Answer:
(From the Grabb and Smith CD-ROM:)
As succinctly stated by physician and dentist Edward H. Angle in 1898, “The key to occlusion is the relative position of the first molars. In normal occlusion, the mesiobuccal cusp of the upper first molar is received in the buccal groove of the lower first molar. This positioning is Angle’s class I.
With class II malocclusion the lower first molar is located distal to this relation; with class III malocclusion the lower first molar is located mesial to this relation. The Angle classification of malocclusion describes the relation of the teeth but does not indicate the cause. Class III malocclusion may be caused by mandibular prognathia, maxillary retrognathia, or a combination of the two.
Crossbite: An abnormal buccolingual relation of the teeth. Anterior crossbite is lingual crossbite of the upper incisors. Posterior crossbite is buccal crossbite of the maxillary premolars and molars.
Overbite: Vertical overlap of the incisors, where the upper incisors are in a lower than normal position.
Overjet: Horizontal overlap of the incisors, where the upper incisors are positioned anterior to their normal position.