Muscle function &
malocclusion
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com

ww...









•
•

Introduction
Physical properties of muscle.
Muscle physiology
Role of muscles in functional mandibul...
Introduction
To propel his skeleton ,
man has 639
muscles,composed of 6
billion muscle fibers.each
fiber has 1000 fibrils,...
Physical properties of muscle :

o

Muscle has 2 physical properties:
Elasticity
Contractility

1.

ELASTICITY:



Normal...
2. CONTRACTILITY:
 It is the ability of muscle to shorten its length
under innervational impulse.
 Muscle is 1st stimula...


The strength of muscle contaction depends
on the number of fibers engaged in a activity
at a particular time.



Facto...


ISOMETRIC CONTRACTION:
Isometric contraction occurs when a
muscle is simply resisting an external force
without any act...
Strength of muscle
contraction in
various mandibular
positions:
1.Open mouth
2.Postural
restingposition
3.Occlusal positio...
Muscle physiology


ALL OR NONE LAW :

•

The intensity of contraction of any fiber is independent of strength of
the exc...


MUSCLE TONUS

•

Muscle tonus is a state of slight constant
tension which is a characteristic of all healthy
muscle.

•...


RESTING LENGTH:

•

The resting length of a muscle is rather
constant & predeterminable
relationship,permitting the mai...
STRETCH OR MYOTATIC REFLEX:









The reflex contraction of a healthy muscle which
results from a pull on its ten...
RECIPROCAL INNERVATION AND
INHIBITION






The inhibition of the tonus or contractility of
the muscle is brought by e...
ROLE OF MUSCLES IN FUNCTIONAL
MANDIBULAR MOVEMENTS






Mandible is the only
movable bone in the head
& face region.
T...


1.

2.
3.

4.
5.

Muscles primarily
responsible for
mandibular functional
movements:
Anterior & posterior
fibers of tem...






During opening of mandible from teeth in
occlusion:
Primary contraction of lateral pterygoid
muscles.
Suprahyoid,...
During closing of mandible:
 Bilateral activity of masseter & temporalis
muscles assisted by smaller madial pterygoid
mus...







During protrusion,lateral & medial pterygoid
contract in unison.
Retrusion is less efficient & less definite.
R...




Normal muscle
activity associated
with normal jaw
relationship & normal
occlusion.
Electromyographic
studies show ev...


In classII malocclusion,
mandibular retrusion &
excessive apical base
difference,middle&
posterior temporalis &
deep ma...








In classII malocclusion
withdeep overbite,the
functional retrusion
tendency is increased.
Posterior temporalis...
COMPENSATORY MUSCLE FUNCTION
IN DIFFERENT MALOCCLUSIONS








Class I malocclusion:
Muscle function is usually norm...







INFANTILE SWALLOWING
MECHANISM:[1st 6 months]
Plunger like action is
associated with
nursing,unopposed by the
p...








MATURE SOMATIC
SWALLOW:[1 yr after]
The dorsum of tongue is
less concave and
approximates palate
during deglut...


Anterior open bite
associated with retained
infantile swallowing habit
& manifest tonguethrusting.



The peripheral p...


FINGER SUCKING
MALOCCLUSION:



Bilateral narrowing of
maxillary arch may be
attributed to tongue
thrusting,lower rest...


Compensatory mechanism:



Retained infantile swallow results in openbite.



To close off the oral cavity for normal...






Open bite accentuates, lips become more
hypotonic as tongue force during function is
greater than opposing lip fo...


Lip sucking , the
cushioning of the
lower lip to the
lingual aspect of the
maxillary incisors
during both rest&
active ...
Compensatory muscle function in classII div 1
malocclusion:


Class II div1 malocclusion involve abnormal muscle
activity...









Class II div 1
relationship:
Lowered tongue posture.
Elongated functional
position.
Narrowed buccal dental
s...










Lower lip cushions to the lingual of the
maxillary incisors, both at postural rest &
during active function...






With compensatory tongue thrust,lower
tongue position & increased buccinator
muscle activity,the maxillary arch n...
Compensatory muscle function in class II
div 2







Activity of cheek & lip muscles is normal.
Tongue accentuates th...


Mandible closes from postural rest position to
point of initial contact.



The lingually inclined maxillary incisors ...
Compensatory muscle function in classIII
malocclusion:








Strong hereditary pattern.
The upper lip is short not...
Electromyographic response of muscles:








Electromyography provides a method of studying
the physiologic basis o...


Ralston states that at present
electromyography is capable of assesing
time only ,duration,and phasic relationship of
m...
CONCLUSION:


Muscle function can be adaptive to morphogenetic pattern. A
change in muscle function can initiate morpholo...
Thank you
For more details please visit
www.indiandentalacademy.com

www.indiandentalacademy.com
Upcoming SlideShare
Loading in...5
×

Muscle function & malocclusion /certified fixed orthodontic courses by Indian dental academy

572

Published on


The Indian Dental Academy is the Leader in continuing dental education , training dentists in all aspects of dentistry and offering a wide range of dental certified courses in different formats.

Indian dental academy provides dental crown & Bridge,rotary endodontics,fixed orthodontics,
Dental implants courses.for details pls visit www.indiandentalacademy.com ,or call
0091-9248678078

0 Comments
2 Likes
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total Views
572
On Slideshare
0
From Embeds
0
Number of Embeds
0
Actions
Shares
0
Downloads
14
Comments
0
Likes
2
Embeds 0
No embeds

No notes for slide

Muscle function & malocclusion /certified fixed orthodontic courses by Indian dental academy

  1. 1. Muscle function & malocclusion INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com www.indiandentalacademy.com
  2. 2.         • • Introduction Physical properties of muscle. Muscle physiology Role of muscles in functional mandibular movements. Compensatory muscle function: Class-I malocclusion Class-II malocclusion Class-III malocclusion Electromyographic response of muscles Conclusion www.indiandentalacademy.com
  3. 3. Introduction To propel his skeleton , man has 639 muscles,composed of 6 billion muscle fibers.each fiber has 1000 fibrils,which means there are 6000 billion fibrils at work at one time or another www.indiandentalacademy.com
  4. 4. Physical properties of muscle : o Muscle has 2 physical properties: Elasticity Contractility 1. ELASTICITY:  Normal relaxed muscle withstands only a certain amount of elongation[about 6/10th of its natural length] before rupturing.  This depends on the muscle involved,the type of stress,the individual resistance,age & possible pathologic conditions which have produced fibrotic changes which limit the extensibility of muscle.  o www.indiandentalacademy.com
  5. 5. 2. CONTRACTILITY:  It is the ability of muscle to shorten its length under innervational impulse.  Muscle is 1st stimulated by electric action potential,causing a contraction.energy for the muscle is provided by breakdown of high energy ATP.  Fatigue in a muscle is produced when lacticacid ,an energy breakdown byproduct ,collects in the tissues,lowering the pH to a level at which the muscle can no longer function effeciently. www.indiandentalacademy.com
  6. 6.  The strength of muscle contaction depends on the number of fibers engaged in a activity at a particular time.  Factors on which contraction depends: Striated or smooth. Number of fibers. Cross section. Frequency of discharge. Muscle fiber length.      www.indiandentalacademy.com
  7. 7.  ISOMETRIC CONTRACTION: Isometric contraction occurs when a muscle is simply resisting an external force without any actual shortening.  ISOTONIC CONTRACTION: Isotonic contraction occurs when there is actual shortening of muscle. www.indiandentalacademy.com
  8. 8. Strength of muscle contraction in various mandibular positions: 1.Open mouth 2.Postural restingposition 3.Occlusal position 4.Overclosure Shaded area is area of greatest strength. www.indiandentalacademy.com
  9. 9. Muscle physiology  ALL OR NONE LAW : • The intensity of contraction of any fiber is independent of strength of the exciting stimulus, provided that stimulus is adequate. • Stimuli below threshold strength do not elicit response;if they are over threshold strength a contraction of maximal intensity is made by the muscle fiber. • All or none law applies when only muscle is in physiologic reacting state. • Merton noticed that when muscle is fatigued,the action potential no longer triggers all or none law. www.indiandentalacademy.com
  10. 10.  MUSCLE TONUS • Muscle tonus is a state of slight constant tension which is a characteristic of all healthy muscle. • Tonus is the basis of reflex posture. • It is purposive and coordinated in the maintenance of various positions. www.indiandentalacademy.com
  11. 11.  RESTING LENGTH: • The resting length of a muscle is rather constant & predeterminable relationship,permitting the maintenance of postural relations & dynamic equilibrium by contraction of the minimal number of fibers,consistent with any particular moment. www.indiandentalacademy.com
  12. 12. STRETCH OR MYOTATIC REFLEX:      The reflex contraction of a healthy muscle which results from a pull on its tendon is called a stretch,or myotatic reflex. The stimulus of stretch reflex is the stretch of the muscle The stretch reflex when elicited ,causes contraction of the stretched muscle. Muscle stretch receptors are proprioceptive nerve endings called muscle spindles. The functional significance of the stretch reflex is that it serves as a mechanism for upright posture or standing.natural stretches are usually imposed on muscles by the action of gravity. The same stretch reflex acts in mandibular musculature to maintain the postural rest position of the mandible in relation to maxilla. www.indiandentalacademy.com
  13. 13. RECIPROCAL INNERVATION AND INHIBITION    The inhibition of the tonus or contractility of the muscle is brought by excitation of its antagonist. Without reciprocal innervation & inhibition, the myotatic or stretch reflexes would make flexion & extension simultaneously antagonistic. The reciprocal innervation helps in control of primary mover. www.indiandentalacademy.com
  14. 14. ROLE OF MUSCLES IN FUNCTIONAL MANDIBULAR MOVEMENTS    Mandible is the only movable bone in the head & face region. The mandible responds to various muscular stimuli. The following diagram shows muscle groups maintaining the balance of the head & vertebral column. www.indiandentalacademy.com
  15. 15.  1. 2. 3. 4. 5. Muscles primarily responsible for mandibular functional movements: Anterior & posterior fibers of temporalis Lateral pterygoid Ant,post,middle components of masseter Suprahyoid Infrahyoid www.indiandentalacademy.com
  16. 16.    During opening of mandible from teeth in occlusion: Primary contraction of lateral pterygoid muscles. Suprahyoid,infrahyoid,genioglossus, mylohyoid &diagastric muscles stabilize the mandible. Temporal,masseter & medial pterygoid muscles show relaxation. www.indiandentalacademy.com
  17. 17. During closing of mandible:  Bilateral activity of masseter & temporalis muscles assisted by smaller madial pterygoid muscles.  More power elicited during closure.  Lateral pterygoid through their controlled relaxation,effect smooth &uninterrupted closure.  During resistance to closure,gerater activity is generated in lateral pterygoid ,suprahyoid & infrahyoid muscles. www.indiandentalacademy.com
  18. 18.     During protrusion,lateral & medial pterygoid contract in unison. Retrusion is less efficient & less definite. Retrusion is largely accomplished by posterior fibers of temporalis muscles,with assistance from geniohyoid,diagastric & mylohyoid muscles. Electromyographic research indicatse role of deep fibers of masseter muscle in retrusion. www.indiandentalacademy.com
  19. 19.   Normal muscle activity associated with normal jaw relationship & normal occlusion. Electromyographic studies show even distribution of anterior,posterior, middle temporalis & deep &superficial fiber activity. www.indiandentalacademy.com
  20. 20.  In classII malocclusion, mandibular retrusion & excessive apical base difference,middle& posterior temporalis & deep masseter fibers show great magnitude of contraction.  This adapts to & enhances the mandibular retrusion. www.indiandentalacademy.com
  21. 21.     In classII malocclusion withdeep overbite,the functional retrusion tendency is increased. Posterior temporalis & deep masseter activity is dominant. Stretch reflex is elicited for lateral pterygoid muscle which insert into articular disk.This serves to pull the disk forward as the condyle is functionally retruded. Condyle may then impinge on retrodiscalpad. www.indiandentalacademy.com
  22. 22. COMPENSATORY MUSCLE FUNCTION IN DIFFERENT MALOCCLUSIONS      Class I malocclusion: Muscle function is usually normal in cases of class I malocclusion. The teeth are in balance with environmental forces. The only exception to normal muscle activity in classI malocclusion is open –bite problems. The greatest share of class I openbite problems is attributed to thumbsucking,retained infantile swallow or visceral swallow or both. www.indiandentalacademy.com
  23. 23.     INFANTILE SWALLOWING MECHANISM:[1st 6 months] Plunger like action is associated with nursing,unopposed by the peripheral portions of the tongue. Associated with tongue thrust is the anterior positioning of the mandible. There is concavity in the midline of the tongue & peripheral portions are raised. www.indiandentalacademy.com
  24. 24.     MATURE SOMATIC SWALLOW:[1 yr after] The dorsum of tongue is less concave and approximates palate during deglutition. The tip of the tongue is contained behind the incisors. Peripheral portions flow between opposing posterior segments. Anterior mandibular thrust has disappeared. www.indiandentalacademy.com
  25. 25.  Anterior open bite associated with retained infantile swallowing habit & manifest tonguethrusting.  The peripheral portions of the tongue do not overlie the posterior occlusal surface during rest.  Thus,postural resting position & habitual occlusion are same,with no demonstrable interocclusal clearence www.indiandentalacademy.com
  26. 26.  FINGER SUCKING MALOCCLUSION:  Bilateral narrowing of maxillary arch may be attributed to tongue thrusting,lower resting tongue posture,and excessive buccal pressures that are a part of infantile swallowing mechanism.  Unilateral crossbites are the result of a “convenience swing”of mandible to one side,with tooth guidance from point of initial contact to habitual occlusion. www.indiandentalacademy.com
  27. 27.  Compensatory mechanism:  Retained infantile swallow results in openbite.  To close off the oral cavity for normal deglutition,either a lipseal or a tongue seal is needed to create negative atmospheric pressure associated with the swallowing phenomenon.  If the finger displaces the maxillary incisors labially ,the lipseal becomes more difficult & the tongue thrust forward between the maxillary incisors to “close-off” the oral cavity. www.indiandentalacademy.com
  28. 28.    Open bite accentuates, lips become more hypotonic as tongue force during function is greater than opposing lip force & no longer contact each other at rest. Mouth breathing is aggravated with each swallow,the lower lip cushions to lingual of maxillary incisors & joins the tongue in natures adaptive attempt to create the oralseal during swallowing. Mentalis activity greatly increases & puckering of chin seen with each swallow. www.indiandentalacademy.com
  29. 29.  Lip sucking , the cushioning of the lower lip to the lingual aspect of the maxillary incisors during both rest& active function & hyperactive mentalis muscle activity enhance malocclusion & prevent normal deglutition. www.indiandentalacademy.com
  30. 30. Compensatory muscle function in classII div 1 malocclusion:  Class II div1 malocclusion involve abnormal muscle activity.  A change in muscle function is a requisite ,expansion is a t/t objective.  With hereditary type of class II malocclusion, the teeth reflect abnormal anteroposterior jaw relationship.  If such a malocclusion exsists, the muscle function adapts to this pattern as best it can in line with the requirements of mastication, deglutition,respiration & speech. www.indiandentalacademy.com
  31. 31.      Class II div 1 relationship: Lowered tongue posture. Elongated functional position. Narrowed buccal dental segments in maxillary arch. Lower lip cushioning to lingual aspect of maxillary incisors during rest & active function. www.indiandentalacademy.com
  32. 32.      Lower lip cushions to the lingual of the maxillary incisors, both at postural rest & during active function. In lip sucking habit lower lip mass almost constantly thrust into the excessive overjet. The lip becomes hypertrophic. The maxillary incisors move further labially,weakly resisted by hypotonic upper lip . The lower incisors buckle as the mandibular segment is flattened by continuosly abnormal mentalis muscle activity. The curve of spee increases. www.indiandentalacademy.com
  33. 33.    With compensatory tongue thrust,lower tongue position & increased buccinator muscle activity,the maxillary arch narrows & assumes V shape. Abnormal muscle activity can create pseudo class II div 1 problems even in harmonius antero posterior jaw relationship. In true classII div 1 to begin with morphology &jaw relationship are abnormal and muscle activity has accentuated the exsisting pattern. www.indiandentalacademy.com
  34. 34. Compensatory muscle function in class II div 2     Activity of cheek & lip muscles is normal. Tongue accentuates the curve of spee & the eruption of the posterior teeth by occupying the interocclusal space. Due to lingual inclination of maxillary central incisors & increased interocclusal clearence & infraocclusion of the posterior teeth. Functional guidance of mandible is common. There is forced retrusion phenomenon. www.indiandentalacademy.com
  35. 35.  Mandible closes from postural rest position to point of initial contact.  The lingually inclined maxillary incisors then guide the mandible into a retruded position during the balance of closing movement to full occlusal contact. www.indiandentalacademy.com
  36. 36. Compensatory muscle function in classIII malocclusion:       Strong hereditary pattern. The upper lip is short not necessarily hypotonic. The lower lip is hypertrophic & redundant & appears passive during the deglutition cycle. During swallowing ,there is greater activity of the upper lip. The tongue is a potent force & lie lower in the floor of the mouth. The maxillary arch does not have the balancing effect of tongue mass & since the peripheral portions of the tongue are less apparent between the occlusal surfaces,the maxillary arch is usually narrow &the interocclusal space is very small or entirely absent. www.indiandentalacademy.com
  37. 37. Electromyographic response of muscles:     Electromyography provides a method of studying the physiologic basis of mastication, deglutition & speech. In classII div 1 malocclusion electrical activity appears in the masseter muscles before the temporal muscles. The temporal muscle ,although more rapid in action,is relatively weaker than the masseter muscle in power. According to moyers the lateral pterygoid preceeds digastric action in mandibular depression. www.indiandentalacademy.com
  38. 38.  Ralston states that at present electromyography is capable of assesing time only ,duration,and phasic relationship of muscle contraction,but not of measuring such function as force ,speed of contraction, and work produced. www.indiandentalacademy.com
  39. 39. CONCLUSION:  Muscle function can be adaptive to morphogenetic pattern. A change in muscle function can initiate morphologic variation in the normal configuration of the teeth and supporting bone, or it can enhance an already existing malocclusion.  The structural abnormality is increased by compensatory muscle activity to the extent that a balance is reached between pattern, environment, and physiology.  It is imperative that the orthodontist appraise muscle activity and that he conduct his orthodontic therapy in such a manner that the finished result reflects a balance between the structural changes obtained and the functional forces acting on the teeth and investing tissues at that time. www.indiandentalacademy.com
  40. 40. Thank you For more details please visit www.indiandentalacademy.com www.indiandentalacademy.com

×