Which is the recommended characteristic of internal line angles in amalgam preparations?

• A. They should be sharp
• B. They should be rounded to reduce stress concentration
• C. They should be perpendicular to margins
• D. They should be ignored

Answer: (B)

Rounded internal line angles reduce stress concentration in an amalgam preparation. When two walls meet at a sharp corner inside the cavity, that junction becomes a focus for occlusal stresses, which can initiate cracks in enamel or dentin and weaken the restoration. By shaping the internal angles with smooth, rounded curves, the forces from chewing are distributed more evenly throughout the cavity and the restoration, lowering the risk of fracture and improving the longevity of the restoration. This also helps with better condensation and adaptation of the amalgam, reducing the chance of marginal leakage. Sharp angles would act as stress risers, and simply orienting angles perpendicular to margins or ignoring them would not provide the necessary mechanical benefit.