[Wannabe]

The "crease" is basically a right angle at the bottom of the breast. I'm no medical expert, but in my observation many people who use suction-style devices and such for breast development starting with a fairly flat chest do not always develop one. Sometimes the breast simply slopes up from the bottom just as it slopes down from the top.

As I understand it, bra wearing can help develop this more right angled appearance. I believe that wearing a well fitting bra during breast growth should help the formation of such an angle.