This 15 year old boy had severe crowding and had 4 bicuspids extracted in order to align and fit the remaining teeth properly.

This 14 year old girl had severe crowding in the lower teeth a lower incisor was extracted. Note the blanching of the gums of the lower canines. Any attempt to straighten the lower teeth without extracting any teeth might force the roots of the lower teeth out of the jaw bone causing gingival recession and gum issues.