It appears that a 14 mm long bone-level implant may be not safe (Fig.5), whereas a 13 (Fig.6) or 12 (Fig.7) mm implant appears to be fine. Prepare 4 mm implant spacer to decide the position of the starter drill and 5 mm implant positioner to determine the diameter of the prospective implant. The depth of 2 mm pilot drill will be 13 mm. Take PA with a calibrated parallel pin. Ambiguous Superior Border of Inferior Alveolar Canal Next Xin Wei, DDS, PhD, MS 1st edition 09/05/2015, last revision 05/15/2020