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THREE-DIMENSIONAL CONE BEAM COMPUTERIZED TOMOGRAPHY
ASSESSMENT OF BASAL BONE PARAMETERS
AND CROWDING.
Gregory David Bell, D.D.S
An Abstract Presented to the Faculty of the Graduate School
of Saint Louis University in Partial Fulfillment
of the Requirements for the Degree of
Master of Science in Dentistry
2008
ABSTRACT
Introduction: Dental crowding can be defined as the
difference between the space available in the dental arch
and the space required to align the teeth.
Crowding is
thought to be related to the apical base.
Unfortunately
the literature has not described a reliable and consistent
way to relate jaw size and crowding.
Purpose: It is the
purpose of this study to investigate the relationship
between the basal bone, alveolar bone and crowding of the
teeth. Using measurements of basal bone, tooth size and
position, an attempt will be made to explain crowding.
Methods: A sample of thirty untreated patients with pretreatment cone beam computed tomography (CBCT) scans and
available pre-treatment plaster models were utilized.
Consecutive patients’ records were collected based on the
following inclusion criteria: 12-17 years of age and
presence of a full complement of teeth with all teeth
erupted except for third molars.
Data collected via CBCT
included measurements of basal bone perimeter and area as
well as tooth angulation.
Model analysis included measures
of tooth width and crowding. Results: Correlations among
the various basal bone measurement parameters were
significant and high.
Some significant, but weak,
1
relationships were detected between crowding and various
basal bone parameters.
Conclusions: With the advances in
cone beam computerized tomography, measurements of hard
tissue can be made with relative ease.
Although the
present study found significant correlations between
crowding and basal bone dimensions, the correlations were
low and are of little value in explaining the relationships
that were investigated.
The value of this study is that it
denies a strongly held belief.
That belief is that there
is a strong relationship between basal bone, the teeth, and
the related alveolar bone.
2
THREE-DIMENSIONAL CONE BEAM COMPUTERIZED TOMOGRAPHY
ASSESSMENT OF BASAL BONE PARAMETERS
AND CROWDING.
Gregory David Bell, D.D.S
A Thesis Presented to the Faculty of the Graduate School
of Saint Louis University in Partial Fulfillment
of the Requirements for the Degree of
Master of Science in Dentistry
2008
COMMITTEE IN CHARGE OF CANDIDACY:
Professor Rolf G. Behrents,
Chairperson and Advisor
Assistant Professor Ki Beom Kim
Assistant Clinical Professor Donald R. Oliver
i
DEDICATION
I dedicate this project to my loving and supportive
family.
I am thankful for the endless support and
encouragement received from my wonderful wife and to our
baby son for all the joy he has brought us both.
I also dedicate this to my parents for whom I am
grateful for the foundation and opportunities they have
provided in enabling me to reach my goals and dreams.
ii
ACKNOWLEDGEMENTS
I would like to acknowledge the following individuals:
•
Dr. Behrents for his advice and guidance throughout
this project,
•
Dr. Oliver for sharing his knowledge and insight,
•
Dr. Kim for his time and comments,
•
Drs. Matthew and Joachim Bauer for providing access
to my sample and for help with technical issues, and
•
Paula Wilson for assistance with data collection.
My thanks also go to my friends and colleagues who have
helped me throughout the project.
iii
TABLE OF CONTENTS
List of Tables............................................v
List of Figures..........................................vi
CHAPTER 1: INTRODUCTION...................................1
CHAPTER 2: REVIEW OF THE LITERATURE
Measures of Basal Bone...............................6
Modification of Basal Bone...........................9
Tooth Size..........................................12
Measures of Dental Arch Dimension...................12
Cone Beam Computerized Tomography (CBCT)............18
Purpose of the Study................................19
References..........................................21
CHAPTER 3: JOURNAL ARTICLE
Abstract............................................24
Introduction........................................26
Materials and Methods...............................28
Measuring Basal Bone from the
CBCT Images....................................29
Cross-sectional Area...........................30
Perimeter......................................32
Model Analysis.................................36
Error of the Method............................38
Statistical Analysis...........................39
Results.............................................40
Model Analysis.................................40
Basal Bone Measurements........................41
Discussion..........................................48
Relationships Between Crowding and Tooth Size..48
Basal Bone.....................................49
Basal Bone Relationships.......................51
Elliptical Formulaic Estimation................52
Conclusions.........................................54
Literature Cited....................................55
Vita Auctoris............................................57
iv
LIST OF TABLES
Table 3.1: Descriptive statistics: model analysis........40
Table 3.2: Cronbach’s Alpha for Intraclass Correlation
Coefficient of model analysis parameters......41
Table 3.3: Descriptive statistics: cross-sectional basal
bone measurement plane through B point........41
Table 3.4: Descriptive statistics: cross-sectional basal
bone measurement plane through inferior mental
foramen.......................................42
Table 3.5: Pearson’s correlation for perimeter to basal
bone parameters on the cross-sectional basal
bone measurement plane through B point........43
Table 3.6: Pearson’s correlation for perimeter to basal
bone parameters on the cross-sectional basal
bone measurement plane through inferior mental
foramen.......................................43
Table 3.7: Pearson’s correlation for Proffit crowding
analysis to perimeter and area basal bone
measurements..................................45
Table 3.8: Pearson’s correlation for the Little
Irregularity Index to perimeter and area basal
bone measurements.............................45
Table 3.9: Pearson’s correlation for total tooth width to
perimeter and area basal bone measurements....46
Table 3.10: Cronbach’s Alpha for Intraclass Correlation
Coefficient of cross-sectional basal bone
measurement plane parameters through B point..47
Table 3.11: Cronbach’s Alpha for Intraclass Correlation
Coefficient of cross-sectional basal bone
measurement plane parameters through inferior
mental foramen................................47
v
LIST OF FIGURES
Figure 2.1: Reference points for defining the apical base
(from Miethke)................................8
Figure 2.2: Little’s Irregularity Index..................16
Figure 3.1: Representation of standardized orientation
using three dimensional planes...............29
Figure 3.2: Definition of measurement planes.............31
Figure 3.3: Sequence of CBCT image manipulation showing
perpendicular planes (mandibular plane and
mesial second molar plane), sagittal slice and
rotation to occlusal view....................31
Figure 3.4: Sagittal slice through B point rotated to
occlusal view. Basal bone area measurements.32
Figure 3.5: Sagittal slice through B point rotated to
occlusal view. Outside basal bone perimeter
measurements.................................33
Figure 3.6: Diagram showing major and minor axis of ellipse
(modified from Kanaan 2006)..................34
Figure 3.7: Sagittal slice through B point rotated to
occlusal view. Elliptical axis defined .....35
Figure 3.8: Quadrant diagram for straight line
approximations of available arch space(modified
from Little).................................37
Figure 3.9: Little’s irregularity index (modified from
Little)......................................38
Figure 3.10: A scattergram correlation plot comparing the
Little Irregularity Index values to the Proffit
crowding analysis............................44
vi
CHAPTER 1:
INTRODUCTION
Meticulous diagnosis and treatment planning is
critical for establishing a foundation for orthodontic
success.
Elements of such planning are numerous, but
always include an analysis of crowding, malalignment and
protrusion or retrusion of the teeth.
Dental crowding is
determined by comparing the total tooth mass to the arch
length that is available.
While this value, the tooth
mass–arch length discrepancy, is a cornerstone value during
diagnosis and treatment planning, several methods of
estimation are described in the literature.
Of course,
given that several methods are available estimations of
tooth mass and arch length vary.
Van der Linden and McNamara1 define dental crowding as
the discrepancy between tooth size and jaw size that
results in a misalignment of the teeth.
It is generally
believed that when tooth mass is too small relative to
basal bone, interdental spacing or diastemas will likely
occur.
Conversely, if the basal bone in the body of the
mandible is constricted or too small relative to tooth
mass, the teeth will be crowded out of normal arrangement,
or, if normal arrangement is maintained, they will show a
procumbent relationship to the mandibular plane.2
1
Success
in aligning the teeth is therefore, among other factors,
dependent on the size of the basal bone in relation to the
tooth mass.
Salzmann recognized that the size, form and
relationship of the basal bone was independent of the size
of the teeth and that tooth arrangement is greatly
dependent on the size of the basal bone.3
While measures of
tooth size are relatively finite and can be readily
measured, the literature has not supported a reliable and
consistent way to measure jaw size.
As a result, previous
attempts to measure basal bone have resulted in complicated
methods that are time consuming and variable in
estimation.4-7
It is commonly believed that orthodontically
moved teeth that are placed in a ‘normal’ position in the
arch may not be stable if the basal arch over which they
are placed is not sufficiently large enough.
These beliefs
confirm Tweed’s observation that “the irregular dentition
in balance is a far more stable condition that the same
dentition treated orthodontically but forced out of balance
and into a protrusive relationship with regard to the bony
base.2,8
Tweed preached that such unbalanced relationships
between tooth and arch size are usually followed by
relapse.9
2
It is the purpose of this study to seek a reliable
method to measure the perimeter and cross-sectional area of
basal bone from cone beam computerized tomography data.
Using measures of basal bone and tooth mass, an attempt
will be made to explain crowding.
3
CHAPTER 2:
REVIEW OF THE LITERATURE
The term ‘apical base’ was first introduced by Axel
Lundström in 1923. He defined the apical base as the
section of bone upon which the teeth rest or are attached.10
Since the concept was introduced the terms ‘apical base’
and ‘basal bone’ have been used interchangeably, but the
meaning of these terms has varied.
Tweed defined basal
bone as the bony ridge over which the mandibular central
incisors must be situated to produce permanence of
orthodontic results.9
Salzmann expanded the definition to
include the “area in the jaws which begins at the most
constricted point on the body of the maxilla and the
mandible when seen on the profile cephalograms.3
This area
included Downs’ point A, point B and Lundström’s apical
base and it extends around the body of the maxilla or
mandible at the most constricted portions parallel to the
alveolar processes.”3
A more recent definition by Daskalogiannkis defines
basal bone as the bone which supports and is continuous
with the alveolar process.1
4
Brodie noted that the term ‘basal bone’ had never been
satisfactorily defined, although it seemed to be accepted
by most as the skeletal bone which supports alveolar bone.11
We have never investigated the so-called apical base,
and the reason is not hard to find. There is no
method yet devised which will permit its accurate
determination. The term has never been satisfactorily
defined, yet each person practicing orthodontia seems
to be quite certain of what is meant by the term.
Upon critical questioning, however, the definitions
become vague.11
The importance of having a good relation between basal
bone and the dental units was first recognized in a
publication by Tweed in 1944.9
The publication discussed
the importance of successful treatment as having the
mandibular incisors positioned in a normal relation to
their basal bone, so that they are in a mechanical balance
and best resist the forces of occlusion that will otherwise
result in their displacement.9
It is this normal
relationship of mandibular incisor teeth to their basal
bone that is “the most reliable guide in the diagnoses and
treatment of malocclusion.”9
5
Measures of Basal Bone
Clinicians have used various methods to attempt to
locate and quantify basal bone.
However, as Brodie
mentioned the term ‘basal bone’ has never been
satisfactorily defined.11
Regardless, on an historical
basis, apical base relationships have been assessed by
means of palpation or by cephalometric examination.12
Such
apical base measurements commonly employ the use of points
A and B, first described by Downs,12 and their relationship
to the anterior cranial base.
Downs’ points were later
adapted by Riedel13 to study the discrepancy in apical base
relationships between the maxilla and mandible.
Reidel
used points A and B in conjunction with Sella and Nasion to
create two angular measurements, SNA and SNB.13
These
angular measurements are now a mainstay of orthodontics.13
While such measurements describe the relationship of the
anterior limits of the apical bases, they give no
consideration to the size of the basal bone.
One of the earliest attempts to actually measure the
supporting bone was performed by Howes.4
Howes used survey
lines on dental casts and was able to section and remove
the alveolar process and assess the supporting bone.
He
reported the basal arch to be in the apical one-third of
6
the alveolar bone.4
In the mandibular arch he found the
basal arch to be approximately eight millimeters below the
gingival margin of the teeth.4
Rees also conducted a study
using sectioned plaster models and found that points 8-10
mm from the gingival margins of the molars and incisors can
be used as a ‘reasonably accurate’ landmark for locating
supporting basal bone in both arches.6
More recently Miethke et al.5 studied the effects of
Frankel’s functional regulator on apical base dimensions.
They agreed with Howes and Rees and chose to use landmarks
relative to the gingival margins of select teeth to
determine a apical base plane parallel to the occlusal
plane.5
Miethke et al. defined the apical base as the
peripheral connection of six referenced landmarks 5 mm
below the most apical points of the gingival margins of the
lower lateral incisors, canines and second primary molars
or pre-molars (Figure 2.1).
Contrary to the use of landmarks in reference to
gingival margins, Sergl et al.7 utilized a gnathograph
designed by Klueglein14 to survey casts using the most
concave contour of the sulci in relation to the apices of
the teeth.
Recently, Kanaan measured mandibular basal bone
perimeters from traditionally available orthodontic
records.15
He used a combination of dental casts and
7
Figure 2.1: Additional reference points for defining the
apical base. These were located 5 mm below the most apical
point of the gingival margin of the lateral incisors,
canines and second primary molars/premolars (from Miethke).5
cephalometric radiographs to locate basal bone. The
posterior limit of basal bone was defined as a
perpendicular to the functional occlusal plane mesial to
the first molar.15
The cephalometric radiograph was used to
determine basal bone depth by locating B point and creating
a horizontal plane parallel to the functional occlusal
plane.15
The measurements were then transferred to the
dental cast, which was sectioned to expose the basal bone
shelf.
Estimates of perimeter were made from the basal
bone shelf with stainless steel wires and an elliptical
formula.
Measurements of perimeter on the dental casts,
however, did not take into consideration the soft tissue
thickness that covers the anterior ridge anteriorly.15
8
As this review indicates, disagreements concerning the
definition and methods used to measure of basal bone are
numerous.
Authors do agree, however, that an assessment of
basal bone using plaster models does have limitations.
The
importance of an accurate impression, with deep vestibular
rims, is vital for posterior measurement of apical base.5
Also, the capture of buccal tissue along with basal bone is
an unavoidable error in utilizing plaster models.5
Modification of Basal Bone
There has been considerable debate regarding the
ability of orthodontics to modify basal bone.
There is
little doubt that teeth play a definite role in the
development of the jaws, but the ability to alter bony
support structures through orthodontic means is more
controversial.
The controversy emerged when Angle argued that a full
complement of teeth can and must be maintained in
correcting any case of malocclusion.16
Angle further
believed that following the coronal alignment of teeth,
through the stimulation of function, sufficient bone would
be developed to support the teeth properly.16
9
Angle’s
beliefs were later aggressively refuted in a paper by
Lundström10 which contradicted and criticized the teachings
of Angle.
Lundström theorized that the form of basal bone
governed the positions of the teeth and that mechanical
orthodontic therapy was unable to produce any growth in the
apical base.
Salzmann3 supported Lundström’s theory, adding
to the unalterable nature of basal bone.
He felt that the
movement of teeth by orthodontic means into a different
occlusal relationship, whether normal or abnormal, would
not change the form of the basal arch even when the teeth
and alveolar process are altered as the result of
orthodontic tooth movement.3
Brody suggested that the
osseous base is genetically predetermined in size and
further added that the “Apical base... is relatively
immutable.”11
As a result, he felt that extractions were
sometimes necessary to accommodate the dentition.
In 1947,
Howes stated that “a normal occlusion must be supported by
a normal apical base.”
Howes agreed that mechanical
orthodontic therapy cannot directly affect the size of the
apical base.
But he continued, “indirectly, by making
possible normal muscular action in breathing, chewing,
facial expression, etc., it seems plausible that the apical
base could be given an opportunity of achieving more normal
dimensions, although I have been unable to obtain evidence
10
to substantiate such an assumption.4
Many cases with many
models would have to be kept under observation for many
years to prove or disprove such a possibility.”4
In upholding Angle’s belief that basal bone can be
altered, Frankel17 described his functional regulator
appliance that uses vestibular shields to displace the
attachment of the lips and cheeks.
He believed that
through the dynamics of tooth eruption without the pressure
from the lips and cheeks that the appliance could enhance
the development of basal bone.17
More recently, the cyclic nature of such controversies
has again been re-ignited.
Damon has advocated the use of
“very light-force, high tech arch wires in the passive
Damon appliance that alter the balance of forces among the
lips, tongue and muscles of the face.18
This alteration
supposedly creates a new force equilibrium that allows the
arch form to reshape itself to accommodate the teeth even
in severely crowded cases.”
Damon believes that the
extensive clinical research available with the ‘Damon
System’ calls for a shift in thinking and treatment
planning, reducing and even eliminating the need for
extraction.18
11
Tooth Size
Previous studies have shown significant correlations
between the size of teeth and crowding.19,20
Fastlicht
studied the relationship between tooth size and crowding in
untreated patients and found a very significant correlation
between the mesiodistal widths of mandibular teeth and
crowding.19
He concluded that where there was a greater
mesio-distal width of teeth there was likely to be more
crowding.19
The relationship between tooth size and
crowding has also been supported in other studies.20,21
Conversely, other studies have failed to show significant
relationships between tooth size and crowding.22,23
Measures of Dental Arch Dimension
The need for meaningful measurements of dental arch
dimensions and their importance for diagnosis and treatment
planning have been recognized since the early days of
Angle.
Angle advocated the use of his ‘line of occlusion’
for the mandibular arch, which passed over the buccal cusps
of the posterior teeth and the incisal edges of the
anterior teeth.16
12
Since this first description for measuring dental arch
perimeter, others have contributed their own variations.
It is well documented in the orthodontic literature that
space analysis involves the comparison between the amount
of space available for the alignment of teeth and the
amount of space required to place the teeth in the correct
position.2-4,7,10,24-26
Nance described a method of measuring
the “outside” arch perimeter by using a piece of 0.010 inch
brass wire placed along the buccal surfaces of the teeth
from the mesial of one permanent first molar to the mesial
of the opposite first molar.25
The brass wire could then be
straightened and measured accurately.
The use of brass
wire to measure arch perimeter with plaster models is still
a popular method today, although most clinicians no longer
measure the “outside” perimeter as advocated by Nance.
Other clinicians adopted Nance’s method for measuring
arch length and with various modifications made it their
own.27,28
Carey borrowed some basic principles from Nance,
but used a 0.020 inch soft brass wire bent to a symmetrical
arch form and placed over the contact point region of the
posterior teeth and over the incisal edges of the anterior
teeth, held in place with wax.27
He placed marks at the
mesial contact points of the first permanent molars and
then measured the dental arch length between these two
13
marks.
Carey also stated that even though he used the
incisal edges of the anterior teeth, that in certain cases
it was necessary to pass the wire over the incisal edges
“at a point where we judge them to belong.27
He believed
this method represented an accurate survey of the linear
dimension of bone that is available to accommodate teeth.27
Huckaba devised an approach to estimate the space
available.28
He borrowed from the brass wire approach of
Nance, but used a 0.025 inch brass wire centered over the
contact points of the posterior dentition.
In the anterior
the placement of the wire was dependent upon the
inclination of the anterior teeth.
Three situations
existed:
1. If the lower anterior teeth are upright over the
basal bone, the wire is positioned directly over the
incisal edges;
2. If the lower anterior teeth are tipped to the
lingual, the wire should be extended to the labial
of the incisors; and
3. If the lower anterior teeth are tipped to the
labial, the wire should be positioned to the
lingual.
Once contoured, the wire is simply straightened and then
measured.28
14
In 1975 Little described an irregularity index which
was designed to be a quantitative score of mandibular
anterior alignment.24
In order to avoid more subjective
terms associated with crowding, Little established an index
of incisor crowding as a guide in determining treatment
priorities.
The proposed scoring method involved measuring
the linear displacement of the anatomic contact points of
each mandibular incisor to the adjacent tooth anatomic
contact point.
The sum of these five displacements
represents the relative degree of incisor irregularity24
(Figure 2.2).
Each cast is then subjectively ranked on a scale
ranging from 0 to 10, using the following criteria:
0
Perfect alignment
1-3
Minimal irregularity
4-6
Moderate irregularity
7-9
Severe irregularity
10
Very severe irregularity
The Little Irregularity Index is simple and clinically
applicable but has several flaws that must be considered.24
The index is not to be considered an arch length
assessment, but simply a guide to quantifying mandibular
anterior crowding.
In cases that involve spacing, anterior
15
Figure 2.2: Little’s Irregularity Index technique involves
measuring the linear distance from anatomic contact point
to adjacent anatomic contact point of mandibular anterior
teeth, the sum of the five measurements represent the
irregularity index (from Little). 24
spacing without rotation must be differentiated from a case
displaying spacing with irregularity.
Another problem is a
tendency to exaggerate cases with considerable irregularity
but with little arch length.24
A common method for performing a space analysis is one
that is recommended by Proffit and Fields.26
They suggest
using a quadrant approach to determine the amount of space
available.
This is done by dividing the dental arch into
segments that can be measured as straight line
approximations of the arch.
To determine space required
16
the mesiodistal width of each tooth from contact point to
contact point is measured and then summed.
If the sum of
the widths of the permanent teeth is greater than the space
available then there is an arch perimeter deficiency.
Likewise, if the total tooth width is less than the space
available, spacing would be expected.
Space analysis
carried out in this way is based on an important
assumption, that the anteroposterior position of the
incisors is correct; incisors can neither be excessively
protrusive or retrusive.26
When considering crowding it is important to consider
the protrusion of teeth as well as crowding.
There is an
interaction between crowding of the teeth and protrusion or
retrusion: if the incisors are positioned lingually this
accentuates any crowding; but if the incisors protrude, the
potential crowding will at least be partially alleviated.26
Crowding and protrusion are really different aspects of the
same phenomenon.26
If there is not enough room for the
teeth, the result can be crowding, protrusion or likely a
combination of both.
The relationship between crowding and basal bone is
one that has been extensively investigated in the
literature.
Techniques for measuring basal bone have
varied as have its location.
Now, with the advent of cone
17
beam computerized technology, a new and more reliable
technique of measuring bone dimensions exists.
Cone Beam Computerized Tomography
Computerized tomography (CT) was developed by
Hounsfield in 1967 and has evolved into today’s threedimensional cone beam computerized tomography (CBCT)
models.
In comparison to CT scanning, with CBCT the object
to be evaluated is captured as the radiation source falls
onto a two-dimensional detector.
This simple difference
allows a single rotation of the radiation source to capture
an entire region of interest, as compared to conventional
CT devices where multiple slices are stacked to obtain a
complete image.29
The cone beam produces a more focused
beam and considerably less scatter radiation compared to
conventional CT devices.
It has been reported that the
total radiation exposure to the patient is equivalent to a
full mouth periapical radiographic exposure.30
Innovations
in CBCT are ongoing and with the dramatic increase in image
processing and the continuing development of digital
imaging, the use of volumetric imaging is increasing the
opportunity for better diagnosis for the dental
profession.29
18
With present day CBCT technology, all possible
radiographs can be taken in under one minute.
From one
three-dimensional image a practitioner can obtain
diagnostic quality periapicals, panaromic, cephalograms,
occlusal, and TMJ images in addition to other images that
can not be captured by conventional means.
The use of CBCT
in orthodontics has allowed advances in visualizing
impacted canines, airway analysis, and temperomandibular
joint morphology, and permits accurate assessment of
alveolar bone heights and volume.29
Purpose of the Study
Crowding is defined as the discrepancy that exists
between tooth size and arch length.
While tooth size is
relatively finite, arch length can be measured by numerous
methods with varying results.
As a result the amount of
crowding in any particular case is an estimate.
That crowding is directly related to the dimensions of
the apical base has been a strongly held belief by
orthodontists and they plan their treatment on this basis.
This is done in spite of a lack of clear definition of the
anatomical location of the apical base and a way to measure
it.
19
Previous attempts to measure basal bone have resulted
in complicated methods that are time consuming and
imprecise.
With the availability of cone beam computed
tomography, analysis of basal bone parameters can now be
made quickly and more precisely.
It is the purpose of this study to:
1. Seek a reliable method to measure the crosssectional area and perimeter of basal bone from cone
beam images.
2. Determine whether measures of basal bone, in
conjunction with tooth size can explain crowding.
20
References
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Terms. In: Jutle, Daskalogiannkis J, editors. Leipzig,
Germany: Quintessence; 2000.
2. Tweed CH. A philosophy of orthodontic treatment. Am J
Orthod and Oral Surg 1945;31:74-103.
3. Salzmann JA. Orthodontic therapy as limited by
ontogenetic growth and the basal arches. Am J Orthod
1948;34:297-318.
4. Howes AE. Case analysis and treatment planning based
upon the relationship of the tooth material to its
supporting bone. Am J Orthod and Oral Surg 1947;33:499-533.
5. Miethke R, Lindenau S, Dietrich K. The effect of
Fränkel’s function regulator type III on
the apical base. Eur J Orthod 2003;25:311-318.
6. Rees DJ. A method for assessing the proportional
relation of apical bases and contact diameters of the
teeth. Am J Orthod 1953;39:695-707.
7. Sergl HG, Kerr WJ, McColl JH. A method of measuring the
apical base. Eur J Orthod 1996;18:479-483.
8. Tweed CH. The Frankfort-Mandibular plane angle in
orthodontic diagnosis, classification, treatment planning,
and prognosis. Am J Orthod and Oral Surg 1946;32:175-230.
9. Tweed CH. Indications for the extraction of teeth in
orthodontic procedures. Am J Orthod 1944;30:405-428.
10. Lundström A. Malocclusion of the teeth regarded as a
problem in correction with the apical base. Int J Orthod
Oral Surg Radiogr 1923;11:591-602.
21
11. Brodie AG. Appraisal of present concepts in
orthodontia. Angle Orthod 1950;20:24-38.
12. Downs WB. Variations in facial relationships: Their
significance in treatment and prognosis. Am J Orthod
1948;34:812-840.
13. Reidel RA. The relation of maxillary structure to
cranium in malocclusion and in normal occlusion. Angle
Orthod 1952;22:140-145.
14. Kleuglein A. Zur Metrischen Erfassung der Apikalen
Basis-ein Neus Mechanisches Ubertragungsgerat. Mainz 1985.
15. Kanaan W. The correlation between tooth size, basal
bone size discrepancy and long term stability of the lower
arch in Class II Division 1 patients. Masters Thesis.
Orthodontics. Saint Louis: Saint Louis University; 2006: p.
90.
16. Angle E. Treatment of Malocclusion of the Teeth and
Fractures of the Maxilla. Philadelphia: The S.S. White
Dental Manufacturing Company 1900.
17. Frankel R. Decrowding during eruption under the
screening influence of vestibular shields. Am J Orthod
1974;65:372-406.
18. Damon DH. Treatment of the Face with Biocompatible
Orthodontics. In: Graber, Vanarsdall, Vig, editors.
Orthodontics Current Principles and Techniques. St. Louis:
Mosby; 2005.
19. Fastlicht J. Crowding of mandibular incisors. Am J
Ortod 1970;58:156-163.
20. Smith R, Davidson W, Gipe D. Incisor shape and incisor
crowding: A re-evaluation of the Peck and Peck ratio. Am J
Ortod 1982;82:114-123.
22
21. Norderval K, Wisth P, Boe O. Mandibular anterior
crowding in relation to tooth size and craniofacial
morphology. Scand J Dent Res 1975;83:267-273.
22. Howe R, McNamara J, O'Connor K. An examination of
dental crowding and its relationship to tooth size and arch
dimension. Am J Orthod 1983;83:363-373.
23. Radnzic D. Dental crowding and its relationship to
mesio-distal crown diameters and arch dimensions. Am J
Orthod 1988;94:50-56.
24. Little RM. The Irregularity Index: A quantitative score
of mandibular anterior alignment. Am J Orthod 1975;68:554563.
25. Nance H. Limitations of orthodontic diagnosis and
treatment. Am J Orthod 1947;33:177-223.
26. Proffit W, Fields H. Contemporary Orthodontics
Orthodontic Diagnosis: The Developement of a Problem List.
St. Louis: Mosby; 2000.
27. Carey CW. Treatment planning and the technical program
in the four fundamental treatment forms. Am J Orthod
1958;44:887-898.
28. Huckaba GW. Arch size analysis and tooth size
prediction. Dent Clin North Am 1964:431-440.
29. Sukovic P, Brooks S, Perez L, Clinthorne NH. A novel
design of a cone-beam CT scanner for dentomaxillofacial
imaging: Introduction and preliminary results. CARS
2001:700-705.
30. Mah JK, Danforth RA, Bumann A, Hatcher D. Radiation
absorbed in maxillofacial imaging with a new dental
computed tomography device. Oral Surg Oral Med Oral Pathol
Oral Radiol Endod 2003;96:508-513.
23
CHAPTER 3: JOURNAL ARTICLE
Abstract
Introduction: Dental crowding can be defined as the
difference between the space available in the dental arch
and the space required to align the teeth.
Crowding is
thought to be related to the apical base.
Unfortunately
the literature has not described a reliable and consistent
way to relate jaw size and crowding.
Purpose: It is the
purpose of this study to investigate the relationship
between the basal bone, alveolar bone and crowding of the
teeth. Using measurements of basal bone, tooth size and
position, an attempt will be made to explain crowding.
Methods: A sample of thirty untreated patients with pretreatment cone beam computed tomography (CBCT) scans and
available pre-treatment plaster models were utilized.
Consecutive patients’ records were collected based on the
following inclusion criteria: 12-17 years of age and
presence of a full complement of teeth with all teeth
erupted except for third molars.
Data collected via CBCT
included measurements of basal bone perimeter and area as
well as tooth angulation.
Model analysis included measures
of tooth width and crowding. Results: Correlations among
24
the various basal bone measurement parameters were
significant and high.
Some significant, but weak,
relationships were detected between crowding and various
basal bone parameters.
Conclusions: With the advances in
cone beam computerized tomography, measurements of hard
tissue can be made with relative ease.
Although the
present study found significant correlations between
crowding and basal bone dimensions, the correlations were
low and are of little value in explaining the relationships
that were investigated.
The value of this study is that it
denies a strongly held belief.
That belief is that there
is a strong relationship between basal bone, the teeth, and
the related alveolar bone.
25
Introduction
Diagnosis and treatment planning is critical for
establishing a foundation for orthodontic success.
Elements of such planning typically include an analysis of
crowding, malalignment, and protrusion or retrusion of the
teeth.
Dental crowding is determined by comparing the total
tooth mass to the arch length that is available.
While
this value, the tooth mass–arch length discrepancy, is a
cornerstone value during diagnosis and treatment planning,
several methods of estimation are described in the
literature.
Of course, given that several methods are
available, estimations of tooth mass and arch length vary.
Van der Linden and McNamara1 define dental crowding as
the discrepancy between tooth size and jaw size that
results in a misalignment of the teeth.
It is generally
believed that when tooth mass is too small relative to
basal bone, interdental spacing or diastemas will likely
occur.
Conversely, if the basal bone in the body of the
mandible is constricted or too small relative to tooth
mass, the teeth will be crowded out of normal arrangement,
or, if normal arrangement is maintained, they will show a
procumbent relationship to the mandibular plane.2
26
Techniques for measuring basal bone have varied as
have its definition and location.
While measures of tooth
size are relatively finite and can be readily measured, the
literature has not supported a reliable and consistent way
to measure jaw size.
As a result, previous attempts to
measure basal bone have resulted in complicated methods
that are often time consuming to perform and variable in
estimation.3-6
The relationship between crowding and basal bone is
one that has been extensively investigated in the
literature.
There is a long standing belief that a strong
relationship exists between basal bone, the teeth, and
related alveolar bone.
On an historical basis apical base
relationships have been assessed by means of palpation or
by cephalometric examination.7
Now, with the advent of cone
beam computerized technology (CBCT), a new and more
reliable technique of measuring bone dimensions exists.
27
Materials and Methods
A sample of 30 untreated patients’ records were
retrieved from a private orthodontic office.
Records
included pre-treatment images by i-CAT Cone Beam 3D dental
imaging (Imaging Sciences International) and pre-treatment
plaster models.
Consecutive patients’ records were
collected based on the following inclusion criteria: 12-17
years of age and presence of a full complement of teeth
with all teeth erupted except for third molars.
No
consideration for gender was used in selecting the sample.
The use of a single time point for data collection limits
this study to a cross-sectional comparison.
Each patient was assigned a number to eliminate the
possibility of patient identification.
Image data was
stored on an external hardrive and analyzed at Saint Louis
University Center for Advanced Dental Education (SLU-CADE)
using the following software: Dolphin 3D (Dolphin Imaging
10 featuring Dolphin 3D), Image Tool (University of Texas
Health Science Center at San Antonio) and Excel (Microsoft
Co, Redmond WA).
28
Measuring Basal Bone from the Cone Beam CT Images
Cone beam image assessments were achieved using
Dolphin 3D.
The initial step in the analysis involved
standardization of image orientation to the X-plane,
represented by the Functional Occlusal Plane (FOP), the Yplane (a perpendicular plane that varied depending on the
analysis) and the Z-plane (represented by the mid-sagittal
plane.) (Figure 3.1) The Functional Occlusal plane is
defined as a plane that bisects the cusps tips of the first
mandibular molar and the second mandibular pre-molar.
X
Y
Z
Figure 3.1: The standard orientation using three
dimensional planes. Functional occlusal plane (X),
perpendicular plane (Y), mid-sagittal plane (Z).
29
Measurements of basal bone included values of
perimeter and area.
For each of the CBCT images, a common
Hounsfield value was used that allowed elimination of the
soft tissues and prevention of its interference with bone
imaging and measurement.
Cross-Sectional Area
Utilizing a sagittal orientation, two basal bone
measurement planes were established that are parallel to
the FOP (#1 in Figure 3.2).
The first plane passed through
B point (#2 in Figure 3.2) the second through the inferior
most point of the mental foramen (#3 in Figure 3.2).
Cone
beam slices were made in each of these locations and the
resulting planes were used to perform basal bone area
measurements.
On each of the measurement planes, areas
anterior of perpendiculars of the mesial contact of the
second molar (#4 in Figure 3.2) and the mandibular foramen
(#5 in Figure 3.2) were measured inclusive of any tooth
roots that may have been present in the slice.
Figure 3.3
shows the manipulation of cone-beam images to produce the
desired measurement planes.
The area measured is reported
in square millimeters (Figure 3.4).
30
1
2
3
5
4
Figure 3.2: Functional occlusal plane (1). Crosssectional basal bone measurement plane parallel to the FOP
through B point (2). Cross-sectional basal bone measurement
plane parallel to FOP at inferior most point of the mental
foramen (3). Perpendicular plane to the mandibular plane
through the mesial contact of the mandibular second molar
(4). Perpendicular plane to the mandibular plane through
anterior mandibular foramen (5).
Figure 3.3: Sequence of CBCT image manipulation showing
perpendicular planes (mandibular plane and mesial second
molar plane), sagittal slice and rotation to occlusal view.
31
Figure 3.4: Sagittal slice through B point rotated to
occlusal view. Basal bone area measurement from mesial of
bilateral second molar contacts shown by hatched pattern.
Perimeter
Utilizing the same basal bone measurement planes as
discussed for cross-sectional area, values of perimeter
were also measured.
Outside perimeters of basal bone were
measured from both the perpendicular of the mesial contact
of the second molar and the perpendicular of the mandibular
foramen, on both measurement planes (Figure 3.5).
32
Figure 3.5: Sagittal slice through B point rotated to
occlusal view. Outside basal bone perimeter measurement
from mesial of bilateral second molar contacts shown by
dotted line.
In the past, several different curves for measuring
arch perimeter have been used (catenary curves, parabolas,
circles and ovals), but unlike other shapes that have
complex calculations and questionable fit, the perimeter of
an ellipse can be calculated easily and has been shown to
be accurate with high significant correlations to
conventional measurements.8
33
Estimates of basal bone perimeter were also generated
using an elliptical formula.
Necessary for this formula
are measurements of a major and minor axis of the ellipse.
The minor axis for the elliptical perimeter is represented
by the distance between bilateral contact points of the
first and second molars.
The major axis is recorded as the
distance from the most anterior point of basal bone to its
intersection with the minor axis, which represents one-half
of the major axis value (Figure 3.6 and 3.7).
Figure 3.6: Diagram showing major and minor axis of
ellipse (modified from Kanaan).8
34
½X
Z
Figure 3.7: Sagittal slice through B point rotated to
occlusal view. Minor axis shown as distance between
bilateral contact of first and second molars (Z). Major
axis (one-half of total value) shown as intersection of
most anterior point on basal bone to minor axis (X).
Using the equation for perimeter of an ellipse:
P = π (X + Z) / 2
where X is half the length of the major axis and Z is half
the length of the minor axis, the perimeter, P, is
calculated and expressed in millimeters.
35
Model Analysis
Conventional plaster models were utilized to perform
two well established methods of estimating the amount of
crowding.
The first method is recommended by Proffit and
Fields9 and uses a direct approach on the dental casts.
To
measure the space available, the dental arch is divided
into segments that can be measured as straight line
approximations of the arch. Four quadrants are created:
distal of left first molar to the distal of left canine,
distal of left canine to the mesial of the left central
incisor, mesial of the right central incisor to the distal
of the right canine, and distal of right canine to the
distal of the right first molar (Figure 3.9).
Each
quadrant was measured with a digital caliper recorded to
the nearest hundredth of a millimeter.
Space required was
measured as the sum of the individual tooth widths from the
mesial of the mandibular left second molar to the mesial of
the right second molar.
36
Figure 3.8: Diagram depicting quadrants for straight line
approximations of available arch space (modified from
Little).10
In addition, Little’s irregularity index10 was measured on
each mandibular arch.
The scoring method involves
measuring the linear displacement of the anatomic contact
points of the anterior teeth (canine to canine)(Figure
3.10).
The sum of the five displacement values represents
the relative degree of incisor irregularity.
37
Figure 3.9: Little’s irregularity index defined as the
summed displacement of anatomic contact points of the
mandibular anterior teeth. A+B+C+D+E = irregularity index
(modified from Little).10
Error of the Method
A reliability test was performed to evaluate the
measurement error.
Four of the thirty cases were randomly
selected and all measurements were duplicated.
Intraclass
Correlation Coefficient (ICC) was executed on the repeated
measures.
A perfect score equals 1.00; however, a
Cronbach’s Alpha ≥ 0.8 is considered an indicator of a
reliable technique.
38
Cronbach’s alpha was calculated from the formula:
α =
N•r
1+(N-1)•r
Where N is equal to the number of items and r is the
average intra-item correlation among the items.
Statistical Analysis
It is hypothesized that when comparing tooth mass–arch
length variables with basal bone dimensions that no
significant relationships will exist.
In order to test this hypothesis standard descriptive
statistics (mean, range and standard deviation) were
computed for each variable. Pearson’s correlation was used
to analyze whether relationships existed between variables.
SPSS Version 15.1 (SPSS Incorporated, Chicago, Il) was used
to calculate all the statistics.
39
Results
Model Analysis
Descriptive statistics were calculated for the model
analysis measures.
The range, mean and standard
deviations are reported in Table 3.1.
The average space
available (basal sum) over the sample was 85.1 mm, while
the average space required was 86.6 mm, resulting in an
average discrepancy of -1.5 mm.
Intraclass Correlation Coefficient (ICC) was
calculated from error measurement on three patients’
records. (Table 3.2)
Fortunately, it was found that the
measurements were highly repeatable.
Table 3.1: Descriptive statistics for the 30 patients’
model analysis. Values reported in millimeters.
Measurement
N
Minimum
Maximum
Mean
S.D.
Basal Sum
30
76.1
96.0
85.1
4.3
Tooth Size Sum
30
77.0
97.5
86.6
4.4
Discrepancy
30
-8.0
6.6
-1.5
3.9
30
0.1
11.0
3.8
2.7
Proffit Crowding
Little Crowding
Irregularity Index
40
Table 3.2: Cronbach’s Alpha for Intraclass Correlation
Coefficient of model analysis parameters.
Measurement
Cronbach’s Alpha
Proffit Crowding
Basal Sum
0.97
Tooth Size Sum
0.96
Discrepancy
0.96
Little Crowding
0.96
Irregularity Index
Basal Bone Measurements
Descriptive statistics were calculated for each basal
bone parameter for the 30 patients.
The range, mean and
standard deviations for each measurement are presented in
Table 3.3 and 3.4.
Table 3.3: Descriptive statistics for the 30 patients on
the cross-sectional basal bone measurement plane through B
point. Perimeters reported in millimeters, areas reported
in square millimeters.
Measure
N
Minimum Maximum
Mean
S.D.
Perimeter Mesial 7’s
30
89.0
108.6
99.0
5.7
Perimeter Mand. For.
30
133.2
178.8
160.1
9.5
Elliptical Estimation 30
83.0
106.2
92.2
5.6
Area Mesial 7’s
30
619.0
1217.5
887.6
152.7
Area Mand. For.
30
1060.0
1901.5
1492.6
230.1
41
Table 3.4: Descriptive statistics for the 30 patients on
the cross-sectional basal bone measurement plane through
inferior mental foramen. Perimeters reported in
millimeters, areas reported in square millimeters.
Measure
N
Minimum Maximum
Mean
S.D.
Perimeter Mesial 7’s
30
88.2
109.0
99.8
6.5
Perimeter Mand. For.
30
111.07
177.2
147.2
20.6
Elliptical Estimation 30
87.0
107.2
97.5
6.3
Area Mesial 7’s
30
612.4
1210.6
867.8
156.3
Area Mand. For.
30
757.1
1786.2
1214.7
271.3
Outside perimeter values mesial of the second molars
over both basal bone measurement planes were very similar,
99.0 mm for the plane through B point and 99.8 mm for the
plane through inferior mental foramen.
For the basal bone
measurement plane through B point the elliptical formulaic
estimation was 6.8 mm less than the outside perimeter.
On
the basal bone measurement plane through inferior mental
foramen the elliptical formulaic estimation was 2.3 mm less
than the outside perimeter. The cross-sectional area
measurement mesial of the second molars was 19.8 mm2 greater
on the basal bone measurement plane through B point than it
was for the basal bone measurement plane through the
inferior mental foramen.
42
Pearson’s correlation was used to analyze whether
relationships existed between the various basal bone
parameters measured.
Correlations amongst the basal bone
parameters are shown in Table 3.5 and 3.6.
Pearson’s
correlation was also used to compare the two crowding
indexes to the basal bone paramaters (Table 3.7 and 3.8).
Table 3.5: Pearson’s correlation for the perimeter mesial
of the second molars to the other basal bone parameters on
the cross-sectional basal bone measurement plane through B
point.
Correlation Comparison
R
Approx. Sig.
Perimeter Mesial 7’s
Perimeter Mand. For.
Perimeter Mesial 7’s
Elliptical Estimation
Perimeter Mesial 7’s
Area Mesial 7’s
Perimeter Mesial 7’s
Area Mand. For.
&
0.76
<.01
&
0.93
<.01
&
0.91
<.01
&
0.83
<.01
Table 3.6: Pearson’s correlation for the perimeter mesial
of the second molars to the other basal bone parameters on
the cross-sectional basal bone measurement plane through
inferior mental foramen.
Correlation Comparison
R
Approx. Sig.
Perimeter Mesial 7’s
Perimeter Mand. For.
Perimeter Mesial 7’s
Elliptical Estimation
Perimeter Mesial 7’s
Area Mesial 7’s
Perimeter Mesial 7’s
Area Mand. For.
&
0.70
<.01
&
0.97
<.01
&
0.89
<.01
&
0.80
<.01
43
Figure 3.11 demonstrates graphically the correlation that
existed between the two model analyses of crowding, the
Little Irregularity Index and the Proffit crowding
analysis.
Figure 3.10: A scattergram correlation plot that compares
the Little Irregularity Index values to the Proffit
crowding analysis. r=-0.76, p<.001, r2=0.58
44
Table 3.7: Pearson’s correlation for Proffit crowding
analysis to perimeter and area basal bone measurements.
Correlation Comparison
R
Measurement plane through
B point
Proffit Crowding &
0.36
Perimeter Mesial 7’s
Proffit Crowding &
0.30
Area Mesial 7’s
Measurement plane through
inferior mental foramen
Proffit Crowding &
0.40
Perimeter Mesial 7’s
Proffit Crowding &
0.41
Area Mesial 7’s
* Significant correlation at the 95% level
Approx. Sig.
0.049 *
0.104
0.027 *
0.024 *
Table 3.8: Pearson’s correlation for the Little
Irregularity Index to perimeter and area basal bone
measurements.
Correlation Comparison
Measurement plane through
B point
Little Irregularity Index
& Perimeter Mesial 7’s
Little Irregularity Index
& Area Mesial 7’s
Measurement plane through
inferior mental foramen
Little Irregularity Index
& Perimeter Mesial 7’s
Little Irregularity Index
& Area Mesial 7’s
* Significant correlation at the
45
R
Approx. Sig.
-0.40
0.029 *
-0.30
0.110
-0.36
0.048 *
-0.27
0.144
95% level
Pearson’s correlation was used to analyze whether
relationships existed between the total tooth width from
first molar to first molar and the basal bone measurements.
Correlations are shown in Table 3.9.
Table 3.9: Pearson’s correlation for total tooth width
to perimeter and area basal bone measurements.
Correlation Comparison
R
Measurement plane through
B point
Tooth Width 6-6
0.35
& Perimeter Mesial 7’s
Tooth Width 6-6
0.42
& Area Mesial 7’s
Measurement plane through
inferior mental foramen
Tooth Width 6-6
0.21
& Periemter Mesial 7’s
Tooth Width 6-6
0.32
& Area Mesial 7’s
* Significant correlation at the 95% level
46
Approx. Sig.
0.057
0.021 *
0.252
0.084
Intraclass Correlation Coefficient (ICC) was calculated
from error measurement on three patients’ records. (Table
3.10 and 3.11)
Fortunately, it was shown that the
formula’s estimation was highly repeatable.
Table 3.10: Cronbach’s Alpha for Intraclass Correlation
Coefficient of cross-sectional basal bone measurement plane
parameters through B point.
Measure
Cronbach’s Alpha
Perimeter Mesial 7’s
0.99
Perimeter Mand. For.
0.98
Elliptical Estimation
0.98
Area Mesial 7’s
0.97
Area Mand. For.
0.97
Table 3.11: Cronbach’s Alpha for Intraclass Correlation
Coefficient of cross-sectional basal bone measurement plane
parameters through inferior mental foramen.
Measure
Cronbach’s Alpha
Perimeter Mesial 7’s
0.98
Perimeter Mand. For.
0.98
Elliptical Estimation
0.98
Area Mesial 7’s
0.97
Area Mand. For.
0.96
47
Discussion
This study was designed to address strongly held
orthodontic beliefs that relationships exist between the
teeth, basal bone, and crowding.
Relationship Between Crowding and Tooth Size
Two methods of tooth size-arch length discrepancy were
compared in this study.
Pearson’s correlation revealed a
marked level of correlation between the two methods (Figure
3.11)(r=-0.76, p<.001, r2=0.58.)
Contrasts of similar
methods, like the Merrifield anterior space analysis and
the Little irregularity index have been studied in the past
and have revealed positive, but low correlations.11 The
modest correlation is attributed to the fact that they
provide complementary information.11
The space analysis is
more attuned to tooth displacements while the irregularity
index is susceptible to axioversions.11 Because of the
complementary information, it is suggested that no
measurement from the casts alone be used to properly
diagnose a malocclusion.11
Authors have reported that large teeth are more likely
to be crowded than small teeth.12,13
48
It has been suggested
that correlations between the mesio-distal widths of
mandibular incisors are highly and significantly correlated
with crowding.12,13
This study does not support this
finding. Pearson’s correlation was used to compare
relationships between the both the Proffit and Little
crowding analysis and the total tooth width. Correlations
were low but significance at the 95% level was only found
for the Proffit analysis.
Such low correlations have,
unfortunately, almost no value in prediction.
The low
correlations in this study are in agreement with other
studies that failed to show relationships between crowding
and tooth size.14,15
Basal Bone
The importance of having a good relation between the
basal bone and the teeth was first recognized by Tweed in
1944.16
Orthodontists recognize the importance and
significance of having teeth ‘upright over basal bone’, but
when pressed for specific definitions their answers vary.
The challenge in addressing relationships involving basal
bone is that its location has yet to be truly defined and
there is a lack of agreement on methods designed to
quantify apical base.
49
To date, previous investigators have used traditional
orthodontic records, including plaster models and
cephalograms, to attempt to detect relationships involving
basal bone.1-3,8,17
Plaster models have limitations, however,
that include the need for very accurate impressions and
deep vestibular rims especially in the posterior.
There is
also the unavoidable error in that impressions include the
capture of buccal and lingual soft tissues along with basal
bone.
Now, with advances in radiography, cone beam
computerized tomography (CBCT) is increasing in popularity.
The three-dimensional radiographs produced by CBCT allow
analysis of hard tissue perimeters, areas and volumes like
never before.
With the ability to adjust Hounsfield
density values, soft tissue can be simply ‘removed’,
allowing exposure of more dense hard tissue structures.
A new assessment of basal bone parameters was
performed using CBCT in 30 pre-treatment orthodontic cases.
While the present day definition of basal bone may be
vague, this study recorded values of basal bone perimeter
and area across two measurement planes. The superior plane,
through B point, was chosen in an attempt to be consistent
with previous basal bone studies and the inferior plane,
50
through the mental foramen, was selected to avoid the
potential influence of root tips.
Basal Bone Relationships
Values of perimeter and area measured back to the
mandibular foramen were found to be inconsistent.
In
slices of basal bone measurement planes, it was often the
case that due to the inclination of the mandibular ramus,
mandibular bone did not extend as far posteriorly, on the
two-dimensional plane, as the perpendicular to the
mandibular foramen extended.
Because of this lack of
uniformity, little emphasis was placed on measurements
recorded back to the mandibular foramen in this study.
Correlations among the various basal bone measurement
parameters were high and significant with r values ranging
from 0.70 to 0.97.
High correlations are to be expected
within measurement planes due to the similarity and
interaction of measurement variables, (i.e., perimeter is a
value used also in the calculation of area).
Correlations
between the basal bone measurements between both planes
were also significant and high.
This suggests that there
is little justification for selecting a particular basal
bone measurement parameter over another.
51
In addition,
Cronbach alpha values were high, in recognition of the
accuracy of which measurements can be made with CBCT.
Orthodontists share a belief in a strong relationship
between basal bone, crowding and tooth size.
It is logical
to assume that basal bone and tooth size should interact in
such a way so that a small apical base should result in
crowding and/or protrusion of the teeth.
The converse
relationship should also hold; a large apical base with
normally sized teeth should result in spacing and/or
retrusion of the teeth.
The basal bone measures recorded
in this study had low correlations with both tooth width
and crowding (Table 3.7-3.9).
Such low correlations have,
unfortunately, almost no value in prediction.
Therefore,
this study failed to show any strong relationships between
basal bone, tooth size and crowding.
Elliptical Formulaic Estimation
Measurements of basal bone were calculated from flat
parallel planes.
Because of the two dimensional geometric
shape exhibited by these planes an elliptical formulaic
estimation was successful in estimating basal bone
perimeter.
The formulaic estimation for perimeter was less
on both the plane through B point and that of the plane
52
through the inferior mental foramen, by 6.8 and 2.1 mm,
respectively, with similar standard deviations.
It is
important to consider that the formulaic measurement and
the outside perimeter measurement are not measures of the
same perimeter.
The formulaic estimation is a perimeter
measurement from the contact point of the first and second
molars through the basal bone channel to the anterior most
point of basal bone.
It is expected that this value would
less than that of a measurement of outside basal bone
perimeter.
Pearson correlations between the formulaic
estimation of perimeter and the outside perimeter were very
high and significant.
These findings are further supported
in a study by Kanaan which also found the elliptical
formulaic estimation to be a good estimation of basal bone
perimeter.8
When the elliptical formulations were
calculated and compared to crowding or tooth size, again no
productive correlations were found.
53
Conclusions
1.
Correlations among the basal bone measurements over
both planes were significant and high.
This suggests that
there is little justification for selecting a particular
basal bone measurement assessment over another.
2.
Although the present study found significant
correlations between measures of crowding and tooth mass to
basal bone dimensions, they were low.
Such low
correlations have almost no value in prediction.
3.
Orthodontists commonly believe that there is a strong
relationship between basal bone, the teeth, and related
alveolar bone.
This study does not support that belief.
Due to the strong correlations and reliability of the basal
bone measurements, future searches for relationships
between basal bone and crowding should be shifted towards
discovering new methods of estimating crowding, perhaps by
incorporating position and angulation in three-dimensions.
54
Literature Cited
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VITA AUCTORIS
Gregory Bell was born on the 16th of September 1976 in
England.
Dr. Bell is the oldest of three children.
He moved with his family to St. Louis, Missouri in
1986 and graduated from Lafayette High School in 1994.
After that he moved to Kirksville, Missouri where he
attended Truman State University, formerly known as
Northeast Missouri State University.
After graduating in
1998 with a Bachelor’s degree in Biology he relocated to
Cincinnati, Ohio.
While in Cincinnati he attended the
University of Cincinnati and completed a Master’s degree in
Biology in 2000.
Dr. Bell began his dental education
at The Ohio State University in Columbus, Ohio and received
his Doctor of Dental Surgery degree in 2005.
He was
accepted into the orthodontic residency program at Saint
Louis University that same year.
He is happily married to his wife, Lynn, and they have
a young son, Jack, born during his residency in January,
2007.
Dr. Bell and his family are planning to relocate to
Milwaukee, Wisconsin to pursue private practice.
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