The mill abutment is chosen because the margin of a 5.5x7(5) mm cemented abutment is severely subgingival (Fig.4 at #3; ^ gingival margin).  By the same token, a 4.5x3 mm mill abutment is placed at #2.  In fact all of the 3 implants are placed 2-3 mm out of the bone (Fig.5).  To prevent periimplantitis, abundant allograft is placed around the implants/abutments (*).

Mill Abutments

Xin Wei, DDS, PhD, MS 1st edition 08/11/2017, last revision 08/11/2017