# Stage III: how it works

CHAPTER 14 Stage III: how it works

# How does Tip-Edge torque?

It is essential first to understand that a Tip-Edge bracket cannot be torqued by an active archwire in the conventional manner, even with a fully closed bracket slot. Examination of the design of the bracket will explain why (Fig. 14.1). The intact upper and lower finishing surfaces in each bracket (see Fig. 3.2) are offset from one another, and are therefore never directly opposed. Insertion of an actively torqued rectangular archwire will therefore elevate one finishing surface and depress the other. In effect, the torquing effort in the archwire will have dispersed, by increasing the vertical dimension within the Tip-Edge slot. The net result will be a relapse of root uprighting in the mesio-distal direction, rather than any third order torque imparted to the root (Fig. 14.2). This is known as ‘torque escape’.

Paradoxically, the selfsame bracket properties have opened new doors of possibility, allowing a new and entirely original method of torque delivery, simultaneous with tip correction. It represents a big step forward for orthodontics by relieving the rectangular wire of its double function: now the heavy base archwire becomes a passive platform, preserving three-dimensional rectangular control where necessary, while light auxiliary forces provide the flexibility to torque and tip each bracket into conformity with the archwire.

Originally, with the Rx-1 bracket, the Side-Winder spring provided the auxiliary force and this was the first time in orthodontics that an auxiliary spring, acting in the tip plane, had been shown to generate third order torque (those with an interest in the underlying mathematics are referred to Parkhouse & Parkhouse16). While the method might have appeared cumbersome, since it required a Side-Winder for each individual bracket, the Plus bracket has revolutionized Stage III by eliminating the springs altogether. Now, all torquing and tipping can be carried out more simply and less obtrusively with a nickel–titanium auxiliary archwire, threaded through the deep tunnels, beneath the overall security of a stainless rectangular main archwire. This contains t/>