Temporomandibular joint

Why this matters

You will load this joint every time you treat a tooth. Long appointments, wide opening, rubber dam, third molar removal, impressions and dentures all pass force and time through it, and patients present to dentists first when it clicks, locks or hurts. It is also the joint students are taught the most confidently wrong things about, so learning it accurately is partly learning how to tell a measured fact from a diagram that has been copied for sixty years.

The big picture

One bone, two joints, one disc each. The mandible cannot move on one side without moving on the other, so the right and left temporomandibular joints are mechanically a single system. Each joint is synovial, is lined by fibrous tissue rather than hyaline cartilage, and is divided by a fibrous disc into two spaces that do not communicate in an intact joint. The condyle both spins and slides, continuously and simultaneously, along a slope whose form is generally attributed to functional loading during growth.

The 15 cards in this lesson

1. 01A synovial joint lined with fibrous tissue, not hyaline cartilage
2. 02The bony surfaces: a thin hollow behind, a thick slope in front
3. 03The disc: what has been measured, and in whom
4. 04Inside the disc: aligned collagen in the middle, woven cuffs at each end
5. 05How the disc is held: poles, front and back
6. 06The superior lateral pterygoid is not the disc retractor you were taught
7. 07Retrodiscal tissue: what is measured and what is only reasoned
8. 08Capsule and ligaments: two intrinsic, two accessory, and one that may not exist
9. 09Two compartments, and why the difference is clinical
10. 10Rotation versus translation: both, from the first millimetre
11. 11Measuring jaw movement so the number means something
12. 12The muscles that drive it, and what the recordings actually show
13. 13Blood and nerve supply: four nerves, and fewer certainties than the textbooks suggest
14. 14Clinical alert — in the lesson
15. 15The anchor: two, two, two - and where the pain comes from

You have got it when

You can draw the joint in sagittal section with the disc, both compartments, the eminence and the retrodiscal tissue in the right places; you can say what the disc actually measures, by what method and in which population; you can explain why a click is a weak diagnostic sign; you can list the red flags that take a jaw problem out of the dental chair and into emergency care; and you can name which parts of the…