Article
Pre-adjusted edgewise appliances with an MBT prescription, have −6° of labial root torque, which is advantageous in the treatment of Class II cases where the use of Class II intermaxillary traction can lead to lower incisor proclination, which is often best avoided because it may place the lower incisors in unstable positions and compromise aesthetics.
In contrast, when treating Class III incisor relationships, one approach is to remain in round wires in the lower arch. This prevents the creation of a force couple in the rectangular bracket slots, which may move the typically lingually inclined lower incisor crowns in a labial direction. This would compromise camouflage of the Class III incisor relationship.
The use of a round wire eliminates torque expression through the entire arch including the buccal segments. The crowns of the lower molars in Class III cases are often lingually inclined: an attempt by the dento-alveolar compensatory mechanism to achieve an adequate occlusion. Correcting the torque of these buccal segment teeth may in fact be a specific treatment goal, but it cannot be achieved if only round wires are used.
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