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: During development 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

Accelerates until 12th year of life 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) Outer layer 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 -

Stuck in front of articular eminence 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