Muscle physiology /certified fixed orthodontic courses by Indian dental academy

Muscle physiology
and its significance
in orthodontics
INDIAN DENTAL ACADEMY
Leader in continuing dental education
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Introduction
Development of muscle and muscle
changes during growth
Muscle physiology and methods of
studying muscle activity
Orofacial muscles
Basic concepts of neuromuscular system
Role of muscle in functional jaw
orthopedics
Role of muscle in temporo mandibular
dysfunctions
Role of muscle in malocclusion
Role of muscle in orthognathic surgery
Role of muscle retention and relapse

Muscle attachments
Muscles can be divided into two groups with
respect to their attachments.
1. Periosteal
2. Tendinous


MICROSCOPIC ANATOMY


MYOFIBRIL


SARCOMERE


ACTIN AND MYOSIN


MUSCLE CONTRACTION


POWER STROKE AND RO


Methods of studying muscle
activity
1. ANATOMIC
2. FUNCTIONAL:
a. MOVEMENT
b. FORCE AND PRESSURE
c. ELECTROMYOGRAPHY
3. BEHAVIORAL


Histologic method of
studying muscles
The two major classifications are based on the
concentrations of oxidative enzymes and /or
adenosine triphosphatase present in the muscle
fiber. On the basis of the oxidative enzyme
stains, fibers have been designated as oxidative
or glycolytic and functionally correlated with the
speed of contraction and susceptibility to fatigue.
ATPase staining has led to typing of fibers as
either Type I or Type II.

TYPES OF MUSCLE
FIBERS


Type 1 muscle fibers are associated with
small, low tension, slowly contractile motor
units. These units are very resistant to fatigue
and richly supplied with capillaries. These
units possess excellent endurance at low
forces, which make them well sited for the
posture of the mandible. It has been found that
Temporalis, Masseter, Medial and Lateral
pterygoid muscles are composed of Type 1
muscle fibers.

Type II fibers are associated with large,
high tension, rapidly contracting units.
Type II A are fatigue resistant and posses
good capillary circulation. And are found
only in Digastric muscle (30%) where as
Type II B are fatigue sensitive and posses
poor capillary circulation. They are found
in all the jaw muscles, superior posterior
Temporalis, posterior medial pterygoid
and anterior Digastric muscles.

Electromyography
The instrument used for evaluating
the activity of the orofacial muscle is the
electromyograph. It is used to measure
the electrical activity .Two types of
electrodes are used. They are:
1.Surface electrode.
2.Needle electrode.
Surface electrodes record from a larger
population of muscle fibers than do
needle electrodes.

Both types of the electrodes record
the membrane action potentials from
the several to many fibers in a single
motor unit, which arrive at the
electrode at different times giving a
unique signature to that unit as long as
the electrode is not moved. This
permits to study the behaviour of
individual units and how the units are
recruited.

A flat metal plate is placed over the
muscle to be tested. Then, a thin sterile
needle attached to wires of a recording
machine is inserted through the skin into
the muscle. The electrical activity of the
muscle is recorded at rest and during
contraction. It is then displayed as
electrical waves on an oscilloscope and
amplified to produce sounds over an
audio speaker.

The action potentials from the various
units merge together and produce the
typical electromyogram.Although EMG
can give useful information on whether
a muscle is active and defined when the
activity begins and in the muscle fibers
sampled. It is impossible to know how
much of the muscle activity is being
missed.

Triangular force concept
The three major groups of muscles
affecting occlusion during the
swallowing act are:
1. Tongue.
2. Masseter and Buccinator.
3. The Orbicularis Oris muscle.

Neutral zone concept
Buccinator mechanism is like
a continuous band of muscles
that encircles the dentition and
is anchored by the pharyngeal
tubercle.
Opposing this mechanism is a
powerful muscle, the tongue.
These two muscles act in
opposite direction and
maintain the position of the
teeth

MUSCLES OF FACIAL EXPRESSION


Muscles of facial expression



MUSCLES OF FACIAL EXPRESSION

MUSCLES OF MASTICATION


Action of lateral pterygoid
muscle
If both sides contract, the mandible
protrudes and is depressed. If the inferior
head contracts on the right, the mandible
moves to the left and vice versa. The
superior head is an antagonist to the
elevators.

MUSCLES OF TONGUE


Extrinsic muscles of tongue


MUSCLES OF THE FLOOR OF ORAL CAVITY


Muscles of the floor of the oral
cavity


Concepts of orofacial
musculature
Active tension is due to the
contraction of the muscle while, the
passive tension is due to the viscoelastic
properties of the muscle and its
investing tissues. At short muscle
lengths the tension is all active while at
long lengths it is all passive.

Myotactic (stretch) reflex
The myotactic or the stretch reflex is the
only monosynaptic jaw reflex. When a
skeletal muscle is quickly stretched,
this protective reflex is elicited and
brings about a contraction of the
stretched muscle.

A muscle fiber
develops its greatest
tension when there
is optimal overlap
of the thick and thin
filaments. The
tension of the
muscle is maximum
at a Sarcomere
length of 2.2µm.

If the sarcomeres of the muscle fibers are
stretched to the longer length, fewer myosin
cross bridges can make contact with thin
filaments, and the force of contraction
decreases. If a skeletal muscle fiber is
stretched to 175% of its optimal length, no
myosin bridges can bind to the thin filaments
and no contraction occurs. At Sarcomere
lengths less than the optimum, the force of
contraction also decreases.

Muscle tone
A tonic contraction is a continual partial
contraction. At any one moment a small number
of total fibers in a muscle contract, producing a
tautness of the muscle rather than recognizable
contraction and movement.
In brief, involuntary activation of a small
number of motor units causes sustained, small
contractions that give firmness to a relaxed
muscle. This firmness is called muscle tone.

Isotonic contraction
Isotonic contraction is a contraction in which
the tone or tension within the muscle remains the
same, but the length of the muscle changes. The
term isotonic literally means same tension, since
there is a little or no resistance (load) placed on the
muscle in an isotonic contraction. All of the energy
of contraction is used to pull on the thin
myofilaments and thus decrease the length of the
fiber’s sarcomeres.

There are two types of isotonic contraction .
They are
1. Concentric contraction
2. Eccentric contraction


Concentric contraction
In a concentric contraction the
muscle shortens and pulls on another
structure, such as bone, to produce
movement and to reduce the angle at a
joint.
E.g. Picking up a book involves
concentric contractions of the biceps
brachii muscle in the arm.

Eccentric contraction
When the overall length of a muscle
increases during contraction, it is called
an eccentric contraction.
E.g. As you lower the book to place
it back on the table, the previously
shortened biceps gradually lengthens
while it continues to contract.

Isometric contraction
An isometric contraction on the other
hand, is a contraction in which muscle
length remains the same, but in which the
muscle tension increases. The term
isometric means same length. The
isometric contractions can do work by
tightening to resist a force, but they do
not produce movements.

Role of muscle in FJO
Andersen and Haupl claimed that the
activator, which stimulates the protractor
muscles and inhibits the retractor muscle
of the mandible, produces myotactic
reflexes leading to isometric contractions
from the activities of the jaw closing
muscles.

Petrovic in his study of the condylar
cartilage came to similar conclusion that
functional requirement for condylar
growth stimulation is activation of lateral
Pterygoid muscle (LPMs).


Eschler supported Andersen and Haupl, but
claimed that the retractor muscles are
stimulated, not inhibited by the activator. He
attributed the muscle contraction to
proprioceptive stretch reflexes and observed the
occurrence of both isotonic and isometric
contraction with use of the activator. He
described the cycle as at insertion of the
appliance the mandible is elevated by isotonic
muscle contractions, the mandible assumes a
mucostatic position in contact with appliance,
isometric contractions arise.

According to Woodside, a stretch of
the soft tissues primarily requires
dislocating the mandible anteriorly or
opening beyond the postural rest vertical
dimensions.


Between two extremes exemplified by
Andersen and Haupl versus Selmer Olsen,
Witts supported a combination of isometric
muscle contractions and viscoelastic
properties being responsible for the forces
delivered by the activator.


Ahlgren’s electromyography research (1970)
shows that activator function as interference in
producing new contraction patterns in jaw
muscles.
The innervation’s pattern can be adjusted after
a while and the mandible repositioned forward.
He reported that during day time wear of an
activator, there was an increased postural
activity in Masseter and Suprahyoid muscles
but not in the Temporalis.

Clasp knife reflex


Twin block
With in few days of fitting the appliances,
immediate change in the neuromuscular
proprioceptive response is seen provided that all
phasic and tonic muscle activity is affected.
This results in position of muscle balance,
which is altered, so that it becomes painful for
the patient to retract the mandible. This has been
described as the “Pterygoid response” by
McNamara or the formation of a “tension zone”
distal to condyle by Harvold.

Role of Lateral Pterygoid
muscle
The position of the mandible did not
change significantly after fatiguing the
protrusive muscle. Authors agreed that
change in muscle activity diminished
shortly after appliance insertion and
before correction of the jaw
relationship was achieved.

Morphologic change in jaw relationship
appeared that the lateral Pterygoid muscle
might not be responsible for the new
position of the mandible after treatment
with twin block appliance. The
Temperomandibular joint adapted to
displacement of the mandible by condylar
growth and surface apposition in the fossa.

Growth relativity hypothesis
Growth relativity refers to, growth that is
relative to the displaced condyle from actively
relocating fossae. Viscoelasticity is
conventionally applied to elastic tissue
primarily muscles i.e., non calcified tissues,
specifically addresses to the viscosity and flow
of the synovial fluids, the elasticity of the
retrodiscal tissues, the fibrous capsule and other
nonmuscular tissues including LPM
perimysium, TMJ tendons and ligaments, other
soft tissues and bodily fluids.

WOLFF’S LAW
Wolff’s law states that bone architecture is
influenced by neuro musculature. This law may
now be extended for orthopedically displaced
condyle. With orthopedic advancement of the
mandible, the law of growth relativity states that
bone architecture is influenced by the
neuromusculature and the contiguous,
nonmuscular, viscoelastic tissues anchored to
the glenoid fossa and the altered dynamics of
the fluids enveloping bone.

Mode of action of the Frankel
appliance (i.e. FR is a
 FR is not a tooth-moving appliance
tissue borne appliance).
 FR withholds muscle pressure from the developing
jaws and surrounding area having its arena of
operation largely in the vestibule surrounding the
alveolar bone.
 Changes with FR in transverse dimensions is
achieved by relief of force from the neuromuscular
capsule (the buccinator mechanism).
 Changes with FR in sagittal posturing is an entirely
tissue borne manner.

Muscle in TMD
Clenching grinding
(stress response)

Internal joint
pathology

Muscle spasm
and fatigue

TMD symptoms:
pain
Joint noise
limited opening


MUSCLE EXAMINATION IN
TMD

Movements should be routinely palpated
at rest and in isometric contractions (tell
the patient to clench [tic teeth in an
attempt to educe reflex responses to pain.
Often, unbeknownst to the patient,
muscles or parts of the muscles are painful
upon palpation. The Masseter, lateral
pterygoid, and temporalis are those which
most frequently demonstrate myalgia in
patients with

It is especially important to separate temporal tendinous
pain and lateral pterygoid pain from joint capsular pain.
Some patience and practice are required to be certain of
the anatomic site being pressed.
For the temporalis tendon it is easier if one begins by
sliding the finger along the anterior border of the ramus.
As the coronoid process is approached, ask the patient
to open and close the jaw gently, which movement
reveals the exact site of the tendinous attachment.
When palpating the lateral pterygoid muscle and tendon,
make certain finger is not pressing the joint itself.
Palpation of the temporomandibular joint and capsular
ligament is also necessary.

Sequelae of thumb
sucking
Hypotonic upper lip.

1.
2. Proclination and spacing of
upper anteriors.
3. Anterior open bite.
4. Increased over jet.
5. Retroclined lower anteriors.
6. Hyper active lower lip.
7. Compensatory tongue thrusting.
8. Increased buccal musculature
pressure leading on to the
collapse of the maxillary arch.


First stage of swallowing
The first stage is voluntary. The
separation of food bolus is done by
tongue. The bolus is placed on the
dorsum of the tongue and pressed
lightly against hard palate. The tip of
the tongue rests on the hard palate just
behind the incisors. The lips are sealed
and the teeth are brought together. The
presence of the bolus on the mucosa of
the palate initiates a reflex wave of
contraction in the tongue that presses
the bolus backward. It is transferred to
the pharynx.

Second stage
Once the bolus has reached the
pharynx a peristaltic wave caused
by the contraction of the pharyngeal
constrictor muscles carries the bolus
down to esophagus The soft palate
rises to touch the posterior
pharyngeal wall sealing off the
nasal passages.The epiglottis blocks
the pharyngeal air way to the
trachea and keeps the food in the
oesophagus.

Third stage
This stage is of passing of the bolus of the food through out
the length of the esophagus and into the stomach.
Peristaltic waves carry the bolus down the esophagus .As
the bolus approaches the cardiac sphincter relaxes and lets
it enter the stomach .The upper section of the esophagus
muscles are voluntary where as the lower section are
involuntary.


Characteristics of mature
swallow
Teeth are together.
Mandible is stabilized by contraction of
mandibular elevators, which are the primary 5 th
cranial nerve muscles.
Tongue tip is held against the palate above and
behind the incisors.
There are minimum contraction of the lip in
mature swallow.

Characteristics of infantile
swallow
Jaws apart with the tongue between the gum
pads.
Mandible is stabilized by the contraction of the
muscles of the 7th cranial nerve and the
interposed tongue.
The swallow is guided and to a greater extent
controlled by interchange between lips and the
tongue.

Characteristics of retained
infantile
swallow swallowing reflex
This is the persistence of the infantile
even after the arrival of the permanent teeth.
Very few people have this type of swallow.
Teeth occlude on only one molar in each quadrant.
They demonstrate violent contractions of 7th cranial
nerve musculature during swallowing and tongue is
markedly protruded between all teeth during initial
stages of swallow.
The patients will have an expression less face since
facial muscles are used for stabilizing the mandible.

By recording from the Masseter, it is
possible to determine whether or not the
teeth are placed together in swallowing.
The Masseter muscle normally contracts
strongly during the phase of the mylohyoid
contraction to hold the teeth in firm contact.
By recording simultaneously from the
group of circum oral muscles, it is also
possible to illustrate the amount of lip
activity.

Typical records for the "teeth together"
swallow showed the masseteric contraction
is marked and the circum oral contraction is
minimal. Where the teeth are apart in
swallowing, the masseteric contraction is
slight compared with the circumoral activity.
The results of the investigations by RIX
show that the "teeth apart" swallow is
present in a large number of adults,
particularly if they have any degree of
malocclusion.

 Variations described by Rix in 1953, two
sharply contrasting types of atypical
swallowing are recognizable:


Nondispersing behaviour of
tongue:
Those cases in which the
tongue does not come
forward to exert any force on
the lingual surface of upper
and lower incisors. The lips
may or may not contract
excessively. The upper and
lower incisors are upright or
retroclined.

Dispersing behaviour of
tongue:
Those cases in
which the actions of
tongue and lips are
associated with a
dispersal of upper and
lower incisor
relations.

A similar type of behaviour may
be found in Class II, Division 2
malocclusions and Rix refers to
this as the "blunt tongue" swallow.
With the tongue held back
between the arches in this way, a
cross-bite is rarely seen. It does
not necessarily follow that the lip
activity is excessive, but there is
no forward tongue pressure on the
incisor segments. Improvement in
the axial inclinations of incisors
will depend on the possibility of
modifying these atypical forces.

In Class II, Division 1 malocclusions the action
of the tongue and lower lip may be responsible
for the dispersal of the incisor relationship .
When this action is strongly adverse, the
stability of the end result may be jeopardized.
If the relative position of the lower lip is
changed by retraction of the upper incisors, it
may act on their labial surfaces to retain these
teeth but produce secondary effects on the
lower incisors causing them to imbricate.

Simple tongue thrust

It is defined as the tongue thrust with a teeth together
swallow.
Malocclusion which is associated with it is usually a well
circumscribed type of open bite in the anterior region.
Cuspal interferences have not present and there is a
perfect fit of posterior teeth in occlusion.
It is associated with abnormal functioning of lips,
mentalis and circum oral muscles.
As the patient swallows the anterior lip seal is made
partly with the teeth and partly with the lips, the inferior
orbicularis cannot elevate itself, it can be elevated with the
help of mentalis.
The open bite has a definite beginning and ending.

Complex tongue thrust
This is defined as teeth apart swallow.
The malocclusion is characterized by poor occlusal fit
resulting into a slide into occlusion and generalized
anterior open bite .
Absence of temporal muscle contraction during
swallowing.
There is dropping of the mandible and strong
contraction of circum oral muscle.
There are two neuromuscular problems.
Abnormal occlusal reflex and abnormal swallow reflex.

Normal tongue postures

Retracted tongue posture

Retained infantile swallow


Tongue posture is related to skeletal
morphology. In severe class III skeletons the
tongue tends to lie below the plane of occlusion,
and in class II facial skeletons with a short
mandible and steep mandibular plane the tongue
may position forward. Two variations from the
normal posture. They are:
1. The retracted or cooked tongue.
2. Protracted tongue posture.

Protracted tongue posture usually results in an
open bite. There are two forms
1.Endogenous
2.Acquired adaptive
Endogenous protracted tongue posture may be a
retention of the infantile postural pattern.
Acquired posture is due to the transitory
adaptation to the enlarged tonsils, pharyngitis or
tonsillitis.

Functionally abnormal lips
One of the frequent abnormal lip functions is
associated with tongue thrust swallowing.
Mentalis muscle and inferior orbicularis oris
muscle are enlarged causing the gingiva to be
rubefacient and hypertrophied. Gingivitis in the
mandibular region in the absence of maxillary
gingivitis may be indicative of hyperactive
mentalis where as gingivitis in both anterior
regions is indicative of mouth breathing.

Muscle role in orthognathic
surgery
The suprahyoid musculature has
repeatedly been suggested as a primary
cause of relapse after mandibular
advancement surgery.


Effects on lip pressure and
different patterns of post
surgical changes
When incisors are moved within the sphere
of influence of the lips after previously being
outside of it, as when vertically prominent
maxillary incisors are elevated to a new
position beneath the lip, lip pressures will
increase and the incisors will tend to move
lingually post surgically.

When soft tissues are relaxed by the surgical
treatment, as when the mandible rotates upward
and forward following maxillary intrusion, lip
pressures will decrease and the incisors will
move labially.
 In patients in whom the soft tissues are
stretched at surgery, as in mandibular or
maxillary advancement, lip pressures will
increase and the incisors will move lingually
post surgically.

Neuro muscular adaptation is an essential
requirement for stability. Repositioning of
the tongue to maintain air way
dimensions, (change in tongue posture)
occurs as an adaptation to changes
produced by mandibular osteotomy. These
adaptations of the tongue, and adaptation
in lip pressures that also occur post
surgically, contribute to the stability of
tooth positions.

Neuromuscular adaptation affects
muscular length and not muscular
orientation. If the orientation of the
muscle group such as the mandibular
elevators is changed, adaptation
cannot be expected.


Role of muscle in retention and
stability
Alfred Coleman (1865) was the first
person who claimed that muscular
pressure is responsible for relapse .


According to Moyers primary cause of
relapse is specifically that abnormal
seventh nerve action as it affects the
facial muscles, especially abnormal
functioning of the mentalis muscle, is
one of the most frequent causes of
relapse of incisor correction.


Stedman (1961,1967), in a comprehensive
approach to retention, referred to an
enlarged pharyngeal space, emotionally
initiated mentalis or mimetic muscle
hypertension, and anterior component of
force of mandibular third molars
because of insufficient growth as factors
in bringing about undesirable post
treatment changes or relapse.

Strang theorized that the mandibular inter
canine and inter molar arch widths are accurate
indicators of the individual's muscle balance and
dictate the limits of arch expansion during
treatment.
Weinstein et al and Mills stated that the lower
incisors lie in a narrow zone of stability in
equilibrium between opposing muscular
pressure, and that the labio lingual position of
the incisors should be accepted and not altered
by orthodontic treatment.
Reitan claimed that teeth tipped either labially
or lingually during treatment are more likely to
relapse.

Its not easy to blow or
swallow at the same time
PLAUTUS


Thank you
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