One month of open coil spring between UR1 and 3 (18 ss), power chain is placed with 3 loops between UR2 and 3 and 5 loops between UR 1 and 2 (Fig.21, sling shot). 

Severe Crowding

Xin Wei, DDS, PhD, MS 1st edition 02/18/2017, last revision 03/11/2017