Class I Occlusion (ideal bite)

In a class I occlusion, or class I bite, the front cusp of the upper molars fit between the cusps of the lower molars (shown to the left with arrows). The upper canines fit between the cusps of the lower canines and first premolars. Basically, the upper cusps of the upper back teeth fit between the cusps of the lower back teeth and the upper front teeth fit just in front of the lower front teeth. 

Class II Occlusion (overjet, or overbite)

In a class II occlusion, or class II bite, the upper teeth are forward from where they should be compared to the lower teeth. This usually results in the upper front teeth being tipped forward, which gives a "bucked teeth" look. In orthodontics we call this an overjet, although it is often referred to as an overbite. Class II occlusions are the most common malocclusion, or bad bite, in the United States.

Class III Occlusion (underbite)

In a class III occlusion, or underbite, the lower teeth are positioned forward from where they should be compared to the upper teeth. Typically this causes the upper incisors (front teeth) to be in front of the lower incisors. 

Class III Occlusion (underbite)

In a class III occlusion, or underbite, the lower teeth are positioned forward from where they should be compared to the upper teeth. Typically this causes the upper incisors (front teeth) to be in front of the lower incisors.