Mandible and temporomandibular joint

Mandible

The mandible consists of a horizontal part called the body and the vertical part called the ramus

Body of Manible (External surface)

The external surface is made up:

1. Mental foramen

2. Alveolar process

3. Alveolar yolk

4. Mental protuberance.

Mental foramen

1. Mental foramen- there are two mental foramina. The mental nerve and vessels exit through it.

Alveolar process

Alveolar process- this is the tooth-bearing area of the mandible.

Alveolar yolk

These are a series of eminences corresponding to the position of the roots of the teeth.

Mental protuberance

This forms the prominence of the chin.

Internal surface of body of mandible

1. Mylohoid line

2. Submandibular fossa

3. Mental spine

4. Sublingual fossa

5. Digastric fossa

Mylohyoid line

The attachment of the mylohoid muscle

Submandibular fossa

Inferior to the mylohoid line for the submandibular gland

Mental spine

Found at the midline

Sublingual fossa

Found on either sides of the mental spine for the sublingual gland

Digastric fossa

Found at the base of the mandible for the attachment of the anterior belly of the digastric muscle

External surface of ramus of mandible

1. Angle of Mandible

2. Massteric tuberosity

3. Coronoid process

4. Oblique line

5. Condylar process

6. Mandible notch

Angle of mandible

Junction between the body and the ramus of the mandible.

For the attachment of the masseter muscle and the stylomandibular ligament.

Masseteric tuberosity

For the attachment of the massester muscle

Coronoid process

for the attachment of the temporalis muscle.

Mandibular notch

Betwenn the coronoid and teh condylar process.

Internal surface of the ramus of the mandible

1. Condylar process

2. Neck of the mandible

3. Mandiblar foramen

4. Lingula

5. Mylohoid groove

6. Ptyergoid tuberosity,

Condylar process

This consists of the head of the mandible and the pterygoid fovea inferior to it.

The ptergoid fovea is the place of attachment of the lateral ptergoid muscle.

Neck of mandible

Mandibular foramen

paired, superior to the mandibular angle.

Content: Inferior alveolar vessels and nerve enter the mandibular canal through it. These supply the lower part of the teeth

Lingula

for the attachment of the sphenomandibular ligament

Mylohoid groove

For the attachment of the mylohoid muscle

Pterygoid tuberosity

For the attachment of the medial pterygoid muscle

Temporomandibular joint

Type of joint: It is a paired, modified condyloid type of synovial joint.

Articular surface: The head of the mandible with the mandibular fossa of the temporal bone. There is an articular disc between the joint cavity.

Joint Capsule: is loose

Articular disc

Articular disc: This divides the joint into 2 separate compartments this creates separate superior and inferior articular cavities, which are lined by 2 synovial membranes:

1. Superior synovial membrane: lines the fibrous layer of the capsule superior to the articular disc.

2. Inferior synovial membrane: inferior to the articular disc.

Ligaments

1. Lateral ligament:

2. Stylomandibular ligament:

3. Sphenomandibular ligament:

Lateral ligament

This ligament runs from the articular tubercle and attaches to the neck of the mandible

Acts to prevent posterior dislocation.

Stylomandibular ligament

This ligament runs from the styloid process to the angle of the mandible

Sphenomandibular ligament

This runs from the spine of the sphenoid to the lingula of the mandible.

Movements:

1. Elevation: close mouth

2. Depression: open mouth

3. Protrusion: chin goes forward

4. Retrusion: chin goes backwards

5. Lateral movements: chewing

What muscles produce the TMJ movemnts

These are called the muscles of Mastication:

1. Temporalis

2. Masseter muscle

3. Medial and lateral pteygoid muscle

Which muscle is the only opener

the lateral ptergoid muscle is the only opener,

The other muscles close the jaw.

What muscle fills up the temoporal fossa entirely?

Temporalis muscle

Opening and closing of the mouth

• The axis of movement is a transverse line between the manibulae foramina.

• Therefore, opening and closing of the mouth which is the abduction and adduction of the mandible is a combined movement during which:

  • In the first stage, the mandibular base moves inferiorly (depression during opening) or superiorly (elevation during closing).

  • In the second stage, the downward movement of the jaw is followed by the forward movement of the mandibular head onto the articular tubercle.

  • Coversely, during closing, the backward movement of the mandibular head into the mandibular fossanand this is followed by elevation.

  • This movement can also be performed with bothe open and closed jaws.

Note: Anteduction is the same as protrusion/protraction

Retroduction is the same as retrusion/retraction

Grinding (chewing) movement

• During masticatory movements, the TMJ on each side work in an asymmetric manner.

• The working side performs the combination of protraction/retraction (protrusion/retrusion) and medial/lateral rotation as a result of the masticatory muscles.

• And the movements of the working side are passively followed by the balance side.

• The axis of the chewing movement is a vertical axis that intersects with the transverse line between the mandibular foramina.

• During mastication, the working and balance sides keep alternating and the axis of the movement always passes through the balance side.

Note: Anteduction is the same as protrusion/protraction

Retroduction is the same as retrusion/retraction