Dental arches and contacts

Why this matters

Almost everything that goes wrong between two teeth goes wrong in a space three or four millimetres across. Interproximal caries starts there. Interdental attachment loss starts there. Food packing, the commonest complaint after a posterior filling, starts there. Every one of those is decided by four things you can measure before you ever pick up a handpiece: where the two crowns touch, how big and how tight that contact is, how the surfaces diverge into the four embrasures, and how the marginal ridges and cervical contours frame the space.

The big picture

The arch is not a row of independent posts. It is a compressed chain: each tooth is held between its neighbours, hands occlusal load forward through its contacts, and encloses with them a small tissue-filled space whose shape is set by contact position, embrasure form, marginal ridge height and cervical contour. Break one link and the whole geometry changes.

The 15 cards in this lesson

1. 01Arch form is something you measure, not a category you assign
2. 02The gum scallops because of where the teeth touch
3. 03Tapered, ovoid and square are three bins across one continuum
4. 04Arch width peaks in adolescence, then quietly shrinks for the rest of life
5. 05The contact is an area, it grows 3.5-fold front to back, and it stops enlarging in middle age
6. 06Everything on the last card, visible in one untreated mouth
7. 07Contact tightness is a number with units, and the two arches differ 1.7-fold
8. 08Contacts hand occlusal load forward, and an open contact stops the chain dead
9. 09Four embrasures open around every contact, and each one is a cleaning problem
10. 10Whether the papilla fills the gingival embrasure is a measurement, not a judgement
11. 11Marginal ridges close the top of the interproximal space
12. 12The height of contour is where the crown stops bulging and starts narrowing
13. 13Contours do not deflect food away from the gingiva — and the real mechanism is worse news
14. 14Clinical alert — in the lesson
15. 15The arch never stops moving, and the fibre story behind mesial drift is unproven

You have got it when

You can (1) state a dental arch dimension with the landmark it was measured from, and say why a bare 'intercanine width' is meaningless; (2) give the measured size of a proximal contact area at the front and the back of the arch, and say what changes between them; (3) name the four embrasures and say which one the interdental papilla occupies and at what contact-to-crest distance it stops filling it; (4) say what a…