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Efficiency of self-ligating vs conventionallyligated brackets during initial alignment

Emily Ong, Hugh McCallum, Mark P. Griffin, and Christopher Ho

Brisbane and Herston, Queensland, Australia

Introduction: The aim of this study was to comparethe efficiency of self-ligating (SL) and conventionallyligated (CL) brackets during the first 20 weeks ofextraction treatment.

Methods: Study models of 50 consecutive patientswho had premolar extractions in the maxillary or man-dibular arch, 0.022 3 0.028-in slot brackets, and similararchwire sequences were examined. Forty-four archesreceived SL Damon 3MX brackets (Ormco, Glendora,Calif), and 40 arches received either CL Victory Series(3M Unitek, Monrovia, Calif) or Mini-Diamond(Ormco) brackets. The models were evaluated foranterior arch alignment, extraction spaces, and archdimensions at pretreatment (T0), 10 weeks (T1), and20 weeks (T2).

Results: There were no significant differences be-tween the SL and CL groups at 20 weeks in irregularityscores (mandibular arch, P 5 0.54; maxillary arch, P 5

0.81). There were no significant differences in passiveextraction space closures between the SL and CL groups(mandibular arch, T0-T2, P 5 0.85; maxillary arch, T0-T2, P 5 0.33). Mandibular intercanine widths increasedfrom T0 to T2: 1.96 and 2.86 mm in the SL and CLgroups, respectively. This was not significant betweenthe groups (P 5 0.31). Logistic regression did notshow a difference between the SL and CL bracketgroups.

Conclusions: SL brackets were no more efficientthan CL brackets in anterior alignment or passive ex-traction space closure during the first 20 weeks of treat-ment. Ligation technique is only one of many factorsthat can influence the efficiency of treatment. Similarchanges in arch dimensions occurred, irrespective ofbracket type, that might be attributed to the archformof the archwires.

Read the full text online at: www.ajodo.org,pages 138.e1-138.e7.

Am J Orthod Dentofacial Orthop 2010;138:138-9

0889-5406/$36.00

Copyright � 2010 by the American Association of Orthodontists.

doi:10.1016/j.ajodo.2010.04.003

138

EDITOR’S COMMENT

Lately, the efficiency of SL brackets as assessed inclinical trials has received wide attention from investi-gators; as a result, there is a growing body of evidencethat contributes crucial information on this topic. ThisAustralian team studied the efficiency of CL and SLbrackets in extraction patients during the first 20 weeksof treatment. They collected study models of consecutivepatients who had premolar extractions in either arch,0.022-in slot brackets, and similar archwire sequences.Forty-four arches received SL Damon 3MX bracketsand 44 received either Victory Series or Mini-DiamondCL brackets. The models were evaluated for anteriorarch alignment, extraction spaces, and arch dimensionsat pretreatment (T0), 10 weeks (T1), and 20 weeks(T2). There were no significant differences between theSL and CL bracket groups at 20 weeks in irregularityscores (mandibular arch, P 5 0.54; maxillary arch,P 5 0.81), and no significant differences in passive ex-traction space closure (mandibular arch, T0-T2, P 5

0.85; maxillary arch, T0-T2, P 5 0.33). Mandibularintercanine widths increased from T0 to T2: 1.96 and2.86 mm in the SL and CL groups, respectively. Thiswas not significant between the groups (P 5 0.31), andlogistic regression showed no difference. This study con-firms the wide array of clinical trials indicating that thelaboratory-studied variables of SL brackets are not trans-ferred to the clinical situation, since these brackets wereno more efficient than CL brackets in anterior alignmentor passive extraction space closure during the first 20weeks of treatment. Moreover, these authors found sim-ilar changes in arch dimensions, regardless of brackettype—a main outcome in many other studies.

Theodore Eliades

Nea Ionia, Greece

Table I. Sample sizes at T0, T1, and T2

Mandibular arch Maxillary arch

SL CL SL CL

T0 19 18 25 22

T1 19 18 25 22

T2 19 14 25 16

Table II. Descriptive statistics for the irregularity indexand mean extraction space (2-sample t test)

Mandibular arch Maxillary arch

SLmean(SD)

CLmean(SD)

Pvalue

SLmean(SD)

CLmean(SD)

Pvalue

Irregularity

index, T0

10.88

(4.72)

12.52

(5.26)

0.33 11.98

(5.55)

12.53

(7.2)

0.78

Mean extraction

space, T0

7.74

(0.75)

7.78

(0.96)

0.84 7.98

(1.92)

8.12

(1.17)

0.67

Irregularity

index, T1

4.38

(3.63)

4.12

(2.87)

0.81 5.44

(3.72)

5.64

(4.46)

0.87

Mean extraction

space, T1

5.45

(1.43)

4.98

(1.56)

0.35 5.51

(1.74)

5.04

(1.73)

0.37

Irregularity

index, T2

2.84

(1.86)

2.45

(1.72)

0.54 4.37

(2.69)

4.16

(2.59)

0.81

Mean extraction

space, T2

4.02

(1.78)

4.03

(1.65)

0.99 4.30

(2.13)

3.83

(1.76)

0.44

Table III. Mean changes in arch dimensions (T0-T2) inmillimeters (2-sample t test)

Mandibular arch Maxillary arch

SLmean(SD)

CLmean(SD)

Pvalue

SLmean(SD)

CLmean(SD)

Pvalue

Intercanine

width

1.96

(1.78)

2.86

(2.80)

0.31 2.83

(2.49)

3.40

(4.12)

0.63

Intermolar

width

�1.44

(1.54)

�1.34

(2.10)

0.88 0.25

(2.08)

0.14

(1.87)

0.87

Arch depth �1.69

(2.63)

�1.08

(1.03)

0.61 �2.42

(3.99)

�1.37

(2.87)

0.33

American Journal of Orthodontics and Dentofacial Orthopedics Ong et al 139Volume 138, Number 2

Q&AEliades: Do you plan to follow patients to the end oftreatment and reassess variables such as dental archdimensions and time to completion?

Ho: Yes, we are very interested in following thepatients to the end of treatment and reassessingarch dimensions and time of treatment. However,meaningful results might not be forthcoming be-cause differing space-closing mechanics, archforms,and archwire materials were used for the patientsafter the first 20 weeks of this study.

Eliades: How do you think passive ligation might af-fect completion of space closure and anterior maxil-lary torque? Do you see a difference compared withnonextraction treatment, when alignment is oftenachieved with incisor advancement or flaring?

Ho: Maintaining anterior maxillary torque duringspace closure appears to be an issue in some patientstreated with passive SL brackets. Because we havenot used active SL brackets, we could not commenton possible differences between passive and activeself-ligation. At the other extreme, there are individ-ual variations in nonextraction patients. With moder-ate to severe crowding, incisor advancement orflaring is observed when there is little increase inintercanine or interpremolar width.

Eliades: Would you take any precautions for torqueloss on maxillary retraction and would this differbetween bracket types?

Ho: If I could go back in time and start again, I wouldconsider using high-torque brackets to maintain thetorque on the maxillary incisors during retractionin extraction patients. It didn’t matter whether pas-sive SL or CL brackets were used; some patients re-quired the incorporation of torque in the anterior partof the maxillary archwire.

Eliades: What role do archwire material and dimen-sion play in early alignment of teeth after extractions?

Ho: Clinically, I think that the initial archwire type ismore important than the bracket system used in earlyalignment for extraction patients. The flexible andbroad arch form of the initial 0.014-in copper-nickel-titanium (Damon) archwire permits early,complete engagement of teeth with very low resul-tant force levels. Quite rapid early tooth movementand alignment occur irrespective of whether SL orCL brackets are used.