In a Class V cavity preparation, the depth should be shallower near the gingival margin because this area often overlies cementum or very thin dentin. Deeper preparation here risks exposing dentin or even the pulp. Maintaining a shallower depth prevents unnecessary removal of tooth structure and reduces the risk of postoperative sensitivity or pulpal damage. Adequate enamel thickness is preserved to support restoration retention and seal. This approach ensures a balance between conservative tooth structure preservation and optimal restoration durability.

Reference: Sturdevant’s Art and Science of Operative Dentistry, 7th Edition.