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Muscle physiology /certified fixed orthodontic courses by Indian dental academy

  1. 1. Muscle physiology and its significance in orthodontics INDIAN DENTAL ACADEMY Leader in continuing dental education
  2. 2. 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
  3. 3. Muscle attachments Muscles can be divided into two groups with respect to their attachments. 1. Periosteal 2. Tendinous
  10. 10. Methods of studying muscle activity 1. ANATOMIC 2. FUNCTIONAL: a. MOVEMENT b. FORCE AND PRESSURE c. ELECTROMYOGRAPHY 3. BEHAVIORAL
  11. 11. 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.
  13. 13. 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.
  14. 14. 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.
  15. 15. 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.
  16. 16. 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.
  17. 17. 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.
  18. 18. 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.
  19. 19. 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.
  20. 20. 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
  22. 22. Muscles of facial expression
  27. 27. 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.
  29. 29. Extrinsic muscles of tongue
  31. 31. Muscles of the floor of the oral cavity
  32. 32. 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.
  33. 33.
  34. 34. 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.
  35. 35.
  36. 36. 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.
  37. 37. 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.
  38. 38. 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.
  39. 39. 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.
  40. 40. There are two types of isotonic contraction . They are 1. Concentric contraction 2. Eccentric contraction
  41. 41. 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.
  42. 42. 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.
  43. 43. 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.
  44. 44. 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.
  45. 45. 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).
  46. 46. 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.
  47. 47. According to Woodside, a stretch of the soft tissues primarily requires dislocating the mandible anteriorly or opening beyond the postural rest vertical dimensions.
  48. 48. 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.
  49. 49. 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.
  50. 50. Clasp knife reflex
  51. 51. 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.
  52. 52. 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.
  53. 53. 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.
  54. 54. 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.
  55. 55. 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.
  56. 56. 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.
  57. 57. Muscle in TMD Clenching grinding (stress response) Internal joint pathology Muscle spasm and fatigue TMD symptoms: pain Joint noise limited opening
  58. 58. 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
  59. 59. 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.
  60. 60. 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.
  61. 61. 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.
  62. 62. 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.
  63. 63. 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.
  64. 64. 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.
  65. 65. 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.
  66. 66. 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.
  67. 67. 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.
  68. 68. 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.
  69. 69.
  70. 70.  Variations described by Rix in 1953, two sharply contrasting types of atypical swallowing are recognizable:
  71. 71. 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.
  72. 72. 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.
  73. 73. 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.
  74. 74. 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.
  75. 75.
  76. 76. 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.
  77. 77. 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.
  78. 78. Normal tongue postures Retracted tongue posture Retained infantile swallow
  79. 79.
  80. 80. 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.
  81. 81. 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.
  82. 82. 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.
  83. 83. Muscle role in orthognathic surgery The suprahyoid musculature has repeatedly been suggested as a primary cause of relapse after mandibular advancement surgery.
  84. 84. 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.
  85. 85. 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.
  86. 86. 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.
  87. 87. 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.
  88. 88. Role of muscle in retention and stability Alfred Coleman (1865) was the first person who claimed that muscular pressure is responsible for relapse .
  89. 89. 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.
  90. 90. 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.
  91. 91. 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.
  92. 92. Its not easy to blow or swallow at the same time PLAUTUS
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