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University of Southern California Dissertations and Theses
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Whole tooth tip and torque comparison of orthodontically treated extraction cases versus a non-treated near normal group using CBCT analysis.
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Whole tooth tip and torque comparison of orthodontically treated extraction cases versus a non-treated near normal group using CBCT analysis.
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Content
Whole tooth tip and torque comparison of
orthodontically treated extraction cases versus a non-
treated near normal group using CBCT analysis.
Nathan Coughlin
A Thesis Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
MASTER OF SCIENCE
(CRANIOFACIAL BIOLOGY)
May 2013
Copyright 2013 Nathan Coughlin
2
Acknowledgements
I would like to thank Dr. Hongsheng Tong who has generously given his time to help me
through this project. I would also like to thank Dr. Reyes Enciso for guiding me through
the multitude of statistics and tolerating all my questions. I must recognize Dr. Donald
Kwon and Dr. Nicole Sakai for starting this research and working out many of the
problems before I had to begin.
3
Table of Contents
Acknowledgements 2
List of Tables 5
List of Figures 6
List of Graphs 8
Abstract 9
Chapter 1: Background 11
Advancements in appliances: The preadjusted brackets 12
Indirect bonding 15
3Dimensional virtual setups 18
Cone Beam Computed Tomography (CBCT) 21
Dosimetry and radiation safety 24
Previous study by Tong et al. 26
Extraction versus non-extraction treatment 27
Chapter 2: Research Objective 30
Chapter 3: Materials and Methods 31
Photo screening 31
X-ray screening 31
Global 3Dimensional coordinate system 32
Tooth specific 3Dimensional system for locating crown and root centers 33
Arch form 35
Determining tooth tip and torque 35
Reliability of measurements 37
Statistics 37
4
Chapter 4: Results 39
Intra-Class Correlation (ICC) and Normality of Data 39
Left and Right sides compared in extraction group 41
Compared extraction group to near normal 43
Chapter 5: Discussion 47
Chapter 6: Conclusion 52
References 54
5
List of Tables
Table 1: Intra-class correlation coefficient and normality of data 39
Table 2: Left and right side comparison for the four premolar extraction group. 41
Table 3: Compared extraction to near normal group. 43
6
List of Figures
Figure 1: First, second and third order bends. 11
Figure 2: Average prescription of brackets. 13
Figure 3: MBT Prescription 13
Figure 4: Slop between brackets and archwires 14
Figure 5: Indirect bonding: Drawing on cast. 16
Figure 6: Indirect bonding: 3 final steps of placement. 17
Figure 7: Insignia Indirect Bonding 17
Figure 8: OrthoCad software 3Dimensional models. 18
Figure 9: Insignia software for virtual setup. 19
Figure 10: Suresmile software and robotic bending machine. 20
Figure 11: Compare radiation of CBCT to traditional CT. 21
Figure 12: Isotropic versus anisotropic data. 23
Figure 13: Typical CBCT image show via Dolphin Imaging software 24
Figure 14: Adult skull and tissue equivalent phantom. 25
Figure 15: Sample screen picture of research by Tong et al. 26
Figure 16: Pattern of extraction treatment in the past 100 years 27
Figure 17: Lower crowding patient in which expansion was used 28
Figure 18: Typical migration of teeth in extraction cases. 29
Figure 19: Image of all three planes which formed the functional occlusal plane 32
Figure 20: Point being placed at crown center utilizing all three planes of space 33
Figure 21: Point being placed at root center utilizing all three planes of space 34
Figure 22: All teeth digitized with line passing through crown center and root center 34
Figure 23: Maxillary arch form digitized 35
7
Figure 24: Determining mesiodistal angulation. 36
Figure 25: Determining the faciolingual inclination. 37
8
List of Graphs
Graphs A-D: Fluctuation of mesiodistal angulation and faciolingual inclination 45
9
Abstract
Introduction: An important objective of orthodontic treatment is to obtain proper mesiodistal
angulation and faciolingual inclination. In this study we compared a previously defined near
normal group of patients to a group of patients who had undergone four premolar extractions
for orthodontic reasons. The objective was to determine the similarities and differences of the
mesiodistal angulation and faciolingual inclination values of the two groups.
Methods: We screened patients who had undergone cone-beam computed tomography (CBCT)
scans after four premolar extraction treatment. Of those patients 22 were selected who met
our inclusion criteria. Using the custom University of Southern California root vector analysis
software program we were able to digitize each whole tooth long axis and determine their true
mesiodistal angulation and faciolingual inclination. We were then able to compare our values
to those of the previously defined near normal group who had undergone the same digitization
procedures.
Results: The means and standard deviations for each whole tooth tip and torque were
calculated. The left and right sides of the arch were symmetric except for the mandibular
laterals and mandibular first molars mesiodistal values. The maxillary central, lateral, canine,
first and second molars all showed variation in their mesiodistal values as compared to the
near normal group. The maxillary anterior teeth in the extraction group had a significantly
smaller mesiodistal value indicating that their crowns have a tendency of tipping back into the
extraction spaces. Only the mandibular left first molar and the mandibular second molars had
significantly different mesiodistal values then the near normal group. The maxillary and
mandibular anterior teeth (except for the maxillary laterals) along with the premolars had
10
significantly different faciolingual values then the near normal group. The extraction groups
maxillary and mandibular faciolingual values were smaller then the near normal group
indicating more lingual crown inclination (or less labial crown inclination).
Conclusion: We obtained the average mesiodistal angulation and faciolingual inclination of
each whole tooth from a group of patients who had undergone four premolar extraction
orthodontic treatment. We were able to compare this to a group of near normal patients who
had not undergone orthodontic treatment. The results obtained can be used to modify bracket
prescriptions for specific orthodontic treatment.
11
Chapter 1: Background
Orthodontists aim to align teeth into smooth maxillary and mandibular dental arches and place
them in harmony with each other when in occlusion (Currim et al. 2004). During orthodontic
treatment, the alignment of the roots of the teeth in parallel axial inclinations is an important
objective for the correct alignment and occlusion of the teeth and for maintaining a stable
orthodontic result (Bouwens et al. 2004).
These ideas stemmed from Edward Angle (1855-1930) who is considered by most as being the
father of modern orthodontics. His research revealed to him that teeth not only are supposed
to be in natural alignment but they also have a specific mesiodistal angulation and faciolingual
inclination. The wires he fabricated consisted of many first, second and third order bends to
optimize tooth position (Proffit, 2004).
Figure 1: (A)First order bends, horizontal (B) Second order bends, vertical (C) Third order bends,
faciolingual. (Proffit, 2004)
12
Since Dr. Angles initial thoughts there have been many advances in treatment. In 1972 Dr.
Lawrence Andrews published his famous article “The six keys to normal occlusion” in the
American Journal of Orthodontics. He took 120 patients with proper occlusion and measured
their casts intensely. After years of studying and comparing he revealed to the orthodontic
community the six keys to proper occlusion. They consisted of proper molar relationship,
crown angulation, crown inclination, having no rotations, no spacing and a relatively normal
occlusal plane
(Andrews, 1972).
Advancements in appliances: The preadjusted brackets
From Dr. Andrew’s extensive measurements there was now enough data to set up averages for
the proper mesiodistal, faciolingual and in/out position of each tooth. These dimensions,
representing the averages of individual tooth position, were then used to fabricate brackets for
each tooth. When each bracket was precisely positioned at the midpoint of the facial axis and
aligned with the facial axis, they collectively became the straight wire appliance (Creekmore et
al. 1993).
Preadjusted brackets are the most widely used system in orthodontic therapy today. The basic
premise of the preadjusted system is that proper bracket position allows the teeth to be
positioned with a straight wire into an occlusal contact with excellent mesiodistal angulation
and excellent faciolingual inclination (Balut et al. 1992). Yet it is known that even if brackets are
placed properly there are many other factors that determine the overall quality of the
orthodontic result such as; proper size and shape of teeth, proper facial inclination of teeth, no
uneven wear of teeth, etc.
13
Figure 2: Average mesiodistal angulation and faciolingual inclinations of preadjusted
brackets. (Proffit, 2004)
Maxilla Torque Tip Mandible Torque Tip
Central 17 4 Central -6 0
Lateral 10 8 Lateral -6 0
Canine -7 8 Canine -6 3
1st Premolar -7 0 1st Premolar -12 2
2nd Premolar -7 0 2nd Premolar -17 2
1st Molar -20 0 1st Molar -14 0
2nd Molar -10 0 2nd Molar -14 0
Figure 3: MBT prescription used most frequently at the University of Southern California
(USC).
It is well known that using preadjusted brackets do not eliminate the need for wire bending.
Also there is no universal agreement on the torque and tip values of individual teeth as
indicated by the varying prescriptions such as Roth, MBT, Alexander etc. For example the
faciolingual slot angulation for central incisor brackets varies by more than 20 degrees among
several standard prescriptions (Germane et al. 1989). Some of these variations have purpose
such as using high torque anterior brackets in extraction cases to avoid excessive lingual crown
inclination when closing spaces.
14
Not only are there a variety of prescriptions there are also inherent errors in the straight wire
appliance due to five main reasons. The most frequent is bracket placement followed by
variation in tooth size, variation in vertical and horizontal jaw relationship, need for
overcorrection and mechanical deficiencies such as play between bracket and wire (Creekmore
et al. 1993). The orthodontic wire cannot fill each bracket slot completely or else it would be
nearly impossible for the clinician to insert and remove the wire. Not only is there known slop
in between the bracket and wire but the factory also induces its own errors by allowing for a
range of bracket and wire sizes to be sold. A typical 0.018-inch slots range from 0.0182 to
0.0192-inches. A 0.018-inch arch wire is actually 0.0178-inches. Therefore if a clinician were
finishing with a typical 0.016 x 0.022-inch wire in a 0.018 x 0.025-inch bracket there is 11.8
degrees of slop (Creekmore et al. 1993).
Figure 4: Varying arch wire dimensions and their corresponding slop within the two main sizes
of brackets (Creekmore et al. 1993).
Germane et al. also found there were inconsistencies with the facial surface of teeth. They
determined that no single point on the facial surface of teeth had a consistent angulation
amongst varying patients (Germane et al. 1989). These inherent problems with direct bonding
15
and the straight wire appliance left many clinicians dissatisfied with the results. Even if the
teeth appear straight their roots may be displaced because clinically we cannot determine the
roots mesiodistal angulation or faciolingual inclination without the use of a CBCT. Also even
though teeth are in the proper position equilibration of the dentition is often needed to
achieve an optimal result (Roth, 1981).
Indirect bonding
Orthodontists use indirect bonding (IDB) to enhance the accuracy of bonding (Ciuffolo et al.,
2012). Indirect bonding involves bonding brackets to stone models then transferring the
brackets to the patients. Although indirect bonding causes more laboratory time the
advantages are a less stressful environment for bracket placement, less chair time and a more
accurate result (Koo et al., 1999). The indirect technique also reduces the patient’s discomfort
compared with direct techniques. Although exactness is one of the main reasons orthodontists
use IDB, Ciuffolo et al. found no differences in accuracy or shear bond strength using IDB versus
directly bonding to the teeth (Ciuffolo et al. 2012).
Indirect bonding takes a significant amount of lab time. There are differing ways to perform
indirect bonding but most involve slight variations in the following steps. After taking initial
impressions on the patient you then mark the casts very specifically. The lab technician or
orthodontist marks the facial axis of the clinical crown in a parallel fashion. Horizontal marks
are then made at specific heights according to the orthodontist’s preference. One method
suggests measuring clinical crowns to determine slot height of the anterior teeth and molars.
The height of the molar slot to its marginal ridge is needed to determine the height of the first
and second premolar bracket slots (Ciuffolo et al. 2012).
16
Figure 5: Lines drawn on cast parallel to long axis of teeth and horizontal lines drawn at specific
vertical heights. (Ciuffolo et al. 2012).
After this is accomplished the lab technician or assistant can add a separating medium to the
casts then add each bracket to its proper position as determined by the previously drawn lines.
After the brackets are placed the technician or assistant places a thin layer of soft silicone over
the brackets. This will allow the tray to be easily removed from the brackets after bonding.
A thermo-form stronger layer is added on top of the softer layer to give rigidity to the indirect
bonding tray. After soaking the stone in water to dissolve the separating medium, the tray and
brackets are removed from the stone model.
Once the patient is at your office the bonding time is greatly reduced from that of a direct
bonding visit. The patient’s dentition is isolated and prepared as normal. The doctor can apply
self curing adhesive to the brackets and teeth. The tray is then seated and adhesive is allowed
to cure. Once cured the tray and excess flash is removed.
17
Figure 6: A) Initial placement of brackets on cast. B) Soft silicone layer placed over the brackets
to lock them into position. C) Final placement of IDB tray on patient. (Ciuffolo et al. 2012).
There is less chair time involved with an indirect bonding but the overall lab time is increased
significantly. The lab time could be completed by a lab technician or dental assistant thus
reducing overall doctor time significantly. IDB is technique sensitive and requires time to
become properly proficient with bonding and setting up. If not adequately trained any benefit
from better bracket placement with indirect bonding could be offset by higher bond failure
rates (Deahl et al., 2007). Newer and more accurate IDB techniques are being generated
frequently which can dramatically reduce doctor time spent bonding a patient. Insignia, which
will be explained further, offers an indirect bonding jig that is fabricated from machined foam.
Figure 7: Insignia engineered foam jig that is machined for accurate position of brackets.
A B C
18
3Dimensional virtual setups
As technology has grown orthodontists have searched for more efficient and superior methods
of treating their cases. Technology has advanced so much that traditional methods of taking
alginate impressions could be replaced completely with intraoral scanners (Grauer et al., 2012).
These intraoral scans can be transferred to a computer to fabricate digital models. OrthoCad
was the first company to introduce digital models in 1999 (Peluso et al., 2004).
OrthoCad uses alginate impressions to pour up models and digitally transfer them to a
computer via a proprietary process. Polyvinylsiloxane (PVS) bite is used to create an interarch
relationship. OrthoCAD’s virtual set up enables the clinician to simulate and visualize any
desired treatment option including virtual extractions, interproximal reduction, expansion
leveling, and to apply various fixed appliances(Peluso et al., 2004).
Figure 8: OrthoCad software allows the doctor to manipulate individual teeth in a 3Dimensional
fashion and see its effects on treatment.
OrthoCAD claims using their IDB protocol could improve finishing results and save time
(Cadent, 2012). Some authors have argued that OrthoCAD iQ does not currently offer a system
19
that can position orthodontic brackets better or more reliably than traditional indirect bonding
techniques (Israel et al., 2011).
Insignia by Ormco is another product that offers virtual setups and IDB jigs to increase
treatment efficiency. They also start off by using the Polyvinylsiloxane impressions to digitally
fabricate the patient models. Teeth are then segmented from the arch and digital landmarks
are added to each tooth for easier software identification of each individual tooth. After
segmentation and landmark identification root forms are added and occlusion is constructed.
This software and precise occlusal analysis allows Insignia to reverse engineer their appliance
design to be custom fit for that specific patient with the end result in mind (Ormco, 2006).
Figure 9: Insignia software: A) After analyzing and importing the PVS impression into the
software program the teeth are segmented so they can be viewed individually. B) Each tooth
has landmarks that are added to ease software identification of the individual teeth. C) Digital
A
B
C
D
20
partial roots are added to each tooth and virtual setup is completed. D) Occlusion is checked
and analyzed with Insignia’s software. (Ormco, 2006)
Suresmile is a company that is quickly growing with over 350 orthodontists using their product
in the US, Canada, Australia and Germany (Scholz et al., 2007). Suresmile uses a unique
approach to treatment. Typically the orthodontist will bond a case and treat for a few months
before using Suresmile. Once teeth have been allowed to align for several months the doctor
can then use Suresmile’s intraoral camera or CBCT to send information to Suresmile. The CBCT
allows the clinician to view the roots which may be beneficial to treatment. Suresmile software
will set up teeth virtually and a robot is used to bend 3D wires (Figure 10) to achieve optimal
results.
Suresmile has been found to reduce treatment time and give a better treatment outcome then
conventional approaches (Saxe et al., 2010; Moles, 2009). It is important to note that the latest
technology has the ideal finish in mind whereas earlier direct or indirect bonding techniques
hope that their bonding location will lead to an optimal result. The ability to visualize the
finished result may lead to better bracket positioning and finishing.
Figure 10: A) Program interface used for Suresmile and the ability to manipulate individual
teeth using their program. B) Robot used to make specific 3D bend in the arch wires with the
Suresmile system. (Saxe et al., 2010)
A B
21
Cone Beam Computed Tomography (CBCT)
The introduction of panoramic radiographs in the 1960s heralded major progress in dental
radiology providing clinicians with a single comprehensive image of jaws and maxillofacial
structures (Scarfe et al., 2008). Yet panoramic radiographs suffer from what all 2Dimensional
projections suffer from which is: magnifications, distortion, superimposition, and
misrepresentation of structures (Scarfe et al., 2008). Although CBCT may not allow us to
visualize certain orthodontic landmarks more precisely it can be valuable in viewing teeth of
different stages of development, locating impacted teeth, visualizing the temporomandibular
joints, and diagnosing asymmetries in complex craniofacial patients (Grauer et al., 2010).
CBCT involves using a cone-shaped source of ionizing radiation directed through the middle of
the area of interest onto an x-ray detector.
Figure 11: Difference between CBCT x-ray exposures versus a “Fan” x-ray exposure obtained in
traditional CT scans (Scarfe et al., 2008).
The x-ray source and detector rotate around the patient. Because CBCT exposure incorporates
the entire field of view (FOV), only one rotation sequence of gantry is necessary. The rotation
22
normally takes in between 10-30 seconds. The disadvantage of CBCT is that image quality due
to noise and contrast resolution is limited due to scattered radiation.
CBCT scans patients in either sitting, standing or supine. No matter how they are scanned there
are four components to an image production. The four components are (1) acquisition
configuration (2) image detection, (3) image reconstruction, (4) image display (Scarfe et al.,
2008).
The acquisition configuration is relatively simple with the x-ray source producing radiation as
the detector moves synchronously with the scan around a fixed fulcrum. The field of view (FOV)
depends on the detector size and shape, the beam projection geometry and the ability to
collimate the beam.
With image detection it is desirable to increase spatial resolution and therefore provide greater
image detail (Scarfe et al., 2008). Each pixel contains photodiodes that record the image and
transistors that carry the information. The smaller the pixel size the better the image but the
more radiation needed for each patient (Scarfe et al., 2008). Yet the true resolution is
determined by the volume element (voxel). CBCT data acquisition depends on the pixel size of
the area detector and not the acquisition of groups of rows like convention CT. The
composition of a CBCT voxel is equal in all three dimensions, which is also known as isotropic.
23
Figure 12: Depicting the isotropic data that are obtained from a CBCT versus the anisotropic
data obtained from a traditional CT scan (Scarfe et al., 2008).
Once the frames have been acquired data must be processed to construct an image. The
number of individual projection frames may be from 100 to 600, each with more than one
million pixels, with 12 to 16 bits of data assigned to each pixel (Scarfe et al., 2008).
The image display is presented on a screen as a secondary reconstructed image in three
orthogonal planes (axial, sagittal, and coronal). This can be viewed with a variety of
applications. At the University of Southern California it is viewed via the Dolphin Imaging
program.
24
Figure 13: Typical CBCT image shown on the imaging program Dolphin 11.5 Premium edition.
CBCT has many advantages over conventional 2Dimensional images. Not only can we visualize
clearly the surrounding structures but the data suggests it is better at viewing root angulation
at a 1:1 spatial ratio which is integral in treatment of an orthodontic patient (Peck et al., 2007).
Dosimetry and radiation safety
Although CBCT radiation doses are relatively small they are still a concern in dental diagnostic
imaging (Ludlow et al., 2006). The average person is exposed to 2.4mSv of background
radiation a year (Ludlow et al., 2008). Depending on which CBCT scanner used the calculated
doses in mSv are anywhere from 4 to 42 times greater than a conventional panoramic x-ray
(Ludlow et al., 2006). Based on the International Commission on Radiological Protection (ICRP)
a panoramic radiograph produces anywhere from 3 to 24 µSv of effective dose and a
cephalometric radiograph produces roughly 5 µSv (Lorenzoni et al., 2012). The effective dose of
25
an intraoral full mouth series (FMX) is anywhere from 35 to 171 µSv while the effective dose of
a CBCT scan ranges from 30 to 200 µSv (Lorenzoni et al., 2012). The NewTom3G scanner with a
12 inch field of view (FOV) produces in the region of 58.9 µSv of effective dose radiation
(Ludlow et al., 2006).
Figure 14: Adult skull and tissue equivalent phantom showing where dosimeters were placed
for radiation detection (Ludlow et al., 2006).
In order to minimize radiation exposure clinicians should consider lowering the kV, mA,
exposure time, and field of view. Although the effective dose for a CBCT is higher than
panoramic and cephalometric radiographs it is lower than a FMX (Lorenzoni et al., 2012). For a
CBCT scan of 300 µSv the odds of developing fatal cancer is 1 in 50 000
yet until we have a clear
threshold under which patients will not be harmed by radiation we must assume radiology
involves a risk to our patients (Ludlow et al., 2008; Vlijmen et al., 2012).
26
Previous CBCT study by Tong et al.
Our study is part of a larger study original conceived by Dr. Hongsheng Tong et al. They
published two papers in the American Journal of Orthodontics depicting a study which we
duplicated using a different patient pool (Tong et al., 2012; Tong et al. 2012). The authors used
CBCT to measure the faciolingual inclination and the mesiodistal angulation of each whole
tooth with CBCT scans. The main focus of those publications was to establish a “Norm” from
the near normal group of patients.
Figure 15: Screen shot of research conducted by Tong. et al (2012) depicting crown and root
centers of teeth being digitized.
The authors screened 1840 patients and later applied their inclusion and exclusion criteria to
obtain 76 patients for their study. They defined a near normal group as a pool of patients who
met their selection criteria. Except for having four premolars extracted our selection criteria
were similar and are fully described in later chapters. We made all efforts to duplicate their
study so that comparisons could be made.
27
Extraction versus non-extraction treatment
Even with all the advances in orthodontic technology there is still the ongoing debate of
extraction versus non extraction treatment. For over 100 years to extract or not to extract has
been a key question in planning orthodontic treatment (Proffit, 2004). The two main reasons
for extraction is (1) to provide space to align remaining teeth in the presence of severe
crowding and (2) to allow teeth to be moved so protrusion can be reduced or so skeletal Class II
or Cl III problems can be camouflaged (Proffit, 2004; Kumari et al., 2010; Illeri et al., 2011).
Figure 16: Pattern of extraction treatment in the past 100 years
(Profitt, 2004).
Early on Dr. Angle had the strong belief that every person had the potential for an ideal
relationship of all 32 natural teeth and therefore extraction for orthodontics was never needed
(Proffit, 2004). Angle believed that relapse was due to improper occlusion and that if the bite
was correct then virtually any type of malocclusion could be corrected properly with archwires
and rubber bands. In the early 1900’s Angle and the orthodontic profession virtually never
extracted teeth.
By the mid 1930s one of Angles last students, Charles Tweed, decided to retreat his patients
who had relapsed with a new extraction treatment. Tweed, along with Raymond Begg,
28
concluded that the occlusion is more stable with extraction treatment. It is commonly known
that the Tweed-Merrifield philosophy involves a high extraction rate. Their philosophy was to
position and arrange the teeth for maximum facial balance, joint support, efficiency, esthetics,
and harmony with their surrounding structures (Vaden, 1996). Premolars are the most
commonly extracted teeth for orthodontic treatment and extraction treatment may prolong
treatment time as compared to non-extraction treatment (Turkoz et al., 2011).
More recently there has been a swing once again away from extractions. This is in part due to
findings that suggest there is little difference in stability with extraction versus non-extraction
patients (Little, 1999; Burke et al., 1998). The Damon type philosophy involves using expansion
and light forces to align the teeth properly. They use considerable expansion in the buccal
segments producing a broader arch form in balance with the tongue and cheek (Burke et al.,
1998).
Figure 17: A typical severe lower crowding case in which the non-extraction treatment would
involve tipping teeth facially and widening the dental arch (Burke et al., 1998).
Controversy over the role of extraction continues because there are no good data to settle the
issue (Proffit, 2004). What is agreed upon is that extraction spaces close from mesial migration
of the molars and distal movement of the premolars when using traditional mechanics (Chen et
29
al., 2010). Thus if the patient does not like the protruding appearance of their teeth extractions
are a proper treatment modality.
Figure 18: Figure depicting sliding mechanics space closure on patients with premolar
extraction treatment. (Chen et al., 2010)
30
Chapter 2: Research Objective
The purpose of this study is to use CBCT to analyze the mesiodistal angulation and the
faciolingual inclination of whole teeth in a previously defined near normal group versus
patients that have undergone four premolar extractions for orthodontic treatment.
31
Chapter 3: Materials and Methods
The selection criteria were similar to the criteria used for the near normal group performed by
Dr. Tong et al. (Tong et al., 2012; Tong et al., 2012). All of our patients had undergone
orthodontic treatment with four premolars extracted (USC IRB approval #UP-11-00196). The
patients either had all first premolars extracted or all second premolars extracted. For the
purpose of this study all remaining premolars in the extraction group will be numbered as if
they are second premolars (ex: UL5, LL5 etc.).
From April 2004 to October 2009 approximately 2000 cases with CBCT were scanned. Dr. Jenny
Yoo chose boys of at least 14 years old and females that were at least 12 years old. None of the
patients had surgical treatment; no TADs were used; had no congenitally missing teeth; low
decay rate, no large restorations or fixed replacements; and no supernumerary teeth.
Post treatment Photo screening:
1. Overbite and overjet between 0-5mm
2. Minimal spacing, crowding or rotations
3. No apparent arch form asymmetry or cross bites
4. Molar and canine relationship less than ¼ cusp away from Cl I
X-ray screening:
1. No obvious skeletal asymmetry
2. ANB between -1° to 6.5°
3. FMA between 14° to 37°
4. U1/L1 angulation between 110° and 146°
Each CBCT scan was taken using a NewTom 3G under the following conditions: the tube
32
voltage – 110 kVp, tube current – 15 mA, scan time – 17 seconds, grayscale – 12 bit, field of
view – 200 mm (12 inch). Before the scan was acquired, each patient was placed in a supine
position. The DICOMM data was imported into Dolphin 3D and images were rendered. With
the Dolphin software we were able to digitize each individual tooth in all 3 planes of space to
obtain proper tip and torque measurements.
Global 3Dimensional coordinate system
A global three-dimensional coordinate system was used for proper orientation of the head. We
used sagittal, transverse and coronal planes, each perpendicular to the other two. The sagittal
plane evenly divided the right and left sides and passed between the maxillary central incisors.
The coronal plane was at the level of the maxillary first molar buccal grooves. The transverse
plane was the functional occlusal plane which intersected the anterior overbite and molar
overbite at the maxillary first molar buccal grooves.
Figure 19: Image of all three planes A) Coronal slice B) Sagittal slice C) Axial slice D) Full 3D
view
A B
C D
33
Tooth specific 3Dimensional system for locating crown and root centers
A different three perpendicular plane system for each tooth was used for locating each crown
and root center: The anatomical mesiodistal plane, the anatomical faciolingual plane, and the
transverse plane at the crown and root center level. We used the true long axis of the tooth
which was defined as the line connecting the center of the crown to the center of the root. We
did not include the apical third of the root as it has high degree of variability.
Figure 20: Point being placed at crown center utilizing all three planes of space. A) Mesiodistal
slice B) Faciolingual slice C) Axial slice D) Full 3D view
A
C D
B
34
Figure 21: Point being placed at root center utilizing all three planes of space A) Mesiodistal
slice B) Faciolingual slice C) Axial slice D) Full 3D view
Figure 22: All teeth digitized with line passing from crown center to root center. Green lines
represent each whole tooth long axis in 3D.
B
B
A
D C
35
Arch form
Four points (mid incisal, canine, second premolar, and the second molar distal) were digitized
along the right side buccal outline of each dental arch at the crown center level to produce the
maxillary and the mandibular right side half arch. The left side half arch is added as a mirror
image of the right side arch. Once the complete arch form is digitally constructed the software
will add two lines to each tooth. The green line represents the faciolingual plane that is
perpendicular to the arch plane and passes through the crown center. The shorter blue line
represents the mesiodistal plane that also passes through crown center and is perpendicular to
the faciolingual plane.
Figure 23: Maxillary arch form digitized from the arch outline at mid incisal, canine, second
premolar, and the second molar distal.
Determining tooth tip and torque
Determining the mesiodistal angulation of each tooth is done automatically after arch form is
digitized. Four points (mid incisal, canine, second premolar, and the second molar distal) were
36
digitized along the right side buccal outline of each dental arch at the crown center level to
produce the maxillary and the mandibular right side half arch
Figure 24: Determining mesiodistal angulation, tip, of the mandibular first molar in the
mesiodistal view as the angle between the green line and red line. Green line represents the
projection of the tooth long axis in the mesiodistal plane; the red line represents the tooth
specific faciolingual plane.
The torque is computed as the angle between the projection of each tooth long axis in the
faciolingual plane specific to that tooth and the line representing the tooth specific mesiodistal
plane. If the root is lingual to the mesiodistal plane then the value is positive, otherwise it is
negative.
37
Figure 25: Determining the faciolingual inclination, torque, of lower molar in the faciolingual
view as the angle between the green line and red line. Green line represents the projection of
the tooth long axis in the faciolingual plane; the red line represents the tooth specific
mesiodistal plane.
Reliability of measurements
In order to ensure the measurements were reliable the author digitized all 22 cases and then at
a later date re-digitized all cases a second time. Intra-correlation coefficients (ICC) were
calculated between the two time measurements.
Statistics
A Kolmogorov-Smirnov normality test was performed to check for normality in our data (α =
0.05). To check for symmetry between left and right tip and torque we performed a paired T-
test for the normal data. Twelve pairs of mesiodistal angulation and faciolingual inclination
comparisons were analyzed, each with α level adjusted to 0.05/12= 0.004 (Bonferroni
correction). For the four variables that were non-parametric (mandibular central, canine,
38
premolar, and maxillary second molar faciolingual inclinations) we used a Wilcoxon Signed
Rank test to compare the differences between the left and right sides (α = 0.004).
After comparing the left and right sides we were able to combine all left and right values except
for the mandibular laterals and first molars mesiodistal angulations. We ran an independent T-
test comparing the four bicuspid extraction group to the near normal group.
The non-parametric group (mandibular central, canine, premolar, and maxillary second molar
faciolingual inclinations) were analyzed using a Kruskal-Wallis test with a Mann-Whitney post
hoc to determine the differences between the extraction treatment versus the near normal
group.
All statistics were completed using Microsoft Excel and SPSS statistics.
39
Chapter 4: Results
Intra-class correlation coefficient and normality of data
Table 1: ICC and Normality tests to determine reproducibility and distribution of data.
ICC Normality ICC Normality
Mesiodistal angulation Mesiodistal angulation
UR1
0.941
0.200
LR1 0.918
0.200
UR2
0.950
0.200
LR2 0.959
0.200
UR3
0.900
0.200
LR3 0.971
0.200
UR5
0.960
0.112
LR5 0.902
0.200
UR6
0.806
0.200
LR6 0.846
0.200
UR7
0.976
0.200
LR7 0.933
0.200
UL1
0.885
0.200 LL1
0.752
0.200
UL2
0.919
0.200 LL2
0.900
0.081
UL3
0.930
0.200 LL3
0.948
0.200
UL5
0.950
0.110 LL5
0.963
0.111
UL6
0.889
0.200 LL6
0.870
0.200
UL7
0.952
0.200 LL7
0.921
0.200
Faciolingual inclination Faciolingual inclination
UR1
0.984
0.200
LR1 0.957
0.200
UR2
0.959
0.200
LR2 0.950
0.200
UR3
0.951
0.200
LR3 0.924
0.200
UR5
0.882
0.200
LR5 0.917
0.003*
UR6
0.822
0.088
LR6 0.898
0.200
UR7
0.947
0.024*
LR7 0.911
0.169
UL1
0.922
0.200 LL1
0.952
0.021*
UL2
0.919
0.200 LL2
0.959
0.200
UL3
0.935
0.200 LL3
0.932
0.015*
UL5
0.920
0.200 LL5
0.915
0.200
UL6
0.773
0.147 LL6
0.916
0.200
UL7
0.951
0.200 LL7
0.807
0.200
Table 1: All patients were digitized at two different time points which allowed us to determine
ICC values. A Kolmogorov-Smirnov normality test was used to determine if values were
parametric. ICC, interclass correlation; UL, upper left; UR, upper right; LL, lower left; LR, lower
right, 1, central incisor; 2, lateral incisor; 3, canine; 5, second premolar; 6, first molar; 7, second
molar.
*Statistically significant non-parametric value with α level = 0.05.
40
ICC tests were performed on each tooth to determine the repeatability of the two time
measurements (Table 1). ICC was performed for mesiodistal angulation and faciolingual
inclination on all 24 digitized teeth. The average ICC for both tip and torque were above 0.9
(tip=0.914 and torque= 0.917). The first and second digitizations of the same patient were
performed weeks apart. The high ICC values along with the time in between digitizations
means there is a high degree of reproducibility for the digitizations performed. The first molars
ICCs were below average (0.853) indicating difficulty with consistent digitization but still
acceptable to combine the first and second trials.
Tests for normality were performed for the average of the first and second trial tip and torque
of all 24 digitized teeth (Table 1). The Kolmogorov-Smirnov test revealed that all data except
for the UR7, LR5, LL1 and LL3 faciolingual inclinations were parametric. For the non-parametric
data we used Wilcoxon Signed Rank test and Kruskal Wallis with Mann-Whitney post to analyze
them.
41
Left and right side comparison for the four premolar extraction group.
Table 2: Paired t-test to compare the right and left side mesiodistal angulation and
faciolingual inclination (°)
Mean, R SD, R
Mean,
L
SD,
L
Avg
(R,L)
SD, avg
(R,L)
Mean dif
(R-L)
P value (R
and L)
MDA
U1 1.33 4.03 3.19 3.87 2.26 2.63 -1.86 0.152
U2 1.45 3.75 1.75 4.71 1.64 3.24 -0.30 0.803
U3 8.43 4.00 6.98 3.83 7.70 3.10 1.45 0.170
U5 2.42 5.86 5.79 5.76 4.11 4.63 -3.37 0.035
U6 6.69 3.53 6.49 4.61 6.59 3.59 0.20 0.819
U7 2.99 7.55 3.75 7.59 3.37 7.05 -0.76 0.523
L1 -0.95 4.09 0.03 2.35 -0.46 2.28 -0.97 0.361
L2 -2.06 5.00 1.43 4.32 -0.31 4.30 -3.48 0.000*
L3 4.65 4.94 5.19 3.77 4.92 3.68 -0.55 0.601
L5 6.03 4.30 6.78 5.14 6.41 3.64 -0.75 0.567
L6 8.58 4.45 12.63 4.07 10.60 3.88 -4.05 0.000*
L7 10.61 3.56 13.39 5.41 12.00 3.90 -2.78 0.013
FLI
U1 28.69 6.38 28.27 5.94 28.48 5.96 0.42 0.532
U2 29.74 6.25 29.20 5.83 29.47 5.63 0.54 0.569
U3 14.51 6.09 13.86 5.26 14.19 5.19 0.65 0.517
U5 5.05 4.05 7.33 6.51 6.19 4.54 -2.28 0.085
U6 5.92 3.31 5.60 3.84 5.76 2.96 0.33 0.708
U7 9.48 6.55 10.46 6.55 9.97 5.60 -0.98 0.507
Ɨ
L1 21.21 6.36 20.82 5.99 21.01 6.05 0.39 0.480
Ɨ
L2 21.30 5.72 19.59 5.42 20.45 5.33 1.72 0.022
L3 14.53 5.26 12.55 4.65 13.54 4.43 1.99 0.049
Ɨ
L5 2.98 6.15 1.07 4.08 2.03 4.72 1.91 0.057
Ɨ
L6 -7.00 4.85 -9.26 4.94 -8.13 4.35 2.26 0.027
L7 -8.52 5.21 -8.13 4.25 -8.32 3.86 -0.39 0.745
Table 2: Twelve pairs of mesiodistal angulation and faciolingual inclination comparisons, each
with α level adjusted to 0.05/12 = 0.004 (Bonferroni correction). MDA, mesiodistal angulation;
FLI, faciolingual inclination; R, Right; L, left; Avg, average; dif, difference; U, upper (maxillary); L,
lower (mandibular); 1, central incisor; 2, lateral incisor; 3, canine; 5, second premolar; 6, first
molar; 7, second molar.
*Statistically significant differences between the right and left mean values;
Ɨ
Related-samples
Wilcoxon signed rank tests (non-parametric data) were used.
In order to compare the left and right sides for symmetry we used a paired T-Test for
parametric data and a Wilcoxon Signed Rank test for the non-parametric data (Table 2). After
42
applying the Bonferroni adjustment there was two values that were significant. The lower
lateral and first molar mesiodistal angulation showed statistically significant differences
between the left and right sides. The mean mesiodistal difference for the mandibular laterals
was 3.48 degrees and for the first molars it was 3.88 degrees. This is larger than the 2.5 degrees
that is clinically acceptable. The following statistics were done by combining the left and right
sides for all values except for the mandibular laterals and first molars mesiodistal values.
43
Compared extraction to near normal group
Table 3: Independent T-Test and Kruskal Wallis with Mann-Whitney post hoc
comparison of extraction to near normal group
Mean,
Ext
SD,
Ext
Mean,
NN
SD,
NN
Avg (Ext,
NN)
SD, Avg
(Ext, NN)
Mean dif
(Ext - NN)
P value
(Ext, NN)
MDA
U1 2.26 2.63 5.91 3.06 4.09 3.33 -3.65
0.000*
U2 1.64 3.24 6.97 3.46 4.31 4.07 -5.33
0.000*
U3 7.70 3.10 11.39 3.21 9.55 3.53 -3.69
0.000*
U5 4.11 4.63 4.71 3.80 4.41 3.99 -0.60
0.290
U6 6.59 3.59 1.69 4.06 4.14 4.45 4.90
0.000*
U7 3.37 7.05 -6.33 6.98 -1.48 8.15 9.70
0.000*
L1 -0.46 2.28 0.38 1.64 -0.04 1.82 -0.84
0.059
LL2 1.43 4.32 -0.53 3.46 0.45 3.73 1.96 0.030
LR2 -2.06 5.00 -0.94 3.85 -1.50 -0.94 -1.11 0.171
L3 4.92 3.68 4.47 3.71 4.69 3.69 0.45
0.310
L5 6.41 3.64 8.11 3.32 7.26 3.45 -1.70
0.029
LL6 12.63 4.07 9.45 3.38 11.04 3.77 3.18 0.001*
LR6 8.58 4.45 9.82 3.37 9.20 9.82 -1.24 0.118
L7 12.00 3.90 17.50 5.28 14.75 5.49 -5.49 0.000*
FLI
U1 28.48 5.96 33.50 7.14 30.99 7.18 -5.02
0.000*
U2 29.47 5.63 32.36 5.29 30.91 5.47 -2.89
0.020
U3 14.19 5.19 20.75 4.74 17.47 5.55 -6.57
0.000*
U5 6.19 4.54 2.31 4.27 4.25 4.61 3.88
0.001*
U6 5.76 2.96 4.73 3.74 5.25 3.59 1.03
0.093
U7 9.97 5.60 10.83 4.97 10.40 5.11 -0.86 0.729
Ɨ
L1 21.01 6.05 26.44 6.16 23.73 6.51 -5.42 0.001*
Ɨ
L2 20.45 5.33 25.36 5.37 22.90 5.71 -4.91
0.000*
L3 13.54 4.43 19.27 5.14 16.40 5.52 -5.72 0.000*
Ɨ
L5 2.03 4.72 -0.91 3.59 0.56 4.04 2.94 0.004*
Ɨ
L6 -8.13 4.35 -8.51 4.13 -8.32 4.16 0.38
0.360
L7 -8.32 3.86 -12.38 4.92 -10.35 4.98 4.06
0.000*
Table 3: Twelve pairs of mesiodistal angulation and faciolingual inclination comparisons,
each with α level adjusted to 0.05/12 = 0.004 (Bonferroni correction). MDA, mesiodistal
angulation; FLI, faciolingual inclination; R, Right; L, left; LL, lower left, LR, lower right, Ext,
extraction group; NN, near normal group; Avg, average; dif, difference; U, upper (maxillary);
L, lower (mandibular); 1, central incisor; 2, lateral incisor; 3, canine; 5, second premolar; 6,
first molar; 7, second molar.
*Statistically significant differences between the right and left mean values;
Ɨ
Related-
samples Kruskal Wallis with Mann Whitney post hoc tests (non-normal data) were used.
44
This study compared the tip and torque of the four premolar extraction group to the previously
digitized near normal group (Table 3). For the parametric data the independent T- test was
used. For the non-parametric data (U7, L5, L1 and L3 faciolingual inclination) a Kruskal-Wallis
with Mann Whitney post hoc test was used.
Table 3 indicates that the maxillary central, lateral, canine, first molar and second molar all
have significantly different mesiodistal values as compared to the near normal group. The
maxillary premolars have a similar mesiodistal value in both groups. In the mandible only the
left first molar (more) and the second molars (less) show variation in the mesiodistal values as
compared to the near normal group.
Table 3 also reveals that all the maxillary and mandibular anterior teeth (except for the
maxillary laterals) have statistically significant smaller faciolingual torque and premolars have
statistically significant higher faciolingual values as compared to the near normal group. For the
molars, only the lower second molars have significantly more torque than the near normal
group.
45
Graphs A-D: Fluctuation of mesiodistal angulation and faciolingual inclination (right and left side
average values +/- standard deviation) from anterior to posterior in both arches. A, maxillary teeth
mesiodistal angulation. B, Maxillary teeth faciolingual inclination. C, Mandibular teeth mesiodistal
angulation. D, Mandibular teeth faciolingual inclination. Teeth with significant difference
between the near normal and extraction group.
-15
-10
-5
0
5
10
15
20
U1 U2 U3 U5 U6 U7
Angulation in degrees
Tooth number
Upper teeth mesiodistal
angulation of extraction and
near normal groups
Extraction
Near…
-5
0
5
10
15
20
25
30
35
40
45
U1 U2 U3 U5 U6 U7
Inclination in degrees
Tooth number
Upper teeth faciolingual
inclination of extraction and
near normal groups
Extraction
Near normal
-10
-5
0
5
10
15
20
25
L1 L2 L3 L5 L6 L7
Angulation in degrees
Tooth number
Lower teeth mesiodistal
angulation of extraction and
near normal groups
Extraction
Near Normal
-20
-10
0
10
20
30
40
L1 L2 L3 L5 L6 L7
Inclination in degrees
Tooth number
Lower teeth faciolingual
inclination of extraction and
near normal groups
Extraction
Near normal
A
B
C D
46
Graphs A-D allow for easier visualization of the two groups’ mesiodistal and faciolingual values as
compared to each other. The maxillary teeth in the extraction group have smaller mesiodistal
values in the anterior teeth (less mesially angulated crowns) and the molars have a higher value
(more mesially angulated crowns) as compared to the near normal group. The maxillary anterior
teeth in the extraction group also have lower faciolingual values then the near normal group
indicating reduced labial protrusion in these teeth.
The mandibular mesiodistal values are very similar within the two groups. The mandibular arch in
the extraction group has smaller faciolingual values (reduced labial protrusion) for the anterior
teeth as compared to the near normal group.
47
Chapter 5: Discussion
The purpose of this study was to use CBCT images to compare whole teeth tip and torque of
the previously defined near normal group versus patients that had undergone four premolar
extraction treatment. Using the same methodology as Dr. Tong (Tong et al., 2012) we were
able to accurately digitize the crown center and root center using Dolphin 3D. Connecting the
crown and the root centers with a line allowed us to accurately define the true long axis of
each whole tooth. This long axis line was used to measure the faciolingual inclination and the
mesiodistal angulation of each whole tooth using the University of Southern California root
vector analysis program.
The methodology was proven reproducible as our ICC values averaged over 0.9 (Table 1) and
our normality was analyzed using a Kolmogorov-Smirnov test. The first molars ICCs were below
average (0.853) indicating difficulty with consistent digitization when multiple roots are
involved. Besides the resolution issue, there is a certain amount of subjectivity when the center
of the root is defined in 3D.
The extraction group left and right sides were symmetric except for the lower lateral and first
molars mesiodistal values. Except for these four teeth we were able to combine the left and
right sides when comparing our data to the previously analyzed near normal group. The fact
that there is asymmetry in lower lateral and lower molar tip reflected errors in bracket or band
positioning and lack of wire adjustments in these teeth. The reason there is no difference in the
48
expression of torque between the two sides for any teeth may reflect the fact that treatment
may affect tip more than it affects the torque. In another word, the final tip may be more
sensitive to bracket position or wire adjustment, whereas the final torque may not be sensitive
to those factors and is mostly dictated by the biology of tooth positioning inside its micro
environment.
By combining most of our data we were able to properly compare the extraction group to the
previously defined near normal group. There was no significant difference in the mesiodistal
angulation of the premolars but there was a discrepancy for the majority of the maxillary teeth
(central, lateral, canine, first and second molar). The near normal group had a higher positive
mesiodistal value (more mesially angulated crowns) in the anterior segment then the
extraction group. Brackets in the maxillary arch tend to have a high degree of mesiodistal
angulation built in. Although there is mesial crown angulation built into the bracket
prescription it would seem as though the average is still less than the near normal group. A
commonly used prescription for this study was MBT (Figure 3). MBT prescription has a tip value
of 4°, 8° and 8° for the maxillary central, lateral and canine respectively. An average
prescription for the maxillary teeth is 5°, 8° and 10° for the central, lateral and canine (Figure
2). In our study the average mesiodistal values for the extraction group were 2°, 2° and 8° for
the maxillary central, lateral and canine. The near normal group had values that were closer to
what the average prescription is. The near normal group had average tip for of 6°, 7° and 11°
for the central, lateral and canine. It would appear that even though the tip is built into the
bracket not all of the prescription is expressed to the teeth when trying to finish a case. It is
quite unlikely this is due to bracket positioning since this happens almost across the board for
49
all the upper anterior teeth. The retraction of teeth along the archwire may cause the anterior
teeth to lose mesio-crown tip as a result of the slight play between the arch wire and the
bracket slot. The same may be true for the upper molars, but in different direction.
Contrary to the many maxillary teeth that had mesiodistal variability only the lower left first
molar and the lower second molars were significantly different in the two groups. This also
coincides with the average bracket prescriptions available. Figure 2 demonstrates that the
brackets of most of the lower teeth have little or no tip included except for the lower canine
which can be anywhere from 15 degrees mesial tip with a Ricketts prescription to 3 degrees
with a MBT prescription. The little amount of tip built into the average bracket seems to
coincide well with the natural dentition. Another reason maybe there was more crowding in
the lower anterior segment before treatment and the spaces created by the extraction of the
premolars is mostly used to alleviate crowding and minimum retraction of the anterior.
However, the simultaneous reduction of the faciolingual inclination in these teeth seems to
indicate that the lower anterior teeth have been uprighted during treatment. It is possible that
the use of Class II elastics in most of these cases may have counteracted the distal tipping
effect leaving the mesiodistal angulation unchanged. However, there is significant more molars
tipping mesially as a result of mesialization and Cl II elastics wear.
The faciolingual inclination had the greatest variation amongst the two groups. All of the
anterior teeth (except maxillary laterals) had significantly less facial inclination then the near
normal group. Figure 3 shows varying slop in the bracket when using a variety of slot sizes and
bracket sizes. After initial leveling and aligning spaces are then contracted. Ideally, as spaces
50
are closed the anterior teeth would translate perfectly posteriorly. What clinically occurs is the
anterior teeth translate posteriorly and also lose facial crown torque. There is a difference in
size between the bracket and the wire. Even if using a 0.019” x 0.025” SS wire in a 0.022” x
0.028” slot there is still over 10 degrees of play between the bracket and the wire. This means
that when the anterior teeth are pulled posteriorly the crowns will tend to move lingually
which means they will have a lower torque value. This lower torque value is what we are seeing
in our extraction group as compared to the near normal group. It seems the torque
prescriptions have not completely controlled the final torque of teeth, often due to the use of
undersized wires and oversized slots in the brackets. While this may be a welcome effect for
patients who have severe protrusion prior to treatment, for patients who are Class II div (2)
maintaining or obtaining correct faciolingual inclination for the front teeth become a challenge
and should be built into the treatment plan. The use of high torque brackets in these cases may
be recommended.
Analyzing the teeth with the CBCT and the USC root vector analysis system has allowed the
accurate comparison of a near normal group of patients to a group of patients who have
undergone extraction treatment. The results can be explained by visualizing the mechanics
used in extraction cases and the varying prescriptions built into orthodontic brackets.
Although the study showed interesting results it had its limitations. There were only 22 patients
in the extraction group as compared to 76 in the near normal group. The 22 patients were
treated by varying orthodontist with different bracket systems and with varying methods of
treatment. There is no information regarding how much detailing were done and whether
51
progress panoramic radiographs were used to check for root parallelism. There was no singular
protocol all orthodontists followed and the doctors may not have banded or bonded the
second molars. Also not all second molars were digitized in the near normal group thus making
it difficult to compare. It will also be worthwhile to compare the pre-treatment values with the
post-treatment values in the extraction group, although the pre-treatment values would have a
much larger variation due to malocclusions. However, the outcomes of this study is surprisingly
consistent. Knowledge of the changes in the incisors inclination before and after treatment
may offer clear guidance for orthodontists to understand the treatment mechanics and to use
the current bracket prescription system to our advantage.
Further studies should look at specific treatment modalities and their effects on the mesiodistal
angulation and faciolingual inclination of the various teeth. The studies should also include a
larger patient pool.
52
Chapter 6: Conclusion
1. We have confirmed the validity of the University of Southern California Root Vector
Analysis program. The methodology previously developed is highly reproducible as shown
by our ICC values (average tip=0.914 and average torque= 0.917). The analysis program
allows us to compare multiple patients with confidence.
2. The maxillary teeth of the extraction group (maxillary central, lateral and canine) had a
reduction of mesial crown angulation and the molars had an increase of mesial crown
angulation as compared to the near normal group. The built-in mesially-angulated
prescription in the upper anterior brackets is not enough to counteract the distal tipping
effect as a result of space closing.
3. The mandibular left first molar and the second molars, but not any of the anterior teeth,
showed more mesial crown tipping. This may be the result of treatment mechanics,
especially the use of Class II elastics in most of these cases.
4. The faciolingual values had the greatest variation in the two groups. In the extraction group
all of the anterior teeth (except for the maxillary lateral) had less labial crown inclination
then the near normal group. This coincides with the belief that when closing extraction
53
spaces anterior crowns move more distally then the roots. This is why orthodontists prefer
to extract in cases where a patient has protruded incisors.
5. Further studies are needed to compare different treatment methodologies and their
effects on the mesiodistal angulations and faciolingual inclinations. It would be beneficial
to include more patients in this study to confirm our results.
54
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Abstract (if available)
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Asset Metadata
Creator
Coughlin, Nathan
(author)
Core Title
Whole tooth tip and torque comparison of orthodontically treated extraction cases versus a non-treated near normal group using CBCT analysis.
School
School of Dentistry
Degree
Master of Science
Degree Program
Craniofacial Biology
Publication Date
04/03/2013
Defense Date
02/27/2013
Publisher
University of Southern California
(original),
University of Southern California. Libraries
(digital)
Tag
cbct,OAI-PMH Harvest,orthodontics,tip,torque
Language
English
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Electronically uploaded by the author
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Tong, Hongsheng (
committee chair
)
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nathancoughlin@gmail.com
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https://doi.org/10.25549/usctheses-c3-230672
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etd-CoughlinNa-1509.pdf
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230672
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Coughlin, Nathan
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The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the a...
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Tags
cbct
orthodontics
tip
torque