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    Temporomandibular Joint

    (TMJ)

    Temporomandibular Joint

    (TMJ)

    Alex ForrestAssoci ate Profess or of For ensic Od ontol ogyForensic Science Research & Innovation Centre, Griffith University

    Consultant Forensic Odontologist,Queensland Health Forensic and Scientific Services,39 Kessels Rd, Coopers Plains, Queensland, Australia 4108

    Oral Biology

    COMMONWEALTH OF AUSTRALIA

    Copyright Regulations 1968

    WARNING

    This material has been reproduced and communicated to you by, or on

    behalf of, Griffith University, pursuant to Part VB of The Copyright Act 1968(The Act; a copy of the Act is available at SCALEPlus, the legal

    information retrieval system owned by the Australian Attorney Generals

    Department, at http://scaleplus.law.gov.au).

    The material in this communication may be subject to copyright under the

    Act. Any further reproduction or communication of this material by you maybe the subject of Copyright Protection under the Act.

    Information or excerpts from this material may be used for the purposes of

    private study, research, criticism or review as permitted under the Act, and

    may only be reproduced as permitted under the Act.

    Do not remove this notice

    You should be able to describe the structure of the TMJ and

    its movements in preparation for understanding the roles of

    the muscles of mastication in moving the mandible.

    Learning ObjectiveLearning Objective

    StructureStructure

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    The Temporomandibular Joint is the site of articulation

    between the mandible and the cranium.

    It is a bilateral synovial joint, and serves to open and close

    the jaws, and to approximate the teeth of each jaw during

    mastication.

    StructureStructure

    It consists of parts of the

    mandible and temporal

    bones which are covered

    by cartilage, and

    surrounded by several

    ligaments including a

    joint capsule.

    Between the two bones is

    a fibrous articular disk,breaking the joint into two

    separate synovial-lined

    compartments.

    http://www.tmj.com/b1_patient.html

    Structure

    Several pairs of muscles

    attached to the mandible

    produce movements

    required to suckle, ingest

    and masticate food,

    swallow and yawn, andproduce speech.

    They are called the

    muscles of mastication

    and the accessory

    muscles of mastication.

    http://e-ortho.tripod.com/orofacialPain.htm

    The mandible possesses two articular surfaces, the

    condyles, which are located on the upper end of each of

    the bilateral condylar processes.

    Alex Forrest 2008

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    Each condyle articulates with a meniscus (articular disk)

    which lies between it and the temporal bone.

    http://chiropracticresearch.org/NEWS_chiropractic_and_tmj.htm

    The condyles, which

    are characteristically

    "football-shaped, are

    directed at an oblique

    angle, so that if the

    planes of the long

    axes were continuedthey would meet at

    the front of the

    foramen magnum.

    Modified from: Scott, JH & Dixon, AD. Anatomy for Students

    of Dentistry. Edinburgh, Churchill Livingstone, 3rd Edition

    1972. p. 150.

    The Temporal BoneThe Temporal Bone

    The site of articulation on the temporal bone is on the inferior

    surface of the zygomatic process. It is called the glenoid fossa

    or the mandibular fossa.

    Grays Anatomy,

    35th Ed, Longman,London 1973, p.

    293.

    Alex Forrest 2008

    While on the dried skull the mandibular condyle appears to

    articulate within the glenoid fossa between the bony articular

    tubercle and the post-glenoid process, in real life it probably

    articulates about the tubercle.

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    TheAr ticu lar Disk (meniscus) is a compact, dense fibrous

    connective tissue plate.

    It is roughly oval in shape and lies between the mandibular

    condyle and the articular eminence of the temporal bone.

    http://cpmcnet.columbia.edu/dept/dental/Dental_Educational_Software/TMJ/LatTMJ2.gif

    Its inferior surface is concave to fit the convex surface of

    the condyle. Superiorly, its surface is concavo-convex.

    The disk is thickest at its periphery and thinnest in the

    stress-bearing part of the joint.

    Modified from: Posselt, U, Physiology of Occlusion and Rehabilitation, Blackwell

    Scientific, Oxford, 2nd Edition 1973.

    The coverings of the

    articular surfaces of the

    condyle and articular

    eminence are composed of

    dense fibrous connective

    tissue.The heaviest stress-

    bearing areas of the disk

    are also fibrocartilage, and

    indeed the whole disk may

    become fibrocartilaginous

    in later life.

    http://e-ortho.tripod.com/orofacialPain.htm

    These fibrocartilaginous

    structures are all

    essentially avascular, butthey are bathed in

    synovial fluid which

    provides nourishment as

    well as lubrication.

    http://e-ortho.tripod.com/orofacialPain.htm

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    LigamentsLigaments

    Anatomy textbooks describe several ligaments around the

    TMJ.

    They do not always clearly differentiate between the

    ligaments of the joint (which are true ligaments), and the

    accessory ligaments, some of which are not true

    ligaments, but are simply thickenings in sheets of fascia.

    LigamentsLigaments

    From Grays Anatomy, 35th Ed, Longman, London 1973, p. 408

    The ligaments of the joint comprise thejo in t capsule, and the

    medial and lateral ligaments.

    The capsule is reinforced along its medial and lateral margins

    by bundles of collagenous fibres.

    From Grays Anatomy, 35th Ed, Longman, London 1973, p. 408

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    The medial part is a slight thickening of the capsular ligament

    and the lateral part, which is more strongly reinforced, is known

    as the lateral ligament ortemporomandibular ligament.

    From Grays Anatomy, 35th Ed, Longman, London 1973, p. 408

    Accessory LigamentsAccessory Ligaments

    The accessory ligaments are basically thickenings in sheets of

    fascia. They are not ligaments in the true sense, and they

    definitely are not strong enough to fulfil the "suspensory" role

    sometimes assigned to them in textbooks.

    Instead, they have stretch receptors which feed into reflex

    control loops and thus prevent excessive opening and

    protrusion of the mandible.

    Accessory LigamentsAccessory Ligaments

    The sphenomandibular

    ligament is a derivative of

    Meckel's cartilage, and

    runs between the spine of

    the sphenoid bone and the

    lingula of the mandible.

    It is clinically importantbecause if local

    anaesthetic solution is

    deposited anterior to it

    during an inferior dental

    block injection, it will

    prevent the diffusion of the

    solution posteriorly and

    result in a failed block.From Grays Anatomy, 35th Ed, Longman, London 1973,

    p. 408

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    The stylomandibular

    ligament is a

    thickening of the deep

    cervical fascia, and

    extends from the

    styloid process of the

    temporal bone to theposterior border of the

    angle of the mandible.

    From Grays Anatomy, 35th Ed, Longman, London 1973, p. 408

    InnervationInnervation

    The joint capsule is sensitive, and is heavily endowed

    with sensory endings from the mandibular division of the

    trigeminal nerve, primarily through its auriculotemporal

    branch.

    Additional fibres to the joint are derived from the

    masseteric branch of the mandibular nerve.

    Blood SupplyBlood Supply

    Blood supply is via the maxillary artery and by branches ofthe superficial temporal artery.

    Venous drainage is via the pterygoid plexus, and lymphatic

    drainage is via the buccal and submandibular lymph nodes.

    Movements of the TMJMovements of the TMJ

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    During its movements, the mandible swings on its elevator

    muscles, and on the other tissues which suspend it from

    the cranium.

    The mandible may be depressed, elevated, protruded,

    retruded, moved laterally, and returned to its resting

    position. It may be rotated around an axis passing

    roughly through both condyles.

    Chewing i s a combination of all of these movements.

    MovementsMovements

    Jaw Opening is a combination of protrusion, depression,

    and rotation about the intercondylar axis.

    Jaw Closing is a combination of retrusion, elevation and

    rotation.

    Protrusion cannot occur without depression to

    disocclude the teeth.

    MovementsMovements

    When the mandible is swung to one side, the contralateral

    condyle is pulled forwards, downwards and medially.

    The ipsilateral condyle remains in its fossa, undergoing only

    slight movement, being slightly depressed, swung slightly

    laterally, and rotated around a vertical axis.

    This is sometimes known as "Bennett Movement".

    MovementsMovements

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    Ligaments & FunctionLigaments & Function

    Ligaments act to limit t he range of a movement in a joint .

    The limiting fu