Malocclusions are normally classified into three categories based on how sets of teeth such as molars (usually the lower and upper) relate to one another. This includes how your teeth align from back to front.
The classifications are:
Class I malocclusions: Dental arches may be creating too much space or become crowded. A class I malocclusion may be accompanied by overlapping teeth, or crossbites and rotations.
Class II malocclusions: Upper molars meet slightly forward to the lower molars, forcing the chin to shift backward.
Class III malocclusions: Lower molars meet forward to the upper molars, causing the chin to protrude. The lower molars are far forward and do not fit into their corresponding upper molars. A class III malocclusion may be accompanied by a crossbite.
Generally, braces are worn for as long as three years; some people respond quickly to braces, and can have them removed after only a period of a year or less. Everyone is different.