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An overview of the dental and skeletal relationships in individuals of Vietnamese ancestry

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An overview of the dental and skeletal relationships in individuals of Vietnamese ancestry

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An Overview of the Dental and Skeletal
Relationships in Individuals of Vietnamese
Ancestry

Tiffany Hudson
May 2019

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

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Table of Contents
I. Abstract ………………………………………………………………………………………... 3
II. Introduction …………………………………………………………………………………... 5
III. Literature Review ……………………………………………………………………………. 6
a. Background ……………………………………………………………………………… 6
b. Angle Classification ……………………………………………………………………... 7
c. Overjet and Overbite …………………………………………………………………… 11
d. Shovel-Shaped Incisors ………………………………………………………………… 14
e. Crossbite ……………………………………………………………………………….. 16
f. Arch Form ……………………………………………………………………………… 17
g. Cephalometrics ………………………………………………………………………… 25
IV. Materials and Methods …………………………………………………………………….. 29
V. Results ……………………………………………………………………………………… 33
a. Angle Classification……………………………………………………………………… 33
b. Overjet and Overbite …………………………………………………………………….. 35
c. Shovel-Shaped Incisors ………………………………………………………………….. 36
d. Crossbite ………………………………………………………………………………… 36
e. Arch form ………………………………………………………………………………... 37
f. Cephalometrics …………………………………………………………………………... 41

VI. Discussion ………………………………………………………………………………….. 42
a. Dental Relationships …………………………………………………………………… 42
b. Skeletal Relationships ………………………………………………………………….. 46
c. Limitations ……………………………………………………………………………... 47
VII. Conclusion ………………………………………………………………………………… 48
VIII. References ………………………………………………………………………………... 50

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I. Abstract
Background: Orthodontic treatment norms that have traditionally been used have been based off
of the dental and skeletal relationships found in Caucasians. Studies have since been conducted
on a variety of ethnic groups in order to provide reference standards specific to different
populations. Limited literature exists, however, on the Vietnamese population, which reduces
the ability to appropriately diagnose and treat individuals of such descent accordingly.
Objective: The purpose of this study was to explore and establish a general overview of the
dental and skeletal topography in patients of Vietnamese descent.
Materials and Methods: Initial records, which included study models and lateral cephalograms,
were collected in a private orthodontic practice in Canoga Park, California and de-identified by
the private practitioner prior to use in this study. Inclusion criteria were as follows: immigrant or
first generation Vietnamese-American, complete diagnostic records, no previous orthodontic
treatment, permanent first molars erupted into occlusion, absence of pathology, no edentulous
spaces as a result of caries or congenital reasons, and a medical history void of syndromes or
craniofacial abnormalities. Of 124 initial records collected, 119 were used for this study. Study
models were evaluated by a single investigator for the Angle classification (right and left
molars), overjet, overbite, presence of shovel-shaped incisors, crossbite tendency, and arch form.
Lateral cephalograms were digitally traced by the private practitioner using Steiner and Wits
analyses. Descriptive statistics were then completed on the collected data and compared to
corresponding data previously published on other ethnicities.
Results: A Class I, II, and III molar relationship was observed in both the total sample and each
gender in order of decreasing frequency. The mean overjet of the sample was 3.5 ± 2.8 mm and
4

the mean overbite of the sample was 2.7 ± 1.8 mm. Maxillary incisors in 39.5% of the sample
exhibited the tooth shoveling quality. Crossbite relationships of any kind were present in 47.9%
of the patients, while an edge-to-edge anterior relationship was present in 3.4%. Ovoid arch
forms were the most common in the sample, being observed in 68.0% of the maxillas and 60.5%
of the mandibles of the patients. The mean ANB of the sample was 3.1 ± 2.5° while the mean
SN-GoGn was 37.3 ± 5.5°. Wits appraisal was calculated with a mean value of -0.67 ± 3.14 mm
for the males and -0.92 ± 3.76 mm for the females in the study.
Conclusion: Vietnamese individuals of the sample displayed Class I, II, and III molar
relationships in decreasing order of prevalence. Additional dental features observed in the
sample included elevated overjet and overbite values compared to ideal standards, increased
crossbite distribution, and a common tendency for ovoid arch forms. Tooth shoveling was
present and expected in the sample, but the prevalence was not as high as anticipated based on
previous reports. On average, Vietnamese individuals presented with an elevated ANB and
steeper mandibular plane angle compared to Caucasians, and a more negative Wits value for the
females than the males.

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II. Introduction
Vietnam is a country in Southeast Asia, bordered by southern China, Cambodia, Laos,
and the South China Sea. The ancestral roots of present-day Vietnamese originated from
present-day northern Vietnam and southern China. While considered Southeast Asian, past
history of Chinese influence has molded the culture of Vietnam closer to that of their immediate
northern neighbors of southern China (Anh et al., 2016). Nonetheless, the Vietnamese have
evolved to develop their own unique set of physical and cultural characteristics that has set them
apart from their Asian counterparts.
Much of the treatment norms historically used have been determined based off of studies
conducted on Caucasian populations. Different ethnic groups, however, exist with a vast range
of physical features and cultural values as a result of geographical and social adaptations. Not
every person can be evaluated or treated with the same universal reference standard.
Establishing dental and skeletal norms specific to different ethnicities has been the intent of
many studies in recent years in order to better diagnose and treat patients with respect to their
physical adaptations and cultural ideals. While many ethnic groups, including various Asian
populations, have been studied for this reason, limited literature exists on those of people of
Vietnamese descent. Thus, the purpose of this study was to quantify and present a cursive
overview of the dental and skeletal relationships characteristic to the Vietnamese. Dental
features evaluated in this current study include Angle classification, overbite, overjet, shovel-
shaped incisors, crossbites, and arch form. Skeletal relationships examined in this study were
based on cephalometric measurements, such as the A point-nasion-B point angle (ANB), the
sella-nasion to gonion-gnathion angle (SN-GoGn), and Wits appraisal.

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III. Literature Review
a. Background
In 1962, Coon classified humans into five races: Caucasoid, Mongoloid, Australoid,
Negroid (also known as Congoid), and Capoid. According to Coon’s classification, Caucasoids
were composed of Europeans, Middle Eastern Whites from Morocco to West Pakistan, Indians,
and the Ainu of Japan. Mongoloids consisted of East Asians, Indonesians, Polynesians,
Micronesians, American Indians, and the Eskimo. Australoids included Melanesians, Papuans,
some tribal folk of India, and Negritos of South Asia and Oceania. Negroids were people of
Central and South Africa. Indigenous South Africans, such as the Bushmen, Hottentots, and
other tribes, made up the Capoid group (Coon, 1962). Many classifications and criteria have
been proposed by anthropologists, but it has generally been agreed that the major groups are
Caucasoids, Mongoloids, Negroids, and Australoids (Rawlani et al., 2018). Members of the
Mongoloid group, particularly Southeast Asians, were of primary focus in the present study.
Southeast Asia stretches southeast from Burma to eastern Indonesia. The region has
harbored evidence of the early migration of hominids from Africa into Asia about a million years
ago. Southeast Asia also serves as the source-region for the populations of Australia and the
Pacific Islands. About 40,000 years ago, these indigenous Australo-Melanesian people were
replaced by the Southern Mongoloids, whom the majority of the present-day inhabitants of
Southeast Asia have descended from (Bellwood, 1999).
Fossil discovery and analysis, particularly of teeth, has forged a path from which to trace
the migration patterns and origins of people in different parts of the world. Turner proposed
classification of the dentitions of Northeast and Southeast Asian Mongoloids into groups called
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Sinodont and Sundadont respectively (Turner, 1989). Sinodont dentitions have been
characterized by tooth shoveling, upper first premolars with one root, and lower first molars with
three roots (Kimura et al., 2009). All prehistoric teeth from Southeast Asia were deemed
Sundadont, ruling out southern expansion by the Northeast Asian Mongoloids. The teeth of
Australian Aborigines and Melanesians started to diverge morphologically from their Sundadont
cousins at least 40,000 years ago. It has therefore been suggested that direct gene flow into
Southeast Asia was likely to come from areas of Mongoloid development in southern China,
south of the Yangtze River (Turner, 1989).
Migration patterns, agricultural and economic shifts, partnered with cultural influences
have therefore created characteristics specific to the Southeast Asia region. Dental and
craniofacial anatomy have changed over time with the evolution of the inhabitants. For example,
a reduction in tooth size was noticed in Southeast Asians, which was theorized to be a result of
an increased availability of softer foods (Bellwood, 1999). In addition, people of Asian descent
have a tendency for flattened nasal bones, leading to skeletal prognathism to incline the
maxillary incisors labially enough to occlude anteriorly to the mandibular incisors (Yaacob et al.,
1996). Many Asians have a brachycephalic head shape as well, leading to an increased tendency
for Class III dental and skeletal relationships (Chang et al., 2014). The dental and skeletal
relationships to follow were of interest in this study, especially to establish a platform from
which to learn more about the unique anatomical and developmental nature of various
populations.

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b. Angle Classification
Edward Angle first classified malocclusion into three classes: Class I, II, and III. Overall,
the molar Angle classification presents as Class I, II, and III, going from most to least prevalent.
The frequency of each classification varies, however, between ethnicities.
Establishing the distribution of malocclusion types between various ethnic groups
provides insight on the kinds of diagnoses and treatment that may prevail in certain patient
populations. For instance, the highest prevalence of Class III malocclusion has been found in
Southeast Asian populations at 15.8% (Ngan and Moon, 2015). On the other hand, Class III
malocclusion has been reported to be the least prevalent in the Caucasian population (Bukhary,
2005). For a general comparison, a Class III malocclusion has been reported in 13% of Japanese
(Lew and Foong, 1993), 19% of Koreans (Lim et al., 1990), 14.5% of Chinese (Chan, 1974), and
3% of Caucasians (Battagel, 1993). An increased likelihood of Class III malocclusion can
therefore be anticipated in patients of Southeast Asian descent, creating a greater need to check
for potential early interceptive treatment with Phase I orthodontics. Multiple studies have
therefore been conducted on various ethnic populations to create a library of data on the
distribution of malocclusion types around the world (Table 1).

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Table 1. Prevalence of Class I, II, and III malocclusion in different ethnic groups (Joshi et al.,
2014).

Two studies on Caucasian samples both had similar results: a decrease in prevalence
from Class I to Class III. Salonen et al. found that the distribution of Angle Class I, II, and III
relationships in a Swedish Caucasian adult sample were 71%, 23%, and 5% respectively
(Salonen et al., 1992). Meanwhile, the reported distribution of molar relationships among a
sample of Australian Caucasian adults was 67.1% Class I, 28.7% Class II, and 4.2% Class III
(Tod and Taverne, 1997).
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Several studies on different Asian populations have shown varying results not only from
Caucasians, whom many reference standards are based on, but also from each other. For
example, a study conducted by Lew et al. on Chinese children between the ages of 12 to 14 years
found that the most prevalent Angle classification was a Class I relationship (65.9%). Class II
division 1 and Class II division 2 relationships were observed in 18.8% and 2.7% of the sample
respectively. A Class III relationship was seen in 12.6% of the sample (Lew et al., 1993). Tang
conducted a study on adult Chinese males from Hong Kong, revealing a representation of 64.8%
Class I, 15.87% Class II, and 19.4% Class III. Tang’s findings revealed a greater prevalence of
Class III than Class II malocclusion, which may be attributed to continued mandibular growth
into adulthood (Tang, 1994).
A study by Soh et al. compared the molar relationships between Chinese, Malay, and
Indian males (Table 2). Class I molar relationships were the most common among the three
ethnic groups combined, followed by Class II and Class III molar relationships. The right molar
relationship presented as Class I, II and III in 49.9%, 24.5%, and 24.2% of the total sample
respectively. The left molar relationship presented as Class I, II, and III in 53.1%, 25.1%, and
21.2% of the total sample respectively. There was no significant difference in the distribution of
molar relationships between the three ethnic groups (P > 0.05) (Soh et al., 2005).

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Table 2. Distribution of Angle’s molar relationships of Chinese, Malay, and Indian males as a
collective sample and as individual groups (Soh et al., 2005).

Vietnamese individuals of age 12 and 18 years were compared by Nguyen et al. The
prevalence of the malocclusion types in the total sample was 67% Class I, 17.5% Class II, and
15.5% Class III. An increased proportion of the 12-year-olds exhibited a Class I malocclusion
(72%) than the 18-year-olds (62%). Class II malocclusions were equally observed between the
12- and 18-year-olds at 17.5% of each age group. Class III malocclusions were more prevalent
in the 18-year-olds (20.5%) compared to the 12-year-olds (10.5%), consistent with the concept of
continued mandibular growth into adulthood (Nguyen et al., 2014).
c. Overjet and Overbite
Both overjet and overbite describe the spatial relationships between the maxillary and
mandibular incisors. Overjet refers to the horizontal overlap of the incisors while overbite refers
to the vertical overlap of the incisors. In a normal position, the incisors are in contact, with the
maxillary incisors anterior and covering the incisal edges of the mandibular incisors. An ideal
overjet value has been defined as 2 to 3 mm, and an ideal overbite value has been determined to
be between 1 to 2 mm.
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The extent of overjet often coincides with the Angle classification of the individual.
Increased overjet values, for example, may suggest a Class II molar relationship, while negative,
or reverse, overjet is often found in Class III malocclusions. Thus, the range of overjet values
varies in different ethnic groups depending on the racial tendencies for the three Angle
classifications. It is also important to note that ethnic differences can be found in overbite values
as well. Deep bites over 5 mm, for instance, are twice as prevalent in Caucasians than in African
Americans or Hispanics. Open bites of more than 2 mm, however, are five times as common in
African Americans than in Caucasians or Hispanics (Proffit et al., 2013).
Overjet values have been recorded and compared among multiple Asian ethnic groups.
For instance, Lew et al. conducted a study on Chinese children between the ages of 12 to 14
years and found that they exhibited a positive overjet up to 3 mm in 68.2%, a positive overjet of
more than 3 mm in 19.2%, an edge-to-edge relationship in 2.7%, and a negative overjet in the
remaining 9.9% of the sample (Lew et al., 1993). Poeung et al. evaluated the dental relationships
present in Cambodian children 13 to 15 years in age. Increased overjet of 6 mm or more was
recorded in 3.6% of the females and 6.1% of the males. An even greater overjet value of 9 mm
or more was found in 3.6% of the females but was not observed in the males. However, 3.0% of
the males presented with a negative overjet while a negative overjet was not evident in the
females (Poeung et al., 2011). A study by Sather et al. compared Caucasian, Japanese-Brazilian,
and Mongoloid adolescents. The mean overjet was greatest in the Japanese-Brazilian group
(2.96 ± 1.22 mm), followed by the Mongoloid group (2.79 ± 0.76 mm) and Caucasian group
(2.66 ± 0.66 mm) (Sathler et al., 2014). According to a study by Soh et al., the combined sample
of Chinese, Malay, and Indian males exhibited overjet values of less than 2 mm in 20.9%, 2-3
mm in 36%, and 4 mm or more in 43.1%. An overjet greater than 6.5 mm was observed in 6%
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of the total sample. The distribution of overjet values within each ethnic group that made up the
sample in the study by Soh et al. is depicted in Table 3 (Soh et al., 2005).
Studies by Sather et al. and Soh et al. also measured and compared the overbite values
between ethnic groups. Sather et al. evaluated the overbite values of Caucasian, Japanese-
Brazilian, and Mongoloid individuals to find that the mean overbite was found to be greatest in
the Caucasian group (2.99 ± 1.15 mm), followed by the Mongoloid group (2.57 ± 1.11 mm) and
the Japanese-Brazilian group (2.23 ± 1.40 mm) (Sathler et al., 2014). Overbite values observed
in the study by Soh et al. on Chinese, Malay, and Indian males are further described in Table 3.
The findings by Soh et al. concluded that an overbite measurement of over 2 mm and up to 4 mm
was most common, presenting in 37.5% of the three ethnic groups collectively. An overbite of
more than 4 mm was seen in 11% of the total sample, while an open bite was present in 4%. A
minimal overbite of 0 to 0.5 mm was present in 12.4% of the sample. There was no significant
difference (P > 0.05) in overbite distribution between the three ethnic groups (Soh et al., 2005).

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Table 3. Distribution of overjet and overbite (in mm) for the total sample of Chinese, Malay, and
Indian males as a collective sample and as individual groups (Soh et al., 2005).

Nguyen et al. also evaluated the overjet and overbite values in the sample of 12- and 18-
year-old Vietnamese individuals. An overjet of over 3.5 mm was present in 36.6% of the
combined sample of 12- and 18-year-old Vietnamese patients, while an overbite of more than 3.5
mm was found in 26.3% of the sample. Increased overjet and overbite measurements were more
prevalent in the 12-year-olds than in the 18-year-olds, further suggesting changes in dental
relationships as a result of continued mandibular growth into adulthood (Nguyen et al., 2014).
d. Shovel-Shaped Incisors
Teeth display a variety of qualities, all of which can not only present differently between
person to person individually, but also between ethnic groups. For instance, shovel-shaped
incisors are a distinguishing feature found in Mongoloids. These shovel-shaped teeth are a result
15

of the fusion of the marginal ridges to a raised cingulum, forming a deep lingual fossa. The
pronounced marginal ridges extend to the incisal edge, creating the “shovel” or “scoop” shape
that gives rise to its name (Rawlani et al., 2018). This feature has been found in about 90% of
Mongoloids, inclusive of Eskimos and American Indians (Lunt, 1974). Shovel-shaped incisors
have been frequently observed in Asia, with an increasing trend from south to north, but has been
minimal or absent in Africa and Europe (Mizoguchi, 1985). Caucasoids, on the other hand, more
often exhibit “chisel-shaped” anterior teeth with smaller and smoother lingual surfaces
comparatively (Haines, 1972). Tooth shoveling has further been deemed a polygenic inheritable
trait (Blanco and Chakraborty, 1976). A high concordance rate for tooth shoveling has been
observed in monozygotic twins. The heredity of shovel-shaped incisors has been reported to be
about 0.75 in Asians and Native Americans (Haniharai et al., 1975).
While many different factors are at play, both genetically and environmentally, it has
been suggested that a mutation in EDAR may be responsible for the shovel-shaped incisor
phenotype. A nonsynonymous substitution has been found on a single nucleotide polymorphism,
rs3827760, in the ectodysplasin A receptor gene (EDAR). This mutation has been predominantly
found in East Asian populations but absent in African and European populations. Dysfunctional
mutations in both EDAR and the ectodysplasin A gene (EDA) can lead to hypohidrotic
ectodermal dysplasia, a genetic disorder characterized by abnormal morphogenesis of teeth, hair,
and sweat glands, suggestive of its effect on the development of ectodermal organs (Kimura et
al., 2009). Also, the EDAR 1540C allele has been associated with hair thickness in Asians
(Fujimoto et al., 2008). Furthermore, the study by Kimura et al. found that the number of copies
of the EDAR 1540C allele showed a high correlation with the tooth shoveling grade (Kimura et
al., 2009).
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e. Crossbite
Crossbites are a dental relationship observed between the maxillary and mandibular teeth.
In the posterior sextants of the arch, crossbites occur due to a transverse discrepancy in which the
working cusps are not the usual maxillary lingual and mandibular buccal cusps. Posterior
crossbites can therefore present as either buccal or lingual in nature. Anterior crossbites, on the
other hand, present as an anteroposterior discrepancy in which the maxillary anterior teeth are
positioned lingual to the mandibular anterior teeth.
Various factors can result in crossbites, including both excessive and inadequate
mandibular growth, condylar resorption, asymmetric growth patterns, habits, and crowding. The
incidence of crossbites can therefore vary between different ethnic groups and exist for various
reasons that may be more unique to certain ethnicities. Lew et al., for example, found that 8.1%
of Chinese children age 12 to 14 years had a posterior crossbite of any kind (Lew et al., 1993).
Poeung et al. evaluated the incidence of crossbites in Cambodian children similar in age to the
sample used in Lew et al., but compared based on gender. Females of Cambodian descent
presented with anterior and posterior crossbites in 17.9% and 25% respectively. The prevalence
of anterior and posterior crossbites was found in 12.1% and 18.2% of the male Cambodian group
respectively. Based on the findings reported by Poeung et al., it appeared that both anterior and
posterior crossbites were more prevalent in Cambodian females as opposed to the males (Poeung
et al., 2011).
In the study by Soh et al., a posterior buccal crossbite (16.8%) was the most prevalent in
the total sample of Chinese, Malay, and Indian adult males. Anterior crossbites (14.7%) were
the next most prevalent, followed by posterior lingual crossbites (13%) in the total sample.
Anterior crossbites and posterior buccal crossbites were more frequently observed in the Malay
17

and Indian males compared to the Chinese males. However, there was no significant difference
in the distribution of crossbites between the three ethnic groups (P > 0.05) (Soh et al., 2005).
Nguyen et al. found that crossbites were present in 22.8% of the total sample of 12- and
18-year-old Vietnamese patients. Crossbites were more prevalent though in the 18-year-olds
(30.5%), which coincided with the increased prevalence of Class III malocclusions previously
reported in the same age group. Again, this increased tendency for crossbites can be attributed to
the increased post-pubertal mandibular growth that also contributes to the increased Class III
prevalence at this age (Nguyen et al., 2014).
f. Arch Form
The dental arch shape is determined by the anatomy of the alveolar ridge, tooth eruption,
and perioral musculature (Triviño et al., 2008). It has been described in many different shapes in
the past, such as a parabola, hyperbola, ellipse, or catenary curve. In 1932, arch forms were
further classified into ovoid, tapered, and square (Chuck, 1934).
Correct classification and maintenance of a patient’s arch form is an essential practice to
achieving a stable and functional treatment result. Maintaining the mandibular intercanine
width, in particular, is an integral part of achieving post-treatment stability (McLaughlin and
Bennett, 1999). Furthermore, it is believed that the maxillary arch form is dictated by that of the
mandible. Thus, many orthodontists have set out to identify and maintain individual arch forms
for patients throughout treatment, with many focusing on the mandibular arch. Both objective
and subjective approaches have been introduced to distinguish arch form shape in patients.
Objective methods introduced in the past have included mathematical modeling with
polynomial functions (AlHarbi et al., 2008; Noroozi et al., 2001; Nouri et al., 2016), medoids
18

clustering and silhouette methods (Lee et al., 2011), two-dimensional (2D) analysis using clinical
bracket point measurements (Kook et al., 2004), and three-dimensional (3D) analysis with facial
axis points (Lee et al., 2013; Trang et al., 2015). Subjective analysis is a common modality for
determining the arch form and, therefore, the pre-fabricated archwire in a clinical setting.
Transverse dimension measurements, such as the intercanine width (McLaughlin and Bennett,
1999), may be taken in some cases of subjective evaluation, but often times, a subjective method
of arch form determination is completed by visual examination and comparison to existing
archwire shapes. However, this method introduces an increased degree of error and
intraexaminer or interexaminer inconsistency when compared to alternative objective methods.
Subjective evaluation of arch forms, on the other hand, has been found to be generally in
agreement between different operators with tapered and square arch forms. Interexaminer
agreement has been shown to vary more though with the intermediate ovoid arch form (Arai and
Will, 2011).
Properly identifying the shape of the dental arch is not only important for preventing
post-treatment relapse, but can assist in determining the differences in the amount of anterior and
posterior overjet seen with certain arch forms. Differences in overjet projection can be
especially noticed in cases with mismatching arch forms between the maxilla and mandible.
According to Kim et al., tapered arch forms appeared to have about 0.5 mm more overjet than
the ovoid and square arch forms, with the exception of the central incisor area. In the central
incisor area, the largest overjet was observed in square arch forms. The tapered and ovoid arch
forms tended to have homogenous overjet between the anterior and posterior. On the other hand,
square arch forms exhibited an increased anterior overjet compared to that of the posterior (Kim
et al., 2011).
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Certain arch shapes have been found to predominate certain ethnic populations than
others. Mongoloids, for instance, tend to have a parabolic arch shape (Rawlani et al., 2018)
while Caucasoids tend to have narrow V-shaped arches (Aitchison, 1965). Genetic and
environmental factors have further created tendencies for one arch form over another in certain
racial groups. Square arch forms are common to large dental arches while tapered configurations
are common to atrophic arches with reduced intercuspal dimensions. Tapered arch forms may
therefore be more common in patients with a thin periodontal biotype, acting as a natural body
compensation to preserve periodontal health. Appropriate identification of arch shape and size
tendencies specific to each ethnicity can therefore assist in individualized treatment and
enhanced post-treatment stability.
i. Egyptian vs. North American Caucasian
Bayome et al. revealed a relatively even distribution of ovoid (39%), square (31%), and
tapered (30%) arch forms in an Egyptian sample. A corresponding North American Caucasian
sample displayed an ovoid (42%) arch form most frequently, followed by tapered (37%) and
square (21%). The square arch form was the least frequent in the Class I and II groups in both
Egyptians and Caucasians, but the most frequent in the Class III groups. Furthermore, the
Egyptian patients had significantly smaller intermolar widths and therefore narrower arch forms
compared to the Caucasian patients (Bayome et al., 2011).
ii. Turkish vs. North American Caucasian
Celebi et al. performed a study comparing the mandibular arch forms of a Turkish group
and a North American Caucasian group. Ovoid and tapered arch forms collectively made up
more than 80% of the Caucasian group and 69% of the Turkish group. Tapered arch forms were
20

the most common in the Caucasian group while ovoid arch forms were the most frequently
observed in the Turkish group. A square arch form was more frequent in the Turkish,
representing 30.3% of the group, as opposed to 18.1% of the Caucasians. When categorized by
Angle classification, the square arch form was the most common in the Class III Caucasian
individuals while the ovoid was the most common in the Class III Turkish individuals. Class II
individuals for both groups had a decreased number of ovoid arch forms and an increased
number of tapered arch forms compared to the Class I individuals. Greater intercanine and
intermolar widths were present in the North American Caucasian group, concluding that they
exhibited wider arch forms than the Turkish group (Celebi et al., 2016).
iii. Korean vs. North American Caucasian
A study conducted by Kook et al. compared the mandibular arch forms between Korean
and North American Caucasian individuals. The square arch form was the most frequently
observed in the Korean group and the tapered arch form was the frequently observed in the
Caucasian group. Over 80% of the mandibular arches in the Caucasians were composed of
ovoid and tapered arch forms, compared to 53% of the arches in the Koreans. The square arch
form was found in 46.7% of the Korean group and only 18.1% in the Caucasian group. More
than 90% of the Caucasians with a Class I relationship demonstrated either an ovoid or tapered
arch form, compared to 55% of the corresponding Koreans with Class I relationships. The
frequency of ovoid and tapered arch forms increased to 96% in the Class II arches of the
Caucasian group and almost 60% in that of the Korean group. Both Caucasian and Korean
groups showed an increase in square arch forms with Class III malocclusion, at 44% and 54%
respectively. A significantly smaller intercanine and intermolar width was observed in the
Caucasian group for all Angle classifications as well, indicating the presence of a wider arch
21

form in Koreans than in North American Caucasians (Kook et al., 2004). Another study by Park
et al., however, was completed on a Korean sample, reporting that an ovoid arch form was the
most common in the maxilla (52%) and mandible (56%) of young Korean adults, as opposed to
the popular square arch form previously reported by Kook et al. (Park et al., 2017).
iv. Japanese vs. Caucasian
Japanese and Caucasian mandibular arch forms were compared in a study conducted by
Nojima et al. Tapered arch forms (43.8%) were most frequently observed in the Caucasian
sample, followed by ovoid (38.1%) and square (18.1%). The Japanese sample, on the other
hand, exhibited a square arch form (45.6%) most frequently, followed by ovoid (42.5%) and
tapered (11.9%). In Class II subjects, the frequency of tapered arch forms increased in both
Caucasian (60%) and Japanese (24%) groups. The square arch form was the most common in
both Class III Caucasian and Japanese groups, comprising 44% and 58% respectively.
Regardless of the Angle classification, the arch forms in the Caucasian sample were narrower at
the canine and molar regions in comparison to those of the Japanese sample (Nojima et al.,
2001).
v. Indian vs. Bhutanese
Arch forms were classified and compared between Indian and Bhutanese populations in a
study by Sahoo et al. The arch form classification differed in this study in comparison to others
previously mentioned, with classification types including narrow, wide, mid, pointed, and flat, as
opposed to ovoid, square, and tapered. Wider arch forms were found in the Bhutanese group
than in the Indian group. The wide arch form made up 90% of the total Bhutanese sample. A
22

narrow arch form was found in 50% of the Indian sample, followed by mid (30%) and wide
(20%) arch forms (Sahoo et al., 2016).
vii. Vietnamese vs. North American Caucasian
Trang et al. conducted a study comparing the mandibular arches of Vietnamese and North
American Caucasian individuals (Table 4). In terms of arch shape, a square form was most
frequently observed in the Vietnamese group (63.7%).
Table 4. Distribution of arch form types in Caucasian and Vietnamese populations (Trang et al.,
2015).

Ovoid, tapered, and square arch forms were distributed relatively evenly within the
Caucasian sample. Arch form distribution was further evaluated based on Angle classification
(Figure 1). Class I and II Caucasian individuals exhibited a square arch form in 34% and 30%
respectively, but 61% and 62% respectively in the corresponding Vietnamese individuals. The
Caucasians with Class III relationships had primarily square arch forms (49%), followed by
ovoid (32%) and tapered (19%) arch forms. A square arch form (69%) was exhibited the most
frequently in Class III Vietnamese individuals, followed by tapered (17%) and ovoid (14%) arch
forms. Caucasians had a narrower arch dimension for all arch forms compared to their
Vietnamese counterparts (Trang et al., 2015).

23

Figure 1. Frequency distribution of arch form types according to malocclusion in Caucasians and
Vietnamese (Trang et al., 2015).

viii. Vietnamese vs. Korean
Lee et al. compared mandibular arch forms in Korean and Vietnamese patients. The
study found that a square arch form was the most common in both the Korean (44.1%) and
Vietnamese (61.5%) groups, consistent with the findings of Kook et al. (Kook et al., 2004) and
Trang et al. (Trang et al., 2015). While the most prevalent, square arches were significantly
more common in the Vietnamese (P < 0.001). The ovoid and tapered arch forms then followed
in order of decreasing frequency in both Korean (29.4% and 26.5%, respectively) and
Vietnamese (26.9% and 11.5%, respectively) groups. Frequency distribution of the arch forms
was further reported according to Class I and II dental relationships in the Vietnamese and
Korean groups (Figure 2). Furthermore, Vietnamese patients showed a greater arch depth and
slightly greater arch width than the Korean patients (Lee et al., 2013).

24

Figure 2. Frequency distributions of the arch forms in Vietnamese and Korean individuals
according to Angle’s classification of malocclusion and ethnicity (Lee et al., 2013).

ix. Caucasian
In a study by Paranhos et al., mandibular casts of a generalized group of Caucasian
individuals were evaluated for arch morphology. Ovoid arch forms (41%) were the most
prevalent, followed by square (39%) and tapered (20%) arch forms (Paranhos et al., 2011). An
ovoid arch shape was also found to be the most common type of arch morphology in a Caucasian
group studied by Lombardo et al. (Lombardo et al., 2015). For both studies by Paranhos et al.
and Lombardo et al., the ethnic make-up of the Caucasian groups was not described. Ferro et al.,
on the other hand, specifically studied a sample of Italian adolescents in regards to arch
morphology of both the maxilla and mandible. Maxillary arch forms in the Italian adolescents
were predominately ovoid (46.2%), followed by tapered (43.4%) and square (10.4%).
Meanwhile, the mandibular arch forms in the same sample demonstrated an even distribution of
tapered (42.5%) and ovoid (42.5%), followed by square (15.1%) (Ferro et al., 2017).
25

Multiple studies in the past have included Caucasian samples, bouncing between tapered
and ovoid as the most common. Tapered arch forms were found to be the most common in the
North American Caucasian samples evaluated by Celebi et al. (Celebi et al., 2016), Kook et al.
(Kook et al., 2004), and Trang et al. (Trang et al., 2015). North American Caucasians included
in the study by Bayome et al. favored ovoid arch forms instead (Bayome et al., 2011).
Furthermore, the Caucasian sample examined by Nojima et al. favored tapered arch forms over
ovoid arch forms (Nojima et al., 2001).
g. Cephalometrics
Cephalometrics were first introduced by Broadbent in 1931 for the purpose of studying
craniofacial growth and development (Broadbent, 1981). It has aided in orthodontic diagnosis
and treatment planning by revealing the skeletal and dental patterns in relation to each other in a
different light than clinical examination or study models permit. However, cephalometric norms
have traditionally been based off of findings reported in Caucasians, affecting the utility of the
cephalogram as a universal diagnostic aid. In response, studies have been conducted over the
years to determine cephalometric norms for different ethnic groups.
A study conducted by Chan on a Chinese, specifically Cantonese, sample found that they
exhibited the largest mean mandibular plane angle (33.3 ) when compared to those of Australian
Aborigines (21.9 ) (Craven, 1958), American-Japanese (24.3 ) (Cotton et al., 1951), African
(28.8 ) (Altemus, 1960), and Caucasian (21.9 ) patients (Downs, 1948). Bimaxillary maxillary
protrusion was also observed more in the Chinese sample than in the Caucasian sample (Chan,
1972).
26

Chen et al. conducted a study on Chinese children between 11 to 13 years and 10 months
of age (Chen et al., 2015). This study found larger sella-nasion-A point (SNA), sella-nasion-B
point (SNB), and interincisal angle values in comparison to the Japanese norms established by
Miura et al. Meanwhile, the SN-GoGn angle values were smaller in the Chinese children
compared to the Japanese norms (Chen et al., 2015; Miura et al., 1965). Wu et al. noted a
significant difference (P < 0.05) in cephalometric values between the male and female 12-year-
old southern Chinese children in their study. According to the study, males exhibited more
retrognathic mandibles, steeper mandibular plane angles, and a larger lower face height than the
females (Wu et al., 2007).
Naranjilla and Rudzki-Janson compared a Filipino sample to a matching German sample.
Based on the results of the study, Filipino patients were found to have larger ANB values
compared to the corresponding German sample. Bimaxillary dental protrusion was also
observed in the Filipino patients, supporting its general finding in Asians as a collective whole
(Naranjilla and Rudzki-Janson, 2005).
The various skeletal relationships can further present with different growth patterns and
dental compensations in individuals of different ethnic backgrounds. For instance, the
mandibular plane angle was significantly increased in Japanese females with Class III skeletal
malocclusion than with a corresponding group of Caucasian females (P < 0.05). The maxillary
incisors were also found to be more procumbent in the Japanese females compared to their
Caucasian counterparts. Asians, in general, have been found to have a reduced anterior cranial
base in comparison to Caucasians, supporting the finding of a relatively larger mandible to the
cranial base and maxilla in skeletal Class III patients of Asian descent. Combined with the
excessive proclination of the maxillary incisors observed in Japanese females, such a skeletal
27

Class III relationship creates a need for greater orthodontic and surgical correction in such
individuals (Ishii et al., 2002).
In a study conducted by Anh et al. on an adult Vietnamese sample, the mean Steiner
measurements found were significantly different from those of Caucasians. The ANB angle was
increased on average in the Vietnamese patients comparatively, suggesting a greater tendency for
bialveolar protrusion (P < 0.001) when considering the increased SNA and SNB angle values
also reported. A significant difference in ANB measurements was also found between males
(mean 3.29 ) and females (mean 2.45 ) of Vietnamese descent (P < 0.05). In addition, a more
acute interincisal angle was observed in Vietnamese patients on average, lending greater
protrusion in both maxillary and mandibular incisors to match the increased tendency for
bialveolar protrusion. The mean mandibular plane angle was found to be reduced in comparison
to that of Caucasians, suggesting a more horizontal growth pattern in Vietnamese patients.
Steiner cephalometric values were further compared to norms of other ethnicities, and are
depicted in Table 5 (Anh et al., 2016).
Table 5. Comparison of cephalometric values of a Vietnamese population with Caucasians,
Japanese, Koreans, Indians, and Mexican Americans using Steiner’s reference norm (Anh et al.,
2016).

28

Since the ANB angle can be affected by a multitude of factors, Jacobson developed the
Wits appraisal as an additional assessment for the anteroposterior jaw relationship. He found
that the line from B point perpendicular to the occlusal plane (BO) was ahead of the line from A
point perpendicular to the occlusal plane (AO) in males, with a mean of -1.2 ± 1.9 mm. AO and
BO tended to coincide instead in females, with a mean of -0.1 ± 1.8 mm (Jacobson, 1975). Wits
values have been explored in various populations, lending a vast range of values and the ability
to therefore establish norms appropriate to the different ethnic groups (Tables 6 and 7). For
example, a southern Chinese population exhibited a mean Wits value of -4.9 ± 3.6 mm in males
and -4.5 ± 4.2 mm in females (So et al., 1990). A western Saudi sample, on the other hand,
exhibited a mean Wits value of -0.73 ± .48 mm in males and 1.79 ± 2.06 in females (Zawawi,
2012).
Table 6. Comparison of Wits mean values between Saudi males from the western region and
previous reports (Zawawi, 2012).

29

Table 7. Comparison of Wits values between Saudi females from the western region and
previous reports (Zawawi, 2012).

IV. Materials and Methods
Initial records of 124 patients (74 female, 50 male) of Vietnamese descent were collected
from a private orthodontic practice in Canoga Park, California. The initial records included
plaster study models and lateral cephalograms. All patient records were collected by the sole
private practitioner between the years of 2012 to 2018, and de-identified by the same practitioner
prior to collection and use for this study. The only personal information made available was the
age and gender of the patient. The patients ranged in age from 10 years and 10 months to 38
years. Inclusion criteria were as follows: immigrant or first generation Vietnamese-American,
complete diagnostic records, no previous orthodontic treatment, permanent first molars erupted
into occlusion, absence of pathology, absence of abnormal tooth morphology, absence of
edentulous spaces as a result of caries or due to congenital reasons, and a medical history void of
syndromes and craniofacial anomalies. Five records were excluded due to the inability to access
the full records and obtain the appropriate measurements, resulting in a total of 119 patient
records (70 female, 49 male) for use in this study.
30

Lateral cephalograms were taken on the same ORTHOPHOS XG 5 (Dentsply Sirona,
York, Pennsylvania) cephalostat in natural head position and centric occlusion (CO). In the case
of a shift between centric relation (CR) and CO, the lateral cephalogram was recorded in CR via
wax bite registration. The lateral cephalograms were digitally traced by the private practitioner
with Dolphin Imaging software (Dolphin Imaging and Management Solutions, Chatsworth,
California) using the Steiner and Wits analyses. Of the available measurements recorded, the
following were the focus for this study: ANB, SN-GoGn, and Wits appraisal.
Plaster study models were fabricated from alginate impressions while wax bites were
recorded in CO for trimming of the study model bases. In the case that a CO-CR shift was
observed, wax bites were recorded in CR. All models were analyzed and measured by a single
investigator for the following:
1. Angle classification: The molar Angle classification was recorded for both the right and left
sides on each patient. The extent of a Class II or III classification was not quantified and
recorded for the purpose of this study. A molar relationship was considered Class I if the
mesiobuccal cusp tip of the maxillary first molar aligned with the buccal groove of the
mandibular first molar. Any mesial or distal positioning of the mesiobuccal cusp tip of the
maxillary first molar away from the buccal groove of the mandibular first molar was recorded as
either Class II or Class III respectively.
2. Overjet and overbite: Overjet and overbite were measured according to the guidelines set by
the American Board of Orthodontics. Thus, positive overjet was measured as the greatest
distance between the labial surface of the more lingual mandibular incisor and the middle of the
incisal edge of the more facial maxillary incisor. If a negative overjet was present, the
measurement was taken as the distance between the facial of the more lingual maxillary tooth to
31

the middle of the incisal edge of the more facial mandibular incisor. Overbite was measured as
the greatest distance between the incisal edges of two antagonistic incisors (2015). Overjet and
overbite were measured by hand with a ruler, rounding to the nearest 0.5 mm.
3. Shovel-shaped incisors: The presence and absence of shovel-shaped maxillary incisors were
determined subjectively by visual inspection and recorded.
4. Crossbite: Patients were recorded as either positive, negative, or edge-to-edge for this
category. The minimum requirement for a positive classification was a single tooth in crossbite.
If an edge-to-edge bite was not present, the patient was classified as either positive or negative
for a crossbite, regardless if it was in the anterior or posterior. Should a crossbite and an edge-to-
edge relationship be present simultaneously, the patient was categorized based on the presence of
the more extreme relationship, the crossbite. The buccal or lingual nature of a posterior
crossbite, if present, was not recorded for this study.
5. Arch form: Both maxillary and mandibular arches were evaluated for each patient. The arch
form was determined subjectively using the arch form templates (OrthoForm, 3M Unitek,
Monrovia, California) for reference. Arches were classified as either ovoid, square, or tapered.
Examples of the arch forms observed in the study sample can be seen in Figure 3.

32

Figure 3. Examples of maxillary and mandibular arch forms observed in the present study.

Descriptive statistics were completed using Microsoft Excel 2016 (Microsoft
Corporation, Redmond, Washington). Resulting statistical values were rounded to the first
decimal place. The sample was assessed as a whole, followed by further categorization based on
Angle classification and gender for some of the dental and skeletal relationships evaluated. The
values were then compared with previously established dental and skeletal norms of other ethnic
groups.
To evaluate intraexaminer reliability, the measurements and analyses completed on the
study models were repeated 11 weeks after initial data collection. Ten cases were chosen at
random to do so. The intraclass correlation coefficient was calculated for the following study
model recordings: right molar Angle classification (1.00), left molar Angle classification (1.00),
overjet (0.99), overbite (0.99), presence of crossbite (1.00), presence of shovel-shaped incisors
(0.90), maxillary arch form (0.90), and mandibular arch form (1.00).
33

Approval to conduct this study was granted by the University of Southern California
Institutional Review Board on September 7, 2018 (study ID UP-18-00512).
V. Results
a. Angle Classification
Occlusal relationships were recorded as Class I, II, and III in order of decreasing
frequency among the 119 patients in this study (Table 8). The order of prevalence of each Angle
classification was consistent between right and left sides of the mouth. Class I, II, and III
relationships were present on the right in 55%, 29%, and 16% respectively (Figure 4). On the
left, a molar Class I, II, and III relationship was reported in 45%, 32% and 23% of the sample
respectively (Figure 5).
Table 8. Angle classification distribution in total sample.
Right Molar (n) Left Molar (n)
Class I 65 53
Class II 35 38
Class III 19 28

34

Figure 4. Right molar Angle classification distribution in the total sample.

Figure 5. Left molar angle classification distribution in the total sample.

55%
29%
16%
RIGHT MOLAR ANGLE
CLASSIFICATION
Class I
Class II
Class III
45%
32%
23%
LEFT MOLAR ANGLE
CLASSIFICATION
Class I
Class II
Class III
35

The total sample was further separated into male and female groups to assess the
distribution of Angle classifications based on gender (Figure 6). Recordings of the right molar
Angle classification were utilized for this evaluation. Class I, II, and III relationships were
exhibited in 41%, 39%, and 20% of the male patients respectively. In the female patients, Class
I, II, and III relationships were present in 64%, 23%, and 13% respectively.
Figure 6. Right molar Angle classification distribution according to gender.

b. Overjet and Overbite
The mean overjet of the total sample was 3.5 ± 2.8 mm, with recorded values ranging
from -4 to 11.5 mm. A positive overjet was exhibited in the majority, at 85.7% (n=102) of the
patients. A negative overjet presented in 10.1% (n=12) of the patients. The remaining 4.2%
(n=5) of the sample exhibited an end-to-end anterior bite.
36

Overbite values of the total sample ranged from -2.0 to 8.0 mm, with a mean of 2.7 ± 1.8
mm. Less than 1% (n=1) of the entire sample exhibited an open anterior bite. An edge-to-edge
vertical incisal relationship was observed in 10.9% (n=13) of the total sample. The majority of
the patients (88.2%, n=105) therefore presented with a positive vertical overlap of the incisors.
c. Shovel-Shaped Incisors
Shovel-shaped incisors were found in 39.5% (n=47) of the sample (Figure 7). Of the
patients with 3 mm or more of overjet (n=74), 41.9% (n=31) exhibited shovel-shaped teeth.
Figure 7. Distribution of shovel-shaped incisors in the total sample.

d. Crossbite
Figure 8 depicts the crossbite representation in the sample. The presence of a crossbite,
whether located anteriorly or posteriorly, or buccal or lingual in nature, was observed in 47.9%
of the patients. An edge-to-edge anterior bite relationship was observed in 3.4% of the sample.
The remaining 48.7% of the patients did not demonstrate a crossbite of any kind. An edge-to-
edge posterior bite was not observed in this sample population.
No Yes
Shovel Shaped 72 47
0
10
20
30
40
50
60
70
80
Number of Patients
Distribution of Shovel-Shaped Incisors
37

Figure 8. Crossbite distribution in the total sample.

e. Arch Form
Both maxillary and mandibular arch forms were assessed in this study. Table 9 presents
the distribution of each arch form in the sample. The percent distribution of maxillary arch
forms is depicted in Figure 9 while the percent distribution of mandibular arch forms is depicted
in Figure 10. The ovoid shape was the most frequently observed arch form in both the maxilla
and mandible, at 68.0% and 60.5% of the patients respectively. Tapered and square arch forms
were equally as frequent in the maxilla, each representing 16.0% of the maxillary arches.
However, the square arch form was the second most frequent in the mandible at 27.7%, followed
by the tapered arch form at 11.8%.

Yes Edge-to-Edge No
Crossbite Distribution 57 4 58
0
10
20
30
40
50
60
70
Number of Patients
Crossbite Distribution
38

Table 9. Arch form distribution in the maxilla and mandible.
Arch Form Maxillary (n) Mandibular (n)
Ovoid 81 72
Square 19 33
Tapered 19 14

Figure 9. Maxillary arch form distribution in the total sample.

68%
16%
16%
MAXILLARY ARCH FORM
DISTRIBUTION
Ovoid
Square
Tapered
39

Figure 10. Mandibular arch form distribution in the total sample.

When separated into groups of Class I, II, and III based on the right molar classification,
the ovoid arch form was still the most prevalent in the maxilla, comprising 72.3%, 65.7%, and
57.9% of each group respectively. The tapered arch form was the second most prevalent in the
maxilla of Class I (16.9%) and II (20.0%) patients. Maxillary square arches were the least
common in Class I and II patients, making up 10.8% and 14.3% respectively. Square arch forms
(36.8%) were more prevalent, however, in the maxilla of Class III patients than the tapered arch
form (5.3 %). Figure 11 describes the overall distribution of maxillary arch forms in patients
with each Angle classification.

60%
28%
12%
MANDIBULAR ARCH FORM
DISTRIBUTION
Ovoid
Square
Tapered
40

Figure 11. Maxillary arch form distribution based on the Angle classification.

Similar to the maxilla, the ovoid arch shape was the most common in the mandible of the
Class I, II, and III patients at 63.1%, 57.1%, and 57.9% respectively. Square arch forms were the
next most prevalent in the mandible of Class I and II patients. They were observed in 26.2% of
the Class I patients and 34.3% of the Class II patients. Tapered arch forms were the least
prevalent in the Class I and II patients, being recorded in 10.8% and 8.6% respectively. In the
Class III patients, there was an even distribution of tapered and square arch forms, each
comprising 21.1% of the group. Figure 12 describes the distribution of mandibular arch forms in
patients under each Angle classification.

47
7
11
23
5
7
11
7
1
0
5
10
15
20
25
30
35
40
45
50
O V O ID S Q U AR E T AP E R E D O V O ID S Q U AR E T AP E R E D O V O ID S Q U AR E T AP E R E D
C LA S S I C LA S S II C LA S S II I
MAXILLARY ARCH FORM DISTRIBUTION
BASED ON ANGLE CLASSIFICATION
41

Figure 12. Mandibular arch form distribution based on the Angle classification.

f. Cephalometrics
The mean ANB of the total sample was 3.1 ± 2.5 with values ranging from -5.6 to 8.4 .
Males had a mean ANB value of 2.8 ± 2.4, while females had a mean ANB value of 3.3 ± 2.5 .
ANB values ranged from -2.3 to 7.6  in the males. A larger range of -5.6 to 8.4  was observed
for the ANB measurements in the females.
The mean SN-GoGn of the total sample was 37.3 ± 5.5 with values ranging from 23.5 
to 49.8 . Patients were evaluated as well for the SN-GoGn value based on gender. Males
exhibited a mean value of 35.8 ± 5.9 while females exhibited a mean value of 38.3 ± 5.1.
Wits appraisal was calculated for males and females separately. Male patients had a mean
Wits value of -0.67 ± 3.14 mm, with values ranging from -10.9 to 6.3 mm. Female patients had
a mean Wits value of -0.92 ± 3.76 mm, with values ranging from -16.3 to 9.0 mm.
41
17
7
20
12
3
11
4
4
0
5
10
15
20
25
30
35
40
45
O V O ID S Q U A R E T A P E R E D O V O ID S Q U A R E T A P E R E D O V O ID S Q U A R E T A P E R E D
C LA S S I C LA S S II C LA S S II I
MANDIBULAR ARCH FORM
DISTRIBUTION BASED ON ANGLE
CLASSIFICATION
42

VI. Discussion
Over the years, a multitude of studies have been completed to determine dental and
skeletal norms in various ethnic groups. Of the Asian ethnicities, the Chinese, Korean, and
Japanese populations have been of greater focus in past studies, resulting in more published and
established data on their behalf. Few existing studies have been completed on Vietnamese
individuals, warranting a need for more evaluation and recognition of their dental and skeletal
norms. The aim of the present study was therefore to provide insight on the general dental and
skeletal patterns in people of Vietnamese descent.
a. Dental Relationships
The prevalence of the different Angle classifications found in the study sample were
reflective of the common trend of a decrease in frequency from Class I to Class III relationships.
This prevalence pattern was evident on both right and left sides of the mouth. Furthermore, the
order of prevalence of the Angle classifications in this sample was consistent with that of the
samples studied by Lew et al. (Lew et al., 1993), Nguyen et al. (Nguyen et al., 2014), and Soh et
al. (Soh et al., 2005). Tang, on the other hand, found Class III relationships to be more prevalent
than Class II relationships. According to Tang’s study, Class III molar relationships were
present in 16% on the right and 23% on the left (Tang, 1994). While still the least frequently
observed of the three Angle classifications in general, Class III relationships were more
commonly observed in the Vietnamese sample in this current study compared to that reported in
previous studies by Salonen et al. and Tod and Taverne on Caucasian samples (Salonen et al.,
1992; Tod and Taverne, 1997).
43

The mean overjet of the Vietnamese patients was 3.5 mm, greater than the ideal overjet
value of 2 to 3 mm (Proffit et al., 2013). Not only was the mean overjet of the sample greater
than the ideal norm, but it was also greater than the mean overjet of 2.79 mm previously reported
in Mongoloids by Sathler et al. (Sathler et al., 2014). The mean overbite value of the sample was
2.7 mm, also greater than the ideal overbite of 1 to 2 mm (Proffit et al., 2013).
Shovel-shaped incisors were a common characteristic in the sample, accounting for
39.5% of the patients. However, the prevalence of tooth shoveling in this sample was not as high
as a previous report that the characteristic was present in 90% of Mongoloids (Lunt, 1974). The
reduced prevalence of tooth shoveling, on the other hand, may reflect the categorization of
Vietnamese individuals under the Southeast Asian umbrella of Sundadont teeth (Kimura et al.,
2009). Since this study included first generation Vietnamese-Americans, it could be speculated
that environmental differences, including diet, of the patients played a role in the lowered
prevalence rate.
Thick marginal ridges, which contribute to the unique tooth morphology of shovel-
shaped incisors, often creates increased overjet. Enameloplasty of the marginal ridges can be
performed in these instances to minimize overjet and therefore create a better functional
occlusion. Only 41.9% of the patients, however, with an overjet value of 3 mm or more
exhibited maxillary shovel-shaped incisors. Tooth shoveling may have therefore contributed to
the increased overjet in a portion of the patients, but other dental or skeletal factors can be
attributed to the remaining majority with increased overjet measurements. An increased amount
of enameloplasty procedures should be considered nonetheless during the finishing stages of
orthodontic treatment in Vietnamese individuals should tooth shoveling be present.
44

A quantitative analysis was conducted on the total sample for any kind of crossbite or
crossbite tendency (edge-to-edge). Negative overjet suggests a Class III malocclusion, affecting
3% of children and 5% of adolescents and adults in the United States (Proffit et al., 2013).
Anterior crossbites, recorded as negative overjet for this study, were present in 10.1% (n=12) of
the patients, affecting a greater portion of the sample population compared to that of the United
States. The increased proportion of patients with anterior crossbites, or any kind of crossbite, in
this study matched the increased prevalence of Class III malocclusion in this sample. However,
the prevalence of crossbites overall was not consistent with that reported by Nguyen et al.,
presenting in 47.9% of the patients in this study compared to the 22.3% of the 12- and 18-year-
old Vietnamese evaluated by Nguyen et al. (Nguyen et al., 2014).
Ovoid arch forms were found to be the most common in both the maxilla and mandible in
the total sample. Previous reports, however, concluded that a square mandibular arch form was
the most prevalent in the Vietnamese population (Lee et al., 2013; Trang et al., 2015).
According to Arai and Will, it is possible that the neutral ovoid arch form often found in the
sample could be categorized as either tapered or square instead by another examiner or with
objective approaches, altering the overall arch form distribution (Arai and Will, 2011). The arch
form distribution within each Angle classification in this sample also differed with the
corresponding findings by Trang et al. Class III patients in this study exhibited ovoid, square,
and tapered arch forms in decreasing order of frequency. Trang et al., on the other hand, found
that Class III patients had square, tapered, and ovoid arch forms in decreasing order of
frequency. The Vietnamese sample included in the study by Trang et al. included some casts
collected from clinics in Hanoi, Vietnam, suggesting that a portion of the population the data was
collected from was of northern Vietnamese descent (Trang et al., 2015). A study conducted by
45

Anh et al. also utilized a sample of Vietnamese individuals from Hanoi, Vietnam, finding that a
flat mandibular plane angle was common to the local population (Anh et al., 2016). With a
brachycephalic skeletal pattern, a square arch form tends to be more common, which was
consistent with the findings by Trang et al. (Trang et al., 2015). The present study consisted of
patients or patients with parents who immigrated from the southern region of Vietnam,
suggesting that the difference in arch form prevalence was affected by genetics and
environmental factors that molded the dental and skeletal patterns of the patients.
As a generalization, Asians tend to be brachycephalic and are horizontal growers. Those
who exhibit more horizontal as opposed to vertical growth are more likely to exhibit a Class III
skeletal pattern. Horizontal growth also welcomes a square arch form. Based on the findings by
Kim et al., square arch forms had the greatest overjet at the central incisors of the three types of
arch forms, which can further be speculated to be a compensatory mechanism to achieve positive
overjet in Class III skeletal bases. Ovoid arch forms, however, were found in the greatest
number of patients in this sample. Ovoid arch forms tended to have an equal amount of overjet
in the anterior and posterior portions of the arch according to Kim et al., which agreed with a
Class I malocclusion being of the highest prevalence in the sample (Kim et al., 2011). Natural
dental compensations were therefore not necessary for the Class I cases as they would be with
Class III cases.
Maxillary and mandibular arch form distributions differed in this study, where not every
patient exhibited matching arch forms. To best achieve post-treatment stability, it has been
suggested that maintaining the original arch form and mandibular intercanine width are essential
factors to minimize the potential for relapse. With different opposing arch forms, it has therefore
been advised to utilize the mandibular arch as the primary arch form guide during treatment.
46

Transverse dimensions were not recorded for use in this study as the focus was placed on
the arch form shape instead. Comparisons in arch width between the sample and those of pre-
existing study reports could therefore not be completed. Varying ages, and therefore varying
stages of development, between the patients of the sample further limited the ability to
adequately compare transverse arch dimensions should the measurements have even been
recorded.
b. Skeletal Relationships
Various measurements are included in the Steiner analysis. Of the measurements
included in the Steiner analysis, only the ANB and SN-GoGn values were analyzed for the
purpose of this study. In addition, the Wits appraisal was accounted for to provide an additional
assessment of the relationship between the maxilla and mandible.
The mean ANB of this sample was 3.1 , greater than the mean ANB of 2.9  previously
reported in a Vietnamese sample studied by Anh et al. Both reported mean ANB values were in
agreement in that they are both greater than the Caucasian norm of 2 . The present study also
showed an increased mean SN-GoGn value (37.3 ) in comparison to that reported in the
Vietnamese sample (26.5 ) studied by Anh et al. Steiner norms for Caucasian patients show an
SN-GoGn value of 32 . The previous reported mean SN-GoGn value of 26.5  by Anh et al. was
reduced in comparison to that of the established Caucasian norm, suggesting a more horizontal
growth pattern in Vietnamese individuals. However, the finding of a mean SN-GoGn value of
37.3 in this study was greater than the Caucasian norm, suggesting Vietnamese individuals have
a more vertical growth pattern compared to their Caucasian counterparts. As previously
mentioned, the study by Anh et al. was conducted and based on a sample collected in Hanoi,
47

Vietnam, suggesting that at least a portion of the patients were of northern Vietnamese descent.
Thus, differences in genetic make-up and environmental influences are reasoned to have played a
role in the findings of low mandibular plane angles in the study by Anh et al. compared to the
high mandibular plane angles found in this study (Anh et al., 2016).
Norms for Wits appraisal values were originally determined by Jacobson based on
gender. Male Vietnamese patients exhibited a mean value of -0.67 mm, a more positive value
than the norm of -1.2 mm set by Jacobson. The opposite comparison was observed in the
females of this study, with a more negative value of -0.92 mm next to Jacobson’s norm of -0.1
mm. It appears that the occlusal plane was therefore flatter in the females than in the males,
considering the increased ANB and SN-GoGn values common to the study sample.
c. Limitations
Considering that this study was conducted as an initial step in deciphering the dental and
skeletal topography of Vietnamese patients, a few obstacles that appeared during data collection
and analysis were not resolved and a less than ideal methodology was implemented.
Improvements can however be made for future advancements of the study. In regards to the
study sample itself, an even distribution of males and females would create a fairer assessment
and comparison between genders. Recognition of which patients were immigrants or first
generation Vietnamese-Americans would also shed light on the possible effects of growing up in
different countries. It would also be wise to note what specific region of Vietnam each patient or
family of each patient originated. An adequate number of adult patient records, that also met the
inclusion criteria, could also not be provided by the private practitioner at the time of data
collection. Due to changes in dental and skeletal relationships as a result of growth, future
studies would be best conducted on an adult population. This would therefore provide increased
48

confidence in the reliability of the findings and allow better comparison of the Angle
classification, overjet, overbite, and crossbite tendencies to other ethnic groups. As mentioned
previously, it would also allow adequate measurement of transverse dimensions to help progress
our understanding of the dental arch morphology between individuals of different ethnic groups.
In regards to the data collection, objective methods would be better proposed than the subjective
methods used to increase data accuracy and consistency. Furthermore, digitized, 3D assessment
would be preferred in regards to the study model measurements. Two levels of distortion could
have occurred with the alginate impressions, one when taking the impression and another after
pouring the impression with plaster. Measurements taken directly off the model may have
therefore been skewed. While scanning of the study models is an option, it may also compound
the error with its own innate amount of error it introduces. Intraoral scanning of the patients with
quantitative computer analysis would therefore minimize the error potential. Interexaminer and
intraexaminer reliability would also be eliminated as a factor when recording the measurements.
Furthermore, cephalometric values were limited to the ANB, SN-GoGn, and Wits for this study,
which did not allow as comprehensive of an assessment. An assessment using a greater number
of cephalometric measurements would therefore provide a more in depth understanding of the
dental and skeletal relationships to each other.
VII. Conclusion
This study was completed to achieve an initial overview of the dental and skeletal norms
in people of Vietnamese descent. The primary findings of this study include the following:
1. The patients exhibited molar relationships of Class I, II, and III in order of decreasing
frequency.
2. Mean overjet and overbite values were increased compared to ideal values.
49

3. Only 39.5% of the patients exhibited tooth shoveling, which did not account for all
increased overjet values but was a contributing factor in this group of Vietnamese
individuals.
4. Crossbites were present in almost half of the sample.
5. Ovoid arch forms were the most common in the maxilla and mandible.
6. Patients on average exhibited an increased ANB value and steep mandibular plane angles
compared to traditional Steiner norms.
7. Wits values were more positive in males and more negative in females in this study,
suggesting a flatter occlusal plane in females.
Although the findings of this study were not consistent with previous reports, the results can
nonetheless be used as an aid to better diagnose and tailor treatment for Vietnamese patients,
respecting the anatomic nature specific to their ethnic group.

50

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Creator Hudson, Tiffany Lee (author)

Core Title An overview of the dental and skeletal relationships in individuals of Vietnamese ancestry

School School of Dentistry

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Degree Program Craniofacial Biology

Publication Date 03/11/2019

Defense Date 02/22/2019

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