TMJ & Infratemporal Fossa Flashcards
What is the temporomandibular joint?
Articulation between the mandible and the cranium
Bilaterally symmetrical in the antero-posterior plane (2 joints)
What are the articular surfaces of the temporomandibular joint?
SUPERIOR (underside of squamous part of temporal bone)
= mandibular fossa (posterior & concave) + articular tubercle (anterior and convex)
INFERIOR (significantly smaller s.a. compared to superior surface)
= condyle of mandible has a rounded superior edge & an ellipsoid circumference (fits into mandibular fossa when the jaw is closed)
What are the factors which limit displacement of the temporomandibular joint?
Articular tubercle limits anterior displacement
Post-glenoid tubercle limits posterior displacement
What are the components of the temporomandibular joint capsule?
Modified synovial joint (direct bone-bone contact does not occur)
Fibrous capsule (very strong & thin; prone to subluxation)
- superior attachment = circumference of mandibular fossa + articular tubercle
- inferior attachment = neck of condyle of mandible
Meniscus (dense fibrous connective tissue); prevents bones from making direct contact & improves congruency of surfaces
- upper surface = concavo-convex (fit mandibular fossa & articular tubercle)
- lower surface = concave (fits condyle of mandible)
- thicker at periphery (where it attaches to the articular capsule) but almost perforated in the centre
- little stretch/recoil
- lined by fibrocartilage (NOT by hyaline cartilage; this would be worn away quicker due to the presence of Type II collagen instead of type I collagen)
Upper cavity =
- gliding/translational movements (horizontal plane) but condyle itself moves obliquely
- articulates with underside of temporal bone & upper surface of articular disc
Lower cavity =
- modified hinge joint (rotational movements) - when condyle is engaged with the mandibular fossa
- articulates with inferior surface of the articular disc & mandibular condyle
note: high amount of force is required to create crushing forces (but difficult to repair therefore theoretically talking/chewing should be restricted to short periods)
note: at birth, the fibrocartilage is lined by a synovial membrane, but this has disappeared by adulthood
What ligaments strengthen the temporomandibular joint?
Temporomandibular ligament (lateral extracapsular ligament):
- tightens during …..
- attaches at lower border of zygoma to the posterior border of the neck & ramus of the mandible (blends with capsule)
Sphenomandibular ligament:
- constant length & tension for all positions of mandible
- prevents inferior dislocation of joint (internal lateral)
Stylomandibular ligament:
- thickening of deep parotid fascia separating parotid & submandibular glands
- prevents inferior dislocation of joint (posteriorly)
+ 2 medial extracapsular ligaments (less significant)
When is the temporomandibular joint most stable?
Jaw is closed i.e. mandibular condyle in contact with mandibular fossa
—> teeth in occlussal contact (straight teeth)
Therefore people with no teeth (edentulous people) are prone to temporomandibular joint
Describe the movements of the temporomandibular joint.
note: it is always the mandible which is displaced
Active opening (i.e. not due to gravity)
- condyles pulled forwards by lateral pterygoids —> protrusion (gliding movement, therefore upper joint cavity)
- digastric muscles help pull chin down & back (hinge movement, therefore lower joint cavity)
Closing
- posterior fibres of temporalis pull mandible backwards (upper joint cavity) —> retraction of mandible
- remaining fibres of temporalis, masseter, and medial pterygoids (lower joint cavity) —> elevation of mandible
Give some examples of temporomandibular joint disorders.
Knacking = loud sounds heard when jaw displaces e.g. whilst eating
Bruxism = grinding teeth when asleep
Temporomandibular pain dysfunction disorders (muscular pain)
Mal-occlusion syndromes (muscular pain)
How may fractures of the mandible affect the temporomandibular joint?
May dislocate temporomandibular joint by tearing the joint capsule
Risk of damage to auriculotemporal nerve —> temporomandibular joint becomes lax and unstable
What are the contents of the infratemporal fossa?
Nerves: mandibular nerve + otic ganglion
MOTOR =
- masseteric nerve
- deep temporal nerve
- lateral & medial pterygoid nerves
SENSORY =
- meningeal nerve
- buccal nerve
- auriculotemporal nerve
- lingual nerve
- inferior alveolar nerve
- chorda tympani nerve
Muscles:
- lower parts of medial & lateral pterygoid muscles
- temporalis muscle
Arteries:
- DEEP = maxillary artery & middle meningeal arteries (branches from maxillary artery & enters foramen spinosum - most significant branch is the anterior branch)
- SUPERFICIAL = superficial temporal artery (branch of external carotid artery)
Veins:
- maxillary vein
- middle meningeal vein(s)
- pterygoid venous plexus cavernous sinus (via foramen ovale + sphenoidal emissary foramen if present)
note: other openings in infratemporal fossa:
- alveolar canal (posterior superior alveolar vessels & nerves)
- inferior orbital fissure (zygomatic branch of maxillary nerve & ascending branches of pterygopalatine ganglion)
- pterygomaxillary fissure (terminal part of maxillary artery & posterior superior alveolar nerve)
note: tumours can grow in the infratemporal fossa for a long time without detection
note: structures move in AND out of foramen ovale
What nerve blocks apply to the nerves of the infratemporal fossa?
Mandibular nerve block
- anaesthetic injected adjacent to nerve as it enters infratemporal fossa
- affects inferior alveolar nerve, lingual nerve, buccal nerve, and auriculotemporal nerve
Inferior alveolar nerve block (dental treatment):
- anaesthetic injected around mandibular foramen (medial side of mandible)
- affects all mandibular teeth on medial side + skin & mucous membranes of lower lip (mental branch of nerve)
- anaesthetic solution may spread to lingual nerve which lies immediately in front of the inferior alveolar nerve —> tongue goes numb
How can infection of the infratemporal fossa spread?
Pterygoid venous plexus connects to opthalmic veins & anterior facial veins, and drains into the cavernous sinus
Pus in venous plexus causes increased opthalmic venous pressure and cavernous sinus thrombosis —> paralysis of extraocular muscles
What can be felt over the contracted masseter muscles?
Parotid duct
Felt particularly well on anterior border of masseter where it pierces the buccinator
Opens into interior of mouth opposite the 2nd upper molar tooth
Why are the temporomandibular joints prone to dislocation when yawning or eating?
Relaxed muscles of mastication + excessive contraction of lateral pterygoids
—> head of mandible may “click” over articular tubercle and dislocate anteriorly
—> lies alongside the zygomatic arch
