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Flexible bows, such as the Roberts' retractor, are most suitable where a large overjet has to be reduced. When the amount of retraction is small but minor irregularities need to be corrected (and perhaps over-corrected) a less flexible bow may be preferred because it is more precise in its action and needs only a small amount of activation. 19). A coil is placed at the point of emergence of the wire from the tubing. The tubing emerges from the baseplate distal to the canines. The horizontal section of the bow is bent into the smooth curve to which the incisors should conform.

3 An example of reciprocal anchorage where an upper arch is being expanded. ) Anchorage 41 to provide a point of attachment for intraoral elastics, which deliver a force to the anterior aspect of the upper fixed appliance. The reciprocal force is distributed evenly to the lower arch. The method offers the advantage that a removable appliance can be fitted quickly and long before it would be possible to fit a lower fixed appliance and progress to sufficiently rigid archwires to accept class II traction.

Chapter 11 covers the use of removable appliances as retainers. Appliance retention is provided by wires, in the form of clasps and bows. Good retention is essential if treatment is to proceed efficiently and needs to be planned carefully. This is particularly important if headgear is to be worn with the appliance. Even where retention is good it is prudent to reduce to a minimum any forces that tend to displace the appliance. Examples of such forces might be springs acting on cuspal inclines, extraoral force applied in a downward direction, or rocking of the appliance due to contact of the lower incisors upon an excessively undercut anterior bite plane.