A New Low-Friction Ligation System
Many factors can contribute to the frictional resistance of edgewise appliances,1-7 including bracket and wire materials and cross-sections, surface conditions of the archwires and bracket slots, torque at the wire-bracket interface, interbracket distance, the presence of saliva, and the functions of the oral environment.8-11 Schumacher and colleagues found, however, that friction was determined mostly by the type and force of ligation.12
The first self-ligating bracket was the Russell attachment, introduced in the mid-1930s to reduce chairtime and improve operator efficiency.13,14 More recently, two broad classifications of self-ligating brackets have been developed: the active type, in which the spring clip presses against the archwire (SPEED, In-Ovation, Time), and the passive type, in which the clip does not contact the wire (TwinLock, Damon).
Every self-ligating bracket, whether active or passive, uses the movable fourth wall of the bracket to convert the slot into a tube. Several studies have demonstrated a significant reduction in friction with self-ligating brackets compared to conventional designs.3,15-20 This can help shorten treatment, especially in extraction cases, where tooth translation is achieved by sliding mechanics.
Self-ligating systems do have several limitations, however:
This article describes an alternative to self-ligating systems: a ligature that markedly reduces the amount of friction between the archwire and the edgewise bracket. The Slide ligature enables the archwire to apply the desired amount of force without the resistance of conventional ligatures, thus reducing treatment time and producing more stable results.
Low-Friction Ligature System
The Slide ligature, made of a special medical polyurethane, is applied to the bracket in the same way as a conventional elastomeric ligature (Fig. 1). Like a passive self-ligating bracket, it allows the archwire to slide freely in the slot while transmitting its full force to the tooth (Fig. 2). The Slide ligature also forms a buffer between the brackets and the soft tissues, considerably improving patient comfort (Fig. 3).
Slide ligatures are specifically designed for use with STEP brackets, but are available in three sizes to fit any type of edgewise appliance, including ceramic brackets (Fig. 4). To meet the demands of younger patients, the ligatures are manufactured in various colors (Fig. 5).
Slide ligatures can be used in cases where considerable leveling and alignment are required, as well as in patients who need sagittal or transverse expansion. The advantages of the system are especially evident in the early stages of orthodontic treatment, when the archwire can slide freely inside the tunnel between the bracket slot and the ligature.
The system also enables the clinician to apply friction and reduced-friction mechanics simultaneously on the same archwire by using Slide ligatures only in particular segments. For example, during en masse space closure on a rectangular stainless steel archwire, Slide ligatures can be used in the posterior segments to reduce friction, while conventional ligatures are used in the anterior segment to maximize torque expression and control (Fig. 6).
A 12-year-old female presented with a bimaxillary protrusion, severe crowding in both arches, and transposition of the upper right canine and first premolar (Fig. 7). After extraction of the right first premolars, preadjusted STEP brackets were bonded in the upper arch, and an .020" Gold Tone stainless steel archwire and compressed-coil spring were used to move the upper right canine mesially (Fig. 8). In the lower arch, an .014" superelastic nickel titanium archwire was tied into preadjusted STEP brackets with Slide low-friction ligatures. Once the lower left canine had been partially aligned, the archwire was changed to .016" superelastic nickel titanium; the extraction space was closed with elastic chain (Fig. 9). After eight weeks of treatment, the lower left canine was in proper position.
In this 11-year-old female with a Class II malocclusion, the initial upper molar distalization was retained with a modified Nance button (Fig. 10). An upper .014" superelastic nickel titanium archwire was then tied into preadjusted STEP brackets with Slide ligatures (Fig. 11). No lacebacks were required to move the upper right canine. In the lower arch, an .020" Gold Tone stainless steel archwire was placed with bend-backs. After 32 days of this phase of treatment, the upper right canine had been leveled without any intrusive side effects on the adjacent teeth or posterior anchorage reinforcement (Fig. 12).
A 13-year-old female presented with a skeletal and dental Class III malocclusion (Fig. 13). Preadjusted STEP brackets were bonded in the upper arch, and an .016" Gold Tone stainless steel archwire was inserted with a laceback to the left canine (Fig. 14).
Low-friction mechanics were then initiated with an .014" superelastic nickel titanium archwire, using Slide ligatures and no lace- or bendbacks (Fig. 15). Enough space was gained in seven weeks to align the upper right canine (Fig. 16).
The user-friendly Slide low-friction ligature can be employed with any edgewise bracket without altering the clinician's preferred mechanotherapy. This system offers advantages over self-ligating brackets in controlling friction, while increasing patient comfort and potentially reducing treatment time.