Many methods of cephalometric analysis of x-rays use soft tissue variables, but all too often the final decision is biased toward extraction based on a set of numbers developed in the 1960's. The other reason some orthodontists extract is because is simplifies treatment in their hands to the exclusion of what is best for the patient. In our office, normal profiles and a wide pleasant smile are of premiere importance. Facial muscles greatly determine where you can position teeth and have them remain stable. Lip position plays a large roll in this decision.
Full lips are more tolerant of a full smile than thin caved-in lips.
A larger chin will allow a more forward position of the teeth and high cheek bones give a basis for expansion of the molars to pick up room for alignment. Expansion of the upper arch is a main ingredient of this method. Expansion is achieved by various methods, but the bottom line is that a wider beautiful smile is accomplished. I find that much of the crowding in the lower arch is due to the lower front teeth being tipped backward as a result of eruption pattern and lip habits. A lip biting habit will tip the lower front teeth backwards as will a thumb habit.