitive and not learned
Speech:
= is performed on a background of stabilized and learned position of the mandible, pharynx and
tongue
= carried out only poly-phasic and sequential motor activities synchronized closely with breathing
= regular
= requires complicated and sophisticated variations of sensory conditioning elements during
learning
Speech consists of four parts:
1- Language: the knowledge of wards used in communicating ideas
2- Voice: sound produced by air passing between the vibrating vocal cords of larynx
3- Articulation: the movements of the speech organs used in producing a sound as lips, teeth,
palate, tongue, mandible.
4- Rhythm: variation of quality, length, length, timing, and stress of sound, words, and
sentence
If there are no impairments of hearing, sight, or oral sensation, the child will learn to speak from
the speech he hears, reproducing as best he can what he has heard

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Dr. Mohammed Alruby
Speech defects are a loss or disturbance of language, voice, articulation and rhythm or
combination of such losses and disturbances
= At about age 1 month, changes in the quality of infant cry are noticed and are said to indicate
developing needs of the child that are expressed in modification of the reflex infant cry
= In another month or two, babbling appear:
Open mouth vowels as: a, u, I, are followed by labial sounds, p, b, m, and guttural sounds k, ch,
g, ng.
= gradually, through hearing association and experimentation, the child adapts the sounds he
hears others making and drops those he does not hear
= simple words are learned before short sentences, and the child understands what is said to him
sometime before he will speck himself
D- Mature swallow:
== During the latter half of the 1st
year of life, several maturational events occur that alter
markedly the oro-facial musculature’s functioning
The arrival of incisors indicates the more precise opening and closing movements of the mandible,
also a more retracted tongue posture and initiate the learning of mastication
== As soon as the bilateral posterior occlusion is established (usually with eruption of first
primary molars):
- True chewing movements are seen to start
- Learning of mature swallow begins
== the transition from infantile to mature swallow takes place over several months, aided by:
- Maturation of neuromuscular elements
- The appearance of upright head posture, so the change in direction of gravitational force
of mandible
- Dentition development
== most children achieve most features of swallow at 12 -15 months
Characteristic features of mature swallow:
1- The teeth are held together into centric occlusion with the exception of swallowing liquids
from cup
2- The mandible is elevated and stabilized by the mandibular elevators
3- The tongue tip is held against the rugea area of the hard palate just behind the maxillary
incisors
4- Minimal role of the buccinator and lips
5- No contraction of muscles of facial expressions

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Dr. Mohammed Alruby
Neuromuscular regulation of jaw positions and functions
Introduction:
The jaw position is reflexly controlled under conscious level, all different stimuli are received
through a specific receptors present in the muscles, teeth, tongue, periodontal ligament, TMJ, oral
mucosa
Recent investigations have shown that mechanoreceptor present in the TMJ are the primary
contributors to jaw position during rest
Example: sever malocclusion may cause pathologic changes in the joint as in cases of class II div
2 malocclusion which in turn impair the joint receptors and cause an uncoordinated jaw
neuromuscular reflexes
Mandibular postures:
= Mandibular postures are a summation of a number of reflexes acting together at particular time
The primary function of mandibular posture is maintenance of airway, EMG studies have been
shown that, the mandibular rest position is relatively constant from birth until senility. However,
varieties of rest positions can be seen for the same individual at different times
= the postural position of the mandible is affected by many factors including:
- Head posture, psychological factors, occlusal changes
- Sleep, age, stimulus as: hearing, vision, muscle spasm
Muscles controlling the mandibular postures:
1- Muscles of mastication
2- Submandibular muscles
3- Extensor and flexor muscle of the neck
N: B:
Lateral movements: ipsilateral contraction of the temporalis muscle and contralateral contraction
Of external pterygoid and internal pterygoid muscle
Protrusive movements: lengthening contraction of masseter, temporalis, digastric and both
Pterygoids occurs
Retrusive movements: in retrusive from rest position, the masseter, external pterygoid and
Temporalis muscles fix the TMJ. While digastric show greatest electrical
Activity
Mandibular depression: the prime muscle in depression is the external pterygoid with stabilization
Of the part from suprahyoid musculature
= the masseter and temporalis acting to protect the temporomandibular
Articulation from distocclusion
Elevation of mandible: in normal occlusion and intra-occlusal clearance, the temporalis muscle
Initiate closure from habitual rest position to centric occlusion
= the masseter provides the power
Chewing: individuals not capable of lateral excursion without cuspal interference, demonstrate
Electo-myographic patterns associate with the chapping type of chewing
1- Muscles of mastication:

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Dr. Mohammed Alruby
2- Submandibular muscles:
a- Suprahyoid muscles:
- Digastric
- Mylohyoid
- Geniohyoid
- Stylohyoid
b- Infrahyoid muscles:
- Sternohyoid
- Sternothyroid
- Thyrohyoid
- Omohyoid
Digastric muscle:
Origin: originated by two bellies
Anterior belly: from digastric fossa of the mandible
Posterior belly: from the mastoid notch of temporal bone
Insertion: the two bellies meet in an intermediate tendon which attached by fibrous loop to the
Hyoid bone
Action:
- Elevate the hyoid bone during swallowing
- The anterior belly depresses the mandible
N: B:
The anterior belly developed from the 1st
pharyngeal arch so supplied by mylohyoid nerve
The posterior belly developed from the 2nd
pharyngeal arch so supplied by the facial nerve
Stylohyoid muscle:
Small muscle which lies close to the upper border of posterior belly of digastric
Origin: arise from the posterior aspect of the styloid process near its base
Insertion: insertion into the hyoid bone: at the junction of the body with its greater horn
Action: help in elevate the hyoid bone during swallowing
Retract and draw the hyoid bone backward
Mylohyoid muscle:
The 2 mylohyoid muscles meet in the midline to form the floor of the mouth (diaphragm oris)
Origin: from the mylohyoid line of the mandible
Insertion: the greater part of both muscles meet in the median raphe called the mylohyoid raphe
which extend from the symphysis menti the hyoid bone
The posterior part of the muscle is inserted into hyoid bone
Action:
- Elevate the hyoid bone, floor of the mouth and tongue during swallowing
- Depress the mandible
Geniohyoid muscle:
Origin: from the inferior genial tubercle
Insertion: into the anterior surface of the body of hyoid
Actions: pulls the hyoid bone upward and forward in deglutition
Depress the mandible

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Dr. Mohammed Alruby
Sternohyoid muscle:
Origin: arise from back of the sternum and medial end of the clavicle
Insertion: inserted into the lower border oh hyoid bone
Action: depress the hyoid bone after deglutition
Sternothyroid muscle:
Origin: arise from the back of the manubrium sterni and the 1st
costal cartilage
Insertion: into the oblique line of the thyroid cartilage
Action: depress the hyoid bone and larynx during speech and swallowing
Thyrohyoid muscle:
Origin: arise from the thyroid cartilage
Insertion: into the lower border of the greater horn of the hyoid bone
Action: depress the hyoid bone with the other Infrahyoid muscles,
Elevate the larynx and the thyroid cartilage
Omohyoid muscle:
The muscle is formed of superior and inferior bellies
Origin: superior belly: from the hyoid bone lateral to the sternohyoid
Inferior belly: arise from upper border of scapula and subscapular ligament
Insertion: the two bellies meet in an intermediate tendon which lies on the internal jugular vein at
At the level of the cricoid cartilage
Fixed in position by facial sheet which connect the tendon to the clavicle and sternum
N: B:
The action of Infrahyoid muscles are:
1- Fixation of the hyoid bone during movements of the tongue
2- In the first phase of deglutition, the thyrohyoid pulls the larynx up toward the hyoid bone
3- In the second phase of deglutition, the sterno-thyroid pulls the larynx down
N: B:
 The digastric muscle increases the anterior posterior dimension and the oropharynx during
deglutition. While the posterior belly of digastric and stylohyoid muscle acts to prevent
regurgitation of food after swallowing
 Suprahyoid muscles depress the mandible by contracting against fixed hyoid
N: B:
Hyoid bone:
Without it, our facility of maintaining airway, swallowing, and preventing regurgitation and
maintaining the upright position of the head
If the hyoid bone is in the same position before and after orthodontic treatment, the soft tissue must
still be in the same balance, thus possibly reducing the chance of relapse from these soft tissue
forces
If the hyoid position is altered, a longer retention period than normal may be indicated

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Dr. Mohammed Alruby
3-Extensor and flexor muscles:
Variation in the natural head posture have been observed, ranging between extension and flexion
of the head in relation to the vertebral column
These two actions lie under the control of the extension and flexor muscles
These two groups of muscles should be highly coordinated in order to achieve a natural upright
posture of head. Lack of coordination may occur as a result of abnormal stimuli as those resulting
from oral respiration or an abnormal uprighting visual reflex as demonstrating with blind
Abnormalities in head position will automatically followed by abnormal adaptive mandibular
posture.
A- Extensor muscles:
1- Splenius capitis:
Origin: arise from the lower half ligmantum nuchal, spine of 7th
cervical vertebra and spines of
upper three thoracic vertebra
Insertion: mastoid process and lateral third of superior nuchal line
Action: it draws the head backward
2- Splenius cervicis:
Origin: arise from the 3rd
, 4th
, 5th
, 6th
, thoracic spines
Insertion: inserted into the transverse processes of upper 3 cervical vertebra
Action: it draws the head backward
3- Semi spinalis capitis:
Origin: arise from the transverse process of the 7th
cervical and upper 6 thoracic vertebra
Insertion: into the median area between the superior and inferior nuchal line
Action: extend the head
Slightly rotate the face to the opposite side
4- Spinalis capitis:
Origin: arise from the 7th
cervical spine and 1st
transverse thoracic process
Insertion: into the median area between the superior and inferior nuchal line
Action: it extends the head
5- Longissimus capitis:
Origin: arise from the four thoracic transverse process
Insertion: into the mastoid process
Action: extend the head
Rotate the face to the same side
6- Rectus capitis minor and major:
Both are inserted into the medial area between inferior nuchal and foramen magnum
Action: both extend the head
7- Oblique capitis superior:
Origin: arise from the transverse process of atlas
Insertion; between superior and inferior nuchal lines
Action: tilt the head backward

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Dr. Mohammed Alruby
B- Flexor muscles:
1- Platysma muscle:
Origin: skin and CT fascia over the pectoralis major and deltoid
Insertion: inferior border of the mandible
Lower part of the face
Orbicularis oris
Action: it depresses the mandible and angle of the mouth
2- Sterno-mastoid muscle:
Origin: originated by two heads:
Medial head: sternal: from the front of sternum
Lateral head: clavicular: from medial third of clavicle
Insertion: both heads into the mastoid process and lateral half of superior nuchal line
Action: flex the head and neck
3- Scaleni muscle:
Anterior, middle, posterior
All flex the neck
4- Prevertebral muscles:
Include: longus coli, longus capitis, rectus capitis
Action: all are flexor muscles
N: B:
== Variation in head posture is followed by variation in the mandibular posture
== if the head is tilted back (extended), the mandible will be rotated downward and interocclusal
clearance increase
== on the other hand, when the head is tilted forward (flexor) the mandible will be rotated upward
and the inter-occlusal space decrease
Positions of the mandible
- Postural resting position
- Centric relation
- Initial contact
- Centric occlusion
- Most retruded position: terminal hinge position
- Most protruded position
- Habitual resting position
- Habitual occlusal position
1- Postural resting position:
In the infant, those muscles associated with suckling or the intake of food are relatively well
developed from the start
But when the child is not engaged in taking food, the mandible assumes a rest position. Thus the
mandibular resting position is one of the earliest postural positions to be developed

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= the mandible is suspended from the cranial base by the cradling musculature, the jaws are not
clamped together, but they are separated by a rather constant distant
EMG AND CEPHALOMETRIC studies:
== demonstrated the relative constancy of this postural resting position from infancy to senility
== even though the muscles are not in active function, limited number of fibers are apparently still
contracting to maintained the relaxed position of the mandible and posture of the head
Factors affecting the postural position:
a- Body and head posture
b- Sleep
c- Occlusal changes such as attrition
d- Pain
e- Muscle disease
f- TMJ disease
g- Age
h- Psychic factor influencing muscle tonus
2- Centric relation:
= Refers to the position of the mandibular condyle in the articular fossa
= The unstrained, neutral position of the mandible in which the anterior superior surfaces of the
mandibular condyle are in contact with the concavities of the articular disks as they approximate
the posterior inferior third of their respective articular eminentia
= Does not require occlusal contact
3- Initial contact:
As the mandible moves from psychologic rest position toward occlusion of teeth, if all is normal it
maintain a centric relation position
The movement that occur in the TMJ is almost completely the rotation of the condyle in the lower
joint cavity
= if there is a normal occlusion the point of initial contact produces no changes in the function of
TMJ, and all the inclined planes are brought together simultaneously in the maxillary and
mandibular teeth
= in normal individuals, the initial contact is the same as centric occlusion but if there is
malocclusion or premature contact of one or more teeth in each jaw, the initial contact is not the
same as the centric occlusion.
In case of premature contact, the traumatic forces will be exerted on the teeth and environmental
tissues and more over can produce:
- Sever TMJ symptoms of crepitus
- A symmetrical activity
- Pain
4- Centric occlusion:
State of balance with maximal contact of inclined planes of the opposing teeth with:
a- Bilateral symmetrical activity
b- Balanced and unstrained relationship of TMJ structures
If there is no malocclusion or malfunction, the centric occlusion is a static position easily produced
by bring the teeth together

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Dr. Mohammed Alruby
Factors influencing the centric occlusion:
a- Premature contact
b- Loss of teeth
c- Over eruption of teeth
d- Over extension of the restoration
e- Malposition of individual teeth
5- Most retruded position: terminal hinge position:
Because premature contacts frequently disturb the occlusal relationship of upper and lower teeth,
many dentists believe that by forcing the mandible into its most posterior position, it is easier to
eliminate occlusal prematurity that exist
It is possible for any person to move the mandible a millimeter or more posteriorly from the
position of centric relation and centric occlusion
There are individuals who cannot retrude at all from habitual occlusion while others can move 1
to 2mm------------------ {some cases retruded 6mm}
6- Most protruded position:
The most protruded position in the mandible is more variable from individual to individual than
the retruded position
The inclination of the condyle path is considered more important than actual terminal protruded
position
Where there is an inherent flaccidity to the capsular structures, some patient can dislocate their
mandible in the extreme protrusive position
Some cases the condyle rides over the anterior margin of the disk. In others the disk is drawn too
far anterior and the condyle rides over the posterior periphery of the articular disk
N: B:
When the condyles are locked anterior to the articular eminence, the stretch reflexes of the
associated muscles are elicited
7- Habitual resting position:
The habitual resting position may not be the same as the true physiologic postural position, as,
there are certain type of malocclusion that prevent the patient from achieving a physiologic rets
position
In cases of sever class II div 2 malocclusion with the maxillary incisors markedly inclined to the
lingual, there is a tendency to force the condyles posteriorly and superiorly in the articular fossa
EMG:
= Seems to show greater activity in the muscles associated with the mandibular postures than
would be normal for an unstrained position at rest
= in many cases the removal of the abnormal guiding force of the lingually inclined maxillary
incisors allow the mandible to come forward and a demonstrable reduction in electrical activity at
this new resting position can be seen
Pathologic condition that interfere with the establishment of normal postural position of the
mandible:
1- Abnormal atmospheric pressure in the oral cavity
2- Selective paralysis induced by poliomyelitis
3- Markedly enlarged adenoid

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Dr. Mohammed Alruby
4- Certain systemic disease
5- Pathologic in TMJ
6- Confirmed mouth breathing
7- Psychic trauma and pain
8- Habitual occlusal relation:
In normal occlusion, the centric occlusion and habitual occlusion should be the same, but the
occlusal relationship is much more susceptible to:
a- Environments
b- Tooth loss
c- Improper restoration
d- Functional aberrations
N: B:
It is vitally important that dentist make sure that the habitual occlusal position and the centric
occlusal position are the same and they are in harmony with centric relation and postural resting
position
Some clinical implications
1- The effect of neuromuscular behavior on growth of craniofacial skeleton:
= The functional view of facial growth is best and most strongly stated by Moss, Moss extended
Vander Klauw’s adeas, saving that the growth of bone itself is secondary
= Since all growth changes seen in bone reflect the growth and function of tissue system associated
with the bones
= He has given the term (functional matrix) to all the functional units with which the craniofacial
skeleton units are associated
= He includes in the functional matrix concept, the brain, muscles, tendons, gland, vessels, teeth,
even empty spaces
Wolf’s law stated that, in general, the structure and shape of the bone become progressively
adapted to the sum of all the changing mechanical forces exerted on it
When those forces attain equilibrium with the physical properties of the bone, growth presumably
ceases as such and the morphology of the bone is then in balance with its various functions
a- Muscle growth and skeletal growth:
During fetal life, skeletal muscle grows by division of muscle cells or differentiation of muscle
forming cells
Sometime during the second trimester, this generalized muscle growth stops and muscle tissues
grows from that time on the hypertrophy of individual fibers
As the bones to which the muscles are attached grow, the muscles themselves must change their
size
Adjustments between muscle and bone takes place in several ways:
1- The muscles holding relatively the same relationship to the skeleton with growth
2- The area of origin and insertion of muscles may change due to a synchrony of
musculatures and skeletal growth
3- Muscle fibers may be replaced largely by tendon

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b- Muscle migration and attachment:
During growth, muscles must migrate to occupy relatively different position with time
As the skeleton grows, there is a constant adjustment of the attachment relationship between
muscle and skeleton, a process complicated by the fact that the outer bone surface in region of
muscle attachment frequently are resorptive as well as depository
Complex muscle migration occurred and provide an effective balance of the head over the upright
vertebral column
c- Function and bone growth:
It is known that disuse and use determine, to some extent, the thickness of the cortical plate of limb
bones
Example: arm bones have thicker cortical bone according to the hardness of the individuals,
furthermore, there is a decrease in cortical thickness seen during muscular paralysis of the limb
muscles
After adult length is achieved, neither disuse nor paralysis affects the length of a bone
d- Response of the craniofacial skeleton to variation in function:
1- Regional or local effects:
== Skeletal regions whose form and size are dependent entirely on function. Wash Burn, has
shown that the removal of the temporal muscle in experimental animals, there is loss in the
coronoid process due to absence of stimulation of temporal contraction
on the other hand: Castelli and Ramirz show evidenced that the changes in form may be due to the
loss of vascularization in such experiments
alveolar process appears only with the eruption of the teeth and is lost with their extraction
== skeletal regions that develop more fully with function:
Walt and Williams, studied the facial growth in two groups of rats, one fed hard food require more
muscle function to chew the food, showed localized thickening and heaviness in the area of
attachment of mandibular muscles than the second that take softened diet
== skeletal structural elements related to muscle function apparently through phylogenic
development only:
Townsley: showed that mechanically determined structure may be present as hereditary features
in young bones that have protected experimentally from muscle contraction and weight bearing
2- General effects:
a- Mouth breathing:
There is a relationship between mouth breathing and facial growth, the mouth breather is reported
to have:
- Narrower nasopharyngeal passage
- Higher and narrow palate
- Maxillary dentoalveolar protrusion
- Steep mandibular plane
{for more details see etiology of malocclusion}
b- Variation in masticatory functions:
Eskimo has a massive facial features that developed as a result of extensive use of muscles of
mastication
Close examination produce evidence that the areas of muscle attachment in Eskimo are more
strongly developed than in many racial group

17. 17
Dr. Mohammed Alruby
Selmer –Olsen: reminded us that, the Lapps, living under conditions similar to Eskimo, have
characteristically delicate craniofacial skeleton features
Weidenreich: showed that variation in muscle function had a mechanical influence on the super
structure only and not on form and development of the cranium itself
N: B:
The mandible has been divided into three elements:
1- Basal or neural elements
2- Tooth bearing elements
3- Muscle attachment region
Variation in muscle function affect greatly the areas of muscle attachment and the development
and use of dentition affect the alveolar process
== Harvold and Moyers et al stated that muscle function can have a more general effect on the
size and form of the mandible
2-Neuromuscular aims in orthodontic therapy:
Orthodontic appliances often are directed at attaining better tooth position within a more balanced
craniofacial skeleton
The primary neuromuscular aims in orthodontic therapy are:
a- To obliterate all neuromuscular reflexes affecting adversely the dentition or craniofacial
skeleton (thumb sucking) (functional cross bite) (mouth breathing)
b- To create an ideal inter-cuspal relationship
= the clinician removes disharmonies influences on tooth position on the assumption that balanced
neuromuscular behavior is more advantageous and he utilizes the primitive reflexes positions of
the mandible to stabilize his therapeutic result
3-The effect of orthodontic treatment on the musculature:
Ranszo and Thilander: found that, severe, malocclusion provoked pathologic changes in
TMJ articulation, which in turn impaired the joint receptors, causing orthodontic patient to have
a less precise determination of mandibular position than subjects with normal occlusion
After orthodontic treatment, however there was a statistically significant reduction in the range in
mandibular position and an improvement in the determination of mandibular position
Jacob: demonstrate that occlusal equilibrium on treated patient changed a significant number of
teeth a part swallow to teeth together swallow
Moyers: reported occlusal disharmonies to be a most important cause of most relapse in an
anterior posterior direction
N: B:
Adaptive muscular changes following orthodontic therapy may include:
- Lip posture
- Tongue posture
- Mandibular posture
- Chewing strock
- Method of breathing