The AO & BO in Wits appraisal is relationship of:

THE WITS APPRAISAL The Wits appraisal is a measure of the extent to which the maxilla and the mandible are related to each other in the antero-posterior or sagittal plane. The Wits appraisal is used in cases, where the ANB angle is considered not so reliable, due to factors such as position of nasion and rotation of the jaws. A function occlusal plane is drawn through the overlapping cusps of first premolars and first molars. Perpendiculars are drawn to the occlusal plane from points A and B. The points of contact of these perpendiculars on the occlusal plane are termed AO and BO. The distance between points AO and BO gives the anteroposterior relation between the two jaws. In case of males, point BO is ahead of AO by 1 mm, while in case of females, the points AO and BO coincide. In case of skeletal Class II tendency, BO is usually behind AO (read as a positive reading) while in skeletal Class III pattern, the point BO is located ahead of AO (read as a negative reading).