Cementum and periodontal ligament

Why this matters

Every tooth you will ever treat is hanging from fibres. Cementum is the thinnest and least mineralised of the three dental hard tissues, it is what root surface debridement removes, and it is added to at about two micrometres a year, far too slow to be called healing. The periodontal ligament is a fifth to a third of a millimetre of connective tissue that carries the whole load of chewing, senses it, and is the tooth's only sense organ. When acellular cementum fails to form, teeth fall out of a healthy mouth. When the ligament is lost, the tooth ankyloses and stops behaving like a tooth.

The big picture

Two mineralised surfaces that never touch, bridged by fibres embedded at both ends. Cementum exists to bury one end of those fibres; the ligament holds the other end, feeds the tissue, senses the load and supplies the cells that repair it. Everything else in this lesson is a consequence of that one arrangement.

The 15 cards in this lesson

1. 01A tooth is suspended in its socket, not cemented into it
2. 02One low-power field contains the whole argument
3. 03Cementum is classified on two axes at once, not one
4. 04The two cementums drawn with their fibres, not just their cells
5. 05Cervical cementum is thinner than paper; molar cementum can exceed a millimetre
6. 0665 / 23 / 12 has to be a weight triple, and you can prove it in one line
7. 07The attachment is built fibre-first, then buried in mineral
8. 08The sheath must break before anything can attach
9. 09Four studies, four species labels, and no human answer is possible
10. 10Cementum grows for life, at roughly two micrometres a year
11. 11The principal fibres are one continuous system, bone to cementum
12. 12The ligament is a cell reservoir, not just a set of ropes
13. 13The ligament is the tooth's sense organ, and an implant does not have one
14. 14Clinical alert — in the lesson
15. 15Cementum can be resorbed and repaired, but it is not remodelled

You have got it when

You can name the four cementum types you must know on both of Schroeder's axes, say why the grid has a fifth cell, and say which type attaches anything; state cementum thickness with its study, site and method rather than as one number; prove from densities alone that 65 / 23 / 12 must be a weight triple; name the principal fibre groups and say which carries axial load; explain why an implant cannot feel a bite; and…