Reasons for severe or moderate malocclusion include disproportionate sizes of the two jaws on the one hand and that between tooth size on the other or that between the respective sizes of the upper and lower jaw.
Type 2 is known as retrognathism. This occurs due to the overbite caused due the teeth in the upper jaw overlapping the teeth in the lower jaw.
Type 3 is known as prognathism. In this condition, the lower jaw protrudes more than the upper jaw does so that the lower teeth extend over the upper teeth. This results in an underbite.