Session 4: The Temporal Region and Temperomandibular Joint Flashcards
What does the temporal region include?
The temporal region includes the temporal and infratemporal fossae.
[*] The temporal fossa, lying on the lateral aspect of the skull, comprises the temporalis muscle and its neurovascular supply structures.
[*] The infratemporal fossa, which lies beneath the base of the skull between the pharynx and the ramus of the mandible, contains some muscles of mastication (lateral and medial pterygoid muscles), branches of the mandibular nerve (division of the trigeminal nerve), maxillary artery and other important structures such as the otic ganglion and chorda tympani (a branch of the facial nerve)
What is the TMJ?
The temporomandibular joint (TMJ) (aka mandibular joint or jaw-joint) is the articulation between the condylar head of the mandible and the mandibular fossa of the temporal bone (part of the cranium).
[*] It is the only joint allowing for use of the term ‘skull’ and dislocate very easily.
[*] It is found anterior and roughly level to the tragus of the ear
[*] The supraorbital foramen, infraorbital foramen and mental foramen occur in the same vertical axis
[*] The TMJ is effectively 2 joints (1 on each side). Both sides have to be working effectively for the joint to work.
[*] It is a modified synovial joint, whose movements are produced mainly by muscles of mastication. It is the most complex joint in the body.
- Like all synovial joints, the TMJ has a fibrous capsule. The capsule is very strong in itself but is also thin and loose to permit movements of the joint.
Describe the articulatory surfaces of the TMJ
Superior (Cranial)
- Much larger than the inferior articulatory surface
- On the under surface of the squamous part of the temporal bone, there are 2 articular sites with sinuous cross-sectional presentation:
- Mandibular Fossa (Posterior and concave) - set relatively superiorly
- Articular tubercle (Anterior and convex) (Eminentia Articularis) - set relatively inferiorly
Inferior (Mandibular)
- The condyle (head) of the mandible has a rounded superior edge and ellipsoid circumference with its major axis postero-medial (effectively oblique) – this means it can be bisected across its minor cross-sectional profile by its minor axis and bisected across its major cross-sectional profile by its major axis.
- It moves anteriorly to articulate with the anterior superior articular surface. This movement is known as translation or protrusion.
- Translation movements of the condyle are in an oblique plane.
- When the jaw is closed, it articulates with the posterior superior articular surface. Rotational movements occur when the condyle is engaged in the concavity of the posterior superior articular surface (hinge type movement)
So there are 2 articulatory surfaces on the squamous temporal under surface and 1 articulatory surface on each side of the mandible
Describe the intracapsular anatomy of the joint
- Direct bone-to-bone articulation does not occur.
- A fibrous disc known as the articular disc or meniscus separates bony surfaces from making direct contact.
- The articular disc allows for creation of 2 cavities within the TMJ capsule: an upper cavity & a lower cavity
- Upper and lower cavities of the TMJ allow for 2 separate types of independent movements (or displacements of the joint)
A gliding joint (translational movements in the upper cavity). Protrusion is done by the lateral pterygoid, medial pterygoid and masseter muscles. Retrusion is done by temporalis and masseter muscles.
A modified hinge joint (rotational (pivoting) movements in the lower cavity)
What is meant by the Upper and Lower Joint Cavities. Describe the incongruity between articulatory surfaces of the TMJ
Upper Joint Cavity:
- It is enclosed in its own synovial cavity
- Articulating surfaces are:
- Articular surface of the under surface of the temporal bone
- Upper surface of the articular disc
Lower Joint Cavity:
- It is enclosed in its own synovial cavity
- Articulating surfaces are:
- Inferior surface of the articular disc
- The mandible condyle
Incongruity between articulatory surfaces of the TMJ:
Superior and inferior articular surfaces are morphologically incongruous.
- Superior surface: convexo-concave (antero-posteriorly)
- Inferior surface: condyloid with an oblique trajectory superiorly
- The articular disc of meniscus between bony articular surfaces makes them congruent, improving their fit
What is the lining of the articulatory surfaces of the TMJ? Describe the articular disc
Lining of Articulatory surfaces of the TMJ
They are lined with fibrocartilage (not hyaline cartilage) (hence why TMJ is considered to be a modified synovial joint)
Articular Disc (aka meniscus) of TMJ:
- It is composed of dense fibrous connective tissue
- Same composition as the fibrocartilage lining the articulatory surfaces. Hyaline cartilage would not work in the TMJ because it would be worn down quickly due to the crushing forces created by the jaw. However although fibrocartilage can withstand a lot of force, it has a very long repair time.
- It intervenes between superior and inferior articular surfaces of bones of the TMJ
- Upper surface is concavo-convex (antero-posteriorly) to fit both the mandibular fossa and articular tubercle.
- Its under surface is concave for reception of the condyle of the mandible.
- It is thicker at its periphery where it attaches to the articular capsule (so thickness of the disc changes)
- It can recoil or stretch a little with movement.
- It is thinner centrally, sometimes almost perforated.
- Its function is to make the articulating surfaces congruent.
What are fibrous capsular attachments of the TMJ?
- Superiorly: the circumference of the mandibular fossa and the articular tubercle
- Inferiorly: the neck of the condyle of the mandible
- It is strengthened by extracapsular ligements:
- Lateral (n=1=strong)
- Medial (n=2)
It remains liable to sublaxation or complete displacement owing to its looseness (capsule is thin and loose to permit movements of the joint)
Describe the extracapsular attachments of the TMJ
Lateral ligament: Temporomandibular ligament which is laterally placed and the strongest ligament of the capsule (most important in reinforcement of the jaw joint). Its deep fibres blend with the capsule.
- Attachments: lower border of zygoma to posterior border of neck and ramus of mandible
- It tightens the head in retrusion (closing and pulling jaw backwards)
There are also 2 medial ligaments that strengthen the joint capsule but relatively less significant – they are the accessory ligaments.
Accessory Ligaments of the TMJ:
- Sphenomandibular ligament: it remains constant in length and tension for all positions of the mandible and prevents inferior dislocation of the joint
- Stylomandibular ligament: extends from near the apex of the styloid process of the temporal bone to the posterior border of the ramus of mandible near its angle . It is a thickening of the deep parotid fascia and separates the parotid gland from the submandibular gland.
Describe the stability of the TMJ
- More stable when jaw is closed
- Mandibular condyle in contact with mandibular fossa.
- Teeth are in occlussal contact (teeth come together and interlock)
- Perfect occlusion further stabilises the TMJ
- Least stable when the jaw is open
- TMJ is unstable and liable to spontaneous dislocation in edentulous people (people lacking teeth)
- Anatomical factors aiding stability of the joint
- Posterior displacement of the joint is limited by the post glenoid tubercle.
- Passive anterior displacement of the joint is limited by the articular tubercle.
- Inferior dislocation is prevented by the sphenomandibular ligament (internal lateral) and stylomandibular ligament (posteriorly)
Describe the opening movements of the TMJ
It is always the mandible that displaces in order for movements to occur. Movements occur by displacements in the:
- Superior joint cavity (gliding): protrusion and retraction
- Inferior joint cavity (hinge/rotation): depression of the mandible, elevation of the mandible
Opening movements of the TMJ:
- Active opening is a simple movement.
- The condyles are pulled forwards – protrusion (gliding movement) by the lateral pterygoid muscles (3) (occurs in the upper joint cavity). The lateral pterygoid muscles contract, pulling jaw forward so chin is brought forward. Chin drops as it comes to meet the articular tubercle (set relatively inferiorly), depressing the jaw => opening it
- The chin is pulled down and back (hinge movement) by the digastric muscles (lower joint cavity). Digastric is not a prime mover for joint opening. Prime mover is gravity.
- Suprahyroid and infrahyoid muscles are also involved – can depress the mandible against gravity
- The mandible is protruded and depressed when mouth is wide open.
- If the condyle overshoots, it will end up on the other side of the articular tubercle. Medical intervention is needed to bring it back.
Describe the closing movements of the TMJ
- Retraction of the Mandible: posterior fibres of the temporalis muscle pull the mandible backwards (superior joint cavity)
- Elevation of the mandible: remainder of temporalis muscle (1), masseter muscles (2) (all its layers), medial pterygoid muscles (4) (occurs in the inferior joint cavity)
- Mouth closed (mandible retruded and elevated)
What is meant by Knacking, Bruxism, Temporomandibular Pain Dysfunction and mal-occulsion syndromes?
[*] Knacking: (loud sounds heard when the jaw displaces) e.g. when chewing
[*] Bruxism (grinding teeth when asleep) (often associated with stress)
[*] Temporomandibular Pain Dysfunction Disorders (muscular pain)
[*] Mal-occlusion syndromes (muscular pain) (due to incongruity between the upper and lower dental structures)
Describe fractures of the mandible and dislocations of the TMJ
- Fractures of the mandible may be accompanied by dislocation of the TMJ. The close relationship of the auriculotemporal nerve (a branch of the mandibular division of the trigeminal nerve) to the joint makes it vulnerable to injury when there is a traumatic dislocation of the joint accompanied by tearing of the joint capsule and associated structures. The joint then becomes lax and unstable.
- Dislocations of the TMJ: sometimes during yawning or taking a large bite, excessive contraction of the lateral pterygoids may cause the heads of the mandible to dislocate anteriorly (pass anterior to the articular tubercles).
[*] In this position the mouth remains depressed and the person is unable to close their mouth.
- Dislocation of the TMJ commonly results from a side-ways blow to the chin when the mouth is open, dislocating the TMJ on the side that received the blow but may also accompany fractures of the mandible.
Describe the Infratemporal Fossa
[*] It is an irregularly shaped cavity of anatomical and clinical importance, on the lateral aspect of the skull. Its importance derives from the importance of structures within it.
[*] It is a site from which clinical procedures can be carried out.
[*] Anatomical Relationships of the Infratemporal Fossa
It lies:
- Below the middle cranial fossa
- Medial and deep to the zygomatic arch
- Beneath the maxilla
It communicates with the temporal fossa through the interval between the zygomatic arch and cranial bones
What are the borders of the infratemporal fossa?
- Anterior border: infratemporal surface of the maxilla (posterolateral wall of the maxillary sinus?) and descending ridge of its zygomatic process
- Posterior border: articular tubercle of the temporal bone (zygomatic arch) and spina angularis of the sphenoid; carotid sheath
- Superior border: infratemporal surface of the greater wing of sphenoid, foramen ovale, foramen spinosum
- Inferior border: alveolar border of the maxilla (no border in some books)
- Medial border: lateral pterygoid plate; tensor and levator palalti muscles; superior constrictor muscle
- Lateral border: ramus and condylar process of mandible
What are the contents of the infratemporal fossa?
It contains muscles, nerves, arteries, veins, foramina, canals and fissures
What are the muscular contents of the infratemporal fossa?
[*] Muscular contents of the Infratemporal Fossa
- Lower part of the medial pterygoid muscle
- Lower part of the lateral pterygoid muscle
- Lower part of the temporalis muscle
[*] Clinical Importance of the Infratemporal Fossa
- It is also a potential anatomical space of clinical importance
- Pathologies within this region can evolve without detection up until it is too late
What are the arteries of the infratemporal fossa?
[*] Arteries of the Infratemporal Fossa
- Maxillary artery is the main artery of the infratemporal fossa (large terminal branch of external carotid artery)
[*] Deep arteries of the Infratemporal Fossa
- Maxillary and middle meningeal arteries (middle meningeal artery is a branch of the maxillary artery)
- Anterior branch of the middle meningeal artery is extremely significant (especially in fractures involving the Pteryion)
- Middle meningeal arteries enter the cranium through foramen spinosum
[*] Superficial arteries of the Infratemporal Fossa
- Superficial temporal artery (smaller terminal branch of the external carotid artery)
What are the veins of the infratemporal fossa?
- Maxillary vein
- Middle meningeal vein (5)
- Pterygoid venous plexus (confluence of a lot of veins including veins draining the eye. The plexus sits between medial and lateral pterygoid muscles and stagnation of blood can lead to contraction of muscles (yawning reflex)
1 – Superior ophthalmic vein which drains directly into 2:
2 – Anterior intercavernous sinus
3 – Inferior ophthalmic vein
4 – Pterygoid plexus
5 – Middle meningeal vein
Describe the nerve contents of the infratemporal fossa
- The mandibular nerve and most of its branches are found in the infratemporal fossa.
- Its branches:
- Auriculotemporal nerve
- Inferior alveolar nerve
- Lingual nerve
- Buccal nerve
- Chorda tympani (branch of facial nerve)
- Otic ganglion
- The mandibular nerve leaves the cranium through the foramen ovale
