Download A comparative study of conventional ligation and self

A comparative study of conventional ligation and
self-ligation bracket systems
Prasanna Kumar Shivapuja, BDS, MDS (Ortho), DDS, MS (Ortho)," and
Jeff Berger, BDS, Dip. Orth."
Detroit, Mich.
The increased use of self-ligating bracket systems frequently raises the question of how they
compare with conventional ligation systems. An in vitro and clinical investigation was undertaken to
evaluate and compare these distinctly different groups, by using five different brackets. The Activa
("A" Company, Johnson & Johnson, San Diego, Calif.), Edgelok (Ormco, GIendora, Calif.), and
SPEED (Strite Industries Ltd., Cambridge, Ontario) self-ligating bracket systems displayed a
significantly lower level of frictional resistance, dramatically less chairtime for arch wire removal and
insertion, and promoted improved infection control, when compared with polyurethane elastomeric
and stainless steel tie wire ligation for ceramic and metal twin brackets. (AM J ORTHODDENTOFAC
ORTHOP 1994;106:472-80.)
A
review of the orthodontic literature
from the last few years reveals a proliferation of
publications evaluating the r01e of friction in the
orthodontic system.T M However, many of these
Publications concentrate on how a particular facet,
such as bracket width,2"'~ wire material, ~'4'~9"~21~
and bracket material s'6,s';5,'7,t8 impacts, either individually or in combination, on the level of friction
produced in the system. Some of the more recent
articles have highlighted the increasing use of selfligating bracket s y s t e m s 3"t6 and the role they may
play in affecting the level of friction in the system.
W i t h the introduction of the Edgelok bracket
(Ormco, GI6ndora, Calif.) ~9 in 1972, the SPEED
system (Strite Industries Ltd., Cambridge, Ontario)
in 1980,20 and the Activa bracket ("A" Company,
Johnson & Johnson, San Diego, Calif.) in 1986,*
several independent claims have been made that
share a common theme. All three inventors report a significant reduction in the level of friction,
in addition to shorter treatment time-and chairtime, when compared with conventional bracket
systems.~9'2~ The fact that similar advantages
were noted 47 years earlier with the use of the
first Edgewise self-ligating bracket, the Russell
Lock,22"z3 lends a certain degree of credence to
From the University of Detroit.
"Assistant Professor, Department of Orthodontics.
Cop)Tight 9 1994 by the American Association of Orthodontists.
0889-5406/94/$3.00 + 0 8/1147901
*Personal communications with E. Pletcher and A. J. Wildman ('A'
Company, Sathar Kucharia).
472
these current observations. T o assess the authenticity of these claims an~l to examine the more
recent bracket systems, a study was designed to
evaluate and compare the three different selfligating bracket appliances with conventional elastomeric and stainless stee ! ligation systems.
This article will examine these two contrasting
groups of bracket systems from both an in vitro
aspect, as well as by clinical measurements and
subjective observations.
The in vitro portion of the study was designed
to examine the static resistance and dynamic frictional resistance for sliding mechanics both between and within each of the two different groups.
Since elastomeric power modules are often used as
an alternative means of space closure to either
closing-loop arch wires or intraoral elastics, the
effect of their use on frictional resistance was also
investigated.
As more orthodontic offices up-date or expand
existing sterilization techniques to meet current
requirements, 24"~ a greater demand is placed on
the doctor-staff time to maintain the same level of
efficiency in patient care. To assist in balancing this
new equilibrium the sign!ficant decreased time factor associated with the use of self-ligating brackets 21"23"26 may be one of the greatest hidden virtues
of the ligatureless system. To evaluate this claim,
the clinical portion was designed to Observe the
time taken to remove and replace the ligating
mechanism for the conventional bracket systems
and to open and close the clips of the self-ligating
bracket systems.
Shivapuja attd Berger
American Journal of Orthodontics and Dentofacial Orthopedics
Volume 106, P,'o. 5
473
Fig. 1. Scanning electron micrograph of live types of brackets used in study.
Table I. T y p e s o f b r a c k e t s a n d v a r i o u s m e t h o d s o f ligation e v a l u a t e d
Group
[
I
II
II1
IV
V
VI
VII
Bracket
Standard metal twin Standard metal twin
Activa
SPEED
Ceramic series 2000*
Ceramic series 2000*
Edgelok
I
Ligation
0.012-inch GAC steel tie
Polyurethane elastomeric module
Lever arm
Spring clip
0.012-inch GAC steel tie
Polyurethane elastomeric module
Sliding cap
*Unitek Corp./3M, Dental Products Division, Monrovia, Calif.
MATERIAL AND METHOD
The samples for the initial portion of the investigation consisted of five different types of 0.022 x 0.028inch [0.55 x 0.71 mm] brackets (Fig. 1) divided into
seven groups depending on the type of ligation system
used (Table I). Each bracket was mounted on an acrylic
cylinder and an 0.018-inch [0.45 mm] arch wire ( G A C
International, Inc., Central Islip, N.Y.) was ligated into
each bracket slot, either with 0.012-inch [0.30 mm] stain-
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Shivapttja and Berger
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American Journal of Orthodontics and Dentofacial Orthopedics
November 1 9 9 4
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STATIC
300
250
m 200
Z
I
cn 15o
O3
lOO
I
!
TMT TET SPD ACT CMT CRT EDL
BRACKET TYPE
Fig. 2. Graph indicating mean static resistance produced by
sliding O.018-inch steel wire with different types of ligating
systems. TMT, Standard twin ligated with metal tie; TET,
standard twin ligated with polyurethane elastomeric tie; SPD,
SPEED self-ligating bracket; ACT, Activa self-ligating bracket;
CMT, ceramic bracket ligated with metal tie; CRT, ceramic
bracket ligated with polyurethane elastomeric tie; EDL,
Edgelok self-ligating bracket.
less steel ties (GAC) with a tie force of approximately
150 gm," or with 0.40 mm (0.106 inch) polyurethane
elastomeric ties (Las-Tie Carousel Elasto-Ring, GAC) or
self-ligation. A new bracket and arch wire were used for
each test to avoid creating any changes in the surface
topography of the arch wire or the bracket slot, which
may cause a greater level of frictional resistance to be
recorded. Is
The mode of self-ligation varied for each ligatureless
bracket. In the Edgelok appliance a labially positioned
cap, the sliding lock, is slid horizontally across the top of
the arch wire slot until it abuts against a smaller fixed
cap, the lock stop, creating a rectangular slot or tube.
The Activa appliance possesses a self-ligating latch clip,
which resembles a bib with curled arms. The latch clip is
able to rotate freely around the horizontal axis of the
bracket and closes in a gingival direction to form a solid
outer labial wall for retaining the arch wire. ,~gain, as
with the Edgelok bracket, a tube or rectangular slot is
created thereby permitting complete freedom of movement of the arch wire. However, the inherent flexibility of
t h e spring clip in the SPEED bracket imparts a dynamic
aspect to this system that differentiates this form of
self-ligation from all others. The ability of the spring clip
to deliver continuous force vectors in all three spatial
planes permits precise control of tooth movement,
through the influence of this spring clip on the arch wire.
The spring clip requires an occlusally directed force,
applied at the gingival end of the lingual arm, to spring
the clip into the open position, and a much lighter
gingivaUy directed force against the curved occlusal surface to reseat it. In the slot-closed position, the lingually
inclined labial arm of the spring clip retains the arch wire
by forming the fourth and outer wall of the arch wire slot.
Each bracket group consisted of twelve samples and
the frictional force for each group was evaluated with a
Universal Instron testing instrument (Instron Corp.,
Canton, Mass.) with each arch wire being moved through
a distance of 1.0 inch [25.4 mm] at a crosshead speed of
0.001 inch [0.0254 mm] per minute, using a full scale load
of 1 pound [454.5 gm]. Two different measurements were
then retrieved and analyzed for each sample: The maximum force needed to initiate movement of the wire,
which was considered as the force needed to overcome
static resistance, and the maximum load through the
tracking distance of l:lJ inch, which was interpreted as
the dynamic resistance.
This Instron test was initially carried out with an
artificial salivary medium (Saliva substitute, Roxan Labs,
Columbus, Ohio) for each bracket system. However, this
artificial saliva produced higher frictional resistance possibly because of the rapid rate of desiccation with the
cellulose content adhering to the arch wire. It was
therefore decided to examine the various bracket systems
using a normal saline solution. The data collected were
analyzed through the Anova Analysis using the Systat
program.
The second portion of the investigation was designed
to evaluate the influence of the elastomeric power module (GAC Energy Chainette)on the translatory movement of teeth.
The elastomeric power module was placed on each of
12 samples of the Activa, Edgelok, and SPEED brackets
with the bracket clips in the open position. An 0.018-inch
[0.45 mm] stainless steel wire was engaged into the
bracket slot, and the clip was closed to secure the wire
into the bracket. The samples were subjected to the
Instron testing machine as previously described in the
first phase of the study. The results obtained were
subjected to the t test.
The final phase of the study involved a comparative
clinical evaluation of the time required to remove and
replace the mode of ligation in either the maxillary or
mandibular arch from the right second premolar to the
left second premolar, in 20 separate arches. The time
recorded was solely related to the removal or replacement of the ligature tie and did not involve manipulation
of the arch wire.
RESULTS
T h e results o f the static resistance, as shown
graphically in Fig. 2, d e m o n s t r a t e no statistical
difference, p < 0.05, in the .force values to initiate
wire m o v e m e n t for the Activa, Edgelok, S P E E D ,
Shirapjua attd Berger
American Journal of Orthodontics and Dentofacial Orthopedics
Volume 106, No. 5
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DYNAMIC
120
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f
DYNAMIC WITB EZ,ASTOMJYRIC POlrs
MODUs
B00
A"
250
Z
b~
O~
110
100
Z
O~
200
03
90
80
150
Z
Q
p~
Q
100
70
60
N
50
50
40
0
30
TMT TET
SPD
ACT
CMT
CRT
EDL
SPD
BRACKETTYPE
Fig. 3. Mean dynamic resistance produced by sliding 0.018inch steel wire with different types of ligating systems.
ACT
EDL
BRACKETTYPE
Fig. 4. Mean dynamic resistance produced by sliding O.018inch steel wire with elastomeric power modtJles placed under
arch wire with self-ligating brackets.
Table II. Mean of the time taken in seconds to remove ligation / open bracket and replace
ligation / close bracket
T)pe of bracket
and ligation
Time taken to remove
tie / open bracket
Time taken to replace
tie / close bracket
Twin with metal tie
Twin with rubber tie
SPEED
Activa
Edgelok
180
60
30
45
52
300
80
I1
60
40
and twin bracket with metal tie. However, the
variability in t h e force values was higher for the
twin bracket with metal tie.
For measurements of dynamic frictional resistance (Fig. 3), the twin metal bracket with the.
elastomeric tie and the ceramic brackets with either the metal tie or the elastomeric tie all proved
to be statistically different from the other four
groups (I, III, IV, VII) at p < 0.05. The ceramic
bracket with the elastomeric tie (group VI) offered
the most resistance to movement with a mean value
of 10.84 ounces (308.15 gm).
T h e use of the elastomeric power module revealed a higher level of mean frictional resistance
of 3.07 ounces (87.26 gm) with the S P E E D bracket
system (Fig. 4) when compared with either the
Activa bracket system, which had a mean value of
12.64 ounces (35.91 gm) or the Edgelok bracket
system, with a mean value of 1.42 ounces (40.40
gm).
The time involved to open the self-!igated
brackets in groups ili, IV, and VII (Table II and
Fig. 5), Table II illustrated a significant decrease in
time when compared with either of the o t h e r two
forms of conventional ligation methods, groups I
and V or groups II and VI. This time difference
was even more evident when the time for closing
any of the self-ligating bracket systems was compared with that for replacing the stainless steel
ligature tie or the elastomeric mode of ligation
(Fig. 5, Table II).
DISCUSSION
The ceramic brackets, as a group, ,~ffered more
resistance to movement, with group VI displaying
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Shivapuja and Berger
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A'orember 1994
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'
W
ope~ '
[IIT~ close
300
250
200
150
100
50
Fig. 6. Scanning electron micrograph of ceramic bracket.
Note roughness of the surface.
TMT
TET
SPD
ACT
EDL
BRACKET TYPE
Fig. 5. Graph indicating time taken in seconds to open/untie
and close/retie different ligating systems.
the greatest value. This finding, which is in agreement with that of Pratten et al., ~ Kusy and Whitley, 5
and Tanne et al., TM could possibly be related to the
roughness of the bracket slot (Fig. 6), in addition to
the mechanical binding between the elastomeric tie
and the ceramic bracket surface.
The frictional resistance associated with the use
of elastomeric ties in groups II and VI was higher
than when steel ties were used with the same
bracket'system, groups I and V, Fig. 3. In previous
studies, elastomerie ties have also demonstrated
higher frictional resistance when compared with
other modes of ligation and in particular with
self-ligation. "~'2~This, combined with the rapid rate
of decay for these elastomeric ties and their predilection for harboring large quantities of plaque and
the resultant decalcification, suggests tliat there is
little merit in their use, especially in translatory
movement and sliding mechanics..
In observing the inconsistency in force values
associated with the twin bracket and metal ties
(group I), one could postulate that this fluctuation
could be attributed either to the binding effect of
the steel tie or to the intimate relationship of the
cut end of the tie wire where it was tucked under or
over the main arch wire.
Perhaps the most noticeable features of Figs. 2
and 3 were the dramatically low levels of mean
resistance as exhibited by the Activa, Edgelok, and
SPEED self-ligating systems when measured
against either the elastomeric or steel tie ligation
groups. All three of the seif-ligating systems revealed a remarkably similar range of measurements
from lowest value to highest value and a statistically
insignificant difference in their respective mean
force values. This no doubt is readily explained by
the lack of any tight contact as exhibited by a steel
tie or elastomeric tie around the arch wire. Furthermore, the outer labial wall in all three selfligating brackets would, in the closed position, tend
to create a tunnel, or tube, in which to house the
arch wire (Fig. 7).
These differences of arch wire entrapment in
the self-ligating group necessitate critical evaluation before constructing the experimental model.
Both the horizontal labial wall of Edgelok and the
concave fourth wall of Activa are inflexible, solid
arms that create a hollow rectangular tube permitting free uninhibited movement of the arch wire.
However, in the SPEED bracket the outer labial
wall is formed by the lingually inclined, resilient
spring clip that undergoes constant positional
change to effect rotational, tip, and torque control.
If in the experimental design the flexible spring clip
is subjected to a constant force in any one of these
spatial planes during movement of the arch wire
through the arch wire slot, as in the study by
Bednar et al., '~ then the spring clip will be maintained continuously in a displaced condition while
the arch wire is pulled past it. Consequently, the
experimental model would tend not to represent an
accurate design for the SPEED bracket system and
would produce results with a higher level of friction. Therefore, to compare each system equally in
American Journal of Orthodontics and DentofacialOrthopedics
Vohone 106, No. 5
Shirapuja attd Berger
477
Fig. 7. Scanning electron micrograph of sagittal view of self-iigating brackets indicating individual
ligation methods holding O.018-inch arch wire in position.
this study, the arch wire was movcd parallel to the
arch wire slot for each bracket. Regrettably, this
portion of the study, as with all in vitro studies, is
really a comparative study and in no way is capable
of simulating clinical conditions with all the attended variables.
From the scanning'electron microscopic views
of the Activa, SPEED, and Edgelok brackets, with
the elastomeric power module in place under the
arch wire (Fig. 8), it would appear that the anatomic design of each bracket could have created
the noticeable difference in the levels of mean
resistance produced by each, system. With the
Activa bracket, each elastomeric power module can
readily be looped behind the lever arm ensuring a
distant location from the arch wire. The same
configuration is evident for the elastomeric power
module and the Edgelok bracket. Unless the elastomeric power module is engaged between the base
of the SPEED bracket body and the spring clip,
both incisally and gingivally, then the opportunity
for extended contact between the arch wire and the
elastomeric power module is dramatically increased. This problem is exacerbated if the elastomeric power module is placed after the seating of
the arch wire and closure of the spring clip, as is
routinely performed by clinicians for convenience
(Fig. 9). This technique negates the advantage of
the low frictional resistance offered by the SPEED
bracket. However, the advent of the recently designed SPEED bracket with a mushroom hook
(Fig. 10) permits the gingival positioning of the
elastomeric power module and, hence, the chances
of frictional drag between the arch wire and the
elastomeric power module become nonexistent.
This portion of the study did not investigate the
frictional resistance involved with the use of elastomeric power modules over twin metal brackets
because the initial pilot study demonstrated that
the force values were very similar to that of the
twin brackets with elastomeric modules. The alternative technique of employing elastomeric power
modules over brackets tied with metal ligatures
also revealed similar force values as that of wire
restrained solely with elastomeric modules over the
twin brackets.
Significantly less chairtime was required for
arch wire removal and insertion when any of the
Activa, Edgelok, or SPEED bracket systems
(groups III, IV and VII) were employed, (Fig. 5,
Table II). Opening of either the sliding cap of
Edgelok or the spring clip of the SPEED bracket
showed a greater variability than with the lever-pull
action of the Activa bracket. This could be ex-
478
Shivapuja and Berger
American Journal of Orthodontics and Dentofacial Orthopedics
November 1994
Fig. 8. Sagittal view of scanning electron micrograph of three self-ligating brackets with elastomeric
power module placed under 0.018-inch steel wire. Note the lack of contact of the wire with the power
module in the Activa bracket.
plained by the difference in the structural design of
each bracket body in addition to the material
composition of both the highly resilient SPEED
spring clip and the retaining mechanism for the
sliding cap of Edgelok, as opposed to the nonresilient lever arm of the Activa bracket (Fig. 1).
Closing the self-ligating component of each bracket
system was equally easy.
Clinically, it was of interest to note the absence
of accidental soft tissue laceration or impingement
from tie wire ends. The" smooth round shape of
each self-ligating systems further added to tissue
comfort.
CONCLUSION
By using bracket systems that are self-ligating
tends to address two important concerns of orthoFig. 9. Sagittal View of the scanning electron micrograph
indicating a SPEED bracket with elastomeric power module
placed over arch wire after clip closure.
.
.
.
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American Journal of Orthodontws and Dentofacta/ Orthopedics
Volume 106. No. 5
Shivapuja and Berger
479
d o n t i s t s today. A d e c r e a s e in frictional resistance,
b o t h static a n d d y n a m i c , has to benefit t h e h a r d
a n d soft tissues, w h e r e a s a d e c r e a s e in t h e t i m e o f
a r c h wire r e m o v a l a n d i n s e r t i o n a d d r e s s e s b o t h
e r g o n o m i c a n d e c o n o m i c c o n s i d e r a t i o n s . T h e serfligating b r a c k e t systems a r e a d v a n t a g e o u s in that
t h e y d o n o t p r o m o t e p o o r o r a l hygiene, as with
e l a s t o m e r i c ties, a n d e l i m i n a t e a n y c h a n c e o f soft
tissue l a c e r a t i o n to b o t h t h e p a t i e n t a n d the o r t h o d o n t i s t f r o m the use o f stainless steel tie wires.
Besides enhancing public relations between the
o r t h o d o n t i s t a n d t h e p a t i e n t with r e s p e c t t o b o t h
p a t i e n t c a r e a n d infection c o n t r o l in t h e o r a l cavity,
a self-ligating system is also a p p r e c i a t e d by t h e
s u p p o r t staff, b o t h at t h e c h a i r s i d e a n d in sterilization. It is n o t u n r e a l i s t i c to e x p e c t t h a t o n e d a y
self-ligating b r a c k e t systems will b e c o m e t h e
b r a c k e t system o f choice.
We acknowledge the contribution made, in the clinical" portion of this investigation, by Dr. Jim Wildman for
his invaluable expertise with the use of the Edgelok
bracket. In addition, we thank Dr. David Edgar and Dr.
Thurle Hice for detailed answers concerning the development and use of the Edgelok bracket and also Dr.
Erwin Pletcher for information on his design and observations of the Activa straight-wire appliance. We also
thank Mrs. Janice Lipshy for her help in the preparation
of this manuscript.
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Reprint requests to:
Dr. Prasanna Kumar Shivapuja
19128 E. Ten Mile Rd.
East Point, MI 48021
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