University of Southern California Dissertations and Theses

Comparison of self-ligating brackets to conventionally-ligated twin edgewise brackets for root resorption

(USC Thesis Other)

Comparison of self-ligating brackets to conventionally-ligated twin edgewise brackets for root resorption

PDF

Download a page range

Download transcript

Copy asset link

Request this asset

Transcript (if available)

Content
COMPARISON OF SELF-LIGATING BRACKETS TO CONVENTIONALLY-
LIGATED TWIN EDGEWISE BRACKETS FOR ROOT RESORPTION

by

Derek Wong

A Thesis Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
MASTER OF SCIENCE
(CRANIOFACIAL BIOLOGY)

May 2009

Copyright 2009 Derek Wong

ii

Dedication

This thesis is dedicated to my wife, Jaime. Without her continued love and support, I
would not have been able to accomplish the success that I have had in my life and
career.

iii

Acknowledgements

Dr. Glenn Sameshima: To my research advisor and chair of my thesis committee.
Thank you for your guidance with this project. Your extensive knowledge on this
topic was extremely helpful.

Dr. Derick Tagawa and Dr. Richard Curtis: Thank you for granting access to your
office, staff, and records for data collection. This research would not have been
possible without your generosity and help.

Table of Contents

Dedication ii

Acknowledgements iii

List of Tables iv

List of Figures v

Abstract vi

Chapter One: Introduction 1

Chapter Two: Literature review 5

I. Development of Edgewise Brackets 5
1. The E-Arch 5
2. Pin and Tube 6
3. Ribbon Arch 7
4. Edgewise 7

II. Development of Self-ligating Brackets 9

III. Philosophy of Self-Ligating Proponents 18

IV. Friction in Orthodontics 22
1. Ligation Method 22
2. Friction 24

V. Properties of an Ideal Orthodontic Ligation System 26
1. Secure robust ligation 26
2. Full bracket engagement 26
3. Quick and easy 26
4. Low friction 27
5. Improves Patient Comfort and Hygiene 27

VI. Root Resorption 28

VII. Biologic Factors 31
1. Genetics 31

2. Systemic Factors 33
3. Gender 33
4. Age 33
5. Root Morphology 33
6. Specific Tooth Vulnerability to Root Resorption 34
7. Presence of Resorption Before Orthodontic Treatment 34
8. Endodontically Treated Teeth 34

VIII. Mechanical Factors 35
1. Type of Appliance 35
2. Intermaxillary Elastics 35
3. Extraction, Nonextraction, and Serial Extraction 36
4. Orthodontic Movement Type 36
5. Orthodontic Force 37
6. Extent of Tooth Movement 39
7. Duration of Treatment 39

IX. Clinical and Diagnostic Aids in Identifying Root Resorption 41

Chapter Three: Hypothesis 43

Chapter Four: Materials and methods 44

Chapter Five: Results 52

Chapter Six: Discussion 58

Chapter Seven: Conclusion 68

References 69

iv

List of Tables
Table 1: Number of each ethnicity in the Conventional bracket group 47

Table 2: Number of each ethnicity in the Damon™ bracket group 48

Table 3: Average age and treatment time in the Conventional bracket group 48
Table 4: Average age and treatment time in the Damon™ bracket group 48
Table 5: Conventional and Damon Bracket Archwire Sequence 49
Table 6: Mean root resorption by treatment group 52
Table 7: Mean difference in root resorption between Conventional and Damon™ 53
groups in the maxillary arch

Table 8: Mean difference in root resorption between Conventional and Damon™ 53
groups in the mandibular arch

Table 9: Mean root resorption in the maxillary arch between the two groups 54

Table 10: Mean root resorption in the mandibular arch between the two groups 55

Table 11: Differences in root resorption between mandibular and maxillary 56
teeth in the Conventional Group

Table 12: Differences in root resorption between mandibular and maxillary 56
teeth in the Damon Group

Table 13: Mean difference in root resorption between ethnicities: 57
Conventional Group

Table 14: Mean difference in root resorption between ethnicities: 57
Damon™ Group

v

List of Figures

Figure 1: Angle‘s expansion E-arch 6
Figure 2: The pin and tube appliance 6
Figure 3: The ribbon arch 7
Figure 4: The edgewise mechanism 8
Figure 5: The Russell attachment in open and closed positions 10
Figure 6: The Edgelok bracket in open and closed positions 11
Figure 7: The SPEED bracket in open and closed positions 12
Figure 8: The Activa bracket in open and closed positions 13
Figure 9: The Time bracket in open and closed positions 13
Figure 10: The TwinLock bracket in open and closed positions 14
Figure 11: The Damon™ SL I & SL II brackets 15
Figure 12: The GAC In-Ovation R bracket 16
Figure 13: The Unitek SmartClip bracket 16
Figure 14: Traditional archwire ligation vs. Damon self-ligating brackets 19
Figure 15: Root resorption scoring system by Levander and Malmgren 29
Figure 16: A tooth undergoing a normal amount of apical root resorption 29
Figure 17: A tooth undergoing a moderate amount of apical root resorption 30
Figure 18: IL-1 gene cluster on long arm of chromosome 2 (2q13) 32

vi

Abstract
The purpose of this study was to evaluate whether there are significant
differences in external apical root resorption between patients treated with self-
ligating brackets (Damon™ SL) and conventionally-ligated edgewise brackets.
Damon™ SL brackets eliminate the need for elastic or metal ligatures because they
have a built-in metal gate that opens and closes to accommodate an archwire. Pre-
and post-treatment full mouth radiographs were obtained from one orthodontic
practice and the amount of root resorption for both bracket systems was measured.
Thirty-seven Damon™ cases were matched with an equal amount of conventional
cases according to pre-determined inclusion and exclusion criteria. Results indicated
that there was a significant difference in the mean root resorption between the
conventional and Damon™ bracket groups (p=.0076). The maxillary anterior teeth
showed the most statistically significant difference in root resorption. From this
study, it can be concluded that self-ligating brackets offer a significant advantage
over conventionally ligated brackets with regard to root resorption in the anterior
teeth.

1

Chapter One: Introduction
The specialty of orthodontics has continued to evolve since its advent
in the early 20
th
century. Changes in treatment philosophy, mechanics, and
appliances have helped shape our understanding of orthodontic tooth
movement. In the 1890‘s Edward H. Angle published his classification of
malocclusion based on the occlusal relationships of the first molars. This was
a major step toward the development of orthodontics because his classification
defined normal occlusion. Angle then helped to pioneer the means to treat
malocclusions by developing new orthodontic appliances. He believed that if
all of the teeth were properly aligned, then no deviation from an ideal
occlusion would exist. Angle and his followers strongly believed in non-
extraction treatment. A later shift in thought occurred when one of his pupils,
Charles Tweed, observed that some of the patients formerly treated by Angle
exhibited a noticeable amount of relapse. Tweed then re-treated a number of
these cases by extracting four bicuspids to resolve the crowding and in turn,
developed his own treatment mechanics. Tweed‘s followers adamantly
believed that tooth extraction was necessary in some cases while Angle‘s
followers thought that good occlusion could only be achieved with a full
compliment of teeth. This debate still continues today, but there is an
increasing trend toward non-extraction treatment.
Another shift in orthodontics occurred when Larry Andrews introduced

2

the ―straight wire‖ appliance. Instead of bending wires to place teeth in the
proper orientation with an edgewise bracket, Andrews‘ appliance had the
angulation and torque values built into the brackets commonly known as the
―appliance prescription.‖ In theory, these pre-adjusted brackets eliminated the
need to repeatedly bend first, second, and third order bends each time the
patient progressed to the next wire. The straight wire appliance revolutionized
orthodontics by making the bracket much more efficient. Since then, many
orthodontic companies have developed their own bracket systems with specific
prescriptions, treatment philosophies, and mechanics.
The introduction of elastomeric ligatures is also another milestone in
orthodontics. Before their advent in the 1970‘s, archwires were held in place
by tying a metal ligature wire around the bracket wings to engage the wire in
the bracket slot. This was a time consuming procedure and Maijer and Smith
(1990), and Shivapuja and Berger (1994) have shown that wire ligation is very
slow compared to elastomerics. Harradine (2003) found that the use of wire
ligatures added almost 12 minutes to the time needed to remove and replace
two archwires. This is the reason many orthodontist prefer to use elastomeric
ligatures. However, elastomers also have an undesirable effect on tooth
movement by introducing a greater amount of friction into the system. When
compared to elastomers, wire ligatures have been shown to produce only 30-50
percent of the elastomeric friction (Shivapuja et al, 1994). With this in mind,
orthodontic clinicians and manufactures have sought a bracket design that

3

could potentially reduce friction while still maintaining operator efficiency and
reduced ligation times.
More recently, bracket systems that do not require any type of ligatures
to hold the wire in place have received a great deal of attention because they
further decrease treatment chair-time. These brackets are appropriately termed
self-ligating brackets. Although this technology was first developed in 1935,
with the introduction of the Russell Lock, self-ligating brackets have only
started to gain popularity in the 1980‘s.
These brackets have a built-in metal labial face (a clip or gate) that can be
repeatedly opened and closed to hold wires in position. A few advantages of
these brackets include decreased chair-time, increased ability for the patient to
maintain good oral hygiene, and decreased number of visits to complete
treatment (Harradine, 2001). Perhaps the most exciting advantage of self-
ligating brackets is their ability to provide a near ―frictionless‖ environment
that allows the archwires to express themselves. Many studies comparing
friction levels between self-ligating and conventionally-ligated brackets have
come to a similar conclusion that there is significantly more friction between
the archwire and the bracket when conventional elastomeric ligatures are used,
than when self-ligation are used (Read-Ward et al, 1997, Redlich et al, 2003,
Tecco et al, 2005). Although many aspects of self-ligated brackets have been
studied, some of their effects on the dentition have yet to be explored.

4

Recent advances in bracket technology have introduced new variables
that may affect external apical root resorption. Irreversible root resorption
observed mid- or post-treatment is an undesirable consequence of orthodontic
treatment. Studies using conventional brackets have shown that root resorption
can be affected by many factors including force magnitude, duration of
treatment, and tooth morphology. However, further research is needed to help
determine if self-ligating brackets have any effect on root resorption.

5

Chapter Two: Literature Review
I. Development of the Edgewise System
Edward Angle‘s position as the ―father of modern orthodontics‖ is
based not only on his contributions to classification and diagnosis but also
on his creativity in developing new orthodontic appliances. The majority
of the fixed appliances used in contemporary orthodontics are based on
Edward Angle‘s designs from the early 20
th
century. Angle developed four
major appliance systems (Proffit, 3
rd
ed):
1. The E-Arch
In the late 1800‘s, most orthodontic appliances were composed
of a rigid framework to which teeth were tied to. The E-arch was an
improvement on this design and consisted of bands on molar teeth and
a heavy labial arch wire extended around the arch (Figure 1). The end
of the wire was threaded, and a small nut placed on the threaded
portion of the arch allowed the arch wire to be advanced so that the
arch perimeter increased. Individual teeth were ligated to this
expansion arch. Teeth were moved primarily through tipping.

6

Figure 1: Angle‘s expansion E-arch (Courtesy of Steiner, 1933)

2. Pin and Tube
The E-arch was only capable of tipping teeth toward the labial
wire. In order to overcome this shortcoming, Angle developed the Pin
and tube appliance which had bands with vertical tubes on all of the
teeth. A soldered pin from a smaller arch wire was placed into the
tubes (Figure 2). Tooth movement was accomplished by repositioning
the individual pins at each appointment. This appliance was very labor
intensive and difficult to master.

Figure 2: The pin and tube appliance (Courtesy of Steiner, 1933)

7

3. Ribbon Arch
Angle‘s next appliance modified the tube on each tooth to
provide a vertically positioned rectangular slot behind the tube. A
ribbon arch of 10 x 20 gold wire was placed into the slot and held with
pins (figure 3). This appliance became extremely popular because the
arch wire had good spring qualities and was efficient in aligning teeth.
The major drawback of this appliance was that it provided relatively
poor control of the roots.

Figure 3: The ribbon arch (Courtesy of Steiner, 1993)

4. Edgewise
Perhaps the most important change in bracket design occurred
in 1982 when Angle reoriented the slot from vertical to horizontal and
inserted a rectangular wire rotated 90 degrees to the orientation it

8

formerly had with the ribbon arch, hence the name ―edgewise‖. This
design allowed for excellent control of both crown and root position
(Figure 4).

Figure 4: The edgewise mechanism (Courtesy of Steiner, 1933)

9

II. Development of Self-Ligating Brackets
A decade after the edgewise appliance was introduced, Larry Andrews
developed bracket modifications for specific teeth to eliminate the need to
repeatedly bend first, second, and third order bends with each wire change.
This was appropriately named the ―straight wire‖ appliance. Since then,
many bracket variations and systems have been brought to the orthodontic
marketplace, but they all shared one common characteristic – ligatures
must be placed around tie wings on brackets to hold arch wires in the
bracket slot. Routinely using wire ligatures to tie in archwires has been
largely replaced by elastomers due to their ease of removal and
replacement. Maijer and Smith (1990), and Shivapuja and Berger (1994)
have shown that wire ligation is very slow compared to elastomerics.
When compared to elastomeric ligation, Harradine (2003) found that the
removal and replacement of two archwires using wire ligation took nearly
12 minutes longer. Although the use of elastomeric ligatures greatly
increased treatment efficiency, they also increased the amount of friction
between the archwire and bracket slot. In most instances, increased friction
is an undesirable effect. Interestingly, wire ligatures have been shown to
exert only 30-50% of the friction caused by elastomeric ligatures
(Shivapuja et al, 1994). Clinicians and manufacturers alike sought to
develop a product that could replicate the time saving properties of
elastomeric modules while lessening or eliminating the friction they

10

caused. This eventually led to the development and popularization of self-
ligating brackets because they satisfy both criteria. Studies have shown
that self-ligating brackets require less time to change archwires and they
also provide less friction than conventionally ligated brackets (Berger
1994, Pizzoni et al, 1998).
Self-ligating brackets were first introduced in the mid-1930s in the
form of the Russell attachment by Dr. Jacob Stolzenberg. The bracket had
a flat-head screw seated snugly in a circular, threaded opening in the face
of the bracket that allows for quick and simple archwire changes
(Stolzenberg, 1935). Loosening the screw made the system passive and
allowed bodily translation on a round wire while tightening it made it
active and provided root torquing on a square or a rectangular wire (Figure
5). The bracket system was more comfortable for the patient and resulted
in shorter office visits as well (Berger, 2000). Unfortunately, the Russell
attachment did not gain much popularity and virtually disappeared from the
market.

Figure 5: The Russell attachment in open and closed positions (Courtesy of Berger, 2000)

11

For nearly three decades, self-ligating brackets fell out of favor and
were not used. In 1971, Dr. Jim Wildman developed the first modern self-
ligating bracket, the Edgelok bracket. This bracket consisted of a round body
with a rigid labial cap (Wildman 1972). A special tool was used to open the
metal cap and finger pressure was used to close it. Once closed, the bracket
became ―passive,‖ allowing the wire to slide freely (Figure 6). This was the
first passive self-ligating bracket that attained a good degree of commercial
success.

Figure 6: The Edgelok bracket in open and closed positions (Courtesy of Berger, 2000)

Four years later, Dr. Herbert Hanson created the SPEED™ (Spring-
loaded, Precision, Edgewise, Energy, Delivery) bracket, which was finally
introduced into the market in 1980 (Hanson, 1980). The main components of
appliance are a multi-slotted bracket body, a stainless steel spring clip, and a
specially shaped foil-mesh base. The highly resilient spring clip opens and
closes in a vertical manner to permit arch wire removal and insertion (Figure

12

7). At the time, the SPEED™ bracket was unique in its manner of operation
because when the spring clip was closed, it was engaged with the arch wire
making it an ―active‖ appliance (Berger 1994). The spring is stiff enough to
contain the archwire in the slot even under high transient stresses, yet it is very
well suited for sliding mechanics when smaller arch wires are used (Hanson,
1986).

Figure 7: SPEED™ bracket in open and closed positions (Courtesy of Berger, 2000 and
Hanson, 1986)

In 1986, the self-ligating Activa™ bracket offered a different type of
self-ligating bracket system. This bracket had an inflexible, curved arm that
rotated around the cylindrical bracket body (Figure 8). The arm could be
opened and closed with finger pressure alone. Although the Activa™ bracket
was easy for the operator to use, it was equally simple for the patient to
inadvertently open and close as well (Berger 2000).

13

Figure 8: The Activa™ bracket in open and closed positions (Courtesy of Berger, 2000)

In 1995, the Time™ bracket was brought to the marketplace. Although
it was similar in appearance to the SPEED™ bracket, it differed in both its
design and mode of action. This bracket features a rigid, curved arm that
wraps occlusogingivally around the labial aspect of the bracket body (Figure
9). A specific instrument is used to open and close the gates. Because the arm
is rigid, it does not substantially interact with the wire, thereby rendering the
Time™ bracket a ―passive‖ system.

Figure 9: The Time™ bracket in open and closed positions (Courtesy of Berger, 2000)

14

The TwinLock™ was introduced in 1998. It has a flat, rectangular
slide that is housed between that tie wings of an edgewise twin bracket (Figure
10). The slide is moved occlusally into the slot-open position with a universal
scaler. When the slide is moved gingivally into the slot-closed position with
finger pressure, it becomes a passive system (Berger, 2000).

Figure 10: The TwinLock™ bracket in open and closed positions (Courtesy of Berger, 2000)

Perhaps the most renowned self-ligating bracket system was introduced
by Dr. Dwight Damon in 1996 (Berger 2000). The Damon™ SL I is an
edgewise twin bracket with a metal labial cover that straddles the tie wings. In
1999, the next generation Damon™ SL II was brought to the market (Figure
11). It differed from the original Damon™ SL I by incorporating a flat,
rectangular slide between the tie wings. A special plier is used to open the
metal gates incisally in the maxillary arch and gingivally in the mandibular.
Once the slides are closed, the bracket becomes a passive tube.
The Damon™ SL bracket system was designed to satisfy the following
major criteria (Damon 1998):

15

a. Andrews Straight-Wire Appliance concept
b. Twin configuration
c. Slide forming a complete tube
d. Passive slide on the outside face of bracket
e. Bracket opening inferiorly in both arches

Figure 11: The Damon™ SL I open (A) and closed positions (B) (Courtesy of Berger, 2000),
Damon™ SL II (C) (Courtesy of Ormco)

A B C

In 2002 the In-Ovation R™ by GAC was introduced. This bracket
features an ―interactive‖ clip because it can provide both passive and active
control depending on the archwires used. Round leveling wires can freely
move to correct rotations during the initial leveling and aligning phase, while
full size rectangular wires are fully engaged into the base of the bracket by the
clip in the later stages of treatment for better torque control (Figure 12). A
new In-Ovation C™ is now available which has a partial ceramic face for
better esthetics.

16

Figure 12: The GAC In-Ovation R™ and In-Ovation C™ bracket (Courtesy of GAC
International)

In 2002, Unitek introduced the SmartClip™ self-ligating bracket,
which is different form other self-ligating brackets in that it does not have a
slide or clip to hold the wires (Figure 13). Instead it contains a nickel-titanium
clip on each side of the twin bracket that locks in the wire. The archwire is
inserted by using finger pressure to push it past the flexible clip. Remove
requires a special instrument from 3M Unitek™.

Figure 13: The Unitek SmartClip™ bracket (Courtesy of 3M Unitek)

With the increasing popularity of self-ligating brackets, many different

17

bracket designs are brought to the orthodontic marketplace each year. When
choosing a self-ligating bracket system, it is important to understand the
different types of systems (active vs. passive) in order to obtain the best and
most efficient orthodontic results.

18

III. Philosophy of Self-ligating Bracket Proponents
When the Damon™ self-ligating bracket was introduced to the market
in 1996, a novel orthodontic treatment philosophy also followed. In 1998,
Dr. Dwight Damon published an article titled ‗The rationale, evolution and
clinical application of the self-ligating bracket,‘ that stirred the orthodontic
community. Regardless of the type of appliance or treatment mechanics,
most orthodontists using conventional brackets believe in ―filling the slot‖
with the largest wire possible as soon as possible. In turn, this provides
them with a certain degree of control as they dictate the direction and
magnitude of force needed to move teeth. With enough force, teeth
eventually move to the desired position. Because archwires were held into
place with either metal or elastic ligature ties, heavy forces must be
introduced into the system in order to overcome the friction created at the
bracket/archwire interface before tooth movement can occur (figure 14).
However, Dr. Damon argues that the heavy forces generated by large sized
wires and traditional ligation methods are not physiologic because they
create force systems high enough to overpower the lip, tongue and cheek
muscular. Instead, he offers a philosophy of orthodontic treatment that
greatly differs from this classical school of thought.

19

Figure 14: Traditional archwire ligation vs. Damon self-ligating brackets
(Photo courtesy of www.dmdortho.com)

TRADITIONAL BRACES
WITH LIGATURES

Elastic ligatures create friction and
require more force and more
frequent adjustments.
DAMON SELF-LIGATING
BRACES

Damon braces allow freedom of
movement, resulting in faster
treatment with gentler forces.

Light forces are the key to self-ligation. Dr. Damon suggests that low-
force, low-friction systems allow teeth to travel to their physiologic position
because they do not overpower the musculature or compromise the periodontal
tissues. Ischemia is not induced in the surrounding periodontal tissues because
the forces generated by the small dimension, high-tech archwires are too low to
completely occlude the periodontal vascular supply (Damon, 1998). Heavy
forces on teeth cause hyalinization in the periodontal ligament space which
brings tooth movement to a halt. Self-ligating brackets place enough force on
the teeth to stimulate tooth movement without completely disrupting the
vascular supply and therefore, tooth movement is more effective and
physiologic. The final position of the teeth after treatment with the Damon™
self-ligating bracket system is determined by the balanced interplay between
the oral musculature and periodontal tissues and not by heavy orthodontic
forces.

20

The design of the Damon™ self-ligating bracket also enables teeth to
move in the path of least resistance. When the gate is in its‘ closed position,
the bracket essentially becomes a tube in which the flexible nickel-titanium
archwire can move freely. By greatly reducing the amount of friction with
passive self-ligating brackets, low force archwires can work to peak expression
and stimulate teeth to move in a more biologically compatible method. Tooth
movement is also more efficient when they are allowed to move individually,
and passive self-ligating brackets offer more freedom for each tooth to move to
their natural position even though they are still interconnected because the
archwire is never tightly engaged with the bracket slot (Damon, 1998).
The Damon bracket allows the dental arches to develop through light
forces and thus Ormco recommends the following archwire sequence that is
most compatible with the Damon™ System:
Light Round Wire Phase

.014 Damon Copper Ni-Ti Initial archwire – Start tooth movement,
leveling, begin arch form development, prepare for next archwire.

.016 Ni-Ti SE - Used occasionally as second archwire in severely
crowded adult cases that are not quite ready for the second phase
archwire.

High-Tech Edgewise Phase

.014 x .025 Damon Copper Ni-Ti - the workhorse of the second phase.
Placed in upper and lower well-prepared arches.

018 x .025 Damon Copper Ni-Ti - the wire in the high-tech edgewise
phase. Excellent wire to prepare for insertion of the working stainless
steel transition wire.

21

.017 x .025 Damon Ni-Ti - used with 20° of anterior torque and reverse
curve; superb for division 2 second wire. If only intrusion needed, use
the same size wire without the torque in the anterior.

.019 x .025 Damon Ni-Ti - used with 20° of anterior torque and reverse
curve. Great follow-up wire on challenging division II cases. If only
intrusion needed, use the same size wire without the torque in the
anterior.

22

IV. Friction in Orthodontics
1. Ligation Method
Several commonly used ligation methods in orthodontics
include: stainless steel wires, elastomeric ligatures, and brackets with a
built-in sliding gate or clip. Each has their own distinct advantages and
disadvantages. Stainless steel ligatures were the first ligation method
and have several positive properties. They do not deform in the oral
environment, are more hygienic and easier to clean than their
elastomeric counterparts, and when they loosely tied, they are generally
thought to exert less friction than elastomers (Bednar et al., 1991).
However, their biggest disadvantage is the amount of time it takes to tie
them in. One study noted that on average, it took six to seven minutes
to tie in a single arch using stainless steel ligatures (Berger, 2001).
Tissue laceration can also occur if the ends of a ligature wire are not
tucked in properly or the patient inadvertently exposes the sharp ends.
Also, the amount of force and friction placed on the archwire-bracket
system is dependent on the ligation force placed on it by the operator
(Ridley, 1979).
A second ligation method is elastomeric ligatures. Introduced
to the orthodontic marketplace in the 1970‘s, they became widely
popular due their ease of use and efficiency. The time required to

23

ligate one arch using elastomers is about two minutes whereas stainless
steel ligatures require six to seven minutes (Berger, 2001). Another
desirable property of elastomeric ligatures is that they can be used as a
chain for closing spaces or moving teeth in sliding mechanics.
However, it should be noted that elastomeric ligatures and chains
greatly increase friction and, therefore, increase the resistance to tooth
movement. When tied in a figure-8 configuration to fully engage an
archwire, friction increases another 70-220 percent over the standard
elastomeric configuration (Sims, 1993). Another disadvantage of
elastomeric ligatures is that they exhibit a rapid rate of force decay and
deformation both in vivo and in vitro (Ash, 1978). Lastly, they are less
hygienic than stainless steel ligatures because they can accumulate
more oral debris and are difficult to keep clean.
Self-ligating brackets are ligatureless and have a metal gate or
clip that when closed (with the exception of SmartClip™), converts the
slot into a tube by forming the fourth wall. From an efficiency
standpoint, they require the least amount of time for an archwire
change (Berger, 2001). Numerous studies have also shown dramatic
decrease in friction for self-ligating brackets and therefore require less
force to move teeth (Pizzoni, 1998, Shivapuja, 1994, Thorstenson,
2001). Several investigators have found significant reduction in chair

24

time as well as shortened treatment times (Hanson, 1986, Maijer,
1990,Shivapuja et al, 1994). Self-ligation also increases patient
comfort, protects the patient from soft-issue lacerations (when
compared to steel ligatures), and in most cases, improved hygiene.
However, in patients with poor oral hygiene, the metal slides and clips
may become blocked from the accumulation of calculus, but this can
usually be remedied with some light scaling on the affected areas.
Possibly the largest drawback of self-ligating brackets is their cost. On
average, they are three to four times price of conventional brackets.
2. Friction
In orthodontics, sliding mechanics is commonly used to move
teeth. Friction is defined as ―the resisting force tangential to the
common boundaries between two bodies when, under the action of an
external force, one body moves or tends to move relative to the surface
of the other‖ (Kajdas et al, 1990). The frictional force acts in the
direction opposite to the force causing the motion, and it is proportional
to the normal force, which is exerted perpendicular to the sliding
direction. Friction can be divided into two categories: static (the force
required to initiate tooth movement) and kinetic (the force that resists
motion). It is thought that static friction is more important in
orthodontics because when a tooth slides along an archwire, tooth

25

movement occurs in a series of short jumps instead of one continuous
movement. Static friction is needed to be overcome each time the tooth
moves a little and stops (Read et al., 1997).
Because sliding mechanics is important in orthodontics, a
considerable amount of research has concentrated on developing
archwires and brackets that can decrease the amount of static friction.
Redlich et al (2003) described 6 major variables that contribute to
orthodontic friction: the angulation of the archwire and bracket,
dimension and shape of the bracket and archwire, oscillating
displacements, repeated use of brackets, wet and dry situations, and
ligation method. Kapur et al (1999) confirmed that the mean frictional
force increased with repeated bracket use. Downing et al (1995)
studied the effect of artificial saliva on the static and kinetic frictional
forces

of stainless steel wires and found that, in most instances,
frictional forces were increased with the addition of saliva. Another
group confirmed the above information but also found that the kinetic
coefficient of friction in the wet (saliva) state was observed to be
reduced by 50 per cent when β-titanium archwires were used (Kusy et
al. 1991). Numerous studies have concluded that self-ligating brackets
significantly reduce friction when compared to brackets tied with
stainless steel or elastomeric ligatures (Hain 2002, Khambay et al.
2004, Thomas et al. 1998).

26

V. Properties of an Ideal Orthodontic Ligation System
Regardless of the type of bracket and ligation used, there are several
desirable properties for an ideal orthodontic ligation system described by
Harradine (2003):
1. Secure and Robust ligation :
Once a wire is ligated, it is desirable that it is secure and resistant to
inadvertent loss of ligation. Wire ligatures and self-ligating brackets
are good in this respect while elastic ligatures are more easily lost.
Elastic ligatures also experience significant force decay over time
(Taloumis et al, 1997).
2. Full Bracket Engagement:
In the finishing stages of treatment, full archwire engagement into the
bracket slot is desirable to attain full expression of torque. Wire
ligation and self-ligating bracket systems that are ―active‖ can maintain
adequate archwire engagement between office visits. Elastic ligatures
on the other hand frequently exert insufficient force even on fairly
flexible wires. A ―figure-8‖ configuration of elastic ligatures is better
in this respect but is still not as reliable as wire ligation.
3. Quick and Easy:
Wire ligation is a lengthy procedure and this is the main reason they are
not frequently used. Elastic ligatures are much faster to remove and

27

replace but self-ligating brackets have proved to be the most efficient in
this category (Maijer et al, 1990, Shipapuja, 1994).
4. Low Friction:
For sliding mechanics, brackets that experience low friction are the
most desirable. Low friction with self-ligating brackets have been
shown by many authors and they are far superior to brackets ligated by
elastic ligatures (Berger, 1990, Khambay et al, 2004, Tecco et al,
2005,Thorstenson, 2001). Stainless steel ligatures are also better than
elastic ligatures in this respect (Shivapuja et al, 1994).
5. Improves Patient Comfort and Hygiene:
Wire ligatures can cause tissue laceration if the cut ends are exposed
but they are very hygienic. Elastic ligatures are more comfortable than
wire ligatures but have the side effect of being less hygienic. Self-
ligating brackets with smooth labial slides or clips improves patient
comfort and are easy to clean (Damon, 1998).

28

VI. Root Resorption
External apical root resorption is an iatrogenic phenomenon that is
frequently associated with orthodontic treatment. Although most root loss
resulting from orthodontic treatment does not decrease the function or
longevity of the affected tooth, it is still an undesirable occurrence.
Orthodontic forces applied to a biologic system act similarly on both bone and
cementum. Usually, cementum is more resistant to resorption and instead,
bone is resorbed and tooth movement occurs. However, cementum and dentin
can also be resorbed. The exact mechanism of root resorption is still unknown,
but several studies have shown that resorption lacunae can appear as early as
10 days after the application of orthodontic force (Reitan, 1974). If a small
amount of resorption has occurred, the root can heal but more severe instances
are permanent. When the applied force decreases below a certain threshold,
root resorption ceases and the affected teeth are allowed to begin the healing
process. A diagrammatic example of the different stages of root resorption, as
described by Levander and Malmgren, is shown below (Figure 15).

29

Figure 15: Root resorption scoring system by Levander and Malmgren (Photo courtesy of
Janson et al, 2000). Grade 0 – absence of resorption; Grade 1 – mild resorption, normal length
with slight irregularity in root contour; Grade 2 – moderate resorption, slight loss of root
structure at the apex with a straight contour; Grade 3 – severe resorption, loss of almost 1/3 of
the root length and apical blunting; Grade 4 – extreme resorption, greater than 1/3 of root
length.

Actual examples of root resorption after 3 and 6 months of orthodontic
treatment are shown in figures 16 and 17. Figure 16 shows a tooth with an
ordinary amount of root resorption whereas figure 17 is an example of a tooth
that has undergone moderate resorption after 6 months of treatment.

Figure 16: A tooth undergoing a normal amount of apical root resorption (Photo courtesy of
Levander et al, 1998); initial radiograph (A1), after 3 months of treatment (A2), after 6 months
of treatment (A3).

30

Figure 17: A tooth undergoing a moderate amount of apical root resorption (Photo courtesy
Levander et al, 1998); initial radiograph (B1), after 3 months of treatment (B2), after 6 months
of treatment (B3).

31

VII. Biologic Factors
Root resorption is a multi-factorial problem and it has been linked to the
following factors: age, sex, systemic conditions, type of malocclusion, tooth
anatomy, length of treatment, type of tooth movement, orthodontic force
magnitude, hereditary disposition, and the type of orthodontic appliance (Acar
et al, 1999, Brezniak et al, 1993). The biologic factors are discussed below.
1. Genetics:
Many studies have suggested a strong genetic component for short roots
but few specific genes have been confirmed (Newman, 1975). Recently,
several genes have been identified that contribute to root resorption. Of
particular significance is the Interleukin-1 gene cluster (figure 18). IL-1A
and IL-1B encode two proinflammatory cytokines, IL-1α and IL-1β
respectively, which are known to be potent stimuli for bone resorption (Al-
Qawasmi et al, 2003). IL-1RN encodes the protein IL-1ra which acts as a
receptor antagonist. IL-1β has been implicated in the process of resorption
during orthodontic treatment because increased levels of this cytokine have
been found in the gingival crevicular fluid and periodontal tissue of
orthodontic patients. In a mouse study comparing orthodontically treated
IL-1β knock-out mice to wild-type mice concluded that there was increased
apical root resorption in the IL-1βKO mice (Al-Qawasmi et al, 2004). This
study suggests that increased root resorption may be a consequence of

32

decreased bone remodeling due to the prolonged stress of the tooth against
alveolar bone in absence of IL-1β. In a human study composed of 35
white families, a polymorphism in IL-1B allele 1 was found to be
associated with relatively low production of IL-1β. The results of this study
indicate that orthodontic patients homozygous for the IL-1B allele 1
polymorphism have a 5.6 fold increase in external apical root resorption
over non IL-1B homozygous patients. They concluded that this gene
could account for up to 15% of maxillary incisor root resorption (Al-
Qawasmi et al, 2003). The increased susceptibility of some individuals to
root loss has been well documented and there is still ongoing research in
this area.

Figure 18: IL-1 gene cluster on long arm of chromosome 2 (2q13) (courtesy of Al-Qawasmi et
al, 2003)

33

2. Systemic Factors:
According to Becks (1936), endocrine problems such as
hypothyroidism, hyperthyroidism, and hyperpituitarism are related to
root resorption. Other systemic factors and pathologies have been
suggested but have yet to be confirmed. Hormonal imbalances have
also been implicated to exacerbate root resorption as well.
3. Gender:
Studies on gender and root resorption have conflicting results. Many
have shown no significant differences between the two sexes while
others suggest a stronger predilection for the females. Newman (1975)
found the idiopathic root resorption ratio to be 3.7:1 females to males,
respectively.
4. Age:
The relationship between orthodontic treatment and chronologic patient
age has been studied extensively. The majority of these studies
reported a positive relationship showing that adults had significantly
more root resorption than in children (Sameshima et al, 2001). Massler
and Malone (1954) claimed that even without orthodontic treatment,
the incidence of root resorption increases with age.
5. Root Morphology:
Research has shown that certain shapes are more prone to post-
orthodontic root resorption. Teeth with pipette-shaped roots experience

34

the most resorption out of all the root types (Levander et al, 1994).
Dilacerated roots also are also more susceptible to resorption.
6. Specific Tooth Vulnerability to Root Resorption:
Because different teeth have dissimilar root morphologies, it is not
surprising that some teeth are more likely to have root resorption. Most
reports show that maxillary teeth have a higher tendency for resorption.
Of all the maxillary teeth, the lateral incisors have the highest amount
of root resorption (Sameshima, 2001). Others have found the
mandibular incisors to be the most affected (Sjolien, 1973). Molars and
bicuspids experience the least resorption.
7. Presence of Resorption Before Orthodontic Treatment:
There is a high correlation between the amount and the severity of root
resorption present before treatment to the root resorption discovered
when the orthodontic appliance is removed (Massler et al, 1954).
Artun et al (2005) found that patients with detectable root resorption on
periapical radiographs during the first 6 months of treatment were more
likely to experience resorption in the following months of treatment.
8. Endodontically Treated Teeth:
Wickwire et al (1974) noted that endodontically treated teeth have
increased severity and frequency of root resorption. Others have found
little to no differences between vital teeth and endodontically involved
teeth (Esteves et al, 2007).

35

VIII. Mechanical Factors
1. Type of Appliance:
Several studies have stated that the degree of root resorption is a
function of the appliance used. Linge et al (1983) concluded that fixed
appliances are more detrimental to the roots and removable ones.
Another study found that an edgewise appliance demonstrated
significantly less resorption when compared with patients treated with a
Begg appliance (McNab et al, 2000). The Begg and Tweed appliances
displayed similar amounts of root resorption (Beck, 1994). Reukers et
al (1998) concluded that the degree of root resorption was independent
of the appliance used when comparing edgewise and strightwire
appliances. Blake et al (1995), showed that males treated with
edgewise brackets showed more root resorption than the male Speed
bracket (self-ligating) group. With the increase in the number and
types of appliances available, there will surely be more research
devoted to this topic.
2. Intermaxillary Elastics:
Linge and Linge (1983) found significantly more root resorption on the
side where elastics were used in a split-mouth study. They suggested
that jiggling forces the result of function combined with elastics are
responsible for the incisor root resorption in their study. Mandibular

36

first molar distal root resorption was increased in patients using Class
III elastics in a study by Rudolph (1940).
3. Extraction, Nonextraction, and Serial Extraction:
Several studies have found no difference in root resorption in extraction
versus nonextraction treatment (McFadden et al, 1989, VonderAhe,
1973). However, more recent studies how shown the opposite (Blake
et al, 1995, Sameshima et al, 2001) and this may be due to other
variables such as contemporary treatment modalities and appliances.
Serial extractions without orthodontic treatment gave the least root
resorption when compared to serial extractions with orthodontic
treatment or to four premolar extraction treatment followed by fixed
appliance treatment (Kennedy et al, 1983)
4. Orthodontic Movement Type:
Every type of orthodontic tooth movement can cause root resorption.
However, intrusion has proven to cause the most resorption in many
instances (McFadden et al, 1989, Dermaut et al, 1986). Some have
postulated that this is due to the root shape of the incisors (Thurow,
1982). Because the incisors are tapered and cone-shaped, the intrusive
pressure from the axial component of orthodontic forces will be
maximized at the root apex. Parket et al (1998) found that apical and
incisal vertical movements and increase in incisor proclination were the

37

positive predictors of external apical root resorption. They also noted
that incisor intrusion with an increase in lingual root torque together
were the strongest predictors of root resorption. Kaley et al (1991) also
found that approximation of the maxillary incisor roots to the lingual
cortical plate and root torque greatly increased the severity of root
resorption. According to Reitan (1964) the risk of resorption due to
bodily tooth movement is less than that for tipping.
5. Orthodontic Force:
The degree of force has been shown to be related to the amount of root
resorption in many cases. Harry and Sims (1982) found the distribution
of resorbed lacunae was directly related to the amount of stress on the
root surface and the rate of lacunae development was more rapid with
increasing applied forces. Their study concluded that higher stresses on
teeth cause more root resorption. Another study found that the optimal
force for tooth movement was between 20-26 gm/cm
2
. Owman-moll et
al (1996) noted that there was not significant change in tooth movement
or resorption when the orthodontic force was doubled from 50g to
100g. However, when the force was increased four-fold (200g), this
same group found that root resorption did not increase significantly but
the amount of tooth movement did (Owman-moll et al, 1996). In both
studies, the authors found large variations in both the frequency and
severity of root resorption and attributed this to each patient‘s

38

individual biologic response to the applied orthodontic force rather than
just increasing force magnitude. In another study, the hardness and
elasticity of human premolar cementum was compared after applying
light or heavy orthodontic forces for 4 weeks. The authors found that
heavy forces decrease both the elasticity and hardness of cementum
(Chutimanutskul et al, 2006). This finding is important because if the
hardness of root cementum is related to root resorption, then harder
teeth should resorb less and the utilization of light orthodontic forces
could be used to lessen apical root resorption. Heavy forces also alter
the mineral content of cementum (overall decrease in Ca content in the
cementum in areas under PDL tension) while light forces do not (Rex
et al, 2006). The authors of this study postulated that heavy
orthodontic forces may induce a decrease in pH in the surrounding
tissues, and in turn, cause an inhibition of osteoblasts and the
stimulation of osteoclasts. The net effect would be demineralization of
cementum in areas under heavy forces. Another study using a
microcomputed tomography scan noted that premolars intruded under
heavy forces (225g) exhibited larger and more resorption craters than
premolars intruded with 9 times less force (Harris et al, 2006). 3D
studies have also shown that teeth subjected to heavy orthodontic
forces cause more resorption by volume than light force and control
groups (Darendeliler et al, 2004). Other researchers have also

39

postulated that using intermittent orthodontic forces may be better than
continuous forces because they allow the resorbed cementum to heal
and prevents further resorption (Reitan, 1964).
6. Extent of Tooth Movement:
Many researchers believe that the farther a tooth is moved, the greater
the root resorption. The maxillary incisors are moved more often than
other teeth and it is not surprising that they experience the highest
degree of root resorption. A meta analysis of treatment-related factors
of external apical root resorption concluded that there is a high
correlation between total apical root displacement and mean apical root
resorption (Segal et al, 2004). Several studies have found a significant
correlation between the amount of overjet correction and retraction of
maxillary incisor apices with the degree of root resorption (de Freitas et
al, 2007, Sameshima 2001). Most studies have also found a positive
correlation between the amount of overbite and the degree of root
resorption. In particular, anterior open bite and deep bite patients have
been shown to experience more root resorption (Harris et al, 1992).
7. Duration of Treatment:
Most studies report that the severity and frequency of root resorption is
directly related to treatment duration. Levander and Malmgren (1988)
found that 34% of examined teeth showed root resorption after 6 to 9

40

months of treatment, whereas at the end of active treatment, lasting 19
months, root resorption increased to 56%. Taithongchai (1996) found
that the duration of treatment was the factor most highly correlated with
root resorption in maxillary incisors. In a sample of 625 patients,
Apajalahti et al (2007) determined that the mean duration of treatment
of patients with little to no resorption was 1.5 years while those in
treatment for a mean of 2.3 years had severe root resorption. Sengal et
al (2004) also found treatment duration to be highly correlated to root
resorption.

41

IX. Clinical Diagnostic Aids in Identifying Root Resorption
Radiographs are an important diagnostic tool in orthodontics. They are
used to identify key structures, detect caries, and assess developing teeth.
Typically, orthodontists utilize at least two types of radiographic films:
panoramic and cephalometric. These films are usually ordered as pretreatment
radiographs to help in diagnosis and treatment planning. They are also good
patient education tools. However, these two forms of radiographic films are of
limited use when fine details such as root form and resorption need to be
studied.
When individual teeth need to be examined in greater detail, periapical
films are the radiograph of choice. Panoramic films have a magnification
factor of 20-35% (Wyatt et al, 1994) whereas periapical films have less than
5% magnification when taken correctly (Larheim et al., 1979). In a study by
Gher and Richardson (1995), panoramic films were compared to periapicals in
order to determine which film was more accurate in determining the actual
length of a dental implant. They found that periapical films were accurate to
within 0.3mm of the actual implant length while panoramic films
overestimated the implant length from 0.4 mm to 1.7mm.
Abnormal root shape is also a factor associated with apical root resorption.
Sameshima et al (2001) noted that roots found to have an abnormal shape on
periapical films were rated normal on panoramic films in a large number of

42

cases. For orthodontic patients with a history of root resorption or those that
already posses short roots, periapical films are particularly important.
More recently, computed tomography has become more readily available
to the dental community. A study by Dudic et al (2008) compared the
accuracy of digital periapical films to micro computed tomography in detecting
orthodontically induced apical root resorption. This group found that less than
half of the cases with root resorption identified using the CT scanner were
identified by radiography. Another study demonstrated that 3D images of root
resorption craters was highly accurate and repeatable (Chan and Darendeliler,
2004). As cone beam computed tomography becomes more assessable and
affordable to orthodontists, it will surely become an excellent diagnostic tool
for detecting root resorption.
In clinical practice, friction generated at the bracket/archwire interface
tends to impede the desired tooth movement. The force applied must
overcome this frictional component before teeth can be moved. The method of
archwire ligation is an important factor in determining the generation of
friction. An alternate approach to reducing friction is to avoid using any
ligatures. With self-ligating brackets, this is possible. The consequence of a
reduction in friction is that lower levels of forces need to be applied to initiate
orthodontic tooth movement by sliding mechanics. Less force applied to the
teeth may also decrease the degree and frequency of external apical root
resorption.

43

Chapter Three: Hypothesis
I. Research Hypothesis, H
a
:
External apical root resorption is significantly lower for cases
treated with self-ligating Damon™ brackets than for cases treated
with conventionally-ligated brackets.

II. Null Hypothesis, H
0
:
There is no significant difference in external apical root resorption
between cases treated with self-ligating Damon™ brackets and
those treated with conventionally-ligated brackets.

44

Chapter Four: Materials and Methods
This study was approved by the University of Southern California
Health Sciences Institutional Review Board (HSIRB). The IRB approval ID is
HS-08-00428.
The sample was selected from orthodontic patients treated with either
self-ligating Damon™ SL brackets (N=37) or conventionally-ligated twin
edgewise brackets (N=37) from a private practice in Southern California. The
sample patients were predominantly of Caucasian or Hispanic ethnic
background. The Damon™ SL cases were selected randomly according to the
inclusion and exclusion criteria explained below. The conventionally-ligated
cases were selected such that they matched the Damon™ SL cases. The
matching criteria are explained below. Patient records include pre-treatment
and post-treatment facial and intra-oral photographs, full mouth radiographs,
panoramic and cephalometric radiographs, and treatment notes. Root length
was measured from the root apex to the right and left cementoenamel junctions
using a Cen-Tech™ Digital Caliper and then averaged. Root resorption was
calculated by subtracting the following root lengths: pre-treatment – post-
treatment.
Inclusion Criteria:
The criteria for inclusion were the following:
1. Same ligation method: Patient treatment that consisted of using the

45

same ligation method for the entire treatment and by the same
orthodontist; patients who were transferred into the practice after
treatment or was started elsewhere were not considered for this study.
2. Molar classification: Angle class I
3. Overjet: 2-3 mm
4. Overbite: 2-3 mm
5. Extraction Pattern: Non-extraction only
6. Maxillary anterior crowding: 3-4 mm
7. Mandibular anterior crowding: 3-4 mm
8. Gender: Female
9. Age: between 12-30 years of age
10. Ethnicity: Caucasian or Hispanic
11. Root formation: All roots must be completely formed at the start of
treatment
Exclusion Criteria:
In addition, the exclusion criteria for case selection were the following:
1. Expansion: Patients whose treatment required the use of any maxillary
or mandibular expansion device (e.g. rapid palatal expander, quad
helix, Schwartz appliance) were excluded from the study.
2. Extraoral appliances: Cases that utilized extraoral traction appliances
(e.g. facebow and headgear, reverse-pull headgear, J-hook headgear)
were excluded.

46

3. Functional appliances: Patients whose treatment included the use of
functional appliances (e.g. Herbst, MARA, twinblock, Forsus,
Bionator) were excluded.
4. Impactions: Cases with impacted teeth were excluded from the study.
5. Surgical treatment: Any patients whose orthodontic treatment was
combined with surgical treatment were excluded from the study.
6. Asymmetries: Cases with skeletal asymmetries were excluded from the
study.
7. TMJ dysfunction: Patients who had symptomatic TMJ‘s prior to
treatment or developed TMJ symptoms during treatment were excluded
from the study.
8. Parafunctional habits: Patients with parafunctional oral habits were
excluded.
9. Anterior open bite: Patients with an anterior open bite, whether skeletal
or dental were excluded from the study.
10. Trauma: Patients with a history of trauma to their teeth were excluded.
11. Abnormal root morphology: Patients with abnormal root morphology
such as dilacerations and pipette shaped roots were excluded from this
study.
12. Endodontically treated teeth: Endodontically treated teeth were
excluded.

47

Data Collection:
The following information was obtained and calculated using patients‘
treatment records and personal history forms:
1. Age at the start and completion of treatment
2. Treatment time in months
3. Ethnicity
4. Gender
5. Root lengths pre- and post-treatment
The following tables summarize the number of each ethnicity in both of the
groups:

Table 1: Summary of number of each ethnicity in the Conventional bracket group

Ethnicity
Ethnicity Frequency Percent
Cumulative
Frequency
Cumulative
Percent
Caucasian 31 83.78 31 83.78
Hispanic 6 16.22 37 100.00

48

Table 2: Summary of number of each ethnicity in the Damon™ bracket group

Ethnicity
Ethnicity Frequency Percent
Cumulative
Frequency
Cumulative
Percent
Caucasian 31 83.78 31 83.78
Hispanic 6 16.22 37 100.00

The following tables summarize the average start ages and treatment
duration of each group:

Table 3: Summary of average age and treatment time in the Conventional bracket group

Variable N Mean ± SD
(mm)
Age in Months 37 167.19 (41.95)
Age in Years 37 13.93 (3.49)
Treatment time in months 37 31.08 (6.65)
Treatment time in Years 37 2.59 (0.55)

Table 4: Summary of average age and treatment time in the Damon™ bracket group

Variable N Mean ± SD
(mm)
Age in Months 37 164.49 (40.02)
Age in Years 37 13.71 (3.34)
Treatment time in months 37 29.14 (8.13)
Treatment time in Years 37 2.43 (0.68)

49

Case Matching Criteria:
Cases in the Damon™ SL group and sub-groups were matched to cases
in the conventionally ligated group and sub-groups according to the following
criteria:
1. Overjet: Within 1 mm
2. Overbite: Within 1 mm
3. Mandibular anterior crowding: Within 1 mm
4. Maxillary anterior crowding: Within 1 mm
5. Extraction Pattern: Non-extraction
6. Ethnicity: Equal number of Caucasian and Hispanic patients in
both groups
Archwire sequence:
Table 5: Conventional and Damon Bracket Archwire Sequence
Conventional Bracket
0.018 inch slot
Damon Bracket
0.022 inch slot
014 ss or 0.175 twist 014 NiTi
016 ss 018 NiTi
018ss 18x25 NiTi PRN
16x22ss or 17x25 TMA PRN
17x25ss 19x25 TMA
18x25ss 19x25 ss PRN

50

Assumptions:
There are many factors that could potentially influence the rate of
orthodontic tooth movement, thus influencing the amount of external apical
root resorption. Therefore, this study was based on the following assumptions:
1. The biological differences in the rate of root resorption due to
orthodontic forces among patients are controlled for by the size of
the sample.
2. Patients do not have a known predisposition to root resorption

3. The treatment protocol (archwire sequence, treatment mechanics,
etc.) is assumed to be similar for all of the cases in the 2 groups
(Damon™ and conventional edgewise).
4. The cases in the two groups are matched closely and appropriately
for the purpose of this study.
5. Differences in treatment mechanics among patients do not
significantly affect treatment duration.
6. All the cases considered in this study are finished similarly with
respect to dental irregularities and quality of finish.
7. The protocol used for this study is appropriate and reproducible

51

Method Error:
The root lengths for each tooth in this study were re-measured 2 weeks
after the original data was collected. No significant differences were found.
The same operator measured all of the root lengths each time. Because of the
retrospective nature of this study, the error from the radiographic procedure
could not be studied. However, patients for this study were selected based on
the knowledge that the initial and final periapical radiographs were taken on
the same x-ray machine. The same dental records laboratory was used for all
of the conventionally treated brackets. For the self-ligating bracket group, the
same in-office digital x-ray machine was used and all of the radiographs were
taken by one operator. Any radiographs exhibiting foreshortening or
elongation were excluded from this study. Variables that could not be
controlled include: film/patient position, film developing solutions and times
(for the conventional group), accuracy of the x-ray unit, and the ability of the
x-ray technician to follow the instructions of the x-ray unit manufacturer.
These sources of error are assumed to be insignificant.

Statistical Analysis:
All data were entered into Microsoft Excel worksheet and were
analyzed using Excel and Statistical Package for Social Sciences (SPSS)
version 17.0. Independent t-tests or one-way Anova tests were performed to
compare the two groups. Significance was established at alpha = 0.05.

52

Chapter Five: Results
There is a statistically significant difference in mean root resorption
between the conventional and Damon™ bracket groups (p=.0076). The mean
root resorption of the conventional group was 0.59 mm while the Damon™
group was 0.42mm (table 5).

Table 6: Mean root resorption by treatment group
Group Mean ± SD
(mm)
Conventional 0 .59 ± 0.12
Damon 0.42 ± 0.16
(Conventional- Damon) 0.17 ± 0.14

There is a statistically significant difference in root resorption in the upper
right canine (p=.0072), the upper right lateral (p=.006), and the upper left
lateral (p=.01) between the conventional bracket and Damon bracket group.
There is a marginally significant difference in root resorption in the upper left
central (.052) between the Conventional and Damon bracket groups (table 6).
There was no significant difference in root resorption between the two groups
in the mandibular teeth (table 7).

53

Table 7: Mean difference in root resorption between Conventional and Damon groups in the
maxillary arch

Tooth Mean Difference (mm) P-Value
UR3 0.45 ± .63 0.0072
UR2 0.58 ± .58 0.0006
UR1 0.19 ± .53 0.20
UL1 0.30 ± .53 0.052
UL2 0.52 ± .73 0.01
UL3 0.15 ± 1.03 0.62

Table 8: Mean difference in root resorption between groups in the mandibular arch

Tooth Mean Difference (mm) P-Value
LR3 -0.16 ± .55 0.33
LR2 0.22 ± .43 0.08
LR1 0.13 ± .52 0.40
LL1 0.07 ± .37 0.53
LL2 0.16 ± .40 0.16
LL3 0.08 ± .30 0.34

The tooth with the largest amount of root resorption in the maxillary arch for
both groups was the upper right lateral incisor. The upper right lateral incisor
in conventional group had 1.08mm of root resorption while the Damon group
had .49mm of resorption (Table 8). The tooth with the least amount of
resorption in the maxillary arch was the upper left canine (0.52mm) in the
conventional group and the upper right canine (0.27mm) in the Damon group.

54

The upper right lateral incisor had the greatest difference in root resorption
(0.58mm) between the two groups in the maxillary arch.
Table 9: Mean root resorption in the maxillary arch between the two groups
Tooth Treatment N Mean ± SD
(mm)
UR3 Conventional 30 0.72 ± 0.71
UR3 Damon 30 0.27 ± 0.53
UR2 Conventional 36 1.08 ± 0.84
UR2 Damon 33 0.49 ± 0.44
UR1 Conventional 35 0.64 ± 0.77
UR1 Damon 34 0.45 ± 0.39
UL1 Conventional 34 0.76 ± 0.75
UL1 Damon 35 0.46 ± 0.46
UL2 Conventional 36 0.96 ± 1.17
UL2 Damon 36 0.44 ± 0.30
UL3 Conventional 32 0.52 ± 1.60
UL3 Damon 30 0.37 ± 0.55

The tooth with the largest amount of resorption in the mandibular arch was the
lower right lateral incisor (0.67mm) for the conventional group and the lower
right canine for the Damon group (0.73mm). The tooth in the mandibular arch
with the lowest amount of root resorption was the lower left central incisor
(0.43mm) in the conventional group (Table 9). The teeth with the least amount
of root resorption in the Damon group were the lower left central incisor
(0.37mm) and the lower left lateral incisor (0.37mm). The tooth with the

55

greatest difference in root resorption between the two groups was the lower
right lateral incisor.
Table 10: Mean root resorption in the mandibular arch between the two groups
Tooth Treatment N Mean ± SD
(mm)
LR3 Conventional 31 0.57 ± .61
LR3 Damon 32 0.73 ± .68
LR2 Conventional 35 0.67 ± .64
LR2 Damon 37 0.45 ± .32
LR1 Conventional 35 0.60 ± .70
LR1 Damon 36 0.47 ± .50
LL1 Conventional 35 0.43 ± .54
LL1 Damon 35 0.37 ± .29
LL2 Conventional 35 0.53 ± .59
LL2 Damon 37 0.37 ± .30
LL3 Conventional 35 0.53 ± .41
LL3 Damon 32 0.45 ± .28

For the Conventional group, there is no statistically significant difference in
mean root resorption between the mandibular and maxillary teeth (p=.76, table
10). For the Damon group, there is a slightly significant difference in mean
root resorption between the mandibular and maxillary teeth (p=.52). Both of
these tests were done using a two sample test (table 11). For the conventional
bracket group, there was no statistically significant difference in mean root
resorption among the canine, lateral, and central teeth (p=.24) in both arches.

56

For the Damon bracket group, there was no statistically significant difference
in mean root resorption among the canine, lateral, and central teeth (p=.26) in
both arches.
Table 11: Difference in root resorption between mandibular and maxillary teeth in the
Conventional Group

Group Mean ± SD
(mm)
Mandibular 0.60 ± 0.13
Maxillary 0.58 ± 0.13
Mandibular-maxillary 0.02 ± 0.13

Table 12: Difference in root resorption between mandibular and maxillary teeth in the
Damon Group

Group Mean ± SD
(mm)
Mandibular 0.41 ± 0.08
Maxillary 0.37 ± 0.12
Mandibular-maxillary 0.04 ± 0.10

There is no significant difference between the two groups with regard to start
age, treatment time, and the frequency of each ethnicity (tables 1-4). There is
no statistically significant difference in the root resorption between ethnicities
in the conventional group (table 12). Only the lower right canine (p=0.009)
showed a statistically significant difference in root resorption between the two
ethnicities in the Damon group (table 13).

57

Table 13: Mean difference in root resorption between ethnicities: Conventional Group

Tooth Mean Difference (mm) P-Value
UR3 0.28 ± .72 0.41
UR2 0.51 ± .83 0.18
UR1 0.19 ± .17 0.59
UL1 0.26 ± .78 0.49
UL2 0.25 ± 1.19 0.64
UL3 -0.10 ± 1.63 0.90
LR3 0.13 ± .62 0.67
LR2 0.33 ± .64 0.26
LR1 0.38 ± .70 0.23
LL1 0.30 ± .53 0.21
LL2 0.26 ± .59 0.34
LL3 0.04 ± .41 0.82

Table 14: Mean difference in root resorption between ethnicities: Damon Group

Tooth Mean Difference (mm) P-Value
UR3 -0.028 ± .53 0.29
UR2 0.25 ± .43 0.24
UR1 -0.10 ± .39 0.73
UL1 0.21 ± .46 0.31
UL2 -0.19 ± .29 0.16
UL3 -0.02 ± .56 0.95
LR3 0.46 ± .67 0.009
LR2 0.06 ± .32 0.66
LR1 0.13 ± .51 0.58
LL1 -0.06 ± .29 0.66
LL2 -0.02 ± .30 0.91
LL3 0.19 ± .27 0.14

58

Chapter Six: Discussion
The primary purpose of this study was to compare treatment data from
patients treated with two different types of brackets; the Damon™ self-ligating
bracket and the twin edgewise conventionally-ligated bracket. We
hypothesized that, on average, patients treated with self-ligating Damon™
brackets would have less external apical root resorption than cases treated with
conventionally-ligated twin edgewise brackets.
Sample Analysis
The sample was collected from a private practice according to specific
predetermined inclusion and exclusion criteria (materials and methods). The
mean start age, treatment length, and frequency of Caucasian and Hispanic
females were similar in both groups.
Treatment Outcomes
All the selected cases were treated by the same orthodontist in a private
practice setting. Thus, it is assumed throughout this study that the treatment
outcomes of the selected cases are comparable. However, no initial or final
dental irregularity index (PAR or ABO) was used to confirm this assumption.
The results and conclusions of this study could be discounted if this
assumption (which is central to this study) is not satisfied. Therefore, caution
must be used in interpreting the results and generalizing conclusions drawn
based on these interpretations. Interestingly, a study by Eberting (2001)

59

reported that their treatment outcomes showed higher ABO scores for cases
treated with Damon™ brackets than conventional twin brackets.
Significance of the Findings
External apical root resorption occurs mainly in the anterior teeth.
Therefore, this study only collected data from canine to canine in both dental
arches. There was no significant difference in the amount of root resorption
between the left and right sides or between the maxillary and mandibular
arches in both cases. There was no significant difference in resorption between
the two ethnicities, start ages, or treatment time between the two groups.
The greatest difference in the amount of root resorption between the
groups was found in the maxillary anterior teeth. Root resorption in the
maxillary anterior teeth ranged from 0.52mm to 1.08mm for the conventional
group while the range for the Damon group was 0.27mm to 0.49mm. The
lateral incisors had the largest difference in the amount of resorption between
the two groups. This confirms the findings of other studies that also found
maxillary lateral incisors to be the most affected (Brezniak et al, 1993,
Sameshima et al, 2001). Several reasons can be attributed this. The roots of
maxillary lateral incisors are often displaced mesially and need to be moved a
significant distance distally to orient them correctly. Lateral incisors have
narrow and/or curved roots which can lead to a greater frequency and degree of
resorption. The maxillary centrals and canines also had a significant difference
in amount of resorption between the two groups.

60

The mandibular teeth did not show a significant difference in root
resorption between the groups. This could be due to the fact that all the cases
in the study began in Angle Class I molar occlusion, had mild anterior
crowding, and a relatively level Curve of Spee. Various studies have shown
that intrusive movements cause an increased amount or resorption of the
incisors because the orthodontic force is focused on the apex of the incisor
roots (Beck et al, 1994, Parker et al, 1998). Another study, comparing deep
overbites treated with accentuated and reversed curve of Spee in the archwire
against patients with normal overbites, concluded that the deep overbite
patients experienced significantly more root resorption when the incisor apices
were displaced vertically (Chiqueto et al, 2008). In this study, there was very
little need to intrude lower incisors since overbite and overjet were normal at
the beginning and end of treatment. Therefore, it is not surprising that the root
resorption in lower incisors did not differ by a large extent between the groups.
Additionally, a study by Scott et al (2008) found no significant difference in
mandibular incisor root resorption or alignment efficiency between the
Damon3 system and cases treated with conventionally ligated brackets which
further supports the findings of this study.
The primary difference between the two groups in this study was the
type of ligation. The Damon system is a passive, ligatureless bracket system.
Traditionally, archwires are secured into place with ligature wires or elastic

61

modules. The friction created between the archwire/bracket/ligature interfaces
need to be overcome before tooth movement can occur. In a passive, self-
ligating system, the archwires are never completely locked into place and the
teeth are free to move in the path of least resistance. In turn, lower force levels
are needed to move teeth. This may be beneficial to orthodontists because
studies have shown that higher force levels can lead to increased root
resorption (Owman et al, 1996). In this study, every tooth in the Damon
group, except for the mandibular right canine, showed less mean root
resorption than it‘s counterpart in the conventionally treated group. The cases
in both groups were closely matched for gender, start age, treatment duration
and my other factors thought to be associated with increased incidences of root
resorption.
No exact criteria have been found to accurately predict which patients
will experience overt root resorption and which will exhibit little resorption
under the same treatment regimens. This study attempted to decrease the
number of variables that could affect the amount of resorption. Therefore,
only patients that received non-extraction treatment were chosen for this study.
Extraction treatment usually extends treatment time and also increases the
distance certain teeth must be moved. These two factors have been shown to
increase root resorption in some instances and therefore were excluded from
this study.

62

There are several possible reasons why the patients‘ treated with the
Damon self-ligating bracket experienced less external apical root resorption in
this study. Multiple sources have shown that heavy orthodontic forces increase
root resorption. The Damon system incorporates a passive self-ligating bracket
with a low-force, nickel-titanium wire sequence. Unlike conventionally ligated
brackets that require a stainless steal or elastic ligature to hold the archwire in
the bracket slot, the Damon self-ligating bracket does not tightly bind the
archwire to the bracket. In turn, there is less friction created between the
archwire and the bracket slot which ultimately results in less force required to
move teeth. Recent studies have shown that heavy forces can exhibit a 3.31
fold greater total resorption volume on cementum than light forces
(Darendililer et al, 2004). When an unknown amount of friction is created
between the bracket/archwire interface in a conventionally ligated appliance,
the orthodontist must somehow determine the appropriate amount of force to
apply to the teeth in order for tooth movement to occur. Mal-aligned teeth
differ in the amount of force needed to move each tooth due to differences in
tip, torque, and rotations. The orthodontist must then use their best judgment
to determine how much force they must introduce to the system to move teeth,
and often, heavy forces must be applied to overcome the high friction in
conventionally ligated brackets. On the other hand, self-ligating brackets can
theoretically allow small dimension, low force wires to fully express

63

themselves for each individual tooth because they are not tightly bound to the
bracket. Different forces can be applied to each tooth, but the lip, cheek, and
tongue muscles are not overpowered. Because the teeth are allowed to move
in a more ―physiologic‖ manner, less root resorption can be expected and this
could be one of the reasons for the results obtained in the study.
Another possible reason for less external apical root resorption in the
patients treated with the Damon appliance could be related to the changes in
the elasticity and hardness of cementum in response to different force levels.
Chutimanutskul et al (2006) found that heavy forces decrease both the
elasticity and hardness of cementum when heavy forces were applied to
premolars while low forces had no effect on those properties. Theoretically,
harder teeth should experience less root resorption. If orthodontic force is
increased, the hardness of a tooth is inversely affected, and root resorption is
more likely to occur. If future research validates this belief, self-ligating
brackets would be a better alternative than conventionally ligated brackets for
patients prone to root resorption.
A study by Chan and Darendeliler (2006) provides evidence that
orthodontic force magnitude positively correlates with root resorption. They
determined that there was more resorption in areas under heavy compression
and tension than similar areas under light compression and tension.
Proponents of passive self-ligating brackets believe that the blood supply to the

64

teeth is not occluded because the light forces exerted on the periodontal
ligament space do not completely occlude the vasculature to the extent that
sterile necrosis or hyalinization occurs. Instead, light forces only partially
compress these vessels in the PDL and no hyalinization occurs. It has been
reported that hyalinization precedes root resorption (Thilander et al, 2000) and
as the necrotic hyalinized tissues are removed by osteoclasts and other
multinucleated cells, cementum may also be removed. If the process
hyalinization can be prevented or decreased by using lighter forces, then self-
ligating brackets have a distinct advantage over conventionally ligated brackets
with regard to root resorption.
The difference in torque expression between a passive self-ligating
bracket system and a conventionally ligated bracket system is another variable
that could explain the differences in root resorption found in this study
between the two groups. In a study by Mornia et al (2008), the torque
expression of six different brackets including the Damon2 and a stainless steel
bracket were measured. All of the brackets were 0.022 inch slot and 20
degrees of torque was placed into a 19x25 stainless steal archwire. The
stainless steel bracket presented with the greatest torquing moment while the
Damon2 bracket had a 7-fold decreased moment in contrast. Another study
comparing torque expression between active and passive self-ligating brackets
concluded that torque expression was higher for active self-ligating brackets up
to 35 degrees of torsion (Badawi et al, 2008). In the finishing stages of

65

orthodontic treatment, active self-ligating brackets are comparable to
conventionally-ligated brackets because the wire is firmly engaged in the
bracket slot. In this study, the conventionally treated cases were finished with
a 18x25ss archwire in a 0.018 inch slot bracket. The majority of Damon
treated cases were finished with a 19x25 TMA wire in a 0.022 inch slot.
According to Proffit (2000), the effective torque in an 18-slot bracket with a
18x25 stainless steal archwire is much greater than an 19x25 stainless steal
archwire in a 22-slot bracket with the average difference in effective torque
being around 8 degrees. Many studies have shown that increased torque of
maxillary incisors and moving roots against the lingual cortical plate increases
root resorption. With more play in a passive self-ligating system such as the
Damon system and comparatively smaller rectangular archwire used in the
Damon cases, less effective torque is expressed on the maxillary incisors and
this could account for the results of this study. Additionally, TMA wires
deliver much less torque than stainless steal wires of the same dimensions
(Gioka et al, 2004). The cases treated with Damon brackets in this study were
primarily finished with TMA whereas the conventionally ligated cases used
stainless steal archwires. Lastly, a study by Pandis et al (2006) found no
difference in the angulation of maxillary incisors after treatment with a
conventionally ligated bracket and the Damon2 bracket. Both groups followed
the same archwire sequence: 014 Niti, 016NiTi, and 19x25 stainless steel.

66

However, the study by Pandis et al did not treat the Damon2 cases according to
Ormco‘s recommended archwire sequence and perhaps the results of their
study may have been different if they had done so.
Finally, it is interesting to note that another study evaluating external
apical root resorption between patients treated with conventional and self-
ligating brackets found no significant difference between the two groups
(Pandis et al, 2007). However, the patients in this pool included both sexes,
treatment finished in stainless steal wires for both groups, only a 0.022 inch
bracket slot were used, extraction and non-extraction cases were included, and
the root measurements were collected from panoramic radiographs instead of
periapical films. The combination of all of these factors could account for the
contradicting results between their study and our current findings. Further
investigation is necessary to elucidate if different ligation methods do affect
root resorption.
With the increasing body of evidence that links force magnitude and
increased incisor torque to higher rates of external apical root resorption, more
studies are likely to ensue to determine if self-ligating brackets do indeed
decrease the frequency and severity of root resorption.

67

Limitations
There were several limitations in this study:
1. The retrospective nature of the study.
2. Difficulty in controlling all the variables that affects root resorption,
including but not limited to biology of tooth movement of each
individual patient, patient cooperation, changing treatment mechanics,
and unknown documentation of a predisposition to resorption.
3. Limited number of practices with available cases for data collection.
Our sample was obtained from one private practice and represents the
situation in that practice only.
4. Lack of use of a measure for quality of treatment. We did not use ABO
or PAR indices to compare quality of treatment outcome. However,
because all the patients were treated by one practitioner, it was assumed
that they were treated to equivalent dental irregularities. The treating
orthodontist is a diplomat of American Board of Orthodontics and was
also a Tweed instructor for many years.
5. The treatment philosophy of the treating orthodontist may have
changed significantly during the period from which the data is
collected.

68

Chapter Seven: Conclusion
Although external apical root resorption is still largely unpredictable,
patients treated with self-ligating brackets may experience less root resorption
overall. The results of this study indicate that there is less mean resorption in
virtually every tooth treated with the self-ligating bracket. Patients treated
with self-ligating brackets had significantly less root resorption in their
maxillary anterior teeth than their conventionally ligated counterparts. These
findings may be due to the lower forces and decreased torque levels applied to
the dentition by self-ligating brackets. These results add to the many
advantages that self-ligating brackets possess. Further research is needed to
help determine if similar results can be obtained when different variables are
introduced into the study such as adult patients, patients that have undergone
extraction treatment, and different ethnicities. With the increasing availability
of cone-beam computed tomography, extremely precise root measurements
will soon be possible and hopefully this study can be further validated. The
results of this study should be interpreted with the knowledge that they may
only be relevant to the patients selected in this very specific sample group and
should not be universally applied.

69

References

1. Acar A, Canyurek U, Kocaaga M, Erverdi N. Continuous versus
discontinuous force application and root resorption. Angle Orthod. 1999;
69:159–164.

2. Al-Qawasmi RA, Hartsfield JK, Everett ET, Flury L, Liu L, Foroud TM,
Macri JV, Roberts WE. Genetic predisposition to external apical root
resorption. Am J Orthod Dentofac Orthop. 2003; 123:3:242-52.

3. Al-Qawasmi RA, Hartsfield JK Jr., Everett ET, Weaver MR, Foroud TM,
Faust DM. Roberts WE. Root resorption associated with orthodontic force
in inbred mice: genetic contributions. European Journal of Orthodontics
2006; 28(1):13-9.

4. Al-Qawasmi RA, Hartsfield JK Jr., Everett ET, Weaver MR, Foroud TM,
Roberts WE. Root resorption associated with orthodontic force in IL-1B
knockout mouse. J Musculoskel Neuron Interact 2004; 4(4):383-385.

5. Apajalahti S. Peltola JS. Apical root resorption after orthodontic treatment
-- a retrospective study. European Journal of Orthodontics 2007;
29(4):408-12.

6. Artun J. Revisiting root resorption. Am J Orthod Dentofac Orthop. 2000;
118:14 A letter to the editor.

7. Artun J. Smale I. Behbehani F. Doppel D. Van't Hof M. Kuijpers-Jagtman
AM. Apical root resorption six and 12 months after initiation of fixed
orthodontic appliance therapy. Angle Orthodontist 2005; 75(6):919-26.

8. Ash LJ, Nikolai RJ. Relaxation of orthodontic elastomeric chains and
modules in vitro and in vivo. Journal of Dental Research 1978;57(5-
6)685-90.

9. Badawi HM, Toogood RW, Carey JP, Heo G, Major PW. Torque
expression of self-ligating brackets. Am J Orthod Dentofacial Orthop.
2008;133(5):721-8

10. Beck BW, Harris EF. Apical root resorption in orthodontically treated
subjects: analysis of edgewise and light wire mechanics. Am J Orthod
Dentofac Orthop. 1994; 105:350–361.

70

11. Becks H. Root resorption and their relation to pathologic bone formation.
INT J OR'ntOD 1936;22:445-82.

12. Bednar JR, Gruendeman GW, Sandrik JL. A comparative study of
frictional forces between orthodontic brackets and archwires. Am J Orthod
Dentofacial Orthop 1991;97:219-28.

13. Berger JL. The influence of the SPEED bracket‘s self-ligating design on
force levels in tooth movement: A comparative in vitro study. American
Journal of Orthodontics and Dentofacial Orthopedics 1990;97(3):219-28.

14. Berger JL, Byloff FK. The clinical efficiency of self-ligating brackets.
Journal of Clinical Orthodontics 2001;35(5):304-08.

15. Berger JL. Self-ligation in the year 2000. Journal of Clinical
Orthodontics 2000;35(2):74-81.

16. Berger JL. The SPEED appliance: A 14-year update on this unique self-
ligating orthodontic mechanism. American Journal of Orthodontics and
Dentofacial Orthopedics 1994;105:217-23.

17. Blake M, Woodside DJ, Pharoah MJ. A radiographic comparison of apical
root resorption after orthodontic treatment with the edgewise and speed
appliances. Am J Orthod Dentofac Orthop. 1995; 108:76–84.

18. Brezniak N, Wasserstein A. Root resorption after orthodontic treatment:
Part 1. Literature review. Am J Orthod Dentofac Orthop. 1993; 103:62–66.

19. Brezniak N, Wasserstein A. Root resorption after orthodontic treatment:
Part 2. Literature review. Am J Orthod Dentofac Orthop. 1993; 103:138–
146.

20. Cacciafesta V, Sfondiri MF, Ricciardi A, Scribante A, Klersy C, Auricchio
F. Evaluation of friction of stainless steel esthetic self-ligating brackets in
various bracket-archwire combinations. American Journal of Orthodontics
and Dentofacial Orthopedics 2003;124:395-402.

21. Chan EK. Darendeliler MA. Exploring the third dimension in root
resorption. Orthodontics & Craniofacial Research. 2004; 7(2):64-70,.

22. Chan E. Darendeliler MA. Physical properties of root cementum: part 7.
Extent of root resorption under areas of compression and tension. American
Journal of Orthodontics & Dentofacial Orthopedics. 2006; 129(4):504-10.

71

23. Chiqueto K. Martins DR. Janson G. Effects of accentuated and reversed
curve of Spee on apical root resorption. American Journal of Orthodontics
& Dentofacial Orthopedics 2008; 133(2):261-8.

24. Damon DH. The rationale, evolution and clinical application of the self-
ligating bracket. Clinical Orthodontics and Research 1998;1:52-61.

25. Damon DH. The Damon low-friction bracket: a biologically compatible
straight-wire system. Journal of Clinical Orthodontics 1998;32(11):670-
80.

26. Darendeliler MA, Kharbanda OP, Chan EKM, Srivicharnkul P, Rex T,
Swain MV, Jones AS, Petocz P. Root resorption and its association with
alterations in physical properties, mineral contents and resorption craters in
human premolars following application of light and heavy controlled
orthodontic forces. Orthod craniofacial Res 2004; (7) 79-97.

27. Dermaut LR, De Munck A. Apical root resorption of upper incisors caused
by intrusive tooth movement: a radiographic study. American Journal of
Orthodontics & Dentofacial Orthopedics 1986;90:321-6.

28. Downing A, McCabe J, Gordon PH. The effect of artificial saliva on the
frictional forces between orthodontic brackets and archwires. British
Journal of Orthodontics 1995;22:41-6.

29. Dudic A. Giannopoulou C. Martinez M. Montet X. Kiliaridis S. Diagnostic
accuracy of digitized periapical radiographs validated against micro-
computed tomography scanning in evaluating orthodontically induced
apical root resorption. European Journal of Oral Sciences 2008;
116(5):467-72.

30. Eberting JJ, Straja SR, Tuncay OC. Treatment time, outcome, and patient
satisfaction comparisons of Damon and conventional brackets. Clinical
Orthodontics and Research 2001;4:228-34.

31. Esmaili S. Ligation properties of a self-ligating composite bracket: An in
vitro study. (Masters Thesis) Goteborg University Faculty of Odontology,
Sweden 2004.

32. Esteves T. Ramos AL. Pereira CM. Hidalgo MM. Orthodontic root
resorption of endodontically treated teeth. Journal of Endodontics. 2007;
33(2):119-22.

72

33. Fink DF, Smith RJ. The duration of orthodontic treatment. American
Journal of Orthodontics and Dentofacial Orthopedics 1992;102(1):45-51.

34. de Freitas MR. Beltrao RT. Janson G. Henriques JF. Chiqueto K.
Evaluation of root resorption after open bite treatment with and without
extractions. American Journal of Orthodontics & Dentofacial Orthopedics
2007; 132(2):143-150.

35. Gher ME, Richardson AC. The accuracy of dental radiographic techniques
used for evaluation of implant fixture placement. Int J Periodont Rest Dent.
1995;15:268–283.

36. Gioka C, Eliades T. Materials-induced variation in the torque expression
of preadjusted appliances. American Journal of Orthodontics and
Dentofacial Orthopedics 2004; 125(3): 323-8.

37. Hain M, Dhopaktar A, Rock P. The effect of ligation method on friction in
sliding mechanics. American Journal of Orthodontics and Dentofacial
Orthopedics 2003;123:416-22.

38. Hanson GH. On the SPEED bracket. Journal of Clinical Orthodontics
1986;20(3):183-9.

39. Hanson GH. The SPEED system: A report on the development of a new
edgewise appliance. American Journal of Orthodontics and Dentofacial
Orthopedics 1980;78(3):243-65.

40. Harradine NWT. Self-ligating brackets: Where are we now? Journal of
Orthodontics 2003;30:262-73.

41. Harradine NWT. Self-ligating brackets and treatment efficiency. Clinical
Orthodontics and Research 2001;4:220-27.

42. Harris DA. Jones AS. Darendeliler MA. Physical properties of root
cementum: part 8. Volumetric analysis of root resorption craters after
application of controlled intrusive light and heavy orthodontic forces: a
microcomputed tomography scan study. Am J Orthod Dentofac Orthop.
2006;130(5):639-47.

73

43. Harris EF, Butler ML. Patterns of root resorption before and after
orthodontic correction in cases with anterior open bites. Am J Orthod
Dentofacial Orthop 1992;101:112-9.

44. Harris EF. Root resorption during orthodontic therapy. Semin Orthod.
2000; 6:183–194.

45. Harry MR, Sims MR. Root resorption in bicuspid intrusion: a scanning
electromicroscopic study. Angle Orthod 1982;52:235-239.

46. Hartsfield JK Jr., Everett ET, Al-Qawasmi RA. Genetic factors in external
apical root resorption and orthodontic treatment. Crit Rev Oral BIol Med
2004; 15(2): 115-122.

47. Hendrix I, Carels C, Kuijpers-Jagtman AM, Van 'T Hof M. A radiographic
study of posterior apical root resorption in orthodontic patients. Am J
Orthod Dentofac Orthop. 1994; 105:345–349.

48. Iwasaki LR, Beatty MW, Randall J, Nickel JC. Clinical ligation forces and
intraoral friction during sliding on a stainless steel archwire. American
Journal of Orthodontics and Dentofacial Orthopedics 2003;123:408-15.

49. Janson GR, De Luca Canto G, Martins DR, Henriques JF, De Freitas MR.
A radiographic comparison of apical root resorption after orthodontic
treatment with 3 different fixed appliance techniques. Am J Orthod
Dentofac Orthop. 2000; 118:262–273.

50. Jil-Agopian, A. A comparison of self-ligating brackets to conventionally-
ligated twin edgewise brackets for treatment time and number of
appointments. University of Southern California, Master‘s Thesis 2006.

51. Kaley J, Phillips C. Factors related to root resorption in edgewise practice.
Angle Orthod. 1991; 61:125–132.

52. Kapur R, Sinha PK, Nanda RS. Frictional resistance in orthodontic
brackets with repeated use. American Journal of Orthodontics and
Dentofacial Orthopedics 1999;116:400-404.

53. Kapur R, SInha PK, Nanda RS. Frictional resistance of the Damon SL
bracket. Journal of Clinical Orthodontics 1998;32:485-89.

74

54. Kennedy DB, Joondeph DR, Osterberg SK, Little RM. The effect of
extraction and orthodontic treatment on dcntoalveolar support. AM J
ORTIIOD 1983;84(3):183-90.

55. Khambay B, Millett D, McHugh S. Evaluation of methods of archwire
ligation on frictional resistance. European Journal of Orthodontics
2004;26:327-32.

56. Kjar I. Morphological characteristics of dentitions developing excessive
root resorption during orthodontic treatment. Eur J Orthod. 1995; 16:25–
34.

57. Kjaer I. Revisiting root resorption. Am J Orthod Dentofac Orthop. 2000;
117:23 A letter to the editor.

58. Killiany DM. Root resorption caused by orthodontic treatment: an
evidence-based review of literature. Semin Orthod. 1999; 5:128–133.

59. Koenig HA, Burstone CJ. Forces from an ideal arch – large deflection
considerations. Angle Orthodontist 1989;59:11-16.

60. Kusy RP, Whitley JQ. Influence of archwire and bracket dimensions on
sliding mechanics: derivations and determinations of the critical contact
angles for binding. European Journal of Orthodontics 1999;21:199-208.

61. Kusy RP, Whitley JQ, Prewitt MJ. Comparison of the frictional
coefficients for selected archwire-bracket slot combinations in the dry and
wet states. Angle Orthodontist 1991;61:293-302.

62. Larheim TA, Eggen S. Determination of tooth length with a standardized
paralleling technique and calibrated radiographic measuring technique.
Oral Surg. 1979;October:374–378.

63. Levander E, Malmgren O. Early radiographic diagnosis of apical root
resorption during orthodontic treatment: a study of maxillary incisors. Eur
J Orthod. 1998; 20:57–63.

64. Levander E, Malmgren O, Eliasson S. Evaluation of root resorption in
relation to two orthodontic treatment regimes. A clinical experimental
study. Eur J Orthod. 1994; 16:223–228.

65. Linge BO, Linge L. Apical root resorption in upper anterior teeth. Eur J
Orthod. 1983;5:173-83.

75

66. Maijer R, Smith DC. Time saving with self-ligating brackets. Journal of
Clinical Orthodontics 1990;24:29-31.

67. Massler M, Malone AJ. Root resorption in human permanent teeth. AM J
Orthod. 1954;40:619-33.

68. McNab S, Battistutta D, Taverne A, Symons AL. External apical root
resorption following orthodontic treatment. Angle Orthod. 2000; 70:227–
232.

69. Morina E, Eliades T, Pandis N, Jäger A, Bourauel C. Torque expression of
self-ligating brackets compared with conventional metallic, ceramic, and
plastic brackets. The European Journal of Orthodontics 2008 30(3):233-
238.

70. Newman WG. Possible etiologic factors in external root resorption. AM J
Orthod. 1975;67:522-39.

71. Owman-Moll P, Kurol J, Lundgren D. Effects of doubled orthodontic force
magnitude on tooth movement and root resorption. An inter-individual
study. Eur J Orthod. 1996; 18:141–150.

72. Owman-Moll P, Kurol J, Lundgren D. The effect of four-fold increased
orthodontic force magnitude on tooth movement and root resorption. An
intra-individual study. Eur J Orthod. 1996; 18:287–294.

73. Owman-Moll P, Kurol J, Lundgren D. Repair of orthodontically induced
root resorption in adolescents. Angle Orthod. 1995; 65:6403–408.

74. Owman-Moll P, Kurol J. The early reparative process of orthodontically
induced root resorption in adolescents—location and type of tissue. Eur J
Orthod. 1998; 20:727–732.

75. Owman-Moll P, Kurol J. Root resorption after orthodontic treatment in
high- and low-risk patients: analysis of allergy as a possible predisposing
factor. Eur J Orthod. 2000; 22:657–663.

76. Pandis N, Nasika M, Polychronopoulou A, Eliades T. External apical root
resorption in patients treated with conventional and self-ligating brackets.
Am J Orthod Dentofacial Orthop 2008;134:646-51.

77. Pandis N, Polychronopoulou A, Eliades T. Self-ligating vs conventional
brackets in the treatment of mandibular crowding: a prospective clinical

76

trial of treatment duration and dental effects. Am J Orthod Dentofacial
Orthop. 2007;132(2):208-15.

78. Pandis N, Strigou S, Eliades T. Maxillary incisor torque with conventional
and self-ligating brackets: a prospective clinical trial. Orthod Craniofac
Res. 2006;9(4):193-8.

79. Parker RJ, Harris EF. Directions of orthodontic tooth movements
associated with apical root resorption of the maxillary central incisor. Am J
Orthod Dentofac Orthop. 1998; 114:677–683.

80. Parker WS. Root resorption—long-term outcome. Am J Orthod Dentofac
Orthop. 1997; 112:119–123.

81. Pizzoni L, Ravnholt G, Melsen B. Frictional Forces Related to Self-
Ligating Brackets. European Journal of Orthodontics Jun 1998;20(3):283-
91.

82. Proffit WR. Contemporary Orthodontics, 3
rd
edition, Mosby 2000.

83. Read-Ward GE, Jones SP, Davies EH. A comparison of self-ligating and
conventional orthodontic bracket systems. British Journal of Orthodontics
1997;24:309-17.

84. Redlich M, Mayer Y, Harari D, Lewinstein I. In vitro study of frictional
forces during sliding mechanics of ―reduced-friction‖ brackets. American
Journal of Orthodontics and Dentofacial Orthopedics 2003;124:69-73.

85. Reukers EA, Sanderink GC, Kuijpers-Jagtman AM, Van 'T Hof M.
Radiographic evaluation of apical root resorption with 2 different types of
edgewise appliances. Results of a randomized clinical trial. J Orofac
Orthop. 1998; 59:100–109.

86. Ridley J, Garret S, Moon P. Frictional forces of ligated plastic and metal
edgewise brackets. Journal of Dental Research 1979;(58):98

87. Reitan K. Effects of force magnitude and direction of tooth movement on
different alveolar bone types. Angle Orthod 1964;34(4):244-55.

88. Rex T, Kharbanda OP, Petocz P, Darendeliler MA. Physical properties of
root cementum: Part 6. A comparative quantitative analysis of the mineral
composition of human premolar cementum after the application of
orthodontic forces. Am J Orthod Dentofacial Ortho. 2006;129:358-67)

77

89. Robb SI, Sadowsky C, Schneider BJ, BeGole EA. Effectiveness and
duration of orthodontic treatment in adults and adolescents. American
Journal of Orthodontics and Dentofacial Orthopedics 1998;113:383-6.

90. Rudolph CE. An evaluation of root resorption occurring during orthodontic
treatment. J Dent Res. 1940;19:367-71.

91. Sameshima GT, Asgarifar KO. Assessment of root resorption and root
shape: periapical vs panoramic films. Angle Orthodontist 2001 Jun;71(3):185-
9.

92. Sameshima GT, Sinclair PM (2001). Predicting and preventing root
resorption: Part I. Diagnostic factors. Am J Orthod Dentofacial Orthop
119:505–510.

93. Sameshima GT, Sinclair PM. Predicting and preventing root resorption:
part II. Treatment factors. Am J Orthod Dentofac Orthop. 2001; 119:511–
515.

94. Scott P, DiBiase AT, Sherriff M, Cobourne MT. Alignment efficiency of
Damon3 self-ligating and conventional orthodontic bracket systems: a
randomized clinical trial. Am J Orthod Dentofacial Orthop. 2008
Oct;134(4):470.e1-8

95. Segal GR, Schiffman PH, Tuncay OC. Meta analysis of the treatment-
related factors of external apical root resorption. Orthod Craniofacial Res.
2004; 7:71-78.

96. Shivapuja PK, Berger J. A comparative study of conventional and self-
ligation bracket systems. American Journal of Orthodontics and
Dentofacial Orthopedics 1994;106:472-80.

97. Sims APT, Waters NE, Birnie DJ, Pethybridge RJ. A comparison of the
forces required to produce tooth movement in vitro using two self-ligating
brackets and a pre-adjusted bracket employing two types of ligation.
European Journal of Orthodontics 1993;15:377-85.

98. Sims APT, Waters NE, Birnie DJ. A comparison of the forces required to
produce tooth movement ex vivo through three types of pre-adjusted
brackets when subjected to determined tip or torque values. British
Journal of Orthodontics 1994;21:376-73.

78

99. Sjolien T, Zachrisson BU. Periodontal bone support and tooth length in
orthodontically treated and untreated persons. American Journal of
Orthodontics, 1973;64:28-37.

100. Taithongchai R, Sookkorn K, Killiany DM. Facial and dentoalveolar
structure and the prediction of apical root shortening. Am J Orthod
Dentofacial Orthop 1996;110:296-302.

100. Taloumis LJ, Smith TM, Hondrum SO, Lorton L. Force decay and
deformation of orthodontic elastomeric ligatures. American Journal of
Orthodontics and Dentofacial Orthopedics 1997;111:1-11.

101. Tecco S, Festa F, Caputi S, Traini T, Di Loria D, D‘Attilio M. Friction
of Conventional and Self-Ligating Brackets Using a 10 Brackets Model.
Angle Orthodontist 2005;75(6):828-32.

102. Thilander B, Rygh P, Reitan K. Tissue reactions in orthodontics. In:
Graber TM, Vanarsdall RL, editors. Orthodontics, current principles and
techniques. 3rd ed. St Louis: Mosby;2000. p. 117-92.

103. Thomas S, Birnie DJ, Sheriff M. A comparative in vitro study of the
frictional characteristics of two types of self-ligating brackets and two
types of preadjusted edgewise brackets with elastomeric ligatures.
European Journal of Orthodontics 1998;20:589-96.

104. Thorstenson GA, Kusy RP. Resistance to sliding self-ligating brackets
versus conventional stainless steel twin brackets with second-order
angulation in the dry and wet (saliva) states. American Journal of
Orthodontics and Dentofacial Orthopedics 2001;120:361-70.

105. Thorstenson GA, Kusy RP. Comparison of Resistance to sliding
between different self-ligating brackets with second-order angulation in
the dry and saliva states. American Journal of Orthodontics and
Dentofacial Orthopedics 2002;121:472-82.

106. Thorstenson GA, Kusy RP. Effect of archwire size and material on the
resistance to sliding of self-ligating brackets with second-order
angulation in the dry state. American Journal of Orthodontics and
Dentofacial Orthopedics 2002;122:295-305.

79

107. Tselepis M, Brockhurst P, West V. The dynamic frictional resistance
between orthodontic brackets and arch wires. American Journal of
Orthodontics and Dentofacial Orthopedics 1994;106:131-8.

108. Thurow RC. Edgewise orthodontics. 4th ed. St Louis: CV Mosby, 1982.

109. VonderAhe G. Postretention status of maxillary incisors with root-end
resorption. Angle Orthod. 1973;43:247-55.

110. Vlaskalic V, Boyd RL, Baumrind S (1998). Etiology and sequelae of
root resorption. Semin Orthod 4:124–131

111. Wickwire NA, McNeil MH, Norton LA, Duell RC. The effects of tooth
movement upon endodontically treated teeth. Angle Orthod.
1974;44:235-42.

112. Wildman AJ, Hice TL, Lang HM, Lee IF, Strauch EC. Round Table-
The Edgelock Bracket. Journal of Clinical Orthodontics 1972;6(2):613-
24.

113. Willems G, Clocheret K, Celis J-P, Verbeke G, Chatzicharalampous E,
Carels C. Frictional behavior of stainless steel bracket-wire
combinations subjected to small oscillating displacements. American
Journal of Orthodontics and Dentofacial Orthopedics 2001;120:371-7.

114. Wyatt DL, Farman AG. Accuracy of dimensional and angular
measurements from panoramic and lateral oblique radiographs.
Dentomaxillofac Radiol. 1994;24:225–231.

Abstract (if available)

Abstract The purpose of this study was to evaluate whether there are significant differences in external apical root resorption between patients treated with self-ligating brackets (Damon SL) and conventionally-ligated edgewise brackets. Damon SL brackets eliminate the need for elastic or metal ligatures because they have a built-in metal gate that opens and closes to accommodate an archwire. Pre- and post-treatment full mouth radiographs were obtained from one orthodontic practice and the amount of root resorption for both bracket systems was measured. Thirty-seven Damon cases were matched with an equal amount of conventional cases according to pre-determined inclusion and exclusion criteria. Results indicated that there was a significant difference in the mean root resorption between the conventional and Damon bracket groups (p=.0076). The maxillary anterior teeth showed the most statistically significant difference in root resorption. From this study, it can be concluded that self-ligating brackets offer a significant advantage over conventionally ligated brackets with regard to root resorption in the anterior teeth.

Linked assets

University of Southern California Dissertations and Theses

Conceptually similar

PDF

A comparison of treatment time and number of appointments in active self-ligating brackets and conventionally ligated twin edgewise brackets

PDF

A comparison of root resorption between Invisalign treatment and contemporary orthodontic treatment

PDF

Three-dimensional assessment of tooth root shape and root movement after orthodontic treatment: a retrospective cone-beam computed tomography study

PDF

Effect of cyclooxygenase inhibitors on rat root resorption and tooth movement

PDF

3D assessment of virtual bracket removal for modern orthodontic retainers: a prospective clinical study

PDF

Comparison between tooth mesiodistal angulation measurements from constructed panoramic images and three-dimensional volumetric images

PDF

Bonding accuracy of a novel lingual customized orthodontic appliance (INBRACE™): an in-vivo study

PDF

Monitering of typodont root movement via crown superimposition of single CBCT and consecutive iTero scans

PDF

Classification of 3D maxillary incisor root shape

PDF

Shear bond strength comparison of mesh, sandblasted and laser-etched orthodontic brackets

PDF

Proper mesio-distal angulation and bucco-lingual inclination of the whole tooth in three-dimensional space -- a standard for orthodontic patients

PDF

Cirtual 3D placement of temporary orthodontic anchorage implants

PDF

An evaluation of bond strength using sham lingual brackets with differences in base morphology and preparation

PDF

A cone beam-ct evaluation of the availability of bone for the placement of miniscrews

PDF

Root shape frequency and direction of dilaceration: a CBCT study

PDF

An exploration of predictor variables for changes in self-esteem and self-concept as a result of orthodontic treatment

PDF

Slow maxillary expansion for the treatment of unilateral crossbite in pre-adolescents: a long-term retrospective study of the changes in arch dimension

PDF

Sexual differences and early eruption timing of the permanent dentition in Mexican adolescents- a comparison with the Caucasian standards

PDF

Mandibular plane angle changes with or without premolar extraction treatment in adult orthodontics measured using 3-D cone beam technology

PDF

3D ssessment of bracket position accuracy for lingual appliances using CAD/CAM technology: a pilot study

Asset Metadata

Creator Wong, Derek (author)

Core Title Comparison of self-ligating brackets to conventionally-ligated twin edgewise brackets for root resorption

School School of Dentistry

Degree Master of Science

Degree Program Craniofacial Biology

Degree Conferral Date 2009-05

Publication Date 05/11/2009

Defense Date 03/23/2009

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag bracket,conventionally-ligated,OAI-PMH Harvest,orthodontics,root resorption,self-ligating

Language English

Contributor Electronically uploaded by the author (provenance)

Advisor Paine, Michael L. (committee chair), Moon, Holly (committee member), Sameshima, Glenn T. (committee member)

Creator Email derekwon@usc.edu,derekwongdds@gmail.com

Permanent Link (DOI) https://doi.org/10.25549/usctheses-m2195

Unique identifier UC171294

Identifier etd-Wong-2792 (filename),usctheses-m40 (legacy collection record id),usctheses-c127-239360 (legacy record id),usctheses-m2195 (legacy record id)

Legacy Identifier etd-Wong-2792.pdf

Dmrecord 239360

Document Type Thesis

Rights Wong, Derek

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Repository Name Libraries, University of Southern California

Repository Location Los Angeles, California

Repository Email cisadmin@lib.usc.edu