TMJ

TMJ?

TEMPOROMANDIBULAR JOINT

The only joint in the head?

No

Type of the joint?

Synovial

Bone

Muscle

Ligaments

Innervation

Function

LEARNING OBJECTIVE

Describe the anatomical structures of the joint Explain the articulating surfaces of the bones Describe the embryology of the joint Identify: capsule, synovial membrane, ligament

and articulating disc Describe the muscles and the movements that

take place in the joint Describe the nerve and blood supply to the joint Explain how dislocation of the joint can occur

TMJ

Joint/ articulation? Connection between two separate parts of skeleton Mandible and the two temporal bones Craniomandibular joint Bilateral articulation the only visible movable joint in the head

Exercise Palpate the TMJ

Three articulating parts: Articular eminence (or tubercle) Articular fossae Mandibular condyle

Enclosed by fibrous connective tissue capsule

Mandibular condyle

Surface covered by thickened layer of fibrous connective tissue

Articular fossa and articular eminence

Articular fossa – non functioning portion

Articular eminence functioning portion Just anterior to the articular fossa Lined by thicker layer of fibrous tissue

Articular disc

Tough oval pad of dense ficrous connective tissue

Surface – smooth

Thinner in the centre than around the edges

Concave anteriorly to fit under the articular eminence

Convex posteriorly to conform to the shape of articular fossa

Flattened disc problems

Articular disc

Function: Partitioning the complex condylar movement into

upper and lower functional components Lubricating with synovial fluid Stabilising condyle Cushioning the loading Reducing physical wear and strains Helping regulate movements of the condyle

http://www.youtube.com/watch?v=4CVbHsnB3Rk

How does TMJ differ from other synovial joints?

TMJ develops between 8 – 14 weeks compared to 5-8 weeks for other synovial joints

TMJ – initially widely separated temporal and condylar blastema that grow towards each other

Limb joint develops to adulthood by cavity fromation within single blastema

Fibrous cartilagerather than hyaline cartilage

Embryology

10 – 12 weeks pc

Ossification of the temporal components begins independently of the events in the mandible

the condylar cartilage is present at the most superior aspect of the ramus.

the embryonic connective tissue (mesenchyme) between the growing condyle and temporal bone condenses to form the articular disc

Inferior compartment form first (10 weeks) , upper (11.5)

cavitation forms the lower joint compartment and then the upper compartment

14 weeks Joint development completed

Development

Infants: Articular fossa, articular eminence and condyle – flat About the same level as occlusal plane Why?

During development Articular fossa deepens Articular eminence - > prominent – when? Condyle becomes rounded

Growth Structure grow laterally – widening of the neurocranium Mature disc – changes shape, more compact, less cellular, more

collagen Condyle contains cartilage

After eruption of permanent dentition, articular tubercle becomes prominent

Accelerates until 12th year of life

Fibrous capsule Sheet/sac/tube of tissue Encloses the joint Fairly thin Lateral – temporomandibular ligament Attachment – upper – circumference of articular

fossa Lower – neck of the condyle

Two layers: Inner layer (synovial membrane)

Lines fibrous capsule Covers the bone Secretes synovia – lubricates and nourishes

Outer layer Thicker layer of fibrous tissue Accessory ligaments

Ligaments

Capsular ligament – restricts posterior movement of condyle Temporomandibular ligament

Attachment – upper – zygoma arch, lower – side and back of condyle neck

keeps condyle close to the fossa Helps prevent lateral and posterior displacement

Stylomandibular ligament Posterior to the joint Attached at the _____ and _____

Sphenomandibular ligament Medial to the joint Limit maximum opening Attached to ______ and _______

Articular disc Dense fibrous connective tissue Between mandibular condyle and articular

fossa/eminence Thinner – center

Anteriorly and laterally

Act as a buffer

Muscles

Muscles of mastication Masseter Temporalis Medial pterygoid Lateral pterygoid

Masseter

Most superficial, powerful

Quadrilateral

Origin: Zygomatic arch – inferior and medial surface and temporal process of zygomatic bone

Insertion: lateral surface of the ramus

Function: closes jaw, crushing

Temporalis muscle

Fan shaped, large but flat muscle

Origin: entire temporalis fossa (part of frontal and parietal bone, squamous part of temporal and greater wing of sphenoid)

Directed downward (anterior), downward, anteriorly (posterior part) – passing medial to zygomatic arch

Insertion: coronoid process, anterior border of ramus and temporal crest

Action: elevator, retractor

Medial pterygoid

Medial to ramus

Origin: medial surface of lateral pterygoid plate and pterygoid fossa, pyramidal process of palatine bone

Pass downward, laterally towards the angle of mandible

Insertion: medial surface of mandible in triangular region

Action: elevator

Lateral pterygoid

Horizontal fibres

Short, thick

Located in the infratemporal fossa

Prime mover of mandible except closing

Origin: 2 heads – upper head – infratemporal surface on great wing of sphenoid

Lower head – lateral side of pterygoid plate on sphenoid bone

Insertion: upper head – neck of condyle and anteroposterior surface of capsular ligament, into disc

Lower head – roughened pterygoid fovea on anterior surface of neck of condyle

Action: opening the jaw

Pulling articular disc and condyle forward down onto articular eminence

Innervation

Proprioceptive neurons in capsule and disc

Trigeminal nerve (cranial nerve V) – auriculotemporal branch of ______

Branches of mandibular division of the TN (auriculotemporal, deep temporal and masseteric) supply the joint

Blood supply

branches of external carotid artery

Ascending pharyngeal and superficial temporal branches

Anterior tympanic

Massteric

Middle meningeal branch of maxillary artery

-

Problem

Dislocation • Extreme

opening of the jaw – laughing, dental treatment

Condyle moves too

far

Stuck in front of articular

eminence

Muscle spasm

RECAP

Name the bony components of TMJ?

Muscles that close the jaw

Nerve innervate the joint