Temporomandibular Joints Question And Answers

The Temporomandibular Joints, Teeth, And Muscles, And Their Functions

Question 1. Describe the structure and functions of muscles of mastication. Deglutition/stages of deglutition. (or) Lateral pterygoid muscle. (or) Masseter muscle. (or) Muscles of mastication.
Answer:

Muscles of mastication:

• Masseter muscle:
  • It is quadrilateral in shape.

Muscles of mastication Extend:

• From the zygomatic arch to the ramus and body of the mandible.

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Muscles of mastication Insertion:

• Extends from the second molar to the posterior lateral surface of the ramus.

Muscles of mastication Structure:

• The masseter muscle is partly covered by the platysma and risorius muscle and to a variable degree with the parotid gland tissue.
• The superficial part of the muscle is separated from the deeper layer at the posterior upper part of the muscle.

Muscles of mastication Nerve supply:

• Massetric nerve – a branch of the anterior division of the mandibular nerve.

Muscles of mastication Actions:

• Elevates mandible to close the mouth to bite.

 Temporalis Structure:

• It is fan-shaped.
• It has three component parts.

 Temporalis Origin: It originates in the temporal fossa.

• Insertion:
  • Anterior border and the mesial surface of the coronoid process of the mandible.
  • Along the anterior border of ascending ramus.

 Temporalis Functions:

• The anterior part is active in clenching.
• The posterior part retracts the protruded mandible.
• The Temporalis muscle also helps in side-to-side grinding movement.

 Temporalis Nerve supply:

• 2 deep temporal branches of the mandibular nerve.

Lateral pterygoid Structure:

• It is short and conical in shape.
• It has upper and lower heads.

Lateral pterygoid Origin:

• Upper smaller head
• Infratemporal surface
• Crest of the greater wing of the sphenoid.
• Lower larger head.
• The lateral surface of the lateral pterygoid plate.

Lateral pterygoid Insertion:

• Pterygoid fovea.
• Anterior margin of articular disc and capsule of the temporomandibular joint.

Lateral pterygoid Actions:

• Depress mandible to open mouth
• Protrude the mandible.
• Contralateral abduction.
• The superior head is active during chewing and clenching of the teeth and stabilizes the condylar head during mandibular closing.
• The inferior head assists in the translation of the condyle during jaw opening.

Lateral pterygoid Nerve supply:

• The branch from the anterior division of the mandibular nerve.

Medial Pterygoid Structure:

• It is quadrilateral
• It has a small superficial and a large deep head.

Medial Pterygoid Origin:

• Superficial head
• From maxillary tuberosity
• Deep head.
• From the medial surface of the lateral pterygoid plate.

Medial Pterygoid Insertion:

• Medial surface of angle of the mandible.
• Ramus upto mandibular foramen.

Medial Pterygoid Actions:

• Elevation and lateral positioning of the mandible
• Protrudes the mandible.

Medial Pterygoid Nerve supply:

• Branch of the main trunk of the mandibular nerve.

Question 2. Enumerate the ligaments and functions of TMJ.
Answer:

Ligaments:

1. Fibrous capsule:

• Attached above to the articular tubercle, mandibular fossa, and below to the neck of the mandible.

2. Lateral/temporomandibular ligament:

• Attached above to the articular tubercle.
• Below to the posterolateral aspect of the neck of the mandible.
• It reinforces and strengthens the capsular ligament.

3. Sphenomandibular ligament:

• It is an accessory ligament.
• It arises from the spine of the sphenoid and from the petrotympanic fissures and ends at the lingula of the mandible.
• It is a remnant of Meckel’s cartilage.

4. Stylomandibular ligament:

• It is also an accessory ligament.
• It is attached above the lateral surface of the styloid process and below to the angle and ramus of the mandible.

5. Otomandibular ligaments:

• These are discomalleolar and tympano mandibular ligaments.
• They connect callers to the TMJ disk and to the sphenomandibular ligaments.

Temporomandibular Joints Functions:

1. Protraction/forward movement of the mandible.

• During this movement the articular disc of the TMJ glides forward over the upper articular surface, the head of the mandible moving with it.

2. Retraction of mandible:

• During this, the articular disc glides backward over the upper articular surface.

3. Slight opening of the mouth.

• The head of the mandible moves on the undersurface of the disc.

4. Wide opening of the mouth.

• It is followed by protraction.

5. Chewing movements/side-to-side movements of the mandible.

Question 3. Enumerate the stages of deglutition and describe each stage.
Answer:

Deglutition:

1. Deglutition First stage – oral stage:

• The anterior part of the tongue is raised and pressed against the hard palate by the intrinsic muscle of the tongue.
• The movement takes place from the anterior to the posterior side.
• This pushes the food bolus into the posterior part of the oral cavity.
• The soft palate closes down and helps to form the bolus.
• The hyoid bone is moved upwards and forwards.
• The posterior part of the tongue is elevated upwards and backward.
• This pushes the bolus through the oropharyngeal isthmus to the oropharynx.

2. Deglutition Second stage – pharyngeal stage:

• The food is pushed from the oropharynx to the lower part of the laryngopharynx.
• The nasopharyngeal isthmus is closed by elevation of the soft palate.
• This prevents the food bolus from entering the nose.
• The inlet of the larynx is closed, this prevents.
• The food bolus from entering the larynx.
• The larynx and pharynx are elevated.
• The bolus is pushed down over the posterior surface of the epiglottis.

3. Deglutition Third stage-Oesophageal stage:

• Food passes from the lower part of the pharynx to the esophagus.
• It is brought about by the inferior constrictor of the pharynx.

Question 4. Articular capsule.
Answer:

• The TMJ is enclosed in it.

Articular capsule Attached to:

• Borders of the articulating surfaces of the mandibular fossa.
• The eminence of the temporal bone.
• The neck of the mandible.

Articular capsule Consists of:

• Internal synovial layer.
• The outer fibrous layer contains veins, nerves, and collagen fibers.

Articular capsule Nerve supply:

• Trigeminal nerve.

Articular capsule Blood supply:

• Maxillary, temporal, and masseteric arteries.

Question 5. Articular disc.
Answer:

• It is an oval fibrous plate that divides TMJ into compartments.

Articular disc Compartments:

• Upper compartments permit gliding movements
• Lover compartment – permits rotatory as well as gliding movements.

Articular disc Surfaces:

• Superior surface – concavoconvex.
• Inferior surface – concave.

Articular disc Composed of:

• Anterior extension
• Anterior thick band
• Intermediate zone
• Posterior thick band
• Bilaminar region.

Question 6. Neural control of deglutition.
Answer:

• Deglutition is triggered by afferent impulses
• These impulses arise from
  • Oral mucous membrane and pharynx
  • Posterior pharyngeal wall;
  • Soft palate and
  • Epigoltis.
• These impulses travel in trigeminal glossopharyngeal and vagus nerves.
• This stimulates a group of nerve cells located in the floor of the ventricle.
• The efferent fibers pass through motor fibers of hypoglossal) nerves to the pharyngeal musculature and the tongue.