Download a comparison of upper incisor torque between two methods of

A COMPARISON OF UPPER INCISOR TORQUE BETWEEN TWO METHODS OF
EXTRACTION SPACE CLOSURE
Kyle Jamison, D.M.D.
A Thesis Presented to the Graduate Faculty of
Saint Louis University in Partial Fulfillment
of the Requirements for the Degree of
Master of Science in Dentistry
2014
COMMITTEE IN CHARGE OF CANDIDACY:
Associate Clinical Professor Donald R. Oliver,
Chairperson and Advisor
Professor Eustaquio A. Araujo
Associate Professor Ki Beom Kim
i
DEDICATION
To my wife, Dayna, whose love and support through the
years has made everything possible.
To my parents, Brad and Shaunna, who have always
believed in me and have supported me in every endeavor I
have pursued.
To my children, Kylie, Tre, and Kellen, whose
unconditional love has given me more joy than I could have
ever imagined.
ii
ACKNOLWLEDGEMENTS
Thank you to Dr. Oliver for his mentorship and for his
attention to detail throughout this process.
Without his
guidance this would not have been possible.
Thank you to Drs. Araujo and Kim for serving on my
committee and helping me to organize my study.
Thank you to Dr. Behrents for helping me with random
questions about cephalometrics along the way, and helping
to find my sample.
iii
TABLE OF CONTENTS
List of Tables. . . . . . . . . . . . . . . . . . . . .
vi
List of Figures. . . . . . . . . . . . . . . . . . . . .vii
CHAPTER 1: INTRODUCTION
Description of the problem. . . . . . . . . . . . . .1
CHAPTER 2: REVIEW OF THE LITERATURE
Introduction and History. . . . . . . . . . . . . . 3
Defining Torque. . . . . . . . . . . . . . . . . . .5
Torque, Occlusion and Arch-Length. . . . . . . . . . 6
Measuring Torque. . . . . . . . . . . . . . . . . . .9
Sources of Torque Variation and Expression. . . . .11
Torsional Play. . . . . . . . . . . . . . . . 12
Manufacturing Processes. . . . . . . . . . . .14
Torque and Bracket Systems. . . . . . . . . . . . . 14
Comparing Bracket Systems. . . . . . . . . . . 16
Self-Ligating Brackets and Torque. . . . . . . 17
Archwire Properties and Torque. . . . . . . . . . . 19
Effects of Loops. . . . . . . . . . . . . . . .20
Summary and Purpose. . . . . . . . . . . . . . . . .21
Literature Cited. . . . . . . . . . . . . . . . . . 24
CHAPTER 3: JOURNAL ARTICLE
Abstract. . . . . . . . . . . . . . . . . . . . . . 27
Introduction. . . . . . . . . . . . . . . . . . . . 29
Materials and Methods. . . . . . . . . . . . . . . .32
Method. . . . . . . . . . . . . . . . . . . . .32
Standard Edgwise Sample. . . . . . . . . . . . 35
Retranol® Sample. . . . . . . . . . . . . . . .36
Error of the Method. . . . . . . . . . . . . . 37
Reliability. . . . . . . . . . . . . . . . . . 37
Results. . . . . . . . . . . . . . . . . . . . . . .38
Sample Demographics. . . . . . . . . . . . . . 38
Age and Treatment Duration. . . . . . . . 38
ANB and SN-GoGn. . . . . . . . . . . . . . . . 39
Upper Incisor. . . . . . . . . . . . . . . . . 40
Lower Incisor. . . . . . . . . . . . . . . . . 42
Upper Molar. . . . . . . . . . . . . . . . . . 43
Lower Molar. . . . . . . . . . . . . . . . . . 45
E Plane. . . . . . . . . . . . . . . . . . . . 46
Discussion. . . . . . . . . . . . . . . . . . . . . 46
Sample Demographics. . . . . . . . . . . . . . 46
Age. . . . . . . . . . . . . . . . . . . .47
iv
Growth. . . . . . . . . . . . . . . . . . . . .47
Upper Incisor. . . . . . . . . . . . . . . . . 48
Comparison to Previous Studies. . . . . . . . .48
Standard Edgewise Studies. . . . . . . . .48
Reverse-Curve NiTi. . . . . . . . . . . . 49
Conclusions. . . . . . . . . . . . . . . . . . . . .50
Literature Cited. . . . . . . . . . . . . . . . . . 51
Appendix. . . . . . . . . . . . . . . . . . . . . . . . .54
Vita Auctoris. . . . . . . . . . . . . . . . . . . . . . 57
v
LIST OF TABLES
Table 2.1:
Theoretical and measured torque loss with
different bracket-wire combinations. . . . . 13
Table 2.2:
Torque values for three bracket prescriptions.
. . . . . . . . . . . . . . . . . . . . . . .16
Table 3.1:
Summary of ages and treatment time for standard
edgewise and Retranol® groups. . . . . . . . 39
Table 3.2:
Summary of ANB and SN-GoGn for both standard
edgewise and Retranol® groups. . . . . . . . 39
Table 3.3:
A summary of the upper incisor (U1) changes for
standard edgewise and Retranol® groups. . . .41
Table 3.4:
A summary of the lower incisor changes with
standard edgewise and Retranol® groups. . . .43
Table 3.5:
Summary of upper molar (U6) changes with
standard edgewise and Retranol® groups. . . .44
Table 3.6:
Summary of lower molar (L6) changes with
standard edgewise and Retranol® groups. . . .45
Table 3.7:
Summary of upper and lower lips to E-Plane in
both standard edgewise and Retranol groups. .45
Table 3.8:
Comparison of upper incisor inclinations from
previous extraction studies. . . . . . . . . 49
Table A.1:
Landmarks and Definitions. . . . . . . . . . 54
Table A.2:
Measurement Abbreviation Key. . . . . . . . .55
vi
LIST OF FIGURES
Figure 2.1:
Improperly inclined anterior crowns result in
all upper contacts being mesial, leading to
improper occlusion. . . . . . . . . . . . . .7
Figure 2.2:
Improper anterior torque may lead to incorrect
assumption of a Bolton discrepancy. . . . . .8
Figure 3.1:
X-Y coordinate grid system constructed from
SN-7 degrees and SN-7 degrees perpendicular.33
Figure 3.2:
Angular Measurements. . . . . . . . . . . . 34
Figure 3.3:
Vertical and Horizontal measurements. . . . 35
Figure 3.4:
Upper incisor (U1) and upper molar (U6)
changes in the standard edgewise and Retranol®
group. . . . . . . . . . . . . . . . . . . .41
vii
CHAPTER 1: INTRODUCTION
Description of the Problem
In orthodontics, having proper buccolingual
inclination, or torque, of the anterior teeth is critical
for successful treatment. Not only is torque important for
esthetic reasons, but it also has space and occlusal
considerations as well.
In extraction cases, torque
control is of vital importance because this treatment often
involves large retractions of the anterior teeth that often
results in lingual tipping of the upper incisors.
The
orthodontist should have a thorough understanding of how
their appliances and mechanics affect the final upper
incisor torque following anterior tooth retraction.
There have been numerous studies comparing the changes
in upper incisor inclination after various different
treatments.
However, no study has compared upper incisor
inclinations in four bicuspid extraction cases comparing
patients treated using a standard edgewise (zero tip, zero
torque) appliance with rectangular stainless steel
archwires and closing loops, and patients treated with a
Roth appliance and a Retranol® (a preformed, accentuated
curve “work-hardened” nickel titanium) archwire and
elastomeric chain with sliding mechanics. The prime
1
motivation of this study is to evaluate differences in
upper incisor inclinations before and after orthodontic
treatment, following the above described methods of space
closure.
This study will also evaluate other dental and
soft tissue changes that occurred as a result of treatment,
specifically, measurements will be made on the upper and
lower incisors (horizontal and vertical), the upper and
lower molars (horizontal and vertical), and the position of
the lips (in relation to E-plane).
2
CHAPTER 2: REVIEW OF THE LITERATURE
Introduction and History
The inclination of the upper incisors (sometimes
called torque) is important to the esthetics of a smile and
as such has been recognized for decades if not centuries.
As part of orthodontic biomechanics, orthodontists have
concerned themselves with achieving the best upper incisor
inclination for their patients.
In the late 1800s and
early 1900s various appliances were developed to affect
torque.
Examples include the E-arch, the pin and tube, and
the ribbon arch. These early appliances were either too
difficult to use, or had relatively poor ability to control
root position.
Introduced in 1928, Angle’s edgewise
appliance using gold and gold-platinum alloys ultimately
became the basis of most modern systems.
After much
experimentation, Angle settled on a .022 X .028 inch
bracket slot, with a .022 X .028 inch precious metal wire.
This appliance was found to be more user friendly and
allowed for excellent control of crown and root position in
all three planes of space.1
Eventually steel archwires replaced the gold wires
used in Angle’s edgewise appliance.
Because steel
archwires are considerably more stiff than gold, a
3
reduction of the bracket slot size to .018 inches was
possible while still maintaining similar forces and torque
control to the original .022 inch appliance when using a
full size steel archwire.
However, the use of undersized
wires in an edgewise appliance is a good way to reduce the
frictional component when sliding teeth along an archwire
(Proffit suggests at least .002 inches of clearance to
minimize friction1).
Therefore, the original .022 inch slot
would have an advantage over the .018 inch slot when
closing spaces, but would be at a disadvantage with torque
control because the springiness and range of action are so
limited in full size steel wires that effective torque is
nearly impossible.1 To overcome the torque issues associated
with using the .022 bracket slot, orthodontists employ
torqueing auxiliaries, undersized steel wires with
exaggerated inclinations, and rectangular NiTi and betaTitanium (TMA) wires.1
Over the years, Angle’s original appliance has gone
through many changes, but the basic idea of a rectangular
wire in a rectangular slot has remained.
One major change
came in 1970 when Andrews introduced the Straight-Wire
Appliance to orthodontics.2
He developed the appliance in
order to minimize the amount of arch-wire bends needed to
4
finish an orthodontic case.
Among his improvements was the
addition of “torque” in the bracket, which was inclined for
each individual tooth type.2
This was the beginning of the
so-called “prescription appliance”.
Today, most
orthodontists use some variation of a prescription
appliance, however, there are many who continue to utilize
a standard edgewise appliance with zero tip and zero torque
incorporated into the brackets.
Defining Torque
Rauch defined torque as “the force that enables the
orthodontist to control the axial inclinations of teeth and
to place them in the harmonizing positions that are so
desirable for a nicely finished result.”3 Torque can either
be passive, which puts no action or force on the tooth when
engaged in the appliance, or, active, which has a definite
action or force on the tooth crown.3 Rauch further defines
torque on the basis of action upon the crown of the tooth.
Thus, buccal or labial torque, tend to tip the crown of the
tooth buccally or labially, and the roots of the tooth
lingually.
Lingual crown torque moves the crown of the
tooth lingually, and the roots of the tooth buccally.3
5
Torque, Occlusion and Arch-length
In 1972, Andrews developed his “six keys to normal
occlusion.”4 His third key deals with Crown Inclination
(labiolingual or buccolingual inclination) or torque.4
In
his paper Andrews describes the importance of proper
anterior crown inclination (torque) because it not only
affects the overbite, but the posterior occlusion as well.
In speaking of the anterior crown inclination, he explains
that “when too straight-up and –down they lose their
functional harmony and overeruption results…the upper
posterior crowns are forward of their normal position when
the upper anterior crowns are insufficiently inclined.”4
(See Fig. 2.1) In other words, if the upper incisors are
inadequately torqued, complete Class II correction may be
difficult or impossible to achieve unless tooth structure
is removed in the lower arch.
6
Fig.2.1. A, Improperly inclined anterior crowns
result in all upper contacts being mesial, leading to
improper occlusion. B, Demonstration on an overlay
that when the anterior crowns are properly inclined
the contact points move distally, allowing for normal
occlusion. (Adapted from Andrews, 19724.)
He further illustrates that improper anterior torque may
often lead to the incorrect assumption of a tooth-size
discrepancy if the posterior teeth are in correct occlusion
and there are remaining spaces between the anterior and
posterior occlusion as shown in Figure 2.2.4
7
Fig. 2.2. Improper anterior torque may lead to incorrect
assumption of a Bolton discrepancy if there is no remaining
overjet and there are spaces between the anterior and
posterior occlusion. (Adapted from O’Higgins, 19996).
While Andrews described this problem of insufficient
anterior tooth inclination, several researchers have
attempted to quantify the loss of arch length that results
from improper incisor angulation.5,6 Most recently,
O’Higgins and colleagues designed a study to investigate
Andrew’s hypothesis that there are space implications with
improper crown torque of the incisors.
Using acrylic and
natural teeth on typodonts, the investigators measured
arch-length changes as the inclinations of the incisors
were changed.
For natural teeth, they found on average
8
that a 5 degree increase in inclination of the upper
incisors resulted in a 1mm increase in arch length.6
Thus,
in orthodontic cases which require Class II correction, and
especially in extraction cases, maintenance and control of
upper incisor torque is of vital importance for complete
Class II correction.
Measuring Torque
Clinically, torque refers to the buccopalatal
crown/root inclination of a tooth.7
Typically the
buccopalatal inclination or torque of the upper incisors is
measured cephalometrically by tracing the long axis of the
upper central incisor and extending the line until it
intersects with a stable reference line, such as the S-N
line or palatal plane. In the Steiner cephalometric
analysis, the upper incisor inclination is measured by the
angle of intersection with the Nasion-A point line, with a
calculated norm value of 22 degrees. There have been
several studies that have used U1-NA to compare Steiner’s
analysis to specific populations8,9.
Perhaps the most commonly used measure of upper
incisor inclination in the literature is U1-SN.
U1-SN is
the angle of intersection between a line extending from
through the long axis upper incisor to the Sella-Nasion
9
line. The University of Michigan performed a growth study
with 47 males and 36 females where they took lateral
cephalograms every year from the ages of 6 to 16.
The
results of this study were published in An Atlas of
Craniofacial Growth10.
The researchers found that from the
ages of 8-years-old to 16-years-old, U1-SN stays relatively
stable, ranging from 102.6 to 105.6 in both male and female
populations10.
Several researchers have used U1-SN to measure upper
incisor inclinations before and after treatment.11,12,13,14 In
Luppanapornlarp and Johnston’s sample of 30 Caucasian
patients treated with four bicuspid extractions, the
average U1-SN angle was 104.3 degrees before treatment, and
99.7 degrees after standard edgewise orthodontic
treatment.11
Demir and colleagues studied the effects of
upper premolar extraction only on the dentofacial
structures in Class II div. 1 patients treated with an
edgewise appliance and headgear.
The initial pre-treatment
mean U1-SN value was 103.7 degrees, which decreased to 97.7
degrees post-treatment, a difference of -6.0 degrees.12
Bishara and colleagues also studied the effects of
extractions in Class II div. 1 patients compared to
patients treated without extractions.
10
There was a -9.8
degree change in U1-SN in the extraction patients and a
-3.2 degree change in U1-SN in the non-extraction group, a
significant difference14.
Işiksal and colleagues compared
smile esthetics among extraction and non-extraction
patients treated with an edgewise appliance, and an
untreated control group.
In this study, the final U1-SN in
the non-extraction and control groups was 104.7 +/- 6.12,
and 103.3 +/- 4.8 degrees respectively, while the
extraction group U1-SN was 100.2 +/-5.3 degrees, a
significant difference.13
Pandis et al. compared changes in
U1-SN in extraction and non-extraction orthodontic cases
using a .022 inch Roth prescription.
In this study, the
extraction spaces were closed using a 0.019 X 0.025 inch
NiTi wire with reverse curve of Spee and elastomeric chain
(similar to the method of closure in the current study).
They found that the mean changes for U1-SN were not
significant between extraction and non-extraction groups.15
Sources of Torque Variation and Expression
While orthodontists have long understood the
importance of anterior torque control, the maintenance and
expression of torque has remained a difficult challenge.
The difficulty with torque control arises from several
11
different sources, including material properties,
manufacturing processes, and clinical procedures.16
Torsional Play
Perhaps one of the most important variations in torque
expression is the interaction of the archwire and bracket
slot (along with the initial position of the tooth).
In a
typical orthodontic sequence, the orthodontist gradually
progresses from light round wires, to heavy rectangular
wires.
It is by engaging the edges of the rectangular
wires with the edges of the bracket slot that torque can be
maintained or expressed.
However, in most clinical
situations, the orthodontist almost never completely fills
the bracket slot because of the patient discomfort
associated with larger archwires and the difficultly of
wire insertion into the slot.16
When the slot remains
incompletely filled by the archwire, a portion of the
torque built into the slot remains unexpressed, which gives
rise to slot-wire “play” or third order clearance.16
Sebanc
et al. describe the torsional play as “the amount of
rotation that the wire initially, in the passive state,
must be twisted to engage the bracket and generate
biomechanical torque.”17 Meling and colleagues further
describe the concept of “effective torque,” which “will
12
equal bracket torque plus incorporated wire torque minus
torsional play.”18
Several investigators have calculated
and measured the amount of archwire-slot play that exists
between different archwire-slot combinations (See Table 1).
The data from Table 1 show the difference between the
theoretical (calculated or nominal) torque loss and the
actual (measured) torque loss.
Table 2.1 shows that almost
100% of the built-in torque can be lost if a low-torque
prescription is used.16 For example, if a Roth appliance,
which uses 12 degrees of torque on the upper central
incisor, is used with a .019 X .025 inch rectangular
archwire in a .022 inch slot, there may be up to 14.5
degrees of archwire-slot play (in each direction), which is
2.5 degrees greater than the built-in bracket torque.
Table 2.1. Theoretical and measured torque loss with
different bracket-wire combinations. (Table adapted from
Gioka et al.)16
Wire crosssection (in)
0.016 X 0.022
Slot Size
(in)
0.018
Torque loss
(degrees)
theoretical*
9.5
Torque loss
(degrees)
measured
14.1
0.017 X 0.025
0.018
6.0
6.2
0.018 X 0.025
0.022
15.2
20.1
0.019 X 0.025
0.022
10.5
14.5
*Theoretical values derived from trigonometric estimation
of slot-wire play.
13
Manufacturing Processes
Play between the archwire and bracket slot is not the
only source of variation to affect clinical torque
expression, but the manufacturing process of brackets and
wires itself can produce inaccuracies and errors that may
lead to discrepancies between estimated (nominal) and
measured (actual) torque.16
The process of bracket slot
manufacturing introduces grooves, metal particles, and
striations that may prevent complete archwire seating
within the bracket slot.16
Any manufacturing process
produces minor variations in slot size and torque
consistency.
Gioka and Eliades report that the reported
torque values can differ from the actual torque values by
as much as 5% to 10%.16
In addition, bracket manufacturers
often slightly increase the size of the bracket slot and
decrease the wire size to prevent the possibility of the
wire not fitting within the bracket slot.
Companies will
often also round or bevel the edges of the archwire to
allow easier archwire insertion.16
Torque and Bracket Systems
Various bracket prescriptions have been developed with
a wide range of values for the upper incisor torque (Table
2.2). The original edgewise appliance, which is still in
14
wide use today, uses zero degrees of torque for all
brackets.
The Andrews appliance, developed in the 1970s,
had brackets for extraction and non-extraction cases, which
were then subdivided into different bracket sets based on
the amount of crowding in the lower arch.19
To reduce the
need for a large inventory of brackets, Roth developed a
set of brackets that would be applicable to most
orthodontic cases. Among Roth’s changes to the Andrews
appliance, he increased both tip and torque on brackets in
the anterior region.19
McLaughlin, Bennett and Trevisi
(MBT) then introduced their own prescription to the
orthodontic market.
One alteration in the MBT prescription
was an increase in palatal root torque in the upper
anterior teeth.
It was their observation that there was a
loss of torque in other appliances in the upper anterior
region, especially during overjet reduction or space
closure.19,20
15
Table 2.2. Torque values for three bracket prescriptions
(degrees). (Adapted from Thickett et al.)19
Upper
Lower
MBT
17
10
-7
-7
-7
-14
-14
Roth
12
8
-2
-7
-7
-14
-14
Andrews
7
3
-7
-7
-7
-9
-9
TEETH
1
2
3
4
5
6
7
Andrews
-1
-1
-11
-17
-22
-30
-33
Roth
-1
-1
-11
-17
-22
-30
-30
MBT
-6
-6
-6
-12
-17
-20
-10
Comparing Bracket Systems
Many researchers have performed studies to determine
the effects of different bracket systems on the upper
incisor torque.
Moesi and colleagues found that nine
experienced orthodontists could not subjectively
distinguish between orthodontic cases treated with either a
Roth or MBT prescription.20
In another study, Ugur et al.
compared upper incisor inclinations in non-extraction
orthodontic cases treated with either a standard edgewise
appliance or a Roth prescription.
They found that there
was no significant variation between mean upper incisor
torque values comparing standard edgewise and Roth
treatment groups with non-extraction treatment.21
16
Self-Ligating Brackets and Torque
The advent of self-ligating bracket systems has
spurred researchers to investigate claims of improved
torque expression because of more consistent wire
engagement due to the absence of elastic modules that
degrade over time.15
Conversely, there is also the argument
that torque control is perhaps more difficult with selfligating brackets (in particular, passive self-ligating
brackets) because of the absence of elastic modules or
steel ligation that help to seat the archwire in the base
of the slot22.
brackets.
There are two basic types of self-ligating
Passive self-ligating brackets have a clip, that
when closed, does not actively seat the archwire in the
bracket slot.
Active self-ligating brackets have a clip
that exerts a force on the labial surface of the archwire
to seat it in the base of the slot.
Pandis and colleagues15 performed a randomized clinical
trial to assess the efficiency of self-ligating and
conventional brackets in torque control in extraction and
non-extraction cases. The authors found no difference in
upper incisor inclinations (U1-SN) between the two bracket
systems.
It was their conclusion that the efficiency of
self-ligating brackets in delivering torque to the upper
17
incisors is equal to the performance of the conventionally
ligated brackets in extraction and non-extraction cases.15
It has been proposed that because the active clip on
an active self-ligating bracket invades the bracket slot,
it might place an effective torqueing force at a smaller
“slop” angle than a passive bracket22.
Badawi and
associates23 tested this theory and compared torque
expression between active and passive self-ligating
brackets with .019 X .025 inch stainless steel archwires in
an .022 inch bracket slot.
They found that there was a
significant difference in the engagement angle between the
two bracket types.
On average, torque started to be
expressed at 7.5 degrees of torsion for active selfligating brackets, and at 15 degrees of torsion for passive
self-ligating brackets23.
The author’s conclusion is that
active self-ligating brackets are more effective in torque
expression than passive self-ligating brackets.23
Sifakakis and colleagues compared maxillary incisor
torqueing moments with reverse-curve NiTi archwires using
conventional and self-ligating brackets.24
The conventional
brackets in their study had the lowest torqueing values
(10.8 N/mm), while the self-ligating brackets had torqueing
values between 16.5-16.9 N/mm.24
18
This finding suggests that
self-ligating brackets may be more efficient than
conventionally ligated brackets at delivering torque to
upper incisors when reverse-curve NiTi wires are used
during leveling.
Archwire Properties and Torque
Torque expression is also greatly influenced by the
properties of the archwire used in the appliance. In
orthodontics, archwires of different dimensions and
composition are used based on the preference of the
orthodontist and the needs of the case.
The most common
materials used for archwires are nickel-titanium (NiTi),
stainless steel, and beta-titanium (TMA).
Archambault and colleagues compared the torque
expression between stainless steel, TMA, and nickeltitanium wires in self-ligating brackets.25
They found that
for low twist angles (<12 degrees) the differences in
torque expression between wires were not statistically
significant. This is because at 12 degrees of wire torsion,
the wire was near the end of the torque play region and at
the beginning of the partially engaged region. When the
wire was twisted over 24 degrees, stainless steel wires
showed 1.5 to 2 times the torque expression of TMA and 2.5
to 3 times that of NiTi.25
19
Meling and colleagues examined different stainless
steels wires tested in torsion.18
The authors were working
under the assumption that the ideal torqueing moment for a
single tooth is 1500 g/mm, or 15 N/mm, and that 20 N/mm is
the upper limit and 5 N/mm is the lower limit. They also
measured the amount of torsional play in the wire-bracket
combinations and found that with an .018 inch bracket slot
and a 0.016 X 0.022 inch wire, there was a mean torsional
play of 18.5 degrees, with a range of 16.6 degrees to 20.4
degrees. They found that the amount of twist necessary to
achieve a 20 N/mm moment ranged from 24.6 degrees to 29.2
degrees.18 They attribute this variation to the wide range
in torsional play, and as a result, makes the precise
delivery of torsional moments difficult achieve using
stainless steel wires.18
Effects of Loops
A common method for space closure in orthodontic
extraction cases is with the use of closing loops.
After
initial leveling, aligning, and canine retraction, closing
loops are typically bent into a 0.019 X 0.025 inch
stainless steel archwire in the standard edgewise
appliance.
One advantage of the closing loops is that the
anterior teeth can be retracted without the need for the
20
teeth to slide along the archwire (sliding mechanics).
Odegaard and colleagues describe that a negative side
effect of the closing loop is that the application of force
creates a tipping moment to the anterior segment; therefore
it is necessary to apply torque to the anterior segment of
wire to negate the tipping action.26 In addition, because
loops increase the length of the archwire between brackets,
there is a loss of torsional stiffness to the anterior
segment while retraction is taking place.26
Summary and Purpose
From the above review of the literature, the
importance of upper incisor torque control, for reasons of
arch-length preservation and occlusal stability has been
presented.
Furthermore, the sources of torque variation
and the effect that closing loops have on the torsional
stiffness of archwires has been shown. With these factors
in mind, is there any advantage to extraction space closure
using Retranol® (a preformed, accentuated curve “workhardened” nickel-titanium) wires and elastomeric chain over
closing loops on .019 X .025 inch stainless steel
archwires?
The rationale for using preformed, accentuated curve
NiTi wires for space closure is several-fold.
21
First, NiTi
wires have increased springback over stainless steel.
Higher springback is beneficial to delivery of torque
because it enables larger activations with resultant
increased working times.18
Thus, a greater degree of torque
can be pre-activated into the wire and remain active over a
longer period of time.
Second, a pre-formed reverse curve
NiTi wire is a continuous archwire, and therefore does not
have the same torsional issues that arise with wires that
have closing loops.
A third benefit is the constant bite-
opening effect the pre-formed NiTi wires afford.
While
anterior teeth are moved posteriorly into an extraction
space, there is a tendency for extrusion.
The accentuated
curve of the pre-formed NiTi wire provides a constant
counteraction to this extrusion, as well as from the
extrusive force on the anterior teeth from Class II
elastics.
Fourth, reverse curve NiTi wires have been shown
to produce torqueing values between 16.5-16.9 N/mm when
used with active self-ligating brackets.24
This is within
the accepted range of 5-20 N/mm, and near the ideal of 15
N/mm for torqueing an upper central incisor.18
Pandis and colleagues used a similar method of space
closure to compare extraction and non-extraction groups
using a Roth prescription.
The results of the study were
22
unique among studies of this type because the final U1-SN
was similar between extraction and non-extraction groups.15
Did the use of pre-angulated brackets using a Roth
prescription make the difference in this study, or was it
the use of the pre-formed NiTi archwires during space
closure?
There have been comparisons between standard
edgewise and pre-torqued brackets in relation to upper
incisor angulation in which the differences were not
significant.21
But, the comparison of upper incisor
angulation has yet to be made comparing standard edgewise
to pre-angulated brackets in four bicuspid extraction cases
using the above described two methods of space closure.
23
Literature Cited
1. Proffit WR, Fields Jr HW, Sarver DM. Contemporary
orthodontics: Elsevier Health Sciences; 2006.
2. Andrews LF. The straight-wire appliance, origin,
controversy, commentary. J Clinic Orthod. 1976;10:99114.
3. Rauch ED. Torque and its application to orthodontics. Am
J Orthod. 1959;45:817-30.
4. Andrews LF. The six keys to normal occlusion. Am J
Orthod. 1972;62:296-309.
5. Hussels W, Nanda RS. Effect of maxillary incisor
angulation and inclination on arch length. Am J
Orthod Dentofacial Orthop. 1987;91:233-9.
6. O'Higgins EA, Kirschen RH, Lee RT. The influence of
maxillary incisor inclination on arch length. Br J
Orthod. 1999;26:97-102.
7. Archambault A, Lacoursiere R, Badawi H, Major PW, Carey
J, Flores-Mir C. Torque expression in stainless steel
orthodontic brackets. A systematic review. Angle
Orthod. 2010;80:201-10.
8. Atit M, Deshmukh S, Rahalkar J, Subramanian V, Naik C,
Darda M. Mean values of Steiner, Tweed, Ricketts and
McNamara analysis in Maratha ethnic population: A
cephalometric study. APOS Trends in Orthod.
2013;3:137.
9. Garcia CJ. Cephalometric evaluation of Mexican Americans
using the Downs and Steiner analyses. Am J Orthod.
1975;68:67-74.
10. Riolo ML, Moyers RE, McNamara JA, Hunter WS. An atlas
of craniofacial growth: cephalometric standards from
the University School Growth Study, the University of
Michigan: Center for Human Growth and Development,
University of Michigan; 1974.
11. Luppanapornlarp S, Johnston Jr LE. The effects of
premolar-extraction: a long-term comparison of
outcomes in "clear-cut" extraction and nonextraction
Class II patients. Angle Orthod. 1993;63:257-72.
24
12. Demir A, Uysal T, Sari Z, Basciftci FA. Effects of
camouflage treatment on dentofacial structures in
Class II division 1 mandibular retrognathic patients.
Eur J Orthod. 2005;27:524-31.
13. Işiksal E, Hazar S, Akyalçin S. Smile esthetics:
Perception and comparison of treated and untreated
smiles. Am J Orthod Dentofacial Orthop. 2006;129:8-16.
14. Bishara SE, Cummins DM, Zaher AR. Treatment and
posttreatment changes in patients with Class II,
Division 1 malocclusion after extraction and
nonextraction treatment. Am J Orthod Dentofacial
Orthop. 1997;111:18-27.
15. Pandis N, Strigou S, Eliades T. Maxillary incisor
torque with conventional and self-ligating brackets: A
prospective clinical trial. Orthod and Craniofacial
Research. 2006;9:193-8.
16. Gioka C, Eliades T. Materials-induced variation in the
torque expression of preadjusted appliances. Am J
Orthod Dentofacial Orthop. 2004;125:323-8.
17. Sebanc J, Brantley WA, Pincsak JJ, Conover JP.
Variability of effective root torque as a function of
edge bevel on orthodontic arch wires. Am J Orthod.
1984;86:43-51.
18. Meling TR, Odegaard J, Meling EO. On mechanical
properties of square and rectangular stainless steel
wires tested in torsion. Am J Orthod Dentofacial
Orthop. 1997;111:310-20.
19. Thickett E, Taylor NG, Hodge T. Choosing a pre-adjusted
orthodontic appliance prescription for anterior teeth.
J Orthod. 2007;34:95-100.
20. Moesi B,
bracket
outcome
Orthod.
Dyer F, Benson PE. Roth versus MBT: Does
prescription have an effect on the subjective
of pre-adjusted edgewise treatment? Eur J
2013;35:236-43.
21. Ugur T, Yukay F. Normal faciolingual inclinations of
tooth crowns compared with treatment groups of
standard and pretorqued brackets. Am J Orthod
Dentofacial Orthop. 1997;112:50-7.
25
22. Graber LW, Vanarsdall Jr RL, Vig KW. Orthodontics:
current principles and techniques: Elsevier Health
Sciences; 2011.
23. Badawi HM, Toogood RW, Carey JP, Heo G, Major PW.
Torque expression of self-ligating brackets. Am J
Orthod Dentofacial Orthop. 2008;133:721-8.
24. Sifakakis I, Pandis N, Makou M, Eliades T, Bourauel C.
A comparative assessment of the forces and moments
generated at the maxillary incisors between
conventional and self-ligating brackets using a
reverse curve of Spee NiTi archwire. Aus Orthod J.
2010;26:127-33.
25. Archambault A, Major TW, Carey JP, Heo G, Badawi H,
Major PW. A comparison of torque expression between
stainless steel, titanium molybdenum alloy, and copper
nickel titanium wires in metallic self-ligating
brackets. Angle Orthod. 2010;80:884-9.
26. Odegaard J, Meling T, Meling E. The effects of loops on
the torsional stiffnesses of rectangular wires: an in
vitro study. Am J Orthod Dentofacial Orthop.
1996;109:496-505.
26
CHAPTER 3: JOURNAL ARTICLE
Abstract
Purpose: The purpose of this study is to determine if there
is a significant difference in upper incisor inclination
(torque) in four bicuspid extraction cases between two
different methods of space closure. Materials and Methods:
Two samples of 30 adolescent, Caucasian, Class II div. 1
patients treated with four bicuspid extractions were
obtained from two separate private orthodontic practices.
The first group was treated using the Tweed-Merrifield
approach using a standard edgewise (zero-tip, zero-torque)
appliance with rectangular stainless steel archwires with
closing loops for space closure.
The second group used a
pre-angulated, self-ligation, Roth prescription appliance
with Retranol® (“work-hardened” reverse-curve NiTi)
archwires and sliding mechanics.
Pre-treatment and post-
treatment cephalograms were used to measure four angular
and 12 linear measurements. Independent T-tests were
performed to analyze the differences between the groups
before and after treatment.
Results: There was a
statistically significant difference between the final
upper incisor inclination (U1-SN), and final lower incisor
inclination (IMPA) between the groups.
27
There were no other
significant differences between the groups as measured in
the upper and lower molars, the vertical and horizontal
position of the upper and lower incisors and the upper and
lower lips in relation to the E-plane. Conclusions: The
Retranol® group had significantly higher upper incisor
inclination at the end of treatment.
Lower incisor
inclination (IMPA) was also significantly higher in the
Retranol® group.
There were no other significant
differences in the measured variables between the groups.
28
Introduction
Having the correct buccolingual inclination of the
upper incisors is important for correct occlusal
relationships, anterior guidance, and proper esthetics in
orthodontic treatment.1
Insufficient upper incisor torque
affects the arch-length and may inhibit complete Class II
correction.2 Studies have shown that for every 5 degrees of
change in anterior inclination, about 1mm of arch length is
gained.3,4,5
When premolars are extracted, the anterior teeth often
require large increments of retraction that can cause
lingual tipping of the upper incisors (torque-loss).
Many
studies have shown that there is often a significant loss
of anterior torque in premolar extraction cases with
traditional edgewise mechanics.6,7,8,9
One study compared an
extraction group with space closure on a reverse-curve NiTi
wire using a Roth prescription to a non-extraction group.
They found the mean changes for U1-SN was not significant
between the groups.10
Torque expression is generally achieved by increasing
archwire dimensions, until the edges of a rectangular wire
engage the edges of the bracket slot.
However, the
dimensions of the final wire almost never completely fill
29
the bracket slot, and a certain amount of “play” or “slop”
exists, which leaves a certain amount of torque
unexpressed.11 The amount of archwire-bracket-slot “play”
has been theoretically and experimentally calculated,11 and
there often exists a considerable discrepancy between the
two values.12
The variation between theoretical and experimentally
calculated torque values can be attributed to several
factors including, variations in archwire13,14,15 and bracket12
slot dimensions, archwire beveling, bracket deformation16,
tooth position, and bracket placement errors.17
There have been numerous advancements in bracket
torque prescriptions to counteract torque loss2,18,19.
Many
researchers have compared different bracket systems with
respect to upper incisor inclination19,20.
Ugur and
colleagues compared upper incisor inclinations in nonextraction patients treated with a standard edgewise
appliance and a Roth prescription appliance, and they found
no difference between the groups20.
Researchers have also examined the effects of selfligating brackets on upper incisor torque control.10,21,22,23
Badawi et al. compared torqueing moments with active and
passive self-ligating brackets.
30
They found a significant
difference between the engagement angle between the groups
(7.5 degrees for active, 15 degrees for passive).22
Sifakakis et al. compared torqueing moments using reversecurve NiTi wires with conventional and self-ligating
brackets.
They found that torqueing moments were higher
with the self-ligating brackets.23
Many researchers have compared different types of
archwires tested in torsion.24,
25
Meling and colleagues
found that precise torque delivery with stainless steel
wire is difficult due to torsional play and the narrow
working range of twist to achieve the ideal torqueing
moment.24
Closing loops are commonly used in orthodontics to
close extraction spaces because teeth can be retracted
without friction.
Odegaard and colleagues have described
that when activated, closing loops create a lingual tipping
moment on the anterior teeth, and therefore it is necessary
to apply torque to the anterior segment.26 Closing loops
have also been shown to decrease the torsional stiffness of
the wire and therefore also decreases the torsional moment
delivered to the upper incisors.26
Several researchers have utilized and proposed using
pre-torqued or reverse-curve NiTi wires for torqueing or
31
space closure applications.10,27,23 Sifakakis describes that
reverse-curve NiTi wires deliver an intrusive force to the
anterior teeth, as well as a labio-palatal torqueing
moment.23 Pandis et al. used reverse curve of Spee NiTi
wires during space closure in four bicuspid extraction
cases.10
Materials and Methods
Method
Pre-treatment and post-treatment cephalograms from two
different samples were hand-traced.
Two reference planes
were constructed on each cephalogram similar to the method
used previously by Lemery28. The reference planes served as
an X-Y coordinate grid and were used to make the linear
measurements (with exception of the upper and lower lips to
E-plane).
A horizontal line was made at the Sella-Nasion
line minus 7 degrees (SN-7) through Sella.
A vertical line
was constructed perpendicular to the SN-7 line, also
through Sella (Fig. 3.1). Four angular (ANB, U1-SN, IMPA,
and SN-GoGn)(Fig. 3.2) and twelve linear (U1 vertical, U1
horizontal, L1 vertical, L1 horizontal, U6 vertical, U6
horizontal, L6 vertical, L6 horizontal, E-plane to upper
lip, E-plane to lower lip, Menton vertical, Menton
horizontal)(Fig. 3.3) measurements were made on both the
32
pre-treatment and post-treatment cephalograms and all data
were entered into an Excel spreadsheet for data analysis
and manipulation.
Fig 3.1. X-Y coordinate grid system constructed from SN-7
degrees and SN-7 degrees perpendicular.
33
Fig. 3.2. Angular measurements: ANB, U1-SN, IMPA, SN-GoGn.
34
Fig. 3.3. Vertical and horizontal (AP) measurements.
Standard Edgewise Sample
A sample of 30 Caucasian, previously treated Class II
div. 1 patients was obtained from a single private practice
orthodontist who practices using the Tweed-Merrifield
approach. All patients were treated with a standard
edgewise appliance (zero tip, zero torque), and had four
bicuspids extracted before treatment. As part of their
orthodontic treatment, all patients had extraction space
closure with rectangular stainless steel wires and closing
loops.
Headgear and Class II elastics were used to treat
35
this group of patients at the discretion of the
orthodontist. Of the 30 patients that met the inclusion
criteria, 25 were female, and 5 were male.
Each patient
required a pre-treatment and post-treatment cephalogram of
good quality, with the teeth in occlusion and the lips
relaxed.
Retranol® Sample
A sample of 30 Caucasian, previously treated Class II
div. 1 patients was obtained from a single private practice
orthodontist.
All patients were treated with a Roth
straight-wire appliance, and had four bicuspids extracted
before orthodontic treatment.
Extraction space closure was
done using .019 X .025 inch Retranol® wires with
elastomeric chain (sliding mechanics), after retraction of
the cuspids.
Headgear, temporary anchorage mini-screws,
and Class II elastics were used as needed at the discretion
of the orthodontist.
A sample of 25 female and 5 male
patients was chosen from the patients that met the
inclusion criteria in order to closely match the patient
profile of the standard edgewise group. Each patient
required a pre-treatment and post-treatment cephalogram of
good quality with the teeth in occlusion and the lips
relaxed.
36
Error of the Method
The Retranol samples radiographs were calibrated using
Dolphin Imaging and printed to actual life size.
A
correction for magnification of -12.9% was applied to the
standard edgewise group to account for the magnification in
the sample. This value was calculated using a calibrated
bar in the radiographs. This amount of correction for
magnification is similar to that applied in the Michigan
Growth Study29.
Reliability
Cronbach’s alpha was used to determine consistency of
the measurements.
Reliability is considered to be
“adequate” when intra-class correlations re greater than or
equal to 0.80.
Ten percent of both samples (3 patients
from each group) were randomly selected and re-measured to
test for intra-examiner reliability.
The actual results of
the Cronbach’s alpha were well above 0.90 for all variables
measured.
This showed that the measured and repeated
measurements were at an acceptable level of reliability for
accuracy of measurements.
37
Results
All data were imputed in SPSS and independent t-tests
were used to analyze the linear and angular measures for
both pre-treatment and post-treatment results for both
groups, with a significance level of p ≤ 0.05.
When considering the vertical and horizontal changes
of the incisors and molars that occurred during the
treatment, one must account for growth of the maxilla and
mandible during this period.
Attempts were made to match
the samples by age, gender distribution, and treatment time
to minimize any differences that may occur due to growth.
Sample Demographics
Age and Treatment Duration
The starting and final ages for both groups is
summarized in table 3.1. There were no significant
differences in either start or final ages between groups.
There was a significant difference in average
treatment time between the groups (p=0.002).
However,
treatment duration is a complex issue and the efficiency of
the two treatments was not a primary focus of this study.
The age and treatment duration for the two groups is
summarized in Table 3.1.
38
Table 3.1. Summary of ages and treatment time for standard
edgewise and Retranol® groups.
Age or
Treatment
time
Start Age
Standard
Edgewise
Mean ± SD
12.8 ± 1.5
Retranol®
Mean ± SD
t
Sig. (2tailed)
13.2 ± 1.2
-1.036
.305
Final Age
15.2 ± 1.6
15.3 ± 1.2
-2.50
.803
2.2 ± 0.2
3.17
.002*
Treatment
2.5 ± 0.5
Duration
*denotes p≤0.05
ANB and SN-GoGn
The start and final ANB and SN-GoGn were similar for
both groups.
There were no significant differences between
the groups.
See table 3.2 for a summary of ANB and SN-GoGn
changes.
Table 3.2 Summary of ANB and SN-GoGn for both standard
edgewise and Retranol® groups.
Measurement
ANB Start
ANB Final
SN-GoGn
Start
SN-GoGn
Final
Standard
edgewise
Mean ± SD
4.6 ± 1.9
2.2 ± 1.7
30.9 ± 4.8
Retranol®
Mean ± SD
t
Sig. (twotailed)
4.2 ± 1.7
2.4 ± 1.5
32.3 ± 5.2
1.024
-.422
-1.045
.301
.674
.301
31.5 ± 5.7
32.3 ± 6.6
-.514
.609
39
Upper Incisor
The standard edgewise group had a starting U1-SN of
106.1 ± 6.0 degrees.
The Retranol® group had a starting
U1-SN of 103.4 ± 7.2 degrees.
The average starting
difference of U1-SN between the groups was 2.7 degrees.
However, this difference was not significant (p=.125).
The standard edgewise group had a final U1-SN of 101.9
± 6.9 degrees (see Fig. 3.2).
This represented a
difference of -4.2 degrees from the start U1-SN value. The
Retranol group had a final U1-SN of 106.1 ± 6.1 degrees.
This represented a difference of +2.7 degrees from the
start value. The difference between the groups was
statistically significant (p=.015).
The start and final vertical and horizontal position
of the upper incisors was not significant between the
groups.
A summary of the upper incisor changes can be
found in table 3.3.
40
Fig. 3.4. Upper incisor (U1) and upper molar (U6) changes
in the standard edgewise group (Black line) and the
Retranol® group (Gray line). Solid lines: pre-treatment.
Dotted lines: post-treatment. Figure is not to scale.
Table 3.3. A summary of the upper incisor (U1) changes for
standard edgewise and Retranol® groups.
Measurement
U1-SN Start
U1-SN Final
Standard
Edgewise
Mean ± SD
106.1 ±
6.0
101.9 ±
6.9
65.1 ± 4.2
U1 Vertical
Start
U1 Vertical 67.3 ± 4.1
Final
U1
67.6 ± 5.8
Horizontal
Start
U1
64.4 ± 5.6
Horizontal
Final
*denotes p≤.05
Retranol®
Mean ± SD
t
Sig. (2tailed)
103.4 ±
7.2
106.1 ±
6.1
65.2 ± 3.7
1.556
.125
-2.495
.015*
-.082
.935
66.8 ± 3.9
.459
.648
65.5 ± 6.0
1.433
.157
63.6 ± 6.1
.528
.599
41
Lower Incisor
The starting IMPA difference between the groups was
not significant (p=.594).
The final IMPA in the standard edgewise group was 90.5
± 5.8 degrees, a difference of -3.1 degrees.
The final
IMPA in the Retranol® group was 95.9 ± 6.5 degrees, a
difference of +1.3 degrees.
The difference in final IMPA
was significant between the groups (p<.001).
A summary
comparing the treatment effects of the lower incisor can be
found in Table 3.4.
The start and final position vertical and horizontal
position of the lower incisors was not significant (Table
3.4).
42
Table 3.4. A summary of the lower incisor changes with
standard edgewise and Retranol® groups.
Measurement
Standard
Edgewise
Mean ± SD
93.6 ± 6.0
Retranol®
Mean ± SD
t
Sig. (2tailed)
94.6 ± 7.2
-.535
.594
± 5.8
95.9 ± 6.5
-3.370
<.001*
± 4.4
62.7 ± 3.5
-1.530
.131
± 3.8
65.6 ± 3.8
-.271
.788
± 5.5
61.3 ± 5.5
.495
.622
± 5.8
60.5 ± 5.9
.802
.426
IMPA Start
(degrees)
IMPA Final 90.5
(degrees)
L1 Vertical 61.2
Start (mm)
L1 Vertical 65.3
Final (mm)
L1
62.0
Horizontal
Start (mm)
L1
61.7
Horizontal
Final (mm)
*denotes p<.05
Upper Molar
Vertical and horizontal starting position and changes
to the upper molar (U6) in both the standard edgewise and
Retranol® groups were similar and there were no significant
differences between groups.
A summary of the U6 changes
can be seen in Table 3.5.
43
Table 3.5. Summary of upper molar (U6) changes with
standard edgewise and Retranol® groups.
Measurement
U6 Vertical
Start
U6 Vertical
Final
U6
Horizontal
Start
U6
Horizontal
Final
Standard
Edgewise
Mean ± SD
55.1 ± 3.4
Retranol®
Mean ± SD
t
Sig. (2tailed)
56.2 ± 2.8
-1.405
.165
58.1 ± 3.4
59.4 ± 3.1
-1.528
.132
29.6 ± 4.4
29.3 ± 4.3
.230
.819
32.5 ± 4.8
33.4 ± 5.3
-.650
.518
Lower Molar
Vertical and horizontal starting position and changes
to the lower molar (L6) in both the standard edgewise and
Retranol® groups were similar and there were no significant
differences between groups.
A summary of the L6 changes
can be seen in Table 3.6.
44
Table 3.6: Summary of lower molar (L6) changes with
standard edgewise and Retranol® groups.
Measurement
L6 Vertical
Start
L6 Vertical
Final
L6
Horizontal
Start
L6
Horizontal
Final
Standard
Edgewise
Mean ± SD
60.7 ± 3.6
Retranol®
Mean ± SD
t
Sig. (2tailed)
61.0 ± 3.0
-.297
.767
64.2 ± 3.9
64.6 ± 3.2
-.430
.669
29.0 ± 4.7
28.0 ± 4.6
.803
.425
33.4 ± 5.2
33.8 ± 5.4
-.319
.751
E Plane
There were no significant differences between the
groups with the upper and lower lip to E plane before or
after treatment.
Table 3.7 provides a summary of the upper
and lower changes during treatment.
Table 3.7. Summary of upper and lower lips to E-Plane in
both standard edgewise and Retranol groups.
Measurement
L Lip/E
Plane Start
L Lip/E
Plane Final
U Lip/E
Plane Start
U Lip/E
Plane Final
Standard
Edgewise
Mean ± SD
-1.0 ± 2.8
Retranol
Mean ± SD
t
Sig. (2tailed)
-1.7 ± 2.6
1.018
.313
-4.0 ± 2.4
-4.5 ± 2.4
.933
.355
-2.1 ± 3.2
-3.2 ± 1.6
1.682
.098
-5.9 ± 2.7
-6.0 ± 2.1
.026
.979
45
Discussion
The purpose of this study was to determine if there
was a significant difference in the final upper incisor
angulation between cases treated with a standard edgewise
appliance with closing loops on rectangular stainless steel
wires, and a Roth prescription appliance with space closure
using Retranol® (“work-hardened” preformed, reverse-curve
NiTi) archwires and sliding mechanics.
In addition to
upper incisor angulation (U1-SN), three other angular and
12 linear measurements were made on the upper and lower
incisors, upper and lower molars, Menton, and the upper and
lower lips to E-plane.
Sample Demographics
Attempts were made to match the samples closely in
regard to age, treatment time, and gender composition. The
goal, in this regard, was to minimize any differences in
growth that occurred during the treatment period.
In other
words, if growth is similar between the groups, then any
changes seen in pre-and –post treatment cephalograms due to
growth, will cancel out.
46
Age
There was a 0.4 years difference in starting age
between the groups (standard edgewise = 12.8 +/- 1.5 years,
Retranol® = 13.2 +/- 1.2 years).
was not significant.
This difference, however,
A difference of several months would
unlikely produce any significant differences in size
between the groups at the start of treatment, and indeed,
did not.
The average age of the two groups at the end of
treatment was virtually the same, with a difference of only
0.1 years (standard edgewise = 15.2 +/- 1.6 years,
Retranol® = 15.3 +/- 1.6 years).
The length of treatment
difference was significant between the groups (p=0.002),
however, the purpose of this study was not to determine
efficiency of the space closure or total time in treatment.
Treatment duration is a complex topic and involves
treatment mechanics along with practice management
decisions, and therefore, it is not appropriate to
determine that one method of space closure is more
efficient than another based on this methodology.
Growth
Both groups had similar overall size, and showed
similar growth during the treatment period.
The ANB angle
was similar in both groups before and after treatment.
47
Similar initial size and growth was seen in both vertical
and horizontal directions as measured at Menton, indicating
that mandibular growth was similar in both groups.
Upper Incisor
There was a significant difference between the final
upper incisor inclination (U1-SN) between the groups
(p=.015).
The starting position of the upper incisors in
the standard edgewise group, on average, were more
protrusive than in the Retranol® group (about 2.1 mm more
anterior, and 2.7 degrees greater U1-SN).
However, these
starting differences were not statistically significant.
After final treatment, the standard edgewise group lost
-4.2 degrees of torque and the Retranol® group gained +2.7
degrees.
Comparison to previous studies
Standard Edgewise Studies
There have been many previous studies that have shown
a similar loss of upper incisor torque in extraction cases
when treated with a standard edgewise appliance.6,7,8,9
Luppanapornlarp and colleagues,6 saw a torque loss of -4.6
degrees in their sample of standard edgewise patients
treated with four bicuspid extractions.
48
Demir et al. also
saw a significant torque loss in their study using standard
edgewise appliances (-6.0 degrees)7.
Bishara and
colleagues9 saw a loss of -9.8 degrees in U1-SN after
extractions.
Table 3.8. Comparison of upper incisor inclinations from
previous extraction studies.
Study
Treatment
type
Luppanpornlarp6
et al., 1993
Demir7
et al., 2005
Jamison
et al., 2014
Jamison
et al., 2014
Standard
edgewise
Standard
edgewise
Standard
edgewise
Roth
appliance
with
Retranol®
U1-SN
start
(degrees)
104.3
U1-SN
Final
(degrees)
99.7
U1-SN
Change
(degrees)
-4.6
103.7
97.7
-6.0
106.1
101.9
-4.2
103.4
106.1
+2.7
Reverse-curve NiTi
The method of space closure in the Retranol® group was
similar in method to that used in a study by Pandis and
colleagues.10 They compared upper incisor inclination in
extraction and non-extraction groups, and used .019 X .025
inch reverse-curve NiTi wires with elastomeric chain in a
Roth prescription.
This study was the only one found in
which there was not a significant difference in U1-SN in an
extraction case.10 Sifakakis et al.23 found that torqueing
moments with active self-ligating brackets and reverse49
curve NiTi wires were between 16.5-16.9 N/mm.
This value
is within the agreed range (5-20 N/mm) necessary for
torqueing a maxillary central incisor.
While the exact
torqueing moment of the Retranol® wire is unknown, it is
reasonable to assume that based on previous studies, it
would generate a torqueing moment within the biologic range
listed in the literature.
Conclusions
1.
The Retranol® group showed significantly more upper
incisor inclination than the standard edgewise group
at the end of treatment.
2.
Lower incisor inclination (IMPA) was also
significantly higher at the end of treatment in the
Retranol® group.
3.
No other dental or soft tissue variables were
significantly different between the groups.
50
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53
APPENDIX
Materials and Methods Details
Table A.1. Landmarks and Definitions
Abbreviation
Landmark
A
Subspinale
Definition
The deepest midline point of
the curve of the maxilla
between the anterior nasal
spine and prosthion.
The most posterior point in
the midline of the symphyseal
of the mandible in the
concavity between
infradentale and pogonion.
A line connecting the soft
tissue pogonion to the tip of
the nose.
The most anterior and
inferior midline point on the
external contour of the
symphysis of the mandible.
The incisal tip of the lower
central incisor.
B
Supramentale
E-Plane
E-Plane
Gn
Gnathion
L1
Lower
Incisor
L Lip
Lower Lip
L6
Lower Molar
Me
Menton
N
Nasion
Point at the junction of the
nasal bone and frontal bone.
U1
Upper
Incisor
The incisal tip of the upper
central incisor.
U Lip
Upper Lip
The most anterior point on
the curvature of the upper
lip.
The most anterior point on
the curvature of the lower
lip.
The posterior contact (height
of contour) of the mandibular
first molar.
The most inferior point on
the symphyseal outline.
54
Table A.1. Landmarks and Definitions (continued).
Abbreviation Landmark
Upper Molar
U6
S
Sella
Definition
The posterior contact (height
of contour) of the maxillary
first molar.
The center of the pituitary
fossa of the sphenoid bone.
Determined by inspection.
Table A.2. Measurement Abbreviation Key
Abbreviation
ANB
Measurement
Angle formed by connecting
A point, Nasion, and B
point.
The angle formed by the
intersection of the long
axis of the upper central
incisor and the SN line.
The angle formed by a line
extending from the long
axis of the lower central
incisor intersecting the
mandibular plane.
The angle formed by the
Sella-Nasion line
intersecting with a line
formed by the mandibular
plane.
The vertical distance from
the SN-7 line to the upper
central incisor tip
measured perpendicularly.
The horizontal distance
from a line perpendicular
to SN-7 (through Sella) to
the upper central incisor
tip.
The vertical distance from
the SN-7 line to the lower
central incisor tip
measured perpendicularly.
U1-SN
IMPA
SN-GoGn
U1-Vert (mm)
U1-Horizontal (AP) (mm)
L1-Vert (mm)
55
Table A.2. Measurement Abbreviation Key (continued)
Abbreviation
Measurement
L1-Horizontal (AP) (mm)
The horizontal distance
from a line perpendicular
to SN-7 (through Sella) to
the lower central incisor
tip.
The vertical distance from
the SN-7 line to the upper
first molar at the height
of contour on the distal
surface measured
perpendicularly.
The horizontal distance
from a line perpendicular
to SN-7 (through Sella) to
the upper first molar at
the height of contour on
the distal surface.
The vertical distance from
the SN-7 line to the lower
first molar at the height
of contour on the distal
surface measured
perpendicularly.
The horizontal distance
from a line perpendicular
to SN-7 (through Sella) to
the lower first molar at
the height of contour on
the distal surface.
Distance in mm of the
lower lip to the E-plane.
U6-Vert (mm)
U6-Horizontal (AP)
L6-Vert
L6-Horizontal (AP)
Lower Lip/E-Plane
Upper Lip/E-Plane
Distance in mm of the
upper lip to the E-plane.
Menton Vert
The horizontal distance
from a line perpendicular
to SN-7 (through Sella) to
Menton.
The vertical distance from
the SN-7 line to Menton
measured perpendicularly.
Menton Horizontal (AP)
56
VITA AUCTORIS
Kyle Jamison was born July 14, 1981 in West Covina,
California to Brad and Shaunna Jamison.
From the age of 5
years old, he was raised in Folsom, California along with
his five brothers.
After graduating from Folsom High
School, he served a two-year LDS mission in Madagascar
where he learned to speak French and Malagasy.
After his
mission he earned a degree in biology from California State
University Sacramento, where he graduated Summa Cum Laude.
He continued his education at the University Of Nevada Las
Vegas School Of Dental Medicine, where he earned multiple
academics honors including graduating Summa Cum Laude, and
being inducted into the Omicron Kappa Upsilon honor
society.
He was then accepted into the orthodontic program
at Saint Louis University where he will graduate in
December 2014. He plans to move back to California and open
his own orthodontic practice.
Kyle married his wife Dayna in 2003 in California.
They have 3 wonderful children, Kylie, Tre, and Kellen.
57