Why are rounded internal line angles desirable in the preparation of amalgam restorations in primary teeth?

They decreases internal stresses in the restorative material. Due to the small size of primary molars and, therefore, small restorations as well, it is helpful to reduce stresses within the restorative material. It has been demonstrated that rounded internal line angles aid in reducing stress when compared to sharp internal line angles. Many of the burs recommended for use in primary molars have a rounded end to help achieve softened internal line angles.