What is the articulation of the TMJ?
Mandibular condyle and mandibular fossa of the temporal bone.
What makes the TMJ an incongruent joint?
The articular eminence and mandibular condyle are both convex!
How is the incongruence of the joint adressed?
By the articular disc being biconcave.
What is the purpose of the articular disc?
- It allows for the convex surfaces to remain congruent throughout ROM.
- Increases stability
- Minimizes loss of mobility
- Reduces friction and decreases biomechanical stress on TMJ
- Separates joint into superior and inferior joints.
What type of joint is the inferior TMJ?
Simple hinge joint
What type of joint is the superior TMJ?
Functions as a gliding joint.
What components make up the superior joint?
The superior disc and the articular eminence.
What components make up the inferior joint?
The inferior disc and the mandibular condyle.
What are the 4 attachment points of the articular disc?
- Attached to medial and lateral poles of condyles
- Attached to the joint capsule and lateral pterygoid anteriorly
- Attached to the superior lamina and inferior lamina retrodiscal pad posteriorly
What do the attachment points of the disc allow for?
- Medial and lateral poles = free rotation of the condyles on the disc in AP direction.
- Joint capsule and lateral pterygoid = restrict posterior translation of the disc.
- Superior lamina = assist disc in translating anteriorly with mandibular depression.
- Inferior lamina = limits forward translation.
What determines the available motion of the joint?
Elasticity of the joint capsule and ligaments.
What does the joint capsule look like ML and AP?
Medial/lateral = firm
Anterior/posterior = thin and loose
- Predisposes TMJ to anterior dislocation.
What are the primary ligaments of the TMJ?
- Lateral ligament = stabilizes lateral portion of the capsule. Helps guide movement!
- Stylomandibular ligament = weakest with questionable function.
- Sphenomandibular ligament = swinging hinge that suspends the mandible
What is the normal resting position of the TMJ?
Lips closed and teeth several millimeters apart.
Maintained by low level activity of the temporalis muscle.
What are the osteokinematics of the TMJ?
- Depression/elevation
- Protrusion/retrusion
- Left and right lateral excursion (deviation)
What are the arthrokinematics for depression (opening)?
Early phase = posterior roll (lower joint)
Late phase = glide anteriorly (upper joint)
What are the arthrokinematics for elevation (closing)?
Early phase = glide posteriorly (upper joint)
Late phase = rolls anteriorly (lower joint)
What are the arthrokinematics of protrusion?
Anterior and slightly inferior glide of condyle and disc.
What are the arthrokinematics of retrusion?
Posterior and slightly superior glide of condyle and disc.
Does protrusion and retrusion involve both upper and lower joints?
No!
Have no rotation that occurs with protrusion and retrusion because it only involves the upper joint.
What are the arthrokinematics for lateral excursion?
Left lateral excursion = right condyle glides anterior and to the left, while the left condyle spins.
Right lateral excursion = left condyle glides anterior and the to right, while the right condyle spins.
What is the normal value for depression of TMJ?
35-50mm
*mastication requires 18mm of depression
What is the functional screen of mandibular depression?
2 knuckles = functional
3 knuckles = normal
What is the normal value for protrusion?
3-6mm
*lower teeth surpass upper teeth
