TMJ and Muscles of Mastication Flashcards
What are the main parts of the mandible?
Body
Ramus
Angle
Coronoid process
Condylar process - head and neck
What is the mandibular symphysis?
Mandible is in 2 parts during development
This is where the parts are fused
Where is the mental foramen found?
Inferior to the first and second premolars
What is the mandibular fossa and where is it found?
Where the mandible articulates with the skull
Found in the temporal bone, anterior to the external acoustic meatus and near the zygomatic arch
Where does the TMJ articulate?
Mandibular fossa of the temporal bone and the condylar process of the mandible
What type of joint is the TMJ?
Modified hinge (atypical) synovial joint
What type of cartilage is found in the TMJ?
Fibrocartilage
Describe the cavities of the TMJ?
Fibrocartilaginous articular disc separates the joint into superior and inferior articular cavities
What are the ligaments of the TMJ?
2 extrinsic:
Sphenomandibular ligament
Stylomandibular ligament
1 intrinsic:
Lateral ligament
What do the TMJ ligaments do?
Connect the mandible to the cranium
What is the function of the sphenomandibular ligament and where does it run?
Provides primary passive support of the mandible and acts as a fulcrum for the TMJ
Runs from spine of the sphenoid bone to the lingula of the mandible
What is the function of the stylomandibular ligament and where does it run?
It’s technically a thickening of the capsule of the parotid gland - doesn’t contribute to strength
Runs from styloid process to angle of the mandible
What is the function of the lateral ligament and how is it formed?
Strengthens TMJ laterally and acts to prevent posterior dislocation of the joint together with the postglenoid tubercle
Formed by thickened part of the joint capsule
What are the 5 mandibular movements at the TMJ?
Protrusion
Retraction
Elevation
Depression
Lateral movements
Describe protrusion of the TMJ and name the muscles its actioned by
Gliding movements between temporal bone and articular disc in the superior cavity
Actioned by lateral pterygoid, masseter and medial pterygoid
Describe retraction of the TMJ and name the muscles its actioned by
Gliding movements between the temporal bone and articular disc in the superior cavity
Actioned by posterior fibres of temporalis, masseter and geniohyoid and digastric
Describe elevation of the TMJ and name the muscles its actioned by
Hinge and rotational movements between head of mandible and articular disc in the inferior cavity
Actioned by the temporalis, masseter and medial pterygoid
Describe depression of the TMJ and name the muscles its actioned by
Hinge and rotational movements between head of mandible and articular disc in the inferior cavity
Actioned by gravity, digastric, geniohyoid and mylohyoid
Describe lateral movement of the TMJ and name the muscles its actioned by
Grinding and chewing
Actioned by the temporalis on the same side and the pterygoids on the opposite side with support from the masseter
When is the TMJ most unstable and why is this?
During depression as the condylar processes move anteriorly and lie underneath the articular eminences with the mandibular head being vulnerable to anterior dislocation into the infratemporal fossa
Describe anterior dislocation of the TMJ
Heads of the mandible may be dislocated anteriorly so they pass anterior to the articular tubercles through excessive contraction of the lateral pterygoids
Describe posterior dislocation of the TMJ
Uncommon as it is resisted by the postglenoid tubercle and the strong intrinsic lateral ligament
Describe arthritis of the TMJ
TMJ becomes inflamed and resultant abnormal function of the TMJ may cause structural problems such as dental occlusion and joint clicking (crepitus)
Which pharyngeal arch are the muscles of mastication derived from?
1st pharyngeal arch
Where does the temporalis originate and insert?
Originates from temporal fossa and fascia
Inserts at coronoid process of mandible and anterior border of ramus near last molar
What is the function of the temporalis?
Retracts and elevates the mandible
Assists in closing the mouth
Where does the masseter originate and insert?
Originates from maxillary process of zygomatic bone and anterior 2/3 of inferior border of zygomatic arch
Inserts at the angle and lateral surface of ramus
What is the function of the masseter?
Elevates the mandible
Where’s does the lateral pterygoid originate and insert?
Originates from infratemporal surface of greater wing of sphenoid bone and lateral surface of lateral pterygoid plate
Inserts on the front of the neck of the mandible
What is the function of the lateral pterygoid?
Protrudes the mandible
Assists medial pterygoid with lateral movements
Depresses the mandible
Where does the medial pterygoid originate and insert?
Originates from medial surface of lateral pterygoid plate and maxillary tuberosity and pyramidal process of palatine bone
Inserts into medial surface of the ramus and angle of mandible
What is the function of the medial pterygoid?
Elevates the mandible and assists with lateral movements
