Download FORCES RELEASED DURING ALIGNMENT WITH AESTHETIC AND DIFFERENT LIGATION METHODS

FORCES RELEASED DURING ALIGNMENT WITH AESTHETIC AND
STAINLESS STEEL PREADJUSTED APPLIANCES USING
DIFFERENT LIGATION METHODS
Matthew S. Baker, D.D.S.
An Abstract Presented to the Faculty of the Graduate School
of Saint Louis University in Partial Fulfillment
of the Requirements for the Degree of
Master of Science in Dentistry
2009
ABSTRACT
Purpose: The purpose of the study was to examine the
alignment force deflection patterns of a 0.014-inch
superelastic Niti archwire supported in aesthetic and metal
brackets with varying ligation methods. Methods: First
molar tubes and one of four sets of brackets were bonded to
machined steel plates shaped as a maxillary arch. The
brackets used in the study were In-Ovation-R (MSL), InOvation-C (CSL), Ovation (MST), and Mystique (CST) (all
from GAC International, Bohemia, NY). 0.014-inch
superelastic Niti wires were ligated into each bracket set
with either 0.010-inch pre-formed steel ligatures (MST and
CST) or the self-ligating clips (MSL and CSL). The 0.014inch wire was deflected 4 mm palatally, and the subsequent
unloading forces were measured at 0.5 mm increments from
3.5 mm to 0.5 mm. Results: MSL and CSL were significantly
different (p<0.05) at all seven deflection points. MST and
CST were significantly different (p<0.05) at all deflection
points except the 0.5 mm distance. All bracket group
pairings were found to be significantly different (p<0.05)
at all deflection distances except for the following
pairings: CSL and MST at 3.0 mm; CSL and CST at 1.5 mm; MSL
and CST at 1.0 mm; MSL and MST, MSL and CST, and MST and
1
CST at 0.5 mm. Conclusions: MSL produce statistically
larger alignment forces than CSL throughout a 4 mm
deflection of a superelastic Niti wire. MST produce
statistically larger alignment forces than CST for
superelastic wire deflections greater than 2 mm, but
statistically smaller forces for deflections from 1 mm to 2
mm. Where a 4 mm palatally displaced canine is to be
corrected with a 0.014-inch superelastic Niti wire, all the
bracket groups (MSL,CSL,MST,CST) will behave similarly and
provide clinically acceptable alignment forces.
2
FORCES RELEASED DURING ALIGNMENT WITH AESTHETIC AND
STAINLESS STEEL PREADJUSTED APPLIANCES USING
DIFFERENT LIGATION METHODS
Matthew S. Baker, D.D.S.
A Thesis Presented to the Faculty of the Graduate School
of Saint Louis University in Partial Fulfillment
of the Requirements for the Degree of
Master of Science in Dentistry
2009
COMMITTEE IN CHARGE OF CANDIDACY:
Professor Eustaquio Araujo,
Chairperson and Advisor
Assistant Professor Ki Beom Kim
Assistant Clinical Professor Christopher Klein
i
DEDICATION
This thesis is dedicated to my beautiful wife, Brooke,
and our precious “daughter”, Britney, whose tremendous love,
support, and encouragement have helped carry me throughout my
higher education.
ii
ACKNOWLEDGEMENTS
The author would like to express appreciation for the
time and effort provided by his committee members: Dr.
Eustaquio Araujo, Dr. Ki Beom Kim, and Dr. Christopher Klein.
This project would not have been possible without their
support and advice.
A special thanks to Dr. Heidi Israel for her
contributions with the statistics of the project.
The author would also like to thank GAC International
for donating brackets and The Orthodontic Store for donating
preformed ligature ties.
iii
TABLE OF CONTENTS
List of Tables..............................................v
List of Figures...........................................vii
CHAPTER 1: INTRODUCTION.....................................1
CHAPTER 2: REVIEW OF THE LITERATURE
Introduction.....................................4
Alignment Force..................................4
Frictional Components.........................5
Springback Potential..........................8
Leveling and Aligning Mechanics for a Palatally
Malpositioned Canine............................10
Friction in Orthodontics........................12
Superelastic Wire Properties....................14
Aesthetic Brackets..............................16
Bracket Composition and Friction................19
Bracket Ligation and Friction...................21
Summary.........................................24
References......................................30
CHAPTER 3: JOURNAL ARTICLE
Abstract........................................35
Introduction....................................37
Materials and Methods...........................41
Laboratory Tests.............................41
Statistical Analysis.........................46
Results.........................................47
Discussion......................................51
Conclusions.....................................55
References......................................57
Appendix:
Tables..........................................61
Vita Auctoris..............................................70
iv
LIST OF TABLES
TABLE 2.1:
Summarized portion of the studies regarding
bracket composition and friction...............26
TABLE 2.2:
Summarized portion of the studies regarding
bracket ligation and friction................. 28
TABLE 3.1:
Descriptive Statistics: Alignment Force
(grams)....................................... 47
TABLE A.1:
T-Tests Comparing Metal Self-Ligating and
Ceramic Self-Ligating at Seven Deflection
Points (p<0.05)............................... 61
TABLE A.2:
T-Tests Comparing Metal Steel-Tied and Ceramic
Steel-Tied at Seven Deflection Points
(p<0.05)...................................... 62
TABLE A.3:
Bonferroni Post-Hoc Tests for all BracketLigation Groups at the 3.5 mm Deflection
Distance (p<0.05)............................. 63
TABLE A.4:
Bonferroni Post-Hoc Tests for all BracketLigation Groups at the 3.0 mm Deflection
Distance (p<0.05)............................. 64
TABLE A.5:
Bonferroni Post-Hoc Tests for all BracketLigation Groups at the 2.5 mm Deflection
Distance (p<0.05)............................. 65
TABLE A.6:
Bonferroni Post-Hoc Tests for all BracketLigation Groups at the 2.0 mm Deflection
Distance (p<0.05)............................. 66
TABLE A.7:
Bonferroni Post-Hoc Tests for all BracketLigation Groups at the 1.5 mm Deflection
Distance (p<0.05)............................. 67
TABLE A.8:
Bonferroni Post-Hoc Tests for all BracketLigation Groups at the 1.0 mm Deflection
Distance (p<0.05)............................. 68
v
TABLE A.9:
Bonferroni Post-Hoc Tests for all BracketLigation Groups at the 0.5 mm Deflection
Distance (p<0.05)............................. 69
vi
LIST OF FIGURES
FIGURE 2.1:
Arrows representing normal forces exerted in
bracket slots by archwire deflection and
ligation. A, B, C: Facial views of both common
edgewise and self-ligating brackets with wire.
D: A gingival view of a sectioned common
edgewise bracket with wire and ligature. E: A
gingival view of a sectioned self-ligating
bracket with wire and active clip..............7
FIGURE 3.1:
The steel plate with brackets and tubes
attached..................................... 42
FIGURE 3.2:
The steel plate with brackets and wire
positioned in the testing apparatus.......... 45
FIGURE 3.3:
Unloading plot data for the self-ligating
bracket groups at the seven deflection
points....................................... 49
FIGURE 3.4:
Unloading plot data for the steel-tied
bracket groups at the seven deflection
points....................................... 50
FIGURE 3.5:
Unloading plot data for all bracket ligation
groups at the seven deflection points........ 50
vii
CHAPTER 1:
INTRODUCTION
Aesthetic concerns are visible throughout almost every
facet of our present day culture. Orthodontics as a
profession partially functions to meet these aesthetic
demands by transforming patient smiles into beautiful and
visual works of art. The end result of orthodontics is
especially important, however, many patients also seek to
maintain the aesthetics of their smile while undergoing
treatment. With this ever-increasing demand for aesthetics
in orthodontics, many patients desire more attractive
treatment while improving their smile. This is especially
true in the adult population, where patients would rather
be as inconspicuous as possible while receiving orthodontic
care.
Orthodontic suppliers have been developing different
brackets for years in order to meet this demand from both
patients and their clinicians. Some of the first aesthetic
brackets were marketed in the 1970s by manufacturers and
made of plastic materials. These brackets had inherent
structural problems, which led to decreased performance
during treatment. Ceramic brackets were created in the
1980s with the intent to improve the clinical performance
of aesthetic brackets, and they have since maintained their
1
popularity among clinicians. These brackets are not without
their disadvantages, however, as they provide increased
frictional resistance, impeding orthodontic movements and
leading to a decrease in treatment progression.
Self-ligating brackets were introduced into the
marketplace with the intent to improve clinical performance
and have gained acceptance by practitioners over recent
years. Initially, they were only manufactured with metal
components. These brackets failed to meet the aesthetic
demands of patients, but gave their clinicians an increase
in treatment performance. Recently, self-ligating brackets
made of aesthetic materials have emerged. These brackets
hold the possibility of meeting aesthetic and functional
demands, thereby, satisfying both patients and their
orthodontists.
The goal of this research was to determine the
simulated clinical performance of aesthetic self-ligating
brackets when compared to metal self-ligating brackets
using a palatally offset cuspid model. In addition, the
method of ligating with steel ligatures and its application
for improving conventional aesthetic bracket performance
was evaluated. This final investigation was significant
because it may be possible for conventional brackets with
2
steel ligatures to perform as well as self-ligating
brackets.
3
CHAPTER 2:
REVIEW OF THE LITERATURE
INTRODUCTION
This review of the literature begins with an
explanation of the alignment force topic and the components
that are present in the initial stages of orthodontics. The
leveling mechanics for a malpositioned canine are then
examined followed by a discussion of bracket composition
and ligation methods. Comprehending these conceptual ideas
leads to the justification for this research on alignment
forces delivered by metal and aesthetic brackets with
varying ligation methods.
ALIGNMENT FORCE
The alignment force is the force that is placed on a
malpositioned tooth after a wire is deflected and ligated
into its bracket slot. This force is used to level and
align the tooth into the correct arch configuration during
the initial phase of orthodontics. In the absence of
separate oral forces and factors (perturbations, saliva,
4
plaque accumulation, etc.), the alignment force is broken
down into two different components: a frictional force and
a springback potential.
FRICTIONAL COMPONENTS
The frictional force is a negative component, which is
present at the wire-bracket interfaces in orthodontics.
Friction is defined as the force that counters the
tangential movement of two bodies in contact. The Coulomb
model of friction is identified by the following equation:
F = N*µ where F is the frictional force, N is the normal
force, and µ is the coefficient of friction.1,2
The coefficient of friction is determined based on the
surface roughness of two objects that are sliding against
one another; in this case, the Niti wire and the brackets
of the adjacent teeth. The coefficient of friction is a
constant and is associated with the surface characteristics
of the materials. Each material has two coefficients of
friction3: the coefficient of maximum static friction, which
is the force necessary to begin movement, and the
coefficient of kinetic friction, which is the component
5
opposing sliding of one surface over another at a steady
speed.4 The maximum kinetic friction is typically the
greatest resistance that occurs as an object starts to
slide. The kinetic coefficient of friction is usually a
smaller value than the maximum static coefficient of
friction for a system.5,6
The normal force is that which is present at
perpendicular angles where the wire and brackets are in
contact. In this research example, where the wire is
deflected to a palatally malposed, right canine bracket,
the wire could possibly contact the disto-lingual and
mesio-facial edges of the lateral incisor bracket slot and
the mesio-lingual and disto-facial edges of the first
bicuspid bracket slot. The number of normal forces of this
description that occur depends on the magnitude of the wire
deflection; the adjacent bracket edges to the wire
deflection will always come into contact with the wire,
however, the distal ends of the brackets to the deflection
may not. There are also possible contacts between the wire
and ligating mechanism. The ligation securing the wire in
the slot could be a self-ligating door or ligature tie.
Those possible normal forces between the wire and ligating
6
mechanism would be dependent on the direction and magnitude
of the wire deflection within the bracket slot.
Examples of potential normal forces are illustrated in
Figure 2.1.
A
B
D
C
E
Figure 2.1: Arrows representing normal forces exerted in bracket slots
by archwire deflection and ligation. A, B, C: Facial views of both
common edgewise and self-ligating brackets with wire. D: A gingival
view of a sectioned common edgewise bracket with wire and ligature. E:
A gingival view of a sectioned self-ligating bracket with wire and
active clip.
Adapted from Thalman.7
The total factor of the normal forces combined with
the coefficient values lead to the overall frictional
component present in the system which functions as a
7
resistance to the alignment force, and therefore it will
have a negative value.
Unnecessary friction applied in orthodontic therapy
can potentially convert to delayed tooth movement and
consequently longer treatment time. However, friction may
not always be a negative component to orthodontic
mechanics; friction can provide an additional source of
anchorage in certain clinical situations in order to result
in desired tooth movements.8
SPRINGBACK POTENTIAL
The springback component is the force that would be
placed on the malposed tooth if there were no friction in
the system. It is determined by the wire properties along
with the distance that the wire is deflected. Usually, the
further the wire is deflected, the higher that portion of
the springback potential will be.9
The wire diameter and length are other portions of the
springback potential. As the diameter of the wire
increases, the stiffness also will increase. Conversely, as
the length of wire within a section (between two brackets
8
for example) increases, the stiffness of the wire within
that portion will decrease.10,11 As wire size increases, the
stiffness of the wire increases to the power of four for
round wires. Therefore, if a round wire is doubled in its
dimensional size, then the stiffness will increase sixteen
times. The dimension in the direction of flexure has the
greatest influence on stiffness for rectangular wires.10,11
The specific wire material properties will also have
an effect on its stiffness.11 These values have been
determined for stainless steel, Niti alloys, and BetaTitanium alloys.12 Superelastic Niti alloys do not have
specific stiffness values due to their deflection
dependence13 and can vary from 7% to 41% of the stiffness of
stainless steel.10,13
The springback potential is a positive component of
the force that is placed on a malposed tooth, and the
frictional force is subtracted from it to obtain the net
alignment force that is theoretically placed on the tooth
in the absence of oral forces. The archwire that is
deflected and engaged into a malposed tooth’s bracket slot
can create tooth movement using the springback force from
the archwire.14 The net alignment force placed on the tooth
9
must be equal to or larger than the minimal force necessary
to initiate tooth movement.
LEVELING AND ALIGNING MECHANICS FOR A PALATALLY
MALPOSITIONED CANINE
Orthodontic treatment typically starts with a stage
where small and flexible continuous archwires are deflected
and ligated into the bracket slots to provide a force that
is adequate for leveling and aligning all teeth in an arch.
As discussed earlier, for the tooth movement to occur, the
force generated from the springback potential of the
activated archwire must surpass the minimal levels required
for tooth movement. Therefore, the springback potential
must provide an alignment force to the malpositioned tooth
that exceeds the frictional force components opposing the
deactivation of the wire.14-21 During this initial stage in
orthodontics, the excess wire that is deflected into the
malpositioned tooth’s bracket must slide through the
adjacent bracket slots where the frictional forces are
present and then travel out the distal end of the dental
10
arches, given that there are no stops placed on the
wire.15,16
While using a continuous archwire that is ligated into
a palatally offset canine, there are potential
counteractive forces created in the adjacent bracket slots
other than the forces that are placed on the canine. These
forces on the adjacent teeth can result in negative tooth
movements for the clinician who uses straight-wire
mechanics during leveling and aligning.11 With a palatally
offset canine, using a straight wire to level and align the
tooth will tend to tip the adjacent teeth toward the
canine. This can result in the buccal segment being
intruded and lingually inclined since the canine is usually
positioned higher in the palate than the occlusal plane. A
severe outcome of these negative side effects could leave
the patient with a canted occlusal plane, further
complicating the orthodontic treatment. The clinician
should use caution with the extent of archwire deflection
in these cases and assure that strain on adjacent teeth is
not detrimental.22
11
FRICTION IN ORTHODONTICS
As previously discussed, the initial stage of leveling
and aligning is a source of potential problems due to
friction, if the force generated during the deactivation of
the archwire is not adequate to overcome the opposing
frictional forces within the system. If these frictional
forces are strong enough, they can actually supersede the
springback potential of the wire, causing frictional
binding within the system and halting all leveling and
aligning of the teeth in the arch.7,23
Another stage in orthodontics where friction is a
major factor is when sliding mechanics are incorporated
into treatment. The wire will contact the bracket and
ligating mechanism resulting in frictional forces that act
to hinder the orthodontic force being used, thus altering
the movement that the clinician wishes to produce. Frank
and Nikolai5 studied sliding mechanics and stated that tooth
movement is initiated once the orthodontic force generated
exceeds the maximum static frictional forces opposing the
movement. The movement will temporarily stop once the
resistance of the compressed periodontal ligament and the
kinetic friction present overcome the orthodontic force
12
placed on the tooth. Due to the constant change in the
ligament over time, the opposing force associated with the
periodontal ligament will decrease. Since wire stability
and occlusal forces are a factor, the average frictional
forces between the bracket and wire can change resulting in
the break of the frictional binding and commencement of
tooth movement once again. Therefore, tooth movement
appears to occur in short bursts rather than one,
continuous motion. This sliding instability is known as the
“stick-slip” phenomenon.3 This process will occur in sliding
mechanics until the applied orthodontic force is no longer
adequate to overcome the frictional forces within the
system, halting all tooth movement until the appliance is
activated once more.
There are two types of sliding mechanics that are used
in orthodontics. A tooth or group of teeth can have a force
applied to them, and if this force is large enough to
overcome the frictional forces present, movement will occur
in the direction of the force as the brackets slide along
the archwire. The other mechanism used involves an archwire
sliding through brackets positioned on teeth that are
stationary. The teeth that are ligated to the wire in the
anterior portion of the arch during this en masse
13
retraction will travel through bone along with the moving
archwire. There exists a high potential for frictional
binding to occur within this system due to the high forces
required to move the group of anterior teeth at once.24
SUPERELASTIC WIRE PROPERTIES
Superelastic archwires have become the wire of choice
from the clinician’s armamentarium in the initial stage of
leveling and aligning due to their high levels of
elasticity and initial form recognition.25 They have the
ability to be deflected a great distance without undergoing
permanent deformation, making them a perfect choice for
cases where multiple first and second order malalignments
are present. There are two types of superelastic archwires
available on the market today: pseudoelastic alloys and
thermoelastic alloys. They differ in what provokes their
phase transformation from the body-centered austenitic form
to the monoclinic martensitic form.
Pseudoelastic archwires allow the clinician to apply a
fairly constant force to maligned teeth over a wide range
of tooth movement.26 This phenomenon exists due to the
14
wire’s ability to undergo physical property changes during
its loading and unloading cycles. The pseudoelastic
archwire is capable of having its magnitude of strain
increased and decreased as the wire is deflected and
unloaded while maintaining a nearly constant level of
stress (force).25 This can be viewed on a stress-strain
curve where the archwire displays horizontal regions on
both the loading and unloading phases, all while the strain
values are increasing and decreasing. This is due to the
wire’s ability to undergo the phase transition from the
austenitic form to the martensitic form as the strain on
the wire is increased. During the unloading phase, the
reverse transformation occurs, as the strain on the wire is
decreased.19
Thermoelastic archwires undergo phase transformation
as the alloy passes through a certain transition
temperature range. This allows the phase form to change
from martensitic to austenitic once this temperature level
is reached. When the alloy is below the austenitic phase
temperature, the archwire is quite pliable and can be
permanently deformed with little strain placed on the wire.
Once the alloy reaches the austenitic phase transition
temperature, the archwire will exhibit the form memory and
15
return to its original shape.26 There are currently
different phase transformation temperature ranges
commercially available for these archwires, giving the
clinician the ability to deform the alloys in room
temperature and ligate them in the oral cavity where the
wires have the capability to return to their original shape
while leveling and aligning the teeth.
There are currently large variations in physical
properties of wires between and within manufacturers due to
the range of factors that influence these superelastic
archwires. Therefore, clinicians should take care to select
the appropriate archwire for each application due to these
variations in alloy behavior.
The clinician should select
the wire with the appropriate size, shape, and temperature
transformation range (when applicable) to correctly
influence the loading and unloading behavior of the alloy
during the leveling and aligning stage.
AESTHETIC BRACKETS
Orthodontic suppliers have been developing different
brackets for years in order to meet aesthetic demands by
16
both patients and their clinicians. Some of the first
aesthetic brackets were marketed in the 1970s and
constructed from plastic,27 initially being produced from
acrylic substrates and later by polycarbonate materials.
Their acceptance by clinicians was not very positive due to
the inherent problems associated with them. The plastic
materials stained easily after time and their lack of
strength resulted in bonding failures, tie wing fractures,
and permanent deformation.28 This became a significant issue
as treatment progressed, leading to bracket slot
deformation and rendering the brackets insufficient to
express the correct prescription. More recently, high-grade
polyurethane and polycarbonate brackets reinforced with
ceramic or fiberglass have been introduced. These materials
have significantly decreased the deformation issues,
leading to an increased popularity in their production by
manufacturers.
Ceramic brackets were introduced in the 1980s as an
alternative to plastic materials for the aesthetic bracket
market. They provide better color stability and greater
resistance to wear and permanent deformations.27 They are
available in a variety of bracket types and various
appliance systems, making them versatile and providing most
17
clinicians with an available option. Ceramic brackets are
typically composed of aluminum oxide available in two
forms: polycrystalline or monocrystalline structures.
Polycrystalline brackets are manufactured and sintered
using specific binders that fuse the particles together,29
whereas monocrystalline brackets are milled from single
crystals of sapphire using diamond-cutting tools.30 The
largest difference between the two types is their optical
clarity, with the monocrystalline brackets having a better
translucency. Polycrystalline zirconia brackets were later
offered as an alternative to aluminum oxide brackets and
have the highest strength of all ceramics.31 They have
disadvantages, including an opaque appearance and a higher
tendency to stain as treatment lengthens. As the clinical
performance of aluminum oxide brackets has increased in
recent years due to improved physical properties, zirconia
brackets have essentially become obsolete because they are
aesthetically inferior brackets.
18
BRACKET COMPOSITION AND FRICTION
As discussed earlier, the coefficient of friction is a
constant and is related to the surface characteristics of
the bracket materials. This component of the frictional
force is what differs between metal and aesthetic brackets,
and thus could lead to a negative impact on the alignment
force. Ceramic brackets can vary in the extent of surface
roughness among the different types of ceramics and the
range of manufacturers.
Polycrystalline ceramics have a higher coefficient of
friction than monocrystalline ceramics due to their more
porous surface structure.27 Polycrystalline ceramic brackets
are manufactured by one of two processes: injection
moulding, which produces a smooth surface texture, or
machining with diamond cutting tools, which results in a
rougher finish texture. Omana et al.32 found that machined
ceramic brackets produce significantly higher frictional
forces than those that are injection moulded. Another
interesting finding from ceramic bracket frictional studies
is the conclusion that some ceramics can scratch archwires,
leading to a further increase in frictional forces between
the bracket and wire. Thorstenson and Kusy33 found stainless
19
steel debris from the wires on the outer slot wall edges of
the ceramic brackets when completing frictional studies.
It has been shown in the past that aesthetic brackets
composed of ceramic substances typically have higher
frictional levels when compared to stainless steel
brackets.23,33-40 In these studies, both bracket systems were
traditional twin brackets that were ligated with
elastomers. Pratten et al.34 found that two ceramic brackets
with different manufacturers both produced nearly twice the
frictional levels when compared to stainless steel
brackets. Tselepsis et al.36 compared stainless steel
brackets with polycarbonate, sapphire, and porcelain
aesthetic brackets and found that all three types of
aesthetic brackets produced higher frictional levels than
stainless steel. This problem of increased friction in
aesthetic brackets has been partially overcome by
manufacturers placing metal lined slots into the ceramic
brackets. However, the frictional levels are still higher
than those of all metal brackets in most cases.31,41-43 In
addition to the placement of metal slots, some
manufacturers have used silica-lined slots to potentially
decrease the frictional resistance,27 however, this
conclusion has not yet been proven.
20
A summary of a portion of the studies regarding
bracket composition and friction is provided in Table 2.1.
BRACKET LIGATION AND FRICTION
As discussed previously, the ligation of the adjacent
brackets to a malposed tooth is a source of normal forces
impeding the alignment force placed on the malposed tooth.
The ligation force on the adjacent teeth will vary based on
the ligation method used, and therefore higher ligating
forces placed on those brackets will increase the friction
at the bracket and wire interface.44 There are varying types
of ligation methods which can be used: elastomeric
ligatures, wire ligatures, and self-ligating clips or
doors.
Wire and elastomeric ligatures have been the most
common types of bracket ligation used in orthodontics.
Elastomeric ligatures produce the highest ligating forces
initially,16,18,45-47 and thus their use in ligating the
adjacent brackets will induce wire binding at shorter
deflection distances.2,7 However, as the elastomers relax
after having been stretched over the brackets within the
21
oral environment for some time, they have sizable decreases
in ligational force magnitudes.48 Stainless steel ligatures
produce lower frictional levels when compared to
elastomeric ligatures,1,35,45,46,49,50 however, this depends on
how tightly the wire ligatures are tied. Nanda and Ghosh2
found that ligating forces from wire ligatures can range
from 0 to 300 grams. Current literature suggests that
twisting the stainless steel ligatures until taut
(initially contacting the wire with the wire resting
against the base of the bracket slot), and then untwisting
them a quarter turn, reduces friction significantly and
provides an acceptable way to standardize the method of
ligature tying.1,45,49,51 Even though stainless steel ligatures
can produce low frictional levels, they still may not
provide levels equal to those of self-ligating brackets.52
Self-ligating brackets were introduced into the
orthodontic market with the hope of reducing frictional
levels both in the leveling/aligning stages and in sliding
mechanics. They are unique in their method of ligation in
which an integrated door or clip is closed over the slot to
hold the wire in place. There are two types of selfligating brackets: the “active” bracket that contains an
integrated clip which presses larger size wires in the slot
22
in latter stages of treatment; and the “passive” bracket
that usually contains a door mechanism which closes off the
slot and holds the wire in place. The wire is never fully
pressed into the slot of “passive” brackets, therefore
allowing the bracket to move freely along the archwire at
any stage of treatment.
Self-ligating brackets have the advantage of allowing
faster wire removal and insertion at adjustment visit
appointments due to the quick process of opening and
closing their ligating mechanism.53 Some clinicians also
believe that self-ligating brackets provide faster overall
treatment times due to their lower frictional levels and
efficient ability to move teeth. Self-ligating brackets
have shown on numerous accounts to be superior in their
ability to produce less frictional resistance than other
methods of ligation.45,46,54,55 This leads to more of the
wire’s springback potential being expressed in a malposed
tooth as a higher alignment force to be used for leveling
and aligning.17,19
A summary of a portion of the studies regarding
bracket ligation and friction is provided in Table 2.2.
23
SUMMARY
From this review of the literature, it can be clearly
understood that friction and force levels present in
orthodontics are multi-faceted. There are numerous factors
present in the overall complexity of friction in
orthodontics, and both manufacturers and clinicians have
put much time and effort into producing ways to more
efficiently move teeth with less friction. There has been
ample research completed on low friction technology, from
self-ligating brackets to high-tech wires, however, further
research is necessary to describe how aesthetic brackets
can play a part in this process.
With the increasing popularity of “clear” brackets and
“invisible” orthodontic treatment, the idea of applying low
friction technology to aesthetic treatment may play a
significant role in a clinician’s armamentarium. This study
aims to evaluate the differences between aesthetic and nonaesthetic treatment using recently introduced “clear” selfligating brackets and comparing them to metal selfligation. The study will also describe any benefits of this
newer self-ligating technology in comparison to more
24
conventional steel ligating mechanisms when used with
aesthetic and non-aesthetic brackets.
25
Table 2.1. Summarized portion of the studies regarding
bracket composition and friction.
Author
Objective
Sample
Method
Results
Omana et
al.32
Compare
frictional
effects of
various
ceramic and
SS brackets
7 brands of
ceramic
brackets; 1
brand of SS
brackets
Each bracket
was tested on
.018” x .025”
straight
sections of
SS and Niti
wire
Injection
moulded
ceramic
brackets
produce lower
friction than
other ceramic
brackets
Thorstenson
& Kusy33
Determine
effect of SS
inserts in
aesthetic
brackets
Aesthetic
brackets with
and without
SS inserts;
conventional
SS brackets
The brackets
were
evaluated
with various
second-order
angulations
in the dry
and wet
states on
0.457 × 0.635
mm SS wires
Frictional
properties of
aesthetic
brackets with
SS inserts
are between
aesthetic
brackets and
SS brackets
when
clearances
exist
Pratten et
al.34
Compare
frictional
forces among
SS and
ceramic
brackets
2 SS
brackets; 2
ceramic
brackets
Rectangular
SS and Niti
wires were
freely passed
through the
different
brackets in
dry and
artificial
saliva states
The SS
brackets had
a lower
frictional
resistance
than the
ceramic
brackets
under all
conditions
Loftus et
al.37
Evaluate
friction in
various
bracket-arch
wire
combinations
Various SS
(conventional
and s.l.) and
ceramic
brackets
.019” x .025”
SS, Niti, and
TMA wires
were tested
with each
bracket
combination
The ceramic
brackets
generated
significantly
higher
friction than
the other
brackets
26
Table 2.1. Continued.
Author
Objective
Sample
Method
Results
Angolkar et
al.38
Determine the
frictional
resistance
offered by
ceramic
brackets when
used with
wires of
different
alloys and
sizes
Monocrystalli
ne ceramic
brackets;
results from
a similar
study using
SS brackets
SS, cobaltchromium,
TMA, and Niti
wires were
ligated with
elastomers to
the brackets;
the friction
was measured
as the wire
passed
through the
slots
The wires in
ceramic
brackets
generated
significantly
stronger
frictional
force than
they did in
SS brackets
Kusy &
Whitley39
Measure the
coefficients
of friction
for sixteen
arch wirebracket
combinations
One
rectangular
arch wire
from each of
the four wire
alloy groups;
one bracket
from the SS
and
polycrystalli
ne ceramic
groups
When tested
over a series
of eight
incident
angles, the
optical
surface
roughness of
the SS and
ceramic
brackets was
measured
The ceramic
bracket
coupled with
the SS wire
produced a
higher
coefficient
of friction
when compared
to the SS
bracket
Cacciafesta
et al.41
Compare the
frictional
resistance
between
ceramic
brackets,
ceramic
brackets with
SS slots, and
SS brackets
3M Unitek
ceramic
bracket; 3M
Unitek
ceramic
bracket with
SS slot; 3M
Unitek SS
bracket; SS,
Niti, and TMA
wires
Static and
kinetic
friction of
each bracketarchwire
combination
was measured
using a
specially
designed
apparatus
The ceramic
brackets with
SS inserts
produced
significantly
less friction
than the
ceramic
brackets, but
more friction
than the SS
brackets
Kusy &
Whitley43
Compare the
frictional
resistances
of metallined ceramic
brackets and
SS brackets
1 SS lined
ceramic
bracket; 1
gold lined
ceramic
bracket; 2 SS
brackets; SS
archwires
Friction was
measured as
the secondorder
angulations
and ligature
force among
the bracketarchwire
combinations
was varied
Metal-lined
ceramic
brackets can
function
comparably to
SS brackets
and gold
inserts
appear
superior to
SS inserts
27
Table 2.2. Summarized portion of the studies regarding
bracket ligation and friction.
Author
Objective
Sample
Camporesi et
al.18
Compare the
forces
released by
ceramic
brackets
with lowfriction and
elastomeric
ligation
2 ceramic
brackets;
low-friction
ligation
clips;
elastomeric
ligatures;
.014” Niti
wire
Alignment
force was
measured
using the
various
bracket and
ligation
combinations
Significantly
greater
alignment
forces were
measured when
the brackets
were combined
with the lowfriction clip
Hain et
al.45
Compare the
effect of
different
ligation
methods on
friction
“Speed” selfligating
brackets; SS
and ceramic
brackets
ligated with
TP slick
modules,
elastomerics,
and SS
ligatures
Friction was
measured
while the
various
bracketligation
combinations
were moved
along a .019”
x .025” SS
wire
Loosely tied
SS ligatures
produced the
lowest
friction,
followed by
the slick
modules,
“Speed”
brackets, and
elastomers
Henao,
Kusy46
Compare the
frictional
behavior
between
conventional
and selfligating
bracket
systems
4
conventional
and 4 selfligating
bracket
systems; 3
standardized
archwire
sizes
Analyses of
the bracket
types was
completed by
drawing
samples of
three
archwires
through
progressively
malocclused
quadrants
The selfligating
brackets
averaged
significantly
smaller
drawing
forces for
each study
design
implemented
Petersen48
Compare the
alignment
force
between
selfligating
brackets and
both relaxed
and new
elastomers
“InnovationR” brackets
with the
self-ligating
clip in place
and removed;
relaxed and
new
elastomers
used to
ligate
without the
clip; Niti
wire
The unloading
force was
plotted and
measured for
a full arch
minus one
cuspid model
for each
bracketarchwire
combination
Ligating with
relaxed
elastomeric
ligatures
results in
unloading
forces nearly
equal to
those in a
self-ligating
appliance
28
Method
Results
Table 2.2. Continued.
Author
Objective
Sample
Method
Results
Sirisaowaluk
et al.49
To determine
if the type
of ligation
influences
the
frictional
resistance
between SS
wire and
brackets
8 different
variations of
ligation
using
elastomers
and SS
ligatures; SS
brackets; SS
wire
80% of the
minimum force
required to
overcome
static
friction was
applied to
the wire for
8 minutes and
any sliding
measured
Frictional
resistance
was least
when SS
ligatures
were figure-8
twisted until
taut then
untwisted 1/4
turn, and
greatest with
figure-8
elastomerics
Khambay et
al.50
Investigate
the effect
of
elastomeric
and SS
ligatures on
frictional
resistance
using a
validated
method
4 variations
of
elastomers;
pre-formed SS
ligatures;
conventional
SS brackets;
“Damon II”
self-ligation
brackets
Each
bracket/wire
combination
with each
method of
ligation was
tested in the
presence of
human saliva
and the mean
frictional
force was
recorded
SS ligatures
usually
produced
lower
friction than
elastomers;
passive selfligating
brackets are
the only
method of
almost
eliminating
friction
Hain et
al.55
Examine the
frictional
properties
of coated
modules with
those of
other common
ligation
methods
6 elastomeric
variations
(including 1
with a
special
coating);
“Speed”
active selfligating
brackets;
“Damon II”
passive selfligating
brackets
Each bracketligation
combination’s
resistance to
movement was
measured on a
.019” x .025”
SS wire
The “Damon
II” brackets
produced no
recordable
friction of
ligation;
coated
modules
produced 50%
less friction
than all
ligation
methods
except the
“Damon II”
29
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18. Camporesi M, Baccetti T, Franchi L. Forces released by
esthetic preadjusted appliances with low-friction and
conventional elastomeric ligatures. Am J Orthod Dentofacial
Orthop 2007;131:772-775.
19. Wilkinson PD, Dysart PS, Hood JA, Herbison GP. Loaddeflection characteristics of superelastic nickel-titanium
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20. Farrant SD. An evaluation of different methods of
canine retraction. Br J Orthod 1977;4:5-15.
21. Staggers JA, Germane N. Clinical considerations in the
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23. Kusy RP, Whitley JQ. Friction between different wirebracket configurations and materials. Semin Orthod
1997;3:166-177.
24. Nanda RS, Ghosh J. Biomedical considerations in sliding
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25. Miura F, Mogi M, Ohura Y, Hamanaka H. The super-elastic
property of the Japanese NiTi alloy wire for use in
orthodontics. Am J Orthod Dentofacial Orthop 1986;90:1-10.
26. Kusy RP. A review of contemporary archwires: their
properties and characteristics. Angle Orthod 1997;67:197207.
27. Russell J. Current products and practice: aesthetic
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28. Arid JO, Durning P. Fractures of polycarbonate edgewise
brackets: a clinical and SEM study. Br J Orthod
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29. Kusy RP. Morphology of polycrystalline alumina brackets
and its relationship to fracture toughness and strength.
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30. Swartz ML. Ceramic brackets. J Clin Orthod 1988;22:8288.
31. Kusy RP. Orthodontic Biomaterials: From the Past to the
Present. Angle Orthod 2002;72:501–12.
32. Omana HM, Moore RN, Bagby MD. Frictional properties of
metal and ceramic brackets. J Clin Orthod 1992;26:425-32.
33. Thorstenson G, Kusy R. Influence of stainless steel
inserts on the resistance to sliding of esthetic brackets
with second-order angulations in the dry and wet states.
Angle Orthod 2003;73:167–75.
34. Pratten DH, Dupli K, Germane N, Gunsolley JC.
Frictional resistance of ceramic and stainless steel
orthodontic brackets. Am J Orthod Dentofacial Orthop
1990;98:398-403.
35. Griffiths HS, Sherrif M, Ireland AJ. Resistance to
sliding with three types of elastomeric modules. Am J
Orthod Dentofacial Orthop 2005;127:670-75.
36. Tselepsis M, Brockhurst P, West VC. The dynamic
frictional resistance between orthodontic brackets and
archwires. Am J Orthod Dentofacial Orthop 1994;106:131-138.
32
37. Loftus BP, Årtun J, Nicholls JI, Alonzo TA, Stoner JA.
Evaluation of friction during sliding tooth movements in
various bracket-arch wire combinations. Am J Orthod
Dentofacial Orthop 1999;116:336–45.
38. Angolkar PV, Kapila S, Duncanson MG, Nanda RS.
Evaluation of friction between ceramic brackets and
orthodontic wires of four alloys. Am J Orthod Dentofacial
Orthop 1990;98:499–506.
39. Kusy RP, Whitley JQ. Coefficient of friction for arch
wires in stainless steel and polycrystalline alumina
bracket slots: The dry state. Am J Orthod Dentofacial
Orthop 1990;98:300–12.
40. Kusy RP, Whitley JQ, Prewitt MJ. Comparison of the
frictional coefficients for selected archwire-bracket slot
combinations in the wet and dry state. Angle Orthod
1991;61:293–302.
41. Cacciafesta V, Sfondrini MF, Scribante A, Klersy C,
Auricchio F. Evaluation of friction of conventional and
metal-insert ceramic brackets in various bracket-archwire
combinations. Am J Orthod Dentofacial Orthop 2003;124:4039.
42. Kapur Wadhwa R, Kwon HK, Close JM. Frictional
resistances of different bracket-wire combinations. Aust
Orthod J 2004;20:25-30.
43. Kusy RP, Whitley JQ. Frictional resistances of metallined ceramic brackets versus conventional stainless steel
brackets and development of 3-D frictional maps. Angle
Orthod 2001;71:364–74.
44. Edwards GD, Davies EH, Jones SP. The ex vivo effect of
ligation techniques on the static frictional resistance of
stainless steel brackets and archwires. Br J Orthod
1995;22:145-53.
45. Hain M, Dhopatkar A, Rock P. The effect of ligation
method on friction in sliding mechanics. Am J Orthod
Dentofacial Orthop 2003;123:416-22.
46. Henao SP, Kusy RP. Evaluation of the frictional
resistance of conventional and self-ligating bracket
designs using standardized archwires and dental typodonts.
Angle Orthod 2004; 74:202-211.
33
47. Iwasaki LR, Beatty MW, Randall CJ, Nickel JC. Clinical
ligation forces and intraoral friction during sliding on a
stainless steel archwire. Am J Orthod Dentofacial Orthop
2003;123:408-415.
48. Petersen A. Force Decay of Elastomeric Ligatures:
Influence on Unloading Force Compared to Self-Ligation. St.
Louis: Saint Louis University; 2008.
49. Sirisaowaluk N, Kravchuk O, Ho C. The influence of
ligation on frictional resistance to sliding during
repeated displacement. Aust J Orthod 2006;22:141-6.
50. Khambay B, Millett D, McHugh S. Evaluation of methods
of archwire ligation on frictional resistance. Eur J Orthod
2004;26: 327-32.
51. Iwasaki LR. Friction and orthodontic mechanics:
Clinical studies of moment and ligation effects. Semin
Orthod 2003;9: 290-7.
52. Read-Ward GE, Jones SP, Davies EH. A comparison of
self-ligating and conventional orthodontic bracket systems.
Br J Orthod 1997;24:309-17.
53. Turnbull NR, Birnie DJ. Treatment efficiency of
conventional vs. self-ligating brackets: Effects of
archwire
size and material. Am J Orthod Dentofacial Orthop
2007;131:395-399.
54. Henao SP, Kusy RP. Frictional evaluations of dental
typodont models using four self-ligating designs and a
conventional design. Angle Orthod 2005;75:75-85.
55. Hain M, Dhopatkar A, Rock P. A comparison of different
ligation methods on friction. Am J Orthod Dentofacial
Orthop 2006;130:666-670.
34
CHAPTER 3:
JOURNAL ARTICLE
ABSTRACT
Purpose: The purpose of the study was to examine the
alignment force deflection patterns of a 0.014-inch
superelastic Niti archwire supported in aesthetic and metal
brackets with varying ligation methods. Methods: First
molar tubes and one of four sets of brackets were bonded to
machined steel plates shaped as a maxillary arch. The
brackets used in the study were In-Ovation-R (MSL), InOvation-C (CSL), Ovation (MST), and Mystique (CST) (all
from GAC International, Bohemia, NY). 0.014-inch
superelastic Niti wires were ligated into each bracket set
with either 0.010-inch pre-formed steel ligatures (MST and
CST) or the self-ligating clips (MSL and CSL). The 0.014inch wire was deflected 4 mm palatally, and the subsequent
unloading forces were measured at 0.5 mm increments from
3.5 mm to 0.5 mm. Results: MSL and CSL were significantly
different (p<0.05) at all seven deflection points. MST and
CST were significantly different (p<0.05) at all deflection
points except the 0.5 mm distance. All bracket group
pairings were found to be significantly different (p<0.05)
at all deflection distances except for the following
35
pairings: CSL and MST at 3.0 mm; CSL and CST at 1.5 mm; MSL
and CST at 1.0 mm; MSL and MST, MSL and CST, and MST and
CST at 0.5 mm. Conclusions: MSL produce statistically
larger alignment forces than CSL throughout a 4 mm
deflection of a superelastic Niti wire. MST produce
statistically larger alignment forces than CST for
superelastic wire deflections greater than 2 mm, but
statistically smaller forces for deflections from 1 mm to 2
mm. Where a 4 mm palatally displaced canine is to be
corrected with a 0.014-inch superelastic Niti wire, all the
bracket groups (MSL,CSL,MST,CST) will behave similarly and
provide clinically acceptable alignment forces.
36
INTRODUCTION
Aesthetics and treatment efficiency are two seemingly
unrelated topics in orthodontics. However, current attempts
by manufacturers for improvements in these areas by
combining technological advancements to produce an
aesthetic self-ligating bracket may prove otherwise.
Aesthetic brackets have existed in orthodontics for years,
although they have failed to perform as well as their metal
counterparts in clinical situations where less friction is
desired.1-9 Conventional aesthetic brackets ligated with
elastomerics have typically provided a rougher surface area
leading to increased friction, and therefore, decreased
treatment efficiency. A summary of frictional properties in
orthodontics is necessary in order for the interaction
between aesthetic brackets and treatment efficiency to be
fully understood.
Friction and springback potential are two components
that determine the magnitude of force placed on a malposed
tooth, otherwise known as the alignment force. This can be
represented by the following equation:
Alignment Force = Springback Potential – Frictional Forces
37
The springback component is the force that would be
placed on the malposed tooth if there were no friction in
the system. It is determined by the wire properties along
with the distance that the wire is deflected. Generally,
the further the wire is deflected, the higher that portion
of the springback potential will be.10
The frictional force is a negative component that is
present at the wire-bracket interfaces in orthodontics. The
frictional force is composed of two different parts: the
normal force and the coefficient of friction.11-12 The normal
force is present at perpendicular angles where the wire and
brackets are in contact. In the current study, where the
wire is deflected to a palatally malposed, right canine
bracket, the wire could possibly contact the disto-lingual
and mesio-facial edges of the lateral incisor bracket slot
and the mesio-lingual and disto-facial edges of the first
bicuspid bracket slot.
The coefficient of friction is determined based on the
surface roughness of two objects that are sliding against
one another. The coefficient of friction is a constant and
is associated with the surface characteristics of the
materials. Each material has two coefficients of friction13:
the coefficient of maximum static friction, which is the
38
force necessary to begin movement, and the coefficient of
kinetic friction, which is the component opposing the
sliding motion of one surface over another at a steady
speed.14
These components of the frictional force are what
differs between metal and aesthetic brackets and thus could
lead to a negative impact on the alignment force. This
problem has been partially overcome by manufacturers
placing metal lined slots into the ceramic brackets;
however, the frictional levels are still higher than those
of all metal brackets.15-18 The recent release of selfligating ceramic brackets could potentially improve this
problem of aesthetic brackets and high friction.
The ligation force on the adjacent teeth will vary
based on the ligation method used, and therefore, higher
ligating forces placed on those brackets will increase the
friction at the bracket and wire interface.19 Elastomeric
ligatures have been shown to produce the highest ligating
forces and thus their use in ligating the adjacent brackets
will induce wire binding at shorter deflection
distances.12,20 Stainless steel ligatures can produce lower
frictional levels,4,11,21-24 however, they still may not
39
provide levels equal to those seen in self-ligating
brackets.25
With the increasing popularity of clear brackets and
“invisible” orthodontic treatment, the idea of applying low
friction technology to aesthetic treatment may play a
significant role in a clinician’s armamentarium. This study
evaluated the differences between aesthetic and nonaesthetic treatment using recently introduced ceramic selfligating brackets and comparing them to metal selfligation. The study also described any benefits of the new
self-ligating technology in comparison to more conventional
steel ligating mechanisms when used with aesthetic and nonaesthetic brackets.
40
MATERIALS AND METHODS
LABORATORY TESTS
The arch model used in this study was constructed of
0.25-inch steel with pre-determined interbracket distances
based on the standard distances (accurate to within 0.5mm)
given by Moyers et al.26 for a male’s maxillary permanent
dentition. Attached to the outer edge of the plate were two
first molar tubes with zero rotation prescription (GAC
International, Bohemia, NY) and nine brackets with 0.022inch slots from second premolar to second premolar, with
the exception of the right canine. A 12 mm semicircular
area was removed from the plate at the position of the
right canine in order to allow palatal wire deflections.
The fixed appliances used were from a maxillary set of
brackets designated from one of the following types: metal
self-ligating In-Ovation-R brackets (GAC International,
Bohemia, NY), ceramic self-ligating In-Ovation-C brackets
(GAC International, Bohemia, NY), conventional metal
Ovation brackets (GAC International, Bohemia, NY), and
conventional ceramic Mystique brackets (GAC International,
41
Bohemia, NY). Both ceramic bracket groups were composed of
a polycrystalline structure and did not have metal inserts
in their slots or bases. A 0.022-inch stainless steel
archwire bent to match the shape of the plate was used to
align the brackets and tubes. It was determined that this
wire was adequate to completely align the brackets due to
their 0.022-inch wide slots. The appliances were direct
bonded to the plate using Transbond XT (3M Unitek,
Monrovia, CA). See Figure 3.1.
Figure 3.1:
The steel plate with brackets and tubes attached.
The ligating mechanism for the self-ligating brackets
was the resilient clip on the bracket that locked into
42
place over the archwire slot, while the conventional twin
brackets were ligated using 0.010-inch preformed stainless
steel ligatures (The Orthodontic Store, Gaithersurg, MD).
This method has been shown to produce frictional levels
similar to self-ligating brackets in metal bracket
studies,25 however, the magnitude of ligation is an
important factor for the ligatures. For this study, the
stainless steel ligatures were ligated in a manner where
they delivered low ligation forces, allowing them to be
compared to the self-ligating clips. Also, they were
ligated in order to allow the method of ligation to be
standardized for each bracket during all the tests. This
method was approached using the preformed ligatures that
were twisted until taut (initially contacting the wire with
the wire resting against the base of the bracket slot), and
then untwisted a quarter turn. The ligature subsequently
held the wire in the mesial and distal ends of the bracket
slot while potentially allowing a low friction system. A
pilot study was completed performing this method of steel
ligation using a pull-out friction test with a series of
brackets. The various runs produced similar frictional
levels (the differences were within the error range of the
testing machine; i.e. a maximum difference of 3 grams was
measured and the machine had a perceived error range of 2.5
43
to 5.0 grams), and it was therefore concluded that the
method could be standardized for the final laboratory
tests. This method has also been shown in other studies to
provide a standardized method of ligating traditional twin
brackets.11,21-22,27
The experiment was conducted with a universal testing
machine (Model 1011, Instron Corp., Canton, MA) in a dry
field temperature control case (36 ± 5˚ C). The steel plate
assembly was fixed in order for the 0.01-inch-wide blade of
the deflecting rod to contact the wire at the midpoint of
the right canine space. Continuous 0.014-inch superelastic
Niti wires (G&H Wire Company, Franklin, IN) matching the
shape of the steel plate were ligated into the fixed
brackets. See Figure 3.2.
44
Figure 3.2: The steel plate with brackets and wire positioned in the
testing apparatus.
A pilot study (10 runs per group) was completed in
order to use a statistical power analysis to indentify the
sample size. It was then determined that 40 tests per
bracket group (metal self-ligating, ceramic self-ligating,
ceramic conventional ligated with stainless steel, metal
conventional ligated with stainless steel) would provide
adequate statistical results. A new wire was selected for
each individual test (160 wires total were used). During
each test, the 0.014-inch wire was deflected palatally with
the blade at the center of the right canine position. The
wire was advanced to a distance of 4 mm with a cross-head
45
speed of 10 mm per minute and unloaded facially at a speed
of 2 mm per minute. As the wire unloaded, the alignment
force was recorded at every 0.5 mm increment from 3.5 mm to
0.5 mm for statistical analysis.
STATISTICAL ANALYSIS
Alignment force values were analyzed using the SPSS
15.0 for Windows (SPSS Inc., Chicago, IL) statistical
package. Descriptive statistics were generated for each
bracket-ligation group (Table 3.1). Independent T-Tests
were run between the brackets within each ligation group to
evaluate for statistical differences between the means at a
95% probability level. To further assess the results, a
One-Way ANOVA was used to analyze for variance between all
of the bracket-ligation groups at each deflection point.
Bonferroni post-hoc tests were then run to identify
significant differences between the variables at a 95%
probability level.
46
Table 3.1. Descriptive Statistics: Alignment Force (grams)
Deflection
3.5 mm
3.0 mm
2.5 mm
2.0 mm
1.5 mm
1.0 mm
0.5 mm
Group
Metal Self-Ligating
Ceramic Self-Ligating
Metal Steel-Tied
Ceramic Steel-Tied
Metal Self-Ligating
Ceramic Self-Ligating
Metal Steel-Tied
Ceramic Steel-Tied
Metal Self-Ligating
Ceramic Self-Ligating
Metal Steel-Tied
Ceramic Steel-Tied
Metal Self-Ligating
Ceramic Self-Ligating
Metal Steel-Tied
Ceramic Steel-Tied
Metal Self-Ligating
Ceramic Self-Ligating
Metal Steel-Tied
Ceramic Steel-Tied
Metal Self-Ligating
Ceramic Self-Ligating
Metal Steel-Tied
Ceramic Steel-Tied
Metal Self-Ligating
Ceramic Self-Ligating
Metal Steel-Tied
Ceramic Steel-Tied
Minimum
160.0
150.0
145.0
140.0
135.0
125.0
125.0
117.5
127.5
117.5
115.0
112.5
120.0
112.5
105.0
105.0
112.5
107.5
100.0
102.5
97.5
92.5
92.5
97.5
60.0
55.0
60.0
60.0
Maximum
172.5
165.0
155.0
155.0
147.5
135.0
137.5
135.0
137.5
130.0
127.5
125.0
135.0
130.0
117.5
122.5
125.0
127.5
112.5
120.0
110.0
105.0
102.5
110.0
72.5
67.5
67.5
67.5
Mean
167.3
157.3
151.7
144.8
139.8
130.9
130.7
126.1
130.9
123.4
121.3
118.6
126.5
118.2
111.6
114.1
118.3
113.4
106.9
111.4
103.7
99.6
97.6
102.9
64.6
61.6
64.3
65.0
SD
2.6
3.1
2.4
3.6
3.3
2.4
2.9
5.3
2.8
2.9
2.9
3.9
3.5
4.2
2.8
4.3
2.8
4.8
3.3
4.3
3.3
2.8
2.9
3.0
3.3
2.4
2.0
2.0
RESULTS
The mean alignment forces at each deflection point were
analyzed using two statistical tests. Independent T-Tests
were used to compare the means of the metal versus ceramic
bracket types for each ligation group at the seven
deflection points (Tables A.1-A.2 in Appendix). When
comparing within the self-ligating group, the ceramic and
metal brackets were significantly different (p<0.05) at all
47
seven deflection points. Within the steel ligature group,
the ceramic and metal brackets were significantly different
(p<0.05) at every deflection point except the 0.5 mm
distance. In addition, within the steel ligature group, the
metal brackets had higher mean alignment forces for the
3.5-2.5 mm distances; however, the ceramic brackets
provided more alignment force from the 2.0-0.5 mm
distances. The metal brackets tested with higher mean
alignment forces than the ceramic brackets at all
deflection points within the self-ligating group.
A One-Way ANOVA and Bonferroni post-hoc tests were used
to further analyze the bracket-ligation groups in order to
find statistical differences between all four of the
brackets at each deflection point (Tables A.3-A.9 in
Appendix). All bracket group pairings were found to be
significantly different (p<0.05) at all deflection
distances except for the following pairings: ceramic selfligating and metal steel-tied at 3.0 mm; ceramic selfligating and ceramic steel-tied at 1.5 mm; metal selfligating and ceramic steel-tied at 1.0 mm; metal selfligating and metal steel-tied, metal self-ligating and
ceramic steel-tied, metal steel-tied and ceramic steel-tied
at 0.5 mm.
48
Figures 3.3, 3.4, and 3.5 illustrate the unloading plot
data.
160
Force (g)
140
120
100
Metal Self-Ligating
80
Ceramic Self-Ligating
60
40
0.5
1
1.5
2
2.5
3
3.5
Deflection (mm)
Figure 3.3: Unloading plot data for the self-ligating bracket groups
at the seven deflection points.
49
160
Force (g)
140
120
100
Metal Steel-Tied
80
Ceramic Steel-Tied
60
40
0.5
1
1.5
2
2.5
3
3.5
Deflection (mm)
Figure 3.4: Unloading plot data for the steel-tied bracket groups at
the seven deflection points.
160
Force (g)
140
120
100
Metal Self-Ligating
Ceramic Self-Ligating
80
Metal Steel-Tied
60
Ceramic Steel-Tied
40
0.5
1
1.5
2
2.5
3
3.5
Deflection (mm)
Figure 3.5: Unloading plot data for all bracket-ligation groups at the
seven deflection points.
50
DISCUSSION
The unloading plot illustrates the superelastic
behavior exhibited by the 0.014 Niti archwire. For each
bracket-ligation group, there was an area where the curve
leveled off around the 2 mm to 3 mm deflection distance.
Even though the stiffness of the wire would have varied
throughout that distance, the Niti wire still exhibited a
fairly constant force due to the superelastic properties
inherent to the archwire.28 The alignment force in the rest
of the unloading plots varied greatly due to the changing
stiffness of the wire given the varying deflection
amplitudes. Also, the frictional forces in the adjacent
brackets opposed the sliding of the wire throughout the
arch.
Even though the alignment force levels were
significantly different between each bracket-ligation group
at most of the deflection points, Figure 3.5 does
illustrate that the unloading patterns of the groups were
similar throughout the deflection distances. Their
frictional levels varied over most of the plots, however,
they still exhibited similar unloading characteristics.
This was primarily due to the wire properties since the
same SE Niti wire was used for each group. Although, it
51
still remains significant as unloading plots have been
remarkably different in previous studies with varying
ligation methods where the wire was constant throughout the
experiment.20 This shows that even though there were
significant differences in frictional levels for the groups
throughout most of the plots, they were still comparable
enough to provide similar unloading characteristics.
When comparing the ceramic and metal brackets within
the self-ligating group, the metal brackets provided
significantly higher alignment forces throughout the
unloading plots. Since the bracket composition was the
indirect variable among the bracket groups, it can be
concluded that the ceramic composition provided higher
frictional levels, and thus, lower unloading forces for the
palatally offset canine. Pratten et al.3 and Loftus et al.6
produced similar results in experiments with conventional
ceramic and stainless steel brackets. However, this trend
did not hold true for the steel-tied group. The ceramic and
metal brackets within this group were significantly
different at all deflection points except for the 0.5 mm
distance. Further analysis revealed the most significant
finding within this group, that the ceramic brackets
provided higher alignment forces from the 2.0 mm to 0.5 mm
distances. This suggests that when steel ligatures are used
52
to ligate conventional brackets, the bracket composition is
less of a factor when frictional levels are considered.
After analyzing all of the 42 bracket-ligation group
comparisons at the 7 deflection points using the One-Way
ANOVA, there were only 6 pairings that did not show
significant differences between their alignment forces.
Among those non-significant findings, 3 of the groupings
fell within the 0.5 mm deflection distance. These results
suggest that the second indirect variable of ligation added
among these groupings is less of a factor on frictional
levels than the variable of bracket composition when selfligation is compared to steel ligatures. Since most of the
non-significant findings were from the 1.5 mm to 0.5 mm
distances, it can be concluded that the further the
deflection amplitude of the Niti wire, the greater the
variation between the bracket-ligation groups. In other
words, the differing bracket composition and ligation
methods had a greater effect on the frictional levels
within the system as the wire was further deflected to
engage an offset tooth.
Overall, even though most of the comparisons were
statistically significant, the actual differences in the
alignment force magnitudes between each bracket-ligation
group were perhaps clinically insignificant. The unloading
53
plots show the close relationships between the groups, and
it could be assumed that each bracket-ligation combination
would behave very similar in most clinical situations. For
a palatally offset canine, the possible tooth movements
typically expected are tipping, extrusion, or rotation. The
optimum force levels for these movements are between 35-60
g according to Proffit,29 therefore each bracket-ligation
group used in this study were more than adequate for the
desired tooth movements.
Factors not examined in this study that could affect
clinical outcomes include extraneous intraoral forces and
factors, varying interbracket distances, and wire diameter.
The presence of saliva and plaque accumulation are factors
that could both positively and negatively affect the
clinical frictional force levels. Perturbations are
intraoral forces that could momentarily decrease the
frictional levels to zero, providing episodes of maximum
alignment force.30 Altering the local wire curvature by
increasing or decreasing the interbracket distances would
have an affect on the normal forces in the system,
therefore changing the unloading force. Varying wire
diameters have been shown to alter alignment forces, and
the unloading plot characteristics between bracket-ligation
groups could change as well.10
54
Clinical recommendations can be deduced from the
present study. Where there is a demand for maximum
aesthetics and treatment efficiency, using brackets that
are made of ceramic materials containing self-ligating
mechanisms would be advantageous. The ceramic composition
provides a time-tested way to obtain clear braces, while
the self-ligation gives the clinician low friction levels
and rapid wire changes.
CONCLUSIONS
1.
The springback potential of the 0.014-inch superelastic
Niti wire is large enough to supersede the frictional
forces present in all four of the bracket-ligation groups.
2.
Metal self-ligating brackets will produce statistically
larger alignment forces than ceramic self-ligating brackets
throughout a 4 mm deflection of a superelastic Niti wire.
3.
Metal steel-tied brackets will produce statistically
larger alignment forces than ceramic steel-tied brackets
for superelastic wire deflections greater than 2 mm, but
statistically smaller forces for deflections from 1 mm to 2
mm.
4.
Where a 4 mm palatally displaced canine is to be
corrected with a 0.014-inch superelastic Niti, ceramic and
55
metal brackets that are self-ligating or steel-tied will
behave similarly and provide clinically acceptable
alignment forces.
56
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3. Pratten DH, Dupli K, Germane N, Gunsolley JC. Frictional
resistance of ceramic and stainless steel orthodontic
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Orthop 1990;98:499–506.
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10. Fruge BJ. Forces from Superelastic Cu-Ni-Ti Orthodontic
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Saint Louis University; 2008.
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arch wires. Am J Orthod Dentofacial Orthop 1991;100:513522.
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combinations. Am J Orthod Dentofacial Orthop 2003;124:403409.
16. Kapur Wadhwa R, Kwon HK, Close JM. Frictional
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18. Kusy RP, Whitley JQ. Frictional resistances of metallined ceramic brackets versus conventional stainless steel
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19. Edwards GD, Davies EH, Jones SP. The ex vivo effect of
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29. Proffit WR. Contemporary Orthodontics. 3rd Ed. St.
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60
APPENDIX: TABLES
Table A.1. T-Tests Comparing Metal Self-Ligating and
Ceramic Self-Ligating at Seven Deflection Points (p<0.05)
Groups
(mm)
C.S.L.
3.5
C.S.L.
3.0 C.S.L.
2.5 M.S.L.
3.5
Sig.
Diff.
M.S.L.
3.0
M.S.L.
2.5
M.S.L.
2.0
M.S.L.
1.5
M.S.L.
1.0
M.S.L.
0.5
Sig.
Diff.
Sig.
Diff.
Sig.
Diff.
C.S.L.
2.0 Sig.
Diff.
C.S.L.
1.5 Sig.
Diff.
C.S.L.
1.0 Sig.
Diff.
C.S.L.
0.5 61
Table A.2. T-Tests Comparing Metal Steel-Tied and Ceramic
Steel-Tied at Seven Deflection Points (p<0.05)
Groups
(mm)
C.S.T.
3.5
C.S.T.
3.0 C.S.T.
2.5 M.S.T.
3.5
Sig.
Diff.
M.S.T.
3.0
M.S.T.
2.5
M.S.T.
2.0
M.S.T.
1.5
M.S.T.
1.0
M.S.T.
0.5
Sig.
Diff.
Sig.
Diff.
Sig.
Diff.
C.S.T.
2.0 Sig.
Diff.
C.S.T.
1.5 Sig.
Diff.
C.S.T.
1.0 NonSig.
Diff.
C.S.T.
0.5 62
Table A.3. Bonferroni Post-Hoc Tests for all BracketLigation Groups at the 3.5 mm Deflection Distance (p<0.05)
Groups
M.S.L.
M.S.L.
C.S.L.
Sig.
Diff.
C.S.L.
Sig.
Diff.
M.S.T.
Sig.
Diff.
Sig.
Diff.
C.S.T.
Sig.
Diff.
Sig.
Diff.
63
M.S.T.
Sig.
Diff.
Sig.
Diff.
C.S.T.
Sig.
Diff.
Sig.
Diff.
Sig.
Diff.
Sig.
Diff.
Table A.4. Bonferroni Post-Hoc Tests for all BracketLigation Groups at the 3.0 mm Deflection Distance (p<0.05)
Groups
M.S.L.
M.S.L.
C.S.L.
Sig.
Diff.
C.S.L.
Sig.
Diff.
M.S.T.
Sig.
Diff.
Non-Sig.
Diff.
C.S.T.
Sig.
Diff.
Sig.
Diff.
64
M.S.T.
Sig.
Diff.
Non-Sig.
Diff.
C.S.T.
Sig.
Diff.
Sig.
Diff.
Sig.
Diff.
Sig.
Diff.
Table A.5. Bonferroni Post-Hoc Tests for all BracketLigation Groups at the 2.5 mm Deflection Distance (p<0.05)
Groups
M.S.L.
M.S.L.
C.S.L.
Sig.
Diff.
C.S.L.
Sig.
Diff.
M.S.T.
Sig.
Diff.
Sig.
Diff.
C.S.T.
Sig.
Diff.
Sig.
Diff.
65
M.S.T.
Sig.
Diff.
Sig.
Diff.
C.S.T.
Sig.
Diff.
Sig.
Diff.
Sig.
Diff.
Sig.
Diff.
Table A.6. Bonferroni Post-Hoc Tests for all BracketLigation Groups at the 2.0 mm Deflection Distance (p<0.05)
Groups
M.S.L.
M.S.L.
C.S.L.
Sig.
Diff.
C.S.L.
Sig.
Diff.
M.S.T.
Sig.
Diff.
Sig.
Diff.
C.S.T.
Sig.
Diff.
Sig.
Diff.
66
M.S.T.
Sig.
Diff.
Sig.
Diff.
C.S.T.
Sig.
Diff.
Sig.
Diff.
Sig.
Diff.
Sig.
Diff.
Table A.7. Bonferroni Post-Hoc Tests for all BracketLigation Groups at the 1.5 mm Deflection Distance (p<0.05)
Groups
M.S.L.
M.S.L.
C.S.L.
Sig.
Diff.
C.S.L.
Sig.
Diff.
M.S.T.
Sig.
Diff.
Sig.
Diff.
C.S.T.
Sig.
Diff.
Non-Sig.
Diff.
67
M.S.T.
Sig.
Diff.
Sig.
Diff.
C.S.T.
Sig.
Diff.
Non-Sig.
Diff.
Sig.
Diff.
Sig.
Diff.
Table A.8. Bonferroni Post-Hoc Tests for all BracketLigation Groups at the 1.0 mm Deflection Distance (p<0.05)
Groups
M.S.L.
M.S.L.
C.S.L.
Sig.
Diff.
C.S.L.
Sig.
Diff.
M.S.T.
Sig.
Diff.
Sig.
Diff.
C.S.T.
Non-Sig.
Diff.
Sig.
Diff.
68
M.S.T.
Sig.
Diff.
Sig.
Diff.
C.S.T.
Non-Sig.
Diff.
Sig.
Diff.
Sig.
Diff.
Sig.
Diff.
Table A.9. Bonferroni Post-Hoc Tests for all BracketLigation Groups at the 0.5 mm Deflection Distance (p<0.05)
Groups
M.S.L.
M.S.L.
C.S.L.
Sig.
Diff.
C.S.L.
Sig.
Diff.
M.S.T.
Non-Sig.
Diff.
Sig.
Diff.
C.S.T.
Non-Sig.
Diff.
Sig.
Diff.
69
M.S.T.
Non-Sig.
Diff.
Sig.
Diff.
C.S.T.
Non-Sig.
Diff.
Sig.
Diff.
Non-Sig.
Diff.
Non-Sig.
Diff.
VITA AUCTORIS
Matthew Steven Baker was born on August 29, 1979, in
Memphis, TN. Upon graduation from high school in 1997, he
attended Furman University for one year.
Matt then
transferred to Indiana University, where he earned a B.S.
degree in Biology in 2002. On May 25, 2002, Matt was
married to Brooke Dixon in Newburgh, IN.
Following graduation from IU, he entered dental school
at Indiana University School of Dentistry. Matt received
his D.D.S. degree from IU in 2006. Upon graduation, he
entered the graduate program in orthodontics at Saint Louis
University, where he is currently a candidate for the
degree of Master of Science in Dentistry. After graduation
from SLU in December of 2008, Matt and Brooke will relocate
to the state of Florida to begin their professional careers
in orthodontics and university education.
70