Download an assessment of apical base and curve of spee from a

AN ASSESSMENT OF MANDIBULAR APICAL BASE AND CURVE OF SPEE
FROM A DEVELOPMENTAL PERSPECTIVE
Anas Athar, B.D.S. M.S.
An Abstract Presented to the Graduate Faculty of
Saint Louis University in Partial Fulfillment
of the Requirements for the Degree of
Master of Science in Dentistry
2011
Abstract
Introduction: The difference between the mesio-distal width of teeth and the perimeter of
apical base is defined as dental crowding. It is thought that a relationship of teeth to the
apical base is essential for diagnosis and long term stability of orthodontic treatment.
Unfortunately there is no reliable definition of apical base in literature. Researchers have
defined apical base using various methods, but none of the definitions have taken
development into consideration,
Purpose: This study will investigate if there is a relationship between the apical base
measured at inferior alveolar nerve level, arch perimeter and crowding as measured on
the plaster model. An attempt will also be made to determine if there is a relationship
between the curve of Spee and the curve fOlmed by the inferior alveolar nerve when
viewed sagitally.
Method: A sample of 27 randomly selected untreated patients with pre~treatment cone
beam computed tomography (CBCT) scans and available pre-treatment plaster models
were utilized. Patients were selected based on eruption of full pennanent dentition. Data
collected by CBCT included measurements of basal bone perimeter at the level of
inferior alveolar nerve canal, and tracing of the curve of Spee and curve of the inferior
alveolar nerve canaL Model analysis included measures of the arch pedmeter and dental
crowding,
Results: The apical base perimeter and arch perimeter measured on dental cast are
significantly different. A statistically significant difference was also observed between
the two curves (curve of Spee and curve of the inferior alveolar canal).
1
Conclusions: No relationship was established between the apical base measured at
inferior alveolar nerve canal, crowding, and the arch perimeter as measured on model.
Similarly, the curve of Spee was significantly different from the curve formed by the
inferior alveolar canal.
2
COMMITTEE IN CHARGE OF CANDIDACY
Assistant Professor Ki Beom Kim,
Chairperson and Advisor
Professor Eustaquio Araujo
Professor Rolf G. Behrents
DEDICATION
I dedicate this project to the Saint Louis Fire Department and to the doctors and
staff of Saint Louis Children's Hospital for their efforts and knowledge in saving my
daughter's life.
r would also like to dedicate this work to the people and leaders of the U.S.A. for
providing me and my family an environment of success, peace and care.
ii
ACKNOWLEDGEMENTS
I would like to acknowledge the following individuals:
•
Dr. Ki Beom Kim for his support
•
Dr. Behrents for his advice and guidance throughout this project
•
Dr. Araujo for being the most supportive teacher and being there,
whenever needed.
•
Dr. Condoor for his help with data collection
•
Dr. Israel for assistance with statistics
I specially want to thank my wife Samia for her unconditional love and support. My
daughter, Amna for all her hugs and kisses. My son, Mustafa for being a special gift for
me.
iii
TABLE OF CONTENTS
List of Tables ....................................................................................................................... v
List of Figures .................................................................................................................... vi
CHAPTER 1: INTRODUCTION ........................................................................................ 1
CHAPTER 2: REVIEW OF THE LITERATURE .............................................. 4
Methods of Measuring Apical Base ......................................................................... 6
Basal Bone and Tooth Size-Arch Length Discrepancy ........................................... 8
Role of Inferior Alveolar Nerve in Development of Mandible ............................. 12
13
Role of Inferior Alveolar Nerve and Dental Development. .........
Inferior Alveolar Nerve and CBCT ....................................................................... 15
Curve of Spee ............................... :......................................................................... 18
Pllrpose of the Study .............................................................................................. 20
References ..........
21
0 .........................
o ...................................................................................................
CHAPTER 3: JOURNAL ARTICLE
25
Abstract ....................................................................................................
Introduction ............................................................................................................ 27
Materials and Methods .t •••••
29
Measuring Basal Bone from CBCT at the Inferior Alveolar Nerve .......... 29
Model Analysis .......................................................................................... 33
Tracing Curve of Spee ............................................................................... 34
Tracing Curve of Inferior Alveolar Nerve ................................................. 36
Intra-rater reliability ................................................................................... 36
Comparison of Curves ............................................................................... 38
Statistical Analysis ..................................................................................... 40
Results .................................................................................................................... 41
Inferior Alveolar Nerve Perimeter ............................................................. 41
Comparison of Curves ............................................................................... 43
Discussion .............................................................................................................. 45
Inferior Alveolar Nerve as Apical Base ..................................................... 45
Curve of Spee and Inferior Alveolar Nerve .............................................. .47
Conclusions ............................................................................................................ 49
t .............
o . . . . . oo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
to . . . . . . . . . . . . . . . . . .
Literature Cited ...................................................................................................... 50
Vita Auctoris ...................................................................................................................... 52
IV
LIST OF TABLES
Table 3.1:
Descriptive statistics of27 patients' model analysis ................................ .41
Table 3.2:
Cronbach's Alpha for intra-rater reliability .............................................. .42
Table 3.3:
Pearson's correlation for the nerve perimeter and methods of
crowding ................................................................................................... 42
Table 3.4:
Comparison of inferior alveolar nerve pedmeter and arch perimeter by
Proffit's method; analyzed by paired sample t-test. .................................. .42
Table 3.5:
Descriptive Statistics; Measurement of sections in the curve of Spee ...... 43
Table 3.6:
Descriptive Statistics; Measurements of section of the curve of the
inferior alveolar nerve ................................................................................ 43
Table 3.7:
Comparison of Left and Right side curves by paired sample t-test .......... .44
Table 3.8:
Comparison of the curve of Spee and the inferior alveolar nerve at each
section by independent sample t-test ........................................................ .44
v
LIST OF FIGURES
Figure 3.1:
Panoramic radiographs refolTIlatted from CBCT: visibility of inferior
alveolar nerve canal ............................................................... 31
Figure 3.2:
3-Dimensional volumetric image: axial view showing measurement of
inferior alveolar nerve ....................................
32
Ie . . . . . . . . . . . . . . . . . . . . . . . . Ie . . . . . . . . . . . . . . . .
Figure 3.3:
Quadrant diagram for straight line approximations of mandibular arch
perimeter .................................................................................................... 33
Figure 3.4:
Lateral cephalogram reformatted from CBCT ................................. 35
Figure 3.5:
Curve of the inferior alveolar nerve traced on sagittal view of 3dimensional volumetric image ................................................................... 36
Figure 3.6:
Comparison of curves by dividing each curve into five equal segments ... 39
Vi
CHAPTER 1: INTRODUCTION
The most common reason that patients seek orthodontic treattnent is dental
crowding. For treatment of dental crowding it is essential to identify the cause of
crowding. The characteristic features of dental crowding are malaligned teeth, deep curve
of Spee and protrusion or retrusion of teeth. 1 Dental crowding is determined by
comparing the
mesio~distal
width of the teeth to the perimeter of apical base. If the total
width of teeth is greater than the perimeter of apical base, dental crowding is
observed~
whereas, if the total width of teeth is less than perimeter of apical base, spacing between
the teeth is usually noticed. In order to have optimum arrangement of teeth in the arch, a
balance between the measurements of tooth structure and apical base is essential. 2
The significance of the apical base is repeatedly mentioned in orthodontic
literature. Even so there is no satisfactory definition of the apical base. The telID 'apical
base' was first mentioned by Lundstrom in 1923 3, he defined it as the section of bone
upon which teeth rest. Since the introduction of this term several methods have been
developed by investigators to define the apical base. Salzman,4 Downs,s Riedel6 and
several others used lateral cephalogram. While Howes, 7 Sergt 8 Kanaan9 and others used
dental casts to define the apical base. Bell took advantage of advancement in dental
radiography and used cone beam computed tomography (CT) to define the apical baselO.
It is commonly believed that orthodontic ally moved teeth that are placed in a 'nolmal'
position in the arch may not be stable if the basal arch over which they are placed is not
sufficiently large enough. Orthodontists believe that there is a strong relationship not
only bet\veen dental crowding and the apical base, but stability of orthodontic treatment
1
result, the orthodontic literature fails to precisely define apical base. All the studies so far
have attempted to define apical base from the anatomical position of the basal bone.
None of the investigations have attempted to define apical base from a developmental
perspective.
A literature search demonstrated a strong association between inferior alveolar
nerve (IAN) and development of mandible. It has been established that the first sttucture
that is formed in the human mandible is inferior alveolar nerve. The ossification of the
mandible starts at the mental foramen and progresses to fonn the mandible. The inferior
alveolar nerve has been strongly associated with dental development and the bone
sUl1'0unding the teeth. Il • 12. 13, 14
Previously it was difficult to identify the inferior alveolar nerve canal with
conventional 2-dimensional radiographs. This was due to the distortion or
superimposition of anatomic structures. With the advances in dental radiography Cone
Beam CT (CBCT) is becoming popular. Images acquired by CBCT are not only free
from any distortion and superimpositions effects, but they are also free from
magnification. These advantages allow a clinician to accurately identify structures that
were not readily visible on 2-dimensional images. IS
It is evident from the literature that there is a developmental relationship between
the inferior alveolar nerve and the mandible and the inferior alveolar nerve and teeth.
With the introduction of CBCT and advancement in software, it is possible to accurately
identify and trace the inferior alveolar nerve canal. The purpose of this study is to seek a
reliable method of measuring the perimeter of the apical base from a developmental
2
perspective. There will be an assessment to see if a relationship exists between the curve
of Spee and the curvature formed by the inferior alveolar nerve.
3
CHAPTER 2: REVIEW OF LITERATURE
Orthodontics is the area of dentistry concelned with the supervision, guidance and
correction of growing and mature dentofacial structures, including those conditions that
require movement of teeth or conection of malre1ationships and malformations of related
structures by the adjustment of relationships between and among teeth and facial bones
by the application of forces and/or the stimulation and redirection of the functional forces
within craniofacial complex. l
In a report by United States Public Health Services 750/0 population has some
noticeable deviation from ideal occlusion.
16
In this repol1 it was stated that crowded,
mal aligned teeth are the most common single contributor to malocclusion. About 40% of
children and 850/0 of youths had some degree of malalignmentlcrowding within dental
arches. Dental crowding is considered the most conunon form of malocclusion. 17 In
another survey, the National Health and Nutrition Examination Survey (NHANES-III)
repol1ed that only 35% of adults have well aligned teeth. It is obvious from the previous
reports that prevalence of malaligned teeth or dental crowding is high in the US
population.
Crowding is defined as the discrepancy between tooth size and jaw size that result
2
in a misalignment of the tooth position. Many factors such as evolutionary trends,
heredity, environmental effects, lack of attrition, and tooth size have been implicated as
causes of dental crowding. However, the most impo11ant detenninants of crowding and
spacing in dental arches are the size of the teeth and the size of the bony bases. 17
4
Common features of dental crowding are malaligned teeth, a deep curve of Spee
and proclinationlretroclination of teeth. The importance of the basal bone in determining
dental arch crowding has been widely discussed in literature. A common belief is that
when tooth mass is too small relative to basal bone, spacing or diastema is more likely to
occur and when tooth mass is too big in relation to the basal bone the teeth will be
4
crowded out of normal arrangement. Salzmann recognized the importance of basal bone
dimensions in dental crowding. Tweed 19 considered treatment to be successful when the
mandibular incisors were positioned on basal bone; when this is not achieved, relapse of
crowding may be evident. Several studies have suggested important interaction of basal
bone/apical base and dental crowding.
The terms basal bone and apical base are used interchangeably in literature. The
apical base is defined most recently as the portion of the jawbone that gives support to the
3
teeth. 2 The term "apical base" was first mentioned by Axel Lundstrom in 1923 who
defined it as the section of bone upon which teeth rest or are attached; this is very similar
4
to modern definition of apical base. Salzmann discussed apical base in more detail and
according to him the alveolar processes hold the teeth and are not in stress concentrating
areas of jaw. Such areas are located in the constricted portions of the jaw subjacent to the
alveolar processes in mandible and supeljacent to the alveolar process in maxilla. This
area is called the apical base. Although apical base is a widely used term in orthodontics,
it has never been precisely defined. According to Brodie
2o
the reason for this lack of
definition of apical base is the limitation of available methods. He suggested that apical
base may be determined by the limit of absorption of alveolar bone after the teeth are
5
lost. All the definitions of apical base in literature are determined by anatomical location.
The literature search shows no definition of apical base from a developmental aspect of
basal bone. In this study we attempted to define apical base from developmental point of
vIew.
Methods of Measuring Apical Base
Since the advent of term "apical base" by Lundstrom,3 there has been a great deal
of interest in the literature concerning the measurement of the apical base. As mentioned
by Brodie,2o there is no satisfactory definition of apical base. However, several methods
are reported that have attempted to locate and quantify basal bone. Traditionally, the
apical base is assessed by means of palpation or on cephalogram. 8 Cephalometric
methods utilizes point A and B (as described by Downs 5) denoting the apical base in the
region of central incisors, to the anterior cranial base. Both methods have limitations, one
being subjective and other being limited to one isolated relationship. Both these methods
only assess the location of the apical base and not its size. 8
Downs5 (1948) searched for an accurate method to determine the limits of the
basal bone. He introduced two cephalometric landmarks, point A and point B that
represented what he called the denture base. He used these two points, along with other
points, to study the skeletal patteln of the face as a part of his classical cephalometric
analysis. To study the discrepancy in apical base relationships, Riedel6 adapted Downs'
points A and B, and used them in two angular measurements, SNA and SNB. Ever since,
6
points A and B have been used extensively in cephalometric evaluations, and in many
studies, to determine the apical base relationship.
Howes' used dental casts to analyze the relationship between tooth size and the
supporting bone. He found that the supporting bone was above the palatal shelf and over
the apices of the teeth. By using a survey line above the apices of teeth without impinging
on the muco-buccal fold and sectioning horizontally on this line, he was able to remove
the alveolar process and expose the supporting bone. He found the basal arch to be at the
apical pOl1ion of the alveolar bone. In the mandibular arch it is 8 mm below the gingival
21
margin. Falck defined the apical base as "the area resulting from peripheral connection
of two reference points located 14 mm away from buccal cusps of the first primary
molars/premolars." Miethke et. a1. 22 argued that Falck's method of locating the apical
base was inaccurate for comparing treatment outcomes, given that the primary molars
have shorter cusps than the premolars. The difference in the crown height between these
two tooth types would change reference points and thus change the apical base level. To
overcome this limitation, Miethke' s group agreed with Howes 7 and Rees23 by using the
gingival margins as a reference point. They defined the apical base as the area resulting
from the peripheral connection of six reference points located 5 mm below the most
apical points of the gingival margins of the lower lateral incisors, canines and second
primary molars/premolars. In their opinion, the 5 mm distance from the gingival margins
was not a hue reflection of the apical base.
Although some authors have used the gingival margins as a reference to locate
basal bone, SergI, Kerr and McCo1l8 used the most concave contour of the buccal surface
of the casts to measure the basal bone area.
7
Not surprisingly, confusion still exists concerning the location of basal bone,
largely because of the absence of agreement among authors who simply used their
opinion and speculation to locate it.
Basal Bone and Tooth Size-Arch Length Discrepancy
It has been shown that, over a period of many years, there has been discussion of,
and concern for, stability by placing teeth "over basal bone." Unfortunately, one of the
difficulties in orthodontic treatment planning has been the estimation of the size and
dimensions of the basal bone.9
Angle's "line of occlusion" \-vas readily accepted by early orthodontists. 24 It
prompted a search for meaningful measurements of dental arch dimensions that could be
utilized in diagnosis and treatment planning. It was not until 1923 that the potential
relationship between Lundstorm's3 apical base and dental arch form began to be
understood, as well as the realization that one of the most important diagnostic dental
arch dimensions was dental arch perimeter. Lundstrom's theory was effectively translated
into clinical practice by Nance in 1947. 25
In his classic work, Nance25 described a method for measuring the "outside" arch
perimeter by using a piece of a .010 inch brass wire placed along the buccal surfaces of
the teeth from the mesial of one side of pennanent molar to the mesial of the opposite
side of pelmanent molar. Although most clinicians today do not measure the "outside
perimeter" as advocated by Nance, the use of brass wire to determine the available dental
arch perimeter is still a popular method.
8
Carey6with some modification adopted Nance's method. He used 0.020 inch soft
brass wire bent to a symmetrical arch form that was placed over the contact point region
of the posterior teeth and over the incisal edges of anterior teeth. He placed a mark where
the wire crossed the mesial contact point of the first pelmanent molars; dental arch length
could then be measured between these two marks. Even though he used the incisal edges
of the anterior teeth to measure the dental arch perimeter) he suggested that in certain
cases it was necessary to pass the wire over the incisal edges "at a point where we judge
them to belong."
Moorrees 21 presented a variation of the brass wire method for measuring dental
arch perimeter. He used stainless steel tubes welded to a flange. The flange served as a
mean of attaching a wire guide to a plaster model at the mesial aspect of the first
permanent molar, and the tubes allowed the soft 0.15 mm stainless steel wire to be guided
through them. Sticky wax was used to fix the flange to the cast, and the wire was bent
along the buccal cusps of the incisal edges of the teeth, stabilized to the tube with hot
wax, straightened and measured with a sliding caliper.
Huckaba28 described a similar brass-wire approach to measure the dental arch
length. He used 0.025 inch brass wire and centered the wire over the contact points in the
posterior dentition. In the anterior region he positioned brass \vire depending on the
anatomical position of anterior teeth. The wire is then cut and straightened with the
fingers and measured with a boley gauge.
Musich and Acketman29 used a catenometer to measure dental arch perimeter.
Measurements were made based on a catenary curve. In addition to brass wire and chain
techniques, Lundstolm30 suggested calculating the dental arch perimeter with a caliper by
9
measuring and adding straight line segments of the arch in six sections. Hew31 modified
this method and calculated arch perimeter by dividing the basal bone into four segments
and measuring the length of each segment individually. The total length of the four
segments was believed to represent the perimeter of basal bone. He studied the
conelation between tooth mass and available basal arch and found high correlation
between relapse and basal arch deficiency. He fu11her indicated "the reduction of dental
units improve the correlation between tooth mass and basal arch length in relapsed
cases."
Little proposed an irregularity index that would quantify the mandibular anterior
teeth crowding. He used this index as a guide for treatment priorities. The scoring was
done by measuring the linear distance of the displacement of two adjacent contact points.
These measurements were made at five contact points; the sum of displacement of these
five points represents the relative degree of incisor ilTegularity. Although,
Little~s
index
is simple and clinically applicable this method does not measure arch length.
BeGole32 took advantage of improvements in computer science and wrote the first
program to perform dental model analyses, including calculating the tooth size larch
length discrepancy. The program, MODELS, uses a set of 118 inputs to perform
analyses. These inputs are dental landmarks digitized from a photocopy of study model.
Arch perimeter is calculated as "the sum of various connecting line segments drawn
around the dental arch;" the four segments start from mesial surface of lateral incisor, to
the mesial surface of central incisor on the other side, to the distal surface of the lateral
incisor, to the mesial surface of first molar.
10
Direct measurement of photocopied three-dimensional objects has a high potential
for error in cases \vith severe tipping. Champagne33 reported that photocopies are an
unreliable method for arch length measurements and space analysis detennination. On the
other hand, Tran and colleagues
34
compared the manual measurement of the irregularity
index to computer measurements based on photocopies of models. They concluded that
the computer method is a valid and reliable alternative for assessing mandibular incisor
alignment. Kanaan9 did a study to establish a reliable method of measuring length of
basal bone. He used a mathematical fOlmula which he called "elliptical formula" and
tested its validity.
All above mentioned studies involved a 2 .. dimensional measurement of apical
base. To overcome the um'eliability of2-dimensional measurements, 3-dimensional
model analyses were introduced based on scanner-based 3-dimensional digitizers.
35
Yamamoto and associates described an optical method for creating 3-dimensional
computerized models with a laser-beam scan of the dental casts. Later, other attempts
were made to transfer the dental cast into 3-dimensional virtual nl0dels. Kuroda and
colleagues36 introduced a three-dimensional dental cast analyzing system that employs
laser scanning. This computerized model can be used to calculate distances and
perimeters from the 3 -dimensional virtual model.
BentO took advantage of advances in cone beam computerized tomography. He
used cross-sections of 3-dimensional volumetric images at two different levels parallel to
functional occlusal plane. The first cross-section was made at the level of B point, while
the second cross-section was made at the inferior most point of the mental foramen. He
then measured the perimeter using Kanaan's9 elliptical formula. In addition he also
11
measured the area of the basal bone at these two levels. He concluded that there is little
justification for selecting a pruiicular basal bone measurement assessment over another.
This literature review shows that there is no standard way of defining and
measuring apical base. It was obvious from the literature that methods that have been
developed to measure arch length, most do not measure arch length of the apical base.
Therefore, crowding has been commonly measured relative to the perimeter of the dental
arch, but not relative to the dental arch that houses the teeth. In addition to this, all the
definitions of apical base in literature are based on individual perception. No definition of
apical base is discussed on the basis of developmental aspect of apical base. Because hard
and nerve tissues interact during early development, and the hard tissue bears traces of
this interaction3? we will attempt to define basal bone at the level of inferior alveolar
nerve. According to the literature seru'ch, no study has investigated apical base from this
perspecti vet
Role of Inferior Alveolar Nerve in Development of Mandible
Embryologically, nerve tissue forms first and the bone tissue successively fOlms as a
canal around the nerve path. If, for instance no nerve canal appears in the bone tissue
regions where it should normally be present, there can be only two explanations: either
the nervous tissue was never present, or it has been destroyed. The reason cannot be that
nerve tissue has not yet penetrated the hard tissue, because nerve tissue never penetrates
bony tissue. 31
12
The first bony tissue to form in the human mandible is seen about the i h_8 th fetal
week on the external surface of Meckel) s cartilage in the lower border of the later
foramen mentale. 11 ,12,13 This early bone tissue supports the mental nerve. Recent studies
have shown that the mandibular canal in mid fetal life is not one hut three or more
separate canals. 38 These canals contain the nerve supply to the incisors, premolars and
molars, in that ordet.. The nerve branches to the incisors and deciduous molars/premolars
develop before the innervations to the permanent molars, In the final stage of fetallife~
the mandible doubles in size by apposition of bone tissue on the posterior margin of the
mandibular ramus and by resorption on its anterior border. During this process, the canal
openings on the inside of the ramus gradually merge. In this way, by gl'owth and
remodeling processes, the canal openings become one canal opening, corresponding to
the mandibular foramen seen at birth. The nerve pathways to the different tooth groups
thus become one nerve bundle, the inferior alveolar nerve.
Role of Inferior Alveolar Nerve and Dental Development
Nerve growth factor receptor (NGF-R) is expressed close to the developing tooth
buds, and nerves seemingly participate as fine network in the developing dental follicle. 39
Nerve tissue does seem to be essential for tooth development from the moment the dental
follicle forms. It is interesting that the teeth located closest to the nerve stems are the first
ones to be formed.
37
Thereafter, they are formed in the patteln in which ossification
occurs. There is a close relationship not only between tooth development and nerve
development, but also between tooth development and development of stuiounding bone
13
tissue. Studies have shown that canines are the first teeth to be laid down in the primary
dentition. In the anterior region, the upper central incisor form before the lateral incisor,
while opposite is true of the lower jaw, \vhere the pattern of innervation is different. With
regard to the primary molars and premolars the anterior teeth are formed before the
posterior ones in a pattern that corresponds to the innervation sequence and bone
formation. 37
In a report by Jakobsen4o a mandible with unilateral absence of mandibular canal
has been described and agenesis of teeth has been found on the side where the
mandibular canal was absent. The anterior teeth were present, however, and in these
cases a canal opening lingual to the incisors, not normally found was evident. It was
speculated that the innervation to the anterior region occurred via a lingual canal.
In another study by Bang et. a1. 41 the role of inferior alveolar nerve and the
development of teeth was discussed. In this study evidence was presented that the mumps
vitus may destroy myelin sheaths and hence interrupt tooth development by disluption.
This results in a shortening of root. When the myelin sheath grows out again, the
temporarily arrested root development resumes and molar root can accordingly change
form from its normal morphology to a taurodontic root fonn.
Kjaer42 discussed various patterns of tooth agenesis. The traditional regions in
which agenesis occur are: upper lateral incisors, upper second premolars, upper third
molars, lower central incisors, lower second premolars and lower third molars. The
regions in question are all those in which the innervation of the field involved occurs last.
It is evident from the literature that there is a strong relationship between the
inferior alveolar nerve and apical base development, also the inferior alveolar nerve and
14
tooth development. As the literature shows, no studies appear that discuss the relationship
between the apical base and the inferior alveolar nerve. A possible reason for this
omission in literature is that the canal that houses inferior alveolar nerve is not always
readily visible in conventional two dimensional radiographs. However, with the
introduction of more advanced imaging modalities like MDCT, CBCT etc. the inferior
alveolar nerve canal can be readily visualized with precision. 15
Inferior Alveolar Nerve and CBCT
A variety of imaging modalities are available~ including panoramic radiography
(conventional and digital), tomography or computed tomography (CT) and these have
been used for assessing the anatomy of various sttuctures including the inferior alveolar
nerve canaL The contribution of panoramic radiography to maxillofacial diagnoses in the
last 30 years has been significant. Over the last decade, digital panoramic radiography
was introduced and it appears to demonstrate certain advantages compared with filmbased panoramic radiography (e.g., faster image acquisition, elimination of dark room,
lower radiation exposure and availability of various imaging tools).
15
The recently introduced cone-beam computed tomography creates 3-dimensional
image data by a single scan around the imaging volume of interest. Data produced can be
displayed in any clinically meaningful way (e.g., panoramic and cross-sectional images
of maxilla and mandible, or temporomandibular joint sagittal and coronal images). CBCT
is well suited for imaging in the craniofacial area. It provides clear images of highly
contrasted structures and is extremely useful for assessing bone. 43 Images produced are
15
corrected for magnification resulting in accurate measurements. All of these
considerations, along with reduced radiation exposure to patient compared with medical
CT make CBCT a very promising imaging modality for maxillofacial diagnosis. 15
Although CBCT and panoramic radiographs are two different imaging modalities
they have been compared for their diagnostic accuracy. A few studies have compared
these two modalities in evaluating the inferior alveolar canal. Tantanapornku144 evaluated
the diagnostic accuracy of cone beam CT compared with panoramic radiographs in
predicting neurovascular bundle exposure during third molar extraction. CBCT were
superior to panoramic radiographs with sensitivity of93% and specificity of 77%. For
panoramic radiographs similar values were 70% and 63%. Friedland and associates45
presented cases utilizing 3-dimensional reconstructions from CBCT data to evaluate the
anatomic relationship of mandibular canal and impacted mandibular third molars. They
concluded that clinicians should consider the use of CT in selected cases, chiefly when
one or more of the telltale signs are present on panoramic image. Angelopoulos et.al. 15did
a study to compare CBCT reformatted panoramic images and digital panoramic images
for identification of the mandibular canal as part of peri-implant assessment. They
concluded that CBCT reformatted panoramic images were superior to digital panoramic
images for identification of the inferior alveolar canal. In addition to depicting inferior
alveolar canal accurately these reformatted images were free of magnification and
superimposition of neighboring sttuctures, which are inherent problems in panoramic
images. Lofthag-Hansen46 evaluated the visibility of the inferior alveolar canal and the
marginal bone crest and the agreement between observers in images from one CBCT
technique. According to authol'S the visibility of the inferior alveolar canal and the
16
marginal crest, as well as the observer agreement of the location of these structures was
high. Naitoh47 compared multislice computed tomography and cone beam computed
tomography in detection of fine anatomical sttuctures in the mandible such as bifid
mandibular canal, accessory mental and buccal foramina. They concluded that there is no
difference in depiction of various fine anatomical structures between images obtained
using the two modalities. The authors suggested use of CBCT for similar diagnostic tasks
due to low radiation dose to the patients.
It is evident from literature that cone beam computed tomogl'aphy is a reliable
method for inferior alveolar nerve canal identification. Previously we discussed that one
of the characteristic feature of crowding is a deep curve of Spee. Also we have discussed
relationship of the inferior alveolar nerve and development of apical base and teeth.
The o11hodontic literature shows only a few publications discuss the curve of Spee and no
study discusses factors that establish the curve of Spee.
17
Curve of Spee
The "curve of Spee" was first introduced by a German embryologist Ferdinand
Grafvon Spee in 1890. 48 Spee connected the anterior surfaces of mandibular condyles to
occlusal surfaces of the mandibular teeth with an arc of circle, tangent to the surface of a
cylinder lying perpendicular to the sagittal plane. According to him this geometric
arrangement is the optimum for maximum tooth contact during chewing and considered it
an important tenet in denture construction. Nowadays, the curve of Spee is defined
differently in different specialties of dentistry. In prosthodontics the curve of Spee starts
from canine and extends back to the terminal molar. The curve then continues posteriorly
to intersect the anterior surface of the condyle as originally proposed by Spee. In
orthodontics, the curve of Spee commonly refers to the arc of a curved plane that is
tangent to the incisal edges and the buccal cusp tips of the mandibular dentition viewed in
the sagittal plane. The difference in definitions can be due to the difference in patient
population served by two specialties. Orthodontists see mostly young patients, while
prosthodontists usually deal with adult patients. It has been suggested that the deciduous
dentition has a curve of Spee ranging from flat to mild, whereas the adult curve of Spee is
more pronounced. 49
Andrews50 in describing the 6 characteristics of normal occlusion found that the
curve of Spee in subjects with good occlusion ranged from flat to mild, noting that best
static intercuspation OCCUlTed when the occlusal plane was relatively flat. He proposed
that flattening the occlusal plane should be a treatment goal in orthodontics.
18
The curve of Spee is usually measured as the maximum of the perpendicular
distances between the buccal cusp tips of the mandibular teeth and a measurement plane
described by the central incisors and the distal cusp tip of the most posterior tooth in
mandi bular arch. 48
A significant curve of Spee is often evident in malocclusions with deep overbites.
This curve is frequently leveled as pro1 of overbite reduction. The curve of Spee has been
associated with size of the jaw. In retrognathic mandibles a deeper curve of Spee is
observed while in Class III patients a flat curve of Spee is usually observed. 51
Marshall et. a1. 48 did a study to examine the development of the curve of Spee
longitudinally in a sample of untreated subjects with nOlmal occlusion from the
deciduous dentition to adulthood. They found that the curve of Spee develops as the
result of the mandibular permanent first molal' and incisor eruption. The curve maintains
its depth until the mandibular permanent second molars erupt above the occlusal plane,
when it deepens again. During the adolescent dentition stage, the curve depth decreases
slightly and then remains relatively stable into early adulthood. The literature does not
explore the formation of the curve of Spee from a developmental point of view.
19
Purpose of the Study
With the advent of Cone Beam Computed Tomography (CBCT), it is possible to
identify and trace anatomical structures which were considered challenging with
conventional 2-dimensional radiography. The literature shows that inferior alveolar canal
can be accurately identified on images produced by CBCT. As we know embryologically
the inferior alveolar nerve is the first sttucture to be formed in the human mandible and
this nerve has been strongly associated with bone and dental development in human
mandible. Also it has been commonly observed that the residual ridge resorption does not
continue beyond the inferior alveolar canal. We attempted to define the apical base at the
level of inferior alveolar canal. As this canal is not a straight canal and forms a curve
when viewed from sagittal view we also studied whether or not the curve formed by the
inferior alveolar canal is related to curve of Spee, as this has never been studied before.
The purposes of the study are::
1. To establish a method to measure the apical base at the level of inferior alveolar
nerve from a developmental perspective.
2. To assess whether the curve ofSpee is similar to the curve formed by inferior
alveolar nerve when observed from the sagittal view.
20
Reference:
1. Proffit WR. Malocclusion and dentofacial defonnity in Contemporary Society. In:
Proffit, Fields editors. Contemporary Orthodontics. Saint Louis: Mosby 1986
2. Van der Linden EM, McNamara JA. Glossary of Orthodontic Terms. In: Jude,
Daskalogiannkis J, editors. Leipzig, Germany: Quintessence; 2000
3. Lundstrom 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
4. Salzmann JA. Orthodontic therapy as limited by ontogenetic growth and the basal
arches. Am J Orthod 1948 Apr;34:297-319
5. Downs WB. Variations in facial relationships: Their significance in treatment and
prognosis. Am J Orthod 1948;34:812-840
6. Reidel RA. The relation of maxillary structure to the cranium in malocclusion and
in nonnal occlusion. Angle Orthod 1952;22: 140-145
7. 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
8. SergI HG, Kerr WJ, McColl JH. A method of measuring apical base. Eur J Orthod
1996; 18:479.. 483
9. Kanaan W. The correlation between tooth size, basal bone size discl'epancy and
long term stability of the lo\vel' arch in Class II Division 1 patients. Masters
Thesis. Orthodontics. Saint Louis: Saint Louis Univel'sity; 2006.
10. Bell DG. Three-dimensional cone beam computed tomography assessment of
basal bone parameters and crowding. Masters Thesis. Orthdontics. Sain Louis:
Saint Louis University; 2008.
11. Kjaer 1. Histochemical investigations on the symphysis menti in the human fetus
related to the fetal skeletal maturation in the hand and foot. Acta Anat 1975;
93:607-633.
12. Bollobas E. Embryonic development of the mandibular canal. Acta Morphol Acad
Sci Hung 1982; 30(3-4): 233-9.
13. Radlanski RJ, Renz H, Reulen A. Prenatal development of the human mandible
3D reconstructions, morphometry and bone remodeling pattern, sizes 12-117 mm
CRL. Anat Embyol (Bed.) 2003 Oct; 207(3):221-32.
21
14. Smartt JM Jr) Low DW, Battlett SPa The pediatric mandible: 1. A primer on
growth and development. Plast Reconstr Surg. 2005 Jul; 16(4):563-71
15. Angelopoulos C, Thomas SL, Hechler S) Pal'issis N, Hlavacek M. Comparison
between digital panoramic radiography and cone-beam computed tomography for
the identification of the mandibular canal as part of presurgical dental implant
assessment. J Oral Maxillofac Surg. 2008 Oct;66(10):2130-5.
16. Kelly JE, Harvey CR. An assessment of the occlusion of the teeth of youths 12-17
years. Vital Health Stat 11. 1977Feb;(162):1-65
17. Puri N, Pradhan KL, Chandna A, Sehgal V, Gupta R. Biometric study of tooth
size in normal, crowded and spaced permanent dentitions. Am J Orthod
Dentofacial Orthop. 2007 Sep;132(3):279.e7-17
18. Sarver DM, Proffit WR. Special considerations in diagnosis and treatment
planning. In: Grabel', Vanarsdall, Vig, editors. Orthodontics Current Principles and
Techniques. St. Louis: Mosby 2005.
19. Tweed CH. Indications for the extraction of teeth in orthodontic procedure. Am J
Otthod Oral Surg. 1944-45;42:22-45
20. Brodie AG. Appraisal of present concepts in Orthodontia. Angle Otthod
1950~20:24-38.
21. Falck F. Comparative studies on the development of the tooth root following
orthodontic treatment with the active plate and function regulator. Fortschr
Kieferorthop. 1969;30(2):225-9
22. Miethke RR, Lindenau S, Dietrich K. The effect of Frankel's function regulator
type IlIon the apical base. Eur J Otthod 2003;25:311-8.
23. Rees DJ. A method for assessing the propottional relation of apical bases and
contact diameters of the teeth. Am J Orthod 1953;39:695 .. 707
24. Angle E. Treatment of malocclusion of the teeth and fractures of the maxilla.
Philadelphia: The S.S.White Dental manufacturing company; 1900.
25. Nance HN. Limitations of Orthodontic diagnosis and treatment. Am J Orthod
1947;33:177-223,253-301
26. Carey CWo Treatment planning and the technical program in the four fundamental
treatment forms. Am J Orthod 1958;44:887-98
22
27. MOn'ees CF. The dentition of growing child. A longitudinal study of dental
development between 3 and 18 years of age. Boston: Harvard University Press;
1959.
28. Huckaba OW. Arch size analysis and tooth size prediction. Dent. Clin North Am
1964:431·40.
29. Musich DR, Ackelman JL. The catenometer: a reliable device for estimating
dental arch perimeter. Am J Orthod 1973; 63:366~ 75.
30. Lundstrom A. The significance of early loss of deciduous teeth in the etiology of
malocclusion. Am J Orthod 1955 ;41 :819-26
31. Hew SKM. Basal bone contour as related to dental arch form (Thesis). Saint
Louis: Saint Louis University; 1966
32. BeGole EA. A computer progl'am for the analysis of dental arch form using cubic
spline function. Comput Programs Biomed 1979;10:136-42
33. Champagne M. Reliability of measurements from photocopies of study models. J
Clin Orthod 1992;26:648-50
34. Tran AM, Rugh JD, Chacon JA, Hatch JP. Reliability and validity of a computer
based Little irregularity index. Am J Orthod Dentofacial Orthop 1997; 111 :543-53
35. Yamanl0to K, Toshimitsu A, Mikami T, Hayashi S, Harada R, Nakamura S.
Optical measurement of dental cast profile and application to analysis of threedimensional tooth movement in orthodontics. Front Med BioI Eng 1989; 1: 119-30
36. Kuroda T, Motohashi N, Tominaga R, Iwata K. Three-dimensional dental cast
analyzing system using laser seaMing. Am J 011hod Dentofacial 011hop
2004; 125 :716-25
37. Kjaer I. Neuro-osteolgy. Cdt Rev Oral BioI Med. 1998;9:224-44
38. Chavez-Lomeli ME, Mansilla Lory J, Pompa JA, Kjaer I. The human mandibular
canal arises from three separate canals iMervating different tooth groups. J Dent
Res. 1996 Aug; 75:1540-4
39. Christensen LR, Mollgal'd K, Kjaer I, Janas MS. Immunocytochemical
demonstration of nerve growth factor receptor (NGF-R) in developing human
fetal teeth. Anat Embryol. 1993 Sep; 188:247-55
40. Jakobsen J, Jorgensen JB, Kjaer 1. Tooth and bone development in a Danish
medieval mandible with unilateral absence of mandibular canal. Am J Phys
Anthl'0p0l. 1991 May;85:15-23
23
41. Bang E, Christensen LR, Kjaer 1. Etiologic aspects and 011hodontic treatment of
unilateral localized arrested tooth development combined with hearing loss. Am J
Orthod Dentofacial 011hop. 1995 Aug; 108: 154-61
42. Kjaer I, Kocsis G, Nodal M, Christensen LR. Aetiological aspects of mandibular
tooth agenesis-focusing on role of nerve, oral mucosa and supporting tissues. Eur
J Orthod 1994 Oct;16:371-5.
43. Sukovic P. Cone beam computed tomography in craniofacial imaging. Orthod
Craniofac Res. 2003;6 Suppl 1:31-6
44. Tantanapornkul W, Okouchi K, Fujiwara Y, Yamashiro M, Manlola Y,
Ohbayashi N, Kurabayashi T. A comparative study of cone-beam computed
tomography and conventional panoramic radiography in assessing the topographic
relationship between the mandibular canal and impacted third molars. Oral Sur
Oral Med Oral Pathol Oral Radiol Endod. 2007 Feb; 103 :253-9
45. Friedland B, DonoffB, Dodson TB. The use of3-Dimensional reconstructions to
evaluate the anatomic relationship of the mandibular canal and impacted third
molars. J Oral Maxillofac Surg. 2008 Aug;66: 1678.. 85
46. Lofthag Hansen S, Grondahl K, Ekestubbe A. Cone-beam CT for preoperative
implant planning in the posterior mandible: visibility of anatomic landmarks. Clin
Implant Dent Relat Res. 2009 Sep; 11 :246-55
4
47. Naitoh M, Nakahara K, Suenaga Y, Gotoh K, Kondo S, Ariji E. Oral Surg Oral
med Oral Pathol Oral Radiol Endod. 2010 jan;109:e25-31
48. Marshall SD, Caspersen M, Hardinger RR, Franciscus RG, Aquilino SA,
Southard TE. Development of curve of Spee. Am J Orthod Dentofacial Orthop.
2008 Sep;134:344-52
49. Ash M. Wheeler's dental anatomy, physiology and occlusion.
W.B.Saunders; 1993.
i h ed. Philadelphia:
50. Andrews LF. The six keys to normal occlusion. Am J Orthod. 1972 Sep;62:296309
51. Lynch CD, McConnell RJ. Prosthodontic management of the curve ofSpee: use
of Broadrick flag. J Prsothet Dent 2002;87:593-7
52. Little RM. The Irregularity Index: A quantitative score of mandibular anterior
alignment. Am J 011hod 1975;68:554-563
24
CHAPTER 3: JOURNAL ARTICLE
Abstract
Introduction: The difference between the mesio-distal width of teeth and the perimeter of
apical base is defined as dental crowding. It is thought that a relationship of teeth to the
apical base is essential for diagnosis and long term stability of orthodontic treatment.
Unfortunately there is no reliable definition of apical base in literature. Researchers, have
defined apical base using various methods, but none of the definitions have taken
development into consideration.
Purpose: This study will investigate if there is a relationship between the apical base
measured at inferior alveolar nerve level, arch perimeter and crowding as measured on
the plaster model. An attempt will also be made to detelmine if there is a relationship
between the curve of Spee and the curve formed by the inferior alveolar nerve when
viewed sagitally.
Method: A sample of 27 randomly selected untreated patients with pre-treatment cone
beam computed tomography (CBCT) scans and available pre-treatment plaster models
were utilized. Patients were selected based on eruption of full permanent dentition in
mandible. Data collected by CBCT included measurements of basal bone perimeter at the
level of inferior alveolar nerve canal, and tracing of the curve of Spee and curve of the
inferior alveolar nerve canal. Model analysis included meaSU1'es of the arch perimeter and
dental crowding.
25
Results: The apical bas perimeter and arch perimeter measured on dental are significantly
different A statistically significant difference was also observed between the two curves
(curve of Spee and curve of the inferior alveolar canal).
Conclusions: No relationship was established between the apical base measured at
inferior alveolar nerve canal, crowding, and the arch perimeter as measured on modeL
Similarly, the curve of Spee was significantly different from the curve formed by the
inferior alveolar canal.
26
Introduction
Cone Beam CT (CBCT) was introduced in USA in 2001. Since that time it has
become clear that this imaging modality allows the clinician to identify anatomical
structures which were not readily visible in conventional 2-dimensional radiographs.
CBCT has application in all fields of dentistry, particularly in oral surgery and
011hodontics. Due to various advantages, CBCT is used for diagnosis and treatment
planning, which is critical for establishing a foundation for successful orthodontic
treatment.
l
The most common cause to seek orthodontic treatment is dental crowding . Van
der Linden and McNamara2 define crowding as the discrepancy between tooth size and
jaw size (apical base) that results in the misalignment of teeth. It is generally believed
that when the tooth mass is too small relative to apical base, interdental spacing or
diastemas will likely occur. Conversely, if the apical base in the body of the mandible is
constricted or too small relative to tooth mass, the teeth will be crowded out of nOlmal
anangement, or if normal arrangement is maintained, they will show a procumbent
relationship to the mandibular plane.
3
4
The term apical base was first introduced by Lundstrom in 1923 and, since then,
several attempts have been made to define the apical base. Techniques for measuring
basal bone have varied as have its definition and location. Some of these methods to
measure apical base are complicated and time consuming and result in variable
estimations.
An the methods reported to measure basal bone are based on anatomic
location or personal perspective of basal bone. 5-1l
27
It's been shown that there is a strong relationship between the inferior alveolar
nerve and development of mandible, 12·15 This relationship has never been studied to
explain the location of apical base. The relationship between crowding and apical base 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.
Now with advancements in dental radiography, CBCT can be used to identify inferior
alveolar canal and the apical base can be measured at this level. 16·20 By utilizing CBCT,
we will explore the relationship between inferior alveolar nerve and different aspects of
dental crowding.
28
Materials & Methods
Randomly selected 30 pre-treatment records of patients were retrieved from
Orthodontic Department of Center for Advanced Dental Education at Saint Louis
University. Records included pre-treatment images by iCAT Cone Beam Computed
Tomography (Imaging Sciences International, Hatfield, P A) and pre-treatment plaster
models. Inclusion criteria were patients of any age or gender with all teeth erupted except
for third molars. Patients with signs of clinical or radiographic pathology that will
interfere with the visualization of inferior alveolar canal were excluded. Any patient with
impacted teeth in the mandibular arch was also excluded. If any image had an artifact that
would interfere with visualization of inferior alveolar canal} it was not utilized in this
study. 27 recol'ds met the inclusion criteria.
Each patient was identified with a number to eliminate the possibility of patient
identification. Image data was retrieved from the server of orthodontic dep8.liment at
Saint Louis University. All the images were analyzed at Saint Louis University Center for
Advanced Dental Education using Dolphin Imaging version 11.0 (Chatswolih, CA). For
comparison of the curve ofSpee and curve formed by the inferior alveolar nerve canal
Corel DESIGNER X4 version 14.1 (Corel Inc. Mountain view, CA) was employed.
Measuring Basal Bone from Cone Beam CT at the Inferior Alveolar Nerve:
Cone Beam CT images were assessed using Dolphin Imaging version 11.0. All
the images were formatted using the "nerve canal" too]. With this tool the focal trough is
29
constructed by visualizing the inferior alveolar nerve canal on a sequence of the axial
views. The focal trough was traced from the mandibular foramen in the ramus of
mandible of one side to the mandibular foramen on the contralateral side by principal
investigator (who is also a certified oral and maxillofacial radiologist). These tracings
result in the production of a panoramic radiograph clearly depicting the inferior alveolar
nerve canal (Figure 3.1). Using this panoramic radiograph the inferior alveolar canal was
traced. Because the inferior alveolar canal stops at mental foramen, the nerve anterior to
mental foramen was traced by joining the mental foramen of one side to the mental
foramen of the contralateral side following the curvature of the anterior part of the
mandible. This information can be transfen-ed to the multiplanar images including the 3dimensional volumetric image. As the nerve is not a straight linear stlucture, it is
measured in very small segments (less than 5 mm) to compensate for curvatures in the
nerve. These measurements were made placing points using "Landmark" tool in the
Dolphin Imaging software. Landmarks were placed from the apex of distal root of second
permanent molar of one side to the apex of distal root of second pennanent molar of the
contra-lateral side. The landmark tool calculates the orientation of each point in x, y and z
coordinates and produces accurate measurements between two landmarks (Figure 3.2).
These distances were then added to produce the perimeter of nerve from distal root of one
second molar to the distal root of contralateral second molar. This measurement was
considered the perimeter of the apical base.
30
A) Refonnatted panoramic radiograph clearly depicting inferior alveolar canal.
B) Inferior alveolar canal traced
Figure 3.1: Panoramic radiographs reformatted from CBCT.
31
Figure 3.2: 3-Dimensional volumetric image: axial view showing measurement of
inferior alveolar nerve made at very short intervals.
32
Model Analysis
Conventional plaster models were utilized to perfolID two well established
method of estimating crowding. The first method is recommended by Proffit and Fields; 1
it utilizes a direct approach on the dental casts. To measure the arch perimeter (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 the left second molar to
distal of left canine, distal of left canine to the mesial of left central incisor, mesial of
right centl'al incisor to the distal of l'ight canine and distal of right canine to the distal of
right second molar (Figure 3.3). Each quadrant was measured to the nearest hundredth of
a millimeter. Space required was measured as the sum of the individual tooth widths from
the distal of the mandibular left second molar to the distal of the right second molar.
Figure 3.3: Quadrant diagram for straight line approximations of mandibular arch
perimeter (modified from Bell's thesis).
33
In addition, Little's irregularity index was measured on each mandibular arch. The
scoring method involved measuring the linear displacement of the anatomic contact point
of the anterior teeth (canine to canine). The sum of five displacement values represents
the relative degree of incisor irregularity.
Tracing Curve of Spee
3-dimensional volumetric data was refolmatied to generate lateral cephalometric
view of the hemi-mandible. All the mandibles in the study were divided into left and right
and a total of 54 hemi-mandibles were used to trace the curve of Spee. Lateral
cephalometric images of the hemi-mandible \vere generated in a way that all the
incisaVocclusal edges of mandibular teeth from lower central incisors to the second molar
are clearly visualized (Figure 3.4). After lateral cephalometric of the hemi-mandible was
generated, the images were saved and transfen'ed to Corel DESIGNER X4 for tracing the
curve of Spee. Using the 3 point curve tool in Coral DESIGNER X4 a curve was
consttucted to the best fit of cusp tips of all the mandibular teeth.
34
A) Reformatted lateral cephalogram
B) Curve of Spee traced
Figure 3.4: Lateral cephalogram refolmatted from CBCT:
35
Tracing Curve of the Inferior Alveolar Nerve
Using the "Nerve Canal" tool in Dolphin Imaging software the panoramic image
depicting the inferior alveolar canal was generated as described above. This time the
nerve was traced from the mandibular foramen to the mental foramen on both sides. This
nerve tracing was than transferred to
3~dimensional
volumetric image. On 3-dimensional
volumetric image a point \vas marked on the nerve cOll'esponding to the distal root apex
of the second molar and another point was marked at the apex of the lower central incisor
of the same side. These images were then saved and transferred to Corel DESIGNER X4.
Using the same 3 point curve tool in this software a curve was constructed using points
marked on the image and simultaneously fitting the curve to the curvature of the nerve
(Figure 3.5).
Intra-rater Reliability
A reliability test was perfolmed to evaluate the measurement error. Four of the 27
cases were randomly selected and measurements of the nerve perimeter and comparison
of the curve ofSpee and curve of the inferior alveolar nerve 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. SPSS version 18 (SPSS Incorporated} Chicago, IL) was used to calculate
intraclass correlation coefficient.
36
Figure 3.5: Curve of the inferior alveolar nerve traced on sagittal view of3-dimensional
volumetric image
37
Comparison of Curves:
The traced curve of Spee and the curve formed by the inferior alveolar nerve were
isolated from the images using Corel DESIGNER X4. In order to quantitatively compare
the two curves a plane was constlucted between the two ends of each curve. That plane
was then divided into 6 equal segments21 from which perpendiculars were extended to the
base of the curve at each segment (Figure 3.6). The two curves were then compared
mathematically by similar ratios at each segment. Mathematically this comparison can be
explained as:
38
A) Curve of Spee
'"
.1'/
.......................
_-----------.
........
--
-------
--
.------_¥
//
".,.,.,/
B) Curve formed by Inferior Alveolar Nerve
Figure 3.6: Comparison of curves by dividing each curve into 6 equal segments
a) Curve of Spee
b) Curve formed by Inferior Alveolar Nerve
39
Statistical Analysis
It is hypothesized that when comparing apical base at the level of inferior alveolar
nerve and the perimeter of basal bone on plaster model a relationship will be observed.
Also there is a correlation between the nerve perimeter and the crowding estimated by
two established methods. The curve of Spee and curve formed by the inferior alveolar
nerve are similar.
In ordel' to test these hypotheses, descriptive statistics were computed for all the
variables. Paired sample t-test was computed for apical base and perimeter of basal bone
on plaster model comparison. Pearson's correlation was used to analyze whether
relationship existed between variables. SPSS version 18 (SPSS Incorporated, Chicago,
IL) was used to calculate all the statistics.
40
RESULTS
Inferior Alveolar Nerve Perimeter:
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) by Proffit's method over the sample was 104.4 mm, while the average space
available by measuring the inferior alveolar nerve perimeter was 113.5 mm. The average
discrepancy was -1.7 mm by Pfoffi t' s method of cast analysis, while average value for
Little's irregularity index was 4.4 mm.
Intrac1ass Correlation Coefficient (ICC) was calculated from error measurements
on four patients (Table 3.2). It was found that the measurements are highly repeatable.
Table 3.1: Descriptive Statistics for 27 patients~ model analysis. Values repolied in
millimeter
Mesurement
N
Maximum
27
27
27
-8.2
118.9
119.2
9.2
104.4
106.1
-1.7
5.3
6.3
4.1
27
27
0.1
101.1
14.2
128.3
4.4
113.5
3.1
7.1
S.D.
Proffit Cro\vdin
Basal Sum
Tooth size sum
Discrepanc
Little Crowdin
Irregularit Index
Nerve Perimeter
41
Table 3.2: Cronbach's Alpha for Intra-rater reliability
Measurement
Nerve Perimeter
Curves
Section 1
Section 2
Section 3
Section 4
Section 5
Cronbach's Alpha
.96
Spee
Nerve
.90
.97
.91
.98
.97
.89
.94
.99
.98
.95
Pearson's correlation was used to analyze whether relationships existed between
the nerve perimeter and Proffit's method of crowding and nerve perimeter and Little's
irregularity index. It was also assessed if there is any relationship between nerve
perimeter and tooth size sum (Table 3.3). Low values ofR indicate no correlation exists
between the groups.
Table 3.3: Pearson's correlation for the nerve perimeter and methods of crowding.
Measurement
Nerve Perimeter-Proffit Crowding
Nerve Perimeter-Little's Crowding
Nerve Perimeter-Sum of Teeth
R
0.55
0.38
0.53
A paired sample t-test was done to compare the nerve perimeter to the apical base
measured by Proffit's method. Table 3.4 show these two measurements are significantly
different (Sig. (2-tailed) = .000) from each other.
Table 3.4: Comparison of inferior alveolar nerve perimeter and arch perimeter by
P1'0ffit'
I d b>y patre
. d sampe
Itt
; analyze
- est .
1 S me th 0 d
S.D.
Sig. (2-tailed)
Mean
Group
N
27
113.5
7.18
.000
Nerve Length
Arch Perimeter
27
104.4
.000
5.37
42
Comparison of Curves:
Table 3.5 and 3.6 shows the descriptive statistics for each curve. Each curve was
sectioned into five equal segments and these segments were than compared. Means and
standard deviations were calculated for each segment of both the curves.
Table 3.5: Descriptive Statistics; Measurement of sections in the Curve of Spee
Sections
1
2
3
4
5
N
54
54
54
54
54
Mean(mm)
1.18
2.16
2.92
3.27
2.98
S.D. (rom)
.52
.94
1.25
1.40
1.28
Table 3.6: Descriptive Statistics; Measurements of section of the curve of the Inferior
Alveolar Nerve
Sections
1
2
3
4
5
Mean(mm)
3.55
5.75
6.64
6.18
4.10
N
54
54
54
54
54
S.D. (mm)
0.67
1.08
1.34
1.46
1.23
Paired sample t-test was computed to compare the curves of the right side to the curves of
the left side. Table 3.7 shows that the curves on two sides are similar at each section.
43
Table 3.7: Comparison of Left and Right side curves by paired sample t~test.
Section
l~L*
2-L
3~L
4~L
5~L
I~R**
2-R
3~R
4-R
5-R
N
54
54
54
54
54
54
54
54
54
54
Mean (mm)
2.41
4.00
4.81
4.73
3.54
2.33
3.91
4.75
4.72
3.53
S.D. (mm)
1.38
2.11
2.27
2.03
1.35
1.29
2.03
2.29
2.07
1.40
Sig (2~tai1ed)
.74
.81
.90
.99
.97
.74
.81
.90
.99
.97
L*~Left
R**- Right
Independent sample t~test was computed to compare the curve of Spee and the curve of
the inferior alveolar nerve. Data show that the two curves are significantly different and
are not dependent on each other.
Table 3.8: Comparison of the curve of Spee and the inferior alveolar nerve at each section
b
)y '1n
dependent samp.1e tt
- es t .
Mean(mm)
S.D. (mm)
Sig (2-tailed)
Section
N
1.18
I-N*
0.00***
.52
54
2~N
54
2.16
.94
0.00
54
3-N
2.92
1.25
0.00
4-N
3.27
1.40
54
0.00
1.28
5-N
54
2.98
0.00
54
I-S**
3.55
.67
0.00
2-S
54
5.75
1.08
0.00
54
6.64
1.34
0.00
3-S
4-S
54
6.18
1.46
0.00
5-S
1.23
54
0.00
4.10
N*-Nerve
S**~Curve of Spee
*** no correlation
44
Discussion
The purpose of this study was to attempt a new definition of basal bone based on
the embryologic development of mandible. The study was designed to assess if there is a
relationship between apical base measured at inferior alveolar nerve (IAN) and apical
base measured on a plaster model. It was hypothesized that arch perimeter as measured
by He~2 and recommended by Proffit and Fields l in their text book are dependent on the
arch perimeter measured at the IAN (Le., a large basal hone at IAN) will result in a large
perimeter in the cast; the results showed that there is no correlation between these two
measurements.
Inferior Alveolar Nerve as Apical Base
In human craniofacial skeleton the mandible is seen by the
ih_sth week of fetal
life. The ossification of human mandible starts at the point of future mental foramen. The
literature has shown that a single ossification center for each half of the mandible fOlms
lateral to Meckel's cartilage at the bifurcation of the inferior alveolar nerve. 13,14 From this
center, ossification proceeds ventrally to the body and dorsally to contribute to the
mandibular ramus. Bone deposition begins to proceed superiorly around the
neurovascular bundles to provide a bony framework for developing teeth. I5 It is obvious
from the literature that there is a strong association between nerve tissue and osseous
development. Kjaer23 used the term Neuro-Osteology which emphasizes the biologic
connection during development between nerve and hard tissues.
In the orthodontic literature the significance of having teeth upright over the basal
bone has been discussed numerous times. It is a strong belief in orthodontic community
that the stability of the result depends on the relationship of the teeth to the basal bone. 3
45
To date there is no specific definition of apical base/basal bone. This issue was addressed
by Brodie in
1950~
when talking about basal bone he said "upon critical questioning,
however, the definition (of the apical base) become vague." Several attempts have been
made to define the apical base, but none of the methods to define basal bone have
satisfactorily addressed the issue. Previously, several attempts were made to identify the
apical base, using traditional orthodontic records, including plaster models and
cephalogram, surveyors and recently CBCT. s.11
The literature showed a strong association between nerve tissue and osseous and
dental development. 12-15 We attempted to define apical base as the bone which is
surrounding the inferior alveolar canal as this is the first osseous structure to be formed in
mandible. Other than the concept ofNeuro-osteology another factor that leads us to this
belief is that, when observed in an edentulous patient the resorption of residual ridge
continues until it reaches the inferior alveolar canal, at this point the residual ridge
usually stops resorbing. 26
Cone Beam CT is increasing in popularity and literature has shown that
anatomical structures that were not easily identified on 2-dimensional radiographs can be
easily identified by utilizing cone beam CT. 16 Utilizing CBCT, a new assessment of basal
bone parameter was performed in 27 orthodontic patients. We attempted to assess
whether the apical base defined at IAN level is related to arch perimeter measured on
plaster modeL Our results indicated that there was no relationship observed and the null
hypothesis was rejected. This could be due to the difference in the way the measurements
were made. For the measurement of nerve perimeter, curvatures of nerve canal within the
mandible were measured; however, for the perimeter of apical base according to Proffit's
46
method, lineal' measurements were made and curvatures of alveolar crest (apical base)
were not taken into consideration. We chose to measure the perimeter on plaster model
according Proffit's method, as this is the most common way of estimating apical base.
Using CBCT, we can measure the perimeter at the level of cervical margins of teeth; this
will allow us to accommodate curvatures of the alveolar crest. This may produce different
results. A challenge in this method would be find patients with fully developed occlusion
and healthy periodontium.
We measured the inferior alveolar nerve at very small intervals; this was done to
compensate for curved path of the inferior alveolar canal. We used Dolphin Imaging
version 11 for making measurements and this software allowed us to mark points on the
inferior alveolar canal at regular intervals. Orientation of each point was than calculated
in x, y and z coordinates by the software and the exact distance between two points was
calculated, this helped us in eliminating possible human errors.
We used apex of distal root of second permanent molar in our study as the
terminal point for measurement of the inferior alveolar canal, this was done because
Bell il suggested that value of perimeter back to the mandibular foramen were found to be
inconsistent, he suggested that this was the result of the inclination of mandibular ramus.
Curve of Spee and Inferior Alveolar Nerve:
The relationship between the inferior alveolar nerve and development of the teeth
has been discussed in literature. This was the first study that evaluated the relationship of
the curve of Spee to the inferior alveolar nerve. Our results indicate that inferior alveolar
nerve is not related to the development of the curve of Spee. Since, no study has
evaluated the curve ofSpee from developmental aspect; a number of factors may playa
47
role in development of the curve of Spee. We traced the curve of Spee from distal cusp of
second molar to the incisal edge of the central incisor, but had we chosen the central
groove of the second molar instead of the distal cusp, we may have seen different results.
Another factor that may contribute to the development of the curve of Spee is the
path of eruption of teeth. Studies have shown that a close relationship exist not only
between tooth development and nerve development, but also between tooth development
and development of surrounding bone tissue. 12 As bone forms around the teeth in its path
of eruption, studies evaluating factors that determine the path of eruption of teeth may be
helpful in understanding the curve of Spee from a developmental aspect.
We compared the t\vo curves by using a mathematical formula to compare the
curve of Spee. We chose this method because this method would allow us to compare the
two curves in small segments. Both curves were divided into 6 equal segments and than
each segment were compared to conesponding segment on the other curve. A similar
method of comparing curves has been used previously.21 Another method of comparing
curves would be to measure the radius of the arc formed by two curves. This would give
one reading for each curve and it will not compare the curves in small segments. It is
possible that if other methods of comparing two curves are applied, this may produce a
different result.
48
Conclusions
1. A con-elation among the inferior alveolar nerve perimeter and the arch perimeter
measured on plaster model was not observed. This suggests that there is no
relationship between inferior alveolar nerve and dental arch perimeter.
2. A cOll'elation between the nerve perimeter and the Proffit's method of measuring
crowding was slightly higher than the cOll'elation between the nerve perimeter and
Little's in-egularity index. The con-elation for both these values was low. Such
low correlations have almost no value in prediction.
3. Based on the results of this study, development of the curve ofSpee may not be
associated with curve formed by the inferior alveolar nerve when viewed
sagitally.
49
Literature Cited:
1. Proffit WR. Malocclusion and dentofacial deformity in Contemporary Society. In:
Proffit, Fields, Editors. Contemporary 011hodontics. Saint Louis: Mosby 1986
2. Van der Linden EM, McNamara JA. Glossary of Orthodontic Terms. In: Jutte,
Daskalogiannkis J, Editors. Leipzig, Germany: Quintessence; 2000
3. Tweed CH. Indications for the extraction of teeth in orthodontic procedure. Aln J Orthod
Oral Surg. 1944-45;42:22-45
4. Lundstrom A. Malocclusion of the teeth regarded as a problem in correction with the
apical base. Int J Orthod Oral Surg RadiogI' 1923;11:591-602
5. Salzmann JA. Orthodontic therapy as limited by ontogenetic growth and the basal arches.
Am J Orthod 1948 Apl';34:297-319
6. Downs WB. Variations in facial relationships: Their significance in treatment and
prognosis. Am J Orthod 1948;34:812-840
7. Reidel RA. The relationof maxillary structure to the cranium in malocclusion and in
normal occlusion. Angle 011hod 1952;22:140-145
8. Howes AE. Case analysis and treatment planning based upon the relationship of the tooth
material to its supporting bone. Am J Olthod and Oral Surg 1947;33:499-533
9. SergI RG, Ken' WJ, McColl rn. A method of measuring apical base. Eur J Orthod 1996;
18:479-483
10. Kanaan W. The correlation between tooth size, basal bone size discrepancy and long tenn
stability of the lower arch in Class II Division 1 patients. Masters Thesis. Orthodontics.
Saint Louis: Saint Louis University; 2006.
11. Bell DG. Three-dimensional cone beam computed tomography assessment of basal bone
parameters and crowding. Masters Thesis. Ot1hdontics. Sain Louis: Saint Louis
University; 2008.
12. Kjaer I. Histochemical investigations on the symphysis menti in the human fetus related
to the fetal skeletal maturation in the hand and foot. Acta Anat 1975; 93:607-633.
13. Bollobas E. Embryonic development of the mandibular canal. Acta Morphol Acad Sci
Hung 1982; 30(3~4): 233-9.
14. Radlanski RJ, Renz H, Reulen A. Prenatal development of the human mandible 3D
reconstructions, morphometry and bone remodeling pattern, sizes 12-117 mm CRL. Anat
Embyol (Berl.) 2003 Oct; 207(3):221-32.
15. Smartt JM J1', Low DW} Bartlett SP. The pediatric mandible: I. A primer on growth and
development. Plast Reconstr Surg. 2005 Jui; 16(4):563-71
50
16. Angelopoulos C, Thomas SL, Hechler S, Parissis N, H1avacek M. Comparison between
digital panoramic radiography and cone-beam computed tomography for the
identification of the mandibular canal as part of presurgical dental implant assessment. J
Oral Maxil10fac Surg. 2008 Oct~66(10):2130-5.
17. Tantanapornkul W, Okouchi K, Fujiwara Y, Yamashiro M, Maruola Y~ Ohbayashi N,
Kurabayashi T. A comparative study of cone-beam computed tomography and
conventional panoramic radiography in assessing the topographic relationship between
the mandibular canal and impacted third molars. Oral Sur Oral Med Oral Pathol Oral
Radiol Endod. 2007 Feb; 103 :253-9
18. Friedland B, DonoffB, Dodson TB. The use of3-Dimensional reconstructions to
evaluate the anatomic relationship of the mandibular canal and impacted third molars. J
Oral Maxillofac Surg. 2008 Aug;66: 1678-85
19. Lofthag-Hansen S, Grondahl K, Ekestubbe A. Cone-beam CT for preoperative implant
planning in the posterior mandible: visibility of anatomic landmarks. Clin Implant Dent
Relat Res. 2009 Sep; 11 :246-55
20. Naitoh M, Nakahara K, Suenaga Y, Gotoh K, Kondo S, Ariji E. Comparison between
cone-beam and multislice computed tomography depicting mandibular neurovascular
canal structures. Oral Surg Oral med Oral Pathol Oral Radiol Endod. 2010 jan; 109:e2531
21. Behrents RG. The continuity of mandibular form in mandibulofacial dysostosis. J Dent
Res. 1982 Nov;61:1240-2
22. Hew SKM. Basal bone contour as related to dental arch fonn (Thesis), Saint Louis: Saint
Louis Dniversity; 1966
23. Kjaer L Neuro-osteolgy. Crit Rev Oral BioI Med. 1998;9:224-44
24. Brodie AG. Appraisal of present concepts in Orthodontia. Angle Orthod 1950;20:24-38.
25. Sukovic P. Cone beam computed tomography in craniofacial imaging. Orthod Cl'aniofac
Res. 2003;6 Suppl 1:31-6
26. DIm CW, Solar P, Blahout R, Matejka M, Waztek G, Gruber H. Location of the
mandibular canal within the atrophic mandible. Br J Oral Maxillofac Surg. 1993
Dec;31 :370-5
51
VITA AUCTORIS
Anas Athar was bOITI on 15th of October 1979 in Saudi Arabia. Dr. Athar is the
youngest of four children. At the age of four years he moved to Karachi, Pakistan in
1983.
In 1995 he graduated from B.V.S. Parsi High School, he then continued his
education at D.J.Sind Government Science College for his pre-dental education. After
graduating from college, Dr. Athar started his dental education from Baqai Medical
University in 1998. He graduated from dental school and received his Bachelor of Dental
Surgery degree in 2002. Dr. Athar then moved to U.S.A in 2003 and started his postgraduate training in Oral and Maxillofacial Radiology (OMFR) from UMKC School of
Dentistry in Kansas City, MO. He completed his OMFR training in 2005 and joined
UMKC School of Dentistry as an Assistant Professor. In 2006, he received his Master of
Science in Oral Biology from UMKC School of Dentistry. During his time as faculty at
UMKC School of Dentistry, he lectured on various topics in Oral and Maxillofacial
Radiology, nationally and internationally. In 2008, Dr. Athar was accepted into the
011hodontics residency program at Saint Louis University. He has two publications and
has presented research papers at various conferences.
He ma11'ied his wife,
Samia~
in December, 2006. They have two children, a two
years old daughter, Amna and a five month old son, Mustafa, bOlTI during his residency in
August, 2010.
Dr. Athar and his family are planning to move to San Antonio, Texas after
completing his Orthodontic residency.
52