The human maxilla and mandibular each hold sixteen teeth. In the position of maximum intercuspidation, i.e. when the upper and lower teeth are in contact, each one occludes against two antagonist teeth, except for the lower central incisors and the final upper molars, which only occlude against one other tooth. The whole upper group externally overlaps the lower group and all the teeth of the upper group are in a more distal position, i.e. further back than the lower group, such that the upper canine occludes between the lower canine and first premolar. In normal occlusion, defined by Angle, the mesiobuccal cusp of the upper first molar fits into the buccal groove of the lower first molar (29)(30).