Low-friction systems allow shifting (swivelling) of the archwire, particularly if initially very thin wires are used during the leveling and alignment phase. This is a very common occurrence in an orthodontic practice and is often the reason for emergency appointments, as it can lead to pronounced soft-tissue irritation ( Fig. 8.7 ). Shifting of larger archwires can lead to distortion of the dental arch and arch asymmetry. It is therefore very useful to stop the archwires from shifting and sliding freely in the brackets. Table 8.3 summarizes the methods and materials necessary to prevent shifting of archwires.
Annealing. Annealing the distal ends permanently changes the elastic properties of the archwires, as they become formable. This is particularly useful for modern superelastic alignment wires. A conventional cigarette lighter or a blowtorch can be used for this. Following annealing at the desired spot, the wires are cinched back. It appears advisable to turn the ends lingually rather than to the gingival side, as this may prevent trauma to the gums and patient discomfort.
Changing the archwire shape. The shape of a superelastic archwire can be changed without permanently altering its physical properties by using devices such as the Memory Maker, which warms up the archwire in a controlled way using an electric current. This can be applied either to the entire archwire or only to a section of it. During the warming, the archwire can be permanently deformed using appropriate pliers; the original mechanical properties of the wire itself will not change, however. This is particularly useful for initial alignment wires.
Permanent deformation using special instruments. A number of instrument manufacturers offer special instruments for bending wires back, such as hammerhead pliers (originally developed by Hu-Friedy, Inc.). Tuckers can also be used to permanently deform archwires, as can bird-beak pliers, and with some limitations, Weingart pliers as well. However, these tools work best if the wires have previously been annealed—particularly with superelastic wires. Turning archwires back without annealing them is usually only possible with stiff nonresilient wire types such as stainless steel and titanium–molybdenum alloy (TMA).
Application of stops. To secure an archwire’s position, the cinch-back bend should be placed bilaterally, distal of the most distal bracket or tube. Annealing and cinching archwires can be time-consuming, uncomfortable for the patient, and may also lead to inadvertent debonding of brackets, especially when molar tubes are used and the bends are made intraorally. Often, archwires need to be inserted intraorally, cut to size, removed, and then annealed before they can be reinserted and cinched. Cinched archwires can be difficult to remove, as the bent ends usually have to be cut off first. An alternative method is to use stops, which should be placed mesial and distal to a bracket. This prevents shifting of the archwire in a predictable way and at the same time allows the archwire to be removed easily. A number of prefabricated crimpable stops are available on the market. They can be picked up with either ligature cutters or specific crimping pliers. The stops are placed over the archwire using these instruments and then crimped down. A number of manufacturers produce these stops so that the inside is serrated or roughened, which gives them a more secure grip. However, crimpable stops work best on rectangular archwires. They often still slip on small round wires. An alternative to using crimpable stops is to apply light-cured composite on the archwire. It is also sometimes advisable to add composite to a crimpable stop, as these can sometimes feel rough to the patient. Composite is used to give the stop a smooth surface and secure it at the same time. Both of the above composite techniques are suitable for all types and sizes of archwire.