Muscles of mastication

a seminar on MUSCLES OF MASTICATION

1. MUSCLES OF MASTICATION PRESENTED BY:- Dr. ABHILASHA MODERATED BY:- Dr. SHIVAPRASAD DEPARTMENT OF PERIODONTICS M.R.AMBEDKAR DENTAL COLLEGE, BANGALORE

2. INTRODUCTION TYPES OF MUSCLES PHYSICAL PROPERTIES OF MUSCLES EMBRYOLOGY OF MASTICATORY MUSCLES CLASSIFICATION MASTICATORY MUSCLES IN DETAIL CHEWING AND CHEWING CYCLE REFLEXES IN MASTICATORY SYSTEM DISORDERS OF MASTICATORY MUSCLES PERIODONTICS CONSIDERATIONS CONCLUSION REFRENCES CONTENTS

3. INTRODUCTION “MUSCLE” is derived from LATIN word ‘musculus’ which means little mouse. Muscle refers to a group of muscle fibers bound together by connective tissue. Generate force and movement used in the regulation of internal environment. Mastication is the rhythmic opposition and separation of jaws with the involvement of teeth, lips, cheeks, tongue for chewing of food in order to prepare it for swallowing and digestion.

4. Main purpose of mastication is to reduce the size of food particles that is convenient for swallowing (bolus formation) with the help of saliva. The muscles which are required for mastication are known as muscles of mastication. These are group of muscles associated with the movement of mandible.

5. TYPES OF MUSCLES Muscles of the body can be broadly classified based on SITUATION as:- A) Skeletal muscle B) Smooth muscle C) Cardiac muscle Depending upon STRIATIONS:- A) Striated B) Non striated Depending upon CONTROL:- A) Voluntary B) Involuntary

6. SKELETAL MUSCLE SMOOTH MUSCLE CARDIAC MUSCLE Characteristic of fibers -Striated -Tubular -Multinucleated fibers Non striated Spindle shaped Uni -nucleated fibers Striated Branched Uni -nucleated fibers Control -Voluntary - Involuntary Involuntary Occurence -Attached to skeletal MOST MUSCLES OF OROFACIAL REGION - Walls of internal organs - Walls of heart

7. A chart showing features and differences between skeletal, cardiac and smooth muscle

8. PHYSICAL PROPERTIES OF MUSCLES

9. EXCITABILITY -Excitability is defined as the reaction or response of a tissue to irritation or stimulation. It is a physicochemical change. CONTRACTILITY -Contraction is defined as the internal events of muscle with change in either length or tension of the muscle fibers. EXTENSIBILITY -Muscles can be stretched to their normal resting length and beyond to a limited degree. ELASTICITY -Ability of muscle to recoil to original resting length after stretched.

10. EMBRYOLOGY Myogenesis is the formation of muscle tissue during embryonic development from stem cells in the mesoderm ( myoblast ). Muscles of mastication are derived from first or MANDIBULAR ARCH. DAY 17 - 3 germ layers DAY 19 - mesodermal plates cleave -> somitomeres -> somites DAY 20-21 - 42-44 pairs of somites Somites give rise to the myotome (muscle tissue), sclerotome (cartilage and bone), and dermatome (dermis of the skin)

11. LANGMAN’S MEDICAL EMBRYOLOGY (17 TH EDITION; pg 148)

12. LANGMAN’S MEDICAL EMBRYOLOGY (17 TH EDITION; pg 146)

13. 4 th week - The oral pit is surrounded by several masses of tissues. Pharyngeal arches are also evident below the pit and the sides of arches. 5 th – 6 th week - Primitive cells form and differentiate. - Get oriented to its site of origin and insertion. 7 th week - Mandibular arch mass enlarges. Cell migrate to the areas of formation of 4 major muscles of mastication. Cell differentiation occurs before the formation of facial arch. 10 th week - Muscle mass well organized - Nerve masses get incorporated

14. CLASSIFICATION

15. FUNCTIONAL CLASSIFICATION

16. PRIMARY MUSCLES

17. TEMPORALIS Fan shaped muscle Origin & Insertion B.D CHAURASIA’S HUMAN ANATOMY 6 TH edition ;pg 117

18. TEMPORALIS Vascular supply Nerve supply DEEP TEMPORAL ARTERY DEEP TEMPORAL NERVES

19. 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 infratemporal fossa

20. ACTIONS The action of temporalis muscles can be divided into 3 distinct areas according to the fibers direction. Elevation of the mandible- anterior fibers Elevation and retraction of mandible- middle fibers Retraction of mandible- posterior fibers

21. PALPATION An accepted method of determining muscle tenderness or pain is to use the fingers tips of the middle & index finger to palpate specific anatomic sites. It has been proposed that 2 lb of digital pressure on extraoral muscles & 1lb of pressure on intraoral areas held for 3 to 5 seconds are appropriate. Extraorally - Palpation of anterior, posterior and middle region of temporalis. Intraorally - the finger is moved up the anterior border of the ramus until the coronoid process and attachment of tendon of temporalis is felt

22. CLINICAL IMPORTANCE Sudden contraction of temporalis muscle will result in coronoid fracture , which is rare. The temporalis muscle flap may be used for reconstruction of defects of the oral cavity (floor of mouth, tongue, buccal, retromolar trigone , palate), oropharynx , nasopharynx , orbit, maxilla and facial soft tissues Post mortem examination of head- Access to the brain is obtained by stripping back the skin over the poll and removing the temporal muscles .(Diagnostics Techniques in Equine medicine;Second Edition, 2009)

23. MASSETER Origin & Insertion B.D CHAURASIA’S HUMAN ANATOMY 6 TH edition ;pg 117

24. MASSETER Vascular supply Nerve supply MASSETERIC NERVE MASSETERIC ARTERY

25. RELATIONS SUPERFICIAL-Skin, Platysma , Risorius , Zygomaticus major, Parotid gland, Parotid duct, Branches of facial nerve DEEP- Overlies the insertion of temporalis and ramus of the mandible

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

27. PALPATION Superficial portion is palpated extraorally against the ascending ramus . Deep portion is made accessible by placing the index finger inside the mouth, just anterior to anterior border of ascending ramus .

28. CLINICAL IMPORTANCE Masseter muscle rigidity (MMR) , also known as "jaws of steel," occurs following a overdose of succinylcholine and is defined as limb muscle flaccidity with jaw muscle tightness. There is a variable presentation from complete trismus and severe spasticity to a tight jaw response, which makes it difficult to adequately intubate patient , leading to an increased risk of malignant hyperthermia in the patient. BOTOX SURGERY - Non- Surgical reduction of masseter muscle in response to masseter hypertrophy or as cosmetic treatment Also has effects on the denture border.

29. LATERAL PTERYGOID Origin and Insertion ATLAS OF HUMAN ANATOMY ; FRANK H. NETTER, 7 TH EDITION; pg 56

30. VASCULAR SUPPLY PTERYGOID BRANCH OF MAXILLARY ARTERY DUKE’S ANATOMY ATLAS; Copyright © 2004-2013 Duke University School of Medicine

31. NERVE SUPPLY NERVE TO LATERAL PTERYGOID ATLAS OF HUMAN ANATOMY ; FRANK H. NETTER, 7 TH EDITION; pg 58

32. RELATIONS

33. ACTIONS Sole function is to depress the mandible to open the mouth Side to side grinding movements alongwith medial pterygoid muscles.

34. PALPATION Palpated by sliding a finger along the buccal aspect of the maxillary dentition until the tuberosity region is reached and, then, palpating superiorly and medially.

35. CLINICAL IMPORTANCE Lateral pterygoid muscle dystonia is characterized by mandibular displacement towards the opposite side of the affected muscle. Can be treated with the help of botulinum toxin. Bilateral damage to the muscle results in limited opening, loss of protrusion & loss of full lateral deviation Certain exercises to stretch the lateral pterygoid muscles are webbed flexing, tongue workout, lateral stretching and open- wides .

36. MEDIAL PTERYGOID Origin & Insertion ATLAS OF HUMAN ANATOMY ; FRANK H. NETTER, 7 TH EDITION; pg 56

37. Vascular supply Nervous supply

38. RELATIONS Superficial relation- Upper part of the muscle is separated by the lateral pterygoid muscle by: Lateral pterygoid plate Lingual nerve Inferior alveolar nerve -Lower part of the muscle is separated from ramus of the mandible by: Lingual nerve Inferior alveolar nerve Maxillary artery Sphenomandibular ligament Deep relations- The relations are: Tensor veli palatini Superior constrictor of pharynx Styloglossus Stylopharyngeus attached to styloid process

39. ACTIONS Elevates and protrude the mandible Unilateral contraction – mediotrusive movement o the mandible

40. PALPATION Medial pterygoid forms a sling with the masseter muscle around ascending ramus . This area is palpated by placing an index finger in the mouth, just medial and posterior to where mandibular block injection is given.

41. CLINICAL IMPORTANCE Helps to close the jaw and shift the jaw to opposite sides. Hence any problem to this muscle can lead to restricted ability to open the jaw and it can be quite tender to touch. Pain can be felt into the mouth but also around TMJ. Most commonly involved in MYOFACIAL PAIN DYSFUNCTION SYNDROME Trismus following inferior alveolar nerve block is mainly due to involvement of medial pterygoid muscle

42. ACCESSORY MUSCLES

43. DIGASTRIC ORIGIN - Anterior belly from digastric fossa of mandible. - Posterior belly from medial side of mastoid notch of temporal bone INSERTION - Intermediate tendon NERVE SUPPLY - Anterior belly by nerve to mylohyoid - Posterior belly by FACIAL NERVE ACTION –Depresses mandible when mouth is opened widely or against resistance, secondary to lateral pterygoid --Elevates hyoid bone

44. MYLOHYOID Flat , triangular muscle deep to anterior belly of digastric Forms anatomically and functionally floor of the mouth. It is named after its two attachment from the molar teeth ( ‘ mylo ’ in Greek means ‘molar’)

45. ORIGIN - Mylohyoid line on the inner surface of mandible. Fibers run medially and slightly downward. INSERTION - Posterior fibers; body of hyoid - Anterior and middle fibers; median raphe , between the mandible and hyoid bone.

46. NERVE SUPPLY - Mylohyoid nerve BLOOD SUPPLY - Facial artery ACTIONS - Elevates the floor of the mouth in first stage of deglutition. - Helps in depression of mandible and elevation of hyoid bone.

47. GENIOHYOID ORIGIN - Inferior mental spine (lower genial tubercle) INSERTION - Anterior surface of body of hyoid. NERVE SUPPLY - C1 through hypoglossal nerve. ACTION - Elevates hyoid bone -May depress mandible when hyoid is fixed.

48. INFRAHYOID MUSCLES THYROHYOID -Depresses hyoid - Elevates larynx OMOHYOID -Depresses hyoid bone and larynx STERNOHYOID -Depresses hyoid bone STERNOTHYROID -Depresses Larynx

49. CHEWING AND CHEWING CYCLE

50. CHEWING STROKES

51. OPENING STROKE During opening phase there is initial rotation of the mandible for the first 20-27mm of interincisal distance Thereafter there is translatory or bodily shift of the mandible anteriorly and in downward direction Muscle activity begins in the ipsilateral inferior head of the lateral pterygoid muscle Followed by action of the contralateral inferior lateral pterygoid muscles.

52. CLOSING STROKE Crushing Starts when the mandible starts closing. At this point buccal cusp of maxillary teeth are under the buccal cusp of mandibular teeth. As the mandible closes, the bolus of food is trapped. 2) Grinding (SHEARING STROKE) Bolus gets trapped between the cusps and is grounded Bolus is trapped by the buccinator buccally and by the tongue lingually . ( Buccinator mechanism)

53. POWER STROKE During unilateral chewing when patient bites on hard substance on one side TMJ is not equally loaded This occurs because the force of closure is not applied to joint, but instead applied to food Jaw is fulcrum around hard food Contra lateral joint- sudden increase in interarticular pressure Ipsilateral joint- Decrease in interarticular pressure  separation between interarticular surfaces. May lead to dislocation

54. Picture showing FORCE DISTRIBUTION in closing stroke and power stroke

55. . CHEWING CYCLE

56. REFLEXES IN MASTICATORY SYSTEM

57. MYOTACTIC REFLEX

58. Picture depicting MYOTACTIC REFLEX

59. NOCICEPTIVE REFLEX

60. Picture Depicting NOCICEPTIVE REFLEX

61. DISORDERS OF MASTICATORY MUSCLES

62. OKESON’S Classification of Masticatory Muscle Disorders Myofascial pain Myositis Myospasm . Myofibrotic contraction. Centrally mediated myalgia Local myalgia

63. MYOFACIAL PAIN First described by TRAVELL & RINZLER in 1952. In 1969 LASKIN described Myofascial Pain Dysfunction Syndrome. Regional, dull aching muscle pain & presence of localized tender sites(trigger points) in muscle, tendon or fascia Pathogenesis of myofascial pain is not confirmed

64. DIAGNOSTIC CRITERIA FOR MYOFACIAL PAIN Regional dull, aching pain, pain aggravated by mandibular function when the muscles of mastication are involved. Hyperirritable sites (trigger points) frequently palpated within a taut band of muscle tissue or fascia ; Greater than 50% reduction of pain with vapocoolant spray or local anesthetic injection on the trigger point followed by stretch

65. What are trigger points and referred pain???? Trigger points: trigger points are clinically identified as specified hypersensitive areas within the muscle tissue’’ A small,firm,tight band of muscle tissue can be felt Referred pain: Occurs away from pain site and involve active trigger points.

66. Myofascial Pain referred from the Masseter muscle .- Trigger points located at sites in the superficial layer of the Masseter muscle refer to the posterior mandibular and maxillary teeth , the jaw, and the face . Toothache is a common complaint from this source

67. Myofascial pain referred from the temporal muscle - The reference zone of the temporalis muscle includes all the maxillary teeth and upper portion of the face . Headache and toothache are the commonly complaints.

68. Myofascial Pain Referred From Medial Pterygoid Muscle - The reference zone for the medial pterygoid muscle includes the posterior part of the mouth and throat. As well as the temporomandibular and infra- auricular areas

69. Myofascial Pain From Lateral Pterygoid Muscle The lateral pterygoid muscle cannot be adequately palpated, local or referred pains can be provoked only by isometric contraction of the corresponding muscle. The lateral pterygoid muscle pain can radiate to the temporomandibular joint , and superior lateral pterygoid muscle refer to zygomatic area.

70. Myofascial Pain Referred From Digastric Muscle - Myofascial pain in the anterior belly of the digastric muscle often causes referred pain in the lower incisors . Pain felt behind the angle of the mandible and below the ear is common referral site for a trigger point in the posterior belly of diagastric muscle.

71. TREATMENT Reassurance Spray & stretch :- Flouromethane spray anesthetizes area and allows patient to stretch the muscle in spasm Soft diet NSAIDS Discontinuation of parafunctional habits DIAZEPAM 2mg tds -2weeks(anxiety reducing &muscle relaxing)

72. MPDS-myofascial pain dysfunction syndrome Synonyms: Temporomandibular Joint Pain Dysfunction Syndrome Masticatory Myalgia Syndrome Costen’s syndrome Definition: It is a pain referred from a localized tender area or trigger point in a taut band of skeletal muscle Etiology: Trauma Muscular overextension Muscular over contraction Muscle fatigue. Stress

73. Clinical features:- More common in females-80% - 90% Pain of unilateral origin Diffused & less localized.Patient is unable to identify exact site involved Masseter and lateral pterygoid Deviation to unaffected site Pain is more severe in morning and gradually worsens as day progresses Aggravated by chewing and excessive eating Referred to cervical region Inability to open mouth

74. LASKIN′S CRITERIA FOR MPDS Four cardinal signs : 1) Pain in pre-auricular region 2) Tenderness in one or more muscles of mastication 3) Clicking / popping noise in the joint 4) Restricted/ deviated mouth opening Two typical negative disease characteristics 1) Absence radiographic changes in the joint 2) No biochemical evidence of organic changes in the joint

75. Treatment:-

76. MYOSITIS This disorder is characterized by inflammation of the muscle due to a spreading infection, external muscle trauma, or muscle strain. Clinical features : Acute pain within the muscle, which may additionally be swollen and red, with an overlying increased temperature. The muscle is tender to palpation and may cause a limited range of motion. Treatment : No specific medication Corticosteroid like prednisone can be prescribed in severe cases.

77. MYOSPASM This is the involuntary contraction of a muscle, causing pain and interfering with its ability to move. A myospasm of the inferior lateral Pterygoid muscles causes constant involuntary contraction and has a severe effect. Clinical features : Inability to occlude. Limited mouth opening Treatment : Deep massage of the area Local anaesthetic injection In chronic spasm, botulinum toxin injections

78. TRISMUS Trismus-defined as a prolonged,tetanic spasm of the jaw muscles by which the normal opening of mouth is restricted(locked jaw) Avg interincisal opening -13.7mm(5 to 23mm) ETIOLOGY - Trauma to muscles or blood vessels in infratemporal fossa associated with dental injections of local anesthetics. Haemmorhage. LA contaminated with alcohol or cold sterilizing solutions produce irritation of muscles. Low grade infection after injection

79. PREVENTION :- Use a sharp sterile and disposable needle Thorough knowledge of anatomy to avoiD multiple injections and insertions. Use aseptic technique Practice atraumatic injection technique MANAGEMENT :- Heat therapy-hot moist towels 20mins per hr. on affected area. Warm saline rinses Analgesics-aspirin Muscle relaxant-diazepam Physiotherapy-opening closing mouth,lateral excursions,for 5 mins every 4 hrs. Chewing gums(sugar free) Follow up

80. PERIODONTAL CONSIDERATION Role of periodontal fibers-These fibers help the tooth to withstand the naturally substantial compressive forces which occur during chewing and remain embedded in the bone. The periodontal fibres have the mechanoreceptors that respond to the forces applied to the tooth and send impulses to the brainstem The alveolar crest fibers prevent extrusion of tooth and resist lateral tooth movements. The loss of attachment that results from periodontitis involves the loss of some mechanoreceptors. Patients with significant bone loss, significant inflammatory disruption of the integrity of the PDL, or chronic occlusal parafunction may experience the compromised regulation of muscle activity

81. CONCLUSION The masticatory muscles include vital part of orofacial structure and are important both functionally and structurally. It is crucial responsibility of clinician to recognise each patient’s muscular environment and be aware of the problems related wIth excessive or deficient use of muscles and their bearing to the dentition. “YOU CANNOT SUCCESSFULLY TREAT DYSFUNCTION UNTIL YOU UNDERSTAND FUNCTION” - J.P. OKESON

82. REFERENCES B.D. CHAURASIA 6 TH EDITION TEXTBOOK OF PHYSIOLOGY, SEMBULINGAM LANGMAN’S TEXTBOOK OF EMBRYOLOGY, 12 TH EDITION TEXTBOOK OF ORAL MEDICINE, A. G.GHOM, 3 RD EDITION ATLAS OF HUMAN ANATOMY ; FRANK H. NETTER, 7 TH EDITION MANAGEMENT OF TEMPOROMANDIBULAR DISORDERS AND OCCLUSION, JEFFREY P. OKESON, 8 TH EDITION Gilbert AD, Newton JP. The effect of chronic periodontal disease on human jaw muscles: a pilot study using computed tomography. Journal of oral rehabilitation. 1997 Apr;24(4):259-64. Johansson AS, Svensson KG, Trulsson M. Impaired masticatory behavior in subjects with reduced periodontal tissue support. Journal of periodontology . 2006 Sep;77(9):1491-7.