Myology related to prosthodontics / orthodontic seminars


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Myology related to prosthodontics / orthodontic seminars

  1. 1. 1 INDIAN DENTAL ACADEMY Leader in continuing dental education
  2. 2. 2 •Myology – study of muscles. •Muscle is a soft tissue made up of a large number of fibers bound together by connective tissue into bundles, or fascicles. • These bundles are surrounded by connective tissue sheaths and grouped together into still larger bundles.
  3. 3. 3 • The whole muscle is enveloped by a connective tissue sheath, the epimysium. • Blood vessels enter a muscle and branch into smaller vessels that course through these connective tissues to reach the individual muscle fibers, which are also muscle cells.
  4. 4. 4 • Muscles can be Voluntary (skeletal) or invouluntary (smooth or cardiac). • The muscles that are intimately involved with Prosthodontics are skeletal muscles.
  5. 5. 5 • In the majority of skeletal muscles, the origins and insertions are in bone. • However, many of the skeletal muscles involved in complete denture construction have a bony origin but insert into an aponeurosis, a raphe, or another muscle with one exception, the muscles of mastication have their origins and insertions in bone.
  6. 6. 6 • The orbicularis oris has no bony origin or insertions, and its primary function is to close the oral orifice (sphincter). • When the origin and insertion of a muscle are in bone, there is a limitation to the positions and action of the muscles. • When an attachment is in an aponeurosis, a raphe, or another muscle, a more flexible situation exists.
  7. 7. 7 • Knowledge of this relationship is used in making jaw relation records, particularly centric relation or centric position. Centric relation is a bone-to- bone relation controlled by the attached musculature, the tissue-lined bony fossae, the ligaments, and the articular
  8. 8. 8 • The muscles of facial expression, the muscles of the tongue, the suprahyoid muscles, the muscles of the soft palate, and the pharyngeal muscles do not have both origins and insertions in bone. • These are the muscles primarily involved with determining the extent of the denture borders, the contour of the denture bases, and the positions of the teeth.
  9. 9. 9 • The nonbony attachments of these muscles account for the various contours, borders, and positions of teeth that are seen in dentures. Impression techniques are influenced by these attachments. The muscles should not be stretched or left unsupported during an
  10. 10. 10 • The teeth, not the denture borders, support the muscles of facial expression. • The available vestibular spaces should be used to their fullest extent but should not be overfilled.
  11. 11. 11 MUSCLES OF MASTICATION • TEMPORALIS • Origin: • The temporalis arises from the temporal fossa on the lateral aspect of the skull. The area is bounded above by the temporal line, and below by the zygomatic arch. It includes parts of the frontal, parietal, and squarnous temporal and of the greater wing of the sphenoid bone.
  12. 12. 12 • The anterior fibres of the muscle run vertically downwards; the posterior fibres run horizontally forwards; while the intermediate fibres run obliquely to converge in a tendon. The tendon passes deep to the zygomatic arch.
  13. 13. 13 • Insertion: • The muscle is inserted into the coronoid process of the mandible. The region of insertion covers the entire medial aspect of the coronoid process (including its apex, anterior and posterior borders). Some fibres are inserted into the anterior border of the ramus
  14. 14. 14 • Actions: • The temporalis helps to close the mouth by elevating the mandible. • The movements of elevation and depression of the mandible have two components. • Firstly, there is a hinge like movement between the condyle of the mandible and the inferior surface of the articular disc of the temporomandibular joint. The second component is a gliding movement of the disc
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  19. 19.
  20. 20. 20 • MASSETER • The masseter is a quadrilateral muscle placed superficial to the ramus of the mandible • Origin: • The muscle arises from the Zygomatic arch • The more superficial muscle fibres arise from the anterior two thirds of the lower border of the arch; whereas the deeper fibres arise from its deep surface, and from the posterior one third of its lower border. The most anterior fibres arise from the zygomatic process of the maxilla.
  21. 21. 21 • Insertion: • The muscle is inserted into the lateral surface of and angle of the mandible. • Actions: • The masseter elevates the mandible to close the rr Its anterior fibres help in protraction (forward in of the jaw.
  22. 22.
  23. 23. 23 • LATERAL PTERYGOID: • It is seen that the muscle has two heads upper and lower • Upper head arises from: • infratemporal surface, and (ii) the infratemporal crest of the greater wing of the sphenoid bone. • The lower head arises from the lateral surface of the lateral pterygoid plate.
  24. 24. 24 • Insertion: • The fibres of both heads run backwards and laterally to be inserted into a depression (pterygoid fovea) on the anterior aspect of the neck of the mandible. Some fibres are inserted into the intra articular disc and‑ some into the capsule of the temporo mandibular joint.‑
  25. 25. 25 • MEDIAL PTERYGOID • Origin: • The medial pterygoid muscle takes origin from: (a) the medial surface of the lateral pterygoid plate and (b) the adjoining part of the palatine bone (pyramidal process).
  26. 26. 26 (c) A superficial slip arises from the lateral aspect of the pyramidal process of the palatine bone and from the maxillary tuberosity • Insertion: • The fibres of the muscle pass downwards, backwards and laterally to be inserted into the medial surface of the angle of the mandible and the adjoining part of its ramus.
  27. 27.
  28. 28. 28 • Actions of Pterygoid Muscles: • The fibres of the lateral pterygoid , pull the mandible forwards (protraction) and medially. • . The fibres of the medial pterygoid also perform the same actions in addition elevate the mandible.
  29. 29. 29 • (a) The medial and lateral pterygoids of both sides acting together protract the mandible. • (b) The medial and lateral pterygoids of one side acting together pull the mandibular condyle of that side forwards (and medially). As a result the chin moves forwards and to the opposite side. Alternate action of the muscles of the two sides results in side to side chewing movements.
  30. 30. 30 • (c) The two pterygoid muscles have opposite actions as far as opening and closing of the mouth is concerned. The medial pterygoid elevates the jaw. The lateral pterygoid helps in opening the mouth by pulling the head of the mandible forwards along with the intra articular disc‑
  31. 31.
  32. 32. 32 MUSCLES OF THE TONGUE • The extrinsic muscles of the tongue enter it from outside. They are the styloglossus, the palatogloss genioglossus, and the hyoglossus. • The intrinsic muscles lie within the substance of the tongue.
  33. 33. 33 • Styloglossus • The styloglossus arises from the anterior and lateral aspects of the styloid process, and from the upper part of the stylomandibular ligament .It runs downwards and forwards to merge with the side of the tongue.
  34. 34.
  35. 35.
  36. 36. 36 • Palatoglossus • The palatoglossus muscle arises from the anterior side of the palatine aponeurosis (a sheet of fibrous in the soft palate). The muscle passes do nw forwards to be inserted into the side of the tongue. with the mucous membrane covering it, it for palatoglossal arch, which lies anterior to the tonsil
  37. 37. 37 • Genioglossus • The genioglossus lies next to the median plane. It arises from the upper genial tubercles on the posterior of the symphysis menti. • The fibres spread to be inserted into the whole length of the ventral of the tongue. The lowest fibres muscle are attached to the body of the hyoid bone.
  38. 38. 38 • Hyoglossus • The hyoglossus muscle arises from the hyoid bone. The area of origin includes : a. The greater cornu, and b. the lateral part of the body. b. The fibre pass outwards to enter the side of the
  39. 39. 39 • Actions: • The muscles of the tongue move the tongue and alter its shape for movements concerned with speech, mastication and swallowing. • Hyoglossus –depress the tongue • Styloglossus – pulls it upwards and backwards.
  40. 40. 40 • Genioglossus – protrudes the tongue. • Palatoglossus – both sides act together to bring the palatoglossal arches together, thus shutting the oral cavity from the oropharynx. • Intrinsic muscles – alter the shape of the tongue.
  41. 41. 41 MUSCLES OF FACIAL EXPRESSION • The zygomaticus major, zygomaticus minor, levator labii superioris, levator labii superioris alaeque nasi, levator anguli oris, mentalis, depressor labii inferioris, depressor anguli oris, risorius, platysma, incisivus superioris, incisivus inferioris, orbicularis oris, and buccinator muscles are responsible for the expressions seen in the lower half of the
  42. 42. 42 • The actions of these muscles are responsible for various facial expressions including smiling, laughing, and frowning. When these muscles are relaxed, the face lacks expression. The actions of these muscles often reflect the mood and emotional status of an
  43. 43. 43 • MUSCLES OF THE SOFT PALATE • The tensor veli palatini, levator veli palatini, musculus uvulae, palatoglossus, and palatopharyngeus are the muscles of the soft palate, which is a movable curtain extending downward and backward into the pharynx. • During deglutition, it is raised and helps to seal off the nasopharynx: above from the oropharynx below.
  44. 44.
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  46. 46.
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  48. 48. 48 • The Tensor veli palatini is a thin, flat triangular muscle that arises from the scaphoid fossa of the pterygoid plates, spine of the sphenoid bone, and the lateral wall of the auditory tube. • Inferiorly, it becomes a slender tendon that turns around the pterygoid hamulus to enter the palate where it joins the palatine aponeurosis.
  49. 49. 49 • The levator veli palatini is a thick, rounded muscle that arises from the petrous portion of the temporal bone and the medial aspect of the auditory tube. • It courses downward and medially toward the midline of the soft palate, where it interlaces with the same muscle from the opposite side. • The sling that is formed by the joining of these two muscles causes the soft palate to be elevated during
  50. 50. 50 • The palatoglossus muscle and the mucous membrane covering it form the palatoglossal arch that extends from the soft palate to the side of the tongue. • When the two palatoglossi contract, they draw the tongue and soft palate toward each other. This assists in closing the isthmus faucium during deglutition.
  51. 51. 51 • SUPRAHYOID MUSCLES • The functions of the suprahyoid muscles include elevation of the hyoid bone and the larynx and depression of the mandible. • The digastric, stylohyoid, mylohyoid, and geniohyoid muscles compose this group of
  52. 52. 52 • The mylohyoid and the geniohyoid muscles may influence the borders of the mandibular denture. • The mylohyoid muscle is a thin sheet that arises from the whole length of the mylohyoid line. The posterior fibers are inserted into the body of the hyoid bone.
  53. 53. 53 • The geniohyoid muscle arises from the inferior mental spine (genial tubercle), which is located on the inner aspect of the symphysis menti just above the anterior attachment of the mylohyoid muscle. • This muscle presents no problem in complete denture construction unless there is extensive loss of the residual ridge.
  54. 54. 54 • INFRAHYOID MUSCLES: • The origin and insertion of this group of muscles, which consists of the stemohyoid, omohyoid, sternothyroid, and thyrohyoid, have no particular significance in complete denture prosthodontics with respect to any influence on the denture borders. • However, the actions of these muscles are important to the prosthodontist, for they are a part of the kinetic chain of the mandibular movement.
  55. 55. 55 • Their action is to fix the hyoid bone, as it were, to the trunk. It is from this fixed position that the suprahyoid muscles can act on the mandible. • In contrast, these muscles can relax and allow the hyoid bone to be pulled upward by the suprabyoid muscles during deglutition.
  56. 56. 56 • PHARYNGEAL MUSCLES • Of the several pharyngeal muscles, the superior constrictor is the one of most interest in complete denture construction. • The superior constrictor has four sites of origin: the posterior border of the medial pterygoidplate and pterygoid hamulus, the pterygomandibular raphe, the posterior end of the mylohyoid line, and the side of the tongue.
  57. 57.
  58. 58. 58 The muscles that hold move or stabilize the mandible do so because they receive impulses from the central nervous system. Mandibular motion at conscious level results in voluntary movement where as at subconscious level due to stimulation of oral or muscle receptors cause involuntary movement.
  59. 59. 59 Receptors in the oral mucous membrane are stimulated by touch pain thermal changes or pain and pressure where as other receptors are principally located in the periodontal ligaments, mandibular muscles and ligaments provide information as to the location of mandible in space and thus called PROPRIOCEPTORS
  60. 60. 60 • Impulses form oral receptors Trigeminal nuclei • From proprioceptors Mesencephalic nuclei of the brain From these 2 receptors Cerebral cortex
  61. 61. 61 • From the cerebral cortex It comes though three ways Via the thalamus to the sensoriomotor cortex (conscious level) to produce voluntary change in the position of the mandible By way of a reflex arc to the motor nuclei of the Trigeminal nerve to cause involuntary movement By combination of the these two ways through the subcortical areas as the hypothalamus, basal ganglion.
  62. 62. 62 In edentulous patients the periodontal ligament are lost thus the source of control in the positioning of the mandible are lost thus to compensate this centric occlusion must be in harmony with the centric relation and meet evenly in the normal range of functional activity and these impulses can be generated by voluntary thought which are transmitted through the motor nuclei and from there to the muscle of mastication so the mandible performs the desired activity
  63. 63. 63 Mastication is a programmed event residing in a chewing centre located in the brain stem (in the reticular formation of the pons ) The cyclic nature of mastication (jaw opening and closure ,tongue protrusion and retrusion) is a result of of action of this central pattern generation.
  64. 64. 64 The alteration of the chewing pattern or character (rate, force, duration)are related to the consistency of the bolus of the food. The relatively continuous flow of impulses through the specific pathway form the receptors to the CNS and back to the musculature establishes a memory pattern for mandibular movements.
  65. 65. 65 Thus when natural teeth are present a individual sub consciously develops these memory patterns But these patterns are disturbed when the teeth are lost or a new restoration is placed with an occlusion which is not in harmony with mandibular movement leads to pain ,pathosis and mental stress
  66. 66. 66 • Basically the muscles concerned with a prostheses can be simply dealt as : • A. muscles associated with the borders of the prostheses and its importance • B. muscles associated with surfaces of the denture and its importance.
  67. 67. 67 • A. Muscles associated with the borders of the prostheses and its importance • The insertions of the various muscles around the oral cavity, both superficial and deep, are important. These muscles insert partly into the connective tissues of the skin and partly into the mucous membrane of the lips.
  68. 68. 68 • The origins of several of the muscles of facial expression are near enough to the denture-bearing areas that their actions must be considered as definitely influencing the denture borders. • Their influence is in proportion to the contour and quantity of residual ridge present in a vertical direction. The higher the residual ridge, the less influence these muscle attachments will exert.
  69. 69. 69 MAXILLARY DENTURE • The posterior extension of the maxillary denture base rests on the soft palate. The mucous membrane in this area overlies the palatine aponeurosis. • This tendinous sheet lies in the anterior two thirds of the soft palate and is attached to the crest the lower surface of the hard palate near its posterior end.
  70. 70. 70 • Near the hard palate,muscle fibers are very scanty, and the aponeurosis is thick and strong at the junction; the anterior part of the soft palate is therefore more horizontal and less movable than the posterior part.
  71. 71. 71 • The characteristics of the aponeurosis and the overlying mucosa, the activity of the palatine muscles, and the contour of the soft palate determine the extent and the contour of the posterior palatal seal. The seal should be in the soft palate and not over the palatine bones.
  72. 72. 72 • The placing of the posterior palatal seal is the responsibility of the dentist. The extent, depth, and slope of the extension into the soft palate is determined by visual examination and by palpation. • As a general rule, the more acute the angle of attachment between the aponeurosis and the bone, the more active the reflection.
  73. 73. 73 • The more active the reflection, the less the denture base can extend on to the soft palate distally, and the more it must extend vertically into the soft tissues.
  74. 74. 74 • The tensor veli palatini inferiorly, becomes a slender tendon that turns around the pterygoid hamulus to enter the palate where it joins the palatine aponeurosis. • This slender tendon, when taut, can influence the denture contour in the hamular notch area.
  75. 75. 75 • The levator veli palatini medially toward the midline of the soft palate, interlaces with the same muscle from the opposite side. • The sling that is formed by the joining of these two muscles causes the soft palate to be elevated during contraction.
  76. 76. 76 • The action of this muscle bilaterally is critical in closing off the oropharynx from the nasopharynx during swallowing, as well as in determining the position of the vibrating line when developing a posterior palatal seal for a maxillary denture.
  77. 77. 77 MANDIBULAR DENTURE • The mandibular labial frenum contains a band of fibrous connective that helps attach the orbicularis oris muscle. • Therefore frenum is quite sensitive and active and the border has to be given a relief in this area.
  78. 78. 78 • The mentalis muscle elevates the skin of the chin and turns the lower lip outward. • Because its origin extends to a level higher than that of the fornix of the vestibule, the mentalis muscle renders the lower vestibule more shallow when it contracts.
  79. 79. 79 • The contraction of this muscle is capable of dislodging a mandibular denture, particularly when the residual ridge in the anterior region is the same height as the fornix of the vestibule. • Therefore, the mentalis muscle attachment to the alveolar ridge can dictate the level of extension of the labial flange of the mandibular denture below the crest of the ridge.
  80. 80. 80 • The incisivus labii superioris and inferioris muscles arise from the maxillary and mandibular alveolar processes, respectively, and then course laterally to blend with the orbicularis oris muscle. • Their actions on the vestibular fornix are similar to that of the mentalis muscles. • They are small muscles, and it is doubtful that their action alone would dislodge a denture. However, their presence beneath the mucous membrane might present problems associated with flange extension and denture retention.
  81. 81. 81 • The extent of the Buccal border is influenced by the Buccinator muscle, which extends from the modiolus antreriorly to the pterygomandibular raphae postrerioly and has its lower fibres attached to the buccal shelf and the external oblique ridge. • Denture covers completely the buccal shelf, though it rests on fibres of the buccinator because the fibers run parallel to the base and hence its pull cannot displace the denture.
  82. 82. 82 • The distobuccal border at the end of the buccal vestibule must converge rapidly to avoid displacement by the contracting masseter. • Distal extension is limited by the ramus of the mandible, by the buccinator and the superior constrictor of pharynx. • If denture extends onto the ramus – buccinator function is limited, also soreness develops
  83. 83. 83 • The denture should extend approximately one half to two thirds over the retromolar pad as extra pressure on the terminal portion may limit the functions of buccinator, superior constrictor of pharynx fibers and tendons of temporalis which are attached here.
  84. 84. 84 • Lingual borders should not extend below the mylohyoid ridge as it interferes with the function when it contracts and displaces the denturs causing soreness. • The flange must be made parallel to the mylohyoid muscle but posteriorly the border can go beyond the muscle attachment to the mandible because the mucolongual fold is not in this area.
  85. 85. 85 • The palatoglossus muscle and the mucous membrane covering it form the palatoglossal arch assist in closing the isthmus faucium during deglutition. • This action also exerts lateral pressure on the lingual extension of a mandibular denture
  86. 86. 86 • The action of the superior constrictor of pharynx exerts pressure against the distal extremity of the mandibular denture. • Overextension in this area is very painful to the patient, as the denture will perforate the tissue and create a painful lesion.
  87. 87. 87 • B. Muscles associated with surfaces of the denture and its importance • When muscles of facial expression are relaxed, the face lacks expression. The actions of these muscles often reflect the mood and emotional status of an individual.
  88. 88. 88 • The perioral muscles of facial expression generally do not insert into bone and need support from the teeth for proper function. If the muscles of facial expression are not properly supported, either by the natural teeth or by the artificial substitutes, none of the facial expressions appears normal.
  89. 89. 89 • The nasolabial sulcus, the philtrum, the commissures of the lips, and the mentolabial sulcus will not have their normal contours. • Incorrectly positioned teeth or an incorrectly contoured denture base can affect the normal tonicity of these muscles and can affect facial expressions adversely.
  90. 90. 90 • Lack of support allows sagging of the soft tissues of the face, while stretching inhibits the normal contraction of the facial muscles and results in changes in muscle tone.
  91. 91. 91 • In an area situated laterally and slightly above the corner of the mouth is a concentration of the many fibers of this muscle group. • This concentration is known as the muscular node, or modiolus and represents thearea where extrinsic perioral muscles decussate to join the intrinsic fibers of the orbicularis oris muscle.
  92. 92. 92 • Any muscle that inserts into the mucous membrane of the lips is influenced by the position of the teeth and the contours of the denture bases. • . Except in instances of excessive loss of residual ridge, the origins of most of the perioral facial muscles are removed from the denture-bearing area to the extent that their influence on the denture, except at the modiolus, is negligible.
  93. 93. 93 • The labial flanges of the maxillary denture frequently need to be reduced in thickness in the area of the modiolus. When the perioral muscles are stretched during mouth opening, the vestibular space between the muscles in the cheek and the slopes of the residual alveolar ridges is restricted.
  94. 94. 94 • Reduction of the bulk of the flange to accommodate this muscle action helps to prevent the denture from being dislodged when the mouth is opened. • At times, the labial flanges of the mandibular denture base is affected similarly and should be reduced in thickness.
  95. 95. 95 • The buccinator muscle provides support and mobility for the soft tissues of the cheek. It is a wide, muscle that arises from a horseshoeshaped line along the outer surfaces of the maxillary and mandibular alveolar processes in the area of the molar teeth. • In addition, the buccinator originates from the pterygornandibular raphe or ligament. The ligament serves as the junction between the buccinator muscle and the superior constrictor muscle of the
  96. 96. 96 • . A major function of this muscle is to keep the cheeks taut. If this were not so, when the jaws close, the cheeks would collapse and be caught between the teeth. • Another very important function of this muscle is its participation in deglutition.
  97. 97. 97 • It is important to know at this point that the proper external or the polished surface is obtained by the functional influence of buccinator, tongue and lips to provide adequate stability for the denture base. • The polished surface occupies a position of equilibrium among these group of muscles and is referred to as “Neutral zone”
  98. 98. 98 • Its importance is best explained by Fish “ if there is not much ridge, the impression and occlusal surfaces cannot resist lateral displacement. Therefore the only hope lies in the third or polished surface. It must be fashioned to fit the lips, cheeks, and tongue, both at rest and in function.
  99. 99. 99 •The oral cavity is surrounded by muscles. Jaw and soft tissue movements are the products of muscle activity. • If the muscles are strong and their activity well coordinated, they will help the patient use a correctly designed denture. • Conversely, poor denture design, weak muscles, and poor muscle coordination all detract from denture stability and retention.
  100. 100. 100 DIAGNOSIS • Muscle Tonus • The tone of the facial tissue is critical to several steps of denture construction. • Tissue tone that is either too strong or too weak is unfavorable. • As a result, completing clinical procedures may require more than the usual amount of time.
  101. 101. 101 • If the muscles are too tense, cheek and lip manipulations will be difficult; if too slack, the lips and cheeks may be displaced easily by impression materials. • Patients may take more time than usual to learn to use the dentures. • Optimum functioning of the postural and facial expression muscles requires correct support from the natural teeth and ridges or from correctly designed and built prostheses.
  102. 102. 102 • Neuromuscular Coordination • Good muscular control and coordination are essential to the effective use of complete dentures. They also are helpful in denture construction. • For example, when tongue movements are used for border molding the lingual flanges of a mandibular impression, the timing, direction, and amount of movement are critical to the success of the molding. • Similarly, coordination of jaw movements is important during denture construction and use.
  103. 103. 103 • On the whole as a part of physiologic changes of aging muscle activity lacks coordination and the muscle loose tonus. • The cheeks sag, the mandible when it rest appears to drop lightly more in a protruded position. The conduction of nerve impulses also diminishes slightly.
  104. 104. 104 • A patient lacking ability to move the mandible to the right place at the right time reveals the potential for problems in making jaw relation records before they are attempted. • To make an observation of muscular control, the dentist can ask the patient to open the mouth about halfway and move the lower jaw from left to right, then to put the tongue into the right cheek and into the left cheek, to stick it out and to put it up and back inside the mouth.
  105. 105. 105 • The ability, or lack of ability, to do these movements on demand will be apparent. The treatment schedule can be modified accordingly. • If the dentist feels the problems are significant, the patient can be asked to practice jaw movements at home.
  106. 106. 106 • Emphasis can be placed on deliberate border movements ending in centric relation. • Practicing in front of a mirror will allow the patient to visually coordinate the movements.
  107. 107. 107 • Patients with one or more of the following symptoms usually are considered to have a temporomandibular disorder (TMD). • The symptoms include (1) pain and tenderness in the muscles of mastication and the TMJs, (2) sounds during condylar movements, and (3) limitations of mandibular movement. • Quite logically, the TMJs should be healthy before new dentures are made.
  108. 108. 108 • Unhealthy TMJs complicate the registration of jaw relation records. • If it is to be functional position, centric relation depends on the structural and functional harmony of osseous structures, the intra articular tissue, and the capsular ligaments.
  109. 109. 109 • . If these specifications cannot be fulfilled, the patient will not be able to position the mandible in correct centric relation or, for that matter, provide the dentist with a repeatable one. • Thus the importance of the routine evaluation of a patient’s temporomandibular function as an integral part of complete denture treatment.
  110. 110. 110 • Tongue • Apart from the example of tongue movement coordination during impression making, tongue position and coordination are significant in complete denture functioning. • A retruded tongue position deprives the patient of a border seal of the lingual flange in the sublingual crescent and also may produce dislodging forces on the distal regions of the lingual flanges.
  111. 111. 111 • Normally, the tongue should be expected to rest in a relaxed position on the lingual flanges, which, if properly contoured, will allow the tongue to help retain the denture. • A tongue thrust tends to dislodge a lower complete denture by raising the floor of the month and, in so doing, lifting the lingual flanges and by exerting pressure on the anterior teeth.
  112. 112. 112 • Cheeks and Lips • The external form of the cheeks and lips is dependent on their internal structure and their underlying support. This support may be natural teeth and ridges or denture teeth and bases. • The muscles in the cheeks and lips have a critical function in successful use of dentures.
  113. 113. 113 • The denture flanges must be properly shaped to aid in maintaining the dentures in place without conscious effort by the patient. • This involves the development of the correct arch from and tooth positions, as well as the shape of the polished surfaces and the thickness of the denture borders. • The amount of denture space must be considered carefully if fixed implant- supported prosthesis is planned because it does not usually provide a tissue-supporting base.
  114. 114. 114 • Patients with very thick cheeks may present technical problems during some clinical steps. • Thick cheeks often do not allow easy manipulation for border molding of impression materials.
  115. 115. 115 • Various characteristics of the lips not only are significant for denture retention but also are prominent in considerations of esthetics and phonetics. • The tissue around the mouth has wrinkles and the rest of the face does not, lack of lip support can be suspected and significant improvement can be expected.
  116. 116. 116 • Patients with thin lips present special problems. • Any slight change in the labio lingual tooth position makes and immediate change in the lip contour. • The evaluation of anterior tooth position is complicated by short or incompetent lips. • Long lips tend to hide the teeth, Short teeth may expose all the upper anterior teeth.
  117. 117. 117 IMPRESSION MAKING • The insertion of the muscle of facial expression distal to corners of the mouth at the modiolus and the position and action of the orbicularis oris have a definite influence in impression making. • These muscles can be relaxed with the jaws open, and this relaxation is desirable when introducing the impression tray or impression material.
  118. 118. 118 • The patient should be trained to open the jaws and relax the lips and cheeks to avoid interference from a pair of tense lips. • When the lips are tense, a stretching action often results in lacerations at the corners of the mouth and/or distorted impression material.
  119. 119. 119 • The buccinator muscle joins the superior constrictor at the pterygomandibular raphe distal to the retromolar pad area. • It is buccal to this area that the action of the masseter muscle pushes the buccinator muscle toward the retromolar pad.
  120. 120. 120 • The impression will be reflected superiorly and medially forming a groove called the masseter groove • If the distobuccal flange of the mandibular denture base is not contoured to allow freedom for this action, the denture will be displaced.
  121. 121. 121 JAW RELATION RECORDS • The muscles that move that mandible are under voluntary control. • These muscles can be directed to move the mandible in various directions. • At the first consultation appointment, patients can be given a training exercise that will prepare them for the time of jaw relation records.
  122. 122. 122 • This exercise is accomplished at home, in a relaxed atmosphere, three times daily facing a large mirror. • The mandible is relaxed and with the jaws separated slightly more than rest position, not a wide separation, the chin is brought forward (protruded) until it stops. • From this position, the jaw is carried backward (retruded) until the condyles are felt to stop in the fossae.
  123. 123. 123 • This exercise is continued during the construction phase, but make certain that patients are fully aware of when the condyles stop in the fossae. • At the time of recording the jaw relations, patients are first rehearsed, and then with the recording records in place, are directed to protrude, retrude until they feel the condyles stop, and then close on the back teeth (recording media) until the anterior teeth touch.
  124. 124. 124 • With exercise, muscle can alter its shape and size. • This property of muscle provides a method of improving the shape and size of a tongue that is abnormal in size, position, and/or function.
  125. 125. 125 • If a muscle contracts too slowly or too rapidly, the efficiency to do work is decreased. • Maximum efficiency is developed when the velocity of contraction is about 30% of maximum. • If a muscle is in a highly contracted state, it may contract more strongly than normal.
  126. 126. 126 • When an agonist muscle contacts under physiologic conditions, the antagonist muscle relaxes. • Under abnormal conditions, however, the antagonist muscle can become activated, and the result will be change in the agonist muscle.
  127. 127. 127 • If a muscle is already shortened before it is stimulated to contract, the force of contraction is less than normal. • If it is stretched beyond the optimum length before contraction, the force will also be less normal. • These and other physiologic muscle interactions are important in recording the jaw relations and also in educating patients in denture use.
  128. 128. 128 • When a load is placed on a muscle, the muscle elongates, and within limits the greater the load the greater the stretch. • When the load is released, the muscle shortens almost to its original length. If the load is excessive the muscle relaxes reflexly to keep from injuring the muscle. • The property of extensibility should be considered when jaw relations are recorded under manual guidance.
  129. 129. 129 • A muscle contraction is so well graded by the nerves system that almost many degree of contraction can be called forth from a muscle. • The phenomenon of muscle is one of the reason that a reaction of the denture supporting tissues in one individual varies from that of another because the degree of muscle contraction in a given situation can vary from person to person.
  130. 130. 130 • Another interesting property of muscle is its power to undergo physical contracture. • For e.g., If a patient receives complete upper and lower denture with an excessive interocclusal distance, the fibers of the elevator muscles actually shorten and reestablish new muscle lengths approximately equal to the maximum length of the lever system itself, thus reestablishing to produce optimum force of contraction.
  131. 131. 131 • . In contrast, over stretching the muscle makes its normal contraction impossible and will cause a reduction in a force of contraction. • Muscle do not act alone. When one muscle contracts in synergist also contracts but its antagonist must relax. When one muscle is short its antagonist is stretched. • This type of interaction among muscle agonist, synergist and antagonist must be a coordinated effort to ensure efficient physiology activity. When this is lost muscle dysfunction results.
  132. 132. 132 • When a muscle are addressed a certain amount of tone usually remains – Muscle Tone. • Blocking of muscle spindle impulses causes lots of muscle tone and the muscle becomes almost flaccid. • Prolonged and strong contraction of a muscle leads to fatigue
  133. 133. 133 • For fatigue muscle contraction becomes weaker and weaker. • If an individuals mandible is protruded and allowed to remain until fatigue occurs the antagonist action of the retractor and elevator muscle will be weakened. • It would be possible to retrude and elevate the mandible to the centric position against very little or no opposing action from the lateral pterygoid.
  134. 134. 134 • When the artificial teeth are placed in positions that do not support the muscles of facial expression in the manner of the natural teeth or if for other reasons the muscles lose tone, the facial expressions change. • Another problem is cheek biting when the denture teeth are placed in the positions formerly occupied by the natural posterior teeth. With patient training and a return of muscle tone, the problem is minimized.
  135. 135. 135 CONCLUSION • A good sound prosthodontic service cannot be accomplished without accurate impressions and records which in turn depend on neuromuscular co-ordination.
  136. 136. 136 CONCLUSION • Muscle function in general affects: • Impression • Occlusal plane • Arch arrangement • Jaw registration • Esthetics • Polished surface contour • Neuromuscular skills
  137. 137. 137 Thank you For more details please visit