TMJ biomechanics

What TMJ disorders are + presentation

Definition	Presentation
Group of MSK conditions	Pain Joint sounds ( clicking )  +/- locking

Planes + main + subtle mvmts at TMJ

Planes of mvmt for mandible	Main movements at TMJ	Subtle mvmt at TMJ
Sagittal: open + close  Transverse: protrusion/ retrusion  Coronal ( laterotrusion )	Rotation hinge like mvmt in lower joint cavity  Translation gliding like mvmt in upper joint cavity	Pivot around vertical axis  Pivot around AP axis

Opening + closing TMJ biomechanics

Opening + closing

Opening:  Anterior rotation  Anterior translation  Small amount of anterior rotation + ongoing anterior translation  → bilateral L=R  → articular disc moves w/ condyle [ through superior fibres of lateral pterygoid ]  Closing:  Posterior rotation  Posterior translation  Small amount of posterior rotation + ongoing posterior translation → disc pulled back by elastic fibres of retrodiscal tissue

Protrusion/ retrusion TMJ biomechanics

Protrusion + retrusion

Protrusion:  Bilateral anterior translation  → disc + condyles move forward tgt  Retrusion:  Bilateral posterior translation

Laterotrusion TMJ biomechanics

Laterotrusion

to L R condyle translate anteriorly w/ small degree of inferior + medial rotation  L condyle pivots posteriorly

Presentation of TMJ + MOI

1. Pain around jaw + ear + temple 

2. Mechanical jaw symptoms ( e.g. clunking, locking, catching, crepitus ) 

3. Altered jaw biomechanics 

4. Psychosocial + functional implications

Can be unilateral/ bilateral ( X same symptoms on both sides e.g. pain on R side + clicking on L side )

MOI:

1. Traumatic/ sudden onset 

2. Atraumatic/ gradual onset → e.g. stressful period → grinding + clenching more

Co-morbidity of TMD

Cervical issues 

→ different degrees of contributions to pain from jaw + cervical

Types of TMD

Types

Intra-articular TMDs ( Involves TMJ complex )  —> Disc displacements, degenerative joint disease, subluxation

Pain-only TMDs  —> Myalgia: pain on palpation of masticatory muscles ) , arthralgia( pain on palpation of the TMJ ), TMJ related headaches

Differences between Anterior disc displacement w/ reduction  + w/o reduction

	Location of disc before opening mouth	Location of disc after opening mouth
W/ reduction	Anterior to condyle	On top of condyle ( normal )
W/o reduction		Anterior to condyle

Presentation + biomechanics of Anterior disc displacement w/ and w/o reduction

Presentation	Biomechanics
Deviation on opening  → lack of anterior translation on the start ( swing towards affected side )  Mid-range click →caused by reduction of disc	Condyle rotates forwards + disc is anterior to condyle  → reduction of disc as condyle translates anteriorly onto the disc
Deflection on opening → swing towards affected side + stay on that side  Significantly limited opening range Closed lock	Disc stays anterior to condyle throughout early rotation to mid-late translation