EDITORIAL
Marlena Kosior, Joanna Antoszewska, Beata Kawala
Self-Ligating Brackets – the Facts and the Myths
Zamki samoligaturujące – fakty i mity
Department of Orthodontics and Dentofacial Orthopedics, Wroclaw Medical University, Poland
Abstract
Self-ligating brackets are not a new concept in orthodontics, however a revival of interest in them began in the early 2000s. During the last few decades, it is again becoming a popular belief that self-ligating brackets have an advantage over traditional ones. The commercial effect has undoubtedly been supported with clinical theories regarding not only the reduction of friction in the slot, but also shorter chair-side time or total treatment time. Other theses have mentioned the widening effect of the appliance, a lesser tendency for root resorption, a better environment for proper oral hygiene or acceptation of the patient. The aim of the article is to review the literature about self-ligating brackets, which will allow the reader to objectively verify their advantages (Dent. Med. Probl.
2012, 49, 1, 13–17).
Key words: self-ligating brackets, low-friction system.
Streszczenie
Zamki samoligaturujące nie są nowością w ortodoncji, ponowne zainteresowanie nimi zaczęło się jednak na począt-ku lat 20. XX w. W ciągu ostatnich kilpocząt-ku dekad znów rozpowszechnił się pogląd, że systemy bezligaturowe mają przewagę nad zamkami tradycyjnymi. Rezultat komercyjny był niewątpliwie wspomagany teoriami klinicznymi dotyczącymi nie tylko zmniejszenia tarcia łuku w slocie, ale także skróconego czasu trwania wizyt lub samego leczenia. Inne tezy mówiły o poszerzającym działaniu aparatu, mniejszej tendencji do resorpcji korzeni, lepszych warunkach utrzymywania higieny jamy ustnej lub też większej akceptacji pacjenta. Celem pracy jest dokonanie przeglądu piśmiennictwa, który pozwoli na obiektywną weryfikację potencjalnych zalet systemów bezligaturowych (Dent. Med. Probl. 2012, 49, 1, 13–17).
Słowa kluczowe: zamki samoligaturujące, zamki bezligaturowe, system małego tarcia.
Dent. Med. Probl. 2012, 49, 1, 13–17
ISSN 1644-387X © Copyright by Wroclaw Medical University and Polish Dental Society
Self-ligating brackets are not a new concept in orthodontics – they were invented in the ear-ly 1930s by Stolzenberg [1, 2] as Russel’s attach-ments. Their main advantage was supposed to be a more efficient archwire insertion and therefore chair-side time reduction. Due to skepticism by orthodontists and lack of promotion, self-ligating brackets did not become popular and were over-shadowed by traditional brackets. Nevertheless, over the last few decades it has once again become believed that self-ligating brackets have advantag-es over traditional onadvantag-es. Due to this fact, many companies had tried to introduce their brackets, but only some of them have become commercial-ly available [3].
The revival of interest in self-ligating brackets came in the early 2000s, when Keim said that the
key ideas for the future development of orthodon-tics were 3D imaging, self-litigating systems and temporary skeletal anchorage. Since that time, the development of self-litigating brackets has gained steam, which has resulted in the invention of thir-teen types of brackets, which in turn have im-proved their sales [3]. The commercial effect has undoubtedly been supported by clinical theories regarding not only the reduction of friction in the slot, but also the reduction in time spent per vis-it during treatment. Other theories have spoken of the widening effect of the appliance, a smaller ten-dency for resorption, easier hygiene maintenance and wider acceptation by patients [2]. The goal of this study is an analysis of the articles which will allow for an objective verification of the potential benefits of self-litigating systems.
Evaluated Features
Friction
The goal of inventing self-ligating brackets was to eliminate ligating ties, which would create a fric-tion-free background. Uninhibited movement of the archwire in the inflexible slot allowed for more ef-fective sliding, which resulted in biologically accept-ed raccept-eduction of forces and their momentum [4, 5]. This idea aroused the interest of clinicians and in-tense research comparing self-ligating and tradi-tional brackets had begun – the point of which was the reduction of friction. A systematic review by Chen et al. [1] proved that such a reduction is often observed in the case of self-ligating brackets. Fur-thermore, many authors [3, 6] stated significant-ly lower friction in self-ligating brackets when us-ing either NiTi or steel wires. Based on these re-sults, Damon [7] determined that thanks to the reduction in friction, the orthodontic forces on the arch are lower, which allows for more physiological movement of teeth without straining the muscles or periodontal vessels. Damon [7] found opponents to his statement. According to Franchi et al. [8] as well as Petersen et al. [9], the lower friction from self-ligating brackets causes greater force on the archwire in comparison to conventional brackets. They came to this conclusion by measuring forc-es at the tooth leveling stage. Furthermore, Lotfus et al. [10], who compared friction in Damon brack-ets to conventional brackbrack-ets in vivo, didn’t find any significant difference, therefore contradicting Da-mon as well, but in a different way.
The theoretical reduction of friction in self-li-gating brackets allows for faster space closure in cases required extraction. This theory was de-bunked by research conducted by Scott et al. [11] and Miles et al. [12] who did not observe any ad-vantage of self-ligating brackets over tradition-al ones. They observed similar tooth movement times regardless of which of the two bracket sys-tems were used.
Further studies regarding friction required more accurate analysis of the behavior of the archwire in self-ligating bracket slots which con-tained 4 walls: two horizontal – occlusal and gum, one vertical, and one buccal. The latter of these walls can have different forms – a movable flap or a clip. Depending on the construction of the bracket, self-ligating brackets can be divided into two groups – active and passive, the key determin-ing division bedetermin-ing the construction of the slot and the buccal wall [13].
One of the characteristics of self-ligating brack-ets is the slot, which becomes shallower on the ver-tical plane from the occlusal edge towards the
gin-gival edge. This is caused by the difference in the horizontal bracket’s walls: the gingival wall is shal-lower than the occlusal wall. For example, the In-Ovation® bracket’s horizontal gingival wall is 0.195 inches and the occlusal wall is 0.285 inches.
Active brackets are equipped with a spring based clip which, pushing on the archwire, al-lows for all the values built in the bracket to be ex-pressed; it helps to control rotation and torque.
All values built into the bracket may be ex-pressed without the necessity of applying a full-sized archwire [2]. Pushing the clap on the archwire generates friction and forces action of the archi-wire toward the buccal or labial directions, which helps in leveling the teeth. According to Chen et al. [1] and Harradine et al. [14] active brackets have an advantage over passive ones due to the presence of friction at the early stages of leveling the teeth, especially when tooth rotation is supposed to oc-cur. Examples of active brackets are: In-Ovation® (GAC International, Central Islip, NY), SPEED® (Strite Industries, Cambridge, Ontario, Canada), Time® (Adenta, Gilching/Munich, Germany) and Quick® (Forestadent) [2, 14].
In passive brackets, the horizontal walls (gin-gival and occlusal) have the same dimensions. The buccal wall is usually equipped with a slide clip, which doesn’t enter inside the slot and doesn’t de-crease it’s diameter after closure. The slide clip doesn’t push the archwire in the slot – thus allow-ing for it’s uninhibited movement which results in lesser friction in comparison to active brack-ets [15]. This is however, controversial. It cannot be said that the bracket is passive from the beginning of treatment. The slot can be passive only when the teeth are properly aligned in all three dimen-sions, so that they express correct angulation and torque, and the full-sized archwire doesn’t have contact with the walls of the slot [2]. This has been evidenced by Brauchlia et al. [16] who compared the in vitro action of passive and active self-ligat-ing brackets, as well as conventional brackets. The authors didn’t notice any significant difference in the action of non full-sized archwires in active and passive brackets until the teeth had been ful-ly leveled. Friction decreased in the passive brack-ets in later stages. On the other hand, according to Henao et al. [17], the friction in passive brackets is minor in the early stages of treatment, which al-lows for more effective tooth movement along the archwire. Nevertheless, the price that must be paid for this free movement of the teeth is worse move-ment control in the palato-labial direction as well as rotation in comparison to active brackets. Ex-amples of brackets with active slots are: Damon® (Ormco, Glendora, Calif), SmartClip® (3M Unitek, Monvoria, Calif) and Carriere® (Class One).
Shorter Chair-side Time
and Treatment Time
Voudouris [18] had approximately four times shorter chair-side time when using self-ligating brackets in comparison with conventional ones. In cross-sectional studies [19, 20] it has been ob-served that in the case of one archwire, it takes ap-proximately 20 seconds less time to perform liga-ture removal on tradition brackets, but this differ-ence is not statistically significant. Nevertheless, a systematic review performed by Fleming and Jo-hal [21] has proved clearly that the advantage of self-ligating brackets is shorter chair-side time thanks to an opening and closing mechanism al-lowing for quicker archwire removal and inser-tion. Since the shorter chair-side time had been proven, many authors have tried to compare to-tal treatment times depending on bracket type: conventional and self-ligating. Researchers have conveyed total treatment time abridgement of about 4–7 months, based on the assumption that less friction, lesser forces and more physiological tooth movement provide shorter treatment time. The number of appointments could be limited from 4 to 7 [4, 19, 22] as well as their frequency re-duced [5]. The authors also emphasized that arch-wire removal and insertion does not require the help of an assistant, which results in a more ergo-nomic work environment [4]. Nevertheless, assess-ment of real total treatassess-ment abridgeassess-ment with the usage of self-ligating brackets has not been accom-plished with a systematic review.
Dental Arch Expansion
Another feature of self-ligating brackets is better action during crowded leveling. They help to expand dental arches in cases that are on the border between extraction and non-extraction treatment [4]. On the basis of the comparison of the actions of passive and active slots, it is known that it is possible not due to free archwire move-ment in the slot, but due to pressure of the clip to-ward the archwire in the slot of an active bracket. Moreover, in contrast to most traditional brackets, self-ligating brackets have narrower bases, so the spans of the archwire between brackets are lon-ger and the contact between the bracket and the archwire in the slot is shorter. Due to the fact that the force released by an archwire is inversely pro-portionate to its length, a smaller contact between the slot and the archwire generates lesser forc-es, [4] and a longer span between adjacent brack-ets makes the archwire more flexible and gives it more scope of work [23]. Both of these phys-ical qualities can be the reason for better tooth
leveling at the early stages of treatment [4]. Un-fortunately, this concept has not been proven in
in vivo studies. Miles [24] and Ong et al. [25]
com-pared the rate of tooth leveling in self-ligating and traditional brackets and were unable to prove any advantages in one type over another in elimina-tion of crowding or expansion of the dental arch. The effectiveness of traditional brackets, regard-less of the type of ligatures (elastic or wire), was similar after 20 weeks of treatment. It has been rightly observed by the authors that most of the studies about friction of self-ligating brackets are performed in vitro, and the oral background and muscles are not considered despite the fact that they can increase the friction.
Expansion of the dental arches generates bet-ter conditions for minor tooth proclination; there-fore indicators for extraction may be restricted. This has not been proven in studies by Pandis et al. [26] and Fleming et al. [27], who achieved the same proclination of the upper and lower teeth and same inter-canine dimension regardless of the ap-pliance used. However, randomized research [11] and a systematic review performed by Chen et al. [1] have proven that proclination of the inci-sors was about 1.5 mm less in self-ligating brack-ets in comparison to traditional ones due to the advantage of transverse forces over sagittal ones. Space on an alveolar may be created by the wid-ening of the circuit of the dental arch rather than by it’s elongation. This theory has been proven by Fleming et al. [27] and Pandis et al. [28], who re-ported greater dental arch expansion of the level of molars in self-ligating bracket in comparison to traditional ones.
Minor Tendency
for Root Resorption
Contrary to expectations, there is no unequiv-ocal evidence confirming minor root resorption after treatment with self-ligating brackets. Pandis et al. [29] found no statistical significance in root resorption in comparative studies. Moreover, Scott et al. [11] reported larger root resorption when us-ing Damon’s brackets than in conventional brack-ets – 2.26 in the former versus 1.21 in the latter.
Easier Intra-oral Hygiene
In theory, smaller brackets dimensions and less retention spaces (such as the ends of metal ligatures and elastic ligatures) may provide easier hygiene maintenance. Pellegrini et al. [30] proved in retro-spective studies a lower level of Streptococcus in the presence of self-ligating brackets, however Pan-dis et al. [31] did not find any correlation between
the type of brackets and the level of the bacteria – the evaluation of the accumulation of plaque, cal-culus and gingivitis in 50 patients wearing conven-tional brackets and 50 patients wearing self-ligat-ing brackets durself-ligat-ing an 18-month treatment period showed no difference in the mentioned indexes in either groups. In turn, Fortini et al. [32] claim that the hygiene around the brackets is impeded re-gardless of its type and it should be conceded that controversy about this is still ongoing.
Better Patient Tolerance
There are reports about better toleration of self-ligating brackets by patients. However, there is no systematic review confirming this, which may lead to mistaken conclusions [2, 25]. The feeling of less discomfort should be considered as subjective and not an evidence-based symptom [19, 22, 33].
Conclusions
The disadvantages of self-ligating brackets, such as the high cost, the possibility of clap dam-age, and higher vestibule dimensions causing the possibility of mucosa irritation or occlusal
ob-struction are obvious [13]. In addition, self-ligat-ing brackets usually have smaller bases and trans-verse dimensions, what may be the reason for fre-quent debonding – in particular on premolars and molars [34]. Moreover, self-ligating brackets with passive slots may be an impediment in the finish-ing stage [1, 32, 35, 36].
Lower friction, bio-compatible forces, and bet-ter tooth leveling in the early stages are features unduly attributed to self-ligating brackets.
According to the reports cited in the above- -presented literary review, forces when using self- -ligating brackets at early stages of treatment may be larger than in traditional brackets. Moreover, leveling of the teeth proceeds at the same rate re-gardless of the type of brackets.
If the only indisputable and evidence-based advantages of self-ligating brackets are short-er chair-side time and proclination control of the lower incisors, then Stolzenberg’s original sugges-tions, which were reduction of chair-side time and the possibility of decreasing the proclination of the lower incisors by 1.5 degrees, should be used as a guide when deciding whether to use self-ligating brackets or traditional ones. Any other advantages of these brackets should be considered as market-ing hype and requirmarket-ing further evidence.
References
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[35] Kusy R.P.: Orthodontic biomechanics: vistas from the top of a new century. Am. J. Orthod. Dentofac. Orthop. 2000, 117, 589–591.
[36] Thorstenson G.A., Kusy R.P.: Effect of archwire size and material on the resistance to sliding of self-ligating brackets with second order angulation in the dry state. Am. J. Orthod. Dentofac. Orthop. 2002, 122, 295–305.
Address for correspondence:
Joanna Antoszewska
Department of Orthodontics and Dentofacial Orthopedics Wroclaw Medical University
Krakowska 26 50-425 Wrocław Poland Tel./fax: +48 71 784 02 99 E-mail: stomjan@gmail.com Received: 8.12.2011 Revised: 2.01.2012 Accepted: 23.02.2012
Praca wpłynęła do Redakcji: 8.12.2011 r. Po recenzji: 2.01.2012 r.
