Anatomy and Function of TMJs PDF

Anatomy and function of TMJs Dr István Somoskövi The temporomandibular joint (TMJ) Temporal bone Mandible = jaw joint Temporal bone: lateral view  Temporal bone: inferior view Mandibular condyles Design of the Masticatory System Every part is designed for a specific...

Anatomy and function of TMJs Dr István Somoskövi The temporomandibular joint (TMJ) Temporal bone Mandible = jaw joint Temporal bone: lateral view  Temporal bone: inferior view Mandibular condyles Design of the Masticatory System Every part is designed for a specific purpose Teeth need to function in a specific way (type of chewing) The main functions are mastication and swallowing Design of the Masticatory System 1. First you need a fixed socket: mandibular fossa (temporal bone) Design of the Masticatory System 2. You need a lever arm with a fulcrum so the mandible can hinge open and close Design of the Masticatory System 3. Problem: as man became upright the spinal column had to be moved forward. If we stayed on fixed hinge, our airways would be compressed when we open Design of the Masticatory System 4. So you need a movable fulcrum and a disc that serves as a movable socket Design of the Masticatory System 5. You have to limit the movements of the jaw. You add ligaments. Design of the Masticatory System 6. You add the fibrous capsule which encloses the TMJ Design of the Masticatory System 7. You have to add masticatory muscles so the system can function. Design of the Masticatory System 8. Now you can align the teeth. Main characteristics Synovial joint Ginglymo-arthroidal: both hinging and sliding movements Bilateral: unique that the two sides function as one unit, dependent on each other Joint capsule Dense fibrous membrane Attaches to articular eminence, neck of mandible, and disc Surrounds the joint and articular eminence Limits the movements (with the ligaments) 2 layers:  outer fibrous layer (holds)  inner synovial membrane: produces synovial fluid  Articular disc  fibrous extension of the capsule  dense fibrous tissue  biconcave shape  thinest in the middle (1 mm)  anterior band 2 mm  posterior band 3 mm Articular disc Central part Peripherial region denser thicker, but less dense non-innervated innervated non-vascularised vascularised nutrition is from synovial fluid DESIGNED TO BEAR PRESSURE DESIGNED TO POSITION THE FROM CONDYLE CONDYLES IN CENTRIC RELATION Articular disc  articulates with the fossa and the condyle  divides the joint into an upper and a lower compartment (virtual spaces)  attached to the condyle mesially and laterally by the collateral ligaments  anteriorly attached to lateral pterygoid muscle (upper belly) Retrodiscal tissues also referred as bilaminar zone upper and lower layers vascularised, highly innervated (auriculotemporal nerve) upper layer: elastic fibres lower layer: type I collagen fibres Synovial fluid Produced by finger-like projections of the synovial membrane Polysaccharide-protein complex and proteoglycan (hyaluronate) Function:  feeding avascular surfaces  lubrication  carries away waste material  Ligaments  lateral ligament (= temporomandibular): capsule’s thickened part (from zygomatic arch to neck of mand.)  stylomandibular ligament  sphenomandibular ligament  Muscles Lateral pterygoid Medial pterygoid  Lateral pterygoid muscle Upper head: origin: infratemporal surface of sphenoid bone insertion: articular disc and capsule Lower head: origin: lateral plate of pterygoid process insertion: neck of mandible Medial pterygoid muscle Origin: lateral pterygoid plate + superficial fibers from maxillary tuberosity of palatine bone Insertion: distal part of ramus and angle of mandible; joins the insertion of the masseter muscle  Temporalis Masseter Temporalis Origin: temporal fossa Insertion: its tendon crosses the zygomatic arch medially, inserts the coronoid process of the mandible, extending to the retromolar area  Masseter Superficial head: Origin: temporal process of zygomatic bone and lower border of zygomatic arch Insertion: angle and lower ramus of mandible Deep head: Origin: posterior part of zygomatic arch Insertion: upper part of ramus  Suprahyoid muscles:  mylohyoid  digastric  geniohyoid Muscle attachments on the mandible Muscle function during opening inferior lateral pterygoid, anterior digastric, mylohyoid Muscle function during closing masseter, temporalis, medial pterygoid, superior lateral pterygoid Muscle function during protrusion bilateral contraction of lateral pterygoid (lower belly) Muscle function during retrusion middle and posterior temporalis Muscle function during lateral movement ipsilateral temporalis, contralateral inferior lateral pterygoid Blood supply and innervation Superficial temporal and maxillary arteries (both from external carotid) Sensory: auriculotemporal nerve (V/3)  Function of TMJs Unique function Designed for chewing and swallowing +speaking, facial expressions, etc. Complex movements  first ~20 mm opening: pure rotation of condyles  after that: translation, the disc glides anteriorly on the slope of articular tuberculum  lateral movement: rotation on one side (vertical axis) and translation on the other  the two sides must move simultaneously  Lower joint compartment (condyle-disc): rotational movement = initial stage of opening Upper joint compartment (disc- fossa): translation (gliding) = wider opening Closed mouth MRI Fossa Disc Opened mouth MRI Fossa Disc