D1 = 0.48 g/cc, dense cortical bone.
D2 = 0.32 g/cc, dense to thick, porous cortical bone on the crest and coarse trabecular bone.
D3 = 0.16 g/cc, thin, porous cortical bone on the crest and fine trabecular bone.
D4 = 0.08 g/cc, minimal to no crestal cortical bone.