The anchorage provided by teeth depends on the size of the teeth, ie the root area of the teeth. Fig. 1c shows the root surface area of each of the teeth in the upper arch. The more teeth that are incorporated into an anchorage block the less likely unwanted tooth movement will occur. If a removable appliance is used, the base plate and retaining cribs should contact as many of
Fig. 1c The combined root surface area of the anterior teeth is almost the same as the molar and premolar. Attempting to move all the anterior teeth distally simultaneously will result in an equal mesial movement of the posterior teeth the teeth as possible. Figure 2 illustrates the point. If upper canines are to be retracted with a removable appliance, cribs on the first permanent molars and upper incisors will not only help with retention but also increase the anchorage considerably. In addition, the base plate must contact the mesial surface of the upper second premolars and palatal to the upper incisors. If fixed appliances are to be used, the more teeth that are bracketed or banded, the greater will be the anchorage resistance (Fig. 3).
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