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SELF-LIGATING BRACKETS: THEORY AND PRACTICE 197 EXCELLENCE IN ORTHODONTICS 2006

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

198 SELF-LIGATING BRACKETS: THEORY AND PRACTICE EXCELLENCE IN ORTHODONTICS 2006

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 Damon SL brackets had tie-wings and a self-ligation slide and superseded Activa.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

compared


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 clip or slide is functioning properly, it is either fully shut or it is not. Unintentional partial engagement is not possible. There is no problem of decay of the ligature as with elastic ligatures. However, security of ligation will depend on the clip/slide being robust and not inadvertently opening. Until recently, this requirement for security of performance was not fully met by any self-ligation designs. Secure, full archwire engagement maximises the potential long range of action of modern low modulus wires and minimises the need to regain control of teeth where full engagement is lost during treatment.

Low frictionVery low friction has been clearly demonstrated and quantified in work by Sims et al (1993 , 1994) , Berger (1990) and Shivapuja and Berger (1994) for both Activa and Speed brackets and indeed Edgelok. Voudouris (1997) has reported greatly reduced friction with Sigma and Interactwin prototypes and with Damon brackets. The friction is dramatically lower than for elastomeric rings with conventional brackets and seems to be an inherent characteristic of self-ligating brackets. Thomas et al (1998) confirmed extremely low friction with Damon brackets compared to both conventional preadjusted and also Tip-Edge brackets. Kapur et al (1998) found that with NiTi wires the friction per bracket was 41 g with MiniTwin and conventional ligation and 15 gm with Damon brackets whilst with stainless steel wires, these values were 61 gm and only 3.6 gm respectively. Pizzoni et al (1998) have reported that Damon brackets showed lower friction than Speed which in turn had less friction than conventional brackets stating that: In the case


2.5 2 1.5 1 0.5 0 0.014 NiTi 0.0175 TF 0.016x0.022 SS 0.016x0.022 NiTi 0.019x0.025 SS

A Co Damon SL Adenta Time TP TipEdge A Co Std

of rectangular wires, the Damon bracket was significantly better than any of the other brackets and should be preferred if sliding mechanics is the technique of choice. Meling et al (1997), examinin g the effect of friction on wire stiffness concluded that each elastomeric placed in an O configuration produces an average of 50 gm of frictional force. This figure is supported by Khambay et al (2004) using a method which gave zero friction for Damon 2 brackets found mean frictional forces ranging between 43 and 98 gm (0.43 and 0.98 newtons) for various elastomeric/archwire combinations.

Figure 11.1: Data from Thomas et al (1998) showing typically very low friction for self-ligating brackets compared to conventional ligation

Friction in vivo and with active wires It is however, difficult to be certain how accurately any laboratory simulation of friction reproduces the true in vivo situation where other factors including variable archwire activation and its consequent binding exist. A study by Loftus et al (1999) found that in an experiment with a simulated periodontal ligament and with slight tip and rotation of the brackets, the friction with Damon SL was not significantly less than with conventionally ligated brackets. Read-Ward et al (1997) reported that the reduction in friction with self-ligation is much less when the wire is active, but this study also showed the considerable methodological problems in measuring friction with active wires, the standard deviation of repeated measurements being very high. Sims et al (1994) found much lower friction with self-ligating brackets, even at high values of active torque.

stil l

Three papers by Thorstenson and Kusy have investigated aspects of this topic. Thorstenson and Kusy (2001) examined the effects of varying active tip (angulation) on the resistance to sliding. They also found that angulation beyond the angle at which the archwire first contacts the diagonally opposite corners of the bracket slot causes a similar rise in resistance to sliding of both self-ligated (Damon SL) and conventional brackets. However, at all degrees of tip, the Damon brackets produced significantly less resistance to sliding (Table 11.2). At a realistic angulation of 6 degrees for an 0.018" x 0.025" stainless steel wire, the difference is probably of clinical significance. The second paper (2002a) compared different self-ligating brackets for resistance to sliding with active angulations. It quantifies a little more closely the lower resistance to sliding with passive self-ligation and points out that low resistance to tooth movement can lead to unanticipated movement as is mentioned later in this chapter. The third paper (2002b), examined the same factors with wires of different sizes and in the dry state. The increase in friction when larger wires deflect the clips in active self-ligating brackets is quantified and the scanning electron micrographs of the different brackets show very clearly the relationship between small and large wires and active clips and passive slides. Table 11.3 contains data from an abstract of work by Mah (2003), which used an interesting methodology. A known tipping (angulation) moment was applied to brackets able to tip up to 20 degrees and the resistance to sliding was termed dynamic friction and measured for the four bracket types. The reduced friction for both types of self-ligating bracket can be seen and the difference between InOvation and Damon 2 was statistically significant. Further details from this study will be of interest, but toAngulation (degrees ) 0 3.5 6.0 Table 11.2: Damon SL 0 34 0 55 80 140 Conventional Bracket Minitwin Transcend 379 6000 455 238 99 In-Ovation Damon 2

Resistance to sliding (RS). for different bracket

Table 11.3:

Mean dynamic friction for different brackets with

angulations with a 0.018/0.025 archwire Forces in cN Thorstenson and Kusy (2001)

an applied tipping moment on a 0.019/0.025 stainless steel archwire. Forces probably in cN. Mah et al (2003)


date, no subsequent, fuller details of this work have been traced. The study supports the view that selfligation produces less resistance to tooth movement along an archwire in vivo. An interesting study by Cacciafesta et al (2003) showed that Oyster polycarbonate self-ligating brackets had a much higher friction than Damon 2 brackets. In fact the mean friction was more than double at 100gm compared to 40 gm for Damon 2 and indeed was no different from conventional 3M Unitek Victory brackets with elastomeric ligatures. Friction in vivo occlusal and masticatory forces A further factor has been investigated in studies by Braun et al (1999) and OReilly et al (1999) who found that various vibrations and displacements of a test jig (to mimic intra-oral masticatory forces) can substantially reduce the friction with conventional ligation. This is a valid line of enquiry and an interesting finding, but the question then arises as to how accurately these laboratory studies mimic intra-oral masticatory jiggling forces. The full interpretation of laboratory friction studies is clearly difficult and the in vivo situation will show substantial variation. An impressive study by Iwasaki et al (2003) employed an intra-oral device to produce a combination of tipping and ligation forces and measured the effect of chewing gum on the resulting resistance to sliding. They concluded, these results refute the hypothesis that masticatory forces consistently and predictably decrease friction. Measurement of the variables which influence in-vivo friction will remain a challenge, but progress is being made. Meanwhile, the balance of the current evidence from studies and from clinical experience is that self-ligation provides very significant reduction in friction in all dimensions of tooth movement. The clinical significance of low friction in isolation is hard to estimate and it is more helpful to consider the combination of low friction and secure archwire engagement which self-ligating brackets provide. Secure ligation and low friction as a combination Other bracket types - most notably Begg brackets - have low friction by virtue of an extremely loose fit between a round archwire and a very narrow bracket, but this is at the cost of making full control of tooth position correspondingly more difficult. Some brackets with an edgewise slot have incorporated shoulders to distance the elastomeric from the archwire and thus reduce friction, but this type of design also produces reduced friction at the expense of reduced control, since the shoulders which hold the ligature away from the archwire increase the slot depth and reduce the tension in the elastomeric. This reduces the control of rotations or of labiolingual tooth position. Elastomeric rings cannot provide and sustain sufficient force to maintain the archwire fully in the slot without also pressing actively on the archwire to an extent which increases friction. Comparison with a molar tube is helpful in this context, since such an attachment is in essence a passive self-ligating bracket with the slide permanently closed. If a convertible molar tube is converted to a bracket by removal of the slot cap or straps, an elastomeric or even a wire ligature can prove very ineffective at preventing rotation of the tooth if it is moved along the wire or used as a source of intermaxillary traction. These ligation methods simultaneously increase friction while attempting to retain full archwire engagement. An article by Matasa (2001), measured and illustrated the reduction in friction, but the consequent reduced control with such bracket designs which diminish the tight fit of the elastomeric around the archwire. The investigation into three such low friction bracket types by Thorstenson and Kusy (2003) also found no evidence that bumps in the floor of the archwire slots reduced resistance to sliding. With tie-wing brackets and conventional ligation, an improvement in friction is usually at the cost of deterioration in control. The combination of very low friction and very secure full archwire engagement in an edgewise-type slot is currently only possible with self-ligating brackets (or with molar tubes!) and is likely to be the most beneficial feature of such brackets. This combination enables a tooth to be slid along an archwire with lower and more predictable net forces and yet under complete control with almost none of the undesirable rotation of the tooth resulting from a deformable mode of ligation such as an elastomeric. Anchorage consequences of low friction and secure full archwire engagement This combination of properties can in turn conserve anchorage for three reasons:

with low friction, the net tooth-moving forces are more predictably low and the reciprocal forces correspondingly smaller.


lower net forces facilitate release of binding forces between wire and bracket, enhancing sliding of brackets along a wire. individual teeth - for example canines - can be retracted separately along an archwire and thus potentially reduce the overall anchorage demands by reduction of the root area of teeth to be moved at any one time, but with none of the potential disadvantages of other methods of separate canine retraction with conventional brackets e.g.: loss of rotational control. Following such separate canine retraction, the low friction of self-ligating brackets then permits the sensible use of sliding mechanics to retract incisors even though there will now be a minimum of three brackets distal to the remaining space through which archwire sliding must occur. This applies equally to preservation of anterior anchorage in hypodontia cases.

Alignment of severely irregular teeth The other situation in which the combination of low friction and secure full engagement is particularly useful is in the alignment of very irregular teeth and especially the resolution of severe rotations where the capacity of the wire to slide through the brackets of the rotated and adjacent teeth significantly facilitates derotation. This relationship between friction and derotation has been described and quantified by and Burstone (1989) and the potential adverse forces shown to be very large. Low friction therefore permits rapid alignment and more certain space closure, whilst the secure bracket engagement permits full engagement with severely displaced teeth and full control whilst sliding teeth along an archwire. Modern, low modulus wires substantially enhance our ability to harness these benefits. It is this feature which greatly facilitates the alignment of crowded teeth without extractions if this is the desired treatment goal.

Koeni g

Less chairside assistance and faster ligation/ archwire removal The original motive when developing the earlier self-ligating brackets was to speed the process of ligation. For example a paper by Maijer and Smith (1990) demonstrated a fourfold reduction in ligation time with Speed brackets compared to wire ligation of conventional brackets. Shivapuja and Berger (1994) have shown similar results but also that the speed advantages compared to elastomeric ligation are less dramatic (approximately one minute per set of archwires). Voudouris (1997) has also reported a fourfold reduction in archwire removal/ ligation time with prototype Interactwin brackets. A study by Harradin (2001) found statistically significant but clinically much more modest savings in ligation/re-ligation time with e Damon SL - an average of 24 seconds per archwire removal and replacement. It should however be remembered that archwire 'ligation' using self-ligating brackets does not require a chairside assistant to speed the process, since self-ligating brackets require no passing of elastomeric or wire ligatures to the operator during ligation. Although we feel that this is the least significant advantage of self-ligation, it is still perhaps worthwhile.10 9 8 7 6 5 4 3 2 1 0 1234 Wire group Damon open Orthos open Damon close Ortho close

Turnbull and Birnie (2006) investigated the difference in time taken to open and close brackets for different archwire groups with Orthos and Damon 2 brackets. The archwire groups were defined as:

0.014, 0.016 and 0.018 nickel titanium 0.014 x 0.025, 0.016 x 0.025 and 0.016 x 0.022 nickel titanium 0.018 x 0.025 and 0.019 x 0.025 nickel titanium 0.018 x 0.025 and 0.019 x 0.025 stainless steel

Figure 11.2: Opening and closing times per bracket for Damon 2 and Orthos brackets for various archwire groups (from Turnbull and Birnie 2006)


The authors found time savings slightly greater than those of Harradine with Damon 2 brackets being 1 second per bracket for opening brackets and 2 seconds per bracket for closing brackets. It was twice as quick to close Damon 2 brackets as to ligate Orthos brackets. For both bracket systems, the time taken to ligate and unligate archwires decreased with increasing archwire size (and correspondingly better tooth alignment) as shown in Figure 11.2.

Damon

SDS Ormco systemSL

Damon

brackets These self-ligating brackets became available in 1996. They had a slide which moved vertically on the labial surface of an otherwise fairly conventional twin tie-wing bracket. The slide clicked into a positive open or shut position and opened in a downward direction in both jaws to give a full view of the slot. A tiny U-shaped wire spring lay under the slide and clicked into the two labial bulges on the slide to provide positive open and shut positions. These brackets were a major step forward, but suffered two irritating problems - the slides inadvertently opened and were prone to breakage. The study by NH quantified these problems. In 25 consecutive cases in treatment for more than one year, 31 slides broke and 11 inadvertently opened between visits. This compared with 15 broken and lost elastomeric ligatures in 25 consecutive cases treated with conventional brackets. Slide breakage was due to work hardening of the slide corners. The loss of slide was sometimes due to breakage but was also due to the considerable overall length of the slide and the play in the slide/bracket contact. These permitted over-opening of the slide which could pass beyond the stop provided by the underlying U-shaped wire. Damon 2 System brackets (D2) The imperfections in the Damon SL led to the development of Damon 2 System brackets which retain the same vertical slide action and U-shaped spring to control opening and closing, but place the slide within the shelter of the tiewings. Combined with the metal injection moulding manufacture, which permits closer tolerances, these developments almost completely eliminated inadvertent slide opening or slide breakage. Although special and excellent slide-opening tools are provided with these brackets, they can after a little practice be easily opened and closed with conventional light-wire pliers. A side effect of this design change has been to reduce the overall size of the bracket to very compact dimensions, which is a significant advantage - the greater interbracket span giving lower forces - but with the full wire engagement retaining good control. Scope remained for further improvement in the ease and consistency of opening and closing the slides. Whilst the slide closure is very secure, the close fit causes the force required to open the slide to vary. The more recent introduction of metal injection moulded slides has delivered a more consistent force. These continuing developments are typical of self-ligating brackets and illustrate the considerable technical demands in manufacturing an ideal bracket. One unique and useful feature of the slides on all

(2001)

Figure 11.3: (1996)

The Damon SL bracket

Figure 11.4: (2000)

The Damon 2 bracket

Figure 11.5: The Damon 3 bracket (2004). Slide opening is with a tool which engages the labial aperture. Slide closing is by finger pressure.


Damon brackets is that they open inferiorly in both arches in order to give an unobstructed view of the slot.

Damon 3 brackets (D3) brackets have three major changes from previous Damon brackets. These a tooth-coloured composite resin base and upper tie-wing which reduces the visual impact of the bracket a completely new vertically-placed chair-shaped spring clip behind the slide. This has produced a slide which is extremely easy and consistent to open and close. The slide is closed with finger pressure and has a positive tactile and audible signal when fully closed. It is opened with a special opening tool resembling a modified blunt dental probe. The technique is to slide the point of the tool down the V-shaped ramp on the front of the slide until it engages in the small hole at the base of the slide; pressing inwards while continuing to press downwards releases the clip. a rhomboidal shape of the bracket and slide which facilitates bracket siting

The ease of use of the slide mechanism is a huge improvement over previous versions of the Damon bracket. Initial problems with bracket retention were addressed by a specific adhesive Blugloo which has an acrylic resin and therefore binds chemically to the bases. The security of the union between the metal and composite components of the bracket also required further development in the form of additional retentive metal tags. The robustness of the composite tie-wings in the long-term and in deep bite malocclusions remains to be evaluated, but the advent of Damon MX brackets greatly diminishes that issue.

Damon

MX

These brackets brackets are all-metal and have essentially the same slide mechanism as D3 with further refinements. They are designed to be fully compatible with D3. They have a vertical slot behind the archwire slot into which prefabricated click-in auxiliary hooks can be added to any bracket as required.

Bracket identificationThe Damon 2 System has a variety of possible prescriptions for incisors and canines making it a semicustom appliance system. In selecting a semi-custom prescription it is sensible to start with the standard prescription and decide what departures are necessary from this prescription. The only parameter that varies in the variants of the Damon System 2 appliance is inclination. Generally, err on the side of overcorrection; so if correcting retroclined upper incisors, choose a bracket with a higher inclination to try and achieve a measure of overcorrection.

Figure 11.6: The Damon MX bracket (2005). Slide closed

Figure 11.7: (2005). Slide open

The Damon MX bracket

Figure 11.8: The Damon MX bracket (2005). Bracket ID in slot base


Upper arch Central Lateral Canine 1 Colour code Blue Pink Light blue

st

premolar 2 Purple Purple

nd

premolar

Damon standard

ID Distogingival dot

Distogingival dot Distogingival dot \ Distogingival dot /// notches

Distogingival dot /// notches

Prescription 5/7 9/3 6/0 2/-7 2/-7

RothID Distogingival dot occlusal tie wing dash Prescription 5/12 9/8 6/-7 2/-7 2/-7 Distogingival dot occlusal tie wing dash Distogingival dot occlusal tie wing dash

Super torqueID Distogingival dot - black Prescription 5/17 9/10 6/-7 2/-7 2/-7 Distogingival dot - black, notch

Damon 6/7Colour code

Distogingival dot /st

Lower arch Central Lateral Canine 1 Yellow Yellow Light blue

premolar 2 WW hh ii tt ee Wh it e

nd

premolar Red

Damon standard

ID Distogingival dash Distogingival dash Distogingival dash \

Distogingival dash // notches

Distogingival dash /// notches

Prescription 2/-1 2/-1 5/0 2/-17 2/-22

Damon 5/7 Damon 2/-6Table 11.3:

Distogingival dash / Distogingival dash Distogingival dash

Bracket identification and prescription variations for the Ormco Damon System appliance

The prescription options that are available together with their identifying characteristics are shown in Table 11.3. The only identification problem is between Damon Standard (2/-1) and Damon (2/-6) which have the same identification markings; the two brackets can be distinguished by careful inspection. We routinely use the prescription with 6 torque. The Damon 3 System is only available in the standard Damon prescription at the moment and uses Ormcos FacePaint colour identification system which is identical to the coloured dots used on Damon 2 System brackets.

Ultradent Opal brackets This is one of two currently available brackets which are entirely non-metallic.

We have used Opal brackets on a significant number of patients. They were designed and developed by Professor Norbert Abels. The material has to meet the difficult challenge of being sufficiently rigid to function as an effective bracket slot, transmitting the forces as intended, whilst also being sufficiently flexible in the hinge area to open and close. The OPAL design is rather ingenious in this respect but care must be taken not to fatiguefracture the thin hinge part of the bracket by repeated full opening of the cap. Also the cap has to be sufficiently robust to withstand the sharpness of the opening tool and the bond strength needs to withstand the leverage of the initial opening of the cap. The brackets, like most resin brackets, are perhaps best suited to short courses of treatment where these problems of longevity are less of an issue. There are no tie-wings, so elastic chain is placed in the auxiliary slot prior to closing the cap. The other polycarbonate self-ligating bracket is the Oyster, made by Gestenco. An interesting study by Cacciafesta et al (2003) showed that Oyster brackets had a much higher friction than Damon 2 brackets and were indeed no different from conventional 3M Unitek Victory brackets with elastomeric ligatures. This indicates that the lower friction inherent in passive self-ligation counteracts the known higher friction for


Figure 11.9: The Ultradent Opal bracket. The hinge is on the right and the potential auxiliary slot on the left next to the point of application of the opening tool.

Figure 11.10:

The Opal bracket with hinge open

polycarbonate brackets and makes Oyster brackets equivalent to conventional stainless steel brackets in this respect. We have not used Oyster brackets.

GAC In-Ovation brackets These brackets have more recently been re-branded as System R. These are very similar to the SPEEDbracket in conception and design, but are of a twin configuration. They are a good, robust design and no inadvertent opening or slide breakage has been personally experienced or reported. The slides are very easily closed once the wire is fully engaged. Some relatively minor disadvantages are apparent in bracket handling :

some brackets are hard to open. This is unpredictable, but more common in the lower arch where the gingival end of the spring clip is difficult to visualise. Excess composite to the gingival of lower brackets can be hard to see and may hinder opening. The Opin R version (Figure 11.12) should alleviate this problem.

Figure 11.11: The Figure 11.12: The

GAC In-Ovation bracket

more recent Opin R version of the GAC In-Ovation bracket permits opening of the clip using a probe in the labial notch arrowed

these brackets are extremely easy to close inadvertently before the archwire is in position and the downward direction of closure makes this more likely in the lower arch. the security of closure of the flexible clip can be overcome by some rectangular nickel-titanium wires, which can cause spontaneous opening of the clip. This applies more to the narrower R versions of the bracket with their narrower slides. it is possible - as with the Damon 2 bracket slides - to incompletely open the clip and discover the need for the final fraction of opening through difficulty with removing a thicker archwire. when using wire-ligature underties to maintain space closure or lacebacks across extraction spaces, the spring clips


are a real nuisance in competing for the space behind the tie-wing. In 2002, narrower brackets for the anterior teeth became available In-Ovation R (Reduced). This narrower width is welcome in terms of greater inter-bracket span. In-Ovation brackets have an active clip and this is discussed in the next section.

Bracket identificationThe GAC In-Ovation bracket system uses an active clip. It uses the same colour identification system as the Ormco Damon System 2 but is only available in the Roth prescription.

3M Unitek SmartClip brackets This bracket which became available in 2004 is aconventional bracket with additional nickelspring clips mesial and distal to the tie-wings (Figure titanium 11.13). It is a passive self-ligation system. It is still too early to comment in depth from our clinical experience with this bracket, but the following points are pertinent.

Figure 11.13:

3M Unitek SmartClip bracket

the insertion of small diameter archwires is easy. removal of archwires with the special tool needs a little practice but is easy with small diameter wires the spring clip has to cope with providing easy insertion and also no inadvertent loss of ligation for both small flexible and large stiff archwires. This is a testing requirement. Other spring clips (such as on SPEED brackets) with their vertical action have a rigid bracket component to assist the spring in resisting loss of ligation. The spring on the SmartClip has to cover the wide range of requirements for different wire sizes with one shape and stiffness of spring unaided by a rigid component. removal of larger, stiffer wires means overcoming an advertised 2 kilograms of force per bracket with a labially directed force. The question arises as to how comfortable and easy this will prove, especially if the teeth on either side of that bracket are also engaged on the archwire. This force seems high to the operator and to the patient and recently the manufacturers have responded by introducing a more flexible clip. This should permit easier removal of thicker archwires, but may make spontaneous clip opening more frequent time will tell. the effective width of the bracket is wider than for most other self-ligating brackets which have taken advantage of the more secure, full ligation of self-ligating brackets to reduce bracket width, thus lowering forces with no loss of tooth control. The wider SmartClip brackets reduce the inter-bracket span and would be expected to provide higher forces.

Active clip or passive slide?This is an issue which has attracted heated debate consideration. (Matasa 1996) . It is therefore worth a detailed

Speed and In-Ovation brackets both have a sliding spring clip, which encroaches on the slot from the labial aspect, potentially placing an active force on the archwire. Time brackets have a similar clip but for closure it rotates round a tie-wing rather than slides into place. These three brackets all have potentially active clips. In contrast, Damon brackets have a slide which opens and closes vertically and creates a passive labial surface to the slot with no intention or ability to invade the slot and store force by deflection of a metal clip. Smartclip is also a passive system.


The intended benefit of storing some of the force in the clip as well as in the wire is that in general terms a given wire will have its range of labiolingual action extended and produce more alignment than would a passive slide with the same wire. This needs more detailed consideration. It is perhaps helpful to think of the situation with three different wire sizes.

with thin aligning wires smaller then 0.018" diameter The potentially active clip will be passive and irrelevant unless the tooth (or part of the tooth if it is rotated) is sufficiently lingually placed in relation to a neighbouring tooth that the wire touches the clip. In that situation, a higher total force will usually be applied to the tooth in comparison to a passive clip. Even if there is no significant clip deflection there is still a force on the wire which would not exist with a passive clip because the active clip effectively reduces the slot depth from 0.027" (the depth of a Damon slot) to approximately 0.018", either immediately - if the clip is not deflected - or as the wire goes passive if it is deflected. This additional force is unlikely to be detrimental with modern low modulus wires but should be borne in mind. For teeth which were initially placed lingual to their neighbours, the active clip can bring the tooth more labially (up to a maximum of 0.027 - 0.018 = 0.009 inches) with a given wire. These figures are slightly complicated by the fact that the active clip does not reduce the slot depth to the same extent over the whole height of the slot - the clip on Speed, Time and In-Ovation brackets impinges into the slot more at the gingival end than at the occlusal. This is well visualised in the illustrations in Thorstenson and Kusy (2002b This asymmetry would make a difference with small diameter wires depending on the relative vertical positions if neighbouring teeth. The effect of having an active clip at this early stage of treatment can be thought of as having a potentially shallower bracket slot. This will frequently produce higher forces with a given wire but a potential maximum extra 0.009" of labial movement of some teeth for a given small diameter wire. This figure is approximate for the reasons given above.

).

for wires > 0.018" diameter The active clip will place a continuous lingual force on the wire even when the wire has gone passive. On teeth which are in whole or in part lingual to a neighbouring tooth, the active clip will again bring the tooth (or part of the tooth if rotated) slightly more labial than would have been the case with a passive clip at 0.027" slot depth. The maximum difference will be the difference between the labiolingual dimension of the wire and 0.027". For a typical 0.016" x 0.022" intermediate wire, this would give a maximum difference of 0.005". 0.016" x 0.025" or 0.014 x 0.025 nickel titanium wires are recommended as the intermediate aligning wire for Damon and this wire reduces this potential difference to 0.002". Lingually placed teeth would have a slightly higher initial force with an active clip and wires of this intermediate size. With an active clip, an active lingually-directed force will remain on the wire even when it is passive w ith thick rectangular wires An active clip will probably make a labiolingual difference in tooth position of 0.002" or less which is very small. The suggestion that continued lingually-directed force on the wire from an active clip (or from a conventional ligature) will cause additional torque from an undersized wire is interesting and probably reflects a degree of misunderstanding about the generation of torque in an edgewise slot. Figure 11.14 shows that Figure 11.14: Diagram of a SPEED bracket whatever the orientation or shape of the with conventional and bevelled rectangular wires, rectangular wire, the clip in fact places a both showing the reduced gingival slot wall depth and consequent reduction in torquing ability in one diagonally directed lingual force on the wire which direction. Torque rails on some brackets with a does not contribute to any third order interaction correspondingly narrower clip are intended to between the wire corners and the walls of the address this issue. Selective use of significantly bracket slot - which is the origin of torquing force. higher palatal root torque values would be sensible in upper incisor brackets In fact, the need for an active clip to invade the


slot reduces the available depth of one side of the slot and this means the rectangular wire is not fully engaged. This increases the slop between the rectangular wire and the slot and also reduces the moment arm of the torquing mechanism. Errors in torque can appear as errors in height or as labiolingual contact point errors. SPEED brackets have recently addressed this problem on upper incisors by extending the gingival walls of the slot either side of the clip as torquing rails. This should indeed restore the torquing effectiveness, but at the cost of a reduced mesiodistal width of the clip and therefore reduced rotational control in a bracket which is already narrow. In-Ovation brackets have a small central portion of the slot wall which is at the full slot depth and provides full torquing capacity on that section. Another possible response to this potential problem is to place higher torque values in the direction of the inefficiency in torquing the problem only existing in one direction for a given bracket. This would need to be selectively applied to prevent certain teeth being overtorqued in the opposite direction.

Overall advantages or disadvantages of an active The clipactual clinical consequences of having a potentially active clip impinging into the slot are perhaps

harder to assess than a first thought suggests. It is probable that with an active clip, initial alignment is more complete for a wire of given size to an extent which is potentially clinically useful. However, the increased clearance between a given wire and a passive slide will generate lower forces and may facilitate dissipation of binding forces and the ability of teeth to push each other aside as they align. With modern low modulus wires it is possible to subsequently insert thicker wires into a bracket with a passive clip and arrive at the working archwire size after the same number of visits ie: to store all the force in the wire rather than dividing it between wire and clip. The relative stiffness of archwires and the spring clip is not well documented. If it is assumed that the spring clip has the same stiffness as the thicker nickel titanium wire, then both mechanism would produce the same labiolingual aligning force. Once in the thick working archwire, the potential disadvantages of an active clip are increased friction and potentially reduced torquing capacity in one direction. To put the friction levels in context, these higher friction forces are still much lower than those found with elastomeric ligatures on a conventional tie-wing bracket. All other factors being equal, higher friction is a disadvantage, but again it is hard to assess the loss of clinical performance which arises from this level of increased friction. Finally, there are the questions of robustness, security of ligation and ease of use. Is a clip, which is designed to flex, more prone to breakage or permanent deformation or to inadvertent opening or closing? This question has not been formally investigated.

AgingEliades and Bourauel (2005) have mentioned the possibility of the clips on active self-ligating appliances aging as a result of repeated activations within the oral environment thus reducing the pressure applied to the archwire. Both nickel-titanium and stainless steel alloys undergo significant reduction in their force delivery characteristics as a result of intraoral exposure. In fact a similar argument can be levelled against passive self-ligating appliances which may be subject to wear of the indent that holds the clip shut as a result of repeated opening and closing. There is little direct evidence to support either of these hypotheses but both remain possibilities.

ConclusionThe question of active clip or passive slide may not be the most fundamental aspect of self-ligation, but it is clear that lower force levels are achieved with passive self-ligation. This issue may also be related, through associated design features, to other factors such as security of ligation or ease of use. Although the different effects can be elucidated, it is hard to weigh the extent to which the differences between active and passive affect clinical performance. However, it is hoped that this section of the chapter usefully informs a consideration of the claims made in this context.


Clinical tips when using selfligating bracket s These tips apply in varying degrees to all self-ligating brackets.Further clinical tips in the review article by NH (2003).

Changing treatment mechanics It is useful to briefly list some of the ways that treatment can bechanged to take advantage of the combination of low friction and full, secure bracket engagement.Figure 11.15: TP Traction Hook used to bring upper lateral incisor into the line of the arch while space opening is occurring. The low friction facilitates space opening.

Longer appointment intervals The ability to ensure full and secure wire engagement of modern, low modulus wires makes an extension of the interval between appointments a logical step. Eight to ten-week intervals are usually appropriate. This is a clear advantage for operator and patient. More traction on lighter wires The increased effectiveness of light forces and the decreased loss of control combine to enable more mesiodistal tooth movement to be sensible on lighter, more flexible wires. Compressed coil springs to move teeth apart can appropriately be placed from the first visit in many instances. Separate movement of individual teeth The control of rotation during traction on an individual tooth makes this option much more attractive when required. This can conserve anchorage in a variety of situations without a penalty in loss of tooth control or disproportionate lengthening of the treatment. Parallel processing These mechanical features make it sensible in some malocclusions to retract separately canines to a class 1 relationship whilst simultaneously reducing the overbite. By the time the overbite reduction permits upper incisor retraction, the canines are already class 1, but in good rotational control and the case is further advanced with anchorage conserved. Squeezing teeth into alignment Crowded teeth seem to align more rapidly. If the clinician wishes to align crowded teeth without making space with extractions, these brackets facilitate the alignment. Some clinicians, for example Dwight Damon, have exploited this capacity to an impressive extent. Very interestingly, randomised prospective studies by Peter Miles (personal communication) in press with the Angle Orthodontist have shown no measurable increase in initial alignment at 10 and 20 weeks comparing both Damon 2 and Smartclip brackets with conventional ligation. Perhaps, the cases were not sufficiently irregular to show a difference, perhaps the clinical impression of faster alignment is incorrect, perhaps it is better control of alignment in the later stages that is more significant in potential reduction of treatment duration. Time and further study will tell.

Bracket placement and bondup placement as always is critical to the long-term success of the treatment. Bracket

It is felt that normally, both maxillary and mandibular arches should be bonded at the same time and that bonding should include second molar to second molar in each arch. It is routinely possible to take records (photographs and study models), bond second molar to second molar in each arch and place upper and lower archwires in 60 minutes. For teeth that are well displaced from the archwire or where there is insufficient space to place a bracket in an ideal position, it is helpful to use a TP Traction Hook 224-011 to gain some early control of these teeth;


this can be used to either tie the tooth to the archwire with Power Tube (normally with a space opening coil spring) or to pass through the archwire through the lumen of the traction hook to facilitate early alignment of the tooth. For rotated teeth, it is useful to offset the traction hook so that it is on the part of the crown furthest from the line of the arch to gain some spontaneous derotation. Ormco Damon 2 System Bracket placement is initially a little tricky and takes some getting used to. This is because all the Damon System 2 bracket bodies are rectangular but the edges of the pad are shaped to give the orthodontist the siting cues. The consequence of this is that it is sometimes possible to place the brackets so that the tip is not fully expressed. Damon 3 and Damon MX are rhomboidal brackets.

Opening and closingThere are three components to handling archwires with self-ligation locating the archwire in the slot, closing the slide or clip and opening the slide or clip. Vision In order to close and open the doors or clips easily, it is necessary to be able to see clearly whether the archwire is fully seated in the slot or not. Most problems in closing the doors are due to failure to fully locate the archwire in the slot. It is strongly recommended that operators work under mild magnification (1.5 to 3 times) in order to visualise the relationship between the archwire and the slot. Magnifying loupes do not need to be expensive or elaborate. We have experience of Donegan Optical Companys OptiVisor (extremely practical but not very elegant! Guide price 40.00), the Edroy Products Opticaid (practical, fits existing glasses, guide price 25.00) and NuViews Voroscope MXL (variety of magnification and excellent light source, approximately 400.00). The Voroscope now comes with an LED light which extends the (rechargeable) battery life considerably and has a slightly bluish white light.

Figure 11.16:

The NuView Voroscope MXL

Locating the archwire in the slot With self-ligating brackets it is much more important to fully engage the wire before clip closure rather than attempt to close the clip and simultaneously engage the wire (with SmartClip brackets, this separation of engagement and closure is not possible). There are three reasons why an archwire does not seat in the slot:

there is something in the slot preventing the archwire seating the archwire is not sufficiently deflected (but can be) to seat fully in the slot the archwire cannot be deflected (too stiff) to seat fully in the slot

Plaque or food debris in the slot can be sufficient to prevent the archwire seating fully in the slot; it is suggested that at each visit after the removal of the archwires, patients are given a disposable pre-pasted toothbrush (e.g.: Plak Smacker Pre-Pasted Disposable) to clean their teeth with before the new archwire is placed. This both emphasises the importance of good oral hygiene and ensures that the slots are brushed clean. If this is not possible, then blowing out the slots and tubes with a 3-in-1 syringe will achieve the same effect. Occasionally, some calcified material will be found in the slot and this needs to be removed by the orthodontist.


Key Point: If you cannot see that the archwire is fully seated in the slot then the door will not close; either remove any debris from the archwire slot, deflect the archwire further or choose a less stiff archwire

Tools If the wire is passive labiolingually, a tool is not required. Finger pressure is often sufficient to engage early aligning wires. However, if archwire engagement and clip/slide closure is difficult for a particular tooth, several practical tools and techniques are worth knowing.

for Damon 2 brackets: where a tooth is significantly displaced from the line of the arch, it may help to half-close the door, tuck the archwire behind the half-closed door and then fully close the door. for all bracket types, the wire can be held into the slot with a variety of tools or instruments. Simple tools such as an amalgam plugger, ligature tucker, or Mitchell's trimmer may suffice. However, these only push on one side of the bracket and may fail to fully engage the wire across the whole width of the slot. The Cool Tool (see below) is excellent and pushes on both sides of the bracket. whereas engagement of an irregular tooth with an elastomeric ligature can involve considerable pulling on the tooth, with a self-ligating bracket, a pushing force is required. Reduction of a pulling force on the tooth when placing an elastomeric is difficult, but it is easy to reduce the net push on the tooth when engaging a wire in a self-ligating bracket use a labiolingual squeeze technique. As you push from the labial (e.g. with a Cool Tool), also push the tooth from the lingual/palatal with a thumb of the same hand. The net force on the tooth is greatly reduced and the wire is fully engaged more easily and comfortably if the tooth is very rotated and one end of the slot is too close to the adjacent tooth for an instrument to be used to seat the wire, dental floss or a ligature wire looped over the archwire can be used to fully engage the wire on that side another occasionally useful manoeuvre on a very rotated or displaced tooth with any selfligating bracket, is to first close the clip or slide and then thread the aligning wire through the closed bracket before engaging the other brackets i.e.: to first convert it to a molar tube! once the wire is fully engaged, In-Ovation brackets, Damon 3 and Damon MX brackets and Speed brackets can be closed with a finger. Damon 2 brackets can be closed with ordinary light-wire or bird beak pliers American Orthodontics/Adenta Time brackets are opened with a probe or other fairly sharp instrument such as a Mitchells trimmer using the hole in the clip. Speed brackets and InOvation (System R) brackets can be opened by vertical pressure on the tail of the clip behind the bracket (eg: with a Mitchells trimmer) or can be opened via the hole/notch in the labial surface of the clip (e.g. with a probe).THE TOOL COOL

Figure 11.17: he Cool Tool facilitates archwire engagement when necessary.

The Cool Tool is a specific tool which is rather akin to a torquing key. Dwight Damon has developed this instrument for engagement of wires, via balanced pressure on both sides of the bracket. GAC has more recently developed the R tool, which resembles a double ligature tucker and works in the same way. These specific tools work very well and can reassure the clinician that slide closure is not being attempted over an incompletely seated wire. They can also assist cheek/lip retraction during slide closure and such a tool is firmly recommended as a routine part of slide closure on teeth where the wire requires lingual pressure for full engagement. With thermally active wires, it is theoretically


Plier/Tool Locating archwire in slot Closing door Opening door Damon Cool Tool Damon double-ended tweezer Damon closing pliers RDK Kasso D2 plier Non specialist plier

Table 11.4: The relative effectiveness of different tools in locating the archwire in the slot, closing and opening the doors in the Damon System 2 appliance

easier to insert a wire in some awkward teeth if the Cool Tool is kept in the freezer (as its name suggests).ORMCO SYSTEM DAMON 2

The Damon 2 system is unusual in always requiring an instrument to close the slide. Other brackets can be closed by finger pressure unless there is no space for the finger around a tool being used to fully engage the archwire, in which case any slim instrument can serve instead of the finger. It can be seen from Table 11.4:, that there is no single tool that performs all three actions required to close the doors at the highest level. The best all-round tool was the Damon double-ended tweezer which is very good at locating the archwire and reasonably good at opening and closing the doors. It is important to hold this tool at right angles to the bracket to ensure that it opens and closes the slide without slipping. The door slide was modified in 2004 to have a slightly thicker lip that facilitates the use of the double-ended tweezer. For closing the doors, it is helpful to use it with a two-handed approach. For example, to close a lower central incisor bracket, hold the tweezer in the right hand and use it to locate the archwire in the slot; place the thumb of the left hand behind the tooth to support it and then use the index finger of the left hand to close the door while the right hand uses the tweezer to press the archwire into the slot. It requires a modest amount of force to close the doors and applying the force close to the end of the tweezer makes closure much easier than attempting to do it in a rather daintier fashion! Unfortunately, manufacture of the tweezer has now been discontinued as it has proved very useful for engaging and closing D3 and D3 MX brackets! The Damon closing plier resembles modified distal end cutters. It is excellent for closing the doors but less good for opening the doors in the lower premolar regions. They work better if there is a slight downward rotation to the opening movement. The RDK Kasso D2 plier is slightly more difficult to use than the Damon closing plier but opens and closes the doors without difficulty. These pliers may be recommended for all first-time users since they make all slides very easy to open. Importantly, no downward rotation is required when using these pliers. For more experienced users, the recent redesign of the lower second premolar brackets has made opening and closing easier with the standard Damon pliers. Finally it should be said that the doors can be opened and closed with almost any plier (bird-beaks, light-wire pliers, Weingart utility pliers) although this is marginally more difficult than using a specialist plier.DAMON 3 AND DAMON MX

The opening and closing of these Damon brackets is much easier than with the Damon 2 System. The brackets can be closed with finger pressure and a simple tool resembling a modified probe is used to open the bracket. It is as easy as that!Figure 11.18: Kasso D2 plier RDK Specialties


Biting out

Archwire s

Initial placement When placing the initial archwires, do not include the second molars. The patient will frequently bite an 0.014" archwire out of the second molar tubes; it is better to terminate the archwires at the first molars for the first visit and then pick up the second molars on the first nickel titanium rectangular archwires (0.014" x 0.025" or 0.016" x 0.025"). Long unsupported spans

use tie-backs with flexible wires over extraction sites to lessen the effects of occlusal forces on unprotected spans of wire use small tubes bonded to deciduous teeth to reduce the length of the span support the wire with lengths of hard tubing just shorter than the unsupported space to allow for tooth movement

Prevention of swivellingLow friction increases wire displacement. Ironically, the problems of wire displacement resulting from low friction are perhaps the most convincing and immediate clinical evidence that the low friction found in laboratory studies is readily apparent in vivo . Even with very irregular teeth, the very low friction with selfligating brackets, especially in bracket systems that use a passive slide, enables aligning archwires to slip through the brackets and an archwire end to protrude. This is clearly a potential nuisance. Steps to prevent this can include:

small sections of stainless steel tube crimped onto the archwire. This is quick, easy, versatile and recommended. 0.5 mm tubing (approx. 0.020" internal diameter) is a good size for smaller diameter wires. With larger wires, 0.7 mm tubing is required, but a crimp-on hook may be a better option since it is harder to crimp tubing securely onto the flat surface of a rectangular wire. Stops are usually placed in the lower anterior region and in the upper premolar region and should normally be placed anterior to the crowding one is usually sufficient unless there are very long interbracket spans (such as partial fixed appliances in the mixed dentition) when one either side of a bracket may be required. It is recommended that the stop is not placed on a significantly active part of the archwire. This would diminish the range of action of the wire where it is most needed placing a crimpable split stop on the archwire. Two sizes are available 0.016" and 0.022" and are available from manufacturers such as 3M Unitek and Orec Speed. Damon archwires are now available with small sections of steel tube already loaded and temporarily fixed in the midline by wax. This stop can be moved to the desired position and crimped. This is very convenient. flowable composite (e.g. Kerr Revolution 2) can be bonded to the archwire. The archwire must be dry. thorough turning in the ends of flexible archwires. An interesting innovation in this respect is the Bendistal plier described by Khouri (1998) . This is designed to place an effective distal end bend in a superelastic wire without the need for over-bending which can be difficult and uncomfortable and also risks the loss of a bonded molar tube selective locking of individual brackets to the archwire with elastomerics can be helpful in those designs which have a full conventional tie-wing assembly small V-shaped notches in the midline of flexible wires can also limit the scope for wire swivelling. These are commercially available or can be bent into nickel-titanium wires with triple beak pliers. Pre-notched wires are usually more expensive. Sometimes in the lower arch the notches are too large for the available inter-bracket span. Also, some notches can creep into the adjacent bracket and cause irregularity of that tooth. For these reasons, this particular method is not personally recommended


Archwire SequenceOrmco Damon brackets systems Archwire sequencing is a little different with self-ligating brackets principally because of their excellent control between bracket and archwire. It is important to give each archwire time to work out fully and so treatment intervals of 8-10 weeks are suggested. For patients with very irregular teeth, it may be necessary to continue the initial archwire for more than one visit; the emphasis is on light forces and giving the archwires the time to fully express their potential aligning capacity. The primary archwire sequence is as follows:

0.014" nickel titanium superelastic 0.014" x 0.025" nickel titanium superelastic o consider an OPG once this wire has been in place for one visit to check root angulations 0.019" x 0.025" nickel titanium superelastic 0.019" x 0.025" stainless steel

Where teeth are significantly displaced from the archwire and there is insufficient space to accommodate them in the dental arch, space should be made using an open nickel titanium coil spring. The coil spring should be approximately one bracket width wider than the space in which it is going to fit for normal interbracket spans. At the same time, a narrow attachment, such as a TP Traction Hook, should be bonded to the displaced tooth and tied on to the archwire with elastic thread (e.g.: PowerTube). This prevents proclination of the teeth during space opening by placing a lingual or palatal restraining force on the arch wire and speeds up the alignment process. Once sufficient space is available and the displaced tooth is close to the line of the arch, an initial aligning archwire can be placed through the traction hook to bring the displaced tooth into the arch prior to replacing the traction hook with a self-ligating bracket. Once tooth alignment has been achieved, a continuous wire ligature can be used to prevent space opening up in the labial segments. Secondary archwires and wires are as follows:

0.016" x 0.025" nickel titanium superelastic archwire o this archwire is useful in cases with less irregularity as the next archwire step from the initial 0.014" nickel titanium superelastic archwire straight lengths of 0.014" x 0.025" or 0.019" x 0.025" nickel titanium superelastic archwire o used for crossbite correction requiring arch expansion. Evidence on effectiveness required. 0.019" x 0.025" RCOS (reverse curve of Spee) nickel titanium superelastic archwire o used for managing deep overbites in both the upper and lower arches 0.019" x 0.025" RCOS nickel titanium superelastic torqued (SET) archwire o used where additional torque is required 0.019" x 0.025" TMA o useful for individual tooth movements at the end of treatment where archwire bends are required, especially for inclination (torque) adjustments. Consider using low friction variants if space closure required on this archwire 0.021" x 0.025" TMA o used if full expression of bracket prescription is required; however not always as effective as one might think and may require other solutions

Distal endsThere is no need to turn down the distal ends of the archwires as the wires are already stopped by the crimpable stop. In addition, turning down archwires distal to second molars is a frequent source of soft tissue trauma. Archwires should be cut flush with the distal end of the tube on the terminal molar. We


experience no debonding of molar tubes when using distal end cutters and this may be partially due to taking care that the plane of the distal end cutters is the same as the archwire plane i.e.: the plane of the archwire bisects the joint of the distal end cutters. This prevents torquing forces being placed on the wire at the moment of cutting. In the upper arch, this necessitates lifting one's elbow up considerably to align the distal end cutters with the plane of the archwire. When cutting stainless steel archwires prior to insertion in the mouth, cut the wire at an angle to provide a tapered end for insertion into the first and second molar tubes. In extreme cases, gentle reduction of the terminal portion of the wire with a green stone may facilitate insertion into the molar tubes.

Archfor m T he Damon archform does not distinguish between upper and lower archforms.

The argument is that as the upper arch is a little forward of the lower arch and that this provides the differential size requirement required; in practice this seems to work satisfactorily. The Damon archform provides expansion in the premolar and molar regions but not in the intercanine region. Customisation of archform cannot obviously take place until the working archwires stage.

ElasticsMost self-ligating brackets, such as Damon brackets, have sufficiently large tie wings to easily accommodate two links of elastomeric chain, allow the wire ligation of blocks of teeth or accept elastics to settle in the occlusion in the final phases of treatment. Possible configurations of elastics are shown in Figures 11.19 to 11.24. Damon MX brackets permit the instant placement of a ball-ended hook on any tooth. Speed brackets and Opal brackets have no tie-wings

Debondin g Self-ligating brackets are more rigid than conventional siamese brackets because of the engineeringrequirements of the body of the bracket and the need to provide a rigid housing for the clip or door. This means that at debonding, bracket removal does not occur by failure of the bracket adhesive interface by

Figure 11.19: Class 2 elastics; cutting distal to the lower first molars speeds up the rate of correction

Figure 11.20: Class 3 elastics; cutting distal to the upper first molars speeds up the rate of correction

Figure 11.21: Posterior V elastics are used to develop interdigitation in the buccal segments

Figure 11.22: An anterior trapezoidal elastics is used to close down anterior open bites

Figure 11.23: A Kobayashi ligature placed on one of the lower central incisor brackets makes it more comfortable to wear an anterior cross elastic

Figure 11.24: Triangular elastics or Schudy elastics can be used to develop buccal segment interdigitation in the last few weeks of treatment


deformation of the bracket but by direct failure of the bracket adhesive interface, cohesive failure of the adhesive, direct failure of the adhesive enamel interface or a combination of any of these. The risk of enamel fracture has always been present with stainless steel and ceramic brackets, particularly in teeth where the integrity of the crown is compromised. The risk of enamel fracture is now increased by:

brackets with a rigid, non-deformable body structure the higher bond strengths delivered by adhesion enhancers and improved adhesives (3M Unitek have recently issued a warning that 3M Adper Prompt L-Pop Self Etch is unsuitable for orthodontic use because of the high bond strengths generated)

The best way to debond Damon 2 System brackets is by squeezing two tiewings only with a conventional debonding plier. The bracket will silently float off the adhesive.

Retentio nDr Dwight Damon uses upper and lower clear overlay retainers as well as a bonded upper and a bonded lower

2|2

retainer

3|3

retainer. The upper retainer is made from 0.016" x 0.022" Reliance Hilgers Bond-

a-Braid which is a flat braided archwire. That is placed flat on the cingulae of the upper incisors to prevent spontaneous debonding. In the lower arch, a 0.025" single strand stainless steel wire is bonded to the lingual surface of the lower canines only; the ends of the retainer are sandblasted to aid retention. Clear overlay retainers are used in addition on a night time only basis. Also the chapter on Retention Stability and

Cost and treatment efficiency Currently available self-ligating brackets are more expensive than most good quality tie-wing brackets.

A modest balancing factor is the cost of elastic ligatures which are, of course not required. However this significant extra cost must be measured against savings in time - an expensive commodity. If self-ligating brackets save any appreciable chairside time as the studies by Maijer and Smith (1990) and Shivapuja and Berger (1994) suggest, this would provide an offsetting saving. The study of treatment efficiency (Harradine 2001) using matched pairs of cases found the following:

a very modest average time saving from a reduction in archwire placement/removal of 24 seconds per arch a mean reduction of four months in treatment time (from 23.5 to 19.4 months) a mean reduction of four visits during active treatment. (from 16 to 12). the same reduction in PAR scores for matched cases

This finding of a mean reduction of four months in treatment time using Damon SL brackets was also reported by Dr Bob Fry in a presentation at the AAO Annual Session in Toronto 2001. He had converted one of his two offices to Damon SL. The office management software subsequently revealed that his treatment times reduced by an average of four months compared to his other office where he had, for the time being, stayed with conventional ligation. A study by Eberting et al (2001) of intra-practitioner differences in three practices found an average reduction in treatment time of 7 months (from 30 to 25) and


7 visits (from 28 to 21) for Damon SL cases compared to conventional ligation. The final average ABO occlusal regularity score was higher (better) for the Damon cases. These three reports support a view of clinically significant improvements in treatment efficiency with passive self-ligating brackets. The more recent bracket types would be expected to show still better treatment efficiency. More evidence is required and random controlled trials are currently comparing treatment times in conventional and self-ligating brackets.

ReflectionCurrently available self-ligating brackets offer the very valuable combination of extremely low friction and secure full bracket engagement and deliver much of the potential advantages of this type of bracket. Some recent bracket types have excellent handling characteristics for opening and closing the slide. These developments offer the possibility of a significant reduction in average treatment times and also in anchorage requirements in cases requiring large tooth movements. An additional area of development has been the introduction of more aesthetic self-ligating brackets. Whilst further refinements are desirable and further studies essential, current brackets are able to deliver measurable benefit with excellent robustness and ease of use. It is probably true to say that if the self-ligating appliance is viewed just as another bracket system then the orthodontist will not get the best out of it. The combination of minimal friction, low forces and extended time between adjustment visits allows tooth movements to occur which can be argued are technically not possible with conventional bracket systems. The orthodontist is technically able to more easily treat many cases without extraction that previously would have required extractions for the technical success of treatment (compare the management of a mildly crowded class 2 division i case with four first premolar extractions to reduce the overjet and establish a class 1 molar relationship and the management of the same case with a functional appliance, no extractions and upper and lower fixed appliances). Non-extraction treatment has two potential disadvantages: damage to the periodontium in the form of bony dehiscences and gingival recession and increased potential for relapse. Both of these need continuing investigation before we fully understand the balance to be achieved between the possibilities of technical achievement and the biologic limitations of periodontal health and occlusal stability. In the meantime, we are enormously enthusiastic about this high technology development in orthodontics and it has been the mainstay of our clinical practice since 2001.

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Wildman AJ (1998) The Wildman TwinLock bracket Clinical Impressions published by Ormco Corporation 7 (2): 2-5