POINT/COUNTERPOINT

Self-ligating brackets increase treatmentefficiency

Nigel HarradineBristol, United Kingdom

1

S ince an early stage in the development ofself-ligating brackets, authors have proposedadvantages in relation to treatment effi-

ciency.1-4 Increased efficiency can be defined asachieving a result that is as good or better, with an in-crease in factors that are valued by the provider or therecipient of a service. In orthodontic treatment, thesefactors could include fewer appointments, shorter ap-pointments, more comfortable treatment, practicalprocedures that are technically easier for the clinicianor the patient, less need for extractions, and less painor anxiety for the patient. There could also be factorsrelating to outcome, such as less decalcification orroot resorption, and more certain or better results. Allof these have been proposed by some authors in rela-tion to self-ligation. The core assets of self-ligation,which form the basis of any such proposal, can be sum-marized as follows: secure, full archwire engagement;lower resistance to sliding between bracket and arch-wire; faster ligation and archwire removal; and lessneed for chair-side assistance.

SECURE, FULL ARCHWIRE ENGAGEMENT

Absolute security of archwire engagement—as pro-vided by a molar tube—would inherently reduce treat-ment inefficiencies compared with conventionalligation. Although the potential for decay or loss ofelastomeric ligatures is well known, only decay hasbeen extensively investigated. One study did quantifythe loss of elastomeric ligatures, finding 15 lost liga-tures in 25 consecutively seen patients in a 12-monthtreatment period.5 Some early self-ligating bracketsdid not deliver the secure engagement of a molartube, but today most self-ligating brackets have mech-anisms to deliver this advantage and would by defini-tion ensure full engagement of all archwires and

Consultant orthodontist, Bristol Dental Hospital, Bristol, United Kingdom.Reprint requests to: Nigel Harradine, Bristol Dental Hospital, Lower MaudlinSt, Bristol BS1 2LY, Bristol, United Kingdom; e-mail, nigel.harradine@bristol.ac.uk.Am J Orthod Dentofacial Orthop 2013;143:10-90889-5406/$36.00Copyright � 2013 by the American Association of Orthodontists.http://dx.doi.org/10.1016/j.ajodo.2012.10.011

0

eliminate the need to regain control of the teethwhen full engagement is lost.5 In a recent study of ca-nine retraction with 0.018-in stainless steel wires, self-ligating brackets were found to give better rotationalcontrol of the canine than conventionally ligatedbrackets.6 Furthermore, 80% of the canines rotatedmore than 10� with conventional brackets, as opposedto 33% with self-ligating brackets, over the 12-weekperiod.

FASTER LIGATION AND ARCHWIRE REMOVAL

The original motive when developing self-ligatingbrackets was to speed the process of archwire ligation.Several authors have shown self-ligating brackets to bebetter in this respect, with savings of up to 9 minutesper visit compared with wire ligation and approxi-mately 2 minutes compared with elastomeric liga-tion.5,7-10 In these studies, unassisted archwireligation with self-ligating brackets was comparedwith conventional ligation performed with a chair-side assistant to speed the process. It is probable thatmany of the more recent bracket types would showgreater time savings for archwire changes because themechanisms have become significantly easier to use.Interestingly, almost no recent studies with these newerbrackets have emerged, probably because the speedand ease of use of the more modern self-ligatingbrackets is now taken for granted.

LOWER RESISTANCE TO SLIDING

When drawing wires through well-aligned brackets,friction is the only source of resistance to sliding, andfriction has consistently been measured as much lowerin self-ligating brackets than in conventionally ligatedbrackets.8,11-18 Studies typically report values of almostzero with self-ligating brackets and values from 43 to98 g per bracket for various elastomeric-archwire com-binations. The obvious next requirement was to inves-tigate resistance to sliding with active archwires, wherebinding is an important contributor; this has been thor-oughly investigated, particularly by Thorstenson andKusy.19-22 These authors examined the effects of vary-ing active tip (angulation) on the resulting resistance to

12 Point

J

sliding (Table). They calculated that for an 0.018 30.025-in stainless steel archwire, an activation of 6�

was clinically the most relevant, since beyond that an-gle uprighting forces from the archwire would limit fur-ther tipping and cause the tooth to “walk” along thearchwire in a series of binding and releasing move-ments around this angle. At this angulation of 6�, thedifference in resistance to sliding is 60 g per bracket.Fig 10 in Thorstenson and Kusy's paper,19 which illus-trates these data, shows “clinically relevant illustrationsshowing that in terms of sliding with second order an-gulation, this bracket is superior to the conventionalbracket.” Interpretation of this important point canvary widely, even when the same research is being

For self-ligation, the core features ofsecurity of ligation, lower resistance

to sliding, and more rapid andconvenient archwire changesremain and are increasinglysupported by good studies.

quoted. For example, Brauchliet al23 correctly quoted datafrom Thorstenson and Kusy19 tothe effect that for an 0.018 30.025-in wire and a self-ligatingbracket “with angulations of 7�

between the archwire and slot,more than 94% of the [resistanceto sliding] is caused by binding.”However, this has been taken to

imply that the contribution to resistance to slidingfrom the lowered friction of self-ligating brackets istherefore irrelevant when archwire activation causesbinding. In fact, it is the low friction with self-ligating brackets that makes any binding componentsuch a high percentage of the overall resistance to slid-ing. If the friction is zero—and it is usually close to zerowith self-ligating brackets—the binding componentwill correspondingly constitute 100% of the resistanceto sliding. Pliska et al24 also found that at high anglesof tip, the reduction in friction with self-ligatingbrackets is drowned by the high binding, but at lowerand clinically more relevant levels of activation, reduc-tions in resistance to sliding averaging 40 g were foundwith self-ligating brackets. Studies of aligning wiresplaced in irregularly aligned brackets have also shownlarge reductions in resistance to sliding with self-ligating brackets in all 3 planes of space.25-29 Threeof these articles specifically measured the other sideof the equation: the net residual aligning force avail-able to act on the displaced tooth after the lossesfrom resistance to sliding. Typically in these studies,a bracket displaced by 4 mm from its neighbors hasno residual aligning force with conventional ligationbut 80 g of aligning force with self-ligating brackets.Peterson et al29 showed that artificial aging of elasticsreduced this differential, but Matasa30 demonstratedthe consequent trade-off for elastomerics with the

anuary 2013 � Vol 143 � Issue 1 American

loss of ligating force available for tooth control. Inter-estingly, these laboratory results were similar to an in-vivo study by Crawford et al,31 who commented that“the results of our in situ study concur with those ofthe best outcomes from the laboratory studies.” Well-designed in-vitro studies may indeed give a good in-sight into in-vivo conditions. In a systematic reviewof this question, the authors concluded that the caseis proven for lower resistance to sliding with self-ligation with round wires, but not for the larger rectan-gular wires where more evidence is still required.32 Aninteresting facet of the study selection for this reviewwas that 2 of the seminal articles by Thorstenson andKusy referred to above were not mentioned.

Journal of Orthodontics a

Lower resistance tosliding in clinical useseems probable, as doesthe effectiveness of lighterapplied forces, since lessforce for the desired toothmovement is “eaten up” asresistance to sliding.29 Thequestion is whether thisdifference translates into

any measurable improvements in the treatment processor the outcome.

MORE RAPID TREATMENT

Several consecutive case series studies found thattreatment with self-ligating brackets was quicker,required fewer visits, and resulted in as good or betterfinal alignment and occlusion than treatment withconventional appliances.4,32-34 However, other similarstudies35-37 and all randomized controlled studiesto date38-43 have found no difference in these parame-ters between self-ligating and conventional brackets invarious parts of the treatment process. Two recent sys-tematic reviews have understandably concluded thatthere is insufficient evidence to support the view thattreatment with self-ligating brackets results in fewervisits or shorter treatment.44,45 It seems probable thatself-ligating brackets, by themselves, do not confera blanket advantage of reduction in duration of treat-ment and that randomized controlled trials with a gen-eral case mix when the bracket type is the only testedvariable and all other treatment mechanics are identicalwill continue to find no difference in average treatmentduration. It is possible that in certain patients and witharchwires and reappointment intervals customized tomatch the biomechanical differences of lower resistanceto sliding and better ligation control, self-ligation mightreduce treatment duration. However, no randomized

nd Dentofacial Orthopedics

Table. Resistance to sliding for different bracket an-gulations with an 0.018 3 0.025-in archwire19

Angulation (�) Damon SL (cN) Conventional bracket (cN)0 0 343.5 0 556.0 80 140

The difference in forces is 60 g at 6� of angulation.

14 Point

J

controlled trial has succeeded in supporting the viewthat fully preadjusted straight-wire brackets are superiorto plain edgewise brackets, although their superior effi-ciency is universally assumed and adopted. Similarly, af-ter several decades of use, only 1 recent study hassucceeded in supporting the view that nickel-titaniumaligning archwires are more effective than multistrandstainless steel—and then, only with Begg brackets, notwith preadjusted edgewise brackets.46 Randomized con-trolled trials are vitally important, and I have been an au-thor of and a participant in several, but in orthodontics,the authors of these studies have for various reasonsstruggled to find differences between treatment modal-ities.

IS TREATMENT LESS PAINFUL WITH SELF-LIGATION?

The notion that treatment with self-ligatingbrackets is less painful has 2 possible explanations:the forces on the teeth are lower because lighter arch-wires can be used with equal effectiveness, and theteeth move more readily in response to the appliedforces because of decreased resistance to sliding. How-ever, although it is probable that lower applied forceswill be more effective with self-ligation because lessforce will be lost through resistance to sliding, lowernet forces are certainly not inevitable and, with self-ligating brackets, are correspondingly more sensitiveto the choice of archwire.25-29 Three studies foundthat patients reported lower pain levels with variousself-ligating brackets34,47,48; 2 others found no differ-ence.48,49 The authors of a systematic review concludedthat the balance of evidence from the 3 published ran-domized controlled trials on this topic just favor a re-duction of pain during alignment with self-ligation.44

An interesting split-mouth study examined the ques-tion via a different measure of pain—the level of theneuropeptidase substance P in gingival crevicular fluid,which is a marker of inflammation and associated painresulting from orthodontic forces.50 These authorsfound that treatment with self-ligating brackets

anuary 2013 � Vol 143 � Issue 1 American

significantly lowered the levels of this marker of painand inflammation when compared with conventionalligation at 24 hours after archwire placement. At theleast, there is reason to believe that lower resistanceto sliding and the use of lighter but still effective arch-wires might be less painful for our patients.

DOES THE REDUCTION IN RESISTANCE TOSLIDING LEAD TO A DIFFERENT PATTERN OFTOOTH MOVEMENT?

Investigators using 2 sophisticated systems formeasuring forces and moments in the laboratoryhave in almost all instances shown distinctly differentforce distributions with self-ligating brackets com-pared with conventional brackets in varioussimulated malocclusions; this suggests that corre-spondingly different patterns of in-vivo tooth move-ment can be expected.51-57 One such pattern isa reduction in undesirable buccally directed force,which in turn has led to the hypothesis that incisorflaring can be reduced with a consequently increaseddistal or buccal movement of the teeth. As yet, no in-vivo studies have supported these hypotheses, but itwould be surprising if these marked differences inforce distribution had no clinical consequences.

CONCLUSIONS

Some of the enthusiastic claims on behalf of self-ligation ran ahead of the evidence to firmly supportthem. In this respect, self-ligation is not alone in or-thodontics. Functional appliances continue to bejustifiably popular as effective and efficient meansof correcting many Class II malocclusions, althoughthe original hope and proposal that they would pro-duce a reliable and significant enhancement of man-dibular growth has been shown to be unfounded. Forself-ligation, the core features of security of ligation,lower resistance to sliding, and more rapid and con-venient archwire changes remain and are increasinglysupported by good studies. The most effective use ofthese advantages is still being explored, and the de-sign of the brackets themselves has, as with func-tional appliances, continually and significantlyimproved. Meanwhile, we should all ask why weare so happy to have tubes on our molars and notconventionally ligated brackets. Is it because of thecombination of excellent archwire control (evenwhen we pull on the hook that is always placed onthe attachment for that tooth), lower resistance tosliding, and rapid insertion and removal of the arch-wires? If molar tubes were newly introduced now,

Journal of Orthodontics and Dentofacial Orthopedics

16 Point

J

could we rapidly prove that they added to our treat-ment efficiency?

REFERENCES

1. Hanson GH. JCO/interviews Dr. G. Herbert Hanson on thedevelopment of the SPEED bracket. J Clin Orthod 1980;20:183-9.

2. Harradine NWT, Birnie DJ. The clinical use of Activa self-ligatingbrackets. Am J Orthod Dentofacial Orthop 1996;109:319-28.

3. Damon DH. The Damon low friction bracket: a biologically com-patible straight-wire system. J Clin Orthod 1998;32:670-80.

4. Damon DH. The rationale, evolution and clinical application ofthe self-ligating bracket. Clin Orthod Res 1998;1:52-61.

5. Harradine NWT. Self-ligating brackets and treatment efficiency.Clin Orthod Res 2001;4:220-7.

6. Mezomo M, de Lima ES, de Menezes LM, Weissheimer A,Allgayer S. Maxillary canine retraction with self-ligating and con-ventional brackets. Angle Orthod 2011;81:292-7.

7. Maijer R, Smith DC. Time saving with self-ligating brackets. J ClinOrthod 1990;24:29-31.

8. Shivapuja PK, Berger J. A comparative study of conventional li-gation and self-ligation bracket systems. Am J Orthod Dentofa-cial Orthop 1994;106:472-80.

9. Voudouris JC. Interactive edgewise mechanisms: form and func-tion comparison with conventional edgewise brackets. Am J Or-thod Dentofacial Orthop 1997;111:119-40.

10. Turnbull NR, Birnie DJ. Treatment efficiency of conventional vsself-ligating brackets: effects of archwire size and material. AmJ Orthod Dentofacial Orthop 2007;131:395-9.

11. Sims APT, Waters NE, Birnie DJ, Pethybridge RJ. A comparison ofthe forces required to produce tooth movement in vitro usingtwo self-ligating brackets and a pre-adjusted bracket employingtwo types of ligation. Eur J Orthod 1993;15:377-85.

12. Sims APT, Waters NE, Birnie DJ. A comparison of the forces re-quired to produce tooth movement ex vivo through three typesof preadjusted brackets when subjected to determined tip or tor-que values. Br J Orthod 1994;21:367-73.

13. Berger JL. The influence of the SPEED bracket's self-ligating de-sign on force levels in tooth movement: a comparative in vitrostudy. Am J Orthod Dentofacial Orthop 1990;97:219-28.

14. Thomas S, Birnie DJ, Sherriff M. A comparative in vitro study ofthe frictional characteristics of two types of self ligating bracketsand two types of preadjusted edgewise brackets tied with elasto-meric ligatures. Eur J Orthod 1998;20:589-96.

15. Kapur R, Sinha PK, Nanda RS. Frictional resistance of the DamonSL bracket. J Clin Orthod 1998;32:485-9.

16. Pizzoni L, Raunholt G, Melsen B. Frictional forces related to self-ligating brackets. Eur J Orthod 1998;20:283-91.

17. Meling TR, Ødegaard J, Holthe K, Segner D. The effect of frictionon the bending stiffness of orthodontic beams: a theoretical andin vitro study. Am J Orthod Dentofacial Orthop 1997;112:41-9.

18. Khambay B, Millett D, McHugh S. Evaluation of methods of arch-wire ligation on frictional resistance. Eur J Orthod 2004;26:327-32.

19. Thorstenson GA, Kusy RP. Resistance to sliding of self-ligatingbrackets versus conventional stainless steel twin brackets withsecond-order angulation in the dry and wet (saliva) states. AmJ Orthod Dentofacial Orthop 2001;120:361-70.

20. Thorstenson GA, Kusy RP. Comparison of resistance to slidingbetween different self-ligating brackets with second-order

anuary 2013 � Vol 143 � Issue 1 American

angulation in the dry and saliva states. Am J Orthod DentofacialOrthop 2002;121:472-82.

21. Thorstenson GA, Kusy RP. Effect of archwire size and material onthe resistance to sliding of self-ligating brackets with second-order angulation in the dry state. Am J Orthod Dentofacial Or-thop 2002;122:295-305.

22. Thorstenson GA, Kusy RP. Effects of ligation type and method onthe resistance to sliding of novel orthodontic brackets withsecond-order angulation in the wet and dry states. Angle Orthod2003;73:418-30.

23. Brauchli LM, Senn C, Wichelhaus A. Active and passive self-liga-tion—a myth? Angle Orthod 2011;81:312-8.

24. Pliska BT, Beyer JP, Larson BE. A comparison of resistance tosliding of self-ligating brackets under an increasing applied mo-ment. Angle Orthod 2011;81:794-9.

25. Matarese G, Nucera R, Militi A, MazzaM, Portelli M, Festa F, et al.Evaluation of frictional forces during dental alignment: an ex-perimental model with 3 nonleveled brackets. Am J Orthod Den-tofacial Orthop 2008;133:708-15.

26. Heo W, Baek SH. Friction properties according to vertical andhorizontal tooth displacement and bracket type during initialleveling and alignment. Angle Orthod 2011;81:653-61.

27. Baccetti T, Franchi L, Camporesi M, Defraia E, Barabato E. Forcesproduced by different nonconventional bracket or ligature sys-tems during alignment of apically displaced teeth. Angle Orthod2009;79:533-9.

28. Franchi L, Bacetti T, Camporesi M, Giuntini Z. Forces released bynonconventional bracket or ligature systems during alignment ofbuccally displaced teeth. Am J Orthod Dentofacial Orthop 2009;316:e1-6.

29. Peterson A, Rosenstein S, Kim KB, Israel H. Force decay of elas-tomerics ligatures: influence on unloading force compared toself-ligation. Angle Orthod 2009;79:934-8.

30. Matasa CG. Brackets' shape influences friction. Orthod Mater In-sider 2001;13:2-5.

31. Crawford NL, McCarthy C, Murphy TC, Benson PE. Physical prop-erties of conventional and Super Slick elastomeric ligatures afterintraoral use. Angle Orthod 2010;80:175-81.

32. Ehsani S, Mandich MA, El-Bialy TH, Flores-Mir C. Frictional re-sistance in self-ligating orthodontic brackets and conventionallyligated brackets. Angle Orthod 2009;79:592-601.

33. Eberting JJ, Straja SR, Tuncay OC. Treatment time, outcome andpatient satisfaction comparisons of Damon and conventionalbrackets. Clin Orthod Res 2001;4:228-34.

34. Tagawa D. The Damon system vs. conventional appliances:a comparative study. Clin Impressions 2006;15:4-9.

35. Vajaria R, BeGole E, Kusnoto B, Galang MT, Obrez A. Evaluationof incisor position and dental transverse dimensional changes us-ing the Damon system. Angle Orthod 2011;81:647-52.

36. Ong E, McCallum H, Griffin MP, Ho C. Efficiency of self-ligatingvs conventionally ligated brackets during initial alignment. Am JOrthod Dentofacial Orthop 2010;138:e1-7.

37. Ollivere P. Treatment efficiency of self-ligating brackets. OrthodUpdate 2012;5:15-9.

38. Miles PG. SmartClip versus conventional twin brackets for initialalignment: is there a difference? Aust Orthod J 2005;21:123-7.

39. Miles PG, Weyant RJ, Rustveld L. A clinical trial of Damon 2 vsconventional twin brackets during initial alignment. AngleOrthod 2006;76:480-5.

40. Miles PG. Self-ligating vs conventional twin brackets duringen-masse space closure with sliding mechanics. Am J OrthodDentofacial Orthop 2007;132:223-5.

Journal of Orthodontics and Dentofacial Orthopedics

18 Point

J

41. Pandis N, Polychronopoulou A, Eliades T. Self-ligation vs con-ventional brackets in the treatment of mandibular crowding:a prospective clinical trial of treatment duration and dental ef-fects. Am J Orthod Dentofacial Orthop 2007;132:208-15.

42. Scott P, DiBiase AT, Sherriff M, Cobourne MT. Alignment effi-ciency of Damon3 self-ligating and conventional orthodonticbracket systems: a randomized clinical trial. Am J Orthod Dento-facial Orthop 2008;134:470.e1-8.

43. Fleming PS, DiBiase AT, Sarri G, Lee RT. Efficiency of mandibulararch alignment with 2 preadjusted edgewise appliances. Am J Or-thod Dentofacial Orthop 2009;135:597-602.

44. Fleming PS, Johal A. Self-ligating brackets in orthodontics. Asystematic review. Angle Orthod 2010;80:575-84.

45. Chen SSH, GreenleeMG, Kim JE, Smith CL, Huang GJ. Systematicreview of self-ligating brackets. Am J Orthod Dentofacial Orthop2010;137:726.e1-18.

46. Sandhu SS, Shetty VS,Mogra S, Varghese J, Sandhu J, Sandhu JS.Efficiency, behavior, and clinical properties of superelastic NiTiversus multistranded stainless steel wires. Angle Orthod 2012;82:915-21.

47. Pringle AM, Petrie A, Cunningham SJ, McKnight M. Prospectiverandomized clinical trial to compare pain levels associated with 2orthodontic fixed bracket systems. Am J Orthod Dentofacial Or-thop 2009;136:160-7.

48. Scott P, Sherriff M, Di Biase AT, Cobourne MT. Perception of dis-comfort during initial orthodontic tooth alignment using a self-ligating or conventional bracket system: a randomized clinicaltrial. Eur J Orthod 2008;30:227-32.

49. Fleming PS, Di Biase AT, Sarri G, Lee RT. Pain experience duringinitial alignment with a self-ligating and a conventional fixed or-thodontic appliance system. Angle Orthod 2009;79:46-50.

anuary 2013 � Vol 143 � Issue 1 American

50. Yamaguchi M, Takizawa T, Nakajima R, Imamura R, Kasai K. TheDamon system and release of substance P in gingival crevicularfluid during orthodontic tooth movement in adults. World J Or-thod 2009;10:141-6.

51. Badawi H, Toogood RW, Carey JPR, Heo G, Major PW. Three-di-mensional orthodontic force measurements. Am J Orthod Dento-facial Orthop 2009;136:518-28.

52. Fok J, Toogood RW, Badawi H, Carey JP, Major PW. Analysis ofmaxillary arch force/couple systems for a simulated high caninemalocclusion: part 1. Passive ligation. Angle Orthod 2011;81:953-9.

53. Fok J, Toogood RW, Badawi H, Carey JP, Major PW. Analysis ofmaxillary arch force/couple systems for a simulated high caninemalocclusion: part 2. Elastic ligation. Angle Orthod 2011;81:960-5.

54. Fansa M, Keilig L, Reimann S, J€ager A, Bourauel C. The levelingeffectiveness of self-ligating and conventional brackets forcomplex tooth malalignments. J Orofac Orthop 2009;70:285-96.

55. Pandis N, Eliades T, Bourauel C. Comparative assessment offorces generated during simulated alignment with self-ligatingand conventional brackets. Eur J Orthod 2009;31:590-5.

56. Sifakakis I, Pandis N, MakouM, Eliades T, Bourauel C. A compar-ative assessment of the forces and moments generated at themaxillary incisors between conventional and self-ligatingbrackets using a reverse curve of Spee NiTi archwire. Aust OrthodJ 2010;26:127-33.

57. Pandis N, Eliades T, Partowi S, Bourauel C. Moments gen-erated during simulated rotational correction with self-ligating and conventional brackets. Angle Orthod 2008;78:1030-4.

Journal of Orthodontics and Dentofacial Orthopedics