16 - TMJ and muscles of mastication Flashcards
What is the function of the mandible?
- site for muscle attachments
- foramina for passage of neuromuscular structures
- teeth in alveolar processes
What is the mandibular symphysis?
Fused bone, as the mandible is in two parts when born
Describe the location of the TMJ.
- articulates in the mandibular fossa of temporal bone
- condylar process of the mandible
Describe the TMJ.
- modified hinge (atypical) synovial joint
- articular surfaces covered in fibrocartilage (not hyaline)
- fibrocartilaginous articular disc separates joint into superior and inferior articular cavities
Describe the ligaments associated with the TMJ.
- 2 extrinsic and 1 intrinsic
- connect mandible to cranium
- sphenomandibular ligament
- stylomandibuiar ligament
- lateral ligament
What is the role of the sphenomandibular ligament?
- primary passive support of mandible
- helps swing mandible
- attaches from the spine of the sphenoid bone to the lingula
What is the role of the stylomandibular ligament?
- thickening of the parotid capsule
- doesn’t contribute to strength
- attaches from the styloid process to the angle of the mandible
What is the role of the lateral ligament?
- strengthen TMJ laterally
- works with the postglenoid tubercle to prevent posterior dislocation
What are the 5 movements of the mandible?
- protrusion
- retraction
- elevation
- depression
- lateral
What muscles aid protrusion of the mandible?
Lateral pterygoid (assisted by medial pterygoid)
What muscles aid retraction of the mandible?
- posterior fibres of temporalis
- deep part of masseter
- geniohyoid
- digastric
What muscles aid elevation of the mandible?
- temporalis
- masseter
- medial pterygoid
What muscles aid depression of the mandible?
- digastric
- geniohyoid
- mylohyoid
- (infrahyoid muscles work to fix the hyoid so that the mandible opens against resistance)
- (gravity)
What muscles aid the lateral movements of the mandible?
- ipsilateral temporalis
- contralateral medial and lateral pterygoid
- masseter
Which cavity of the TMJ is active during protrusion?
- superior cavity
- gliding movement between temporal bone and articular disc
Which cavity of the TMJ is active during retraction?
- superior cavity
- gliding movement between temporal bone and articular disc
Which cavity of the TMJ is active during elevation?
- inferior cavity
- hinge and rotational movement between head of mandible and articular disc
Which cavity of the TMJ is active during depression?
- inferior cavity
- hinge and rotational movement between head of mandible and articular disc
What type of dislocation is most common in the TMJ?
Anterior dislocation
What causes dislocation of the TMJ?
- excessive contraction of lateral pterygoid
- adequate posterior support
- poor anterior support and no stop for head of condyle
What nerve supplies the muscles of mastication?
CN V3
What is the origin of temporalis?
Temporal fossa and fascia
What is the origin of masseter?
Maxillary process of zygomatic bone and anterior 2/3 of inferior border of zygomatic arch
What is the origin of medial pterygoid?
Deep head - medial surface of lateral pterygoid late (sphenoid bone)
Superficial head - pyramidal process of palatine bone
What is the origin of lateral pterygoid?
Upper head - infratemporal surface of great wing of sphenoid bone
Lower head - lateral surface of lateral pterygoid plate (sphenoid bone)
What is the insertion of temporalis?
Coronoid process of mandible and anterior border of ramus
What is the insertion of masseter?
Angle and lateral surface of ramus
What is the insertion of medial pterygoid?
Medial surface of mandible and angle
What is the insertion of lateral pterygoid?
Upper head - capsule of TMJ and articular disc
Lower head - pterygoid fovea
What is the action of temporalis?
Retracts and elevates mandible
What is the action of masseter?
Elevate mandible
What is the action of medial pterygoid?
Elevate and assist with lateral movement of mandible
What is the action of lateral pterygoid?
Protrude, depress and assist with lateral movement of mandible
