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Alveolar process inclination as related to tooth inclination on near normal patients -- in three dimensional space

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Alveolar process inclination as related to tooth inclination on near normal patients -- in three dimensional space

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ALVEOLAR PROCESS INCLINATION AS RELATED TO TOOTH INCLINATION ON NEAR
NORMAL PATIENTS – IN THREE DIMENSIONAL SPACE

By

Virginia Pham

________________________________________________________________________

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 Virginia Pham

i
Table of Contents

List of Tables .................................................................................................................. ii

List of Figures ................................................................................................................ iii

List of Graphs ................................................................................................................. vi

Acknowledgements ...................................................................................................... v

Abstract ............................................................................................................................. vi

Chapter 1: Introduction .............................................................................................. 1

Chapter 2: Literature Review ................................................................................... 4

Chapter 3: Objective ..................................................................................................... 17

Chapter 4: Hypothesis ................................................................................................ 18

Chapter 5: Material and Methods .......................................................................... 19

Chapter 6: Statistics ..................................................................................................... 28

Chapter 7: Results ........................................................................................................ 29

Chapter 8: Discussion ................................................................................................. 36

Chapter 9: Conclusions ............................................................................................... 44

References ....................................................................................................................... 45

ii
List of Tables

Table 1: Overall ICC ..................................................................................................... 29

Table 2: DFLI .................................................................................................................. 30

Table 3: APFLI ............................................................................................................... 31

Table 4: D-APFLI-D ...................................................................................................... 32

Table 5: Summary Chart ............................................................................................ 32

iii
List of Figures

Figure 1: Angle prototype of ideal occlusion ..................................................... 1

Figure 2: Tong et al. ..................................................................................................... 3

Figure 3: Andrew’s WALA ridge ............................................................................. 5

Figure 4: Periodontal breakdown .......................................................................... 6

Figure 5: Commercial arch wire shapes .............................................................. 7

Figure 6: Periodontal exacerbation ...................................................................... 8

Figure 7: Torque Prescription ................................................................................. 9

Figure 8: SWA deficiencies ........................................................................................ 10

Figure 9: Example of a DICOM ................................................................................ 14

Figure 10: Straightwire appliance ......................................................................... 15

Figure 11: 3D Bone Imaging .................................................................................... 16

Figure 12: Global Coordinate System .................................................................... 22

Figure 13: Digitization point ..................................................................................... 22

Figure 14: Digitization of the interproximal center points ........................... 24

Figure 15: Digitization of the mandibular alveolar apical centers ........... 24

Figure 16: Digitization of the maxillary alveolar apical centers ................. 25

Figure 17: Digitization of the lower alveolar bony arch ................................ 25

Figure 18: Adjustment of the digitization points ............................................. 27

Figure 19: Measurement of the APFLI ................................................................. 27

iv
List of Graphs

Graph 1: Maxillary Arch Fluctuations .................................................................. 33

Graph 2: Mandibular Arch Fluctuations .............................................................. 34

Graph 3: Comparison of Inter -arch fluctuations of D-APFLI-D ................. 35

v

Acknowledgements

I would like to thank my research mentor, Dr. Hongsheng Tong who has helped me greatly
through this whole process. He has given me invaluable guidance and advice and has
devoted countless hours to help me complete this research project. In addition, I would like
to thank Dr. Bita Moalej who helped with the initial digitizations and suffered through the
trials and errors of starting this project. Dolphin created the program that allowed us to
collect the data from the digitized points, without their help there would be no research.
Lastly, I would like to thank Dr. Enciso for helping me with the final statistics.

vi
Abstract

PROJECT TITLE
Alveolar Process Inclination as Related to Tooth Inclination on Near Normal Patients – In
Three Dimensional Space

BACKGROUND
CBCT opens new opportunities for alveolar bone studies by allowing precise
measurements of teeth and their alveolar housing. This could provide new insights into the
role of tooth and bone geometry in normal occlusions.

PURPOSE
To determine whether correlations are present between torque of teeth and torque of bone
in patients with normal occlusion.

METHODS
CBCT images of a sample of 76 near-normal cases were acquired. Maxillary and mandibular
teeth were digitized. Alveolar process centers were also digitized at each interproximal
area. Torque was calculated and compared for all teeth and all interproximal areas. Paired
T-tests and Wilcoxon signed rank tests were used to compare (1)right and left
measurements (2) bone and tooth measurements. The significance level was adjusted for
multiple comparisons with the Bonferonni correction to keep the overall type 1 error at
alpha =(0.05/7=0.0071).

RESULTS
We found that bone and teeth torque values follow similar trends.

CONCLUSIONS
There are correlations between the inclinations of teeth and the inclinations of bone. This
information can be used in addition to crown standards for positioning the entire tooth,
crown and root, within bone.

1
Chapter 1: Introduction

Malocclusions and dental irregularities adversely affect quality of life (Feu, De
Oliveira, De Oliveira, Kiyak, and Miguel, 2010). Orthodontic treatment can provide esthetic,
psychosocial and functional improvements by aligning teeth and jaws(Oliveira, and
Sheiham, 2004; Locker, 2004). The specialty of orthodontics continues to progress since its
beginning in the early 1900s. Edward H. Angle is considered the father of modern
orthodontics for his popularized classification of malocclusion based on the occlusal
relationships of the first molars (Angle, 1907). Clinical observation would reveal that
proper occlusion had many other significant characteristics other than molar occlusion
(Katz, 1992).

Larry Andrews would expand on this concept of ideal occlusion by identifying
The Six Keys of Normal Occlusion.; Class I molar relationship, mesiodistal crown
angulation, crown inclination, no rotations, tight contacts and flat occlusal planes. These
keys are still fundamental goals in all orthodontic treatment plans today and are linked to
long-term stability (Andrews, 1976, 1972, 1979, 2000).

Figure 1. Angle’s prototype of ideal occlusion

2
Orthodontic relapse is a common and significant problem (Nett and Huang, 2005).

Few risk factors have been identified, and the role of bone has only recently been
investigated. Considering teeth are supported in and orthodontically moved through
alveolar bone, little research has been done to evaluate this intimate relationship
(Davidovitch, 1991). Some research on animal models have demonstrated that teeth move
faster and show greater relapse in animals with decreased bone density (Ashcroft,
Southard, and Tolley, 1992; Bridges, King, Mohammed, 1988).

Another retrospective study
of orthodontically treated patients by Rothe showed that decreased mandibular cortical
thickness, a measure of bone mass, density, and size, on panoramic and lateral
cephalograms was shown to be a risk factor for incisor relapse (Rothe et al, 2006). It was
further hypothesized that increased cortical thickness might contribute to stability because
it is correlated with increased bone volume in the mandibular incisor region (Chaison,
Chen, Herring and Bollen, 2010). Bone geometry indeed demonstrates relationship to the
dentition (Little, 1990).
It is popular belief that positioning of roots upright over basal bone might help
reduce the amount of relapse (Little, 1990).

It’s common for orthodontists to check for root
alignment and parallelism though the American Board of Orthodontics acknowledges the
limitations especially in the canine, first premolar areas (Nett and Huang, 2005).
Faciolingual inclination, otherwise known as torque, is particularly hard to evaluate on 2D
images. Tong et al. recently developed a root vector analysis program to evaluate crown
and root angulations directly from CBCT volumetric images (Tong, Enciso, Van Elslande,
Major, Sameshima, 2012; Tong, Enciso, Kwon, Sakai, Sameshima, 2012).

3

Figure 2. Tong et al. evaluating whole tooth, crown and root, geometry with CBCT

The recent introduction of cone-beam computed tomography (CBCT) in orthodontic
diagnosis allows for (3D) imaging and measurements of volume. Its accuracy and reliability
in linear measurements have been shown to exceed those of traditional radiographs (Mah,
2004).

It is fast becoming a key diagnostic tool for assessing alveolar bone height and
volume. This technology opens new opportunities for alveolar bone studies by allowing
precise measurements of teeth and their alveolar housing. This could provide new insights
into the role of tooth and bone geometry in normal occlusions (Sheridan, 2011).

4
Chapter 2: Literature Review
I. Basal Bone Anatomy
The size and shape of the arches have significant impact in orthodontic diagnosis
and treatment planning. It affects the space available, dental aesthetics, and overall stability
of the dentition (Lee, 1999). Edward Angle

believed that each individual had the potential
for growth and development with orthodontic therapy, stating that “The best balance, the
best harmony, the best proportions of the mouth in its relation to the other features,
requires that there shall be a full complement of teeth and that each tooth shall be made to
occupy its normal position — normal growth (Angle, 1907).”
In 1925, Lundstrom, however, highlighted the need to consider the apical base in
determining the occlusion: “Orthodontic experiments show that a normal occlusion
attained by mechanical treatment is not necessarily accompanied by a development of the
apical base in harmony with the position of the teeth, with the result that the occlusion
obtained cannot be maintained (Lundstrom, 1925).” Lundstrom’s apical base is the
junction of alveolar and basal bones of the maxilla and mandible in the region of the apices
of the teeth. Andrews further expanded on this definition by defining the base as the WALA
ridge; the band of keratinized soft tissue directly adjacent to the mucogingival line.

5

Figure 3. Andrews’ WALA ridge

In relation to arch shape, in 1955 Hawley

proposed a geometric method for
predetermining the dental arches; the ideal arch was based on an equilateral triangle with
a base representing the inter intercondylar width (Hawley, 1925). The lower anterior teeth
were arranged on the arc of a circle with a radius determined by the combined width of the
lower incisors and canines, with the premolars and molars aligned with the second and
third molars turned toward the center. Various authors have used different curved
mathematical models since, but the stability of these arch forms has not been established.
A dental arch form is initially established by the configuration of the bony ridge and
then by tooth eruption, perioral muscles, and intraoral functional forces (Profitt, 1986).
Even though most patients with a malocclusion have an altered dental arch form, the
alterations achieved with mechanics during orthodontic treatment should not affect the
balance between bone and dental and muscular structures; the arrangement of these
structures adjacent to teeth and jaws should be considered the limit for orthodontic

6
movement (Profitt, 1986; Halazonetis, Katsavrias and Spyropoulos, 1994).

To minimize
relapse, clinicians have investigated the most effective approach for the correct
repositioning of teeth to provide esthetics, function, and stability, and to define the size and
configuration of the dental arch (Harris, 1997).

Figure 4. Instability in arch wire changes can result in periodontal breakdown,

recurrence of crowding of the buccal segments, or increased crowding

(Mershon, 1936)

Customizing commercially available arch wires appears to be necessary for all
patients to obtain optimum long-term stability because of the great individual variability in
dental arch forms. There are studies that demonstrate small variations in intercanine
widths of the maxilla and the mandible in Class I, Class II, and Class III malocclusions
(Uysal, Memili, Usumez and Sari, 2005; Staley, Stuntz, and Peterson, 1985; Braun, Hnat,
Fender and Legan, 1998; Nie and Lin, 2006). Compared with Class I occlusions, Class II
patients appear to have narrower maxillary and mandibular dental arches, and Class III
subjects often have narrower maxillary arches and wider mandibular arches (Ball, Miner,
Will, and Arai, 2010). There are clearly therefore a number of features in arch dimensional
changes that should be considered in treatment planning.

7

Figure 5. Commericial archwires come in many shapes, clinicians should try to pick the
archform most similar to the patient

II. Bone response to orthodontic movement
Three biologic responses make orthodontics possible; bone formation, bone
resorption and iatrogenic external root resorption (Krishnan and Davidovitch, 2006). Root
resorption poses a significant risk to orthodontists (Reitan, 1960; Davidovitch, 1991,
1988).

3D research on finite element systems are demonstrating force diagrams that
visually illustrate the stresses on not only the tooth but also the structures surrounding it,
the PDL and the alveolar bone (Hohmann, Kober, Young, Dorow, Geiger, Boryor, and
Sander, 2011).
One of the problems that often arises in the orthodontic treatment of adult patients
is the presence of periodontal disease and loss of bone support. Previous research have
shown that as roots are displaced and moved away from the center of alveolar bone, there
is increased risk of creating of worsening alveolar defects. Consequences can include
gingival recession, dehiscences and fenestrations (Mershon, 1936; Bishara, Chadra, and

8
Potter, 1973; Fuhrmann, 1996).

Occurrence depends on several factors, such as direction of
movement, frequency and magnitude of orthodontic forces and the volume and integrity of
the periodontal tissues. A CBCT scan before orthodontic treatment, can show area of thin
alveolar bone and that are at higher risk for complications (Wehrbein, Bauer, and Diedrich,
1996; Dorfman, 1978). According to the literature, dehiscence is more frequently found in
the mandible whereas fenestrations are more frequent in the maxilla (Lascala, 2004). Thus,
for patients with thin attached gingiva, a correct diagnosis of bone support in the
periodontal evaluation is necessary. A diagnosis of the relationship of the craniofacial
structures should also be made to moderate the tooth movement and consequently reduce
the risk of gingival changes (Wehrbein, Bauer, and Diedrich, 1996; Dorfman, 1978).

Figure 6. Orthodontic movement can exacerbate periodontal problems.

III. Proper buccal-lingual crown inclination (torque)
Objectives of orthodontic treatment are to correct tooth positions in 3 planes of
space, so that they come close to identified cephalometric and occlusal standards. The

9
importance of establishing appropriate axial inclinations with ideal torque is frequently
mentioned in the orthodontic literature. This faciolingual inclination of tooth crowns is of
prime importance in obtaining a correct alignment of the teeth in their respective apical
bases and a normal occlusion of the upper and lower teeth.

From his historic study of 120
casts of nonorthodontic patients with normal occlusions, Andrews stated that the proper
mesiodistal inclination and facial-lingual inclination are required for ideally positioned
teeth. The torques built into the brackets of Andrews’ (Andrews, 1976, 1972, 1979, 2000)
original straight-wire appliance were based on faciolingual data derived from a study of
120 untreated normal occlusions. The torque measurements were made at LA point of each
tooth and the mean value obtained for each particular tooth was incorporated into the
brackets of his straight-wire appliance. Theoretically, these brackets should be positioned
at the same point at which the average torque values were first obtained in order to
express the prescription accurately.

Figure 7. Prescription brackets have torque built into the bracket and its prescription is
inherent that the bracket is placed correctly and that all facial contours are equal

10
Faciolingual torque positions tooth crowns for optimal dental occlusion and
posterior articulation. Presumably torque also positions roots to best withstand the forces
of occlusion (Andrews, 1976, 1972, 1979, 2000).

Since various types of teeth in the same
mouth have differences in facial contours, edgewise mechanics sometimes requires third-
order, or torquing bends in the arch wire. The pre-adjusted straight wire appliance
eliminates some need for third order bends by building torque into the bracket. When an
arch wire fits passively in the slots, the teeth move to the prescribed positions. However
not all facial contours are not alike, thus standardized bracket torques can produce
different torques on different teeth, requiring the need for compensation bends (Andrews,
1979).

Figure 8. Even with the SWA, compensation bends are sometimes necessary; in this case it
is resolved by flipping the bracket

IV. Panoramic Radiography
Until recently, two dimensional (2D) radiographic imaging has been the standard of
care to help orthodontists evaluate the dentition, skeleton and soft tissues of interest for

11
proper diagnosis, treatment planning and evaluation of growth and development. These
radiographs commonly include a lateral cephalogram and a panorex (Steiner, 1959).

Panoramic radiography was developed in 1948 by Paatero. It has traditionally been the
gold standard for care due to the advantages of low patient radiation dose, convenience,
ease and speed of the procedure (Macri and Athanasiou, 1997). Panoramic radiography is
often used before, during and after orthodontic treatment to assess root parallelism,
mesiodistal tooth angulation and root resorption. However disadvantages of panoramic
radiography include lack of fine detail, magnification and distortion. The distortion is
created by the angle between inclined teeth and is the result of vertical and horizantal
distortions. Assessing mesiodistal angulations of teeth and bone should be done so with
caution due to this inaccuracy (Macri, and Athanasiou, 1997; Baumrind and Frantz, 1971;
Carlson, 1967). Research done by McKee et al. demonstrated mesiodistal angulation
measurements from panoramic radiography were statistically different from true
mesiodistal angulations. The largest amount of angulation distortion can be found in the
canine premolar region of both arches. The ABO does not take off points for any roots in
the canine region due to this well known inherent distortion (Nett and Huang, 2005).
V. Cone Beam CT
3-dimensional imaging was first introduced into medical practice in 1971 by Dr
Hounsfield in England. In dentistry, Loma Linda introduced CBCT in 2000 (Scarfe, Farman
and Sukovic, 2006).

Since then, CBCT imaging has been used for head and neck applications
mainly due to reduced costs and reduced radiation exposure relative to conventional CT.
Orthodontic applications include locating impacted teeth,

applications to orthognathic
surgery, growth modification, analysis of facial asymmetries, soft tissues, and airways,

12
visualization of root resorption and inclination, and improved cephalometric landmark
identification(Ludlow, Davies and Brooks, 2003).

Clinical disadvantages include initial
setup costs, equipment size, and risks associated with relatively high radiation doses. In
recent years continued software advancements include increased speed of image
acquisition, improved image resolution and better software programs to process and
analyze the 3D images (Scarfe, Farman and Sukovic, 2006; Ludlow, Davies and Brooks,
2003, 2006) .
One fundamental difference between traditional dental imaging and orthogonal
projections is that in traditional dental imaging there is much distortion. This is because
there is always some projection error because the area being x-rayed, is always some
distance away from the film, and is projected onto it. Panoramic radiographs have an
unusual projection because the main path of the x-ray beam comes from a slightly negative
angulation. In CBCT, the x-ray beams are approximately parallel to one another, and,
because the object is much closer to the sensor, distortion is minimal (Scarfe, Farman and
Sukovic, 2006).
The legal implications of acquiring a CBCT image is a controversial issue in
orthodontics. More information than the conventional diagnostic records is obtained
through a full 3D image of the head and neck, leading to responsibility and accountability
issues regarding the diagnosis of pathology outside the region of interest.
Despite many reports in the literature on the various uses of cone-beam computed
tomography (CBCT), studies on its accuracy and image quality for assessing bone
morphology have been limited (Mah, 2004; Sheridan 2011). Also, no studies have assessed
the use of CBCT to study alveolar bone morphology in vivo. Instead, most studies used

13
radiographic phantoms, which do not accurately represent some anatomic structures such
as tooth sockets and alveolar bone margins (Lamichane, Anderson, Rigali, Seldin and Will,
2009).

Other studies have used human skulls, but the defects measured were created by the
operator(Adams, Alcan, and Erverdi, 2002). Other studies compare CBCT to multi-slice
spiral computed tomography, multidetector-row helical computed tomography, or spiral
computed tomography as gold standards (Locker, 2004).

The problem with comparing
CBCT to other computed tomography (CT) machines is that all have some measurement
errors. In addition, multi-slice spiral CT, multidetector-row helical CT, and spiral CT use
more radiation and have higher costs, limiting their use for routine dental radiography
(Mah, Danforth, Bumann and Hatcher, 2003).
.

VI. Dicom
The American College of Radiology and National Electrical Manufacturers
Association standardized the coding of images collected from CT and MRI imaging. The
term digital imaging and communications in medicine (DICOM) was adopted in 1993. A
DICOM record consists of (1) a DICOMDIR file which consists of patient information,
specific information about image acquisition and a list of images that correspond to axial
slices forming the 3D image; (2) a number of sequentially coded images that correspond to
axial slices. When all the axial slices are combined in order they form the 3D image (Grauer,
Devidanes and Profitt, 2009; Pianykh, 2008).

14

Figure 9. Example of a DICOM record

A 3D image is composed of a stack of 2D images or slices. In a similar fashion that a
2D image is composed of pixels, a 3D image is composed of voxels. Each voxel has a gray-
level value based on indirect calculation of the amount of radiation absorbed or captured
by the charge-coupled device and calculated through a filtered-back projection algorithm.
Visualization is based on a threshold filter. This filter assigns a binary value, either
transparent or visible, to each voxel based on its gray-level value. The user defines the
critical value that splits the voxels into visible and invisible. The result is a rendered image
on the screen composed of all visible voxels (Grauer, Cevidanes, and Profitt, 2009).
VII. Buccal-lingual inclination of bone and its applications
It seems possible then, that if teeth have a certain inclinations that are ideal, then,
bone must as well. Little 3D research has been done on bone characteristics alone. If like
teeth, bone has an ideal inclination, and if these inclinations can be determined, brackets
could be customized not to just place the tooth in correct inclination, but to place it in

15
correct inclination within bone. Standard bracket torques do not account that all bone
contours are different. Ideal pre-adjusted appliance with a single faciolingual torque for all
patients is not possible unless bracket slots are individually tailored. The inclination of
tailored individual slots could be designed to position crowns in the best possible
occlusion. It is clear that biologic variation exists and technologic advances have not yet
fully addressed this question in terms of the straight wire appliance.

Figure 10. The straightwire appliance builds the prescription into the bracket

The soft-tissue paradigm has paved the road toward 3D diagnosis, treatment
planning, and computer-aided design and computer-aided manufacturing orthodontics.
Because of the advances in both CBCT scanners and software designed to manage CBCT
data, it is possible to take advantage of CBCT information in a clinical setting. One of the
latest advancements in orthodontic technology that has been utilizing 3D technology is
SureSmile. Suresmile combines 3-D imaging, treatment planning software and a robot to
create finishing wires. The orthodontist can use a CBCT scan or an intraoral scanner to scan
the occlusion. Then, with a virtual “clincheck” the orthodontist can design and simulate the
teeth moving into their final positions. Lastly, a robot bends the wire with a precision to

16
1/10
th
of a millimeter that is not possible by hand. The result is faster treatment time,
fewer wire changes and better precision (Mah and Sachdeva, 2001).

Figure 11. Orthodontists can now simulate outcomes with respect to bone and they can
know if the roots will be in the target zone prior to executing a treatment plan.

This is an extraordinary and interesting time in orthodontics. E-dentistry or online
dentistry is just one of the newest forms of technologies that is revolutionizing
orthodontics. In a few years, all specialties will be able to interact, predict results, and
improve their outcomes by taking advantage of the virtual patient.

17
Chapter 3: Objective
This article will discuss characteristics observed in a study of 76 orthodontic
patients with normal occlusion. Similar to Andrews, this study did a deliberate seeking of
patients, who by our inclusion and exclusion criteria, needed little orthodontic treatment.
By looking at specific characteristics of the alveolar process with CBCT, results from these
near normal occlusions could help us see bone trends that are inherent across all normal
occlusions and give us characteristics to strive for in successful treatment. The primary
purpose of this study was to use CBCT imaging to determine if there were any differences
in facio-lingual inclination measurements between teeth and their alveolar process housing
in patients with near normal occlusion. It was hypothesized that in normal and stable
occlusion, long axes of teeth and the alveolar processes coincide, with the tooth perfectly
centered inside its alveolar housing.

18
Chapter 4: Hypothesis
I. Research Hypothesis, H a:
The facio-lingual tooth inclination measurements from CBCT are similar to the
facio-lingual alveolar process inclination measurements from CBCT
II. Null Hypothesis, H 0:
The facio-lingual tooth angulation measurements from CBCT are different from
the facio-lingul bone angulation measurements from CBCT

19

Chapter 5: Materials and Methods
This study was approved by the University of Southern California Health Sciences
Institutional Review Board (HSIRB). The IRB approval ID is APP-12-04878.
This study is a continuation of a previous study reported. From April 2004 to
October 2009, 1840 patients had full head CBCT images taken as part of their initial
orthodontic records at the Advanced Orthodontic Program of the University of Southern
California (Tong, Enciso, Van Elslande, Major, Sameshima, 2012; Tong, Enciso, Kwon, Sakai,
Sameshima, 2012). From this sample, 125 patients were considered “near normal.” After
evaluating the images, 26 patients were removed for poor imaqe quality, and 23 more
patients were removed after applying the exclusion criteria. 76 patients remained in the
“near normal” sample. A NewTom 3G Volumetric scanner (NewTom QR, Verona, Italy) was
used with the following settings: 110 kV, 15 mA, 17-second exposure time, 12 inch field of
view, and 12-bit gray scale.
Before the scan was acquired, each patient was placed in a supine position and oriented
perpendicular to the rotation axis of the CBCT x-ray source. The patient was to remain as
still as possible during the entire scan time to minimize distortion and noise in the final
image.
I. Case Selection Criteria
The patients in this study are a subset from the previous study designed to obtain the
standard mesiodistal angulation and faciolingual inclination for each tooth for a group of
patients whose occlusions are close to normal. The selection criteria for the “near normal”

20
group were comparable with those used by Andrews: no history of past orthodontic
treatment; subjects in good health and exhibiting normal growth; well-related vertical,
transverse, and anteroposterior relationships; pleasing profile; arches well aligned with no
supernumerary teeth; normal-appearing teeth; low decayed, missing, filled tooth index
numerical value; no large restorations or fixed replacements. Furthermore, all subjects had
close to Angle Class I molar relationships, and overjet and overbite close to within normal
limits.
Photo Screening
1. Complete dentition (a few cases with the second molars not fully erupted; as
long as the anatomy of the crowns are preserved, we have accepted some
cases with large fillings or crowns)
2. Molar relationship from <1/2 step Class II to 1/4 step Class III
3. OB/OJ between 0-5 mm
4. Spacing < 6 mm
5. Crowding < 4 mm (limit to 3 teeth max)
6. Rotation < 15
0
(limit to 3 teeth max)
7. Dental X-bite limited to no more than 1 tooth
8. No apparent arch form asymmetry.
X-Ray Screening
1. Panoramic X-rays show generally parallel roots
2. ANB between -1
o
to 6.5
o

3. FMA between 14
o
to 37
o

4. U1/L1 angulation between 110
o
to146
o

21
5. No obvious skeletal PA and vertical asymmetry

II. CBCT Methodology for Measuring Tooth and Alveolar Process Faciolingual Inclination
In 2012 a University of Southern California root vector analysis program was developed by
Dolphin Imaging to accurately measure each whole tooth mesiodistal angulation and
faciolingual inclination directly from Cone Beam Computed Tomography (CBCT)
volumetric images.
67
Using the software, Tong et al. measured whole tooth mesiodistal and
faciolingual inclination of 76 patients with near normal occlusion.
66
For purposes of this
study, we modified the application of the above software program to obtain faciolingual
inclination measurements from alveolar process long axes. Results from this study will be
compared to previously recorded dental measurements.
III. Global Three-Dimensional Coordinate Systems
Once the images were converted into DICOM files, the three-dimensional images were
rendered in Dolphin’s 3-dimensional program. A global coordinate system is first
generated for the proper orientation of the head and the maxillofacial structure. We use a
sagittal plane, a coronal plane, and a transverse plane, each perpendicular to the other two.
The sagittal plane is the plane that evenly divides left and right, the coronal plane is the one
that is perpendicular to the sagittal plane at the buccal grooves of the right and left first
molars, and the transverse plane is the functional occlusal plane, defined as the plane that
intersects the incisal overbite and the molar overbite (defined at the buccal groove of the
upper first molars) (Figure 12).

22

Figure 12. Image of all 3 planes established at the functional occlusal plane (Intersection of
the overbite of the central incisors and first molars at the buccal groove of the upper
molars).

IV. Tooth-Specific Three-Dimensional System for Locating Crown and Root Centers

The method was described in the previous publication. Briefly, A different three-
perpendicular-plane system specific for each tooth was used for locating each crown and
root center: the anatomical mesio-distal plane, the anatomical bucco-lingual plane, and the
transverse plane at the crown and root center level

Figure 13. Locating crown and root centers in 3 planes of space

23

V. Digitization of the Alveolar Process Long Axes and Measurement of the Alveolar Process
inclination

In order to compare the inclination of the teeth and their alveolar process housing, it
would be logical to measure the long axes at the center of the alveolar process where teeth
are located. However, the presence of roots often times disturbs the natural surface
morphology of the alveolar process. Therefore the facio-lingual inclination at each
interproximal area was initially measured instead. First, alveolar process centers were
digitized in the axial slice view interproximally between each tooth in the maxillary and
mandibular arch at the level of the alveolar crest (Fig 14). Then the axial plane was moved
to the apical level. For the mandible, this is at the same level as the cepalometric B point(
Fig 15). For the maxilla, this level is below the cephalometric A point, but at the same level
as the posterior border of the incisal canal (Fig 16 sagittal slice view). After the apical
center points were digitized at the apical level, the axial level was moved back to the crest
level and the alveolar process bony arches were digitized in the axial slice view based on
the following interproximal crest center points (Fig 17) on the right side half arch: between
the centrals, between canine and first premolar, between second premolars and first molar,
and distal to second molar. The software program will duplicate the right side half arch to
the left side, constructing a symmetrical arch form.

24

Figure 14. Digitization of the mandibular alveolar crest interproximal center points

Figure 15. Digitization of the mandibular alveolar apical centers at the apical level that
passes through the cephalometric B point. The blue line represents the axial plane.

25

Figure 16. Digitization of the maxillary alveolar apical centers at the apical level that
passes through the posterior border of the incisal canal. The blue line represents the axial
plane.

Figure 17. Digitization of the lower alveolar bony arch in axial slice view using four
interproximal points as guide: between central incisors, between right canine and first
premolar, between second premolar and first molar, and distal to the second molar.

26
Once the arch form is constructed, the customized program will add a tooth-specific
coordinate system (Fig 17). For each interproximal center (dark blue point) at the alveolar
crest level, the green line represents the facio-lingual plane that is perpendicular to the
arch plane; the shorter blue line represents the mesio-distal plane that is perpendicular to
the facio-lingual plane.
Later the axial image was rotated, so that the interproximal crest center point, here
using the point between lower right lateral and lower right canine as an example, is placed
at the coordinate origin and its tooth specific faciolingual plane goes vertical and
mesiodistal plane goes horizontal (Fig 18 C). The alveolar process centers at both the crest
and apical levels are then adjusted in the faciolingual plane ( Fig 18B). This adjustment not
only ensures that these points are perfectly centered, it also took away any mesiodistal
angulation that may be there from the initial apical point digitization. This is called
neutralization of the mesiodistal angulation of the interproximal alveolar process long axes.
The facio-lingual inclination of the alveolar process at each tooth interproximal
should be measured from the neutralized alveolar process long axis to the vertical line
formed by the intersection of the mesio-distal plane and the facio-lingual plane (Fig 19 B).
If the alveolar process center at the apical base level is lingual to the center at the alveolar
crest level, the measurement is positive, otherwise it is negative. At this point, the program
can calculate the measurements automatically.

27

Figure 18. Adjustment of the digitization points interproximal between lower right canine
and first premolar at the alveolar crest and apical levels in the tooth specific faciolingual
plane (red) to ensure that these points are centered perfectly.

Figure 19. Measurement of the alveolar process faciolingual inclination (APFLI) in the
tooth specific faciolingual plane at the interproximal between lower right lateral and lower
right canine.

B A
D
C
C D
B
A

28
Chapter 6: Statistics:
All data was entered into Microsoft Excel worksheet and were analyzed using Excel
and Statistical Package for Social Sciences (SPSS) version 19.0.
To ensure the digitization and the measurements by the investigators are consistant
and reliable, 10 cases were randomly selected to be digitized twice by two different
examiners or the same examiner but at two different time points. Inter- and intra-examiner
correlation coefficients (ICC) tests were conducted.
The data was tested for normality with Kolmogorov-Smirnov tests. For parametric
variables, Paired t-tests were used to compare (1) left and right measurements of dental
faciolingual inclination (DFLI); (2) left and right measurements of alveoloar process
faciolingual inclination (APFLI); (3) left and right dental and alveolar process faciolingual
inclination differences (D-APFLI-D). Wilcoxon signed rank test were used to compare non-
parametric variables. The significance level was adjusted for multiple comparisons with the
Bonferonni correction to keep the overall type 1 error at alpha =(0.05/6=0.0083).

29
Chapter 7: Results
The mean inter-(or intra) class correlation coefficient for 10 randomly selected
subjects with 2 time APFLI measurements for all bone centers for examiner 1 was .878 and
.931 for examiner 2. Since the ICCs were less than ideal, all cases were digitized twice and
the averages of the 2 time measurements were used for the analyses. (Table 1).
1. Method Error:

Table 1. Overall ICC for repeated measurements for the alveolar process inclination from
ten randomly selected cases

Test ICC
Investigator 1 0.878142857
Investigator 2 0.931742857

30
2. Right and Left Comparison
Multiple paired t-tests were performed to compare the DFLI, APFLI, and their D-
APFLI-D between right and left side for all 76 cases. The Bonferroni adjustment was made
with the α level set at 0.05/12=0.00416. The differences between the right and left side
measurements were not significant and therefore the measurements were combined in
Table 2, Table 3 and Table 4.

DFLI

Mean
R
SD R Mean
L

SD L Avg
(R&L)
SD
avg
(R&L)
Mean
diff
(R-L)
P
value
(R-L)
U1 33.03 7.50 33.96 6.98 33.50 7.14 -0.93 0.0018*
U2 32.02 5.91 32.70 5.05 32.36 5.29 -0.68 .0516
U3 20.33 5.29 21.18 4.83 20.75 4.74 -0.85 .0405
U4 5.69 5.46 6.13 5.01 5.91 4.70 -0.44 0.4063
U5 2.41 5.04 2.21 4.69 2.31 4.27 0.20 0.7071
U6 4.51 4.20 4.96 4.38 4.73 3.74 -0.45 0.3533
U7 10.88 5.28 10.90 5.54 10.83 4.97 -0.02 0.8704
L1 26.54 6.13 26.34 6.35 26.44 6.16 0.20 0.2720‡
L2 25.36 5.74 25.35 5.35 25.36 5.37 0.01 0.8680‡
L3 19.71 5.40 18.82 5.34 19.27 5.14 0.88 0.0150
L4 8.01 4.74 7.56 4.79 7.79 4.50 0.44 0.2267
L5 -0.24 3.94 -1.58 4.08 -0.91 3.59 1.35 0.0016*
L6 -7.99 4.42 -9.02 4.80 -8.51 4.13 1.03 0.0322
L7 -12.09 5.22 -12.80 5.40 -12.38 4.92 0.71 0.2084

Table 2. Paired t tests to compare the right and left side DFLI (Tong et. al) Only the
maxillary central incisor and mandibular second premolar torque values showed
statistically significant differences between the 2 sides with mean right and left differences
of 0.93° and 1.35° respectively. These mean differences were well below the 2.5° for clinical
significance. The 2 side measurements matched closely despite statistical differences
shown at the 2 tooth locations. Therefore the 2-side data were combined and averaged.
*statistically significant differences between right and left values; ‡Related-samples
Wilcoxon signed rank tests for nonnormal data were used.

31

Table 3. Paired T-tests were run to compare the right and left side APFLI for the bone area
corresponding to each tooth. Only the maxillary canine and mandibular first premolar
torque values showed statistically significant differences between the 2 sides with mean
left right and left differences of -1.23° and -.98° respectively. These mean differences are
below the 2.5° for clinical significance. The 2 side measurements matched closely despite
statistical differences shown at the 1 tooth location. Therefore the 2-side data was
combined and averaged. *statistically significant differences between right and left values

APFLI

Mean
R
SD R Mean
L

SD L Avg
(R&L)
SD
avg
(R&L)
Mean
diff
(R-L)
P
value
(R-L)
U1 41.21 4.96 41.49 4.73 41.35 4.81 .27 .033
U2 42.39 4.91 43.05 4.74 42.71 4.71 -.66 .006
U3 36.28 4.96 37.51 5.14 36.89 4.83 -1.23 .001*
U4 26.47 5.18 27.39 5.21 26.93 4.89 -.91 .026
U5 17.08 5.15 17.69 5.05 17.38 4.82 -.61 .119
U6 9.08 4.19 9.78 4.40 9.43 3.84 -.70 .116
L1 26.75 6.02 26.79 6.09 26.77 5.99 .03 .810
L2 27.09 5.62 27.15 5.78 27.12 5.61 -.06 .808
L3 23.38 -3.68 22.83 5.73 23.61 5.59 -.45 .081
L4 14.52 5.72 15.50 5.37 15.01 5.36 -.98 .004*
L5 3.78 5.37 4.84 5.38 4.31 5.09 -1.07 .008
L6 -9.23 5.50 -9.21 5.56 -9.22 5.27 -.02 .959

32

Table 4. Dental and Alveolar Process Faciolingual Inclination Differences (D-APFLI-D) for
each tooth site was calculated. Paired T-tests were run to compare the right and left side.
Statistically significant differences between the 2 sides were shown at the mandibular
canines, mandibular first premolars and mandibular second premolars locations with
mean right and left differences of 1.33°, 1.42° and 2.41° respectively. These mean
differences are below the 2.5° for clinical significance. The 2 side measurements matched
closely despite statistical differences shown at the three tooth location. Therefore the 2-
side data was combined and averaged. *statistically significant differences between right
and left values

Faciolingual
inclination
DFLI
Mean
DFLI
SD
APFLI
MEAN
(R,L)
APFLI
SD
(R,L)
DAPFLI-
D
MEAN
D-APFLI-D
SD
(R,L)
U1 33.03 7.50 41.21 4.96 8.18 5.43
U2 32.36 5.29 42.71 4.71 10.36 4.36
U3 20.75 4.74 36.89 4.83 16.14 4.47
U4 5.91 4.70 26.93 4.89 21.02 5.11
U5 2.31 4.27 17.38 4.82 15.07 4.82
U6 4.73 3.74 9.43 3.84 4.70 3.74
L1 26.54 6.13 26.75 6.02 -0.22 4.19
L2 25.36 5.37 27.12 5.61 1.76 3.09
L3 19.27 5.14 23.61 5.59 4.34 3.58
L4 7.79 4.50 15.01 5.36 7.22 4.35
L5 -0.91 3.59 4.31 5.09 5.22 4.56
L6 -8.51 4.13 -9.22 5.27 -0.71 4.35

Table 5. Summary chart of Right and Left averages
D-APFLI-D

Mean
R
SD R Mean
L

SD L Avg
(R&L)
SD
avg
(R&L)
Mean
diff
(R-L)
P
value
(R-L)
U1 -8.18 5.43 -7.52 5.08 -7.85 5.08 .64 .035
U2 -10.37 4.52 -10.35 4.72 -10.36 4.36 -.03 .943
U3 -15.95 4.70 -16.32 4.96 -16.14 4.47 .37 .379
U4 -20.79 5.46 -21.26 5.80 -21.02 5.11 .47 .387
U5 -14.67 5.41 -15.48 5.31 -15.07 4.82 .81 .138
U6 -4.58 4.44 -4.83 4.11 -4.70 3.74 .25 .603
L1 -0.22 4.19 -0.45 4.00 -0.33 3.92 -.23 .382
L2 -1.73 3.47 -1.80 3.36 -1.76 3.09 .07 .839
L3 5.67 3.99 -5.01 3.86 -4.34 3.58 1.33 .001*
L4 -6.51 4.60 -7.93 4.63 -7.22 4.35 1.42 .000*
L5 -4.01 4.84 -6.43 5.05 -5.22 4.56 2.41 .000*
L6 1.23 4.67 0.19 4.79 0.71 4.35 1.05 .016

33

Graph 1. Maxillary arch fluctuations of APFLI as compared to DFLI

To investigate the intra-arch fluctuation of faciolingual inclination from tooth and
bone, the 2 sided average values were plotted from anterior to posterior. The maxillary
(DFLI) started at 33° for central incisors and followed a soft “S” curve down to about 2° at
the second premolars and then turned back up to 5° for the second molars.
The (APFLI) follows a similar trend as the (DFLI) with a general reduction in
inclination from the anterior to the posterior. For the maxillary arch, the APFLI always
stays above DFLI, with the difference between the two at about 8
0
at central incisor. This
difference increases at each following tooth until first premolar where the difference
reaches the largest about 20
0
. After that, this difference decreases at the second premolar
and reaches the smallest at about 5
0
at the first molar.

34

Graph 2. Mandibular arch fluctuations of APFLI as compared to DFLI

The mandibular DFLI also started highest at 26.5° and gradually decreased
posteriorly, reaching about 0° at the second premolars but then continued to decrease to -
9° for the second premolars.
It is interesting to note that APFLI and DFLI seem to follow very similar trends in
that faciolingual inclinations from anterior to posterior fluctuated along smooth curves. It
is also worth noticing that at lower central incisor and lower first molar locations, APFLI
and DFLI are about the same.

35

Graph 3. Comparison of the maxillary and mandibular Inter-arch fluctuations of D-APFLI-D

DFLI was subtracted from the corresponding APFLI and plotted in Chart 3. Maxillary
teeth started with differences in faciolingual inclination of almost 8° and hitting its highest
at 21° in the first premolar region, only to gradually decrease to almost 4.7° by the first
molar. Mandibular faciolingual differences also followed a similar parabolic pattern,
starting at almost no difference at the centrals, hitting the highest also at the first
premolars at around 7° ,and then decrease back down to almost no difference by the first
molars. The D-APFLI-D was larger for the maxilla than for the mandible by an average of
about 10
0
.

36
Chapter 8: Discussion

Edward Angle is considered the father of modern orthodontics and his contributions
from over a century ago have had long lasting impact on orthodontic practices today
(Angle, 1907). His influences span from the diagnosis of malocclusions, to theories of
harmonious facial and dento-skeletal balances, and to various modifications of the edge-
wise appliance (Angle, 1907). About half a century ago, Larry Andrews added his six keys
to ideal occlusion by studying 120 subjects who had naturally optimal occlusions. These six
keys were common features occurring in those subjects, and collectively they
demonstrated proper tooth relationships required to achieve ideal occlusions in patients
after orthodontic treatment (Andrews, 1976, 1972, 1979, 2000).

But even with these
guidelines and standards, beautifully finished cases are no less susceptible to relapse
(Little, 1990; Reitan, 1960). Thus there seem to be more factors other than crown and
molar occlusion characteristics that may affect occlusal stability. One limitation of
Andrews’ six keys is that it did not address the relationship between teeth and the
supporting structures like the periodontal ligament and the basal bone. Throughout
orthodontic history, there has been a lack of research tools that would allow us to study
individual tooth position and its relationships to the surrounding structures. The lateral
cephalogram, a two-dimensional radiograph, only slightly portrays this relationship for the
maxillary and mandibular central incisors (Macri, and Athanasiou, 1997). It has been
popularly hypothesized that teeth function maximally when teeth are centered in bone.
Thus goals of orthodontic treatment are to position teeth in the middle of the alveolar bone
in belief that it contributes to stable and functional occlusions; however, these hypotheses
remain untested still.

37
The advent of CBCT imaging has offered new tools to see true positional
relationships between individual teeth and their supporting structures in three
dimensional spaces. Taking advantage of this new technology, we have collaborated with
Dolphin (Chatsworth, CA) in developing a custom University of Southern California root
vector analysis program that measures each whole tooth faciolingual inclination. In one of
our previous articles, we tested the validity of this program by using CBCT images of
typodont teeth (Tong, Enciso, Van Elslande, Major, Sameshima, 2012). The same program
was used again in our next article studying whole teeth mesiodistal angulation and
faciolingual inclination in 76 patients with near normal occlusion, who needed little
orthodontic treatment (Tong, Kwon, Shi, Sakai, Enciso, Sameshima, 2012).

In this study, we
have applied the same program to measure the same 76 near normal patients’ APFLI at
each tooth area to compare it to the tooth’s own DFLI.
The primary purpose of this study was to determine if there were any differences in
faciolingual inclination measurements between teeth and their alveolar process housing in
patients with near normal occlusion. It was hypothesized that in normal and stable
occlusion, long axes of teeth and the alveolar processes coincide, with the tooth perfectly
centered inside its alveolar housing.
The 76 CBCT images studied in this research differed in some respects, but all
shared some distinct trends. As hypothesized, in both arches, the APFLI follows similar
trends as the DFLI. There is a general reduction in inclination from the anterior region to
the posterior region; the APFLI always remains larger than the DFLI; and the differences
between the two inclinations are the smallest at the central incisor and first molar areas
and the largest at the first premolar area. At the lower central incisors and lower first

38
molar region, the APFLI and DFLI were essentially the same, meaning these teeth are well
centered inside their alveolar housing. For the maxillary central incisors and first molars,
teeth are 8
0
and 5
0
more lingually inclined, respectively, than their alveolar housing. This
lingual inclination of teeth relative to the alveolar processes increases to 7
0
at the lower
first premolar, the largest difference in the mandible, to as high as a 20
0
difference in the
maxilla at the upper first premolars.
Andrews 1
st
element

of orofacial harmony supports the concept that teeth are in
optimal positions when the roots are centered over basal bone and the crowns are inclined
such that the teeth can interface and function optimally (Andrews, 2000). However, this
requirement for centrally located roots inside the alveolar housing may not be imposed
upon all teeth and their supporting bone equally. The alveolar process around lower
central incisors is fairly narrow, not much wider than the size of the incisors themselves,
leaving very little room for the over-retraction or over-proclination of teeth. This central
location for the lower incisors therefore may be of biological necessity. Maxillary central
incisors, on the other hand, receive biting force from the lingual of the incisal edge, causing
roots to rotate lingually around their center of rotation. Therefore, extra lingual bone may
serve as additional protection for these teeth. Moreover, the presence of the palate may
account for the additional bone found lingual to all the maxillary teeth. From an
evolutionary stand point, past research supports that the geometry of the human jaw bone
undergoes remodeling during growth, with increased bone resorption from the buccal and
deposition on the lingual (Enlow and Bang, 1965).
In the mandibular first molar alveolar process area there is a general enlargement
to accommodate the abrupt increase in the size of the tooth with not much extra bony

39
width. The biting power in this area may also require the teeth to be perfectly centered.
Other teeth, from the lower laterals to the lower second premolars seem to be transitional
teeth. The bony width in these areas is larger than the size of the roots. We found that when
teeth are allowed to incline differently than the alveolar processes, they tend to become
less inclined, or more vertical than their alveolar housing, possibly as a way to resist buccal
shift from occlusal forces.
Previous studies and case reports have shown that, as the roots are displaced and
move away from the center of the alveolar bone there is increased risk of creating or
exacerbating alveolar defects
,
and producing consequent mucogingival changes, such as
gingival recession. Evangelista et al, found that teeth most affected in the mandible were
the central and lateral incisors, and in the maxilla, the first molars (Evangelista,
Vasconcelos, Bumann, Hirsch, Nitka, and Silva, 2010). A possible explanation of this is that
molars and incisors represent the transverse and anterior limits of the arches. Our data
suggest greater caution about molar expansion and tooth proclination in the mandibular
arch, especially in the incisor region; this has been emphasized by many other authors as
well (Wehrbein, Bauer, and Diedrich, 1996; Dorfman, 1978; Artun and Krogstad, 1987;
Yared, Zenobio and Pacheco, 2006) .
Clinically, the ability to see three dimensional images of teeth and bone is quite
revolutionary. Before 3D technology became available, orthodontists could only make
educated guesses as to where in bone they were moving teeth, and how much bone was
covering the root at the end of treatment. Understanding the biological limitations of the
bony arches and weighing treatment compromises pose some of the biggest challenges to
us as orthodontists. By identifying ideal tooth position inside the alveolar process in nature,

40
the outcome of this study could be used as guidelines for successful and stable orthodontic
treatment.
SureSmile (OraMetrix, Dallas, TX) and Insignia (Ormco, Orange, CA) are among a
number of new treatment approaches that are modernizing orthodontics by utilizing 3D
technology to guide mechanotherapy and to forecast treatment outcomes. Their
technologies pride in exact tooth positioning with completely customized appliances,
making orthodontic tooth movement faster, more accurate and more predictable. With
customized brackets and archwires, and ideal bracket placement, routine cases can be
finished with less effort and difficult cases become more manageable. As ethical and
responsible specialists, it is our duty to provide the maximum possible benefit to our
patients (Mah and Sachdeva, 2001). With the help of virtual 3D models of patients’ dento-
skeletal structures in sight, orthodontists can tell how all the teeth relate to their
surrounding bone and how they fit from every angle. Our results can help clinicians better
understand the biological norms of the jaw bones. In combination with imaging technology,
this will give us more predictability and efficiency when carrying out our treatment
mechanics. Additionally, orthodontists can use virtual images of teeth and the supporting
structures as an effective communication tool to demonstrate to patients different
treatment options available, whether ideal, alternative, or compromised.
When interpretating the results of this study, certain limitations should be
considered. One is the near normal sample. It would have been ideal to use records from
patients that had optimal occlusions and truly exhibited all six keys to normal occlusion
and facial harmony. However it becomes an ethical issue to expose patients to harmful
radiation if they in fact do not need any treatment at all. We adjusted our near normal

41
criteria such that we could obtain a reasonable sample size from a total of close to 2,000
patients who had initial CBCT taken and who enrolled in treatment at our USC Advanced
Orthodontic Program. We hope that this study, as part of a series of studies, forms a good
foundation for future more extensive research.
Another limitation was that our custom root vector analysis was specifically
developed for normal or near-normal subjects, as a way of obtaining the normal standard.
The analysis is meant to be used for setting up treatment goals and for evaluation of
treatment outcomes, all of which, hopefully, are close to the normal standard. Our
methodology was not developed for diagnosis of patients with severe malocclusions or
asymmetries. Also patients with extreme dolicofacial or brachyfacial occlusions, would
have resultant decreased and increased occlusal forces respectively, thereby affecting the
geometry of the alveolar process. Results from of our study regarding the proper
relationship between teeth and bone and how they relate to patients with severe
abnormalities remains to be further studied. Additionally, the choice of single occlusal
plane has also made this program hard to apply to patients with large curves of Spee.
We chose the alveolar crest to be the reference level for the most superior level of
the alveolar process. However the choice of reference level for the digitization of the
alveolar apical base center was much more difficult and could potentially affect the position
of the alveolar long axis and thus affect the measurement of the APFLI. Since we are
studying the biological limitations of bone that nature has imposed upon, it would make
sense that we would try to make our measurements as close to the apical base as possible.
But we found that the further the reference plane was moved from the alveolar crest, the
more inconsistencies there were in our digitizations. This is due to the secondary

42
structures like the zygomatic buttress, bone tori, muscle attachments like the massater, and
even superimpositions of the palate. Eventually, the reference levels for the apical bases
were set at a level in which all apices of teeth were still visible. This corresponds to the
posterior border of the incisive canal for the maxilla, and cephalometric B point for the
mandible,. Our definition of the apical base level is more or less in agreement with the
literature (Lundstrom, 1925).
Although CBCT can generate complete images of all dento-skeletal structures and
therefore may potentially replace any or all types of X-rays used in orthodontics, it subjects
patients to more radiation than any single type of X-ray. Consequently, radiation safety is a
concern for both orthodontists and patients alike. Guidelines on radiation protection
recommend the ALARA principle, such that imaging should be based on patient’s clinical
need, while exposing the patient to as low as a radiation dose as possible (Scarfe, Farman,
and Sukovic, 2006). There is no question that CBCT, when used properly, can improve
quality and efficiency of patient care. For example, results from this study could be useful in
designing new custom orthodontic appliances and providing guidance for orthodontic
treatment planning and finishing. It might also help improve the virtual model setups used
in Invisalign, Suresmile, Incognito and Insignia (Mah and Sachdeva, 2001).

Fully pre-
adjusted appliances require precise goals for all the teeth with crowns following Andrews’
six keys to normal occlusion, and with roots properly positioned within its bony housing.
This will require individualized adjustments in the arch wire for each patient, or better,
individually customized brackets and wires compensating for all biologic variations. 3-D
approaches to orthodontic diagnosis and treatment planning, as well as implementation of
treatment mechanics may lead to more efficient tooth movement and less discomfort to the

43
patients or damage to the teeth and their supporting tissues. Future orthodontics will,
therefore, increasingly become biologically correct and, consequently, more patient-
friendly.

44
Chapter 9: Conclusions

1. By using the custom University of Southern California root vector analysis program
in Dolphin 3D, we measured and obtained average faciolingual inclination values for
the alveolar processes corresponding to each tooth from 76 patients with near-
normal occlusion;
2. We found distinctive trends in the intra-arch relationships in the faciolingual
inclinations for the alveolar processes;
3. We also found distinctive relationships between dental faciolingual inclination and
alveolar process faciolingual inclinations from the anterior to the posterior teeth
region.

45
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Asset Metadata

Creator Pham, Virginia (author)

Core Title Alveolar process inclination as related to tooth inclination on near normal patients -- in three dimensional space

School School of Dentistry

Degree Master of Science

Degree Program Craniofacial Biology

Publication Date 04/29/2013

Defense Date 02/27/2013

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

Tag alveolar process,bone,cone beam,inclination,OAI-PMH Harvest,tip,tooth,torque

Language English

Contributor Electronically uploaded by the author (provenance)

Advisor Sameshima, Glenn T. (committee chair), Enciso, Reyes (committee member), Paine, Michael L. (committee member)

Creator Email virginiahpham@gmail.com,virginip@usc.edu

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c3-245379

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Legacy Identifier etd-PhamVirgin-1597-0.pdf

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Document Type Thesis

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Type texts

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

Access Conditions 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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