A malocclusion is an incorrect occlusion of teeth, i.e. the manner in which opposing teeth meet. Most people have some degree of malocclusion, although it isn't usually serious enough to require treatment. Those who have more severe malocclusions may require orthodontic treatment to correct the problem.

Malocclusions can be divided mainly into three types:

Class I:
Here the molar relationship of the occlusion is normal but the other teeth have problems like spacing, crowding, over- or under-eruption, etc.

Class II:
In this situation, the upper molars are too far forwards when compared to the lower molars. This results in the entire dentition being too far forwards with/without crowding. The lower jaw may be retrognathic (ie. retruded) and perhaps the orthodontist may consider a functional appliance as a treatment modality. There are two subtypes:

Class II Division 1:
The molar relationships are like that of Class II and the anterior teeth are protruded.

Class II Division 2:
The molar relationships are class II but the central incisors are retroclined and the lateral teeth are somewhat proclined.

Class III:
Is when the lower front teeth are more prominent than the upper front teeth, ie. they are protruded. In this case the patient very often has a relatively large mandible or a small maxilla