Which of the following statements about an amalgam tooth/cavity preparation is true?
Although the amalgam margin must be 90 degrees, the enamel margin may not be 90 degrees, especially on the occlusal surface. Most walls converge occlusally, but many Class V amalgam preparations have walls that diverge externally. No retention form should be placed at the DEJ; otherwise, the adjacent enamel will be undermined and subject to fracture.
The enamel cavosurface margin angle must be 90 degrees.
The cavosurface margin should provide for a 90- degree amalgam margin.
All prepared walls should converge externally.
Retention form for Class Vs can be placed at the DEJ.