Self-Ligating Brackets_ Theory and Practice

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Transcript of Self-Ligating Brackets_ Theory and Practice


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Self-ligating brackets: theory and practiceNigel Harradine and David Birnie


Introductio n Self-ligating brackets have made a major impact in orthodontics in the last seven or so years.

There is no doubt that they add a new dimension to orthodontic treatment and it can be argued that they are more than just a bracket system facilitating tooth movements that are difficult to achieve with conventional appliances. It is easy to focus on the absence of ligatures as the raison for self-ligating brackets. A better d'tre description is that they are ligatureless brackets in that they do not use ligatures but require some procedure to be carried out on the bracket in order to either secure or release the archwire. It is worth trying to think about the other benefits that current self-ligating brackets may offer and some of these concepts are encapsulated in an article by Alan Pollard (2003) . Self-ligating brackets have an inbuilt metal labial face which can be opened and closed. Brackets incorporating their own ligation system have existed for a surprisingly long time in orthodontics - the Russell Lock edgewise attachment being described by Stolzenberg in 1935. Many designs have been patented, although only a minority have become commercially available. We have also used self-ligating Begg brackets in the past. New designs continue to appear, with three new brackets becoming available in the 1990s and at least nine new brackets since 2000. This rapidly accelerating activity is in spite of the fact that until recently, self-ligating brackets had never attracted more than a small percentage of bracket sales. All manufacturers have come to appreciate the capabilities of these brackets. We have a fairly wide range of experience with different self-ligating brackets since 1982, having in the past treated a considerable number of cases with Speed brackets, a few with Mobil-Lock brackets, a large number with Activa brackets from 1986 to 1995, Damon SL brackets from 1995 to 2000 and TwinLock brackets on a few cases. Damon SL brackets had tie-wings and a self-ligation slide and superseded Activa. Damon 2 brackets are a substantial further development of this concept. Damon 3 brackets have a new slide mechanism and are partially made of composite resin to enhance the aesthetics, whilst Damon MX brackets have essentially the same slide mechanism bur are all-metal brackets. Brackets made entirely from composite polymers have also appeared Oyster and Opal. In-Ovation brackets were previously known as Interactwin and Sigma before their commercial release in 2000. They have tie-wings but have an active self-ligation clip. More recently they have been renamed System R. Adenta LT brackets are a lingual version of the Time bracket. The 3M Unitek Bracket Year SmartClip bracket has wire-retaining spring clips added to either Russell Lock 1935 side of a conventional bracket. This chapter looks first at the Ormco Edgelok 1972 requirements of an ideal bracket ligation system and the extent to which the current self-ligating brackets meet these requirements. Forestadent Mobil-Lock 1980Orec SPEED A Company Activa Adenta Time A Company Damon SL Ormco TwinLock Ormco/A Co. Damon 2 Gestenco Oyster GAC In-Ovation GAC In-Ovation R Adenta Evolution LT Ultradent Opal SDS Ormco Damon 3 3M Unitek SmartClip SDS Ormco Damon MX Class One Carrire SLB Table 11.1: designs Self-ligating bracket 1980 1986 1994 1996 1998 2000 2001 2002 2002 2002 2004 2004 2004 2005 2005

Properties of an ideal ligation system We are so used to accepting that tie-wing brackets are the waythat ligation is performed, that it is worthwhile considering a list of ideal properties of any ligation system. This puts in perspective any assessment of the benefits and difficulties with current selfligating systems. Archwire ligation should:

be secure, robust ligation ensure full bracket engagement of the archwire exhibit low friction between bracket and archwire be quick and easy to use permit high friction when required assist good oral hygiene


be comfortable for the patient

Conventional wire and elastomeric ligatures in relation to the requirements for an ideal ligation systemSecure robust ligation It is highly desirable that once ligated, the system is very resistant to inadvertent loss of ligation. Wire ligatures are good in this respect, whilst elastomeric ligatures are much less good, especially if left for too long without being renewed. The force decay of elastomerics has been well documented (Taloumis et al 1997). Full bracket engagement It is a large advantage if the archwire can be fully engaged in the bracket slot and then maintained there with certainty. Wire ligatures do not stretch to an extent that engagement once achieved at ligation is subsequently lost, so they can meet this requirement. Elastomerics are again worse in this respect since they may on occasion exert insufficient force to fully engage even a flexible wire and the subsequent degradation of their elastic performance may cause a significant loss of full engagement as the elastomeric stretches. Twin brackets with the ability to figure of 8 the elastomerics are a significant help in this respect but certainly not a complete answer. Quick and easy to use This is a major weak point of wire ligatures and the principal reason for the enormous decline in their use. Maijer and Smith (1990), and Shivapuja and Berger (1994) have shown that wire ligation is very slow compared to elastomerics. In the latter study, the use of wire ligatures added almost 12 minutes to the time needed to remove and replace two archwires. This is the largest and very understandable reason why so few wire ligatures are now used. Low friction Wire ligatures are again better than elastomerics; producing 30%-50% of the friction forces in the study by Shivapuja and Berger (1994) but the forces still reach undesirable levels relative to the force levels considered ideal for tooth movement. Khambay et al (2004), also found that stainless steel ligatures produced lower frictional forces than elastomerics. Interestingly, the polymeric-coated SuperSlick ligatures (TP Orthodontics Inc. Indiana) which were designed to reduce friction produced more friction than more conventional elastomerics. Also, the force normal to the archwire produced by a wire ligature is very variabl (Iwasaki et al 2003) even after training in a standardised method of ligature tying. This force has e been shown to be more variable for elastomeric ligatures than for passive self-ligation also (Thorstenson and Kusy 2001) High friction It is also helpful under some circumstances if the ligation system can lock a tooth to the wire to prevent unwanted movement of that tooth along the wire. When initially placed, an elastomeric in a figure of 8 configuration increases the friction by a factor of 70-220%. compared to the O configuration 1993) which partially meets this requirement. Easy attachment of elastic chain Some self-ligating brackets such as Opal and Speed have dispensed with tie-wings. This makes attachment of elastic chain and if desired, elastomeric ligatures, less convenient or impossible. Most of the recently developed self-ligating brackets have tie-wings. Assists good oral hygiene Elastomerics accumulate plaque more than do tie-wires and fluoride releasing elastomerics have yet to reach reliably robust performance levels by way of compensation. The ends of wire ligatures are however an additional obstacle to oral hygiene. An interesting paper by Turkkahraman et al (2005) elastomerics and wire ligatures with respect to various measures of plaque quality and quantity, gingival index, probing depth and bleeding on probing. The bacteriology results slightly favoured wire ligation, but

(Sims et al



not to a significant extent, but the important sign of bleeding on probing was substantially higher with elastomeric ligation. A current study in the United Kingdom is comparing elastomerics with self-ligation in this area of potential concern. Comfortable for the patient Elastomerics are good in this respect, but wire ligatures require careful tucking in of the ends to avoid soft tissue trauma and even then can occasionally be displaced between appointments and cause discomfort.

Summary: What is wrong with conventional ligation? failure to provide and to maintain full archwire engagement high friction for elastomerics, the force (and therefore tooth control) decays and they are sometimes lost potential impediment to oral hygiene wire ligation is very slowWire ties are secure, robust, enable full, partial or distant ligation and have lower friction than elastomerics. Their large drawback is the time required for ligation. Elastomerics are quick but less good in every other respect. Neither method is ideal nor nearly as good as a molar tube assembly which is universally adopted as the ligation of choice on posterior teeth. It is easy to find examples of the deficiencies of conventional ligation, but clinicians have become accustomed to tolerating these shortcomings.

Advantages of self-ligating brackets These advantages apply in principle to all self-ligating brackets although the different makes vary in theirability to deliver these advantages consistently in practice.

more certain full archwire engagement low friction between bracket and archwire less chairside assistance faster archwire removal and ligation

Secure, full archwire engagementFull engagement is a feature of self-ligation because, if a c