In a Class II preparation, the outline form extends onto proximal surfaces with a proximal box.

• A. Only occlusal surfaces.
• B. Proximal surfaces with a proximal box.
• C. Buccal surfaces with a bevel.
• D. Root surfaces.

Answer: (B)

In this situation, the key is that a Class II preparation involves the proximal surface of a posterior tooth. To restore function and maintain the contact with the adjacent tooth, the outline form must extend onto the proximal surface and include a proximal box. The proximal box provides access to the decay or margin, creates space for recreating the proximal contact, and establishes the proper shape for the restoration so the matrix can be placed and the final contours align with the adjacent tooth. Without the proximal box, you cannot reliably restore contact or contour on the proximal aspect, which is essential in a Class II. Choices that keep the outline limited to occlusal surfaces, focus only on buccal margins with a bevel, or address root surfaces do not address the proximal lesion and the need to recreate proximal contact, so they aren’t appropriate for a Class II preparation.