Functional Anatomy of Temporomandibular Joint

FUNCTIONAL ANATOMY OF TEMPOROMANDIBULAR JOINT

Considered as a ginglymoarthrodial joint : - hinging movement ~ ginglymoid joint - gliding movement ~ arthrodial joint

It is formed by mandibular condyle fitting into mandibular fossa and the two bones is separated by articular disc

It is classified as a compound joint ( at least 3 bones ) ~ functionally the articular disc served as a nonossified bone

Diarthrodial synovial paired joint two joint movement which occur in seperate compartement, and one joint cannot operate without otherConsidered as a ginglymoarthrodial joint : - hinging (menggantung) movement ~ ginglymoid joint - gliding (meluncur) movement ~ arthrodial joint

TEMPOROMANDIBULAR JOINTTwo components :PASIF COMPONENTS1.Bone - Fossa mandibularis ossis temporalis - Capitulum mandibula ( condyle ) - Tuberculum articulare ( articular eminence )

2.Capsule and ligaments3.Articular disc

ACTIVE COMPONENTSMasticator musclesMasseterTemporalisPterygoideus medialisPterygoideus lateralisAdditional muscles

MANDIBULAR FOSSA(fossa glenoidalis)Part of the temporal bone ( concave )Anterior : articular eminence a convex bony prominence Posterior : squamotympanic fissure (M-L)The posterior roof is thin ~ not designed to sustain heavy force The articular eminence consists of thick dense bone ~ to tolerate such forces- The steepness of the articular eminence surface ~ dictates the pathway of the condyle

MANDIBULAR CONDYLEIt is the posterior portion of the ramus mandibula that extends upward Mediolateral : 15 20 mm Anteroposterior : 8 10 mmIndividual variation size and angulation between the right and left sideMorphologicchanges developmental variations, malocclusion, trauma, and other developmental abnormalities

CAPSULE AND LIGAMENTSCapsula articularis ~ capsular ligamentIt surrounds the entire TMJSuperior attachmentarticular surface of the mandibular fossa and articular eminenceInferior attachmentcollum mandibularAnterior capsule continous with pterigoidMedially capsule is thin whereas lateraly is thicker and strengthened by TM Ligament - Function : ~ to resist any medial, lateral or inferior forces that tend to separate or dislocate the articular surface ~ to retain the synovial fluid

Collateral ( discal ) ligaments2.Collateral ( discal ) ligaments - From medial and lateral borders of the disc to the poles of the condyle ~ the medial discal ligament ~ the lateral discal ligament - Composed of collagenous connective tissue - Function : ~ allow the disc move passively with the condyle as it glides A PThese ligaments are responsible for the hinging movement between the condyle and the articular disc

Temporomandibular ligamentIt lies at the lateral aspect of the capsula ligamentThe major ligament, the temporomandibular ligament, or lateral ligament, is really the thickenest lateral portion of the capsule.it limits anterior-posterior movement of the condyle and disc

Anatomy of TMJTM ligamentcapsule

Minor ligament4.Sphenomandibular ligament - From the spine of the sphenoid bone and extends downward to lingula mandibula5.Stylomandibular ligament - From the styloid process and extends downward and forward to the angle and posterior border of the ramus mandibula - It limits range movement in lateral direction

ARTICULAR DISCComposed of dense fibrous connective tissue devoid of any blood vessels or nerve fibersSagittal plane ~ can be divided into 3 regions according to thickness - anterior border - posterior border ~ slightly thicker than anterior border - central area is the thinnest ~ intermediate zone ~ in which condyle is located normally

Anterior region of the disc is attached to the capsular ligament - Superior : anterior margin of the articular surface of the temporal bone Inferior : anterior margin of the articular surface of the condyle - Composed of collagenous fibers

Anteriorly the disc is also attached by tendinous fibers to the superior lateral pterygoid muscle

RETRODISCAL TISSUEThe articular disc is attached posteriorly to this regionIt is a loose connective tissue region that highly vascularized and innervatedSuperior : superior retrodiscal lamina ( contains many elastic fibers ) ~ bilaminary zone It attaches the disc posteriorly to glenoid fossa Inferior : inferior retrodiscal lamina ( composed chiefly collagenous fibers ) It attaches distal aspect of neck of the condyle.

Articular Disc

The TMJ is divided into superior and inferior cavity by the articular discSuperior cavity - Superior : fossa mandibula Inferior : discus articularis - Gliding action between condyle and articular eminenceInferior cavity - Superior : discus articularis Inferior : condyle - Hinge action between undersurface of the disc and the rotating surface of the condyle

Articular DiskAcres of CollagenAneural & Avascular

ARTICULAR SURFACE

The articular surface of the mandibular fossa and condyle are lined with dense fibrous connective tissue ~ affords several advantages over hyaline cartilage : - less susceptible to the effects of aging ~ less likely to break down over time - a better ability to repair

The internal surface of the joint cavity are surrounded by specialized endothelial cells that form a synovial lining ~ produces synovial fluid So TMJ ~ a synovial joint

The synovial fluid serves two purposes :Acts as a medium for providing metabolic requirement, since the articular surfaces of the joint are nonvascularAs a lubricant during function

Two mechanisms of the lubrication :Boundary lubrication Prevents friction in the moving jointWeeping lubrication Eliminates friction in the compressed but not moving joint

Condylar HeadBovine Condyle

Condylar HeadA - Fibrous layer

B - Reserve zone

C - Proliferative zone

D - Hypertrophic zone

E - Calcifying zone

F - Bone

MUSCLES OF MASTICATION

A. Temporalis MuscleOrigin: temporal fossa & temporal fasciaInsertion: coronoid process & anterior of ramusFunction: Elevation and positioning of the mandible

B. Masseter MuscleOrigin: zygomatic archInsertion: lateral surface of ramus, coronoid process & angle of mandibleFunction: power with vertical elevation of the mandible; deep portion stabilizes the condyle in protrusive closure

C. Medial Pterygoid MuscleOrigin: medial surface of lateral pterygoid plate, pyramidal process of palatine bone & Mx tuberosity Insertion: medial surface of ramus & angle of mandibleFunction: elevation of the mandible, protrusion of the mandible and lateral movement of the mandible with unilateral activation

Pterygomasseteric Sling

D. Inferior Lateral Pterygoid MuscleOrigin: lateral surface of lateral pterygoid plateInsertion: pterygoid fovea of condyle Function: protrusion, lateral movement and contributes to opening

E. Superior Lateral Pterygoid MuscleOrigin: infratemporal surface greater wing of the sphenoid boneInsertion: pterygoid fovea of the condyle and variable to the discFunction: active with the muscles of closure, especially aiding stabilization of the condyle during the power stroke

Nerve and blood suplayBetween the tragus and the mandibular condyle lie the superficial temporal artery and veins. cont of the external carotid artery the veins course towards the internal jugular veinThe auriculotemporal nerve, locate in posterior to the blood vessels, which it follows cranially. The upper branch of the facial nerve (VII) passes superficially to the blood vessels at the level of the mandibular neck and runs horizontally forwards before breaking up into several terminal branches

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