Which anatomical feature must be reproduced in a class V buccal restoration on tooth #21?

In a class V buccal restoration on tooth #21, the anatomical feature that must be reproduced is the buccal convexity. This area is critical as it contributes to the overall morphology and aesthetics of the tooth. The buccal convexity represents the natural contour and shape of the tooth, allowing it to blend seamlessly with adjacent teeth and maintain proper function and appearance.

Reproducing the buccal convexity ensures that the restoration does not create abrupt transitions or flat areas that may be unesthetic or could lead to plaque accumulation and periodontal issues. This consideration is vital for promoting long-term success and durability of the restoration while ensuring that it matches the natural tooth structure as closely as possible.

The other options include features that are either not relevant to the restoration of a class V lesion or do not primarily define the contour in the buccal aspect of the tooth. Thus, the focus remains on maintaining the natural contour of the buccal convexity during the restorative process.