In tunnel preps, proximal caries is accessed through a sound mesial or distal pit to preserve the overlying marginal ridge and reduce iatrogenic damage. Which option best describes this prep type?

• A. Conventional prep
• B. Amalgam slot prep
• C. Tunnel preps
• D. Composite slot prep

Answer: (C)

Tunnel preps are a minimally invasive approach for proximal caries where the decay is accessed from a small entrance in a sound pit on the adjacent surface, so you can reach the lesion without removing the overlying marginal ridge. This preserves the marginal ridge and the surrounding tooth structure, which helps maintain strength and reduces the risk of iatrogenic damage such as fracture or loss of proximal contact. The description specifically matches tunnel preparation because the caries is treated through a sound pit while keeping the ridge intact. Other approaches involve removing more tooth structure or creating a slot from the side, which does not emphasize preserving the marginal ridge in the same way and is not described by the scenario.