Temporomandibular Joint

Describe Temporomandibular Joint Under The Following Heads:

1. Temporomandibular Joint Classification,
2. Temporomandibular Joint Ligaments,
3. Temporomandibular Joint Movements and muscles bringing movements,
4. Temporomandibular Joint Sets of movements
5. Temporomandibular Joint Axis of movement
6. Temporomandibular Joint Range of mandibular movements
7. Temporomandibular Joint Nerve supply, and
8. Temporomandibular Joint Applied anatomy

Answer: 1.

Temporomandibular Joint Classification

Temporomandibular Joint is also called ginglymoarthrodial joint. It provides

1. Hinge movement, and G
2. living movement

Read And Learn More: Head Anatomy Notes And Important Questions With Answers

Temporomandibular Joint Structurally: Compound, complex, condylar, multiaxial, saddle-shaped,a typical synovial joint.

1. Temporomandibular Joint Compound: Two bones namely the mandible and temporal bones and the articular disc take part in the formation of the TM joint.
   The inferior surface of the mandibular fossa of the squamous part of the temporal bone,
   The superior surface of the head of the mandible, and
   Fibrocartilage articular disc.
2. Temporomandibular Joint Complex: The joint cavity is separated by an articular disc into upper meniscotemporal and lower menisci-mandibular compartments.
3. Temporomandibular Joint Condylar: Left and right condyles of the head of the mandible form a bicondylar articulation.
4. Temporomandibular Joint Multiaxial: The movements are vertical, transverse, and anteroposterior axis.
5. Temporomandibular Joint Saddle-shaped: The articular surface of the head of the mandible is convex.
   the concave surface which articulates with the concavo-convex surface of the mandibular fossa of the temporal bone.
6. Temporomandibular Joint Atypical synovial: The articular surfaces of the head of the mandible and mandibular fossa of the temporal bone are not covered by hyaline cartilage but are covered by fibrocartilage. Here collagen fibres predominate and cartilage cells are few. Because the concerned bones ossify in the membrane.

Temporomandibular Joint Functionally: Diarthrosis.

2. Temporomandibular Joint Ligaments

The ligaments can be divided into

Main ligaments

Fibrous capsule

Attachments

1. Above
   Anteriorly: Anterior to articular tubercle.
   Posteriorly: Posterior to the squamotympanic fissure.
   Medially and laterally: To the margins of the mandibular fossa.
2. Below: The capsule is attached at a higher level near the articular margin of the head of the mandible. Posteriorly, it is attached to the neck lower down.

Nature of the capsule

1. Loose and lax above the disc
2. Lense and thick below the disc

Peculiarities

1. Peculiarities is spacious, lax, and strong.
2. Peculiarities gives attachment to the lateral pterygoid muscle.

Articular disc: It is oval in shape and fibrocartilage in nature (Fig. 10.6).

1. Morphologically, it represents lateral pterygoid muscle.
2. It is attached
   Anteriorly, medially, and laterally near the head of the mandible.
   Peripherally to the inner side of the fibrous capsule.
3. Parts
   Anterior extension.
   Posterior bilaminar extension.
4. Variation in thickness: It is thick peripherally and thin in the center.
5. Peculiarity: Gives attachment to lateral pterygoid muscle.
6. Functionally, it divides the joint cavity into upper and lower compartments.
   The movement in the upper compartment is gliding.
   The movement in the lower compartment is rotatory and gliding.

Lateral ligament of TM joint

1. Lateral ligament of TM joint is a stout band of fibrous tissue.
2. Lateral ligament of TM joint covers a lateral aspect of the capsule and strengthens it.
3. Lateral ligament of TM joint extends from the tubercle of the root of the zygoma to the neck of the mandible.
4. Lateral ligament of TM joint tightens in retraction and protraction and relaxes in the rest position.

Synovial membrane

1. Synovial membrane lines the fibrous capsule above and below the disc but does not cover the disc.
2. Synovial membrane lines the non-articular surface of articulating bones.
3. In newborns, even the articular surfaces are covered by synovial membrane.

2. Temporomandibular Joint Accessory ligaments

Sphenomandibular ligament

1. Introduction: It is an accessory ligament of the temporomandibular joint, which lies on a deep plane away from the fibrous capsule.

Attachments

1. Above to the spine of the sphenoid bone.
2. Below to the lingula of the mandible.

Stylomandibular ligament

1. Stylomandibular ligament is a thickening of deep cervical fascia between the angle of the mandible and the styloid process.
2. Stylomandibular ligament stretches
   From the
   Apex, and
   Adjacent anterior aspect of the styloid process
3. To the Angle of the mandible, and Posterior border.
   Stylomandibular ligament is considered only an accessory to the joint. The function is not exactly known.

3. Temporomandibular Joint Movements and muscles bringing movements

There are three sets of mandibular movements at the TM joint.

1. Movements and muscles bringing movements.

Depression and elevation

1. Depression is produced mainly by the lateral pterygoid. The digastric, geniohyoid, and mylohyoid muscles help when the mouth is opened wide or against resistance.
2. Elevation is produced by the masseter, the temporalis, and the medial pterygoid muscles of both sides.

Side-to-side movement (gliding movement): Lateral or side-to-side movements are produced by the medial and lateral pterygoids of each side acting alternately.

Protraction and retraction
Protraction is done by the lateral pterygoid (principally its inferior head) and medial pterygoids.
Retraction is produced by the posterior fibers of the temporalis.
It may be resisted by the middle and deep fibers of the masseter, the digastric, and the geniohyoid muscles.

2. Position of articular disc and head of the mandible in movements of TM joint

When the chin is depressed

In the upper compartment: Meniscofemoral compartment

1. The articular disc and the head of the mandible move forward.
2. The movement is on the upper articular surface.
   The movement continues till the head of the mandible lies inferior to the articular tubercle.

In the lower compartment

1. At the same time, the head of the mandible rotates on the lower surface C of the disc.
2. The latter movement alone is capable of permitting simple chewing movements over a small range.

When small chewing movements are made without separating lips. The head of mandible moves in the mandibular fossa.

When the mouth is opened wide, the head of the mandible swings forward and downwards.

4. Temporomandibular Joint Sets of movements:

There are three sets of mandibular movements at the TM joint.
These are

1. Depression and elevation

1. In a slight opening of the mouth or depression of the mandible, the head of the mandible moves on the undersurface of the disc like a hinge.
2. In the wide opening of the mouth, the hinge-like movements are followed by the gliding of the disc and the head of the mandible, as in protraction.
   At the end of this movement, the head comes to lie under the articular tubercle.
   These movements are reversed in closing the mouth or elevation of the mandible.
3. Active depression is produced mainly by the lateral pterygoid. The digastric, geniohyoid, and mylohyoid muscles help when the mouth is opened wide or against resistance.
4. Passive depression is produced by gravity.
5. Elevation is produced by the masseter, the temporalis, and the medial pterygoid muscles on both sides.

2. Side-to-side movement (gliding movement): Lateral or side-to-side movements
are produced by the medial and lateral pterygoid of each side acting alternately.

3. Protraction and retraction

1. In protraction, the articular disc glides forward over the upper articular surface, the head of the mandible moving with it.
   The protrusion is done by the lateral (principally its inferior head) and medial pterygoids.
2. In retraction, the articular disc glides backward over the upper articular surface, the head of the mandible moving with it.
   It is produced by the posterior fibers of the temporalis.
   It may be resisted by the middle and deep fibers of the masseter, the digastric, and geniohyoid muscles.

5. Temporomandibular Joint Axis of movement

1. In small movements, the axis is through the head of the mandible.
2. In a wider range of movements, the axis passes approximately through the mandibular foramen.

6. Temporomandibular Joint Range of mandibular movements

1. Opening of the mouth

1. The maximal opening of the jaw is about 50 mm.
2. The functional range of the opening is about 40 mm.
3. Opening of the jaw by rotation is about 25 mm.
4. The last range of 15 mm is by anterior translateral (from side to side) gliding.

2. In protrusion of the mouth: The maximal range of protrusion and lateral displacement is about 10 mm each.

7. Temporomandibular Joint Nerve supply

1. The auriculotemporal nerve is a branch of the posterior division of the mandibular nerve.
2. The masseteric nerve is a branch of the anterior division of the mandibular nerve.

8. Temporomandibular Joint Applied anatomy

Lockjaw

1. Disc displacement: The unique feature of the articular disc is it is made up of elastic cartilage which is flexible.
   It serves as a cushion between two bony surfaces.
   The disc lacks arteries and nerves. Hence, it is pain-insensitive.
   Anteriorly, it continues as lateral pterygoid muscle.
   Posteriorly, it continues as methodical tissue.
   The retrodiscal tissue has a rich nerve supply and blood supply.
2. Disc displacement is the most common disorder. In most cases, the disc is dislocated anteriorly.
   As the disc moves forward, methodical tissue is caught between two bones.
   This can be very painful as it has a rich nerve supply.
3. The forward dislocated disc forms an obstacle for condylar movement. In order to open the jaw fully, the condyle has to jump over the backend with sense.
   This produces a clicking sound. This condition is called disc displacement with reduction.
4. In later stages of disc dislocation, the condyles stay behind all the time unable to set back on the disc, the clicking sound disappears but mouth opening is limited.
   This is usually the most symptomatic stage.
5. The jaw is set to be locked as it is unable to open its wide mouth.
   At this stage, the condition is called disc displacement without reduction.
   Fortunately, in the majority of cases, the condition resolves by itself.
   This is called the natural adaptation of retrodiscal tissue.
   This becomes scar tissue and functionally replaces the disc.
   In fact, it becomes too similar to disc and is called pseudodisc.
6. Forward dislocation is the commonest form of displacement.
   With the mouth open, the condyles are in the articular eminence, and sudden violence, even muscular spasms (a convulsive yawn), may displace one or both temporomandibular joints.
7. Anterior dislocation readily occurs in the edentulous, i.e. person without teeth.
   It is easily reduced; the joint is less stable because the increased elevation of the edentulous mandible permanently elongates the lateral ligament.
8. The reduction of the TMjoint is easily achieved by pressing down on the molar teeth with thumbs placed in the mouth, and at the same time pushing the chin upward and backward.
   The downward pressure on the molar teeth overcomes the tension of the temporalis and masseter muscles which are in spasm.
   Andu the upward and backward pressure on the chin helps the head of the mandible to put into its original position.
9. The lateral ligament of the TM joint is very strong.
   It helps in the following ways:
   It prevents backward falling of the head of the mandible.
   It prevents the fracturing of the tympanic plate.
   This is very much true when a severe blow falls on the chin.
10. The articular disc of the temporomandibular joint may become partially detached
    from the capsule. It results in noisy movements.
    It produces an audible click during movements at the joint.

Factors Responsible For The Stability Of Temporomandibular Joint

The following factors maintain the stability of the temporomandibular joint.

1. Temporomandibular Joint Bones

1. Forward displacement is prevented by articular tubercles, and
2. Backward displacement by post-glenoid tubercle.

2. Temporomandibular Joint Ligament: The lateral ligament of TMJ strengthens the capsule posterolaterally. It prevents the backward dislocation of the mandible.

3. Temporomandibular Joint Muscles

1. The protrusion is limited by the tension in the temporalis.
2. Retraction is limited by the tension in lateral pterygoid muscles.

4. Temporomandibular Joint Position of the mandible: In occlusion, the following factors play an important role in the stabilization of the joint.

1. Teeth themselves stabilize the mandible on the maxilla. No strain is thrown on the joint when an upward blow is received by the mandible.
2. Forward movement of the condyle is discouraged by the
   Prominence of articular eminence, and
   Contraction of posterior fibers of temporalis.
3. Backward movement is prevented by the
   Fibers of lateral ligament, and
   Contraction of the lateral pterygoid.

Articular Disc of TM Joint (meniscus)

Articular Disc of TM Joint Introduction: It is the fibrocartilaginous structure separating the cavity of the TM joint.
1. Morphology

1. Shape—oval
2. Attachments
   Anteriorly to the neck of the mandible.
   Peripherally to the fibrous capsule.
   Medially and laterally to the neck of the mandible.
3. Surfaces: The superior surface of the disc is anteroposteriorly concavo-convex.
   The inferior surface of the disc is concave.
4. Extensions
   Thick anterior band
   Thick posterior band
   Thin in the middle
5. The posterior band divides into two laminae with a venous plexus in between
   Upper lamina: It is attached above the mandibular fossa and is fibroblastic in nature.
   Lower lamina: It is attached to the mandible and is non-elastic.
6. Variation in thickness
   Thick at the periphery, and
   Thin in the center.

2. Articular Disc of TM Joint Peculiarities: It gives attachment to lateral pterygoid muscle.

3. Articular Disc of TM Joint Functions: It divides the joint cavity into upper and lower compartments.

4. Articular Disc of TM Joint Movements

1. Gliding movement in the upper compartment.
2. Gliding and rotation movement in the lower compartment.

Sphenomandibular Ligament

Sphenomandibular Ligament Introduction: It is an accessory ligament of the temporomandibular joint. It lies on a deep
plane away from the fibrous capsule.

1. Sphenomandibular Ligament Attachment: From spine of sphenoid bone to the lingula of mandible.

2. Sphenomandibular Ligament Relations
Laterally: MAIL

1. Maxillary artery.
2. Auriculotemporal nerve.
3. Inferior alveolar nerve.
4. Lateral pterygoid muscle.

Sphenomandibular Ligament Medially:

1. Medial pterygoid muscle.
2. Corda tympani nerve.
3. Wall of the 12arynx.

3. Sphenomandibular Ligament Development: It develops from the mesenchyme of the 1st pharyngeal arch. It is a remnant of the dorsal part of Meckel’s cartilage.

4. Sphenomandibular Ligament  Applied anatomy

Sphenomandibular ligament is ruptured by

1. Fracture of the neck of the mandible, or
2. Dislocation of temporomandibular joint.

It leads to loss of taste sensations due to injury to chorda tympani nerve.