The midline approach

This was the original method proposed when the Plus bracket was introduced, and the one used by the author (Figs 17.1–17.4). It is recommended for newcomers to the technique, since the threading is easy to see from the mesial of every bracket. The midline approach requires a preformed nickel–titanium archwire. This should be cut to length before threading, as there is no point threading an excess of wire and then having to cut off a sizeable length at the back. This can best be done by measuring the wire though the main archwire slots and cutting the ends approximately half way along the molar tubes. (When fitted in the deep tunnels, this will equate to the distal of the molar tubes.)

Fig. 17.1 The starting position (midline approach). The four incisor deep tunnels have been threaded in reverse curvature. The nickel–titanium wire is safely contained within the brackets.

Fig. 17.2 The brackets of upper right quadrant have been threaded.

Fig. 17.3 The upper left quadrant has been threaded.

Fig. 17.4 The deep tunnel wire is eased backwards into the round molar tubes (first premolar extraction case). The midline circle unwinds as it tightens and finally disappears. The rectangular main archwire can now be fitted.

Beginning at the midline, the archwire should be threaded in reverse curvature (Fig. 17.1). This means that the upper left distal end is threaded through the patient’s upper right central and lateral incisors and vice versa. Once the four upper incisors are threaded, the wire retains itself safely in position. There will of course be a large circle of surplus wire protruding at the midline at this stage. Threading backwards through the mesial of the canine and premolars is most efficiently done one side at a time, rather than alternating between sides, during which the midline loop of wire shrinks in diameter (Figs 17.2 & 17.3). Finally, as the uprighting wire is seated fully home, the midline circle ‘flips’ and disappears (Fig. 17.4). It does this as the wire de-stresses by rotating 180 degrees along its length within the deep tunnels. The preformed arch curvature has now conformed to the curvature of the patient. The main arch can now be fitted as per the next chapter.

Care should be taken not to allow the midline loop to pull too tight, as this might cause some discomfort to the patient. It may be helpful to encourage the loop to unravel in the direction it needs to go, gently, between finger and thumb. This is seldom a problem in the upper arch, since the interspace between the upper central brackets is large. In the lower, however, if tooth size is particularly small, the midline interspace may be barely adequate. In such cases, it may be expedient to modify the technique by starting the threading between the lateral incisor and canine on one side, where the inter-bracket space will be larger. Alternatively the distal approach may be preferred (see below).

The distal approach

This requires a straight length of nickel–titanium wire, without a preformed curvature. Trying it for length across the main archwire slots, the wire should be cut slightly longer than with the previous method. This is to allow the last 3 mm of one end to be annealed and bent into a small ‘safety loop’. This will be the free end, which can rest outside the patient’s cheek, without threat to the face, while the end to be threaded is inserted into the distal of the premolar bracket adjacent the molar (Fig. 17.5). Unless using a mirror, this process will be blind, but b/>