Tooth development

Why this matters

Almost every anomaly you will ever be asked about — a missing lateral incisor, a peg tooth, a mesiodens, an odontogenic keratocyst in the ramus, a radicular cyst at an apex, a child who loses primary teeth with the roots still on them — is a record of something that happened to a tooth germ before the patient could speak. Tooth development is not a set of stage names to recite. It is the only reason those findings hang together, and it is the difference between a dentist who sees an isolated oddity and one who sees a developmental history and knows who to refer it to.

The big picture

One sheet of epithelium and one condensation of neural-crest-derived mesenchyme instruct each other in turn. That conversation folds the epithelium into a bud, a cap and a bell, positions the cusps, differentiates two hard-tissue-forming cell layers back to back at the future dentino-enamel junction, and then extends downwards as a root sheath.

The 15 cards in this lesson

1. 01Nothing in a tooth germ contains a plan of a tooth
2. 02The dental lamina is laid down in pieces, and it never fully leaves
3. 03One lamina, two generations, in a single human field
4. 04Bud, cap and bell are shapes. They are not dates, and the table that says otherwise is broken
5. 05Nothing new is added at bell stage — the same epithelium changes geometry
6. 06Cap stage is when a tooth germ acquires its three components
7. 07Four layers and a loop: the enamel organ labelled on human tissue
8. 08The enamel knot: a mouse structure with a human molecular counterpart
9. 09Dentine before enamel, always — and the order is not negotiable
10. 10Two cell layers, back to back, with their two matrices already stacked between them
11. 11One junction, two tissues, opposite fates for the cells that made them
12. 12The root is the crown's epithelium, stripped down and sent south
13. 13Lamina to erupted root, in one frame
14. 14The epithelium left behind is why embryology turns up in your practice
15. 15Clinical alert — in the lesson

You have got it when

You can (1) say what reciprocal epithelial-mesenchymal induction means and name the experiment behind it; (2) recognise bud, cap and bell by shape on a human section and explain why no week number attaches to them; (3) name the four layers of the enamel organ and the cervical loop; (4) state the obligatory order of differentiation and why enamel cannot form first; (5) trace the loop into the root sheath, the…