Adjacent preparations separated by more than how much tooth structure should not be joined?

• A. 0.5 mm
• B. 1 mm
• C. 2 mm
• D. 3 mm

Answer: (B)

The guiding idea is that there must be enough tooth structure between two adjacent preparations to act as a solid connector for a single restoration. If the gap between them exceeds about 1 mm, the connector area becomes too slender to reliably resist occlusal forces or to provide a strong, durable bond. That makes a single, joined restoration prone to debonding, fracture, or marginal leakage. To preserve strength and minimize invasive removal, adjacent preparations separated by more than 1 mm should not be joined; instead, plan two separate restorations or adjust the preparations to reduce the separation. Small gaps, like around 0.5 mm, can often be responsibly joined, while larger separations (2–3 mm) compromise integrity and are not advisable.