During cavity preparation, the incidence of pulpal exposure is higher in class V cavities on first premolars due to the proximity of the margins to the pulp horns.

During cavity preparation, the most common area for exposure is a Class V cavity in the first premolar. A Class V cavity is a five-sided cavity that involves the gingival margin of the tooth and the proximal surface. These cavities are particularly prone to exposure because the gingival tissue in this region can be thin, and the proximity to the bone can lead to inadvertent damage during the preparation process.

In class V preparation, the pulpal wall is not present at all, as the cavity is confined to the cervical third of the tooth. It does not extend into the pulp chamber. 

In Class V restorations, which are located at the gingival third of the facial or lingual surfaces of teeth, the occlusal wall is typically wider than the gingival wall. This design helps in providing retention and resistance to the restoration, as the occlusal wall is more subject to occlusal forces.