Bone density is so high at #21 that 4.5x8.5 and 4.5x10 mm drills are used before placement of a 4.5x10 mm with 12 mm offset in addition to use of cortical tap and back up of the implant several times (Fig.2).
Xin Wei, DDS, PhD, MS 1st edition 09/09/2019, last revision 09/09/2019