Treatment efﬁciency of conventional vs selfligaton

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ORIGINAL ARTICLE

Treatment efficiency of conventionalvs self-ligating brackets: Effects of

archwire size and materialNicholas R. Turnbull and David J. Birnie

Portsmouth, Hampshire, United Kingdom

Introduction: In this prospective clinical study, we assessed the relative speed of archwire changes,

comparing self-ligating brackets with conventional elastomeric ligation methods, and further assessed this

in relation to the stage of orthodontic treatment represented by different wire sizes and types. Methods: The

time taken to remove and ligate archwires for 131 consecutive patients treated with either self-ligating or

conventional brackets was prospectively assessed. The study was carried out in the orthodontic department

of a district general hospital in the United Kingdom. The main outcome measure was the time to remove or

place elastomeric ligatures or open/close self-ligating brackets for 2 matched groups of fixed appliance

patients: Damon2 self-ligating bracket (SDS Ormco, Orange, Calif) and a conventional mini-twin bracket(Orthos, SDS Ormco). The relative effects of various wire sizes and materials on ligation times were

investigated. The study was carried out by 1 operator experienced in the use of self-ligating and conventional

brackets. Results: The Damon2 self-ligating system had a significantly shorter mean archwire ligation time

for both placing (P .001) and removing (P .01) wires compared with the conventional elastomeric system.

Ligation of an archwire was approximately twice as quick with the self-ligating system. Opening a Damon

slide was on average 1 second quicker per bracket than removing an elastic from the mini-twin brackets, and

closing a slide was 2 seconds faster per bracket. This difference in ligation time between the Damon2 and

the conventional mini-twin brackets became more marked for larger wire sizes used in later treatment stages.

Conclusions: The type of bracket and the size of wire used are statistically significant predictors for speed

of ligation and chairside time. The self-ligating system offered quicker and arguably more efficient wire

removal and placement for most orthodontic treatment stages. (Am J Orthod Dentofacial Orthop 2007;131:

395-99)

The reported advantages of self-ligating (SL)

brackets include reduced friction,1-4 full and

secure wire ligation,5 improved oral hygiene,6,7

anchorage conservation,8 chairside time savings and

improved ergonomics,6,9-11 quicker treatment times,

and longer appointment intervals.10,12 The issue of

friction and SL brackets is controversial. Many labora-

tory studies indicated lower friction levels for SL

brackets, but their experimental designs were variable

and might not simulate the dynamics of the oral

environment.

13

However, in this study, we were pri-marily concerned with other characteristics of SL

brackets. Modest savings in chairside time were re-

ported by Harradine10 using the Damon SL bracket

(SDS Ormco, Orange, Calif). However, Berger and

Byloff 9 found more significant reductions in wire

ligation times with the SPEED SL bracket (Strite

Industries, Cambridge, Ontario, Canada), but they as-

sessed exclusively nonextraction patients and only 1

wire type.

The aim of this study was to assess archwire

ligation times for patients with various archwire sizes

and materials that represented a cross-section of orth-

odontic treatment progress. In this way, the effects of

varying the wire size and material were recorded in 2groups of patients, allowing comparison of an SL

bracket14 with a conventional mini-twin design.

SUBJECTS AND METHODS

The Damon2 (D2) self-ligating bracket (SDS Ormco)

was compared with a conventional mini-twin bracket

(Orthos, SDS Ormco). The D2 bracket ligates the

archwire with a vertical metal slide that can be opened

or closed to cover or expose the slot (Fig 1). This is a

passive bracket because the wire is not engaged by an

active clip; Harradine15 wrote an excellent summary of

From the Orthodontic Department, Queen Alexandra Hospital, Portsmouth,

Hampshire, United Kingdom.

Consultant orthodontist.

Reprint requests to: Nicholas R. Turnbull, Orthodontic Department, Queen

Alexandra Hospital, Portsmouth, Hampshire PO6 3LY, United Kingdom;

e-mail, [email protected].

Submitted, January 2005; revised and accepted, July 2005.

0889-5406/$32.00

Copyright 2007 by the American Association of Orthodontists.

doi:10.1016/j.ajodo.2005.07.018

395


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the advantages and disadvantages of SL brackets with

passive or active clips. A special tool (Damon plier) is

used to open and close the D2 slide mechanism.

The time taken to open or close the D2 slides or

remove or replace ligatures on the Orthos bracket was

measured for 140 D2 bonded arches compared with 122

mini-twin bonded arches. This was performed by 1

operator (N.R.T.) with significant experience with both

the D2 bracket and the Orthos (current practice, 60%

D2 and 40% Orthos). Consecutive patients who ful-

filled the following criteria were included in the study:

scheduled for maxillary and mandibular fixed appli-

ances, agreed to take part in the study, age between 11

and 18 years, and due for archwire changes at the

assessment visit. Patients with cleft lip and palate,severe skeletal dysgnathia, and ectopic canines were

excluded because they were to likely represent unusual

outliers in time taken to manipulate archwires.

Times were recorded with a stopwatch, with the

clinician working at a normal rate. A specially designed

proforma recorded sex, age, extraction or nonextrac-

tion, time taken to remove or place archwire, arch

(maxillary or mandibular), number of brackets en-

gaged, number of tubes or bands engaged, and wire size

and material.

The patients represented a balance in terms of

extraction and nonextraction in each group. In mostpatients, the second molars had already been bonded.

Because the clinician had a wide spread of patients in

treatment, it was possible to record ligation times at

various stages of treatment progress so that the full

range of wire sizes was assessed. For statistical analy-

sis, the archwires used were divided into 4 main groups

based on wire size and material (Table I).

To standardize the study as much as possible, a

careful protocol was followed. The time required to

remove or place auxiliaries such as power chain was

not included in the total time recorded. Figure-eight

elastics and metal tie ligatures were not used. All slides

for the D2 brackets were opened to site the archwire

(the wires were not pushed through the closed premolar

brackets as is occasionally possible with the system).

Statistical analysis

The statistical evaluation of the data included anal-

ysis of variance (ANOVA), ttest, and 95% confidence

intervals (CI) for difference of the means. The statisti-

cal software package used was Stats Direct Ltd (Sale,

Cheshire, United Kingdom).

RESULTS

The 2 patient groups (D2 and Orthos) demonstrated

good demographic matching; girls represented 56% of

D2 group and 59% of the Orthos group. The mean ages

were 13.7 years for the D2 group and 14.4 years for the

Orthos group. The ratios of extraction to nonextraction

patients were 39% extraction for the D2 group and 43%extraction for the Orthos group.

The time taken for ligating or removing wires was

expressed as mean units of time (seconds) per bonded

arch and per bracket. Overall, it was quicker to remove

wires than to replace them. This was evident with both

bracket types, but much more significant in the Orthos

patients; the mean wire removal time for the Orthos

brackets was 64.5 seconds per bonded arch (SD 18),

compared with 98.4 seconds (SD 24) for wire

placement. A smaller difference was observed for the

D2 brackets (Table II).

When the different wire sizes were combined, themean time to open slides for the D2 patients per bracket

was 3.7 seconds compared with 4.7 seconds for elastic

ligature removal with the Orthos brackets (Table II).

This difference of 1 second per bracket was statistically

significant when comparing the 2 groups as a whole

(P .01). The 95% CI for the difference between the

per-bracket means was 0.28-1.77. Assessment of the

effect of the 4 wire subgroups also showed significant

differences in time taken for archwire removal between

the D2 and Orthos brackets. The greatest difference

was found for larger wire sizes; it took a mean time of

Fig 1. D2 SL brackets.

Table I. Four archwire groups used in study, based on

wire size and material

Wire

group Wire type

Wire sizes

( 1100 in)

1 Round nickel-titanium 14, 16, 18

2 Small rectangular nickel-titanium 14 25, 16 25,

16 22

3 Large rectangular nickel-titanium 18 25, 19 25

4 Rectangular stainless steel 18 25, 19 25

American Journal of Orthodontics and Dentofacial Orthopedics

March 2007

396 Turnbull and Birnie


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1.6 seconds longer per bracket to remove elastic liga-

tures compared with opening the D2 slides for wire

group 4 (Table III). T h e smallest nickel-titanium

wires (group 1) had a small difference in wire

removal time between the 2 bracket types, but this

was not statistically significant. There was no differ-

ence in time taken for removing maxillary vs man-dibular archwires for either the D2 or the Orthos

patients.

When closing the D2 slides, the mean time per

bracket was 5.7 seconds, compared with 7.6 seconds

for Orthos ligation (P .001). The mean ligation

times were 46.3 seconds (SD 22) for a fully

bonded arch for D2 and 98.4 seconds (SD 24) for

the Orthos brackets. Unpaired t tests showed these

differences to be highly statistically significant (t

3.55; P .001) when comparing the 2 bracket types

as a whole (Table II). The 95% CI for the difference

between the means was 20.3 to 5.8. The CI value

does not include zero, which indicates a true differ-

ence in the mean ligation times between the 2 bracket

systems. For closing slides/religating elastics (ligat-

ing wires), the type of archwire had a significant

effect. The D2 brackets had shorter ligation times for

all wire groups and were statistically significant for

wire groups 2, 3, and 4 (Table III). This is clearly

illustrated inFigure 2by the separation of the plotted

lines for the 2 bracket systems. It also shows that the

relative differences in ligation times are more

marked for the larger wire sizes in both nickel-titanium and stainless steel.

Comparison of the maxillary arch with the mandib-

ular arch showed no difference in wire ligation times

for the Orthos brackets for any wire size. However, in

the D2 group, the ligation time (placing wires) was

significantly slower in the manidbular arch for wire

group 1 (small round nickel-titanium). The mean times

to ligate a round nickel-titanium wire per bracket were

9.1 seconds in the mandibular arch and 6.5 seconds in

the maxillary arch. However, this was only marginally

statistically significant (P .041).

Fig 2. Interaction plot of 4 wire groups for time taken to

close slides/replace ligatures (mean time per bracket in

seconds); note clear separation of 2 time lines for

Orthos and D2 brackets, showing relatively greater

difference as wire size increases (see Table I for wire

group details).

Table II. Mean wire removal and ligation times in seconds (SD) per bonded arch and per bracket for all wire size

groups combined for D2 vs Orthos brackets. Wire removal represents opening D2 slides or removal of elastomeric

rings, wire ligation represents closing D2 slides or replacing new elastic rings

D2 Orthos

Arch

Bracket

Arch

Bracket Difference Significance(n 140) (n 122)

Wire removal 39.8 (13) 3.7 (1.1) 64.5 (18) 4.7 (0.9) 24.7 *

Wire ligation 46.3 (22) 5.7 (2.3) 98.4 (24) 7.6 (1.2) 52.1

*Means different at P .01; means different at P .001.

Table III. Mean times (seconds) for wire removal or

ligation per bracket for different wire sizes (see Table I

for wire sizes), wire removal represents opening D2

slides or removal of elastomeric rings, wire ligation

represents closing D2 slides or replacing new elasticrings

D2 Orthos

Wire group

Mean time

per bracket

Mean time

per bracket Difference Significance

Wire removal

1 3.8 (n 38) 4.2 (n 31) 0.4 NS

2 3.9 (n 31) 4.9 (n 33) 1.0 *

3 3.6 (n 39) 4.8 (n 30) 1.2

4 3.6 (n 32) 5.2 (n 28) 1.6

Wire ligation

1 7.8 (n 38) 8.7 (n 31) 0.9 NS

2 6.5 (n

31) 8.2 (n

33) 1.7

3 4.4 (n 39) 7.1 (n 30) 2.7

4 4.1 (n 32) 6.4 (n 28) 2.3

NS, no significant difference; *means different at P .05; means

different at P .01; means different at P .001.


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Turnbull and Birnie 397


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DISCUSSION

The time taken to remove or ligate orthodontic

wires is of interest but is a less significant characteristic

of SL systems when compared with secure ligation and

the possibility of lower friction/force generation. Nev-ertheless, the ergonomics of archwire manipulation in a

busy clinical environment is important.

For both the D2 and Orthos brackets, it was quicker

to remove wires than to replace them. However, Maijer

and Smith11 found the opposite using the Activa SL

bracket (A Company, San Diego, Calif), which had a

slightly quicker ligation time. A common initial finding

with the D2 bracket is difficulty in opening the

slidesa time-consuming wire removal process

whereas closing slides is relatively simple. It is possible

that the Activa bracket also had similar time-consuming

opening characteristics. However, our study suggeststhat wire removal is slightly quicker than placement

for both bracket types. This is most likely due to the

experience and comfort zone of the operator in D2

slide manipulation. Use of 1 operator removed the

potential interoperator variability in experience lev-

els with the 2 bracket systems. To compare like with

like, the operator needed to be at least as comfortable

with the D2 bracket as the Orthos bracket. This

allowed isolation of bracket type as the determinant

of outcome rather than variation in clinical experi-

ence. A follow-up study will assess effects of the

clinical experience on ligation time by comparingdental students, postgraduate trainees, and estab-

lished specialists.

The ligation times show mean savings of 2 seconds

per bracket for closing slides with the D2 system, and

1 second per bracket for opening slides when compared

with the Orthos elastics. These time savings are more

significant than those reported by Harradine.10 The

mean time for wire placement in a fully bonded arch

with the D2 system was 46 seconds compared with 98

seconds for the Orthos brackets. The difference be-

tween the 2 bracket types was statistically significant

for both placing and removing wires, but is thisclinically significant?

It took approximately twice as long to ligate a wire

by using the elastics and Orthos brackets compared

with the D2 system. The average time saved with the

D2 was about 1.3 minutes per visit. This is approxi-

mately a 10% time saving in an average wire adjust-

ment appointment. In the United Kingdoms National

Health Service, a 10 to 15 minute archwire change

appointment is commonly allocated as standard. If the

time is extended to a full day, a 10% saving could free

up an extra 45 to 60 minutes of clinical time. This could

be used to reinforce oral hygiene measures, discuss

treatment progress, or generally enhance patient or

parent relationships through improved communication.

The D2 brackets offer relatively greater time sav-

ings for larger wire sizes. This can be seen clearly inFigure 2, which represents the mean ligation times of

the 4 wire-size groups. The 2 lines plotted on the chart

diverge as wire sizes increase, indicating less time to

ligate wires with both bracket types, but proportionally

a greater drop in ligation time for the D2 system.

Therefore, time-saving efficiencies appear to be rela-

tively greater for the D2 brackets at later treatment

stages, associated with larger wires when alignment of

the teeth has progressed. This is explained by the

Damon treatment philosophy16 that stresses full en-

gagement of all teeth at the earliest stage. Therefore, it

will take relatively more time to fully engage light

nickel-titanium archwires in all teeth with the D2

system compared with bypassing selected teeth with a

conventional elastomeric appliance. Similarly, the dif-

ference in ligation time for the maxillary vs the man-

dibular arch was found to be significant only in the D2

group and only for small round nickel-titanium wires

(initial alignment). It was statistically significantly

quicker to ligate a wire in the maxillary arch in this

group. This is most likely due to the generally more

severe crowding in the mandibular arch, smaller inter-

bracket distances in the mandibular incisor region, and

attempts to initially fully ligate all teeth with the D2

system.The decreased reliance on assistant support with SL

brackets produces hidden efficiency savings, which are

potentially greater for orthodontic therapists who gen-

erally do not have chairside support from dental assis-

tants; this is required for speedy and efficient elastic

ligation. Chairside time savings are welcome, but other

advantages of SL systems, such as decreased treatment

duration10,12 and absence of bio-hostable elastic mod-

ules5,7 are probably more important. However, an

understated advantage is the absence of the need for

passing, placing, and removing elastomeric ringsa

labor-intensive, tedious, and ergonomically unsatisfac-tory process.

SL brackets are more expensive than most conven-

tional brackets, but this cost can be offset by the

reductions in chairside time9,11 and treatment dura-

tion.10,12 There is also the small financial saving related

to elastomeric rings that are obviously not required.

The D2 bracket is not difficult to open and close,

but it requires a sustained learning period to become

comfortable and skilled in manipulation of the bracket

slide. There are more new brackets on the market with

modified and novel SL mechanisms. Some of these will


March 2007

398 Turnbull and Birnie


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probably be more efficient than others. In this study, we

compared the D2 bracket with the Orthos design. The

Orthos was used because it approximates the size of the

D2 bracket and because larger size standard/regular

twin brackets are less commonly used in the UnitedKingdom. It is theoretically possible that wing size

could affect elastomeric ligation time, with smaller

wings more difficult to ligate. Therefore, the time

savings found in this study relate to a comparison with

mini-twin brackets.

CONCLUSIONS

The D2 SL brackets had significantly quicker mean

archwire ligation times for both placing and removing

wires compared with the conventional Orthos system.

Ligation of wires was twice as quick with the D2

system. The average time savings was almost 1.5

minutes of clinical activity per patient contact. In terms

of clinical time, SL brackets are more efficient for most

wire sizes and therefore at most stages of orthodontic

treatment. However, the improvement in ligation time

became more marked and statistically significant for the

larger archwire sizes used later in treatment. Therefore,

both the type of bracket and the size of the wire appear to

be significant predictors for speed of ligation andchairside

time.

We thank Bernie Higgins, Portsmouth Institute of

Medicine, Health and Social Care, University of Ports-

mouth, for help with statistics.

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Treatment efﬁciency of conventional vs selfligaton