The tooth movement is carried out through a complex biological system, that begin when light and continuous forces, in a range between 6 and 250 grams, are delivered. The delicate balance, mediated by the periodontal ligament, between osteoclasts that destroy bone in the compression area and balanced by osteoblasts that form new bone in the opposite area under traction, determines the movement of the dental element, protecting the integrity of the alveolus. The “engine” that delivers the required force to move the tooth is, hence, the orthodontic archwire. Its features – material, size and shape – significantly affect the biological and biomechanical effects, and the forces applied during the stages of treatment are fundamental for the effectiveness of the therapy itself.
The current Straight-Wire prescriptions recommend an archwires sequence in which the first arches are always round – usually NiTi Thermal – and the force generated, activates the tooth movement mechanism, while the next archwires are often rectangular. In the first stage, however, the system archwire-brakets allows levelling and alignment movements only without delivering the torque information already built into the bracket creating, in this way, the tilt of the crowns buccally, often excessive, reducing the level of the marginal of cortical bone. Torque information is then left to the further steps through the use of rectangular archwires. In short word, in this way we often observe and excessive flaring of the crowns (Fig. A 1).
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