1 Type of Joint

2 Articular Surfaces

Superior Articular Surface

Formed by the following parts of the temporal bone:

1. Tubercle of root of zygoma (zygomatic arch) and its anterior root.
2. Anterior part of mandibular fossa.
3. Posterior non-articular part → formed by the tympanic plate.

Inferior Articular Surface

• Formed by the head of mandible.

3 Ligaments of TMJ

1. Fibrous Capsule

Attached above to:

• Articular tubercle
• Circumference of mandibular fossa in front
• Squamotympanic fissure behind

Attached below to:

• Neck of mandible.

The capsule is:

• Loose above the intra-articular disc
• Tight below it.

• Synovial membrane lines the fibrous capsule and the neck of mandible.

2. Lateral / Temporomandibular Ligament

• Reinforces and strengthens the lateral part of the capsular ligament.
• Its fibres are directed downwards and backwards.

Attached:

• Above → tubercle of root of zygoma and its anterior root
• Below → posterolateral aspect of neck of mandible.

3. Sphenomandibular Ligament

• It is an accessory ligament.
• Lies on a deep plane away from the capsule.
• Attached superiorly to the spine of sphenoid.
• Attached inferiorly to the lingula of mandibular foramen.
• It is a remnant of the dorsal part of Meckel’s cartilage.

Lateral Relations

1. Lateral pterygoid muscle
2. Auriculotemporal nerve
3. Maxillary artery

Medial Relations

1. Chorda tympani nerve
2. Wall of pharynx
3. Near its lower end, it is pierced by the mylohyoid nerve and vessels.

4. Stylomandibular Ligament

• It is another accessory ligament of the joint.
• It represents a thickened part of the deep cervical fascia which separates the parotid and submandibular salivary glands.

Attached:

• Superiorly → lateral surface of styloid process
• Inferiorly → angle and adjacent part of posterior border of ramus of mandible.

4 Joint Cavity and Articular Disc

The disc divides the joint cavity into two compartments:

1. Upper Menisco-temporal Compartment

• Permits gliding movements.

2. Lower Menisco-mandibular Compartment

• Permits gliding movements.
• Permits rotational movements.

Articular Disc

• The disc has:
  • Concavoconvex superior surface
  • Concave inferior surface
• The periphery of the disc is attached to the fibrous capsule.
• The disc represents the degenerated primitive insertion of lateral pterygoid.

Functions of Articular Disc

1. Prevents friction between the articulating surfaces.
2. Acts as a cushion and helps in shock absorption.
3. Stabilises the condyle by filling the space between articulating surfaces.
4. Proprioceptive fibres present in the disc help to regulate movements of the joint.
5. Helps in distribution of weight across the TMJ by increasing the area of contact.

5 Relations of Temporomandibular Joint

6 Blood Supply and Nerve Supply

Blood Supply

Branches from:

• Superficial temporal artery
• Maxillary artery

Nerve Supply

• Auriculotemporal nerve
• Masseteric nerve

7 Movements of TMJ

1. Depression → open mouth
2. Elevation → closed mouth
3. Protrusion → protraction of chin
4. Retrusion → retraction of chin
5. Lateral / side-to-side movements → during chewing or grinding.

Muscles and Factors Responsible for Movements

Side-to-side / Chewing Movements

8 Mechanism of TMJ Movements

1. Meniscotemporal Compartment

• Permits gliding movement.
• Gliding mostly occurs during:
  • Protrusion
  • Retraction
  • Chewing

2. Meniscomandibular Compartment

• Permits rotational movement.

Axes of Rotational Movement

Rotational movements take place around two axes:

1. Transverse Axis

• Passes mediolaterally through the centre of neck of mandible.

2. Vertical Axis

• Passes through the posterior border of ramus of mandible.

Rotation around the transverse axis occurs during:

• Depression
• Elevation

Rotation around the vertical axis occurs during:

• Side-to-side movements.

Depression of Mandible

Depression occurs in three phases:

1. Initial Phase

• Depression is initiated in the lower compartment by forward rotation of mandibular head below the disc.
• The transverse axis passing through the mandibular neck remains fixed.
• The head moves forward and downward in the lower fixed compartments.

2. Middle Phase

• Movement occurs in the upper / meniscotemporal compartment by forward gliding of the disc.
• The disc carries the mandibular heads with it.
• The transverse axis moves itself and allows the head to move forward below the disc.
• The disc and head glide forward together until further movement is prevented by tension of:
  • Posterior fibres of temporalis
  • Upper lamella of articular disc

3. Final Phase

• The transverse axis becomes fixed at one place.
• The head rotates around this axis.
• This produces further forward and downward movements in the lower meniscotemporal compartments.
• The head reaches the summit of the articular tubercle.

Side-to-side Movement

• The mandibular head of one side:
  1. Glides forward in the upper meniscotemporal compartment.
  2. Rotates below the disc around the vertical axis.
• The vertical axis passes through the posterior border of the opposite ramus of mandible.
• This is followed by reverse movement and rotation of the opposite mandibular head.
• This produces side-to-side movement.

9 Range of Mandibular Movements

10 Factors Maintaining Stability of TMJ

The TMJ is supported by the following factors that maintain its stability:

1. Bones

• Articular tubercles → prevent anterior dislocation.
• Postglenoid tubercles → prevent posterior dislocation of TMJ.

2. Ligaments

• Lateral temporomandibular ligament → prevents backward dislocation of TMJ.

3. Muscles

• Tension of the posterior fibres of temporalis → prevents anterior dislocation.
• Tension of lateral pterygoid → prevents posterior dislocation.

4. Position of Mandible

11 Clinical Anatomy

Palpation of TMJ

Ask the patient to:

1. Open and close the mouth several times.
2. Move the opened jaw side-to-side.
3. Move it forward and backward.

• During these movements, the TMJ is palpated by placing a finger into the anterior wall of the outer portion of external auditory meatus.
• The moving condyle of mandible can be felt.
• TMJ can also be palpated by placing a finger about 1.5 cm medial to the tragus of ear.

Dislocation of Mandible

• The mandible is commonly dislocated anteriorly.
• During excessive opening of the mouth:
  • Head of mandible dislocates anteriorly.
  • It slips forward underneath the articular eminence in the infratemporal fossa.
  • The patient cannot close the mouth.

Reduction of Dislocated TMJ

• To reduce the dislocated TMJ, the condyle of mandible must be brought back behind the articular eminence.
• For this:
  • Lower down the ramus of mandible by placing the thumbs on the last molar teeth.
  • Simultaneously elevate the chin with the other fingers.

TMJ Syndrome

Symptoms

1. Facial pain → due to spasm of masseter.
2. Headache → due to spasm of temporalis.
3. Jaw pain → due to spasm of lateral pterygoid.

Clicking Sound at TMJ

• Movement of TMJ may produce clicking sound or jaw popping.
• It may occur due to:
  • Joint function or disorder such as arthritis
  • Broken or dislocated mandibular head
  • Muscular spasm
  • Malocclusion of teeth
  • Infection of parotid glands.

Damage to Nerves During TMJ Surgeries

• Damage to VII nerve or auriculotemporal nerve may occur during TMJ surgeries.