Orthodontic malocclusions are classified based on the position of the teeth and the ratio of the jaw bones. There are basically 3 horizontal facial types; class 1 growth types, class 2 growth types, and class 3 growth types. Any of these 3 types can have an increased, neutral, or decreased vertical facial height component. Being three-dimensional, the final consideration is transversal (width).
A normal bite (the fringe indicates the alignment of the molars), Class I is a normal ratio between the upper and lower teeth and the jaws, or a balanced bite. Class II is where the first lower molar is posterior (or more toward the back of the mouth) than the first upper molar. In this abnormal relationship, the upper front teeth and jaw project further forward than the lower teeth and jaw. There is a convex appearance in the profile with a retracted chin and lower lip.
Class II problems may be due to undergrowth of the lower jaw, overgrowth of the upper jaw, or a combination of both. In many cases, Class II problems are genetically inherited and can be aggravated by environmental factors such as finger licking. Class II problems are treated by redirecting growth to harmonize the upper and lower teeth and jaws. Class III is where the first lower molar is anterior (or more toward the front of the mouth) than the first upper molar.
In this abnormal relationship, the lower teeth and jaw project further forward than the upper teeth and jaws. There is a concave appearance to the profile with a prominent chin. Class III problems are usually due to overgrowth in the lower jaw, a weed of the upper jaw, or a combination of both. Like class II problems, they can be genetically inherited.
It is not enough to categorize orthodontic malocclusions based solely on a classification of teeth.