Normal Disc–Condyle Relationship
The disc caps the condyle in stable centered alignment.
- 12 o'clock: Disc position at rest (over condyle apex)
- ~3 mm: Posterior band thickness (thickest disc region)
- None: Joint clicking (smooth translation)
- ~70%: Normal joints (adults) (asymptomatic population)
Disc anatomy
Biconcave fibrocartilage disc cushions condyle against fossa.
Bilaminar zone
Elastic posterior tissue tethers the disc in place.
Smooth translation
Condyle and disc glide together during opening.
Healthy discs move as one unit with the condyle.
Anterior Disc Displacement
Disc slips forward off the condyle at rest.
- ~30%: Displacement prevalence (of general population)
- Anteromedial: Displacement direction (most common pattern)
- Bruxism: Common risk factor (clenching & grinding)
- 4:1: Female:male ratio (higher in women)
Posterior band tear
Retrodiscal ligament stretches and disc migrates forward.
Lateral pterygoid pull
Muscle traction drags disc anteromedially over time.
Often silent
Displacement can exist without pain or noise.
Many displaced discs cause no symptoms at all.
Condylar Translation During Opening
Condyle slides forward while the disc stays displaced.
- 40–50 mm: Normal max opening (interincisal distance)
- 0–11 mm: Rotation phase (pure hinge movement)
- >11 mm: Translation phase (condyle leaves fossa)
- <35 mm: Restricted opening cutoff (suggests joint pathology)
Two-phase motion
Jaw opening combines rotation then forward translation.
Condyle chasing disc
Condyle moves anteriorly toward the displaced disc.
Deflection pattern
Jaw may deviate toward the affected side.
Uneven translation causes visible jaw deflection on opening.
Disc Reduction & the Opening Click
Condyle catches back under the disc with a click.
- Early–mid: Click timing (opening trajectory)
- Recapture: Click mechanism (condyle passes posterior band)
- DDwR: Diagnosis term (displacement with reduction)
- On closing: Reciprocal click (as disc re-displaces)
Audible catch
Condyle snaps under the disc's thinner center.
Reciprocal clicking
A second click often occurs while closing.
Palpation finding
Clinicians feel the click over the joint.
A single opening click signals reduction, not damage.
Non-Reducing Disc Displacement (Locking)
Condyle can't recapture the disc, opening stays restricted.
- DDwoR: Diagnosis term (displacement without reduction)
- ~25–30 mm: Typical opening limit (hard end-feel)
- Toward affected side: Deflection (no straight opening)
- Disc deformation: Chronic outcome (biconvex or folded shape)
Mechanical block
Deformed disc physically blocks condylar translation.
Click disappears
Locking often follows a history of clicking.
Treatment options
Physical therapy, splints, or arthrocentesis may help.
Sudden loss of clicking can mean the disc stopped reducing.