What are the articulations of the temporo-mandibular joint?
What covers the articular surfaces?
The condylar head of the mandible and the mandibular fossa of the temporal bone and the articular tubercle of the temporal bone
Fibrocartilage
The temporo-mandibular joint isn't a bone-to-bone articulation, what is between the articular surfaces?
A fibrous disc= articular disc It is formed of dense fibrous connective tissue It creates an upper cavity and a lower cavity within the capsule, which are enclosed by their own synovial cavity
What are the two accessory ligaments of the temporo-mandibular joint?
Sphenomandibular ligament
Stylomandibular ligament
What is important about the sphenomandibular ligament?
It remains constant in length and tension for all position of the mandible.
It prevents inferior dislocation
What is important about the stylomandibular ligament?
It is a thickening of the deep parotid fascia and it separates the parotid gland from the mandibular gland
When is the temporo-mandibular joint the most stable?
When the jaw is closed and the teeth are touching
What movements and muscles are involved in the opening of the jaw?
The condyles are pulled forwards (protrusion) by the lateral pterygoids
The chin is pulled down and back by the digastric
What movements and muscles are involved in the closing of the jaw?
Posterior fibres of the temporalis muscle pull the mandible backwards (retraction) Remainder of the temporalis, masseters and medial pterygoids elevate the mandible
What factors are responsible for the stability of the joint?
Posterior displacement limited by the post-glenoid tubercle Passive anterior displacement limited by the articular tubercle Inferior dislocation is prevented by the sphenomandibular ligament and the stylomandibular ligament
What is meant by bruxism?
Grinding of the teeth while asleep
What is the importance of the joint surfaces being lined by fibrocartilage?
Stronger and longer-lasting than hyaline cartilage It can withstand the forces of mastication
Describe the temporomandibular ligament
Extracapsular Strongest ligament to the tmj Its fibres blend with the capsule
What are the anatomical relations of the infratemporal fossa?
Below the middle cranial fossa Medial and deep to the zygomatic arch of the temporal bone Behind the maxilla
What are the muscular contents of the infratemporal fossa?
Lower parts of the lateral and medial pterygoids Lower part of the temporalis muscle
What are the arterial contents of the infratemporal fossa?
Maxillary artery (and the middle meningeal branch)
What are the venous contents of the infratemporal fossa?
Maxillary vein, middle meningeal vein, pterygoid venous plexus
Which nerves can be found in the infratemporal fossa?
The mandibular nerve (off the trigeminal) and its branches (auriculotemporal, inferior alveolar, lingual, buccal) and otic ganglion and chorda tympani
What are the openings of the infratemporal fossa?
Foramen ovale (mandibular division of the trigeminal nerve) Foramen spinosum (middle meningeal artery) Alveolar canal Inferior orbital fissure Ptergo-maxillary fissure
What happens in a mandibular nerve block?
Anaesthetic injected as the mandibular nerve enters the i.t. fossa. Nerves affected are inferior alveolar, lingual, buccal and auriculotemporal
What happens in an inferior alveolar nerve block?
During dental treatment Anaesthetic is injected around the mandibular foramen on the medial side of the mandible All mandibular teeth (on that side), skin and mucous membrane of the lower lip
Why might an infection deep in the infratemporal region be of danger to the eye?
The pterygoid venous plexus drains in to the cavernous sinus and it is also connected to the ophthalmic and anterior facial veins. Pus within the plexi may increase the pressure in the ophthalmic veins or it may lead to a cavernous sinus thrombosis, causing paralysis of the extra ocular muscles
Why does the tongue become numb during an inferior alveolar nerve block?
The lingual nerve lies immediately in front of the inferior alveolar nerve so the anaesthetic solution may spread causing numbness of the anterior 2/3 of the tongue
What structure can be palpated lying on the contracted Masseter muscle when the jaw is clenched tight?
The duct of the parotid gland
Why might dislocation of the tmj happen during yawning or taking very large bites of food?
The lateral pterygoids protrude and depress the jaw. If the other muscles of mastication are relaxed, the lateral pterygoids may contract excessively causing the head of the mandible to dislocate anteriorly over the articular tubercle