Power chain of 3 is placed between UL 3 and 5 (Fig.7: 4.5 months post bracketing, 16x16 ss wires just placed).   The power chain is intentionally twisted in the middle to increase retraction power.  The space is 2.5 of teeth.

2 Bi Extraction Ortho

Xin Wei, DDS, PhD, MS 1st edition 07/29/2015, last revision 07/29/2015