Angle’s class I molar relationship is that the mesiobuccal cusp of the upper first molar occludes in the mesiobuccal groove of the lower first molar

Andrew’s class I molar relationship is that the distal cusp of the upper first molar occludes with the mesial marginal ridge of the lower second molar

Dr. Edward Angle described three (3) classes of malocclusion based on the occlusal relationship of the first molars. Normal relationship is described as the first molars being in the following relationship:

Class I malocclusion has the normal molar relationship but the incorrect line of occlusion

Class II malocclusion has the lower molar placed behind the upper molar. “Overbite”

Class III malocclusion has the lower molar placed forward to the upper molar. “Underbite