When the axis of the immediate implant at the site of #15 is changed according to the opposing dentition (Fig.2 (sagittal section through the buccal roots): #18), the implant could be 3 mm shorter (e.g., 6x11 mm). The 1st 5 mm of this short implant has no threads. It appears that all of threads are buried inside the socket.
Xin Wei, DDS, PhD, MS 1st edition 05/16/2015, last revision 05/16/2015