Figure 28. Scheme illustrating a case with maxillary premolar extraction and the biomechanics for anterior retraction: height of the hook mesial to the canine allows the force action line to pass above the incisors' center of resistance. This procedure generates a anterior counterclockwise moment during simultaneous incisor retraction and extrusion. However, it is important to point out that this procedure may be more difficult to be done at the clinic, due to the possibility of injuring patient's oral mucosa.