I laving set a PIP for a case, controlled upper incisor movement will be needed to reach the goal. It is helpful to plan the upper incisor tooth movements in isolation, and then consider the lower tooth movements. The lower arch may be disregarded at this stage, except as a possible source of anchorage when using Class III elastics. In the following pages, recommended MBT™ mechanics will be described for upper incisor tooth movements in Class III treatment situations.
In mild Class 111 cases, with a normal maxilla but mandibular excess, the pre-treatment upper incisor position may be close to the PIP. In this situation, the case may require relatively little movement of the upper incisors. However, in many Class III cases, there will be a requirement to move the upper incisors mesially. In some maxillary deficiency Class III cases, it can be a challenge to achieve the required mesial movement without excessive proclination. If a Class III case requires mesial movement of upper incisors, it can be achieved in two ways:
1. By proclination and mesial movement of upper incisors within the available bone (Fig. 8.18). Many Class III cases require mesial movement of upper incisors, to keep pace with the growing mandible. When upper incisors are proclined forwards, each 2.5° of proclination creates approximately 1 mm of space per side, or 2 mm in total. For this reason upper premolar extractions are not advisable in many Class III cases. If upper premolars are extracted it can be difficult or impossible to procline upper incisors.
2. By mesial movement of the maxillary bone (Fig. 8.19) as a result of normal growth or orthodontic procedures.
Fig. 8.19 Mesial movement of upper incisor crowns by mesial movement of the maxillary bone, as a result of growth or orthodontic procedures.
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