muscles of mastication, dental applications

muscles of mastication, dental applications

1. MUSCLES OF MASTICATION 1 Presented by: Sohail 1 st year PGT “ Nothing is more fundamental to treating patients than knowing the anatomy” GOOD MORNING

2. CONTENTS Introduction Development / Embryology Muscles of mastication (in detail about each) Movements of mandible at TMJ Physiology of masticatory muscles Mastication – Role of masticatory muscles - Reflexes Investigations Disorders of muscles 2

3. INTRODUCTION MUSCULUS – “little mouse” Is a soft tissue found in most animals Muscle cells -protein filaments of actin & myosin -contraction – changes length & shape of the cell 3

4. DEVELOPMENT INTRODUCTION Day 17 – 3 germ layers Day 19 – mesodermal plate cleaves – diff of somite plate - somites Day 20-21 – 42-44 pairs of somites Myocoele , Sclerotome , Dermatome, Myotome SKELETAL MUSCLES MUSCLES OF MASTICATION 4

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7. 7 By 10th week - muscle masses become well organized & 5th cranial nerve branches are incorporated. By 7th week - cells migrate into areas where they will differentiate into muscles of mastication. During 5th & 6th weeks - primitive muscle cells from mesoderm of mandibular arch begin to differentiate. 4 th week- the oral pit is surrounded by several masses of tissue. Pharyngeal arches are also evident below the pit & on the sides of the neck

8. Skeletal muscle – structure & physiology Cylindrical in shape Average length – 3cms Diameter – 10-100um 8

9. Cell membrane – plasma membrane/ sarcolemma Sarcoplasm 9 Nuclei Myofibril Golgi apparatus Mitochondria Sarcoplasmic reticulum Ribosomes Glycogen droplets

10. MYOFIBRIL Fine parallel filaments present in the sarcoplam Run through the entire length MICROSCOPIC STRUCTURE 10

11. MUSCLES Of MASTICATION 11

12. Rhythmic movement of the jaw is a series of cyclical movements Masticatory system includes Temporomandibular joint Mandible Teeth & Muscles of mastication. 12

13. Participate in all jaw movements involved in mastication, deglutition and other non masticatory movements Voluntary muscles Originate from the skull, span the TMJ, and insert into the mandible. On contraction, they act to move the mandible. 13

14. TYPES 14 Dr.Frank Gaillard et al

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16. MASSETER 16 The width of the muscle at its origin ranges from 27 to 39mm in brachycephalic skulls, its anterior border length 51 – 70mm, and its posterior length 40 – 62mm. Its physiologic cross section is 2.75 cm square About 29.9% of the total masticatory muscle mass. SUPERFICIAL LAYER MIDDLE LAYER DEEP LAYER

17. PAROTID FASCIA Strong layer of fascia Derived from deep cervical fascia Covers the masseter and firmly connected to it Attached – lower border of zygomatic arch Invests the parotid gland 17

18. ZYGOMATIC ARCH ZYGOMATIC BONE 18

19. 19 ORIGIN – Maxillary process of zygomatic bone Ant 2/3rds of inferior border of zygomatic arch INSERTION - Angle Lower post half of lateral surface of ramus ORIGIN AND INSERTION Superficial layer

20. 20 ORIGIN AND INSERTION Middle layer ORIGIN - Medial aspect of ant 2/3rds of zygomatic arch Lower border of post 3 rd of this arch INSERTION - Central part of ramus of mandible

21. 21 ORIGIN AND INSERTION Deep layer ORIGIN - Deep surface of zygomatic arch INSERTION – Upper part of Mandibular ramus Coronoid process

22. RELATIONS Superficial : Platysma , Risorius , Zygomaticus major, Parotid gland, Parotid duct, Branches of the facial nerve Deep Surface : Overlies the insertion of Temporalis &Ramus of the mandible. 22

23. VASCULAR SUPPLY AND INNERVATION 23

24. ACTIONS 24 Elevates the mandible Side to side movement Protraction Retraction

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26. CLINICAL IMPORTANCE 26

27. Massetric hypertrophy Submassetric space infections 27

28. Variations :- Deep masseter fibers may be fused with fibers of the temporalis muscle A connection with the buccinator muscle was observed by Haller (1978) Rare anomaly- phocomelia , the muscle is absent. Some fibres may circle around the mandibular angle and join the medial pterygoid muscle – forming a powerful sling 28

29. TEMPORALIS 29 Accounts for 37.5 % of the total masticatory muscle mass with a crosssectional diameter of 4.1 cm 2 - Mc Donald & Andrews 1953 Zenker 1955 ; Schumacher & Shinker 1960

30. TEMPORAL FASCIA 30

31. 31 ORIGIN Whole part of temporal fossa Deep surface of temporal fascia

32. 32 INSERTION i ) Medial surface, Apex, Ant & post borders Coronoid process ii) Ant border of ramus of mandible upto the last molar tooth

33. Relations Superficial – Skin, temporal fascia, superficial temporal vessels, Auriculotemporal nerve, zygomatic arch , masseter, Anterior border – separated from zygomatic bone by a mass of fat Posterior border – Above – temporal fossa Below – major components of Infra temporal fossa 33

34. VASCULAR SUPPLY 34

35. NERVE SUPPLY 35

36. ACTIONS 36 Elevates the mandible Side to side grinding movements Posterior fibres – retract the protruded mandible

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38. CLINICAL IMPORTANCE When lower dentures are fitted, they should not extend into the retromolar fossa to prevent trauma of the mucosa due to the contraction of the temporalis muscle. 38 A plane exists between the temporal fascia which is attached to the superior surface of zygomatic arch & the muscle beneath the arch… Elevator is introduced into this plane beneath a fractured zygomatic arch/bone in order to reduce the fracture  Gillies approach

39. Variations Variations in the thickness and surface areas of temporalis muscle are relatively common. Occasionally the muscle is placed far superiorly and closely approaches the sagittal suture. The most anterior tendon insertion may extend very close to the third molar Henke (1884) applied the term “ lesser temporalis ” to a bundle that arises from the articular disc of the TMJ lateral to the lateral pterygoid muscle and fuses with the posterior border of the temporalis in the deep layer of the masseter muscle. 39

40. MEDIAL PTERYGOID 40

41. ORIGIN AND INSERTION 41

42. Relations Upper part of muscle is separated from the lateral pterygoid muscle by a) lateral pterygoid plate b) lingual nerve c) inferior alveolar nerve Inferiorly the muscle is separated from ramus of mandible by nerves,the maxillary artery and sphenomandibular ligament. Medial surface – tensor palatine & superior constrictor Lateral surface - Ramus 42

43. Vascular and nerve supply 43

44. 44 Actions 1. Elevation : (bilateral) 2.Protrusion : (bilateral) 3. Contralateral excursion : (unilateral)

45. CLINICAL IMPORTANCE IANB 45 Intraorally ,to palpate the medial pterygoid muscle slide the index finger a little posterior to the insertion site of inferior alveolar nerve block, to where the muscle is felt & press laterally.

46. LATERAL PTERYGOID 46

47. ORIGIN AND INSERTION 47

48. Relations SUPERFICIAL Ramus of the mandible Maxillary artery Tendon of temporalis and masseter DEEP SURFACE Upper part of the medial pterygoid Sphenomandibular ligament Middle meningeal artery Mandibular nerve UPPER BORDER Temporal and massetric branches of the mandibular nerve LOWER BORDER Lingual and inferior alveolar nerve 48

49. BLOOD SUPPLY 49

50. Nerve supply 50 1 for each head – anterior trunk of mandibular nerve A) Upper head ,lateral part of lower head – buccal nerve B ) Medial part of lower head – branch from the anterior trunk

51. ACTIONS : Actions by the inferior Head Protrusion (bilateral): The inferior lateral pterygoids are the 2 prime protractors of the mandible. Depression (bilateral): Contraction of both the lateral pterygoids not only pull the condyles forward but also along with the suprahyoid & the infrahyoid muscles help in the depression of the mandible. Contralateral Excursion (unilateral): The insertion of the lateral pterygoids is lateral to its origin & thus the lateral pterygoid muscle acting singly moves the mandible to the opposite side. 51

52. ACTIONS BY THE Superior Head : The superior lateral pterygoids are inactive during opening. They are active during the mandibular elevation or closing along with Temporalis , Masseter & the Medial pterygoid muscles. The Superior head are particularly active when the teeth ,upon closure, encounter resistance such as a bolus of food. Closure on resistance & the Superior lateral pterygoid play an active role in this. 52

53. 53 Slide the fifth finger along the lateral side of the maxillary alveolar ridge to the most posterior region of the vestibule ( location for PSA nerve block) . Palpate by pressing in a superior, medial, & posterior direction.

54. CLINICAL IMPORTANCE TMJ joint dysfunction – PTERYGOID SIGN 54

55. Together Medial and Lateral Pterygoid muscle Move the mandible to left side Left Lateral Pterygoid Right Medial Pterygoid Move the mandible to right side Right Lateral Pterygoid Left Medial Pterygoid 55

56. Sphenomandibularis-5 th muscle Recently discovered. Previously thought to be a part of temporalis . Origin - From infratemporal surface of greater wing of sphenoid bone. Insertion - Mandible. Blood supply- Maxillary artery, from vessels of medial pterygoid . Nerve supply- Not yet determined. 56

57. ACCESSORY MUSCLES of mastication 57

58. DIGASTRIC Origin – anterior belly from digastric fossa of mandible , posterior belly from mastoid notch of temporal bone. Insertion – intermediate tendon Innervation - anterior belly by mylohyoid nerve , posterior belly by facial nerve. Action – Depresses the mandible , elevates the hyoid bone 58

59. 59 Forms anatomically and functionally floor of the oral cavity. MYLOHYOID The right and left muscles are united in the midline between the mandible and the hyoid bone by a tendinous strip-the mylohyoid raphae .

60. 60 ORIGIN Mylohyoid line on the inner surface of the mandible. Anterior fibers originate from lower border of the mandible. Its most posterior fibers take their origin from the alveolus of the third molar. INSERTION The posterior fibers run steeply downwards medially and forward n gets attached to body of the hyoid bone. Majority of fibers however join those of the contralateral muscles in the mylohyoid raphae .

61. 61 NERVE & VASCULAR SUPPLY: Mylohyoid nerve of the mandibular nerve. Submental artery, Facial artery FUNCTION: Posterior fibers run vertically from the mandible to the hyoid; if mandible is fixed, they lift the hyoid bone, and if the hyoid is in place they depress the mandible. Anterior fibers elevate the floor of the oral cavity there by acts as elevator of the tongue.

62. 62 ORIGIN It arises above the anterior end of the mylohyoid line from the inner surface of mandible including inferior mental spines by a short and strong tendon. INSERTION attached to the upper half of the hyoid body. GENIOHYOID

63. 63 Side to side movements – temporalis (same side), pterygoids ( opp side), masseter TMJ MOVEMENTS

64. Summary of the anatomy 64

65. 65 PHYSIOLOGY OF MASTICATORY MUSCLES “You cannot successfully treat dysfunction unless you understand function”

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67. MASTICATION Human masticatory motor system – remarkable machine Chewing, swallowing, speech Extreme force High force activities Extremely precise movements (speech) 67

68. CONTROL OF MASTICATION Voluntary Reflex Cyclical During closing movement – jaw closing muscles on both sides are activated at the same time Opening – only jaw openers are active Chewing stroke – activity of left masseter is less than right masseter because most of the work is being done by the muscles on the right hand side Highly coordinated activity of masticatory, tongue & cheek muscles 68

69. Mechanisms that modulate muscle activity during chewing 69

70. Forces of Mastication Males – 53-65kg Females – 36-45 kg Increases with age upto adolescence 70

71. Role of individual muscles in chewing Major jaw closing muscles – masseter & temporalis Direction in which the fibres run – indicates the direction in which they apply force Temporalis – most post fibres- pull posteriorly - most ant fibres- pull upwards & anteriorly Lateral pterygoid – imp role in several phases of chewing cycle ( pulls the mandible forward during jaw opening, controls the rate at which the condyle should return to its fossa during closing) Jaw opening muscles – not normally required to exert much force during chewing In jaw opening – contraction of digastric 71

72. INVESTIGATIONS Specialised technique that is used to measure the activity of individual muscles 72 ELECTRO MYOGRAPHY

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74. ETIOLOGY OF FUNCTIONAL DISTURBANCES IN THE MASTICATORY SYSTEM 74 “The clinician who looks only at occlusion is missing as the clinician who never looks at occlusion”

75. Events interrupting normal muscle function Local factors– Restoration in supraocclusion /improperly occluding crown Fracture of a tooth Secondary to Trauma involving local tissues (post injection response following L.A, wide opening of mouth{long dental procedure, yawning}, unaccustomed use{bruxism, biting on hard object, gum chewing}) Deep pain input Systemic factors- Emotional stress Acute illness or viral infections Constitutional patient factors( immunologic resistance)- affected by age, gender, diet 75

76. 76 Activities of masticatory system Muscle hyperactivity Parafunctional activities + general increase in level of muscle tone

77. common finding rarely associated with symptoms Self limiting phenomenon Not related to increased risk 77 BRUXISM IN CHILDREN

78. SIGNS AND SYMPTOMS OF DISODERS OF MUSCLES 78 “You can never diagnose something you have never heard about”

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80. PAIN Most common complaint Central mechanisms Slight tenderness – extreme discomfort MYALGIA Muscle fatigue, tiredness Origin – certain allogenic substances Muscle pain Severity of muscle pain ∞ functional activity of muscle Cyclic muscle spasm Headache 80

81. DYSFUNCTION Common clinical symptom Decrease in range of mandibular movement clinically seen as inability to open mouth widely Acute malocclusion 81

82. 82 Masticatory muscle disorders

83. 83 Clinical masticatory muscle pain model

84. Protective co-contraction (Muscle splinting) First response of muscles to any event CNS response to injury or threat of injury. Co - contraction of antagonist muscles (during opening of mouth increased activity of elevator muscles and vice versa) Normal protective or guarding mechanism. Not a pathologic condition – prolonged – may lead to muscle symptoms 84

85. Etiology - Any change in sensory input from associated structures {High restoration/crown ,deep pain input or emotional stress} Clinically - Muscle weakness following an event No pain occurs when muscle at rest - Use of muscle increases pain. Limited mouth opening but when slowly opened-full opening. Key factor- immediately follows an event(history) If continues ( hrs -days) -muscle can become compromised  local muscle problem 85

86. Treatment – DEFINITIVE TREATMENT Directed towards the reason for co-contraction Trauma – no definitive treatment Altering the restoration, occlusal condition SUPPORTIVE TREATMENT When cause is tissue injury Restrict use of mandible Soft diet NSAIDS 86

87. Local muscle soreness (Non inflammatory myalgia) 1 st response to prolonged co-contraction. Co-contraction- CNS induced muscle response Soreness- changes in local environment of muscle tissue ( release of bradykinin , substance P) Excessive use- ‘delayed onset muscle soreness’ or ‘post exercise muscle soreness’ Co-contraction-cyclic event. Clinically – muscle –tender on palpation, increased pain on function, structural dysfunction, limited mouth opening, acute muscle weakness 87

88. DEFINITIVE TREATMENT Eliminate ongoing altered sensory input Eliminate source of deep pain Restrict mandibular use Reduce non functional tooth movements Decrease emotional stress SUPPORTIVE TREATMENT Mild analgesic –every 4-6hrs for 5-7 days Passive muscle stretching, gentle massage 88

89. Central nervous system effect on muscle pain 1) Secondary to Ongoing deep pain input . 2)Arise from central influences such as upregulation of the autonomic nervous system { Emotional stress } 3)Changes in descending inhibitory system. 89 Clinician should appreciate that muscle pain now has a central origin

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91. Myospasm (Tonic Contraction Myalgia) Myospam of masticatory muscles –not common. Etiology- local muscle conditions (muscle fatigue, changes in electrolyte balances) ,deep pain input Clinically - Structural dysfunction( jaw positional changes  acute malocclusions ), firm muscles on palpation Short lived (similar to leg cramps) Repeated –DYSTONIA Mouth forced open (opening dystonia), or closed(closing dystonia) or even off to 1 side 91

92. DEFINITIVE TREATMENT Reducing the spasm Reducing the pain Passively stretching the involved muscle Manual massage Injection – 2% lignocaine without vasoconstrictor Elimination of the factor Secondary to fatigue –rest SUPPORTIVE TREATMENT Physical therapy Deep massage& passive stretching Muscle conditioning exercises Relaxation techniques 92

93. Myofacial pain (Trigger point Myalgia) 1 st described – Travel & Rinzler -1952 Arises from hypersensitive bands of muscle tissue – TRIGGER POINTS Felt as taut bands when palpated  elicit pain Source of constant deep pain central excitatory effects  referred pain reported as headache pain Etiology - trauma,hypovitaminosis , fatigue,viral infections, emotional stress Clinically – trigger points, no local muscle sensitivity, mostly related to central effects (referred pain) 93 For treatment to be effective, it must be directed towards the source of pain

94. Diagnosis – trigger points (active/latent) Activated by various factors (increased use of muscle, strain on muscle, emotional stress, upper resp. tract infections )  headache returns Other central excitatory effects – secondary hyperalgesia , co-contraction, local muscle soreness 94 Clinical symptoms are associated with the central excitatory effects created by trigger points and not the trigger points themselves

95. DEFINITIVE TREATMENT Eliminate source of deep pain Reduce local & systemic factors Proper sleep (TCA) Elimination of trigger points (spray & stretch, pressure & massage, injection & stretch) SUPPORTIVE TREATMENT Physical therapy Manual techniques(soft tissue immobilization, muscle exercises) Muscle relaxants, analgesics 95

96. Characteristic sign of MPDS------LASKIN'S 4 CARDINAL SIGNS Unilateral pain Muscle tenderness Clicking and popping noise in TMJ Limitation of jaw function or deviation of jaw Laskin also emphasized that other than the above positive signs,,the following signs must be absent There should be absence of clinical,radiographic or biochemical evidence of organic changes in TMJ There should be no tenderness on palpation via external auditory meatus 96

97. Perpetuating factors for Chronic Myalgias LOCAL Protracted cause Recurrent cause Therapeutic mismanagement SYSTEMIC Continued emotional stress Downregulation of descending inhibitory system Sleep disturbances Learned behavior Secondary gain Depression 97

98. 5) Centrally mediated myalgia (Chronic myositis) Originating from CNS effects felt peripherally in the muscle tissues Symptoms similar to inflammatory condition - MYOSITIS Neurogenic inflammation Etiology – Prolonged input of muscle pain + local soreness, central mechanisms Clinically - Continuity of muscle pain ,Constant aching myogenous pain , Pain present during rest and increases with function, muscles are tender to palpate, structural dysfunction. 98

99. DEFINITIVE TREATMENT Recognize condition correctly Restrict mandibular movement Avoid exercise /injections Disengage the teeth NSAIDS SUPPORTIVE TREATMENT Careful physiotherapy Moist heat/cold packs Gentle stretching 99

100. Chronic systemic myalgic disorders (Fibromyalgia) Global musculoskeletal pain disorder Often confused with acute masticatory muscle disorder Tenderness - 11 or more of 18 specific tender point sites throughout the body. Etiology – central mechanism 100

101. DEFINITIVE TREATMENT When other masticatory muscle disorders- present –therapy Perpetuating factors – properly addressed NSAIDS Sleep Depression – managed SUPPORTIVE TREATMENT Physical therapy Manual techniques(moist heat, gentle massage, passive stretching, relaxation) Mild, well controlled exercise 101

102. MUSCULAR DYSTROPHIES Rare , inherited muscle diseases Muscle fibres are abnormal due to a genetic defect Progressively weaker Replaced by fat and CT Deficiency / malfunction of the muscle protein ( dystrophin / dystropin associated proteins) 102

103. Duchenne’s muscular dystrophy Most common form of muscular dystrophy in children Young boys Muscles of pelvis & limbs – 1 st affected Masticatory system – involved later 103

104. Myotonic dystrophy Muscular dystrophy – affects adults 5 in 100,00 104

105. MYOSITIS OSSIFICANS TRAUMATICA Masseter muscle – occasionally affected Uncommon sequel to TRAUMA (surgery) / INFLAMMATION OF MUSCLES Calcified lesions – X rays/ other scans 105

106. GUILLAIN – BARRE’ SYNDROME Generalised neuropathy Inflammation of peripheral nerves Severe weakness & numbness 2 in 100,000….increases with age Triggered by – stress, viral infection , surgery Most people – recover fully 20% - residual sensory / motor defects 106

107. BRUXISM Parafunctional activity Clenching/grinding of teeth 1 of the structures involved- Muscles of mastication Fatigue to muscles of mastication Not giving them time to relax Tender 107

108. Trismus /Lock jaw Inability to open mouth/reduced opening of jaws Causes- inflammation of muscles of mastication, needle prick to medial pterygoid Management- Analgesics, muscle relaxants , antibiotics,physiotherapy 108

109. Mandibular fractures & muscles of mastication Main role in unfavourable fractures 3 muscles exhibit a strong upward pull on the posterior mandible and act to close the mouth Displace posterior segment superiorly Fracture of Condyle – Anteromedial – Lateral Pterygoid 109

110. Space infections Masticatory spaces: Pterygomandibular Submasseteric Superficial temporal Deep temporal 110 Formed by splitting of investing fascia into superficial & deep layers Superficial layer – lies along lateral surfaces of masseter & lower half of temporalis muscle Deep layer – passes along medial surface of pterygoid muscles

111. Submassetric space 3 layers of masseter fused anteriorly, separated posteriorly Space b/n middle & deep heads Insertion – loose intermediate tendon Easy accumulation of pus Submassetric space abscess – pus b/n masseter& ramus Lower 3 rd molars Swelling - 111

112. Pterygomandibular space Involvement – infected 3 rd molars, infection due to contaminated needle used for IANB, infection from maxi 3 rd molar after PSA Established infections- no much swelling on face Severe degrees of limitation of mouth opening Tenderness – soft tissues medial to ant.border of ramus Dysphagia 112

113. Temporal space Secondary to initial involvement of pterygopalatine & infratemporal space (roots of upper molars) Related to temporalis muscle Superficial – b/n fascia & muscle Deep – deep to muscle Pain, trismus , swelling over temporal region 113

114. Points to remember…. Submassetric space abscess – pus b/n masseter& ramus infection from Lower 3 rd molars. Pterygomandibular space - Infected 3 rd molars, infection due to contaminated needle used for IANB 114

115. REFERENCES Gray’s Anatomy – the anatomical basis of clinical practice, 40 th edition, Churchill and Livingstone James L Hiatt, Lesie P.Gartner - Textbook of head and neck anatomy - 3 rd edition - Wolters company, B.D. Chaurasia’s , Human anatomy, vol 3 - 4 th edition - CBS publishers – 2004 T.W. Saddler - Langman’s medical embryology - 9 th edition - Wolters Kluver publishers Management of temporomandibular disorders and occlusion- Jeffrey P. Okeson - 6 th edition Clinical oral physiology- Timothy S. Miles, Peter Svensson 115