Retentive grooves of a proximal box in a class II cavity prepared for amalgam should be:
Sharp and elongated at the dentino enamel junction of the buccal and lingual walls
Sharp and well defined extending from the gingival to the occlusal cavosurface angle along the buccal and lingual line angles
Elongated and rounded in dentine at the buccoaxial and linguoaxial Line angles extending from the gingival wall to the axiopulpal line angle
Short and rounded at the dentino enamel junction of the buccal and lingual walls