They are different methods for reshaping the forehead.
type 1 is usually the least invasive procedure, where as type III is the most invasive procedure which usually involves removing the frontal sinus bone, reshaping it and then re-attaching it to the skull.
What type you need is usually based on how thick the sinus bone is. To make matters even more fun, certain surgeons will have varying opinions on which is the most effective and safe.