Introduction
Class III cavities are, in Black's classification, cavities on the proximal surfaces of incisors and canines that do not involve the incisal angle. This topic covers the two configurations that leave the labial surface untouched: the purely proximal cavity and the proximal-lingual (proximo-palatal) cavity. Front teeth show when the patient smiles, so the labial enamel and the incisal angle are kept.
Configurations and the choice of access
The lesion starts just gingival to the contact area; with the neighbour in contact it cannot be reached directly.
- Proximal configuration – the cavity stays on the proximal surface. Indicated only with direct access: missing neighbour, diastema, the neighbouring surface prepared at the same visit, or teeth separated (wedge, separator).
- Proximal-lingual configuration – opened through the lingual (palatal) marginal ridge; the standard Class III preparation when the neighbour is in contact.
Why the lingual access is preferred
- The labial enamel is preserved – the filling and its margins are almost invisible; shade mismatch and margin staining matter less.
- The lingual embrasure is wider than the labial one in anterior teeth, so the bur reaches the lesion easily.
- Less tissue is removed and the labial surface needs no finishing.
Drawbacks: indirect (mirror) vision and harder instrumentation. Labial access is chosen for mainly labial caries, rotated or lingually placed teeth, or old labial fillings (next topic).
Open a Class III cavity from the lingual whenever possible: keep the labial enamel and keep the incisal angle supported by dentin.