Where possible, lower premolar extractions are generally avoided in Class Il/l cases, because of the need to maintain a mesial position for lower incisors. Therefore, few Class Il/l cases are treated by extraction of four premolars. If four premolars need to be taken, it is often appropriate to choose upper first premolars and lower second premolars, to assist treatment mechanics. A small number of cases may be treated to a Class II molar relationship,5 following extraction of two upper premolars (Case LJ, p. 184).
Sliding mechanics are used to retract upper incisors after premolar extractions, on a normal working steel rectangular wire. The retraction force is delivered from active tiebacks. A small amount of additional torque may need to be bent into the anterior region of the upper rectangular wire in the incisor region, and excess retraction force should be avoided. In this way, upper incisor torque control can be maintained during overjet reduction.
Appropriate anchorage support from either an upper palatal bar, a sleeping headgear, or Class II elastics may be needed (Fig. 8.12, p. 225), or from a combination of these. It is necessary to ensure that good lower arch leveling has been achieved beforehand, so that the overbite is minimal, and lower incisors will not interfere with the retraction process. Diagrams of typical treatment mechanics are shown (Figs 7.19 & 7.20) and may be seen in Case LJ on page 184.
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