The effects of third-order torque and self - Saint Louis University
The effects of third-order torque and self - Saint Louis University
The effects of third-order torque and self - Saint Louis University
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THE EFFECTS OF THIRD-ORDER TORQUE AND SELF-LIGATING<br />
ORTHODONTIC BRACKET TYPE ON SLIDING FRICTION: A COMPARATIVE<br />
STUDY<br />
Michael J. Chung, D.D.S.<br />
An Abstract Presented to the Faculty <strong>of</strong> the Graduate School<br />
<strong>of</strong> <strong>Saint</strong> <strong>Louis</strong> <strong>University</strong> in Partial Fulfillment<br />
<strong>of</strong> the Requirements for the Degree <strong>of</strong><br />
Master <strong>of</strong> Science in Dentistry<br />
2007
Abstract<br />
Few studies have evaluated the effect <strong>of</strong> wire-slot<br />
<strong>torque</strong> on sliding friction. Apparently, no studies have<br />
been published to date that compare friction across<br />
categories <strong>of</strong> <strong>self</strong>-ligating brackets when <strong>third</strong>-<strong>order</strong><br />
positioning is controlled. <strong>The</strong> purpose <strong>of</strong> this study was<br />
to determine the <strong>effects</strong> <strong>of</strong> wire-slot <strong>torque</strong> <strong>and</strong> type <strong>of</strong><br />
<strong>self</strong>-ligating bracket on the average kinetic friction in<br />
sliding mechanics with a 0.019- x 0.025-inch stainless<br />
steel archwire. Five sets <strong>of</strong> crown-attachments (including<br />
In-Ovation R, Time2, Damon 3MX, SmartClip <strong>and</strong> Victory<br />
brackets) were tested for frictional resistance in a<br />
simulated posterior dental segment with -15, -10, -5, 0,<br />
+5, +10, <strong>and</strong> +15 degrees <strong>of</strong> <strong>torque</strong> placed in the maxillary<br />
right second-premolar bracket.<br />
Increasing the <strong>torque</strong> from 0 to ±15 degrees produced<br />
significant increases <strong>of</strong> frictional resistance in all five<br />
<strong>of</strong> the tested attachment-sets. At 0 degrees <strong>of</strong> <strong>torque</strong>, the<br />
sets with passive <strong>self</strong>-ligating brackets produced less<br />
friction than the sets with active <strong>self</strong>-ligating brackets,<br />
<strong>and</strong> all four <strong>self</strong>-ligating bracket sets produced<br />
significantly less friction than the set with<br />
elastomerically ligated Victory brackets. At ±10 degrees
<strong>of</strong> <strong>torque</strong>, all five attachment sets displayed similar<br />
resistances with the exception <strong>of</strong> the In-Ovation R set at<br />
+10 degrees. At ±15 degrees <strong>of</strong> <strong>torque</strong>, the In-Ovation R<br />
<strong>and</strong> the SmartClip sets produced significantly larger<br />
frictional resistances than the other three sets.<br />
<strong>The</strong> data suggest that the presence <strong>of</strong> <strong>third</strong>-<strong>order</strong><br />
<strong>torque</strong> can influence the kinetic frictional resistances in<br />
posterior dental segments during anterior retraction using<br />
sliding mechanics with <strong>self</strong>-ligating brackets <strong>and</strong> that<br />
frictional resistance will increase at a greater rate when<br />
the <strong>torque</strong> exceeds ±10 degrees with the present combination<br />
<strong>of</strong> sizes <strong>of</strong> slots <strong>and</strong> wire. Furthermore, whether a <strong>self</strong>-<br />
ligated bracket is active or passive may not be clinically<br />
significant regarding friction in the presence <strong>of</strong> <strong>torque</strong><br />
approaching <strong>and</strong> exceeding 15 degrees.
THE EFFECTS OF THIRD-ORDER TORQUE AND SELF-LIGATING<br />
ORTHODONTIC BRACKET TYPE ON SLIDING FRICTION: A COMPARATIVE<br />
STUDY<br />
Michael J. Chung, D.D.S.<br />
A <strong>The</strong>sis Presented to the Faculty <strong>of</strong> the Graduate School <strong>of</strong><br />
<strong>Saint</strong> <strong>Louis</strong> <strong>University</strong> in Partial Fulfillment<br />
<strong>of</strong> the Requirements for the Degree <strong>of</strong><br />
Master <strong>of</strong> Science in Dentistry<br />
2007
COMMITTEE IN CHARGE OF CANDIDACY:<br />
Assistant Pr<strong>of</strong>essor Donald R. Oliver,<br />
Chairperson <strong>and</strong> Advisor<br />
Assistant Pr<strong>of</strong>essor Ki Beom Kim,<br />
Adjunct Pr<strong>of</strong>essor Robert J. Nikolai<br />
i
To my wife, Sahrip, <strong>and</strong> my parents...<br />
Thank you for all your love <strong>and</strong> support.<br />
ii
ACKNOWLEDGEMENTS<br />
<strong>The</strong> author wishes to acknowledge all <strong>of</strong> the<br />
individuals who assisted him with this project. He would<br />
like to thank Dr. Donald R. Oliver, Dr. Robert J. Nikolai,<br />
Dr. Ki Beom Kim, Mr. Joe Tricamo, Dr. Heidi Israel, <strong>and</strong><br />
Dr. Binh Tran.<br />
<strong>The</strong> author would also like to thank Mr. John Sherrill<br />
<strong>and</strong> Ormco Corporation, Mr. Kevin Harrison <strong>and</strong> 3M/Unitek<br />
Corporation, Mr. Ted Reed <strong>and</strong> GAC International, <strong>and</strong> Mr.<br />
Brian Horn <strong>and</strong> American Orthodontics for supplying the<br />
brackets for this study.<br />
iii
TABLE OF CONTENTS<br />
List <strong>of</strong> Tables...........................................v<br />
List <strong>of</strong> Figures.........................................vi<br />
CHAPTER 1: INTRODUCTION..................................1<br />
CHAPTER 2: REVIEW OF THE LITERATURE<br />
Classical friction............................3<br />
Friction in orthodontics......................5<br />
Factors influencing friction .................9<br />
Archwires..................................9<br />
Brackets..................................15<br />
Ligation..................................19<br />
Other factors influencing friction........27<br />
Summary......................................34<br />
References...................................35<br />
Tables.......................................47<br />
CHAPTER 3: JOURNAL ARTICLE<br />
Abstract.....................................48<br />
Introduction.................................50<br />
Materials <strong>and</strong> Methods........................56<br />
Results......................................62<br />
Discussion...................................64<br />
Conclusions..................................70<br />
References...................................72<br />
Tables.......................................80<br />
Figures......................................84<br />
Vita Auctoris...........................................90<br />
iv
LIST OF TABLES<br />
Table 2-1: Partial Overview <strong>of</strong> Self-Ligating<br />
Brackets................................. 47<br />
Table 3-1: Frictional-force means <strong>and</strong> st<strong>and</strong>ard<br />
deviations in grams at seven <strong>torque</strong> angles<br />
at the second premolar from five sets <strong>of</strong><br />
crown-attachments.........................80<br />
Table 3-2: Significance levels (α = 0.05) <strong>of</strong><br />
differences in mean frictional forces across<br />
pairs <strong>of</strong> cells, each cell defined by a<br />
<strong>torque</strong>-angle, from five sets <strong>of</strong> crownattachments...............................81<br />
Table 3-3: Summary from Kruskal-Wallis analyses <strong>of</strong><br />
variance <strong>of</strong> frictional forces for seven<br />
<strong>torque</strong>-angles across five sets <strong>of</strong> crownattachments...............................82<br />
Table 3-4: Mean differences in frictional resistances<br />
in grams <strong>and</strong> significance levels (α = 0.05)<br />
between attachment sets at each <strong>of</strong> the seven<br />
<strong>torque</strong> angles.............................83<br />
v
LIST OF FIGURES<br />
Figure 3-1: Four cylinders mounted in aluminum base<br />
plate <strong>of</strong> the friction testing device......84<br />
Figure 3-2: Bracket-slot positioning template.........84<br />
Figure 3-3: Control <strong>of</strong> the <strong>third</strong>-<strong>order</strong> position <strong>of</strong> the<br />
second premolar bracket-slot..............85<br />
Figure 3-4: SLBUCCAL tube.............................85<br />
Figure 3-5: Damon 3MX bracket.........................85<br />
Figure 3-6: SmartClip bracket.........................86<br />
Figure 3-7: In-Ovation R bracket......................86<br />
Figure 3-8: Time2 bracket.............................86<br />
Figure 3-9: Victory bracket...........................87<br />
Figure 3-10: Friction testing setup mounted to the<br />
Instron Universal Testing Machine.........87<br />
Figure 3-11: Plots <strong>of</strong> mean kinetic frictional force<br />
within the dental segment vs. <strong>torque</strong> angle<br />
at the second premolar from five sets <strong>of</strong><br />
crown-attachments.........................88<br />
Figure 3-12: Cross-section diagrams <strong>of</strong> a 0.019- x 0.025inch<br />
wire. <strong>The</strong> buccolingual dimension <strong>of</strong><br />
the wire when rotated 10 degrees (line BD)<br />
is calculated by multiplying cosΦ2 by the<br />
hypotenuse AB.............................89<br />
vi
CHAPTER 1: INTRODUCTION<br />
<strong>The</strong> specialty <strong>of</strong> orthodontics has been going through a<br />
period <strong>of</strong> considerable research interest in the role <strong>of</strong><br />
friction during tooth movement. Within the past 30 years,<br />
studies have focused on both the contact between the wire<br />
<strong>and</strong> the bracket- or tube-slot as a potential source <strong>of</strong><br />
frictional resistance during sliding mechanics <strong>and</strong> the many<br />
associated factors that can affect that resistance to tooth<br />
movement. <strong>The</strong>se experiments have identified variables in<br />
the archwire, bracket, ligature <strong>and</strong> oral environment as<br />
contributors to frictional forces.<br />
With recent advances in orthodontic technologies, such<br />
as new <strong>self</strong>-ligating bracket designs <strong>and</strong> archwire alloys,<br />
orthodontists have developed systems aimed at maximizing<br />
the efficiency <strong>of</strong> treatment. Today fewer archwires are<br />
placed, <strong>and</strong> treatment phases have been merged that were<br />
previously carried out individually. <strong>The</strong> gaining<br />
popularity <strong>of</strong> sliding mechanics has made further research<br />
on the role <strong>of</strong> friction necessary.<br />
Previous studies have evaluated friction by pulling<br />
the wire through the bracket-slot <strong>and</strong> measuring the force<br />
required to produce the sliding displacement. Many<br />
investigations have examined single brackets with various<br />
1
combinations <strong>of</strong> bracket-slot <strong>and</strong> wire materials, ligature<br />
type, slot-positioning <strong>and</strong> other pertinent parameters.<br />
Research designs have recently attempted to simulate<br />
clinical environments with multiple crown-attachments<br />
placed in series or in an archform.<br />
<strong>The</strong> present research was designed to answer several<br />
timely questions about friction in orthodontics.<br />
Apparently no studies have been published to date that<br />
compare friction across categories <strong>of</strong> <strong>self</strong>-ligating<br />
brackets with <strong>third</strong>-<strong>order</strong> positioning controlled. <strong>The</strong><br />
purpose <strong>of</strong> this study was to determine the effect <strong>of</strong> wire-<br />
slot <strong>torque</strong> on friction in <strong>self</strong>-ligating brackets with an<br />
engaged, 0.019- x 0.025-inch, stainless steel archwire. In<br />
addition, the influence <strong>of</strong> the design <strong>of</strong> various ligating<br />
mechanisms on kinetic friction with active <strong>torque</strong> present<br />
in the wire <strong>and</strong>/or slot was also evaluated.<br />
2
CHAPTER 2: REVIEW OF THE LITERATURE<br />
Classical Friction<br />
In the orthodontic literature, friction was discussed<br />
as early as 1960 when Stoner 1 warned <strong>of</strong> the difficulty in<br />
determining the amount <strong>of</strong> force to be applied to a tooth<br />
because <strong>of</strong> the role <strong>of</strong> frictional resistance. Our current<br />
underst<strong>and</strong>ing <strong>of</strong> friction impairing tooth movement is based<br />
largely on long-st<strong>and</strong>ing theories, not directly related to<br />
orthodontics, by Leonardo Da Vinci, Guillaume Amontons, <strong>and</strong><br />
Charles-Augustin Coulomb. Although Da Vinci’s work was not<br />
published until the other investigators had carried out<br />
friction experiments, he left behind the earliest known<br />
studies on the subject in a collection <strong>of</strong> journals in which<br />
he detailed his research. 2 Collectively, these scientists<br />
are credited with establishing the classical laws <strong>of</strong><br />
friction, or the Amontons-Coulomb laws, which state the<br />
following: 1. Frictional force is proportional to normal<br />
force; 2. Frictional force is independent <strong>of</strong> contact-area;<br />
3. Frictional force is independent <strong>of</strong> sliding velocity. 2,3<br />
Friction is defined as the resistance to motion<br />
when one object moves or tends to move tangentially<br />
relative to another object. 4 <strong>The</strong> total contact-force<br />
3
etween the objects is expressed as two components when<br />
there is attempted or actual relative displacement between<br />
surfaces in contact. One component, the normal force, is a<br />
pushing force with an orientation perpendicular to the<br />
shared contact-surface. <strong>The</strong> frictional force component<br />
impedes the motion between the surfaces <strong>and</strong> is, therefore,<br />
opposite in direction to that <strong>of</strong> intended or actual motion. 5<br />
<strong>The</strong> maximum static or the kinetic frictional force (F)<br />
tangent to the two surfaces is <strong>of</strong>ten hypothesized as<br />
proportional to the normal force, as expressed by the<br />
equation F = µN, where µ is the coefficient <strong>of</strong> friction<br />
between the surfaces, <strong>and</strong> N is the normal-force magnitude<br />
against the contact-surface <strong>of</strong> the object to be displaced. 6<br />
Each <strong>of</strong> two coefficients <strong>of</strong> friction is a constant which is<br />
related to characteristics <strong>of</strong> the contacting surfaces <strong>of</strong><br />
the objects; they are known as the static <strong>and</strong> kinetic<br />
coefficients <strong>of</strong> friction. 7 Ordinarily in static situations,<br />
the frictional force is just large enough to prevent<br />
relative tangential movement. Maximum static friction<br />
refers to the resistance to displacement encountered at the<br />
onset <strong>of</strong> motion; it corresponds to the smallest action<br />
required to initiate motion between surfaces that are at<br />
rest. Kinetic friction is the frictional force that<br />
impedes displacement during sliding motion between the<br />
4
surfaces. 6 <strong>The</strong> magnitudes <strong>of</strong> the coefficients <strong>of</strong> friction<br />
are generally between zero <strong>and</strong> one. 5<br />
Friction in Orthodontics<br />
Because frictional force acts in a direction opposite<br />
to the intended path <strong>of</strong> the object to be displaced, <strong>and</strong><br />
sliding mechanics are commonplace in orthodontic therapy,<br />
an underst<strong>and</strong>ing <strong>of</strong> friction is necessary to achieve<br />
optimal clinical results. Fixed-appliance therapy usually<br />
involves some relative wire-slot displacement in various<br />
phases <strong>of</strong> treatment; hence, the generation <strong>of</strong> friction<br />
during tooth movement can be problematic for the<br />
orthodontist. Because a portion <strong>of</strong> the force for delivery<br />
to a tooth-crown may be necessary to overcome frictional<br />
resistance, the orthodontist must be sure to use a force <strong>of</strong><br />
sufficient magnitude to also initiate a biological response<br />
in the supporting tissues. 7 Frictional resistance is<br />
thought play a role in delayed tooth movement, undesired<br />
movement <strong>and</strong> loss <strong>of</strong> anchorage. 6 Examination <strong>of</strong> its effect<br />
on orthodontic anchorage, however, reveals that, in some<br />
situations, the presence <strong>of</strong> friction at the anchor teeth<br />
can be desirable, because it helps to prevent unwanted<br />
movement <strong>of</strong> those teeth. Even so, a problem lies in the<br />
5
fact that the magnitude <strong>of</strong> resistance is unknown. <strong>The</strong><br />
orthodontist is, then, guessing how much force is needed to<br />
move teeth without straining anchorage. 8<br />
<strong>The</strong> application <strong>of</strong> sliding mechanics in orthodontics<br />
has increased since the introduction <strong>of</strong> the pre-adjusted<br />
edgewise appliance system. 9 <strong>The</strong> process can involve the<br />
guidance <strong>of</strong> a tooth along a continuous archwire or the<br />
movement <strong>of</strong> the wire through crown-attachment slots. In<br />
particular, overjet reduction <strong>and</strong> space closure have been<br />
traditionally accepted applications <strong>of</strong> sliding mechanics.<br />
In a first premolar extraction case, a space is created<br />
between the canine <strong>and</strong> the second premolar. In the<br />
presence <strong>of</strong> maximum anchorage, the canine would first be<br />
retracted bodily with the archwire guiding its<br />
displacement. This single-tooth movement would likely<br />
create unwanted friction that could cause “side <strong>effects</strong>”<br />
such as uncontrolled tipping, loss <strong>of</strong> posterior anchorage,<br />
or deepening <strong>of</strong> the overbite. 10 Forces acting posteriorly<br />
on the anterior portion <strong>of</strong> the archwire would then be<br />
created to retract the incisors into the remaining spaces<br />
while allowing the excess wire to slide through the<br />
posterior brackets <strong>and</strong> tubes. Any friction in the buccal<br />
segments would hinder the movement <strong>of</strong> the incisal segment<br />
<strong>and</strong>, therefore, could delay space closure. 11<br />
6
Since the introduction to orthodontics in the 1970s <strong>of</strong><br />
nickel-titanium alloy archwires, sliding mechanics can also<br />
be present in the initial stages <strong>of</strong> orthodontic treatment.<br />
<strong>The</strong>se very flexible archwires have gradually replaced<br />
multi-loop stainless steel wires for leveling <strong>and</strong> aligning<br />
teeth. Nickel-titanium alloy wires exhibit small load-<br />
deformation rates <strong>and</strong> “superelasticity.” <strong>The</strong>se properties<br />
enable relatively light <strong>and</strong> nearly constant forces over<br />
large deflections without significant permanent deformation<br />
<strong>of</strong> the wire, permitting easy engagement into misaligned<br />
bracket-slots. 12 <strong>The</strong> activated wire can then be left to<br />
guide the teeth into position as it returns to its<br />
original/pre-engagement shape. <strong>The</strong> objective <strong>of</strong> this stage<br />
<strong>of</strong> therapy is to produce simultaneous tooth movements such<br />
as leveling the arch, extruding “high” canines, correcting<br />
tooth rotations <strong>and</strong> modifying archforms. 13 A misaligned<br />
dental arch will require greater lengths <strong>of</strong> wire than a<br />
well-aligned arch to compensate for enlarged interbracket<br />
distances. As the brackets come into alignment, the teeth<br />
move into their correct spatial positions, <strong>and</strong> segments <strong>of</strong><br />
an unstopped archwire that were “reaching” to the<br />
misaligned positions will slide through the adjacent<br />
bracket-slots <strong>and</strong> tubes. 11,14,15 In 1997 Meling et al. 14 found<br />
that friction in a crowded dental arch would reduce the<br />
7
sizes <strong>of</strong> forces delivered to the crowns by the wire during<br />
deactivation, especially with a light leveling wire. <strong>The</strong><br />
authors concluded that careful ligation to minimize<br />
friction was important for delivery <strong>of</strong> expected force<br />
magnitudes. It is as early as placement <strong>of</strong> this initial<br />
wire that friction becomes a concern to the orthodontist.<br />
<strong>The</strong> classical laws <strong>of</strong> friction <strong>of</strong>fer only a partial<br />
explanation <strong>of</strong> friction in orthodontic systems. <strong>The</strong><br />
original theories by Amontons <strong>and</strong> Coulomb were derived from<br />
dry friction mechanics with distinct static <strong>and</strong> kinetic<br />
frictional phases, defined by zero velocity <strong>and</strong> constant<br />
velocity, respectively. Tooth movement in orthodontics,<br />
however, occurs at such low velocities, that these two<br />
phases are clinically interrelated. 3 Although the first two<br />
laws <strong>of</strong> friction would be unaffected by this application,<br />
the <strong>third</strong> law <strong>of</strong> friction may not accurately describe<br />
orthodontic friction in vivo. As the velocity <strong>of</strong> tooth<br />
movement approaches zero, instability in steady sliding is<br />
likely, due to interlocking <strong>and</strong> shearing <strong>of</strong> asperities, the<br />
peaks <strong>of</strong> microscopic surface irregularities. This effect<br />
is evident in the phenomenon known as “stick-slip motion”;<br />
a cycle involves a “stick state” where elastic loading<br />
occurs, <strong>and</strong> a “slip” where sudden sliding <strong>and</strong> stress-<br />
relaxation occur. 3,8 Nonetheless, Rossouw’s group 3 concluded<br />
8
that the application <strong>of</strong> the Amontons-Coloumb laws is<br />
justified in orthodontic in vitro analyses if sliding<br />
velocity is assumed constant.<br />
Factors Influencing Friction in Orthodontics<br />
<strong>The</strong> now frequent presence <strong>of</strong> sliding mechanics in<br />
orthodontic therapy has produced considerable research<br />
interest in friction generated between crown-attachment<br />
slot <strong>and</strong> archwire. Many studies have collectively<br />
identified factors that can contribute to friction within<br />
the fixed orthodontic appliance. Although it is known that<br />
many <strong>of</strong> these influences are interrelated, discussing them<br />
individually perhaps helps to better clarify their<br />
relationships to friction.<br />
Archwires<br />
During the past century, orthodontists have made<br />
selections from a wide range <strong>of</strong> marketed archwires. From<br />
gold wires that dominated early in the twentieth century to<br />
today’s ß-titanium <strong>and</strong> nickel-titanium alloys, the<br />
broadening <strong>of</strong> wire property values has continually changed<br />
the way orthodontics is practiced. 16 A number <strong>of</strong> archwire<br />
parameters have been found to contribute to friction at the<br />
9
interface <strong>of</strong> wire <strong>and</strong> crown-attachment slot. <strong>The</strong>se<br />
parameters are alloy composition, surface-roughness, <strong>and</strong><br />
cross-sectional shape <strong>and</strong> size.<br />
Alloy Composition<br />
At angulations in which second-<strong>order</strong> binding existed<br />
<strong>of</strong> the wire within the bracket-slot, Frank <strong>and</strong> Nikolai 5<br />
found that nickel-titanium alloy wires produced smaller<br />
maximum static frictional forces than did a stainless steel<br />
wire <strong>of</strong> the small size, likely due to the smaller modulus<br />
<strong>of</strong> elasticity <strong>of</strong> the former alloy. One <strong>of</strong> the many<br />
important findings from this study was that, due to<br />
variances in modulus <strong>of</strong> elasticity <strong>and</strong> surface roughness<br />
across as-received wires, archwire-alloy influenced<br />
frictional resistance. Since then, dozens <strong>of</strong> studies have<br />
compared frictional force values generated across wires<br />
differing by alloy. Some experimental studies have<br />
suggested that, typically within stainless steel slots,<br />
stainless steel wires tend to produce less sliding friction<br />
than nickel-titanium alloy wires. 17-30 When testing with<br />
second-<strong>order</strong> angulations that produce binding within the<br />
bracket-slot, however, other studies have reported less<br />
friction with the nickel-titanium alloy wires. 4,5,31-34 This<br />
behavior is related to the modulus <strong>of</strong> elasticity for the<br />
10
archwires. At binding angulations, two contacts form at<br />
the ends <strong>of</strong> the bracket-slot, one on the occlusal face <strong>of</strong><br />
the wire <strong>and</strong> one on the gingival face. As the wire<br />
deflects upon activation, those wires with a greater<br />
modulus <strong>of</strong> elasticity will produce larger normal bracket-<br />
wire contact forces at those contact points. 5,48 Several<br />
investigations have found that ß-titanium alloy wires have<br />
greater resistance to sliding than either stainless steel<br />
or nickel-titanium alloy wires, particularly in the absence<br />
<strong>of</strong> binding. 18,20-24,26,27,29,35,36 Tspelepsis <strong>and</strong> associates 33<br />
failed to detect any such differences across the three<br />
alloys.<br />
Surface Characteristics<br />
Frank <strong>and</strong> Nikolai 5 found that, with small, nonbinding<br />
angulations <strong>and</strong> in stainless steel slots, stainless steel<br />
wires exhibited less sliding frictional resistance than<br />
nickel-titanium alloy wires. This difference was thought<br />
to be related to the roughness <strong>of</strong> the wire-alloy surface.<br />
This property <strong>of</strong> a wire is determined by characteristics <strong>of</strong><br />
the alloy, the manufacturing process, any surface treatment<br />
<strong>and</strong>, for some materials, the shelf-time <strong>and</strong>/or use-time. 5<br />
Other researchers have speculated that the greater friction<br />
produced by titanium alloy wires when compared to stainless<br />
11
steel wires could be a result <strong>of</strong> the relative roughness <strong>of</strong><br />
the contacting wire <strong>and</strong> slot surfaces. 5,18,23<br />
Kusy et al. 37 used a laser-spectrometer <strong>and</strong> the<br />
specular-reflectance technique to measure surface-<br />
roughnesses <strong>of</strong> wires <strong>of</strong> four materials, <strong>and</strong> found the<br />
surface <strong>of</strong> a nickel-titanium alloy wire to be the roughest<br />
followed, in <strong>order</strong>, by wire surfaces <strong>of</strong> ß-titanium,<br />
chromium-cobalt, <strong>and</strong> orthodontic stainless steel alloys.<br />
Using the same procedure, Kusy <strong>and</strong> Whitley 38 assessed the<br />
effect <strong>of</strong> surface topography on coefficients <strong>of</strong> friction<br />
for these alloys, <strong>and</strong> concluded that low wire surface<br />
roughness was not a sufficient condition for a small<br />
frictional coefficient. Prososki, Bagby <strong>and</strong> Erickson 11<br />
showed similar results, finding no statistically<br />
significant correlation between surface-roughness <strong>and</strong><br />
frictional resistance from as-received archwires <strong>of</strong> common<br />
alloys. Although the surface <strong>of</strong> a ß-titanium archwire is<br />
less rough than that <strong>of</strong> nickel-titanium alloys, researchers<br />
have consistently shown greater in-slot frictional<br />
resistance to sliding from the former wire. 11,24,38,39<br />
Burstone <strong>and</strong> Farzin-Nia 40 have suggested that the relative<br />
s<strong>of</strong>tness <strong>of</strong> the ß-titanium alloy wire-surface compared to<br />
the harder stainless steel surface is a reason for the<br />
former’s greater frictional resistance.<br />
12
A phenomenon known as “cold welding” has been proposed<br />
as an explanation for greater friction potentials found<br />
with nickel-titanium <strong>and</strong> ß-titanium alloy wires. As the<br />
fraction <strong>of</strong> titanium in the alloy increases, the reactivity<br />
<strong>of</strong> its surface with other alloy-surfaces increases; nickel-<br />
titanium <strong>and</strong> ß-titanium alloys have titanium contents <strong>of</strong><br />
about 50% <strong>and</strong> 80%, respectively. 41 Kusy <strong>and</strong> Whitley 24 found<br />
adhesions in the bracket-slots from scanning electron<br />
micrographs after drawing ß-titanium alloy wires through<br />
stainless steel bracket-slots in <strong>order</strong> to calculate the<br />
coefficients <strong>of</strong> friction. X-ray spectra <strong>of</strong> this debris<br />
were obtained, <strong>and</strong> they showed elements <strong>of</strong> the ß-titanium<br />
alloy. <strong>The</strong> authors concluded that the primary cause for<br />
high frictional resistance with ß-titanium wires was the<br />
reactivity <strong>of</strong> the titanium content <strong>of</strong> the alloy with<br />
stainless steel, leading to “cold welding” <strong>of</strong> the<br />
contacting surfaces. 20,24,39<br />
<strong>The</strong> effort to reduce friction in the fixed appliance<br />
has led to trials with a process called ion-implantation, a<br />
method <strong>of</strong> increasing the hardness <strong>and</strong> altering the surface-<br />
chemistry <strong>of</strong> an alloy by implanting nitrogen ions into that<br />
surface. In laboratory studies, this process had been<br />
shown to decrease friction significantly. 40,42 Clinical<br />
split-mouth studies, however, did not show a significant<br />
13
difference in rate <strong>of</strong> tooth movement on the side with ion-<br />
implanted ß-titanium alloy wires engaged. 43<br />
Cross-sectional Shape <strong>and</strong> Size<br />
Many studies have suggested that the cross-sectional<br />
size <strong>of</strong> an archwire <strong>and</strong> frictional-resistance potential may<br />
be directly related. 5,23,31,34,36,44,45 In 2003 Smith, Rossouw<br />
<strong>and</strong> Watson 34 found significantly greater friction with<br />
larger archwires than smaller ones, <strong>and</strong> they attributed<br />
this difference to greater flexural stiffnesses <strong>of</strong> the<br />
wires having larger cross-sections.<br />
Rectangular wires permit the orthodontist to exert<br />
<strong>third</strong>-<strong>order</strong> control during treatment. <strong>The</strong>se wires are<br />
stiffer than round wires with similar cross-sectional<br />
dimensions. 46 <strong>The</strong> shape <strong>of</strong> the archwire cross-section<br />
influences its bending characteristics. Changes in shape<br />
from round to square to rectangular (e.g., while<br />
maintaining second-<strong>order</strong> slot-clearance), <strong>and</strong> the<br />
corresponding increases in stiffnesses, can cause increases<br />
in frictional resistance. Frank <strong>and</strong> Nikolai 5 found,<br />
however, that the smaller contact areas between the wire<br />
<strong>and</strong> bracket-slot with binding angulations in 0.020-inch<br />
round wires produced greater friction than the stiffer<br />
rectangular wires. <strong>The</strong>y suggested that the point-contacts<br />
14
<strong>of</strong> round wire with the slot created larger intensities <strong>of</strong><br />
normal force than did the line-contacts <strong>of</strong> the rectangular<br />
wires.<br />
Brackets<br />
Orthodontic brackets are marketed in various designs,<br />
dimensions <strong>and</strong> materials, <strong>and</strong> a wealth <strong>of</strong> information<br />
exists in the literature regarding the effect <strong>of</strong> bracket-<br />
parameters on sliding friction. Influences discussed below<br />
include bracket material composition, slot size, <strong>and</strong><br />
bracket width.<br />
Bracket Material Composition<br />
Clinicians have many choices when selecting the<br />
material composition <strong>of</strong> appliances. Stainless steel is the<br />
most common material <strong>of</strong> orthodontic brackets. <strong>The</strong>se<br />
brackets are available to practitioners as cast or<br />
sintered. Traditionally, stainless steel brackets have<br />
been manufactured as castings; thereafter, specific<br />
surfaces are milled. Sintering is a process within which<br />
the stainless steel particles are compressed at elevated<br />
temperature into the desired shapes. When compared with<br />
previous research 23 using the same apparatus <strong>and</strong> wires,<br />
Vaughan et al. 29 found that the slots <strong>of</strong> sintered brackets<br />
15
produced about 40% to 45% less friction than slots <strong>of</strong> cast<br />
brackets.<br />
Ceramic brackets are a popular choice for many adults<br />
because <strong>of</strong> their esthetic appearance. Like stainless steel<br />
brackets, ceramic brackets are also available in multiple<br />
designs. Whether they (including the slots) are single-<br />
crystal sapphire, polycrystalline alumina or zirconia,<br />
these brackets have generally been found to produce more<br />
friction than stainless steel brackets with the same wires<br />
at nonbinding angulations. 4,25-27,36,51,54,80-82 Some<br />
investigators have not found a difference in frictional<br />
resistance between stainless steel <strong>and</strong> ceramic brackets. 35,83<br />
In an effort to maintain the esthetic advantages <strong>of</strong><br />
ceramic brackets, but reduce the friction potentials<br />
associated with them, some polycrystalline alumina brackets<br />
are manufactured with metallic slots. One <strong>of</strong> these, with a<br />
stainless steel slot, the Clarity bracket (3M/Unitek<br />
Corporation, Monrovia, CA), was compared by Cacciafesta’s<br />
group 36 with conventional ceramic <strong>and</strong> stainless steel<br />
brackets. <strong>The</strong>y reported that the steel-slot/ceramic<br />
bracket produced less friction than the conventional all-<br />
ceramic bracket, but more than the stainless steel bracket<br />
with stainless steel, nickel-titanium alloy or ß-titanium<br />
alloy wires. Kusy <strong>and</strong> Whitley 84 found that both the Clarity<br />
16
acket <strong>and</strong> the gold-lined Luxi bracket (Rocky Mountain<br />
Orthodontics, Denver, CO) exhibited frictional resistances<br />
similar to that <strong>of</strong> stainless steel brackets. In general,<br />
ceramic brackets with metallic slots were found to be<br />
acceptable alternatives to all-ceramic brackets. 36,84<br />
Orthodontic brackets have been manufactured from other<br />
materials for various reasons. Esthetic plastic brackets<br />
are available with or without metallic inserts. <strong>The</strong>se<br />
brackets have generally been found to produce less friction<br />
than ceramic brackets, although deformation with tight<br />
ligation (i.e., toward <strong>torque</strong> control) has been a problem. 7<br />
Titanium brackets were introduced in response to concerns<br />
about corrosion <strong>and</strong> potential sensitivity to the nickel in<br />
stainless steel. <strong>The</strong>se brackets were found to be very<br />
similar in frictional resistance to stainless steel<br />
brackets. 19,85<br />
Bracket Width <strong>and</strong> Slot Size<br />
<strong>The</strong>re is conflicting information in the literature as<br />
to the effect <strong>of</strong> bracket width on friction in the fixed<br />
appliance. Andreasen <strong>and</strong> Quevedo 44 measured the friction<br />
produced with three brackets <strong>of</strong> different slot widths <strong>and</strong><br />
six wires at four second-<strong>order</strong> angulations <strong>and</strong> found no<br />
significant differences in frictional resistance across the<br />
17
ackets. Peterson’s group 31 also found that bracket width<br />
had no effect on friction. Frank <strong>and</strong> Nikolai, 5 however,<br />
found that frictional force increased as bracket width<br />
increased. This outcome was allegedly due to decreased<br />
interbracket distance <strong>and</strong> to the wider bracket binding at a<br />
smaller angulation. Other researchers found a similar<br />
effect, but thought the cause was the mesiodistal slot<br />
dimension <strong>of</strong> the wider bracket resulting in greater<br />
stretching <strong>of</strong> the ligature, which in turn, lead to<br />
increased normal forces <strong>of</strong> ligation. 23 A <strong>third</strong> group <strong>of</strong><br />
studies found that narrower brackets produced more friction<br />
than wider brackets. 21,22,81 Drescher’s group 22 believed that<br />
the increased tipping seen in narrow brackets resulted in<br />
greater frictional forces. Using biomechanical analysis<br />
<strong>and</strong> mathematical formulations, Schlegal 86 determined that<br />
neighboring brackets had an extraordinary influence on<br />
friction within a bracket, <strong>and</strong>, due to this influence,<br />
single-bracket studies could not accurately determine how<br />
bracket width affected friction. He concluded that<br />
interbracket distance, wire stiffness <strong>and</strong> relative bracket<br />
position must also be considered when determining the ideal<br />
slot width.<br />
Bracket width may have an indirect influence on<br />
friction due to its relationship with interbracket distance<br />
18
<strong>and</strong> wire stiffness. As bracket width increases, the<br />
distance(s) to the adjacent bracket(s) will decrease,<br />
resulting in shorter <strong>and</strong> stiffer sections <strong>of</strong> wire. 5,7 <strong>The</strong><br />
influence <strong>of</strong> bracket width is more pronounced at greater<br />
angulations.<br />
Slot size has not been found to influence frictional<br />
resistance in the fixed appliance. 21,27 Kusy, Whitley <strong>and</strong><br />
Prewitt 27 evaluated several factors, <strong>and</strong> they concluded that<br />
there was no substantial difference overall in frictional<br />
resistance between a 0.018-inch <strong>and</strong> a 0.022-inch bracket-<br />
slot when each is paired with a comparable-sized archwire.<br />
Ligation<br />
Ligation has become a popular topic among researchers<br />
in the field <strong>of</strong> orthodontics. Orthodontic products have<br />
been developed toward reducing friction potential in the<br />
fixed appliance <strong>and</strong> some seemingly have suppressed a major<br />
contributor by augmenting traditional methods <strong>of</strong> ligation<br />
within modern bracket designs. Current, common categories<br />
<strong>of</strong> ligation are 1) small, ductile, stainless steel wire-<br />
segments, 2) elastomeric o-rings <strong>and</strong> ties <strong>and</strong> 3) <strong>self</strong>-<br />
ligation.<br />
19
Conventional Ligation<br />
Orthodontic ligatures existed prior to the use <strong>of</strong> the<br />
modern fixed appliance. In 1728, Fauchard published a book<br />
called “Le Chirurgien Dentiste” in which he described his<br />
“B<strong>and</strong>eau” device. Ligatures were extended from this<br />
horseshoe-shaped device to facilitate simple tooth<br />
movement. Angle’s edgewise appliance was introduced in<br />
1925, <strong>and</strong> the original design has evolved to the most<br />
commonly used orthodontic appliance today. It was the<br />
first fixed appliance to feature ligatures as an essential<br />
part <strong>of</strong> the appliance. Early ligatures were materially<br />
precious metals. 49,50<br />
In modern clinical orthodontics, the conventional<br />
methods <strong>of</strong> tying archwires into bracket-slots are with<br />
either small stainless steel wires or elastomeric ties.<br />
<strong>The</strong>se ligatures, although relatively inexpensive <strong>and</strong> easy<br />
to place, have been criticized with the recent interest in<br />
orthodontic friction. Studies have shown a relationship<br />
between normal forces <strong>of</strong> ligation <strong>and</strong> resistance to<br />
sliding. Using a pneumatically controlled surface to<br />
simulate the force <strong>of</strong> ligation on a sliding wire, Stannard<br />
et al. 17 discovered a proportional increase in friction with<br />
increasing ligating force. Keith, Jones <strong>and</strong> Davies, 51 with<br />
three magnitudes <strong>of</strong> ligating force, found a similar<br />
20
ligation-friction relationship. <strong>The</strong> importance <strong>of</strong> ligating<br />
technique was demonstrated by Frank <strong>and</strong> Nikolai 5 ; they found<br />
ligature-tie force to be the greatest contributor to<br />
friction at small wire-slot angulations. Berger 52 also<br />
concluded that, at nonbinding angulations, ligature-force<br />
was a major contributor to frictional resistance.<br />
Of the two conventional methods <strong>of</strong> archwire-ligation,<br />
elastomeric ligatures have been the more popular because <strong>of</strong><br />
the ease <strong>and</strong> speed at which they can be placed <strong>and</strong> removed.<br />
In addition, patients have enjoyed selecting from the<br />
numerous colors available. In terms <strong>of</strong> their effect on<br />
friction, however, the difference between stainless steel<br />
<strong>and</strong> elastomeric ligation has not been so clear. Some<br />
studies have been unable to show a difference in frictional<br />
forces generated between these two methods <strong>of</strong> ligation. 5,53<br />
Others have reported that elastomeric ties produced less<br />
friction. 45 Another group <strong>of</strong> studies found stainless steel<br />
ligatures to show less friction. 54-57 <strong>The</strong> inability to<br />
obtain consistent results might be blamed on differences in<br />
experimental methods. 56 In addition, it is possible that<br />
the difficulty in controlling <strong>and</strong> maintaining ligating<br />
forces could be another cause <strong>of</strong> the inconsistency. 17<br />
Stainless steel ligating forces have been reported to range<br />
between 0 <strong>and</strong> 300 grams, depending upon how tightly the<br />
21
ligature is wound. 7 <strong>The</strong> force <strong>of</strong> ligation with elastomeric<br />
ties has been estimated to be from approximately 50 grams<br />
to 225 grams with subsequent decay due to “relaxation” <strong>of</strong><br />
the elastomeric material. 34,58<br />
Recently, an alternative type <strong>of</strong> separate ligation has<br />
become available to the orthodontic community, which is<br />
claimed to retain the ease <strong>of</strong> elastomeric ligation<br />
placement <strong>and</strong> removal while reducing the resistance to<br />
sliding. This ligature, called the Slide (Leone Orthodontic<br />
Products, Sesto Fiorentino, Firenze, Italy), is an<br />
injection-molded polyurethane device that hooks onto the<br />
tie wings <strong>and</strong> is placed over the facial surface <strong>of</strong> a<br />
conventional bracket-slot. By ligating across the slot<br />
instead <strong>of</strong> directly over the wire, the Slide places no<br />
normal force <strong>of</strong> ligation, <strong>and</strong> essentially converts the<br />
bracket into a tube. An in vitro study showed that this<br />
ligature produces significantly less sliding friction<br />
compared to conventional ligation techniques. 59<br />
Self-Ligation<br />
In 1933, Boyd filed a patent for the first <strong>self</strong>-<br />
ligating bracket, the “Boyd b<strong>and</strong> bracket,” which featured a<br />
moving bar that passively entrapped the archwire in the<br />
bracket-slot. Since then, more than 40 <strong>self</strong>-ligating<br />
22
designs have been introduced to the orthodontic community.<br />
Many <strong>of</strong> the early designs featured variations <strong>of</strong> three<br />
basic ligating mechanisms: a passive door, a passive “C-<br />
clip” <strong>and</strong> an active spring. 49,60<br />
It was not until the invention <strong>of</strong> the Edgelok bracket<br />
(Ormco Corporation, Glendora, CA) by Wildman in the early<br />
1970s that <strong>self</strong>-ligating designs gained widespread exposure<br />
to orthodontists. Wildman’s design featured a movable cap<br />
that closed over the facial portion <strong>of</strong> the slot to<br />
passively trap the archwire. Because <strong>of</strong> its passive<br />
nature, orthodontists found precise control <strong>of</strong> tooth<br />
movement to be a challenge. Ormco responded by marketing<br />
auxiliary rotational collars to help address the<br />
limitation. 49,60,61<br />
In 1977, clinical trials began on a new <strong>self</strong>-ligating<br />
design called the SPEED bracket (Strite Industries Ltd.,<br />
Cambridge, Ontario, Canada). Developed by Hanson, 62 this<br />
bracket was innovative in that it featured the first<br />
bracket-mounted stainless steel spring-clip which held the<br />
archwire in the slot with a lingually directed force. <strong>The</strong><br />
claimed benefit <strong>of</strong> this active ligation system was improved<br />
rotational control. 60,62<br />
Several modern <strong>self</strong>-ligating bracket designs have been<br />
commercially available for the past 30 years, but until<br />
23
ecently such brackets have had limited sales. <strong>The</strong> design<br />
<strong>of</strong> orthodontic products specifically aimed at minimizing<br />
friction has resulted in the reintroduction <strong>of</strong> <strong>self</strong>-<br />
ligating bracket systems to mainstream orthodontics. Since<br />
the introduction <strong>of</strong> the Damon 2 (Ormco Corporation,<br />
Glendora, CA) <strong>and</strong> the In-Ovation (GAC International,<br />
Bohemia, NY) brackets in 2000, the use <strong>of</strong> <strong>self</strong>-ligating<br />
systems in orthodontic practices has become more common. 63<br />
Most major orthodontic vendors now <strong>of</strong>fer a <strong>self</strong>-ligating<br />
system in addition to traditional, open-slot, bracket<br />
designs. <strong>The</strong>se newer brackets are claimed to reduce<br />
friction, contribute to improved hygiene, lessen anchorage<br />
loss, <strong>and</strong> shorten chair- as well as treatment-time. 55,63-66<br />
Several studies have reported that <strong>self</strong>-ligating brackets<br />
contribute to lessened sliding-friction potential compared<br />
to that from traditionally tied brackets. 9,48,55,57,67-70<br />
Since the recent gain in popularity <strong>of</strong> <strong>self</strong>-ligation,<br />
several new designs have become commercially available to<br />
the orthodontist. In general, these brackets fall into one<br />
<strong>of</strong> two categories based on the design <strong>of</strong> the slot-closure<br />
(Table 2-1). An “active” clip is a resilient spring-clip<br />
that snaps closed <strong>and</strong> reduces the depth <strong>of</strong> the slot to<br />
approximately 0.018 inches. Because this clip can store<br />
energy when it is activated by a lingual malalignment, a<br />
24
otated tooth or a twisted rectangular wire, it has the<br />
potential to deliver lingual force to the wire <strong>and</strong> help<br />
bring the tooth into its proper position. 60 <strong>The</strong> Speed<br />
bracket, the In-Ovation R bracket <strong>and</strong> the Time2 bracket<br />
(American Orthodontics, Sheboygan, WI) all feature active<br />
clips within their designs. It is suggested by product<br />
literature that active ligation helps deliver full <strong>torque</strong><br />
expression when a rectangular wire is engaged <strong>and</strong> pressed<br />
against the base <strong>of</strong> the slot. Critics <strong>of</strong> the clip design<br />
say, however, that introducing an active component into the<br />
ligation unnecessarily increases frictional resistance.<br />
Some investigators have found that any advantage from<br />
decreased friction with active <strong>self</strong>-ligating brackets is<br />
reduced when rectangular wires are placed. 9,48,65,71-74 Other<br />
researchers have found the same to be true for the passive<br />
Damon SL II. 75 It has also been suggested that the<br />
cantilevered clip delivers a diagonally directed force to<br />
the archwire, in effect reducing the torquing efficiency<br />
<strong>and</strong> causing errors in <strong>torque</strong> expression. 63<br />
In contrast, “passive” ligating mechanisms, like those<br />
<strong>of</strong> the Damon 2, Damon 3 <strong>and</strong> Damon 3MX brackets <strong>and</strong> the<br />
SmartClip bracket (3M/Unitek Corporation, Monrovia, CA), do<br />
not invade the slot <strong>and</strong> place no inherent normal force on<br />
the archwire. <strong>The</strong>se systems feature one <strong>of</strong> two basic<br />
25
designs. <strong>The</strong> passive-slide design <strong>of</strong> the Damon series <strong>of</strong><br />
brackets utilizes a sliding “door” that closes the slot,<br />
effectively transforming the bracket into a tube. <strong>The</strong><br />
SmartClip bracket features a nickel-titanium alloy “C-clip”<br />
lateral to each <strong>of</strong> the mesial <strong>and</strong> distal tie-wings 76 ; an<br />
archwire that is snapped into the bracket-slot may remain<br />
passive in the lumens <strong>of</strong> the clips. <strong>The</strong> claimed benefit <strong>of</strong><br />
passive <strong>self</strong>-ligation is reduced friction with a variety <strong>of</strong><br />
wire sizes, resulting in faster tooth movement. 77 With the<br />
lack <strong>of</strong> a lingually directed force on the archwire,<br />
however, some critics argue that controlling <strong>torque</strong> could<br />
be a problem. 58 In addition, Harradine 63 points out that, in<br />
theory, a passively ligated bracket with an engaged<br />
rectangular wire, having a faciolingual dimension <strong>of</strong> 0.025<br />
inches, could bring a facially displaced tooth only to<br />
within 0.002 inches <strong>of</strong> the adjacent teeth because <strong>of</strong> its<br />
slot depth; usually it is approximately 0.027 inches. An<br />
active clip would, theoretically, not have this problem<br />
because it “squeezes” in the slot an archwire as small as<br />
0.018 inches in the faciolingual dimension. Harradine 63<br />
stated, however, that a remaining, clinically significant<br />
malalignment was unlikely. In two investigations, no<br />
significant difference between either the SmartClip bracket<br />
or the Damon 2 bracket <strong>and</strong> a conventional bracket in regard<br />
26
to incisor irregularity after initial alignment was<br />
found. 78,79<br />
Other Factors Influencing Friction<br />
Saliva<br />
Although the role <strong>of</strong> saliva as a potential lubricant<br />
for the sliding <strong>of</strong> wires through slots has been studied by<br />
several researchers, there has been no clear answer as to<br />
the effect <strong>of</strong> saliva on intraoral friction. In one <strong>of</strong> the<br />
earliest studies, Andreasen <strong>and</strong> Quevedo 44 found no<br />
significant difference in friction between “wet” <strong>and</strong> “dry”<br />
samples. Possible explanations for this finding were the<br />
following: 1. Saliva may not be good lubricant for the slot<br />
<strong>and</strong> wire materials; or 2. Forces at the contact area shared<br />
by the wire <strong>and</strong> bracket-slot were so great that the fluid<br />
was expelled from that area. Tselepis, Brockhurst <strong>and</strong><br />
West 33 found a significant reduction in friction in the<br />
“wet” state. Saunders <strong>and</strong> Kusy 87 similarly found a decrease<br />
in friction when saliva was introduced between two<br />
contacting titanium surfaces. Others have found, however,<br />
some increases in frictional resistance with the addition<br />
<strong>of</strong> saliva. 17,53,83 <strong>The</strong>se conflicting results were suggested<br />
by Kusy, Whitley <strong>and</strong> Prewitt 27 to be related to the surfaces<br />
in contact. <strong>The</strong>y found that the lubricating or adhesive<br />
27
ehavior <strong>of</strong> saliva depended on the material composition <strong>of</strong><br />
the slots <strong>and</strong> wires. For example, when saliva was<br />
introduced in stainless steel slots, it produced decreases<br />
in frictional resistance with ß-titanium alloy wires, but<br />
an adhesive effect with stainless steel wires.<br />
Occlusal Forces<br />
In the human dentition, the deformable periodontal<br />
ligament allows minute movements <strong>of</strong> the teeth to aid in<br />
distribution <strong>of</strong> forces from occlusal function. <strong>The</strong>se<br />
forces, that can arise as a result <strong>of</strong> speaking, swallowing,<br />
or normal masticatory function, are heavy (1 kg to 50 kg)<br />
<strong>and</strong> intermittent, occurring thous<strong>and</strong>s <strong>of</strong> times per day for<br />
one second or less. 8,88 <strong>The</strong>se brief movements <strong>of</strong> the teeth<br />
alter the normal forces between the crown-attachment slot<br />
<strong>and</strong> wire, constantly breaking <strong>and</strong> resetting “friction<br />
locks.” 5 Studies have been conducted to determine the<br />
effect <strong>of</strong> perturbations (extraneous, small actions<br />
simulating mastication, swallowing) on frictional forces in<br />
the orthodontic appliance. Braun’s group, 88 with an in<br />
vitro model, found a reduction in sliding resistance<br />
proportional to the magnitude <strong>of</strong> extraneous forces. Using<br />
a half-arch model, Lingenbrink 89 found an average decrease<br />
in kinetic frictional forces <strong>of</strong> 49% when perturbations were<br />
28
added. Similarly, Bunkall 15 noted reductions in average<br />
kinetic friction <strong>and</strong> maximum static friction <strong>of</strong> 35 to 70%.<br />
Second-Order Angulation, Binding <strong>and</strong> Notching<br />
Several studies have shown that, as second-<strong>order</strong><br />
angulation between the bracket-slot <strong>and</strong> the archwire<br />
increases, friction also increases. 5,21,24,31,33,44,80,90<br />
Classical friction from ligating force is largely<br />
responsible for frictional resistance when the second-<strong>order</strong><br />
angulation is less than the angle at which binding occurs. 5<br />
This angle is called “critical” <strong>and</strong> is defined as the<br />
second-<strong>order</strong> angulation at which the wire just contacts two<br />
diagonally opposing edges <strong>of</strong> the bracket-slot, reducing the<br />
wire-slot clearance to zero. 91 When the angle exceeds the<br />
critical value for the bracket-archwire combination,<br />
binding becomes an influential factor in resistance to<br />
sliding. 92 Factors that affect binding are archwire size,<br />
bracket-slot geometry, <strong>and</strong> interbracket distances. 57<br />
Thorstenson <strong>and</strong> Kusy 93 reported that ligation type seemed to<br />
have an effect on only classical friction because they did<br />
not influence binding when the brackets were positioned at<br />
an angulation beyond the critical contact angle.<br />
If the wire-slot angulation substantially exceeds the<br />
critical contact angle, a physical deformation <strong>of</strong> a round<br />
29
wire at one or both <strong>of</strong> its contact points with the edge <strong>of</strong><br />
the slot, known as mechanical notching, can occur, further<br />
adding to the resistance to sliding. 70,94 In a clinical<br />
study, this damage to the archwire was found to be related<br />
to the design <strong>of</strong> the orthodontic bracket. 95 <strong>The</strong> main effect<br />
<strong>of</strong> archwire-notching on friction is the creation <strong>of</strong><br />
“obstacles” that impede relative wire-slot sliding. 96 It<br />
appears that notching may be a function <strong>of</strong> the materials in<br />
contact. Kusy et al. 30 found that ceramic brackets cause<br />
more notching than stainless steel brackets. Similarly,<br />
Articolo’s group 96 found that notching <strong>of</strong> archwires was<br />
three times more prevalent <strong>and</strong> severe with ceramic brackets<br />
than with stainless steel brackets.<br />
Third-Order Torque<br />
<strong>The</strong> term “<strong>third</strong>-<strong>order</strong> <strong>torque</strong>” in orthodontics pertains<br />
to the rotational control <strong>and</strong> movement <strong>of</strong> a tooth crown or<br />
root faciolingually. This type <strong>of</strong> tooth movement can occur<br />
subsequent to twisting a square or rectangular archwire<br />
along its longitudinal axis, required to place it into the<br />
slot <strong>of</strong> a crown-attachment. In this process, two contact<br />
forces acting on the occlusal <strong>and</strong> gingival walls <strong>of</strong> the<br />
slot by partial archwire deactivation create a <strong>third</strong>-<strong>order</strong><br />
30
couple, resulting in the delivery in the faciolingual plane<br />
<strong>of</strong> torsional forces to the tooth. 97,98<br />
<strong>The</strong> preadjusted edgewise appliance is designed with a<br />
specific amount <strong>of</strong> slot-/pre-<strong>torque</strong> for each tooth in the<br />
arch to aid in achieving optimal crown- <strong>and</strong> root-<br />
positioning. <strong>The</strong>oretically, this <strong>torque</strong> will be expressed<br />
when a full-size archwire is allowed to deactivate<br />
completely over time after being seated in the slot <strong>of</strong> a<br />
properly placed bracket. When a rectangular wire not<br />
completely filling the slot is engaged, a certain amount <strong>of</strong><br />
rotation around the longitudinal axis <strong>of</strong> the wire can occur<br />
before the occlusogingival clearance within the slot<br />
becomes zero <strong>and</strong> <strong>third</strong>-<strong>order</strong> rotational forces are<br />
transmitted to the crown-attachment. This clearance-angle<br />
is known as “slop” or “play,” <strong>and</strong> its magnitude is<br />
primarily dependent on the shape <strong>and</strong> dimensions <strong>of</strong> the wire<br />
<strong>and</strong> slot, as well as the amount <strong>of</strong> edge-bevel in the wire<br />
cross-section. 99-101 <strong>The</strong> difference between the appliance-<br />
<strong>torque</strong> <strong>and</strong> this clearance-angle gives the effective <strong>torque</strong>,<br />
the estimated amount <strong>of</strong> <strong>third</strong>-<strong>order</strong> <strong>torque</strong> that the<br />
bracket-wire combination will express after deactivation <strong>of</strong><br />
the wire. 98 Because most orthodontic treatment is<br />
undertaken with less than full-size archwires, some<br />
preadjusted brackets include accentuated <strong>torque</strong> in the<br />
31
maxillary- incisor brackets so that finishing with 0.019- x<br />
0.025-inch wires will still result in optimal root<br />
positioning. 102<br />
<strong>The</strong> vendor-stated sizes <strong>of</strong> both the wire <strong>and</strong> the slot<br />
are nominal dimensions because <strong>of</strong> manufacturing tolerances<br />
that exist in the fabrication processes. Actual dimensions<br />
are not reported by the vendor. Sebanc et al. 98 measured<br />
dimensions <strong>of</strong> bracket-slots with a traveling microscope <strong>and</strong><br />
the dimension(s) <strong>of</strong> various orthodontic-wire cross-sections<br />
with a micrometer. <strong>The</strong>y found that slot dimensions were<br />
generally larger than their nominal values. Actual wire<br />
dimensions were generally found to be equal to or smaller<br />
than nominal sizes, but all were within 0.0005 inches.<br />
Meling <strong>and</strong> Ødegaard. 100 found a range <strong>of</strong> ±0.0005 inches in<br />
actual wire heights across the wires <strong>of</strong> seven wire-vendors.<br />
Kusy <strong>and</strong> Whitley 94 measured archwires <strong>and</strong> bracket-slots, <strong>and</strong><br />
they found that 30% <strong>of</strong> the wire specimens were larger than<br />
suggested by their nominal dimension(s). Of the bracket-<br />
slots tested, 15% <strong>of</strong> the measurements were smaller than the<br />
vendor-stated values. <strong>The</strong> abilities <strong>of</strong> the manufacturers,<br />
or lack there<strong>of</strong>, to accurately produce wires <strong>of</strong> stated<br />
dimensions can affect the amount <strong>of</strong> <strong>torque</strong> expressed in the<br />
bracket-slots. 101,103<br />
32
Another factor that influences bracket-wire <strong>torque</strong><br />
expression is the elastic modulus <strong>of</strong> the bracket-slot.<br />
Harzer, Bourauel <strong>and</strong> Gmyrek 104 compared slot-deformations,<br />
polycarbonate brackets versus stainless steel brackets, <strong>and</strong><br />
found higher <strong>torque</strong> losses <strong>and</strong> smaller torquing moments in<br />
the plastic brackets. Others found similar results. 105,106<br />
Kapur, Sinha <strong>and</strong> N<strong>and</strong>a 107 compared the structural integrity<br />
<strong>of</strong> titanium brackets with that <strong>of</strong> stainless steel brackets<br />
when both were subjected to torsional forces from an<br />
archwire, <strong>and</strong> concluded that the titanium brackets<br />
demonstrated less deformation.<br />
<strong>The</strong> effect <strong>of</strong> <strong>third</strong>-<strong>order</strong> discrepancies in bracket<br />
alignment on frictional resistance has not been extensively<br />
evaluated in the orthodontic literature. Using an Instron<br />
testing machine, Moore, Harrington <strong>and</strong> Rock 108 discovered a<br />
significant increase in sliding friction with increased<br />
<strong>third</strong>-<strong>order</strong> <strong>torque</strong> in a single-bracket study. Sims <strong>and</strong><br />
colleagues 68 also evaluated friction produced with wires<br />
sliding through three consecutive bracket-slots, with the<br />
middle bracket given predetermined <strong>torque</strong> values. <strong>The</strong>y<br />
reported that, with <strong>third</strong>-<strong>order</strong> activation present, the<br />
<strong>self</strong>-ligating Activa bracket (‘A’- Company, San Diego, CA)<br />
showed consistently less resistance to mesiodistal sliding<br />
than did sets <strong>of</strong> two conventionally ligated brackets.<br />
33
Summary<br />
<strong>The</strong> literature supports the thought that many factors<br />
play a role in the friction generated between the wire <strong>and</strong><br />
bracket-slot in orthodontic treatment. <strong>The</strong>se factors<br />
include properties related to the archwire, bracket,<br />
ligation type, <strong>and</strong> oral environment.<br />
New products, such as low-friction, <strong>self</strong>-ligating<br />
brackets, are being developed to help reduce sliding<br />
resistance associated with tooth movement. To obtain a<br />
thorough underst<strong>and</strong>ing how to best use these products in<br />
clinical orthodontics, it is important to study them in a<br />
simulated dental arch with the variables influencing<br />
friction controlled. It is for this reason, the present<br />
study has been undertaken.<br />
34
References<br />
1. Stoner MM. Force control in clinical practice. Am J<br />
Orthod 1960;46:163-168.<br />
2. Palmer F. Friction. Sci Amer 1951;184:54-60.<br />
3. Rossouw PE, Kamelchuk LS, Kusy RP. A fundamental review<br />
<strong>of</strong> variables associated with low velocity frictional<br />
dynamics. Sem Orthod 2003;9:223-235.<br />
4. L<strong>of</strong>tus BP, Artun J, Nicholls JI, Alonzo TA, Stoner JA.<br />
Evaluation <strong>of</strong> friction during sliding tooth movement in<br />
various bracket-arch wire combinations. Am J Orthod<br />
Dent<strong>of</strong>acial Orthop 1999;116:336-345.<br />
5. Frank CA, Nikolai RJ. A comparative study <strong>of</strong> frictional<br />
resistances between orthodontic bracket <strong>and</strong> arch wire. Am J<br />
Orthod 1980;78:593-609.<br />
6. Rossouw PE. Friction: An overview. Sem Orthod<br />
2003;9:218-222.<br />
7. N<strong>and</strong>a RS, Ghosh J. Biomedical considerations in sliding<br />
mechanics. In: N<strong>and</strong>a R (ed). Biomechanics in Clinical<br />
Orthodontics. Philadelphia, PA, WB Saunders, 1997:pp 188-<br />
217.<br />
8. Pr<strong>of</strong>fit WR. Contemporary Orthodontics, 3rd ed. St <strong>Louis</strong>:<br />
CV Mosby, 2000.<br />
9. Sims APT, Waters NE, Birnie DJ, Pethybridge RJ. A<br />
comparison <strong>of</strong> the forces required to produce tooth movement<br />
in vitro using two <strong>self</strong>-ligating brackets <strong>and</strong> a preadjusted<br />
bracket employing two types <strong>of</strong> ligation. Eur J<br />
Orthod 1993;15:377-385.<br />
35
10. N<strong>and</strong>a RS. Biomechanics <strong>and</strong> Esthetic Strategies in<br />
Clinical Orthodontics. <strong>Saint</strong> <strong>Louis</strong>, MO, Elsevier Saunders,<br />
2005.<br />
11. Prososki RR, Bagby MD, Erickson LC. Static frictional<br />
force <strong>and</strong> surface roughness <strong>of</strong> nickel-titanium arch wires.<br />
Am J Orthod Dent<strong>of</strong>acial Orthop 1991;100:341-348.<br />
12. Burstone CJ, Qin B, Morton JY. Chinese NiTi wire--a new<br />
orthodontic alloy. Am J Orthod 1985;87:445-452.<br />
13. Damon DH. Treatment <strong>of</strong> the Face with Biocompatible<br />
Orthodontics. In: Graber TM, Vanarsdall RL, Vig KWL (eds).<br />
Orthodontics: Current Principles <strong>and</strong> Techniques. <strong>Saint</strong><br />
<strong>Louis</strong>, MO, Elsevier, 2005:pp 753-831.<br />
14. Meling TR, Odegaard J, Holthe K, Segner D. <strong>The</strong> effect<br />
<strong>of</strong> friction on the bending stiffness <strong>of</strong> orthodontic beams:<br />
a theoretical <strong>and</strong> in vitro study. Am J Orthod Dent<strong>of</strong>acial<br />
Orthop 1997;112:41-49.<br />
15. Bunkall DM. <strong>The</strong> effect <strong>of</strong> extraneous forces upon the<br />
frictional characteristics <strong>of</strong> <strong>self</strong>-ligating orthodontic<br />
brackets <strong>and</strong> nickel-titanium archwires utilizing a novel in<br />
vitro model. Master’s <strong>The</strong>sis. Center for Advanced Dental<br />
Education. <strong>Saint</strong> <strong>Louis</strong> <strong>University</strong>. St. <strong>Louis</strong>, MO. 2006.<br />
16. Kusy RP. Orthodontic biomaterials: from the past to the<br />
present. Angle Orthod 2002;72:501-512.<br />
17. Stannard JG, Gau JM, Hanna MA. Comparative friction <strong>of</strong><br />
orthodontic wires under dry <strong>and</strong> wet conditions. Am J Orthod<br />
1986;89:485-491.<br />
18. Garner LD, Allai WW, Moore BK. A comparison <strong>of</strong><br />
frictional forces during simulated canine retraction <strong>of</strong> a<br />
continuous edgewise arch wire. Am J Orthod Dent<strong>of</strong>acial<br />
Orthop 1986;90:199-203.<br />
36
19. Kusy RP, Whitley JQ, Ambrose WW, Newman JG. Evaluation<br />
<strong>of</strong> titanium brackets for orthodontic treatment: part I. <strong>The</strong><br />
passive configuration. Am J Orthod Dent<strong>of</strong>acial Orthop<br />
1998;114:558-572.<br />
20. Kusy RP, Whitley JQ. Effects <strong>of</strong> sliding velocity on the<br />
coefficients <strong>of</strong> friction in a model orthodontic system.<br />
Dent Mater 1989;5:235-240.<br />
21. Tidy DC. Frictional forces in fixed appliances. Am J<br />
Orthod Dent<strong>of</strong>acial Orthop 1989;96:249-254.<br />
22. Drescher D, Bourauel C, Schumacher HA. Frictional<br />
forces between bracket <strong>and</strong> arch wire. Am J Orthod<br />
Dent<strong>of</strong>acial Orthop 1989;96:397-404.<br />
23. Kapila S, Angolkar PV, Duncanson MG, Jr., N<strong>and</strong>a RS.<br />
Evaluation <strong>of</strong> friction between edgewise stainless steel<br />
brackets <strong>and</strong> orthodontic wires <strong>of</strong> four alloys. Am J Orthod<br />
Dent<strong>of</strong>acial Orthop 1990;98:117-126.<br />
24. Kusy RP, Whitley JQ. Coefficients <strong>of</strong> friction for arch<br />
wires in stainless steel <strong>and</strong> polycrystalline alumina<br />
bracket slots. I. <strong>The</strong> dry state. Am J Orthod Dent<strong>of</strong>acial<br />
Orthop 1990;98:300-312.<br />
25. Pratten DH, Popli K, Germane N, Gunsolley JC.<br />
Frictional resistance <strong>of</strong> ceramic <strong>and</strong> stainless steel<br />
orthodontic brackets. Am J Orthod Dent<strong>of</strong>acial Orthop<br />
1990;98:398-403.<br />
26. Angolkar PV, Kapila S, Duncanson MG, Jr., N<strong>and</strong>a RS.<br />
Evaluation <strong>of</strong> friction between ceramic brackets <strong>and</strong><br />
orthodontic wires <strong>of</strong> four alloys. Am J Orthod Dent<strong>of</strong>acial<br />
Orthop 1990;98:499-506.<br />
27. Kusy RP, Whitley JQ, Prewitt MJ. Comparison <strong>of</strong> the<br />
frictional coefficients for selected archwire-bracket slot<br />
combinations in the dry <strong>and</strong> wet states. Angle Orthod<br />
1991;61:293-302.<br />
37
28. Irel<strong>and</strong> AJ, Sherriff M, McDonald F. Effect <strong>of</strong> bracket<br />
<strong>and</strong> wire composition on frictional forces. Eur J Orthod<br />
1991;13:322-328.<br />
29. Vaughan JL, Duncanson MG, Jr., N<strong>and</strong>a RS, Currier GF.<br />
Relative kinetic frictional forces between sintered<br />
stainless steel brackets <strong>and</strong> orthodontic wires. Am J Orthod<br />
Dent<strong>of</strong>acial Orthop 1995;107:20-27.<br />
30. Kusy RP, Articolo LC, Kusy K, Saunders CR. In vivo<br />
notching on arches by ceramic brackets. J Dent Res<br />
1998;77:A696.<br />
31. Peterson L, Spencer R, Andreasen G. A comparison <strong>of</strong><br />
friction resistance for Nitinol <strong>and</strong> stainless steel wire in<br />
edgewise brackets. Quintessence Int Dent Dig 1982;13:563-<br />
571.<br />
32. De Franco DJ, Spiller RE, Jr., von Fraunh<strong>of</strong>er JA.<br />
Frictional resistances using Teflon-coated ligatures with<br />
various bracket-archwire combinations. Angle Orthod<br />
1995;65:63-72; discussion 73-64.<br />
33. Tselepis M, Brockhurst P, West VC. <strong>The</strong> dynamic<br />
frictional resistance between orthodontic brackets <strong>and</strong> arch<br />
wires. Am J Orthod Dent<strong>of</strong>acial Orthop 1994;106:131-138.<br />
34. Smith DV, Rossouw PE, Watson P. Quantified simulation<br />
<strong>of</strong> canine retraction: Evaluation <strong>of</strong> frictional resistance.<br />
Sem Orthod 2003;9:262-280.<br />
35. Downing A, McCabe J, Gordon P. A study <strong>of</strong> frictional<br />
forces between orthodontic brackets <strong>and</strong> archwires. Br J<br />
Orthod 1994;21:349-357.<br />
36. Cacciafesta V, Sfondrini MF, Scribante A, Klersy C,<br />
Auricchio F. Evaluation <strong>of</strong> friction <strong>of</strong> conventional <strong>and</strong><br />
metal-insert ceramic brackets in various bracket-archwire<br />
combinations. Am J Orthod Dent<strong>of</strong>acial Orthop 2003;124:403-<br />
409.<br />
38
37. Kusy RP, Whitley JQ, Mayhew MJ, Buckthal JE. Surface<br />
roughness <strong>of</strong> orthodontic archwires via laser spectroscopy.<br />
Angle Orthod 1988;58:33-45.<br />
38. Kusy RP, Whitley JQ. Effects <strong>of</strong> surface roughness on<br />
frictional coefficients <strong>of</strong> arch wires. J Dent Res<br />
1988;67:A1986.<br />
39. Kusy RP, Whitley JQ. Effects <strong>of</strong> surface roughness on<br />
the coefficients <strong>of</strong> friction in model orthodontic systems.<br />
J Biomech 1990;23:913-925.<br />
40. Burstone CJ, Farzin-Nia F. Production <strong>of</strong> low-friction<br />
<strong>and</strong> colored TMA by ion implantation. J Clin Orthod<br />
1995;29:453-461.<br />
41. Mendes K, Rossouw PE. Friction: Validation <strong>of</strong><br />
manufacturer’s claim. Sem Orthod 2003;9:236-250.<br />
42. Kusy RP, Tobin EJ, Whitley JQ, Sioshansi P. Frictional<br />
coefficients <strong>of</strong> ion-implanted alumina against ion-implanted<br />
beta-titanium in the low load, low velocity, single pass<br />
regime. Dent Mater 1992;8:167-172.<br />
43. Kula K, Phillips C, Gibilaro A, Pr<strong>of</strong>fit WR. Effect <strong>of</strong><br />
ion implantation <strong>of</strong> TMA archwires on the rate <strong>of</strong><br />
orthodontic sliding space closure. Am J Orthod Dent<strong>of</strong>acial<br />
Orthop 1998;114:577-580.<br />
44. Andreasen GF, Quevedo FR. Evaluation <strong>of</strong> friction forces<br />
in the 0.022 x 0.028 edgewise bracket in vitro. J Biomech<br />
1970;3:151-160.<br />
45. Riley JL, Garrett SG, Moon PC. Frictional forces <strong>of</strong><br />
ligated plastic <strong>and</strong> metal edgewise brackets. J Dent Res<br />
1979;58:98.<br />
46. Burstone CJ. Variable-modulus orthodontics. Am J Orthod<br />
1981;80:1-16.<br />
39
47. Schaus JG, Nikolai RJ. Localized, transverse, flexural<br />
stiffnesses <strong>of</strong> continuous arch wires. Am J Orthod<br />
1986;89:407-414.<br />
48. Pizzoni L, Ravnholt G, Melsen B. Frictional forces<br />
related to <strong>self</strong>-ligating brackets. Eur J Orthod<br />
1998;20:283-291.<br />
49. A historical overview <strong>of</strong> <strong>self</strong>-ligation: Strite<br />
Industries, Ltd.; 2006.<br />
50. Wahl N. Orthodontics in 3 millennia. Chapter 2:<br />
entering the modern era. Am J Orthod Dent<strong>of</strong>acial Orthop<br />
2005;127:510-515.<br />
51. Keith O, Jones SP, Davies EH. <strong>The</strong> influence <strong>of</strong> bracket<br />
material, ligation force <strong>and</strong> wear on frictional resistance<br />
<strong>of</strong> orthodontic brackets. Br J Orthod 1993;20:109-115.<br />
52. Berger JL. <strong>The</strong> influence <strong>of</strong> the SPEED bracket's <strong>self</strong>ligating<br />
design on force levels in tooth movement: a<br />
comparative in vitro study. Am J Orthod Dent<strong>of</strong>acial Orthop<br />
1990;97:219-228.<br />
53. Edwards GD, Davies EH, Jones SP. <strong>The</strong> ex vivo effect <strong>of</strong><br />
ligation technique on the static frictional resistance <strong>of</strong><br />
stainless steel brackets <strong>and</strong> archwires. Br J Orthod<br />
1995;22:145-153.<br />
54. Bednar JR, Gruendeman GW, S<strong>and</strong>rik JL. A comparative<br />
study <strong>of</strong> frictional forces between orthodontic brackets <strong>and</strong><br />
arch wires. Am J Orthod Dent<strong>of</strong>acial Orthop 1991;100:513-<br />
522.<br />
55. Shivapuja PK, Berger J. A comparative study <strong>of</strong><br />
conventional ligation <strong>and</strong> <strong>self</strong>-ligation bracket systems. Am<br />
J Orthod Dent<strong>of</strong>acial Orthop 1994;106:472-480.<br />
40
56. Khambay B, Millett D, McHugh S. Evaluation <strong>of</strong> methods<br />
<strong>of</strong> archwire ligation on frictional resistance. Eur J Orthod<br />
2004;26:327-332.<br />
57. Thorstenson GA. SmartClip Self-Ligating Brackets<br />
Frictional Study. Orthodontic Perspectives: <strong>The</strong> System<br />
Approach. 3M-Unitek Publication, Monrovia, CA 2005;12:8-11.<br />
58. Roth RH, Sapunar A, Frantz RC. <strong>The</strong> In-Ovation Bracket<br />
for Fully Adjusted Appliances. In: Graber TM, Vanarsdall<br />
RL, Vig KWL (eds). Orthodontics: Current Principles <strong>and</strong><br />
Techniques. <strong>Saint</strong> <strong>Louis</strong>, MO, Elsevier, 2005:pp 833-853.<br />
59. Baccetti T, Franchi L. Friction produced by types <strong>of</strong><br />
elastomeric ligatures in treatment mechanics with the<br />
preadjusted appliance. Angle Orthod 2006;76:211-216.<br />
60. Woodside DG, Berger JL, Hanson GH. Self-ligation<br />
orthodontics with the SPEED appliance. In: Graber TM,<br />
Vanarsdall RL, Vig KWL (eds). Orthodontics: current<br />
principles <strong>and</strong> techniques. St. <strong>Louis</strong>, MO, Elsevier Mosby<br />
2005:pp 717-752.<br />
61. Wildman AJ, Hice TL, Lang HM, Lee IF, Strauch EC, Jr.<br />
Round Table: <strong>The</strong> Edgelock bracket. J Clin Orthod<br />
1972;6:613-623.<br />
62. Hanson GH. <strong>The</strong> SPEED system: a report on the<br />
development <strong>of</strong> a new edgewise appliance. Am J Orthod<br />
1980;78:243-265.<br />
63. Harradine NW. Self-ligating brackets: where are we now?<br />
J Orthod 2003;30:262-273.<br />
64. Berger J, Byl<strong>of</strong>f FK. <strong>The</strong> clinical efficiency <strong>of</strong> <strong>self</strong>ligated<br />
brackets. J Clin Orthod 2001;35:304-308.<br />
65. Damon DH. <strong>The</strong> Damon low-friction bracket: a<br />
biologically compatible straight-wire system. J Clin Orthod<br />
1998;32:670-680.<br />
41
66. Maijer R, Smith DC. Time savings with <strong>self</strong>-ligating<br />
brackets. J Clin Orthod 1990;24:29-31.<br />
67. Hain M, Dhopatkar A, Rock P. <strong>The</strong> effect <strong>of</strong> ligation<br />
method on friction in sliding mechanics. Am J Orthod<br />
Dent<strong>of</strong>acial Orthop 2003;123:416-422.<br />
68. Sims APT, Waters NE, Birnie DJ. A comparison <strong>of</strong> the<br />
forces required to produce tooth movement ex vivo through<br />
three types <strong>of</strong> pre-adjusted brackets when subjected to<br />
determined tip or <strong>torque</strong> values. Br J Orthod 1994;21:367-<br />
373.<br />
69. Thomas S, Sherriff M, Birnie DJ. A comparative in vitro<br />
study <strong>of</strong> the frictional characteristics <strong>of</strong> two types <strong>of</strong><br />
<strong>self</strong>-ligating brackets <strong>and</strong> two types <strong>of</strong> pre-adjusted<br />
edgewise brackets tied with elastomeric ligatures. Eur J<br />
Orthod 1998;20:589-596.<br />
70. Thorstenson GA, Kusy RP. Resistance to sliding <strong>of</strong> <strong>self</strong>ligating<br />
brackets versus conventional stainless steel twin<br />
brackets with second-<strong>order</strong> angulation in the dry <strong>and</strong> wet<br />
(saliva) states. Am J Orthod Dent<strong>of</strong>acial Orthop<br />
2001;120:361-370.<br />
71. Heiser W. Time: a new orthodontic philosophy. J Clin<br />
Orthod 1998;32:44-53.<br />
72. Henao SP, Kusy RP. Evaluation <strong>of</strong> the frictional<br />
resistance <strong>of</strong> conventional <strong>and</strong> <strong>self</strong>-ligating bracket<br />
designs using st<strong>and</strong>ardized archwires <strong>and</strong> dental typodonts.<br />
Angle Orthod 2004;74:202-211.<br />
73. Read-Ward GE, Jones SP, Davies EH. A comparison <strong>of</strong><br />
<strong>self</strong>-ligating <strong>and</strong> conventional orthodontic bracket systems.<br />
Br J Orthod 1997;24:309-317.<br />
74. Taylor NG, Ison K. Frictional resistance between<br />
orthodontic brackets <strong>and</strong> archwires in the buccal segments.<br />
Angle Orthod 1996;66:215-222.<br />
42
75. Tecco S, Festa F, Caputi S, Traini T, Di Iorio D,<br />
D'Attilio M. Friction <strong>of</strong> conventional <strong>and</strong> <strong>self</strong>-ligating<br />
brackets using a 10 bracket model. Angle Orthod<br />
2005;75:1041-1045.<br />
76. Trevisi HJ. <strong>The</strong> SmartClip Self-Ligating Appliance<br />
System Technique Guide. 3M-Unitek Publication, Monrovia, CA<br />
2005.<br />
77. Weinberger GL. Utilizing the SmartClip <strong>self</strong>-ligating<br />
appliance. Orthodontic Perspectives: <strong>The</strong> System Approach.<br />
3M-Unitek Publication, Monrovia, CA 2005;23:3-7.<br />
78. Miles PG. SmartClip versus conventional twin brackets<br />
for initial alignment: is there a difference? Aust Orthod J<br />
2005;21:123-127.<br />
79. Miles PG, Weyant RJ, Rustveld L. A clinical trial <strong>of</strong><br />
Damon 2 vs conventional twin brackets during initial<br />
alignment. Angle Orthod 2006;76:480-485.<br />
80. Ho KS, West VC. Friction ... Friction resistance<br />
between edgewise brackets <strong>and</strong> archwires. Aust Orthod J<br />
1991;12:95-99.<br />
81. Omana HM, Moore RN, Bagby MD. Frictional properties <strong>of</strong><br />
metal <strong>and</strong> ceramic brackets. J Clin Orthod 1992;26:425-432.<br />
82. Popli K, Pratten DH, Germane N, Gunsolley JC.<br />
Frictional resistance <strong>of</strong> ceramic <strong>and</strong> stainless-steel<br />
orthodontic brackets. J Dent Res 1989;68:245.<br />
83. Downing A, McCabe JF, Gordon PH. <strong>The</strong> effect <strong>of</strong><br />
artificial saliva on the frictional forces between<br />
orthodontic brackets <strong>and</strong> archwires. Br J Orthod 1995;22:41-<br />
46.<br />
84. Kusy RP, Whitley JQ. Frictional resistances <strong>of</strong> metallined<br />
ceramic brackets versus conventional stainless steel<br />
43
ackets <strong>and</strong> development <strong>of</strong> 3-D friction maps. Angle Orthod<br />
2001;71:364-374.<br />
85. Kapur R, Sinha PK, N<strong>and</strong>a RS. Comparison <strong>of</strong> frictional<br />
resistance in titanium <strong>and</strong> stainless steel brackets. Am J<br />
Orthod Dent<strong>of</strong>acial Orthop 1999;116:271-274.<br />
86. Schlegel V. Relative friction minimization in fixed<br />
orthodontic bracket appliances. J Biomech 1996;29:483-491.<br />
87. Saunders CR, Kusy RP. Surface topography <strong>and</strong> frictional<br />
characteristics <strong>of</strong> ceramic brackets. Am J Orthod<br />
Dent<strong>of</strong>acial Orthop 1994;106:76-87.<br />
88. Braun S, Bluestein M, Moore BK, Benson G. Friction in<br />
perspective. Am J Orthod Dent<strong>of</strong>acial Orthop 1999;115:619-<br />
627.<br />
89. Lingenbrink JC. <strong>The</strong> effect <strong>of</strong> extraneous intra-oral<br />
force on wire-slot friction potentially impeding leveling<br />
<strong>and</strong> aligning during orthodontic therapy. Master’s <strong>The</strong>sis.<br />
Center for Advanced Dental Education. <strong>Saint</strong> <strong>Louis</strong><br />
<strong>University</strong>. St. <strong>Louis</strong>, MO. 2006.<br />
90. Ogata RH, N<strong>and</strong>a RS, Duncanson MG, Jr., Sinha PK,<br />
Currier GF. Frictional resistances in stainless steel<br />
bracket-wire combinations with <strong>effects</strong> <strong>of</strong> vertical<br />
deflections. Am J Orthod Dent<strong>of</strong>acial Orthop 1996;109:535-<br />
542.<br />
91. Kusy RP, Whitley JQ. Assessment <strong>of</strong> second-<strong>order</strong><br />
clearances between orthodontic archwires <strong>and</strong> bracket slots<br />
via the critical contact angle for binding. Angle Orthod<br />
1999;69:71-80.<br />
92. Thorstenson GA, Kusy RP. Comparison <strong>of</strong> resistance to<br />
sliding between different <strong>self</strong>-ligating brackets with<br />
second-<strong>order</strong> angulation in the dry <strong>and</strong> saliva states. Am J<br />
Orthod Dent<strong>of</strong>acial Orthop 2002;121:472-482.<br />
44
93. Thorstenson GA, Kusy RP. Effects <strong>of</strong> ligation type <strong>and</strong><br />
method on the resistance to sliding <strong>of</strong> novel orthodontic<br />
brackets with second-<strong>order</strong> angulation in the dry <strong>and</strong> wet<br />
states. Angle Orthod 2003;73:418-430.<br />
94. Kusy RP, Whitley JQ. Influence <strong>of</strong> archwire <strong>and</strong> bracket<br />
dimensions on sliding mechanics: derivations <strong>and</strong><br />
determinations <strong>of</strong> the critical contact angles for binding.<br />
Eur J Orthod 1999;21:199-208.<br />
95. Hansen JD, Kusy RP, Saunders CR. Archwire damage from<br />
ceramic brackets via notching. Orthod Rev 1997;11:27-31.<br />
96. Articolo LC, Kusy K, Saunders CR, Kusy RP. Influence <strong>of</strong><br />
ceramic <strong>and</strong> stainless steel brackets on the notching <strong>of</strong><br />
archwires during clinical treatment. Eur J Orthod<br />
2000;22:409-425.<br />
97. Nikolai RJ. Bioengineering analysis <strong>of</strong> orthodontic<br />
mechanics. Philadelphia: Lea & Febiger, 1985:pp 53-56.<br />
98. Sebanc J, Brantley WA, Pincsak JJ, Conover JP.<br />
Variability <strong>of</strong> effective root <strong>torque</strong> as a function <strong>of</strong> edge<br />
bevel on orthodontic arch wires. Am J Orthod 1984;86:43-51.<br />
99. Johnson E. Relative stiffness <strong>of</strong> beta titanium<br />
archwires. Angle Orthod 2003;73:259-269.<br />
100. Meling TR, Odegaard J. On the variability <strong>of</strong> crosssectional<br />
dimensions <strong>and</strong> torsional properties <strong>of</strong><br />
rectangular nickel-titanium arch wires. Am J Orthod<br />
Dent<strong>of</strong>acial Orthop 1998;113:546-557.<br />
101. Meling TR, Odegaard J, Meling EO. On mechanical<br />
properties <strong>of</strong> square <strong>and</strong> rectangular stainless steel wires<br />
tested in torsion. Am J Orthod Dent<strong>of</strong>acial Orthop<br />
1997;111:310-320.<br />
45
102. McLaughlin RP, Bennett JC, Trevisi HJ. Systemized<br />
orthodontic treatment mechanics. Edinburgh, Scotl<strong>and</strong>,<br />
Mosby, 2001.<br />
103. Gioka C, Eliades T. Materials-induced variation in the<br />
<strong>torque</strong> expression <strong>of</strong> preadjusted appliances. Am J Orthod<br />
Dent<strong>of</strong>acial Orthop 2004;125:323-328.<br />
104. Harzer W, Bourauel C, Gmyrek H. Torque capacity <strong>of</strong><br />
metal <strong>and</strong> polycarbonate brackets with <strong>and</strong> without a metal<br />
slot. Eur J Orthod 2004;26:435-441.<br />
105. Feldner JC, Sarkar NK, Sheridan JJ, Lancaster DM. In<br />
vitro <strong>torque</strong>-deformation characteristics <strong>of</strong> orthodontic<br />
polycarbonate brackets. Am J Orthod Dent<strong>of</strong>acial Orthop<br />
1994;106:265-272.<br />
106. Sadat-Khonsari R, Moshtaghy A, Schlegel V, Kahl-Nieke<br />
B, Moller M, Bauss O. Torque deformation characteristics <strong>of</strong><br />
plastic brackets: a comparative study. J Or<strong>of</strong>ac Orthop<br />
2004;65:26-33.<br />
107. Kapur R, Sinha PK, N<strong>and</strong>a RS. Comparison <strong>of</strong> load<br />
transmission <strong>and</strong> bracket deformation between titanium <strong>and</strong><br />
stainless steel brackets. Am J Orthod Dent<strong>of</strong>acial Orthop<br />
1999;116:275-278.<br />
108. Moore MM, Harrington E, Rock WP. Factors affecting<br />
friction in the pre-adjusted appliance. Eur J Orthod<br />
2004;26:579-583.<br />
46
Tables<br />
Table 2-1: Partial Overview <strong>of</strong><br />
Self-Ligating Brackets.<br />
Year Bracket<br />
47<br />
Mode <strong>of</strong><br />
Action<br />
1933 Boyd b<strong>and</strong> bracket Passive<br />
1933 Ford lock Passive<br />
1952 Russell appliance Passive<br />
1953 Schurter device Passive<br />
1957 Rubin device Passive<br />
1966 Branson Passive<br />
1972 SPEED System Active<br />
1972 Edgelok bracket Passive<br />
1979 Mobil-Lock bracket Passive<br />
1986 Activa bracket Passive<br />
1995 Time bracket Active<br />
1996 Damon bracket Passive<br />
1998 Twinlock bracket Passive<br />
2000 In-Ovation bracket Active<br />
2000 Damon 2 bracket Passive<br />
2002 In-Ovation R bracket Active<br />
2004 Time2 bracket Active<br />
2004 Damon 3 bracket Passive<br />
2005 SmartClip bracket Passive<br />
2006 Damon 3MX bracket Passive<br />
Modified from Woodside, Berger <strong>and</strong> Hanson, 2005 60
CHAPTER 3: JOURNAL ARTICLE<br />
Abstract<br />
Few studies have evaluated the effect <strong>of</strong> wire-slot<br />
<strong>torque</strong> on sliding friction. Apparently, no studies have<br />
been published to date that compare friction across<br />
categories <strong>of</strong> <strong>self</strong>-ligating brackets when <strong>third</strong>-<strong>order</strong><br />
positioning is controlled. <strong>The</strong> purpose <strong>of</strong> this study was<br />
to determine the <strong>effects</strong> <strong>of</strong> wire-slot <strong>torque</strong> <strong>and</strong> type <strong>of</strong><br />
<strong>self</strong>-ligating bracket on the average kinetic friction in<br />
sliding mechanics with a 0.019- x 0.025-inch stainless<br />
steel archwire. Five sets <strong>of</strong> crown-attachments (including<br />
In-Ovation R, Time2, Damon 3MX, SmartClip <strong>and</strong> Victory<br />
brackets) were tested for frictional resistance in a<br />
simulated posterior dental segment with -15, -10, -5, 0,<br />
+5, +10, <strong>and</strong> +15 degrees <strong>of</strong> <strong>torque</strong> placed in the maxillary<br />
right second-premolar bracket.<br />
Increasing the <strong>torque</strong> from 0 to ±15 degrees produced<br />
significant increases <strong>of</strong> frictional resistance in all five<br />
<strong>of</strong> the tested attachment-sets. At 0 degrees <strong>of</strong> <strong>torque</strong>, the<br />
sets with passive <strong>self</strong>-ligating brackets produced less<br />
friction than the sets with active <strong>self</strong>-ligating brackets,<br />
<strong>and</strong> all four <strong>self</strong>-ligating bracket sets produced<br />
48
significantly less friction than the set with<br />
elastomerically ligated Victory brackets. At ±10 degrees<br />
<strong>of</strong> <strong>torque</strong>, all five attachment sets displayed similar<br />
resistances with the exception <strong>of</strong> the In-Ovation R set at<br />
+10 degrees. At ±15 degrees <strong>of</strong> <strong>torque</strong>, the In-Ovation R<br />
<strong>and</strong> the SmartClip sets produced significantly larger<br />
frictional resistances than the other three sets.<br />
<strong>The</strong> data suggest that the presence <strong>of</strong> <strong>third</strong>-<strong>order</strong><br />
<strong>torque</strong> can influence the kinetic frictional resistances in<br />
posterior dental segments during anterior retraction using<br />
sliding mechanics with <strong>self</strong>-ligating brackets <strong>and</strong> that<br />
frictional resistance will increase at a greater rate when<br />
the <strong>torque</strong> exceeds ±10 degrees with the present combination<br />
<strong>of</strong> sizes <strong>of</strong> slots <strong>and</strong> wire. Furthermore, whether a <strong>self</strong>-<br />
ligated bracket is active or passive may not be clinically<br />
significant regarding friction in the presence <strong>of</strong> <strong>torque</strong><br />
approaching <strong>and</strong> exceeding 15 degrees.<br />
49
Introduction<br />
Friction is defined as the resistance to motion when<br />
one object moves or tends to move tangentially relative to<br />
another object. 1 <strong>The</strong> total contact-force between the<br />
objects may be expressed as two components when there is<br />
attempted or actual relative motion between surfaces in<br />
contact. One component, the normal force, is a pushing<br />
force with an orientation perpendicular to the shared<br />
contact-surface. <strong>The</strong> frictional force component impedes<br />
movement between the surfaces <strong>and</strong> is, therefore, opposite<br />
in direction to that <strong>of</strong> intended or actual motion. 2 <strong>The</strong><br />
maximum static or the kinetic frictional force (F) tangent<br />
to the two surfaces is <strong>of</strong>ten hypothesized as proportional<br />
to the normal force, as expressed by the equation F = µN,<br />
where µ is a coefficient <strong>of</strong> friction between the surfaces,<br />
<strong>and</strong> N is the normal force at the shared contact surface <strong>of</strong><br />
the objects. 3 <strong>The</strong> coefficient <strong>of</strong> friction is a constant<br />
which is related to characteristics <strong>of</strong> the contacting<br />
surfaces <strong>of</strong> the objects. 4<br />
Because frictional force acts in a direction opposite<br />
to the intended path <strong>of</strong> the object to be displaced, <strong>and</strong><br />
sliding mechanics are commonplace in orthodontic therapy,<br />
an underst<strong>and</strong>ing <strong>of</strong> friction is necessary to achieve<br />
50
optimal clinical results. Fixed-appliance therapy involves<br />
at least some relative (mesiodistal) wire-slot displacement<br />
in various phases <strong>of</strong> treatment; hence, the generation <strong>of</strong><br />
friction during tooth movement can be problematic for the<br />
orthodontist. Because a portion <strong>of</strong> the force for delivery<br />
to a tooth-crown to be displaced may be necessary to<br />
overcome frictional resistance, the orthodontist must be<br />
sure to use a force <strong>of</strong> sufficient magnitude to also<br />
initiate a biological response in the supporting tissues. 4<br />
<strong>The</strong> application <strong>of</strong> sliding mechanics in orthodontics<br />
has increased since the introduction <strong>of</strong> the pre-adjusted<br />
edgewise appliance system. 5 <strong>The</strong> process can involve the<br />
guidance <strong>of</strong> a tooth along a continuous archwire or the<br />
movement <strong>of</strong> the wire through the crown-attachment slot(s).<br />
In particular, overjet reduction <strong>and</strong> space closure have<br />
been traditionally accepted applications <strong>of</strong> sliding<br />
mechanics. In a first premolar extraction case, a space is<br />
created between the canine <strong>and</strong> the second premolar. When<br />
maximum anchorage is desired, the canine would first be<br />
retracted bodily with the archwire guiding its<br />
displacement. This single tooth movement would likely<br />
create unwanted friction that could cause “side <strong>effects</strong>”<br />
such as uncontrolled tipping, loss <strong>of</strong> posterior anchorage,<br />
or deepening <strong>of</strong> the overbite. 6 Forces acting posteriorly on<br />
51
the anterior portion <strong>of</strong> the archwire would then be created<br />
to retract the incisors into the remaining spaces while<br />
allowing the excess wire to slide through the posterior<br />
brackets <strong>and</strong> tubes. Any wire-slot friction in the buccal<br />
segments would hinder the movement <strong>of</strong> the anterior segment<br />
<strong>and</strong>, therefore, could delay space closure. 7<br />
<strong>The</strong> popularity <strong>of</strong> sliding mechanics in orthodontics<br />
has produced considerable research interest in frictional<br />
forces generated between bracket-slot <strong>and</strong> archwire. Many<br />
studies have identified multivalued factors that can<br />
contribute to or affect friction within the fixed<br />
orthodontic appliance. <strong>The</strong>se parameters include alloy-<br />
composition, 1,8-27 surface-roughness, 2,7,9,14,15,28-31 archwire<br />
cross-sectional shape <strong>and</strong> size, 2,14,22,25,27,32-34 ligation<br />
method, 2,4,5,8,25,34-46 bracket/slot material surface<br />
properties, 1,10,16-18,20,27,35,37,47-52 bracket width, 2,4,12,13,22,33,49<br />
lubrication, 8,18,24,53-55 extraneous occlusal forces, 56-58<br />
second-<strong>order</strong> angulation, 2,12,15,22,24,33,46-48,59,60 <strong>and</strong> <strong>third</strong>-<strong>order</strong><br />
<strong>torque</strong>. 44,61<br />
Several modern <strong>self</strong>-ligating bracket designs have been<br />
commercially available for the past 30 years, but until<br />
recently such brackets did not have widespread use. <strong>The</strong><br />
design <strong>of</strong> orthodontic products specifically aimed at<br />
minimizing friction has resulted in the reintroduction <strong>of</strong><br />
52
<strong>self</strong>-ligating bracket systems to mainstream orthodontics.<br />
<strong>The</strong>se newer brackets are claimed to reduce friction,<br />
contribute to improved oral hygiene, lessen anchorage loss,<br />
<strong>and</strong> shorten chair- time as well as treatment-time. 38,62-65<br />
Several studies have reported that <strong>self</strong>-ligating brackets<br />
generate less sliding friction than elastomerically tied<br />
brackets. 5,38,40,42-46<br />
In general, <strong>self</strong>-ligating brackets fall into one <strong>of</strong><br />
two categories based on the design <strong>of</strong> the slot-closure. An<br />
“active” design features a resilient spring-clip that snaps<br />
closed <strong>and</strong> reduces the faciolingual slot depth to<br />
approximately 0.018 inches. Because this clip can store<br />
energy when it is activated by a lingual malalignment, a<br />
rotated tooth or a twisted rectangular wire, it has the<br />
potential to exert lingual force on the wire <strong>and</strong> help bring<br />
the tooth into its proper position. 66 Critics <strong>of</strong> the clip-<br />
design say, however, that introducing an active component<br />
into the ligation unnecessarily increases frictional<br />
resistance. 67 Some investigators have found that any<br />
advantage from decreased friction with active <strong>self</strong>-ligating<br />
brackets is reduced when rectangular wires are<br />
placed. 5,43,63,68-71 It has also been suggested that the<br />
asymmetric design <strong>of</strong> the cantilevered clip delivers a<br />
diagonally directed force to the archwire, in effect<br />
53
educing the torquing efficiency <strong>and</strong> causing errors in<br />
<strong>torque</strong>-expression. 64<br />
In contrast, a “passive” ligating mechanism does not<br />
reduce the depth <strong>of</strong> the slot <strong>and</strong> places no inherent normal<br />
force on the archwire. <strong>The</strong>se systems have one <strong>of</strong> two basic<br />
designs. <strong>The</strong> passive-slide design utilizes a sliding<br />
“door” that closes the slot, effectively transforming the<br />
bracket into a tube. 67 Another passive ligation design<br />
features a nickel-titanium alloy “C-clip” mechanism lateral<br />
to each <strong>of</strong> the mesial <strong>and</strong> distal tie-wings 72 ; an archwire<br />
that is snapped into the bracket-slot may remain passive in<br />
the lumens <strong>of</strong> the clips. <strong>The</strong> claimed benefit <strong>of</strong> these<br />
passive <strong>self</strong>-ligation systems is reduced friction with all<br />
wire sizes, resulting in faster tooth movement. 73 With the<br />
absence <strong>of</strong> a lingually directed force against the archwire,<br />
however, some critics argue that the inability to control<br />
<strong>torque</strong> could be a problem. 41 For this reason, passive <strong>self</strong>-<br />
ligating brackets are manufactured with a faciolingual<br />
slot-dimension as small as 0.027 inches, instead <strong>of</strong> the<br />
traditional 0.028 inches minimum.<br />
In orthodontics, friction arises when there is contact<br />
<strong>and</strong> a tendency for mesiodistal sliding <strong>of</strong> an archwire<br />
relative to the slot. When a small rectangular wire not<br />
completely filling the slot is engaged, some amount <strong>of</strong><br />
54
unconstrained rotation around the longitudinal axis <strong>of</strong> the<br />
wire can occur. If <strong>and</strong> when the occlusogingival clearance<br />
within the slot becomes zero, <strong>third</strong>-<strong>order</strong> rotational forces<br />
are created to be transmitted to the crown-attachment<br />
through direct contact with the slot. Moore, Harrington,<br />
<strong>and</strong> Rock 61 measured friction in two different brackets with<br />
predetermined tip <strong>and</strong> <strong>torque</strong>. <strong>The</strong> group discovered a<br />
significant increase in friction in the presence <strong>of</strong> active,<br />
<strong>third</strong>-<strong>order</strong> <strong>torque</strong>. Using an Instron testing machine, Sims<br />
<strong>and</strong> colleagues 44 also evaluated friction produced with wires<br />
sliding through bracket-slots positioned to input specific<br />
<strong>torque</strong> values. <strong>The</strong>y reported that, with torsion, the <strong>self</strong>-<br />
ligating Activa bracket (‘A’ Company, San Diego, CA) showed<br />
consistently less resistance to sliding than the two<br />
conventionally ligated brackets.<br />
Apparently no studies have been published to date that<br />
compare friction across categories <strong>of</strong> <strong>self</strong>-ligating<br />
brackets when <strong>third</strong>-<strong>order</strong> positioning is controlled. <strong>The</strong><br />
purpose <strong>of</strong> this study was to determine the effect <strong>of</strong> wire-<br />
slot <strong>torque</strong> on friction in 0.022-inch crown-attachment sets<br />
that included <strong>self</strong>-ligating brackets with a 0.019- x 0.025-<br />
inch stainless steel archwire engaged. <strong>The</strong> effect <strong>of</strong> the<br />
design <strong>of</strong> the various ligating mechanisms on kinetic<br />
55
friction with active <strong>torque</strong> present in the wire <strong>and</strong>/or slot<br />
was also evaluated.<br />
Materials <strong>and</strong> Methods<br />
<strong>The</strong> posterior maxillary right quadrant with a first<br />
premolar extracted <strong>and</strong> canine retracted was simulated to<br />
evaluate the friction produced in a buccal segment during<br />
retraction <strong>of</strong> the half-incisal segment; <strong>third</strong>-<strong>order</strong> <strong>torque</strong><br />
was generally activated at the second premolar position. A<br />
0.019- by 0.025-inch stainless steel wire was selected for<br />
this study because it is frequently selected as the<br />
retraction archwire. <strong>The</strong> two independent variables<br />
controlled in this study were the bracket ligation design<br />
<strong>and</strong> the <strong>third</strong>-<strong>order</strong> <strong>torque</strong> angle at the second premolar<br />
bracket. <strong>The</strong> dependent variable was the kinetic friction<br />
generated in the appliance when a wire was slowly pulled<br />
posteriorly through the crown-attachments.<br />
<strong>The</strong> friction testing device is described in the<br />
Master’s thesis by Bunkall. 58 <strong>The</strong> device consists <strong>of</strong> a<br />
series <strong>of</strong> aluminum cylinders (“teeth”) mounted into a base-<br />
plate in an archform representing a maxillary quadrant.<br />
Through each cylinder is an adjustable stainless steel rod<br />
with an attached brass faceplate that simulates the facial<br />
56
surface <strong>of</strong> a tooth-crown. <strong>The</strong> construction <strong>of</strong> the cylinder<br />
subassembly allows the faceplate to be positioned in all<br />
three dimensions <strong>of</strong> space. <strong>The</strong> mechanism was fabricated to<br />
enable the control <strong>of</strong> multiple bracket-slot locations <strong>and</strong><br />
orientations. In the present study, four aluminum<br />
cylinders, representing the maxillary right canine, second<br />
premolar, first molar <strong>and</strong> second molar, were inserted into<br />
the four posterior mounting holes in the aluminum base-<br />
plate (Figure 3-1). <strong>The</strong> stainless steel rod <strong>and</strong> knuckle-<br />
joint set-screw were rotated 90 degrees on each “tooth” to<br />
aid in the <strong>third</strong>-<strong>order</strong> positioning <strong>of</strong> the 0.022-inch<br />
brackets <strong>and</strong> tubes. Crown-attachments were bonded to the<br />
brass faceplates.<br />
Seven bracket-positioning templates were fabricated<br />
from 0.022-inch-thick steel plates. Each template was<br />
prepared to enable control <strong>of</strong> the positions <strong>of</strong> the slots <strong>of</strong><br />
the four crown-attachments; the slots were temporarily<br />
“engaged” <strong>and</strong> “filled” by the working edge <strong>of</strong> the template.<br />
At the site <strong>of</strong> the second-premolar bracket-slot, a<br />
rectangular section <strong>of</strong> the steel plate was cut away, 0.025<br />
inches from the working edge <strong>of</strong> the template. <strong>The</strong> cutout<br />
left a 0.022- by 0.025-inch cross-section within each <strong>of</strong><br />
the six templates; the small “bar” was inelastically<br />
rotated along its central longitudinal axis to one <strong>of</strong> six<br />
57
specific angles relative to the plane <strong>of</strong> the template to<br />
enable <strong>torque</strong>-placement in the second-premolar slot (Figure<br />
3-2). <strong>The</strong> seventh template was left uncut to place zero<br />
degrees <strong>of</strong> <strong>torque</strong> at the second premolar. Each template as<br />
a whole was initially flat <strong>and</strong> shaped to place the canine<br />
<strong>and</strong> first-molar attachment-slots in zeroed first- <strong>and</strong><br />
second-<strong>order</strong> positions, while also controlling the location<br />
<strong>of</strong> the second-premolar bracket-slot (Figure 3-3). <strong>The</strong><br />
second-molar tube was aligned with a 0.021- by 0.025-inch,<br />
straight wire-segment cantilevered from the three adjacent<br />
attachment-slots set at zero degrees <strong>of</strong> <strong>torque</strong>.<br />
Each “test specimen” consisted <strong>of</strong> two brackets, two<br />
molar tubes <strong>and</strong> a stainless steel archwire. Affixed at the<br />
first-molar site was a <strong>self</strong>-ligating first-molar tube with<br />
a facial slide mechanism <strong>and</strong> a 0.022-inch slot (SLBUCCAL,<br />
Ormco Corporation, Glendora, CA; Figure 3-4). This crown-<br />
attachment can be opened like a st<strong>and</strong>ard converted molar-<br />
tube; it permitted the insertion <strong>of</strong> the slot-positioning<br />
template, <strong>and</strong> the slide was closed during testing to enable<br />
its functioning as a st<strong>and</strong>ard unconverted four-walled<br />
buccal tube. <strong>The</strong> second-molar attachment was a 0.022-inch<br />
slot, maxillary single tube (Part Number 68-172-82; GAC<br />
International, Bohemia, NY). <strong>The</strong> archwires were 0.019- by<br />
58
0.025-inch NuBryte St<strong>and</strong>ard Arch stainless steel wires<br />
(Part Number 03-925-51; GAC International, Bohemia, NY).<br />
Because transmission <strong>of</strong> <strong>third</strong>-<strong>order</strong> <strong>torque</strong>-forces is<br />
directly influenced by wire size, ten percent <strong>of</strong> the test-<br />
wires (21 wires) were arbitrarily chosen <strong>and</strong> measured with<br />
a digital micrometer (Model APB-2D, Mitutoyo Corporation,<br />
Kanagawa, Japan). <strong>The</strong>ir average cross-sectional dimensions<br />
were calculated toward <strong>third</strong>-<strong>order</strong> clearance estimates.<br />
Five different pairs <strong>of</strong> canine <strong>and</strong> second-premolar<br />
brackets, all with 0.022-inch slots, were selected for this<br />
study. <strong>The</strong> “passive” <strong>self</strong>-ligating attachments were Damon<br />
3MX brackets (Ormco Corporation, Glendora, CA) with passive<br />
facial slides (Figure 3-5) <strong>and</strong> SmartClip brackets<br />
(3M/Unitek Corporation, Monrovia, CA) with passive C-clips<br />
(Figure 3-6). <strong>The</strong> “active” <strong>self</strong>-ligating attachments were<br />
In-Ovation R brackets (GAC International, Bohemia, NY;<br />
Figure 3-7) with sliding spring-clips <strong>and</strong> Time2 brackets<br />
(American Orthodontics, Sheboygan, WI; Figure 3-8) with<br />
rotating spring-clips. <strong>The</strong> traditional crown-attachments<br />
were the Victory-series MBT brackets (3M/Unitek<br />
Corporation, Monrovia, CA; Figure 3-9); wires were tied in<br />
the slots with silver Unistick elastomeric ligatures (Part<br />
Number 854-262; American Orthodontics, Sheboygan, WI).<br />
59
Individual test-subsamples had the second-premolar<br />
bracket-slot oriented at <strong>third</strong>-<strong>order</strong> <strong>torque</strong> values <strong>of</strong> -15,<br />
-10, -5, 0, +5, +10, <strong>and</strong> +15 degrees; the other three slots<br />
were fixed at zero <strong>torque</strong>. (A negative/positive <strong>torque</strong>-<br />
angle should produce lingual/facial tooth-crown tipping.)<br />
One set <strong>of</strong> four crown-attachments was used for testing at<br />
all <strong>torque</strong> values. <strong>The</strong> <strong>order</strong> <strong>of</strong> <strong>torque</strong> values during the<br />
testing <strong>of</strong> each set was r<strong>and</strong>omized to reduce the bias due<br />
to slot-wear on the results. <strong>The</strong> research design consisted<br />
<strong>of</strong> all combinations <strong>of</strong> the five crown-attachment/ligation<br />
sets <strong>and</strong> seven <strong>torque</strong> values. Based on previous results, 44<br />
six replications for each bracket-<strong>torque</strong> combination (210<br />
total tests) were anticipated to be sufficient.<br />
Brackets <strong>and</strong> molar tubes were affixed to the brass<br />
faceplates with cyano-acrylate adhesive (Loctite Super Glue<br />
Gel, Henkel Consumer Adhesives, Gulph Mills, PA). <strong>The</strong><br />
brackets <strong>and</strong> tubes were positioned, collectively aligned,<br />
with the slot-positioning templates <strong>and</strong> the previously<br />
mentioned wire-segment. A new archwire was engaged in the<br />
attachment-slots <strong>and</strong> ligated for each test. New<br />
elastomeric ligatures were placed prior to each test with<br />
Victory brackets using a Straight Shooter ligature gun (TP<br />
Orthodontics, LaPorte, IN) to produce the same amount <strong>of</strong><br />
short-term prestretch in all elastomeric ties. With the<br />
60
test-archwire in place <strong>and</strong> ligated, the simulated dental<br />
segment was mounted to the fixed head <strong>of</strong> a universal<br />
testing machine (Model 1011, Instron Corporation, Canton,<br />
MA) with the posterior, held end <strong>of</strong> the archwire oriented<br />
vertically. A custom attachment was fastened to the<br />
moveable head <strong>of</strong> the Instron testing machine (Figure 3-10),<br />
equipped with a ten-pound load transducer. This attachment<br />
was fabricated with a four-pronged “pencil chuck,” by which<br />
one posterior end <strong>of</strong> the test-wire was grasped. <strong>The</strong><br />
testing machine <strong>and</strong> an attached chart rec<strong>order</strong> (Model 2310-<br />
069, Instron Corporation) were turned on simultaneously.<br />
<strong>The</strong> wire was pulled posteriorly through the crown-<br />
attachments at a rate <strong>of</strong> one millimeter per minute for 90<br />
seconds while the chart rec<strong>order</strong> produced a force-versus-<br />
displacement plot. Testing was performed in the dry state<br />
<strong>and</strong> at room temperature. <strong>The</strong> load range was set at 0 to<br />
1000 grams. <strong>The</strong> testing machine was initially calibrated<br />
<strong>and</strong> checked after changes <strong>of</strong> crown-attachment sets. From<br />
each test the mean load, which was virtually equal to the<br />
frictional-force magnitude, was determined from ten plot-<br />
points taken at six-second intervals between the 30-second<br />
<strong>and</strong> 90-second marks on the plot.<br />
61
Results<br />
<strong>The</strong> data were analyzed using SPSS s<strong>of</strong>tware, version<br />
14.0 (SPSS, Inc., Chicago, IL). <strong>The</strong> mean frictional<br />
resistances <strong>and</strong> st<strong>and</strong>ard deviations there<strong>of</strong>, associated<br />
with five individual crown-attachment sets <strong>and</strong> each <strong>of</strong> the<br />
seven <strong>torque</strong> values, are shown in Table 3-1. Figure 3-11<br />
displays the mean frictional resistances from each <strong>of</strong> the<br />
crown-attachment sets; the seven means (associated with<br />
<strong>torque</strong>-angles) for an individual set are connected in <strong>order</strong><br />
by straight lines. Significant differences in mean<br />
frictional resistances across pairs <strong>of</strong> <strong>third</strong>-<strong>order</strong> <strong>torque</strong><br />
values from each set were statistically analyzed with the<br />
Mann-Whitney U test (Table 3-2). Kruskal-Wallis one-way<br />
analyses <strong>of</strong> variance <strong>and</strong> post-hoc Tukey comparisons<br />
determined significant differences (p < 0.05) between<br />
frictional resistances across the five crown-attachment<br />
sets at each <strong>of</strong> the seven <strong>torque</strong> angles <strong>and</strong> are presented<br />
in Tables 3-3 <strong>and</strong> 3-4.<br />
Actual test-archwire dimensions were determined to be<br />
equal to their nominal sizes. <strong>The</strong> average width <strong>and</strong> height<br />
<strong>of</strong> the wires were 0.0190 <strong>and</strong> 0.0250 inches, respectively.<br />
Neither +5 nor -5 five degrees <strong>of</strong> <strong>third</strong>-<strong>order</strong> rotation<br />
resulted in significant changes in frictional force from<br />
62
aseline values at 0 degrees <strong>of</strong> <strong>torque</strong> with the exception<br />
<strong>of</strong> the SmartClip set, significantly greater at both the<br />
positive <strong>and</strong> negative <strong>torque</strong>s, <strong>and</strong> the Time2 set, but only<br />
at +5 degrees <strong>of</strong> <strong>torque</strong> (Table 3-1). Increasing <strong>torque</strong><br />
from 0 to ±10 degrees produced significant increases in<br />
frictional resistance from all four sets <strong>of</strong> <strong>self</strong>-ligating<br />
attachments (Table 3-2). Among the <strong>self</strong>-ligating sets, the<br />
In-Ovation R <strong>and</strong> the SmartClip sets showed significantly<br />
more friction from a further increase from both +10 to +15<br />
<strong>and</strong> -10 to -15 degrees <strong>of</strong> <strong>torque</strong>; the Time2 set displayed a<br />
significant increase only from -10 to -15 degrees. <strong>The</strong><br />
elastomerically ligated Victory sets showed the smallest<br />
overall increase in friction when <strong>torque</strong>-angle was<br />
increased, ranging from 303 grams at 0 degrees to 551 grams<br />
at -15 degrees. <strong>The</strong> SmartClip sets displayed the smallest<br />
mean frictional force <strong>of</strong> 55 grams at 0 degrees, but also<br />
provided the greatest resistance increase, producing a<br />
force <strong>of</strong> 744 grams at +15 degrees (Table 3-1).<br />
At +5, 0 <strong>and</strong> -5 degrees <strong>of</strong> <strong>torque</strong>, the Victory crown-<br />
attachment set generally produced significantly more<br />
friction than the four <strong>self</strong>-ligating sets; the single<br />
exception was the Time2 set at +5 degrees (Table 3-4). <strong>The</strong><br />
Damon 3MX <strong>and</strong> SmartClip sets produced the smallest mean<br />
frictional forces at 0 degrees <strong>of</strong> <strong>torque</strong>.<br />
63
<strong>The</strong>re were no significant differences in mean<br />
frictional forces produced across the five attachment-sets<br />
at -10 degrees <strong>of</strong> <strong>torque</strong>. At +10 degrees, however, the In-<br />
Ovation R set produced significantly greater frictional<br />
resistance than each <strong>of</strong> the other four attachment-sets.<br />
At +15 <strong>and</strong> -15 degrees <strong>of</strong> <strong>torque</strong>, the In-Ovation R <strong>and</strong><br />
SmartClip sets generated significantly greater mean<br />
frictional forces than the other three sets; the forces<br />
from each <strong>of</strong> these two sets were statistically equal at<br />
these <strong>torque</strong> angles (Table 3-4). <strong>The</strong> In-Ovation R <strong>and</strong><br />
SmartClip sets produced forces <strong>of</strong> 757 grams <strong>and</strong> 744 grams,<br />
respectively, <strong>and</strong> 752 grams <strong>and</strong> 736 grams, respectively, at<br />
+15 <strong>and</strong> -15 degrees (Table 3-1). <strong>The</strong> Victory, Time2 <strong>and</strong><br />
Damon 3MX sets produced mean frictional forces that were<br />
statistically equal to each other at these angulations.<br />
Effect <strong>of</strong> Torque<br />
Discussion<br />
Increasing <strong>torque</strong> in the second-premolar slot from 0<br />
to <strong>and</strong> beyond ±10 degrees caused increases in frictional<br />
forces from all <strong>of</strong> the tested attachment-sets except the<br />
Victory set from 0 to -10 degrees. This effect was not<br />
seen from most <strong>of</strong> the sets when the <strong>torque</strong>-angle was<br />
64
increased to only five degrees. <strong>The</strong>se observations tend to<br />
support the suggestion 61 that <strong>torque</strong> will not have a<br />
dramatic effect on mesiodisal sliding friction until it<br />
exceeds the <strong>third</strong>-<strong>order</strong> clearance angle <strong>of</strong> the wire-slot<br />
combination. Reportedly, the clearance <strong>torque</strong>-angle for a<br />
fully drawn, 0.019- x 0.025-inch wire in a 0.022-inch open<br />
slot is about 10 degrees. 74 Presently, beyond 10 degrees <strong>of</strong><br />
<strong>third</strong>-<strong>order</strong> rotation, an increase in friction due to the<br />
creation <strong>of</strong> occlusogingival normal forces between the wire<br />
<strong>and</strong> the bracket-slot would be expected because <strong>of</strong> the<br />
torsional couple transmitted from the twisted archwire. 75<br />
In addition, geometric calculations suggest that a 0.019- x<br />
0.025-inch wire rotated 10 degrees in a bracket-slot would<br />
occupy a buccolingual dimension <strong>of</strong> 0.0276 inches (Figure 3-<br />
12). With the Damon 3MX <strong>and</strong> Smartclip brackets having slot<br />
depths <strong>of</strong> 0.027 <strong>and</strong> 0.0275 inches, respectively, the slots<br />
<strong>of</strong> the two passive <strong>self</strong>-ligated brackets are<br />
“buccolingually filled,” implying that the ligating<br />
mechanism can play a role in frictional resistance with<br />
active <strong>torque</strong>s approaching <strong>and</strong> exceeding 10 degrees.<br />
Active <strong>self</strong>-ligating attachments, such as the Time2<br />
<strong>and</strong> the In-Ovation R brackets, may behave differently from<br />
passive brackets when <strong>third</strong>-<strong>order</strong> rotations are introduced.<br />
Each clip is cantilevered occlusogingivally such that it<br />
65
enters the slot asymmetrically, contacting a rectangular<br />
wire along either a gingival or occlusal edge. An engaged<br />
0.019- x 0.025-inch archwire with zero <strong>torque</strong> would be<br />
expected to deflect the clip <strong>of</strong> either bracket. 76 A <strong>third</strong>-<br />
<strong>order</strong> rotation <strong>of</strong> the slot relative to the archwire,<br />
depending upon its sense, could potentially cause more or<br />
less deflection <strong>of</strong> the clip, thereby affecting the<br />
faciolingual normal forces exerted by the wire <strong>and</strong> the<br />
accompanying components <strong>of</strong> the frictional force system.<br />
<strong>The</strong> Time2 set generated larger frictional forces at +5<br />
degrees than at -5 degrees <strong>of</strong> <strong>torque</strong>. When comparing<br />
frictional resistances at +10 degrees <strong>and</strong> -10 degrees <strong>of</strong><br />
<strong>torque</strong>, both the Time2 <strong>and</strong> In-Ovation R brackets showed<br />
greater forces at the positive <strong>third</strong>-<strong>order</strong> angulation.<br />
This finding might be explained by the asymmetrical nature<br />
<strong>of</strong> the clip-designs.<br />
<strong>The</strong> Victory set also produced a larger mean frictional<br />
force at +10 degrees <strong>of</strong> <strong>torque</strong> than at -10 degrees. One<br />
possible explanation could be the occlusogingival asymmetry<br />
<strong>of</strong> the tie-wings <strong>of</strong> the Victory bracket design (Figure 3-<br />
9); when viewed from a mesiodistal perspective, the<br />
occlusal tie-wing apparently extends farther facially than<br />
the gingival tie-wing, suggesting that the elastomeric<br />
module could have been lying across the wire with more<br />
66
tension on one edge <strong>of</strong> the wire <strong>and</strong>/or the direction <strong>of</strong> the<br />
net normal force from the tie was skewed.<br />
Only the SmartClip set showed a significant increase<br />
in friction with every five-degree increase in <strong>torque</strong> (in<br />
either twist-direction). Because 5 degrees <strong>of</strong> <strong>third</strong>-<strong>order</strong><br />
rotation from 0 degrees does not eliminate the wire-slot<br />
clearance with this bracket-wire combination, a possible<br />
reason for the observed increase in friction could be the<br />
contact <strong>of</strong> the nickel-titanium-alloy “C-clips” with the<br />
wire during testing. Any contact <strong>of</strong> the wire with the<br />
clips during sliding could have produced a notable<br />
contribution to frictional resistance; a previous<br />
orthodontic-materials study found nickel-titanium-alloy<br />
wire to have a relatively large kinetic frictional<br />
coefficient when paired with a stainless steel bracket. 18<br />
Effect <strong>of</strong> Bracket Design<br />
At zero degrees <strong>of</strong> <strong>torque</strong>, the results <strong>of</strong> this study<br />
were similar to those from a previous research-effort 46 that<br />
evaluated friction in both <strong>self</strong>-ligating <strong>and</strong> traditionally<br />
ligated brackets. In the present study, with no <strong>torque</strong><br />
imposed, mean frictional resistance was found to be<br />
significantly less from each <strong>of</strong> the four <strong>self</strong>-ligation sets<br />
when compared to that from the Victory set (brackets tied<br />
67
with elastomeric ligatures). Friction values obtained from<br />
both passive <strong>self</strong>-ligating sets at ±5 degrees remained<br />
significantly smaller than the friction produced by the<br />
Victory set, likely due to the absence <strong>of</strong> any other than<br />
incidental contact from ligation within these <strong>self</strong>-ligating<br />
bracket-slots.<br />
With the exception <strong>of</strong> the In-Ovation R set <strong>and</strong><br />
positive angles, increasing the <strong>torque</strong> from ± 5 to ±10<br />
degrees brought the frictional resistances from the <strong>self</strong>-<br />
ligating attachment-sets to magnitudes similar to those<br />
from the Victory sets. This finding contrasted outcomes<br />
from a previous study 44 that found <strong>self</strong>-ligating brackets to<br />
produce smaller frictional forces than traditionally<br />
ligated brackets with <strong>torque</strong> placed. In the present<br />
research, interaction <strong>of</strong> the wire with the slot walls, as<br />
well as with the ligating mechanism, would be expected to<br />
occur when approaching ±10 degrees <strong>of</strong> <strong>torque</strong>, possibly<br />
tempering the alleged advantage <strong>of</strong> smaller frictional<br />
resistance that is commonly associated with <strong>self</strong>-ligating<br />
brackets. <strong>The</strong> marked increase in friction found in the<br />
<strong>self</strong>-ligating (but not in the Victory) sets when increasing<br />
the <strong>torque</strong> from ±5 degrees to ±10 degrees suggest that<br />
there were faciolingual force additions from substantial<br />
contacts with the ligating mechanisms. <strong>The</strong> In-Ovation R<br />
68
set, when the <strong>torque</strong> angle was increased from +5 to +10<br />
degrees, displayed substantially higher frictional<br />
resistance, possibly a result <strong>of</strong> increased normal forces<br />
due to its “active” <strong>self</strong>-ligation <strong>and</strong> the asymmetrical clip<br />
design.<br />
When the <strong>torque</strong> was increased beyond the <strong>third</strong>-<strong>order</strong><br />
clearance values to ±15 degrees, the friction associated<br />
with the SmartClip <strong>and</strong> the In-Ovation R sets grew to<br />
significantly larger magnitudes than the values displayed<br />
by the other three sets. This finding may be related to<br />
properties <strong>of</strong> the individual ligating mechanisms <strong>of</strong> these<br />
brackets. Interactions <strong>of</strong> the archwires with the clips in<br />
both brackets were likely because <strong>of</strong> the faciolingual<br />
dimensions <strong>of</strong> the ligated slots. Bunkall 58 attributed<br />
larger frictional forces from SmartClip brackets with<br />
first-<strong>order</strong> wire-slot discrepancies to flexure <strong>of</strong> the<br />
nickel-titanium-alloy clips contributing to normal forces<br />
as well as the relative roughnesses <strong>of</strong> the nickel-titanium-<br />
alloy surfaces. <strong>The</strong> clip integral to the In-Ovation R<br />
bracket is made <strong>of</strong> a cobalt-chromium alloy which has been<br />
reported to have a greater frictional potential related to<br />
surface-roughness than stainless steel, 13 <strong>and</strong> it may also<br />
have contributed to the relatively greater resistance<br />
displayed in this study.<br />
69
<strong>The</strong> design <strong>of</strong> this study does not entirely represent<br />
what might occur in clinical situations. Because teeth<br />
tend to tip <strong>and</strong> rotate during tooth movement, 6 the <strong>effects</strong><br />
<strong>of</strong> first- <strong>and</strong> second-<strong>order</strong> angulations on slot-wire<br />
friction should not be ignored when selecting a set <strong>of</strong><br />
crown-attachments. <strong>The</strong> research design <strong>and</strong> execution did,<br />
however, help to highlight <strong>and</strong> evaluate factors associated<br />
with friction in attachment-designs. Observations from<br />
this study lead to the recommendation that measures should<br />
be taken to reduce the amount <strong>of</strong> <strong>torque</strong> in the buccal<br />
segments before beginning en masse retraction <strong>of</strong> the<br />
anterior teeth. Future studies evaluating the collective<br />
contributions <strong>of</strong> tip, rotation <strong>and</strong> <strong>torque</strong> in a multiple<br />
crown-attachment setup could be helpful in determining<br />
optimal treatment-mechanics in certain clinical situations.<br />
Conclusions<br />
<strong>The</strong> results <strong>of</strong> this study confirmed that the presence<br />
<strong>of</strong> <strong>third</strong>-<strong>order</strong> <strong>torque</strong> can contribute to kinetic frictional<br />
resistance in the buccal segments during anterior<br />
retraction using sliding mechanics with crown-attachment<br />
sets including <strong>self</strong>-ligating brackets. At small <strong>torque</strong><br />
angles, friction will tend to be less with passive than<br />
70
with active, <strong>self</strong>-ligating sets. <strong>The</strong> findings suggest that<br />
a noticeable effect from friction will be seen when the<br />
<strong>torque</strong> reaches <strong>and</strong> exceeds the <strong>third</strong>-<strong>order</strong> clearance-angle<br />
<strong>of</strong> the wire-slot combinations. Furthermore, variations in<br />
bracket-ligation design can influence the amount <strong>of</strong><br />
friction produced, particularly at <strong>torque</strong>-values beyond the<br />
clearance-angle. When there is no <strong>torque</strong> present in the<br />
second premolar slot, attachment-sets with either passive<br />
or active <strong>self</strong>-ligating brackets will generate less<br />
friction than sets that include elastomerically ligated<br />
brackets. As <strong>torque</strong> increases toward the clearance-angle,<br />
however, differences in frictional resistances across<br />
crown-attachment sets generally lessen. Beyond this <strong>torque</strong><br />
value, the differences in frictional resistance may not<br />
depend upon the category <strong>of</strong> ligation, but, instead, upon<br />
the basic design <strong>of</strong> the ligation mechanism.<br />
71
References<br />
1. L<strong>of</strong>tus BP, Artun J, Nicholls JI, Alonzo TA, Stoner JA.<br />
Evaluation <strong>of</strong> friction during sliding tooth movement in<br />
various bracket-arch wire combinations. Am J Orthod<br />
Dent<strong>of</strong>acial Orthop 1999;116:336-345.<br />
2. Frank CA, Nikolai RJ. A comparative study <strong>of</strong> frictional<br />
resistances between orthodontic bracket <strong>and</strong> arch wire. Am J<br />
Orthod 1980;78:593-609.<br />
3. Rossouw PE. Friction: An overview. Sem Orthod<br />
2003;9:218-222.<br />
4. N<strong>and</strong>a RS, Ghosh J. Biomedical considerations in sliding<br />
mechanics. In: N<strong>and</strong>a R (ed). Biomechanics in Clinical<br />
Orthodontics. Philadelphia, PA, WB Saunders, 1997:pp 188-<br />
217.<br />
5. Sims APT, Waters NE, Birnie DJ, Pethybridge RJ. A<br />
comparison <strong>of</strong> the forces required to produce tooth movement<br />
in vitro using two <strong>self</strong>-ligating brackets <strong>and</strong> a preadjusted<br />
bracket employing two types <strong>of</strong> ligation. Eur J<br />
Orthod 1993;15:377-385.<br />
6. N<strong>and</strong>a RS. Biomechanics <strong>and</strong> Esthetic Strategies in<br />
Clinical Orthodontics. <strong>Saint</strong> <strong>Louis</strong>, MO, Elsevier Saunders,<br />
2005.<br />
7. Prososki RR, Bagby MD, Erickson LC. Static frictional<br />
force <strong>and</strong> surface roughness <strong>of</strong> nickel-titanium arch wires.<br />
Am J Orthod Dent<strong>of</strong>acial Orthop 1991;100:341-348.<br />
8. Stannard JG, Gau JM, Hanna MA. Comparative friction <strong>of</strong><br />
orthodontic wires under dry <strong>and</strong> wet conditions. Am J Orthod<br />
1986;89:485-491.<br />
9. Garner LD, Allai WW, Moore BK. A comparison <strong>of</strong><br />
frictional forces during simulated canine retraction <strong>of</strong> a<br />
continuous edgewise arch wire. Am J Orthod Dent<strong>of</strong>acial<br />
Orthop 1986;90:199-203.<br />
10. Kusy RP, Whitley JQ, Ambrose WW, Newman JG. Evaluation<br />
<strong>of</strong> titanium brackets for orthodontic treatment: part I. <strong>The</strong><br />
passive configuration. Am J Orthod Dent<strong>of</strong>acial Orthop<br />
1998;114:558-572.<br />
72
11. Kusy RP, Whitley JQ. Effects <strong>of</strong> sliding velocity on the<br />
coefficients <strong>of</strong> friction in a model orthodontic system.<br />
Dent Mater 1989;5:235-240.<br />
12. Tidy DC. Frictional forces in fixed appliances. Am J<br />
Orthod Dent<strong>of</strong>acial Orthop 1989;96:249-254.<br />
13. Drescher D, Bourauel C, Schumacher HA. Frictional<br />
forces between bracket <strong>and</strong> arch wire. Am J Orthod<br />
Dent<strong>of</strong>acial Orthop 1989;96:397-404.<br />
14. Kapila S, Angolkar PV, Duncanson MG, Jr., N<strong>and</strong>a RS.<br />
Evaluation <strong>of</strong> friction between edgewise stainless steel<br />
brackets <strong>and</strong> orthodontic wires <strong>of</strong> four alloys. Am J Orthod<br />
Dent<strong>of</strong>acial Orthop 1990;98:117-126.<br />
15. Kusy RP, Whitley JQ. Coefficients <strong>of</strong> friction for arch<br />
wires in stainless steel <strong>and</strong> polycrystalline alumina<br />
bracket slots. I. <strong>The</strong> dry state. Am J Orthod Dent<strong>of</strong>acial<br />
Orthop 1990;98:300-312.<br />
16. Pratten DH, Popli K, Germane N, Gunsolley JC.<br />
Frictional resistance <strong>of</strong> ceramic <strong>and</strong> stainless steel<br />
orthodontic brackets. Am J Orthod Dent<strong>of</strong>acial Orthop<br />
1990;98:398-403.<br />
17. Angolkar PV, Kapila S, Duncanson MG, Jr., N<strong>and</strong>a RS.<br />
Evaluation <strong>of</strong> friction between ceramic brackets <strong>and</strong><br />
orthodontic wires <strong>of</strong> four alloys. Am J Orthod Dent<strong>of</strong>acial<br />
Orthop 1990;98:499-506.<br />
18. Kusy RP, Whitley JQ, Prewitt MJ. Comparison <strong>of</strong> the<br />
frictional coefficients for selected archwire-bracket slot<br />
combinations in the dry <strong>and</strong> wet states. Angle Orthod<br />
1991;61:293-302.<br />
19. Irel<strong>and</strong> AJ, Sherriff M, McDonald F. Effect <strong>of</strong> bracket<br />
<strong>and</strong> wire composition on frictional forces. Eur J Orthod<br />
1991;13:322-328.<br />
20. Vaughan JL, Duncanson MG, Jr., N<strong>and</strong>a RS, Currier GF.<br />
Relative kinetic frictional forces between sintered<br />
stainless steel brackets <strong>and</strong> orthodontic wires. Am J Orthod<br />
Dent<strong>of</strong>acial Orthop 1995;107:20-27.<br />
21. Kusy RP, Articolo LC, Kusy K, Saunders CR. In vivo<br />
notching on arches by ceramic brackets. J Dent Res<br />
1998;77:A696.<br />
73
22. Peterson L, Spencer R, Andreasen G. A comparison <strong>of</strong><br />
friction resistance for Nitinol <strong>and</strong> stainless steel wire in<br />
edgewise brackets. Quintessence Int Dent Dig 1982;13:563-<br />
571.<br />
23. De Franco DJ, Spiller RE, Jr., von Fraunh<strong>of</strong>er JA.<br />
Frictional resistances using Teflon-coated ligatures with<br />
various bracket-archwire combinations. Angle Orthod<br />
1995;65:63-72; discussion 73-64.<br />
24. Tselepis M, Brockhurst P, West VC. <strong>The</strong> dynamic<br />
frictional resistance between orthodontic brackets <strong>and</strong> arch<br />
wires. Am J Orthod Dent<strong>of</strong>acial Orthop 1994;106:131-138.<br />
25. Smith DV, Rossouw PE, Watson P. Quantified simulation<br />
<strong>of</strong> canine retraction: Evaluation <strong>of</strong> frictional resistance.<br />
Sem Orthod 2003;9:262-280.<br />
26. Downing A, McCabe J, Gordon P. A study <strong>of</strong> frictional<br />
forces between orthodontic brackets <strong>and</strong> archwires. Br J<br />
Orthod 1994;21:349-357.<br />
27. Cacciafesta V, Sfondrini MF, Scribante A, Klersy C,<br />
Auricchio F. Evaluation <strong>of</strong> friction <strong>of</strong> conventional <strong>and</strong><br />
metal-insert ceramic brackets in various bracket-archwire<br />
combinations. Am J Orthod Dent<strong>of</strong>acial Orthop 2003;124:403-<br />
409.<br />
28. Kusy RP, Whitley JQ, Mayhew MJ, Buckthal JE. Surface<br />
roughness <strong>of</strong> orthodontic archwires via laser spectroscopy.<br />
Angle Orthod 1988;58:33-45.<br />
29. Kusy RP, Whitley JQ. Effects <strong>of</strong> surface roughness on<br />
frictional coefficients <strong>of</strong> arch wires. J Dent Res<br />
1988;67:A1986.<br />
30. Kusy RP, Whitley JQ. Effects <strong>of</strong> surface roughness on<br />
the coefficients <strong>of</strong> friction in model orthodontic systems.<br />
J Biomech 1990;23:913-925.<br />
31. Burstone CJ, Farzin-Nia F. Production <strong>of</strong> low-friction<br />
<strong>and</strong> colored TMA by ion implantation. J Clin Orthod<br />
1995;29:453-461.<br />
32. Burstone CJ. Variable-modulus orthodontics. Am J Orthod<br />
1981;80:1-16.<br />
74
33. Andreasen GF, Quevedo FR. Evaluation <strong>of</strong> friction forces<br />
in the 0.022 x 0.028 edgewise bracket in vitro. J Biomech<br />
1970;3:151-160.<br />
34. Riley JL, Garrett SG, Moon PC. Frictional forces <strong>of</strong><br />
ligated plastic <strong>and</strong> metal edgewise brackets. J Dent Res<br />
1979;58:98.<br />
35. Keith O, Jones SP, Davies EH. <strong>The</strong> influence <strong>of</strong> bracket<br />
material, ligation force <strong>and</strong> wear on frictional resistance<br />
<strong>of</strong> orthodontic brackets. Br J Orthod 1993;20:109-115.<br />
36. Berger JL. <strong>The</strong> influence <strong>of</strong> the SPEED bracket's <strong>self</strong>ligating<br />
design on force levels in tooth movement: a<br />
comparative in vitro study. Am J Orthod Dent<strong>of</strong>acial Orthop<br />
1990;97:219-228.<br />
37. Bednar JR, Gruendeman GW, S<strong>and</strong>rik JL. A comparative<br />
study <strong>of</strong> frictional forces between orthodontic brackets <strong>and</strong><br />
arch wires. Am J Orthod Dent<strong>of</strong>acial Orthop 1991;100:513-<br />
522.<br />
38. Shivapuja PK, Berger J. A comparative study <strong>of</strong><br />
conventional ligation <strong>and</strong> <strong>self</strong>-ligation bracket systems. Am<br />
J Orthod Dent<strong>of</strong>acial Orthop 1994;106:472-480.<br />
39. Khambay B, Millett D, McHugh S. Evaluation <strong>of</strong> methods<br />
<strong>of</strong> archwire ligation on frictional resistance. Eur J Orthod<br />
2004;26:327-332.<br />
40. Thorstenson GA. SmartClip Self-Ligating Brackets<br />
Frictional Study. Orthodontic Perspectives: <strong>The</strong> System<br />
Approach. 3M-Unitek Publication, Monrovia, CA 2005;12:8-11.<br />
41. Roth RH, Sapunar A, Frantz RC. <strong>The</strong> In-Ovation Bracket<br />
for Fully Adjusted Appliances. In: Graber TM, Vanarsdall<br />
RL, Vig KWL (eds). Orthodontics: Current Principles <strong>and</strong><br />
Techniques. <strong>Saint</strong> <strong>Louis</strong>, MO, Elsevier, 2005:pp 833-853.<br />
42. Hain M, Dhopatkar A, Rock P. <strong>The</strong> effect <strong>of</strong> ligation<br />
method on friction in sliding mechanics. Am J Orthod<br />
Dent<strong>of</strong>acial Orthop 2003;123:416-422.<br />
43. Pizzoni L, Ravnholt G, Melsen B. Frictional forces<br />
related to <strong>self</strong>-ligating brackets. Eur J Orthod<br />
1998;20:283-291.<br />
75
44. Sims APT, Waters NE, Birnie DJ. A comparison <strong>of</strong> the<br />
forces required to produce tooth movement ex vivo through<br />
three types <strong>of</strong> pre-adjusted brackets when subjected to<br />
determined tip or <strong>torque</strong> values. Br J Orthod 1994;21:367-<br />
373.<br />
45. Thomas S, Sherriff M, Birnie DJ. A comparative in vitro<br />
study <strong>of</strong> the frictional characteristics <strong>of</strong> two types <strong>of</strong><br />
<strong>self</strong>-ligating brackets <strong>and</strong> two types <strong>of</strong> pre-adjusted<br />
edgewise brackets tied with elastomeric ligatures. Eur J<br />
Orthod 1998;20:589-596.<br />
46. Thorstenson GA, Kusy RP. Resistance to sliding <strong>of</strong> <strong>self</strong>ligating<br />
brackets versus conventional stainless steel twin<br />
brackets with second-<strong>order</strong> angulation in the dry <strong>and</strong> wet<br />
(saliva) states. Am J Orthod Dent<strong>of</strong>acial Orthop<br />
2001;120:361-370.<br />
47. Ogata RH, N<strong>and</strong>a RS, Duncanson MG, Jr., Sinha PK,<br />
Currier GF. Frictional resistances in stainless steel<br />
bracket-wire combinations with <strong>effects</strong> <strong>of</strong> vertical<br />
deflections. Am J Orthod Dent<strong>of</strong>acial Orthop 1996;109:535-<br />
542.<br />
48. Ho KS, West VC. Friction ... Friction resistance<br />
between edgewise brackets <strong>and</strong> archwires. Aust Orthod J<br />
1991;12:95-99.<br />
49. Omana HM, Moore RN, Bagby MD. Frictional properties <strong>of</strong><br />
metal <strong>and</strong> ceramic brackets. J Clin Orthod 1992;26:425-432.<br />
50. Popli K, Pratten DH, Germane N, Gunsolley JC.<br />
Frictional resistance <strong>of</strong> ceramic <strong>and</strong> stainless-steel<br />
orthodontic brackets. J Dent Res 1989;68:245.<br />
51. Kusy RP, Whitley JQ. Frictional resistances <strong>of</strong> metallined<br />
ceramic brackets versus conventional stainless steel<br />
brackets <strong>and</strong> development <strong>of</strong> 3-D friction maps. Angle Orthod<br />
2001;71:364-374.<br />
52. Kapur R, Sinha PK, N<strong>and</strong>a RS. Comparison <strong>of</strong> frictional<br />
resistance in titanium <strong>and</strong> stainless steel brackets. Am J<br />
Orthod Dent<strong>of</strong>acial Orthop 1999;116:271-274.<br />
53. Saunders CR, Kusy RP. Surface topography <strong>and</strong> frictional<br />
characteristics <strong>of</strong> ceramic brackets. Am J Orthod<br />
Dent<strong>of</strong>acial Orthop 1994;106:76-87.<br />
76
54. Downing A, McCabe JF, Gordon PH. <strong>The</strong> effect <strong>of</strong><br />
artificial saliva on the frictional forces between<br />
orthodontic brackets <strong>and</strong> archwires. Br J Orthod 1995;22:41-<br />
46.<br />
55. Edwards GD, Davies EH, Jones SP. <strong>The</strong> ex vivo effect <strong>of</strong><br />
ligation technique on the static frictional resistance <strong>of</strong><br />
stainless steel brackets <strong>and</strong> archwires. Br J Orthod<br />
1995;22:145-153.<br />
56. Braun S, Bluestein M, Moore BK, Benson G. Friction in<br />
perspective. Am J Orthod Dent<strong>of</strong>acial Orthop 1999;115:619-<br />
627.<br />
57. Lingenbrink JC. <strong>The</strong> effect <strong>of</strong> extraneous intra-oral<br />
force on wire-slot friction potentially impeding leveling<br />
<strong>and</strong> aligning during orthodontic therapy. Master’s <strong>The</strong>sis.<br />
Center for Advanced Dental Education. <strong>Saint</strong> <strong>Louis</strong><br />
<strong>University</strong>. St. <strong>Louis</strong>, MO. 2006.<br />
58. Bunkall DM. <strong>The</strong> effect <strong>of</strong> extraneous forces upon the<br />
frictional characteristics <strong>of</strong> <strong>self</strong>-ligating orthodontic<br />
brackets <strong>and</strong> nickel-titanium archwires utilizing a novel in<br />
vitro model. Master’s <strong>The</strong>sis. Center for Advanced Dental<br />
Education. <strong>Saint</strong> <strong>Louis</strong> <strong>University</strong>. St. <strong>Louis</strong>, MO. 2006.<br />
59. Thorstenson GA, Kusy RP. Effects <strong>of</strong> ligation type <strong>and</strong><br />
method on the resistance to sliding <strong>of</strong> novel orthodontic<br />
brackets with second-<strong>order</strong> angulation in the dry <strong>and</strong> wet<br />
states. Angle Orthod 2003;73:418-430.<br />
60. Kusy RP, Whitley JQ. Influence <strong>of</strong> archwire <strong>and</strong> bracket<br />
dimensions on sliding mechanics: derivations <strong>and</strong><br />
determinations <strong>of</strong> the critical contact angles for binding.<br />
Eur J Orthod 1999;21:199-208.<br />
61. Moore MM, Harrington E, Rock WP. Factors affecting<br />
friction in the pre-adjusted appliance. Eur J Orthod<br />
2004;26:579-583.<br />
62. Berger J, Byl<strong>of</strong>f FK. <strong>The</strong> clinical efficiency <strong>of</strong> <strong>self</strong>ligated<br />
brackets. J Clin Orthod 2001;35:304-308.<br />
63. Damon DH. <strong>The</strong> Damon low-friction bracket: a<br />
biologically compatible straight-wire system. J Clin Orthod<br />
1998;32:670-680.<br />
77
64. Harradine NW. Self-ligating brackets: where are we now?<br />
J Orthod 2003;30:262-273.<br />
65. Maijer R, Smith DC. Time savings with <strong>self</strong>-ligating<br />
brackets. J Clin Orthod 1990;24:29-31.<br />
66. Woodside DG, Berger JL, Hanson GH. Self-ligation<br />
orthodontics with the SPEED appliance. In: Graber TM,<br />
Vanarsdall RL, Vig KWL (eds). Orthodontics: current<br />
principles <strong>and</strong> techniques. St. <strong>Louis</strong>, MO, Elsevier Mosby<br />
2005:pp 717-752.<br />
67. Damon DH. Treatment <strong>of</strong> the Face with Biocompatible<br />
Orthodontics. In: Graber TM, Vanarsdall RL, Vig KWL (eds).<br />
Orthodontics: Current Principles <strong>and</strong> Techniques. <strong>Saint</strong><br />
<strong>Louis</strong>, MO, Elsevier, 2005:pp 753-831.<br />
68. Heiser W. Time: a new orthodontic philosophy. J Clin<br />
Orthod 1998;32:44-53.<br />
69. Henao SP, Kusy RP. Evaluation <strong>of</strong> the frictional<br />
resistance <strong>of</strong> conventional <strong>and</strong> <strong>self</strong>-ligating bracket<br />
designs using st<strong>and</strong>ardized archwires <strong>and</strong> dental typodonts.<br />
Angle Orthod 2004;74:202-211.<br />
70. Read-Ward GE, Jones SP, Davies EH. A comparison <strong>of</strong><br />
<strong>self</strong>-ligating <strong>and</strong> conventional orthodontic bracket systems.<br />
Br J Orthod 1997;24:309-317.<br />
71. Taylor NG, Ison K. Frictional resistance between<br />
orthodontic brackets <strong>and</strong> archwires in the buccal segments.<br />
Angle Orthod 1996;66:215-222.<br />
72. Trevisi HJ. <strong>The</strong> SmartClip Self-Ligating Appliance<br />
System Technique Guide. 3M-Unitek Publication, Monrovia, CA<br />
2005.<br />
73. Weinberger GL. Utilizing the SmartClip <strong>self</strong>-ligating<br />
appliance. Orthodontic Perspectives: <strong>The</strong> System Approach.<br />
3M-Unitek Publication, Monrovia, CA 2005;23:3-7.<br />
74. Pr<strong>of</strong>fit WR. Contemporary Orthodontics, 3rd ed. St<br />
<strong>Louis</strong>: CV Mosby, 2000.<br />
75. Meling TR, Odegaard J, Meling EO. On mechanical<br />
properties <strong>of</strong> square <strong>and</strong> rectangular stainless steel wires<br />
tested in torsion. Am J Orthod Dent<strong>of</strong>acial Orthop<br />
1997;111:310-320.<br />
78
76. Thorstenson GA, Kusy RP. Effect <strong>of</strong> archwire size <strong>and</strong><br />
material on the resistance to sliding <strong>of</strong> <strong>self</strong>-ligating<br />
brackets with second-<strong>order</strong> angulation in the dry state. Am<br />
J Orthod Dent<strong>of</strong>acial Orthop 2002;122:295-305.<br />
79
Tables<br />
Table 3-1: Frictional-force means <strong>and</strong> st<strong>and</strong>ard deviations in grams at<br />
seven <strong>torque</strong> angles at the second premolar from five sets <strong>of</strong> crownattachments.<br />
Torque (degrees)<br />
-15 -10 -5 0 +5 +10 +15<br />
Victory 551 ± 36 329 ± 84 339 ± 52 303 ± 63 363 ± 84 471 ± 32 549 ± 59<br />
In-Ovation R 752 ± 128 440 ± 34 205 ± 8 221 ± 14 236 ± 35 623 ± 32 757 ± 79<br />
Time2 562 ± 103 407 ± 74 186 ± 50 196 ± 17 335 ± 22 517 ± 50 529 ± 79<br />
Damon 3MX 498 ± 110 358 ± 113 120 ± 17 149 ± 31 165 ± 89 440 ± 81 496 ± 69<br />
SmartClip 736 ± 26 433 ± 73 149 ± 44 55 ± 24 151 ± 47 427 ± 87 744 ± 38<br />
80
Table 3-2: Significance levels (α = 0.05) <strong>of</strong> differences in mean<br />
frictional forces across pairs <strong>of</strong> cells, each cell defined by a<br />
<strong>torque</strong>-angle, from five sets <strong>of</strong> crown-attachments.<br />
Bracket<br />
Victory In-Ovation R Time2 Damon 3MX SmartClip<br />
Torque (degrees) Significance<br />
-15 -10 .004 .004 .025 NS .004<br />
-5 .004 .004 .004 .004 .004<br />
0 .004 .004 .004 .004 .004<br />
+5 .006 .004 .004 .004 .004<br />
+10 .006 NS NS NS .004<br />
+15 NS* NS NS NS NS<br />
-10 -15 .004 .004 .025 NS .004<br />
-5 NS .004 .004 .004 .004<br />
0 NS .004 .004 .006 .004<br />
+5 NS .004 NS .016 .004<br />
+10 .025 .004 .025 NS NS<br />
+15 .004 .004 .025 NS .004<br />
-5 -15 .004 .004 .000 .004 .004<br />
-10 NS .004 .004 .004 .004<br />
0 NS NS NS NS .006<br />
+5 NS NS .004 NS NS<br />
+10 .004 .004 .004 .004 .004<br />
+15 .004 .004 .004 .004 .004<br />
0 -15 .004 .004 .004 .004 .004<br />
-10 NS .004 .004 .006 .004<br />
-5 NS NS NS NS .006<br />
+5 NS NS .004 NS .006<br />
+10 .004 .004 .004 .004 .004<br />
+15 .004 .004 .004 .004 .004<br />
+5 -15 .000 .004 .004 .004 .004<br />
-10 NS .004 NS .016 .004<br />
-5 NS NS .004 NS NS<br />
0 NS NS .004 NS .006<br />
+10 NS .004 .004 .004 .004<br />
+15 .025 .004 .004 .004 .004<br />
+10 -15 .006 NS NS NS .004<br />
-10 .005 .004 .025 NS NS<br />
-5 .011 .004 .004 .004 .004<br />
0 .001 .004 .004 .004 .004<br />
+5 NS .004 .004 .004 .004<br />
+15 NS .006 NS NS .004<br />
+15 -15 NS NS NS NS NS<br />
-10 .004 .004 .025 NS .004<br />
-5 .004 .004 .004 .004 .004<br />
0 .004 .004 .004 .004 .004<br />
+5 .025 .004 .004 .004 .004<br />
+10 .020 .006 NS NS .004<br />
*Not Significant (NS)<br />
81
Table 3-3: Summary from Kruskal-Wallis analyses <strong>of</strong> variance<br />
<strong>of</strong> frictional forces for seven <strong>torque</strong>-angles across five<br />
sets <strong>of</strong> crown-attachments.<br />
Torque (degrees)<br />
-15 -10 -5 0 +5 +10 +15<br />
Chi-square 17.957 7.920 22.774 24.951 22.249 17.044 21.174<br />
df 4 4 4 4 4 4 4<br />
Asymp. Sig. .001 NS* .000 .000 .000 .002 .000<br />
*Not Significant (NS)<br />
82
Table 3-4: Mean differences in frictional resistances in grams <strong>and</strong> significance levels (α = 0.05) between<br />
crown-attachment sets at each <strong>of</strong> seven <strong>torque</strong>-angles.<br />
Torque (degrees)<br />
-15 -10 -5 0 +5 +10 +15<br />
(a) (b) (a-b) † Sig. (a-b) Sig. (a-b) Sig. (a-b) Sig. (a-b) Sig. (a-b) Sig. (a-b) Sig.<br />
Victory In-Ovation R -201 .006 -111 NS 134 .000 82 .003 127 .011 -152 .002 -208 .000<br />
Time2 -11 NS* -78 NS 153 .000 107 .000 28 NS -46 NS 20 . NS<br />
Damon 3MX 53 NS -29 NS 219 .000 154 .000 198 .000 31 NS 53 NS<br />
SmartClip -185 .013 -104 NS 190 .000 247 .000 213 .000 44 NS -195 .000<br />
In-Ovation R Victory 201 .006 111 NS -134 .000 -82 .003 -127 .011 152 .002 208 .000<br />
Time2 190 .010 33 NS 19 NS 25 NS -99 NS 106 .043 228 .000<br />
Damon 3MX 254 .000 82 NS 85 .006 72 .010 71 NS 183 .000 261 .000<br />
SmartClip 16 NS 7 NS 56 NS 166 .000 86 NS 196 .000 13 NS<br />
Time2 Victory 11 NS 78 NS -153 .000 -107 .000 -28 NS 46 NS -20 NS<br />
In-Ovation R -190 .010 -33 NS -19 NS -25 NS 99 NS -106 .043 -228 .000<br />
Damon 3MX 64 . NS 49 NS 66 .045 47 NS 170 .001 77 NS -33 NS<br />
SmartClip -174 .022 -26 NS 37 NS 141* .000 185 .000 90 NS -215 .000<br />
83<br />
Damon 3MX Victory -53 NS 29 NS -219 .000 -154 .000 -198 .000 -31 NS -53 NS<br />
In-Ovation R -254 .000 -82 NS -85 .006 -72 .010 -71 NS -183 .000 -261 .000<br />
Time2 -64 NS -49 NS -66 .045 -47 NS -170 .001 -77 NS 33 NS<br />
SmartClip -238 .001 -75 NS -29 NS 94 .001 14 NS 13 NS -248 .000<br />
SmartClip Victory 185 .013 104 NS -190 .000 -247 .000 -213 .000 -44 NS 195 .000<br />
In-Ovation R -16 NS -7 NS -56 NS -166 .000 -86 NS -196 .000 -13 NS<br />
Time2 174 .022 26 NS -37 NS -141 .000 -185 .000 -90 NS 215 .000<br />
Damon 3MX 238 .001 75 NS 29 NS -94 .001 -14 NS -13 NS 248 .000<br />
*Not Significant (NS)<br />
†<br />
Mean difference in frictional resistance between a <strong>and</strong> b in grams.
Figures<br />
Figure 3-1: Four cylinders mounted in aluminum base<br />
plate <strong>of</strong> the friction testing device.<br />
Figure 3-2: Bracket-slot positioning<br />
template.<br />
84
Figure 3-3: Control <strong>of</strong> the <strong>third</strong>-<strong>order</strong> position <strong>of</strong> the<br />
second premolar bracket-slot.<br />
Figure 3-4: SLBUCCAL tube<br />
Figure 3-5: Damon 3MX bracket<br />
85
Figure 3-6: SmartClip bracket<br />
Figure 3-7: In-Ovation R bracket<br />
Figure 3-8: Time2 bracket<br />
86
Figure 3-9: Victory bracket<br />
Figure 3-10: Friction testing setup<br />
mounted to the Instron Universal Testing<br />
Machine.<br />
87
Friction (grams)<br />
800<br />
700<br />
600<br />
500<br />
400<br />
300<br />
200<br />
100<br />
0<br />
-15 -10 -5 0<br />
Torque (degrees)<br />
+5 +10 +15<br />
Figure 3-11: Plots <strong>of</strong> mean kinetic frictional force within the dental segment vs. <strong>torque</strong><br />
angle at the second premolar from five sets <strong>of</strong> crown-attachments.<br />
88<br />
Victory<br />
In-Ovation R<br />
Time2<br />
Damon 3MX<br />
SmartClip
Figure 3-12: Cross-section diagrams <strong>of</strong> a 0.019- x 0.025-inch wire. <strong>The</strong><br />
buccolingual dimension <strong>of</strong> the wire when rotated 10 degrees (line BD) is<br />
calculated by multiplying cos Φ2 by the hypotenuse AB.<br />
89
VITA AUCTORIS<br />
Michael Ji Hoon Chung was born on December 23, 1975 in<br />
Hollis, New York to Ye Hyun <strong>and</strong> Eun Soon Chung. In 1994,<br />
he received his high school diploma from the Horace Mann<br />
School in Riverdale, New York. From there he went to New<br />
York <strong>University</strong> <strong>and</strong> received a Bachelor <strong>of</strong> Arts degree in<br />
Psychology in May, 1998. From 1999 to 2003, he attended<br />
dental school at Columbia <strong>University</strong> in New York. He was<br />
awarded a Doctor <strong>of</strong> Dental Surgery degree in 2003. <strong>The</strong><br />
following year, Dr. Chung studied as a resident in the<br />
Advanced Education in General Dentistry program at Columbia<br />
<strong>University</strong>. In 2004, he began his graduate studies in<br />
orthodontics at the Center for Advanced Dental Education at<br />
<strong>Saint</strong> <strong>Louis</strong> <strong>University</strong> in <strong>Saint</strong> <strong>Louis</strong>, Missouri, where he<br />
is currently a c<strong>and</strong>idate for the degree <strong>of</strong> Master <strong>of</strong><br />
Science in Dentistry. He expects to graduate in January <strong>of</strong><br />
2007.<br />
Dr. Chung was married to Sahrip Kim in July, 2002.<br />
After graduation, they plan to return to the New York<br />
metropolitan area.<br />
90