Muscles part 2

1. 1 Muscles Muscles Part 2 Part 2 Prepared by: Prepared by: Dr Dr.. Mohammed Alruby Mohammed Alruby M Muscles uscles pa part 2 rt 2 Dr. Mohammed Alruby Dr. Mohammed Alruby

2. 2 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 M Muscles uscles pa part 2 rt 2 Dr. Mohammed Alruby Dr. Mohammed Alruby

3. 3 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 M Muscles uscles pa part 2 rt 2 Dr. Mohammed Alruby Dr. Mohammed Alruby

4. 4 = 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 M Muscles uscles pa part 2 rt 2 Dr. Mohammed Alruby Dr. Mohammed Alruby

5. 5 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 M Muscles uscles pa part 2 rt 2 Dr. Mohammed Alruby Dr. Mohammed Alruby

6. 6 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 M Muscles uscles pa part 2 rt 2 Dr. Mohammed Alruby Dr. Mohammed Alruby

7. 7 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 M Muscles uscles pa part 2 rt 2 Dr. Mohammed Alruby Dr. Mohammed Alruby

8. 8 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 M Muscles uscles pa part 2 rt 2 Dr. Mohammed Alruby Dr. Mohammed Alruby

9. 9 -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 M Muscles uscles pa part 2 rt 2 Dr. Mohammed Alruby Dr. Mohammed Alruby

10. 10 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 M Muscles uscles pa part 2 rt 2 Dr. Mohammed Alruby Dr. Mohammed Alruby

11. 11 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: M Muscles uscles pa part 2 rt 2 Dr. Mohammed Alruby Dr. Mohammed Alruby

12. 12 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: M Muscles uscles pa part 2 rt 2 Dr. Mohammed Alruby Dr. Mohammed Alruby

13. 13 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 M Muscles uscles pa part 2 rt 2 Dr. Mohammed Alruby Dr. Mohammed Alruby