Introduction
Class IV cavities are, in G. V. Black's classification, cavities on the proximal surfaces of incisors and canines that include the incisal angle. The angle is loaded in biting and protrusion and is in full view, so the preparation must give retention and strength while keeping the margin invisible.
Definition and configurations
Class IV: a proximal lesion of an incisor or canine that has destroyed or undermined the incisal angle. With the angle intact, the same lesion is Class III.
It arises when a Class III lesion undermines the angle, when the angle breaks off, or when a large Class III filling fails (fractures of the incisal edge itself are the next topic). The configuration depends on:
- side – mesioincisal or distoincisal; both angles can be lost on one tooth;
- size – small: the angle and part of the incisal third, margins in enamel; large: reaching the middle or cervical third, with much of the incisal edge and dentin lost;
- lingual extension – a simple proximo-incisal cavity, or one extended onto the lingual surface when caries or the fracture spreads there (classically also a lingual dovetail for retention).