After extraction of the oval-shaped residual roots at #12 (Fig.1), osteotomy is initiated in the palatal socket for 18 mm; since the root of the canine curves distal (Fig.2 red dashed line), the osteotomy cannot afford to move mesial and extend more apical.
Xin Wei, DDS, PhD, MS 1st edition 08/25/2018, last revision 11/10/2018