Development of Self-Ligating Bracket Systems
The technique today uses metal or elastomeric ligatures to attach an archwire to a bracket. Ligating the archwire to the bracket slot in this way can be quite time-consuming, particularly when metal ligatures are used, and this is why self-ligating brackets were first developed. The earliest examples (all developed in the United States) date back to the 1930s.
The term “self-ligating bracket” (SL bracket) is used for brackets that incorporate a locking mechanism (such as a ring, spring, or door mechanism) that holds the archwire in the bracket slot.
There are essentially two main types of self-ligating bracket, depending on the design of the locking mechanism, the dimensions of the slot, and the dimensions of the archwires: active brackets and passive brackets. In passive systems (such as the Damon System, Ormco Corporation, Orange, California; and Discovery SL, Dentaurum Ltd., Ispringen, Germany), the slot is locked or shut with a rigid locking mechanism. Once it is engaged, the bracket is effectively turned into a tube, ideally allowing archwires to slide freely within the tube. In active systems (such as Quick, Forestadent Ltd., Pforzheim, Germany; and SPEED, Strite Industries, Cambridge, Ontario, Canada), the locking mechanism generally consists of a flexible but resilient clip that can actively engage wire into the bracket slot once the archwire reaches a certain size or deflection.26
Stolzenberg invented the Russell attachment in 1935 and is one of the pioneers of self-ligating brackets ( Fig. 1.1 ).5 , 12 , 25 Although Boyd (1933) ( Fig. 1.2 ) and Ford (1933) ( Fig. 1.3 ) developed passive, ligature-free systems earlier, these were never widely used.10 Other designs were patented, but only very few of them eventually became commercially available.
It was not until the 1970s that interest in the development of self-ligating brackets resurfaced. In 1972, Wildman introduced the passive EdgeLok bracket,10 , 12 , 30 which in its earlier incarnations had a round bracket body as well as a labial sliding door ( Figs. 1.4 and 1.5 ). This was the first self-ligating bracket to become widely available commercially, but it was eventually taken out of production as more advanced systems appeared. At about the same time (1973), the Mobil-Lock bracket ( Fig. 1.6 ) was introduced by Sander.27 This was the first self-ligating twin bracket that had a variable slot. Due to the eccentric movement of the locking system, the wire could either be locked tightly into the bracket or, with proper adjustment, achieve partial ligation, which was designed to allow the wire to glide freely through the slot.20 These were all passive systems, and none of them are still in use today, as they have been superseded by newer and improved designs.
In the 1980s, Hanson developed a completely new approach to self-ligation: the SPEED bracket ( Fig. 1.7 ). This was the first active self-ligating bracket. The locking mechanism is formed by a flexible clip.5 , 9 , 12 This bracket is still in use today, but has undergone significant modifications during the past 20 years of clinical experience. As mentioned earlier in the text, changes in bracket manufacture techniques have had a significant impact on the bracket design. For example, the locking mechanism, the resilient spring had originally been made from stainless steel, but this has recently been replaced with nickel–titanium (NiTi).
The SPEED bracket was quickly accepted in clinical practice and is still in use today.