Sliding mechanics with light forces

In 1990, a method of controlled space closure was described3 using sliding mechanics. This has proved effective and reliable for many years, and has seen widespread acceptance by-clinicians. The authors recommend the following technique:

• Archwires. Rectangular 019/.025 steel wires ('working wires') (Fig. 9.15) are recommended with the .022 slot, because this size of wire gives good overbite control while allowing free sliding through the buccal segments. Thinner wires tend to give less overbite and torque control. Thicker wires sometimes restrict free sliding of molars and premolars.

• Soldered hooks. The authors continue to prefer 0.7 soldered brass hooks. Soft stainless steel 0.6 soldered hooks can be a useful alternative, and some adult patients prefer the appearance of these. The most common hook positions are 36 mm or 38 mm (upper) and 26 mm (lower), measured along the line of the arch (Fig. 9.16).

T he authors find that the 26 mm lower hook position fits a high percentage of cases, but there is greater variability in hook positions in the upper arch, due to tooth size variation among upper lateral incisors. Therefore, a wider range of upper hook sizes needs to be stocked.

Fig. 9.13 Over-stretched elastic chains can cause unwanted rotations.

• Passive tiebacks. Before starting space closure, it is recommended that the rectangular steel .019/.025 wires be left in place for at least 1 month with passive tiebacks (Fig. 9.17). This allows lime for torque changes to occur on individual teeth and for final leveling of the arches, so that sliding mechanics can proceed smoothly when active tiebacks are placed.

• Active tiebacks using elastomeric modules. In daily clinical practice, these are simple, economical, and reliable. Placement is not difficult and can be delegated routinely, with few complications. Active tiebacks using elastomeric modules are preferred for space closure in most cases, even though nickel-titanium springs have been shown to be more reliable and effective," as discussed below.

• Force levels. F.lastic tiebacks were originally described3 using an elastomeric module, of the type used to hold arch wires on to brackets, stretched to twice its normal size. This was found to give a force of 50-100 gm, if the module was pre-stretched or 'worked' before use. If used direct from the manufacturer, without pre-stretching, the force may be 200-300 gm greater.5 The force delivered by the elastic module varies with the type of module used, pre-stretching before use, and the amount of stretching when placed. It has been reported that different clinicians have successfully used different types of module, with different pre-stretching and different amounts of stretching when placed in (he mouth.6 Despite these variations in technique and force levels, there is widespread acceptance that elastic tiebacks achieve good space closure. It therefore seems that

Pinzas Torque Idividual OrtodonciaPassive Tiebacks
Fig. 9.17 Passive tiebacks are recommended at the time of placement of rectangular .019/.025 steel wires. These are used for at least 1 month to allow torque changes to occur on individual teeth. Later, active tiebacks are used for space closure.
Passive Wire Tieback

Fig. 9.19 The completed type one active tieback. It is helpful to carry one arm of the ligature wire (i) under the archwire. An elastomeric module is stretched to twice its unstretched size (ii).

Fig. 9.20 A type one active tieback just before placement.

Passive Wire Tieback

Fig. 9.18 Before placing the type one active tieback, the .019 /.025 rectangular steel archwire is placed, with elastomeric modules or wire ligatures on all brackets.

precise force levels are not essential for day-to-day success, and that adequate space closure occurs in most cases, provided the general concept is followed.

• Trampoline effect. Clinical experience has shown that space closure can continue for several months in patients who have failed to present for normal adjustments, even when the elastomeric module is in poor condition and apparently delivering very little force. I low can this consistent clinical experience be explained? One can speculate that there may be a 'trampoline effect' which occurs during mastication, and which can result in an intermittent pumping activation.

• Type one active tieback (distal module). The .019/.025 rectangular steel archwire is placed, with modules or wire ligatures on all brackets (Fig. 9.18). The elastomeric module is attached to the first or second molar hook. A .010 ligature is used, with one arm beneath the archwire (I ig. 9.19). This makes the active tieback more stable, and helps to keep the ligature wire away from the gingival tissues.

• Type two active tieback (mesial module). This follows the same principle as the type one, but the elastomeric module is attached to the soldered hook on the archwire. The

.019/.025 rectangular steel archwire is placed with elastomeric modules or wire ligatures on all brackets,

Fig. 9.18 Before placing the type one active tieback, the .019 /.025 rectangular steel archwire is placed, with elastomeric modules or wire ligatures on all brackets.

Fig. 9.19 The completed type one active tieback. It is helpful to carry one arm of the ligature wire (i) under the archwire. An elastomeric module is stretched to twice its unstretched size (ii).

Fig. 9.20 A type one active tieback just before placement.

Fig. 9.21 A lower type one active tieback. This shows minimal activation of the elastomeric, and slightly more stretching could be used.

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except the premolar brackets (Fig. 9.22). A .010 wire ligature is attached to the first or second molar hook, with several twists in the wire, and then attached to an elastomeric module on the archwire hook. Finally, a normal module is placed on the premolar brackets to cover the tieback wire and the archwire (Figs 9.23 & 9.24). With the type one and type two tiebacks, the elastomeric modules are normally stretched to twice their resting size for activation. If oral hygiene is good, adjustment visits may be less frequent; they may be re-activated after 4 to 6 weeks, and remain in place for two visits. If oral hygiene is poor, the elastomeric modules may deteriorate and require replacement at every visit. In some cases, in the final stages of space closure, it may be helpful to use two modules, or to augment the tieback with a 10- or 12-link elastomeric chain from molar to molar.

• Active tiebacks using a nickel-titanium coil spring.

Nickel-titanium springs can be used, instead of elastomeric modules, if large spaces need to be closed, or if there are infrequent adjustment opportunities (Fig. 9.25). Recent work by Samuels et al7 has recommended that the optimal

Fig. 9.22 Before placing the type two active tieback, the .019/.025 rectangular steel archwire is placed, with elastomeric modules or wire ligatures on all brackets, except the premolar brackets.
Active Tie Back Orthodontics

Fig. 9.23 The completed type two active tieback. This follows the same principle as the type one active tieback, but the module is attached anteriorly. The final elastomeric module (e) is placed after the archwire and the tieback. It stabilizes the tieback wire and helps to direct it away from the soft tissues.

Fig. 9.23 The completed type two active tieback. This follows the same principle as the type one active tieback, but the module is attached anteriorly. The final elastomeric module (e) is placed after the archwire and the tieback. It stabilizes the tieback wire and helps to direct it away from the soft tissues.

Sliding Mechanics

Fig. 9.24 Type two active tiebacks (mesial modules) in upper and lower arches. The elastomerics are stretched maximally in this photograph - ideally, in most treatments, slightly less stretching is appropriate. For final space closure, it is sometimes helpful to place two elastomeric modules. See also Figure 9.98, p. 275.

Fig. 9.25 Although nickel-titanium springs produce more consistent space closure than elastomeric modules, the authors consider the ease and simplicity of the modules make these preferable in most treatments. Nickel-titanium springs may be useful in cases where a large amount of space closure is required, or where there are infrequent adjustment opportunities.

Fig. 9.24 Type two active tiebacks (mesial modules) in upper and lower arches. The elastomerics are stretched maximally in this photograph - ideally, in most treatments, slightly less stretching is appropriate. For final space closure, it is sometimes helpful to place two elastomeric modules. See also Figure 9.98, p. 275.

Fig. 9.25 Although nickel-titanium springs produce more consistent space closure than elastomeric modules, the authors consider the ease and simplicity of the modules make these preferable in most treatments. Nickel-titanium springs may be useful in cases where a large amount of space closure is required, or where there are infrequent adjustment opportunities.

force for space closure is 150gm when using nickel-titanium coil springs as the force for space closure. The 150 gm springs were found to be more effective than 100 gm springs, but no more effective than 200 gm springs. This work confirmed their earlier findings'4 that nickel-titanium springs produce more consistent space closure than elastomeric modules. It suggests the use of light closed coil nickel-titanium springs (344-150 and 346-150 3M llnitek) to give a force of 150 gm. Springs should not be expanded beyond the manufacturers recommendations (22 mm for the 9 mm springs, and 36 mm for the 12 mm springs).

Nattrass et al6 confirmed that force decay with elastomeric chains is rapid in the first 24 hours and is affected by environment and temperature. Force decay did not occur to the same extent with nickel-titanium springs. Although the research evidence favors the use of nickel-titanium coil springs for more rapid space closure, the authors continue to use elastomeric modules for space closure in most cases. If spaces are closed too rapidly, incisor torque can be lost, and requires several months to regain at the end of space closure. Elastomeric modules are easy to use, economical, and work well in most clinical situations. Although coil springs can close all the space without requiring replacement at monthly visits, this is largely a theoretical advantage, because it is preferable to take out the wires to check and shorten them eveiy 1 or 2 months during space closure.

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Responses

  • mary garcia
    Why is ligature wire streched before use?
    6 years ago

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