What occlusion would a patient have if they had a chin which is unduly prominent, caused by the mandible being too far forward relative to the maxilla?

• A. Class I
• B. Class II
• C. Class III
• D. Open bite

Answer: (C)

The position of the lower jaw relative to the upper jaw defines the occlusion pattern. When the mandible is too far forward, the bite becomes a Class III malocclusion. This forward-positioned lower jaw often produces an anterior crossbite and a negative overjet, so the lower teeth bite ahead of the upper teeth. The chin may look prominent because the lower jaw sits ahead of the maxilla. In terms of the dental relationships, the lower first molar is mesial (in front of) the upper first molar, which is characteristic of Class III.

This differs from normal alignment (Class I), where the jaws are in harmony; from Class II, where the mandible is retruded relative to the maxilla; and from an open bite, which is defined by a lack of vertical overlap rather than forward-forward jaw positioning.