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A comparative study of caucasian and African American mandibular clinical arch forms

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A comparative study of caucasian and African American mandibular clinical arch forms

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Content A COMPARATIVE STUDY OF CAUCASIAN AND
AFRICAN AMERICAN MANDIBULAR CLINICAL ARCH FORMS

by

John Robert Jerome

A Thesis Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
MASTER OF SCIENCE
(CRANIO-FACIAL BIOLOGY)

May 2012

Copyright 2012 John Robert Jerome

ii
DEDICATION

To my Wife and Son

Sarah Jerome & JJ

iii
ACKNOWLEDGEMENTS

A special thank you to:

Dr Sameshima

Dr McLaughlin

iv
TABLE OF CONTENTS

Dedication ii

Acknowledgements iii

List of Tables v

List of Figures vi

Abstract vii

Introduction 1

Review of Literature 3

Hypothesis 16

Materials and Methods 17

Results 22

Discussion 35

Assumptions 39

Limitations 40

Summary 41

Conclusions 42

Bibliography 43

v
LIST OF TABLES

Table 1: Sample Characteristics 22

Table 2: Comparison of Variables between Caucasian and African 24
American Class I, II, and III Samples

Table 3: Comparison of Frequency Distribution of 27
Square, Ovoid, Tapered Arch Forms between
Caucasian and African Americans

Table 4: Comparison of Variables between Caucasians and 33
African Americans for Square, Ovoid, and
Tapered Arch Form Groups

vi
LIST OF FIGURES

Figure 1: Catenary Curve Arch Form 11
Figure 2: Bonwill-Hawley Arch Form 11
Figure 3: A new concept of mandibular dental arch forms 15
Figure 4: Points digitized on the occlusal photocopy 18

Figure 5: Twelve clinical bracket points, 4 linear, and 19
2 proportional measurements of arch dimension

Figure 6: Shape differences between the three arch forms 20

Figure 7: Class I Caucasian Arch Form Frequency 28

Figure 8: Class I African American Arch Form Frequency 28

Figure 9: Class II Caucasian Arch Form Frequency 29

Figure 10: Class II African American Arch Form Frequency 29

Figure 11: Class III Caucasian Arch Form Frequency 30

Figure 12: Class III African American Arch Form Frequency 30

Figure 13: Caucasian Arch Form Frequency 31

Figure 14: African American Arch Form Frequency 31

vii
ABSTRACT

Introduction: The purpose of this study was to clarify morphologic differences
between Caucasian and African American mandibular clinical arch forms in Class I, II,
and III malocclusions. Methods: The study included 60 Class I, 50 Class II, and 50 Class
III patients from the Caucasian group and 57 Class I, 26 Class II, and 17 Class III patients
from the African American group. Orthodontic study models were photocopied, scanned,
digitized, and measured (4 linear and 2 proportional). The dental arches were classified
into square, ovoid, and tapered forms to compare the frequency distributions between the
2 ethnic groups. Results: The Caucasians had a significantly smaller arch dimensions
than the African American, except for canine depth. African Americans had a higher
frequency of tapered arch forms. Conclusion: There is a significant difference between
frequency of arch forms and arch dimensions of African American and Caucasian
patients. Specifically, there is no arch form unique to any of Angle classification or ethnic
group. The most frequent arch form seen in Angle malocclusion groups was the tapered
one, followed by the less frequent ovoid and square ones.

1
INTRODUCTION

In the late 1920’s there was much consideration of the relationship between the
dental arch form of normal occlusion as a goal of orthodontic treatment on the one hand
and the archwire form of orthodontic appliances on the other (Angle, 1907).
Fifty percent of Orthodontic treatment begins in the mandibular arch. Some would
argue that treating the mandibular arch dictates the position of the maxillary dentition and
that retention along with long-term stability are of the utmost importance in the field. .
Little believed that treatment arch forms should be based on the pre-treatment shape of
the mandibular arch and the maxillary arch should be coordinated to this in order to
increase the chance of a stable result (Little, 1990). Fleming stated that there is a “trend
towards greater acceptance of arch development and expansion has followed advances in
orthodontic appliances and arch wires (Fleming, 2008).
Due to the importance for maintaining dental arch dimensions during orthodontic
therapy, all possible dental arch forms must be evaluated (Trivino, 2008). Ronay et al in
2008 investigated mandibular arch forms and the relationship between dental and basal
Anatomy.
Occording to Oda et al., in 2010, they studied whether or not the various
commercially available orthodontics archwire forms are comparable with the diversity of
natural normal dental arch forms in the Japanese population. In the same population,
Nojima determined that it was the frequency of a particular arch form that varied among
Angle classifications (Nojima, 2001). It is more reasonable to have several preformed

2
arch wires in which to choose from that best fits the patient’s pre-treatment arch form and
taking into consideration both the patient’s ethnicity and malocclusion (Nojima, 2001).
There have been five studies that have addressed ethnicity and the frequency of
the common arch forms in different ethnic populations (Nojima, 2001, Kook, 2004,
Olmez, 2011, Bayome, 2011, Gafni 2011). There were significant differences in the
frequency of arch forms between different ethnic populations and Caucasian patients as
well as differences in arch form between malocclusion types, yet still it is rare for
orthodontists to consider ethnicity when choosing a treatment arch form.
The African American population in the US has been seeking orthodontic
treatment in greater numbers while little is known about their arch forms. The objective
of this study was to determine the characteristics of clinical mandibular arch shapes in
African American and Caucasian patients with Class I, Class II and Class III
malocclusions, testing the hypothesis that there is a difference in arch form and
dimension between the two ethnicities.

1. Determine if there is a difference in the arch form between Caucasian and African
American.
2. Determine if there is a difference in the arch dimensions between Caucasian and
African American.
3. Determine if there is a difference in the arch form between malocclusion types:
Class I, Class II and Class III.
4. Determine if there is a difference in the arch dimensions between malocclusion
types: Class I, Class II and Class III.

3
REVIEW OF THE LITERATURE
NORMAL DENTAL ARCH DEVELOPMENT
On day 17 of fetal human development, the maxillary and mandibular arches
begin to develop with a down-growth of neural crest cells into the surface ectoderm.
During the 5-7
th
week, four primordial processes that surround a central depression called
the oral pit come together and fuse to form the face. These processes are known as the
frontonasal process, two maxillary processes and the mandibular process. The frontonasal
process is a single process located above the oral pit, while the two maxillary processes
are located lateral to the oral pit, and the mandibular process is found below the oral pit.
The maxilla and mandible develop through intramembranous ossification and continue to
grow beyond fetal development to adulthood through primary and secondary
displacement (Proffit, 2007).
While the face is developing, the teeth begin to develop as well, beginning
between the 27
th
and 37
th
day of fetal development. Odontogenesis (tooth development)
is initiated by the inductive influence of neural crest mesenchyme on the overlying
ectoderm. The first indication of tooth development occurs as a thickening of the oral
epithelium, a derivative of surface ectoderm. These U shaped bands or dental laminae
follow the curve of the primitive jaws. The dental laminae is the origin of both the
deciduous and permanent dentition. Tooth development is a continuous process, however
it is usually divided into stages for descriptive purposes on the basis of the appearance of
the developing tooth. These stages are known as the Bud, Cap and Bell stage. There are
ten centers of proliferation from which swellings (tooth buds) grow into underlying

4
mesenchyme. These ten centers represent the ten deciduous teeth that eventually form on
each arch. The permanent teeth with deciduous predecessors begin to appear at about 10
weeks of development, from deep continuations of the dental lamina. The molars without
predecessors develop as buds from posterior extensions of the dental laminae (Moore and
Persaud, 1998).
As the teeth grow and develop the adjacent tissues also are developing from the
dental follicle. The alveolar bone develops intramembranously and during development
attaches to the developing maxilla and mandible. It is the support structure for the
dentition and is defined only after the tooth erupts, and disappears when the tooth is lost
(Bernard, 1997).
Arch dimensions change as the arches grow and teeth erupt. In 1969, Moorrees
stated that there is a large amount of variation between individuals, regarding arch form,
but there is a central tendency for an increase in intermolar width in the transition from
primary to permanent dentition and even increasing up to 18 years old, particularly in
males. Intercanine width increases from primary to permanent dentition, but after
eruption of the permanent canines the width no longer increases. As adults enter their
30s and 40s, their arch depth tends to decrease (DeKoch, 1972). After the age of 12,
there is little to no increase in arch length or arch perimeter (Sinclair, 1983). Stanton in
1922 studied the natural variability in the population and found that most humans with a
normal occlusion vary 5mm in width, from one side to the midpalatal suture, and 13mm
in length, from buccal groove to upper incisal edge, (Stanton, 1922). During the

5
transition from primary to permanent dentition, arch length tends to decrease, and
continues to decrease with age (Shapiro, 1974).
Hellman studied the role of tooth size and its relationship to arch form in humans
and in apes, and through his research, he concluded that there was no relationship
between the size of teeth and the arch form (Hellman, 1919).
While the literature has also touched on the impact of soft tissue on the
development of arch form, the role of soft tissue on arch form development has been a
controversial subject. Scott stated that a case can be made for the importance of the
pressures exerted by the adjacent muscular tissues of the tongue, lips and cheeks in
determining arch form, but the fact that arch form is determined before tooth eruption and
that it depends for its final development on the direction and extent that of alveolar
process growth, would indicate that under normal conditions the soft tissue plays a minor
role in its determination” (Scott, 1957). Alternatively, Brader in 1972 stated “the primary
determinants of arch form morphology are the (muscle) tissue forces of the resting state
in contradistinction to the intermittent forces of muscles in functioning states” (Brader,
1972). Currier postulated that due to the shape of the arches the buccinator had a greater
effect on the maxillary dentition in the second and third molar region creating a more
elliptical shape to the arch. Mandibular arch shape was more dictated by occlusion rather
than the effect of the tongue or other circumoral musculature (Currier, 1969).
McLaughlin stated that, “it is generally accepted that the dental arch form is initially
shaped by the form of underlying bone, and then after eruption of the teeth, the shape
becomes influenced by the oral musculature” (McLaughlin, 2001).

6
With regards to symmetry, the literature supports that symmetry between
contralateral sides of the arch is generally not found. White found that only 6.25% of
natural arch forms could be defined as symmetric (White, 1978). When comparing the
size of the individual arches the maxillary tends to be wider than the mandibular arch in
normal occlusions allowing for proper overbite, overjet and ideal intercuspation of teeth.
Fujita found in 2002 that “the association between the upper and lower dental arches did
not vary by more than 0.3mm, but showed consistent lateral gaps of about 4.3mm for the
opposing canines and 2.8mm for the molars” (Fujita, 2002).
Understanding the process of growth and development, combined with a greater
understanding of tooth size, soft tissue, and symmetry between contralateral arch sides,
builds a foundation for our understanding of dental arch development.

ANGLE CLASSIFICATION DIFFERENCES
Wider mandibular arches and narrower maxillary arches were found in Class III
subjects compared with Class I subjects in studies from Uysal et al, 2005. Nasal
obstruction, low tongue position, and thumb sucking habits are speculations from
clinicians (Uysal, 2005).
Braun et al. in 1998 found that the upper dental arches in Class III groups are 5.1
mm wider than those in Class I groups. Other authors described this finding as surprising.
In a 2010 study, Slaj et al, found that both male and female mandibular dental arches are
wider in the Class III group than in Class II and Class I groups. A shorter and larger
mandibular arch in subjects with Class III could be a consequence of dental

7
compensation in that patients with that malocclusion tend to have the mandibular incisors
inclined to the lingual, and the lateral teeth inclined to the buccal. This has been
attributed to restriction of maxillary growth and development (Uysal, 2005).
The mesiodistal dimensions of mandibular teeth may provide an explanation for
wider arches. Merz et al., in 1999, concluded that the mean mesiodistal diameter of
African American sample’s lower canines, first and second premolars, and first molars
were significantly larger than the mean corresponding teeth in the Caucasian sample.
According to Nojima et al. in 2001, dental arch dimensions could be ethnically
related, but the archforms are not related to a specific ethnic group or to Angle’s dental
Class. This finding concerning Angle’s Classes is contrary to results seen in data from
Slaj et al.

DIFFERENCES IN GENDER
In a study comparing arch forms and dimensions in the Turkish population gender
differences were found to influence morphological structure (Olmez, 2011) . Arch width
and depth were found to be more in boys when compared with girls. Slaj et al. in 2010
found statistically significant differences in the upper dental arch in the incisor region and
intercanine and intermolar widths in the lower dental arch. They also concluded that all
dimensions are more pronounced in males than in females.
Growth of the mandible and maxilla is known to be different in males and
females. 3mm more width due to growth is observed in the maxilla and 2 mm in the
mandible from ages 7-12. Only males tend to grow after the age of 12. Male jaws tend to

8
be wider than female jaws (Lee RT, 1999). Ferrario in 1994 studied the gender
differences in the shape of the dental arches and found that males had similar shaped
maxillary and mandibular arches and are superimposable. The maxillary arch shows a
translation anteriorly to allow for proper overjet. The female dental shape showed a
tendency towards posterior crossbite. The female arches were significantly smaller
primarily in the maxillary arch, while the mandibular arches were more similar in size
(Ferrario, 1994).

DIFFERENCES IN ETHNICITY
There have been many investigators to show differences in mandibular archforms
and dimensions in a number of diverse ethnicities. In 2001, Nojima et al. found that
Caucasians primarily had tapered and ovoid arch forms, with a significantly reduced arch
width and increased arch depth. Japanese had significantly greater number of ovoid and
square arch forms.
Taner in a study of Turkish patients found that pre-treatment maxillary arch forms
were mostly tapered and mandibular arch forms were tapered and narrow (Taner, 2004).
Kook in 2004, studied the difference between Korean and North American white
populations and found that in Caucasian populations the tapered arch form predominated
and the square arch form predominated in Korean populations. Korean arches tended to
be larger and deeper than Caucasian arches (Kook, 2004).
When comparing Indian populations with the Chinese; Irey found that the Indian
population had significantly narrower arechase than did the Chinese population. (Irey,

9
1998). Fijians upper arch was more V-shaped that was wider and longer than aboriginal
populations, which had more of a U-shaped arch (Kasai, 1997).
In 2011, Bayome compared of arch forms between Egyptian and North American
white populations and found that Egyptians arch forms are narrower. The distribution of
the arch form types in Egyptians showed similar frequency, but the square arch form was
less frequent in Caucasians (Bayome, 2011).
Gafni,

in 2011, studied the difference between the Israeli population and the North
American Caucasian group. The most frequent mandibular arch form of the Israeli group
was found to be ovoid as opposed to tapered in the North American white group. The
Caucasian population had statistically significant decreased arch widths and increased
arch depths compared with the Israeli population. The analysis of the Israeli sample
indicated that, as the malocclusion shifts from Class III through Class I to Class II, the
weight of the arch form tends to shift from square and ovoid to ovoid and tapered (Gafni,
2011).

THE NORMAL HUMAN DENTAL ARCH
Orthodontists have sought one ideal arch form since the time of Edward Angle to
be universally applied to all patients, but there has been much controversy and
disagreement among the community. Many authors claimed that there might be a
standard form of dental arch and some geometric or mathematical curve; eg semicircle;
ellipse; parabola; hyperbola; catenary curve; cubic spline function; conic sections;

10
polynomial functions including second-order, fourth-order, and sixth-order polynomials;
Euclidian distance matrices; Fourier series; beta function; and Bezier cubic equation.
Recent studies nullify the existence of a single arch-form template, indicating that
dental arch forms are highly individual, and defining a single generalized shape or using
variations of it should be avoided (Lee, 2011).

Catenary Curve
The type of arch form used during orthodontic treatment will have a clinical
impact on the amount of arch circumference.
MacConaill and Scher described the normal dental arches conform to a catenary
curve or to a regular deviation from that curve (MacConaill, 1944). A catenary curve is
typically 200mm in length and is created when a piece of chain is attached to a horizontal
cross bar. One end of the chain is movable to change the distance between the free ends.
In maxillary arch the apex of the of the curve lies over the gingival papilla
situated between and on the lingual side of the first incisors, The limbs of the chain lie
over the central fossae of the first permanent molars. In the case of the lower arch, the
apex of the catenary is adjusted to lie over the point of contact between the incisive edges
of the first incisors, while the two limbs lie over the buccal cusps of the first permanent
molars. Not all teeth lie in the exact caternary curve, primarily the third molars. These
are typically lingual to the curve, but the overall shape is caternary in form.

11

FIGURE 1: Catenary Curve Arch Form
Bonwill-Hawley
In 1955, Hawley proposed a method to determine the ideal arch using an
equilateral triangle. The triangle leg represented the intercondylar width. The lower
anterior teeth were aligned on the arc of the circle and the radius was determined by the
combined width of the lower incisors and canines with the premolars and molars aligned
with the second and third molar turned toward the center (Hawley, 1925). Bonwill also
believed the arc of the anterior teeth could be related to an equilateral triangle.
Orthodontic supply companies based most preformed arch wires on the Bonwill-
Hawley design, even though this theory has been largely discredited (White, 1978).

FIGURE 2: Bonwill-Hawley Arch Form

12
Brader
Brader in a 1972 paper concluded, “normal dental arches of the sample more
closely approximated curves with elliptic properties than they did a parabola, the catenary
curve or other curves.” The trifocal ellipse is derived form three internal foci and is a
closed, compounded elliptic curve that closely describes the facial surfaces of the
maxillary arch. His theory was justified by the formula PR=C, which accounts for the
pressures of the tissues on the shape of the teeth in an arch (Brader, 1972). Selection of
the Brader arch form is based on the second molars, the shape is related to the facial
surfaces of the teeth and the mandibular arch is always one size smaller than the
maxillary arch form. A common problem with this theory is when it is applied it results
in a severe narrowing of the cuspids (White, 1978).

Mathematical Calculations of Arch Form
Mathematic models have been used for describing arch forms. Lu (1964) claimed
that the dental arch could be satisfactorily described by a polynomial equation of the 4
th

degree. Sanin (1970) investigated the size and shape of ideal arches and confirmed the
views of Lu. Pepe (1975) analyzed a sample of 7 models of normal occlusion by
digitization and curve fits. The results showed that 4
th
order polynomial equations were
better than Catenary curve fits and also suggested that 6
th
degree polynomial equations
appear to have potential as clinical indicators of arch form.

13
Roth Tru Arch Form
The Roth Tru Arch Form was developed from biologically and clinically derived
broad curves observed in patients treated with Cetlin mechanics of functional appliances
such as FR which are referred to as “Natural or Non-Orthodontic”. The Roth Tru Arch
was derived from his extensive clinical testing & recording of jaw movement patterns in
treated patients who were out of retention and had remained stable.
This arch form mainly was wider by a few millimeters, primarily in bicuspid area
when compared to Andrews norms and coincided exactly when superimposed on
Ricketts pentamorphic arch forms.

Segment Concept in Arch Patterns
Robnett in 1980 theorized the segment concept of arch form design where instead
of trying to fit one shape or mathematical formula to determine the shape of the “normal”
human dental arch he based his concept on developing a finite number of arch patterns
that can be adapted to the majority of patients. The pattern consists of canine width,
molar width and the sum of the mesiodistal diameters of the six mandibular anterior
teeth. This theory is used to predict the basic shape of the mandibular arch and allows the
practitioner to determine the canine width at the end of treatment (Robnett, 1980).

Computer-derived Arch Design
Rocky Mountain Data System is a computer derived formula that relies upon
measurments taken from intermolar widths, inter cuspid width, an arch depth as measured

14
from the facial surface of the incisors to the distal surface of the terminal molar. The arch
designs are only applicable to the mandibular arch and facial types are considered.
(White, 1978).

A new concept of mandibular dental arch forms with normal occlusion
Form A (22%)- flattening of the anterior curve region and the origin of the
curvature at the distal region of the lateral incisors.
Form B (15%)- similar configuration as form A—ie, mandibular incisors arranged
in a straight line. However, its intercanine distance was slightly wider than in form A.
Form C (10%)- the anterior teeth are roundly arranged.
Form D (9%)- anterior region of form D is analogous with form C, although this
form has a greater intercanine distance, and the incisors are positioned nearly in a plane,
giving a quadrangular configuration for this form.
Form E (11%)- had a semicircular arrangement of the anterior teeth; therefore,
the posterior region is not strictly straight.
Form F (13%)- example of a catenary curve.
Form G ( 2%)- a pointed anterior region.
Form H (18%)- has a morphology that describes the projection of the mandibular
central incisors and had the second highest frequency.

15

FIGURE 3: A new concept of mandibular dental arch forms

16
HYPOTHESES
Research hypotheses
1. There is a significant difference in the arch form between Caucasians and African
Americans.
2. There is a significant difference in the arch dimensions between Caucasians and
African Americans.
3. There is a significant difference in the arch form between malocclusion types:
Class I, Class II and Class III.
4. There is a significant difference in the arch dimensions between malocclusion
types: Class I, Class II and Class III.

Null hypotheses
1. There is no significant difference in the arch form between Caucasians and
African Americans.
2. There is no significant difference in the arch dimensions between Caucasians and
African Americans.
3. There is no significant difference in the arch form between malocclusion types:
Class I, Class II and Class III.
4. There is no significant difference in the arch dimensions between malocclusion
types: Class I, Class II and Class III.

17
MATERIALS AND METHODS
The Caucasian cases included pre-treatment mandibular orthodontic study models
of 60 Class I, 50 Class II, and 50 Class III cases from the University of Southern
California, Department of Orthodontics and a private practice in San Diego. The African
American cases included pre-treatment mandibular orthodontic study models of 57 Class
I, 26 Class II and 17 Class III cases from the Herman Ostrow School of Dentistry of
USC, Department of Orthodontics. All mandibular study models were subjected to the
following inclusion criteria:
1. Class I, II, and III malocclusions of a dentoalveolar nature
2. Permanent dentitions with normal tooth size and shape
3. 3mm of crowding or less
4. Without restorations extending to contact areas, cusp tips, or incisal edges.
The occlusal surfaces of the mandibular models were photocopied (Canon PC
940, Canon, Lake Success, NY), with a ruler included for magnification correction. The
photocopied images were scanned (Epson 3100C, Epson, Long Beach, Ca), digitized
(Microsoft Digital Image Pro 9, Microsoft, Redmond, Wa), calibrated and measured
(Rootometer, J. Johnson).

18

FIGURE 4: Points digitized on the occlusal photocopy. These points represent the most
facial portions of 13 proximal contact areas.

Four linear measurements were recorded (Figure 5):
1. Intercanine width (distance between the canine clinical bracket points)
2. Intermolar width (distance between the first molar clinical bracket points)
3. Canine depth (shortest distance from a line connecting the canine clinical bracket
points to the origin between the central incisors)
4. Molar depth (shortest distance from a line connecting the first molar clinical
bracket points to the origin between the central incisors)
Two proportional measurements were calculated (Figure 5):
1. Canine width to depth ratio (ratio of the intercanine width and the canine depth)
2. Molar width to depth ratio (ratio of the intermolar width and the molar depth)

19

FIGURE 5: Twelve clinical bracket points, 4 linear and 2 proportional measurements of
arch dimensions. 1, intercanine width; 2, intermolar width; 3, canine depth; 4, molar
depth.

20

FIGURE 6: arch shape differences between the three arch forms; tapered, ovoid and
square (Ortho-form, 3M Unitek, Calif) when superimposed as described by R. P.
McLaughlin, J. C. Bennett and H. J. Trevisi. One of the 3 arch forms that best fits with
the sample’s arch that consists of 8 teeth’s clinical bracket points between 1st premolars
were selected. (Blue = Squared, Green = Ovoid, Black = Tapered)

STATISTICAL ANALYSIS
The means and standard deviations were calculated for each sample using
Microsoft Excel 2011. Ethnic differences in arch dimensions were analyzed by unpaired
t-tests and Levene’s test for equality of variance. The chi-square test was used to
determine differences in frequency distribution of the 3 arch forms. The subjects were
then regrouped into the 3 arch forms and the arch dimensions were re-analyzed using
unpaired t-tests and Levene’s test for equality of variance. The levels of significance were
p < .05 (*), p < .01 (**), and p < .001 (***).

21
All models were evaluated for inclusion criteria and were measured by one
examiner. The method error was assessed by statistically analyzing the difference
between duplicate measurements, by the same examiner 2 weeks apart on 20 casts
selected at random. The intraclass correlation coefficients are .932 for canine width, .958
for molar width, .836 for canine depth and .914 for molar depth.

22
RESULTS
We analyzed 260 mandibular orthodontic study models and a statistical analysis
was completed in order clarify morphologic differences between Caucasian and African
American mandibular clinical arch forms in Class I, II, and III malocclusions.

SAMPLE CHARACTERISTICS (TABLE 1)
The mean (SD) age of the Caucasian patients was 15.4 (5.2) years and of the
African American patients was 15.8 (3.4) years. Each group was predominately female
with the Caucasian group consisting of 84 females and 76 males while the African
American group had 54 females and 46 males.

TABLE 1: Sample Characteristics
Caucasian
Sample n Males Females
Mean Age
(Years)
SD (Years)
Class I 60 23 37 16.6 5.9
Class II 50 26 24 14.7 4.7
Class III 50 27 23 14.5 4.3
Total 160 76 84 15.4 5.2
African American
Sample n Males Females
Mean Age
(Years)
SD (Years)
Class I 57 25 32 17.7 9.9
Class II 26 12 14 14.3 3.3
Class III 17 9 8 15.5 5.1
Total 100 46 54 15.8 3.4

23
COMPARISON OF VARIABLES BETWEEN CAUCASIAN AND AFRICAN
AMERICAN CLASS I, II, AND III GROUPS (TABLE 2)
The results of the unpaired t-tests showed that the Caucasian group had a larger
intercanine width (significant) and intermolar width in all three Angle classifications. In
the Class I group, the African American group had a significantly larger canine and molar
depth. In the Class II group, the Caucasians had a significantly larger molar width-to-
depth ratio. When Class I, II, and III malocclusions were combined there were
statistically significant differences in all measured variables between the Caucasian and
African American ethnic groups, with the exception of canine and molar width-to-depth
ratio. Overall the African American group had significantly larger canine and molar
depths.

24
TABLE 2: Comparison of Variables between Caucasian and African American Class I,
II, and III Samples

CLASS I SAMPLE
Caucasian (n=60)
African American
(n=57)

Variable Mean SD Mean SD P value
Intercanine width (mm) 29.00 1.26 28.4 2.06 0.05*
Intermolar width (mm) 49.20 2.29 48.1 3.5 0.06
Canine depth (mm) 6.29 0.88 6.82 1.04 0.004**
Molar depth (mm) 26.80 1.62 27.65 2.38 0.03*
Canine W/D ratio 4.68 0.56 4.26 0.71 <0.001***
Molar W/D ratio 1.84 0.11 1.75 0.14 <0.001***
CLASS II SAMPLE
Caucasian (n=50)
African American
(n=26)

Variable Mean SD Mean SD P value
Intercanine width (mm) 29 1.22 28.54 2.14 0.32
Intermolar width (mm) 49 2.52 47.89 3.03 0.35
Canine depth (mm) 7 1.12 6.97 1.24 0.51
Molar depth (mm) 27 1.97 28.31 2.92 0.12
Canine W/D ratio 4 0.7 4.22 0.86 0.42
Molar W/D ratio 2 0.16 1.7 0.15 0.05*
CLASS III SAMPLE
Caucasian (n=50)
African American
(n=17)

Variable Mean SD Mean SD P value
Intercanine width (mm) 29 1.7 29.16 2.25 0.81
Intermolar width (mm) 51 2.7 50.04 2.23 0.42
Canine depth (mm) 5.7 1.2 6.25 0.91 0.07
Molar depth (mm) 27 2.6 27.81 2.12 0.26
Canine W/D ratio 5.3 1 4.75 0.69 0.03*
Molar W/D ratio 1.9 0.2 1.81 0.13 0.13

25
TABLE 2: Continued
TOTAL

Caucasian
(n=160)
African American
(n=100)

Variable Mean SD Mean SD P value
Intercanine width (mm) 29.07 1.39 28.56 2.11 0.02*
Intermolar width (mm) 49.41 2.61 48.39 3.26 0.005**
Canine depth (mm) 6.26 1.13 6.76 1.09 <0.001***
Molar depth (mm) 27.08 2.07 27.85 2.48 0.007**
Canine W/D ratio 4.79 0.85 4.33 0.76 1.73
Molar W/D ratio 1.83 0.17 1.75 0.15 1.69

26
COMPARISON OF FREQUENCY DISTRIBUTION OF SQUARE, OVOID AND
TAPERED ARCH FORMS BETWEEN CAUCASIANS AND AFRICAN
AMERICANS (TABLE 3)
In Angle Class I samples, the tapered arch form showed the highest frequency of
70% whereas ovoid and square arch forms were less frequent. The arch form distribution
in Angle Class II malocclusion samples were 70% tapered, 27% ovoid, and 4% square
arch forms. In Angle Class III samples, the square arch form showed the highest
frequency as 47%, following tapered (40%) and ovoid (18%) arch forms (Table 3).
The results of the chi-square test were that in the Class I, Class II, and Class III
combined (Class I, II, and III) groups there were not significant differences in the
frequency distribution of the arch forms between the Caucasian and African American
ethnic groups. In both the African American and Caucasian Class I samples, the tapered
arch form was most often seen, followed by the ovoid and square arch forms respectively.
In the African American and Caucasian Class I samples, the tapered and ovoid
arch forms accounted for over 90% of the group, while the square arch form was rarely
seen. The Class II Caucasian group presented with 96% of either ovoid or tapered arch
forms, with tapered being the clear majority.
The square arch form had the lowest frequency distribution in the Class I and
Class II groups in both African Americans and Caucasians; in the Class III groups, it had
the highest frequency distribution. There was no significant difference in the frequency
distribution of the 3 arch types between the 2 ethnic groups.

27
TABLE 3: Comparison of Frequency Distribution of Square, Ovoid, Tapered Arch
Forms between Caucasian and African Americans

Caucasian

Square Ovoid Tapered

Sample n % n % n %

Class I 5 8.3 27 45 28 47

Class II 2 4 18 36 30 60

Class III 22 44 16 32 12 24

Total 29 18.1 61 38.1 70 44

African American

Square Ovoid Tapered

Sample n % n % n % P value
Class I 3 5 13 23 41 70
0.89
Class II 1 4 7 27 18 70
0.80
Class III 8 47 3 18 6
35 0.09
Total 12 12 23 23 65 65
0.03

28
FIGURE 7: Class I Caucasian Arch Form Frequency

FIGURE 8: Class I African American Arch Form Frequency

8%

45%

47%

Square

Ovoid

Tapered

5%

24%

71%

Square

Ovoid

Tapered

29
FIGURE 9: Class II Caucasian Arch Form Frequency

FIGURE 10: Class II African American Arch Form Frequency

4%

36%

60%

Square

Ovoid

Tapered

4%

27%

69%

Square

Ovoid

Tapered

30
FIGURE 11: Class III Caucasian Arch Form Frequency

FIGURE 12: Class III African American Arch Form Frequency

44%

32%

24%

Square

Ovoid

Tapered

45%

17%

38%

Square

Ovoid

Tapered

31
FIGURE 13: Caucasian Arch Form Frequency

FIGURE 14: African American Arch Form Frequency

18%

38%

44%

Square

Ovoid

Tapered

12%

23%

65%

Square

Ovoid

Tapered

32
COMPARISION OF VARIABLES BETWEEN CAUCASIANS AND AFRICAN
AMERICANS FOR SQUARE, OVOID AND TAPERED ARCH FORMS (TABLE 4)
The results of the unpaired t-tests where the patients were regrouped into their
respective arch forms (square, ovoid, tapered) were that both ethnic groups showed
decreasing intercanine width, intermolar width, canine width-to-depth ratio, and molar
width-to-depth ratio and increasing canine depth and molar depth as the mandibular
pretreatment arch forms changed from square to ovoid to tapered, with the exception
African American ovoid had the largest molar depth.
Between ethnic groups in the square arch form sample the Caucasian patients had
a significantly larger molar width-to-depth ratio. The data from the remaining
measurements was not significant. Between ethnic groups in the ovoid arch form sample
the African America patients had a significantly larger molar depth, canine depth and
intercanine width, and canine width-to-depth ratio. There were no significant differences
between the intermolar width and molar width-to-depth ratio. In the tapered arch form
group there were significantly larger intercanine and intermolar widths for the Caucasian
patients. All other variables were similar and not significant.
Both ethnic groups showed significant decreases in intercanine width, intermolar
width, and canine and molar W/D ratios as the mandibular arches changed in form from
square to ovoid to tapered. In general, the square arch forms were very similar in size,
independent of ethnic group, whereas the tapered and ovoid arch forms varied
significantly in size.

33
TABLE 4: Comparison of Variables between Caucasians and African Americans for
Square, Ovoid, and Tapered Arch Form Groups

Square

Caucasian
(n=29)
African
American
(n=12)

Variable Mean SD Mean SD P value
Intercanine width (mm) 30 1.68 30.55 1.41 0.29
Intermolar width (mm) 52.2 2 51.67 2.04 0.41
Canine depth (mm) 5.27 1.11 5.81 0.79 0.14
Molar depth (mm) 26.2 2.71 27.73 1.96 0.08
Canine W/D ratio 5.86 0.92 5.35 0.76 0.1
Molar W/D ratio 2.02 0.19 1.87 0.11 0.02*

Ovoid

Caucasian
(n=61)
African
American
(n=23)

Variable Mean SD Mean SD P value
Intercanine width (mm) 29 1.34 30.27 1.6 0.01*
Intermolar width (mm) 50 2.27 50.62 3.2 0.2
Canine depth (mm) 6 0.76 6.67 1.08 0.004**
Molar depth (mm) 27 1.78 28.75 2.5 <0.001***
Canine W/D ratio 5 0.48 4.62 0.59 0.02*
Molar W/D ratio 2 0.11 1.77 0.18 0.02

34
TABLE 4: Continued

Tapered

Caucasian
(n=70)
African
American
(n=65)

Variable Mean SD Mean SD P value
Intercanine width (mm) 28 1 27.6 1.71 <0.001***
Intermolar width (mm) 48 2 47.02 2.55 0.02*
Canine depth (mm) 6.9 1.1 6.97 1.06 0.51
Molar depth (mm) 28 1.9 27.56 2.52 0.9
Canine W/D ratio 4.2 0.6 4.04 0.61 0.06
Molar W/D ratio 1.7 0.1 1.71 0.13 0.13

35
DISCUSSION
Orthodontic practices are part of the growing global trend of modern health care.
As socioeconomic status improves, the demand for dental esthetics and orthodontic
treatment surges. This study addresses the pre-treatment arch form and dimensions for
African American and Caucasian samples, which included all three Angle malocclusion
types. The most facial portion of the proximal contact area was identified as the clinical
bracket point, as in studies by Nojima and Kook, and arch form and dimensions were
determined (Nojima, 2001, Kook 2004). Clinically significant findings resulted in this
study that will aid the orthodontist in both determining arch form as well as accurate
ordering of preformed arch wires.

Arch Dimension- Ethnic Variation
Mandibular arch dimensions varied slightly between the African American and
Caucasian groups. The African American arches had significantly larger molar and
canine depths compared to the Caucasian groups.
There were significant differences between the African American and the
Caucasian groups when the samples were regrouped based on. The square arch form
group showed that Caucasians had a significantly larger molar W/D ratio. In the ovoid
arch form group Caucasians had a significantly smaller intercanine width, canine depth,
molar depth, and canine W/D ratio. In the tapered group the Caucasian group had a
significantly larger intercanine width and intermolar width.

36
Arch Form- Ethnic Variation
The African American and Caucasian arch forms followed the same variation
among each dental malocclusion even though there is a difference in the frequency of
arch forms between different ethnic populations; consistent with the findings of
Aitchison, Kook, Nojima, Irey and Kasai.

Arch Dimension- Difference among malocclusion type
Braun, in 1998, found that there were differences in the dimensions of the
dental arch in different malocclusion types. They found Class II mandibular arches were
reduced in arch width and depth and Class III was greater in the arch width dimension
and reduced in arch depth in comparison to Class I arches. Consistent with the findings of
Kook in 2004 and Nojima in 2001, we found that the Class II group had a larger canine
depth and molar depth in comparison to the Class I sample. The Class II also had the
smallest canine width to depth ratio followed by the Class I and then the Class III sample.
Canine depth was the least for the Class III sample.
Arch width was very similar regardless of malocclusion type, with the exception
of the Class III Caucasian and African American samples that had increased intermolar
widths. Intercanine width was the most consistent measurement between the three
malocclusion types.

37
Arch Form- Difference among malocclusion type
There was a general increase in the square arch form in the Class III group, when
compared to both the Class I and II group; this is consistent with the findings of Kook in
2004 and Nojima in 2001. Nojima postulated that this was due to the fact that there is a
“common pathogenesis of Class III malocclusion and the resultant dental compensation
by lingual tipping of the mandibular anterior teeth, causing the anterior part of the
mandibular arch to flatten” (Nojima, 2001).
Class III arches have the highest molar W/D ratio followed by Class I and Class II
arches. In the study of Kook et al. both the canine and the molar W/D ratio is the least in
Class II arches followed by Class I and Class III. Similar results have been found in
studies reported by Nojima et al. and Gafni et al.
Felton et al reported little difference between the arch forms of the Class I and
Class II groups. However, our results agreed with previous studies in that the Class II
arches for Caucasian subjects were associated with a decreased frequency of the ovoid
arch form and an increased frequency of the tapered arch form compared with Class I
arches.
According to our study, there was no significant difference with respect to arch
form variance between Class I and Class II arches. Tapered arch form was seen in high
frequency in both groups whereas the sequence of ovoid arch form was less. Similar
results have been obtained in studies performed by Felton et al.

38
Clinical Implications
Since there are similarities in both arch dimension and frequency of arch form
between the African American and Caucasian sample and among malocclusion type it is
essential to select a best fit arch form for non-adaptable wires and to individualize the
arch form in wires that can be altered, in order to minimize round tripping (Braun, 1999)
of the dentition and to enhance stability (Little, 1990) of the orthodontic result.

39
ASSUMPTIONS
The assumptions made for this study were that the orthodontic patient pool at the
USC Department of Graduate Orthodontics was representative of the general population.
Ethnic groups were assigned based upon last names and photographs. Pre-treatment
models were free of distortion and provided and accurate assessment of patient’s true
arch form and dimensions. Measurements were accurate and reproducible.

40
LIMITATIONS
There were several potential limitations to this study. There were a limited
number of records that satisfied the strict criteria set for the study. The study only used
orthodontic patients as opposed to the general population. Measurements were subject to
human error. Finally, the criteria for assignment into the separate ethnic groups are
difficult to define personal history, surname and appearance are good indicators, but are
not definitive.

41
SUMMARY
The patients used in this study were from a large metropolitan area in the western
United States. The sampling model used would be able to generalize our results to the
rest of the population. One limiting factor was that the sample was specifically pre-
orthodontic patients. The results of this study could affect many aspects of orthodontic
practice. The fact that there was a significant difference arch form and dimension
between African American and Caucasians has implications on orthodontic treatment
planning. Similar arch forms were unique to each Angle classification in each ethnic
group and the frequency of the arch forms was similar between the groups.

42
CONCLUSIONS
1. Comparisons between African Americans and Caucasians indicate that all arch
dimensions are similar in the African Americans sample.
2. There is similarity in the frequency of arch forms between African Americans and
Caucasians, with a majority of African Americans and Caucasians having a
tapered or ovoid arch form.
3. There is similarity in the frequency of arch forms between the different Angle
classifications.
4. There is a difference in arch dimensions between the different Angle
classifications.
With this study, it is foreseen that the arch form should be determined in
relation with each patients’ pretreatment mandibular dental model and especially
in relation with each patients’ ethnic group in order to achieve an esthetic,
functional and stable arch form outcome.

43
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Abstract (if available)

Abstract Introduction: The purpose of this study was to clarify morphologic differences between Caucasian and African American mandibular clinical arch forms in Class I, II, and III malocclusions. Methods: The study included 60 Class I, 50 Class II, and 50 Class III patients from the Caucasian group and 57 Class I, 26 Class II, and 17 Class III patients from the African American group. Orthodontic study models were photocopied, scanned, digitized, and measured (4 linear and 2 proportional). The dental arches were classified into square, ovoid, and tapered forms to compare the frequency distributions between the 2 ethnic groups. Results: The Caucasians had a significantly smaller arch dimensions than the African American, except for canine depth. African Americans had a higher frequency of tapered arch forms. Conclusion: There is a significant difference between frequency of arch forms and arch dimensions of African American and Caucasian patients. Specifically, there is no arch form unique to any of Angle classification or ethnic group. The most frequent arch form seen in Angle malocclusion groups was the tapered one, followed by the less frequent ovoid and square ones.

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Asset Metadata

Creator Jerome, John Robert (author)

Core Title A comparative study of caucasian and African American mandibular clinical arch forms

School School of Dentistry

Degree Master of Science

Degree Program Craniofacial Biology

Publication Date 05/02/2012

Defense Date 03/05/2012

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

Tag arch forms,OAI-PMH Harvest,orthodontics

Language English

Contributor Electronically uploaded by the author (provenance)

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

Creator Email johnjeromedds@gmail.com

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c3-23213

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