Basic concepts….
	1. Space closure occurs during the first 6 months after extraction. It is best to insert the appliance as soon as possible following the exttraction. 2. Loss of space occurs primarily due to a tipping movement of teeth (mesially or distally). In the maxillary molar region, space loss occurs due to rotation (mesial-in) in conjunction with mesial tipping. 3. Erupting premolars usually require 4-5 months to move through 1mm of bone as measured on a BWXR.