Classification of Teeth

Tooth bites are divided into three main classes, which are Class I, Class II, and Class III.

Class I:

This is where the bite is balanced. There is a normal interaction between the jaws and the lower and upper teeth.

Class II:

This class exhibits an abnormal relationship of the jaws and excessive overjet of the teeth. Here, the top front teeth and jaw protrude forward more than the bottom front teeth and jaw. A feature of this abnormality manifests in a convex profile with a retruded chin and everted lower lip. Although this condition can be caused by excess forward position of the top jaw, it is generally due to insufficient growth of the bottom jaw.  Generally, Class II conditions can be genetically acquired, and environmentally worsened by certain habits e.g. thumb sucking. The treatment of Class II malocclusions is best performed in two phases where the lower jaw is brought forward early in growth (age 6 to 9) and the alignment of teeth is corrected from age 11 to 13. 

Class III:

Class III conditions are the opposite of Class II conditions. Here, there is also an abnormal relationship of the jaws but in this case, the bottom jaw protrudes forward more than the top jaw. This manifests as a concave profile with a protruding chin and/or a midface deficiency. This condition is caused by excess growth of the bottom jaw, insufficient growth of the top jaw, or a combination of both. Most cases can be treated early by addressing the underdevelopment if the upper jaw with expansion and protraction (headgear); treatment is benefitted greatly by two-phase treatment.  Phase I is best started at age 6 to 8 with expansion and protraction headgear then Phase II is completed with braces later from age 12 to 14 depending on growth. This malocclusion can be genetically acquired but can also be a result of early airway obstructions from chronic allergies and soft-tissue inflammation. Without early treatment, many of these patients will require facial surgery to correct later.