CHAPTER 17 Stage III: threading the deep tunnels
The all important difference between Plus and the Rx-1 bracket now comes into effect. Overall, Stage III remains the same in principle, whichever bracket is used. The distinction between the two is the power source for the root uprighting. Previous to Plus, individual Side-Winders did the job, generally one to each bracketed tooth, whereas with Plus, a full auxiliary archwire in the deep tunnels performs the same function. So it is a case of uprighting springs versus an uprighting wire. In this, the advantages of Plus will be quickly apparent. In retrospect, Stage III with all the springs did represent an uphill step for our patients to contend with. Although the appearance of the ‘invisible’ Side-Winders was not as conspicuous as the patients feared (unless wearing ceramic brackets) they were always aware of the coils labial to the brackets. These are also more difficult to keep clean and can become distorted by rough use. Although fitting the Side-Winders does get easier for the orthodontist with clinical experience, it is generally agreed, among those who have switched to Plus, that threading the auxiliary nickel–titanium archwire is an altogether more straightforward process. It is quicker too.
With springs, the main archwire goes in first, springs second. With Plus it is the opposite: the deep tunnels must be threaded before the rectangular archwire is fitted, for obvious reasons of accessibility. This has the advantage that if the main archwire should subsequently require adjustment for any reason, it can be removed and replaced directly without having to disturb the uprighting wire, let alone a host of springs!
While the threading of the deep tunnels will normally be at the same visit as the Stage III arches are fitted, readers will note that Dr Kesling sometimes fits the deep tunnel auxiliary at the previous appointment, at the end of Stage II, if his schedule permits. This allows uprighting to begin a little earlier, but care must be taken to ensure that the interval between appointments is kept short. Too long a timespan could allow the uprighting wire to close down the bracket slots to the point where insertion of the rectangular arch becomes difficult.
There are two accepted methods for threading the uprighting auxiliary wire. This can either be done from the mesial approach (usually from the midline) or from the distal of the last premolar. Each will be described in turn. The normal wire for this procedure will be a round .014 inch nickel–titanium, but the choice of size and specification will be discussed later in this chapter.
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. 17.4 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).
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/>