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Prevalence of arch form types and tooth size discrepancy in a Vietnamese population

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Prevalence of arch form types and tooth size discrepancy in a Vietnamese population

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Content Prevalence of arch form types and tooth size discrepancy in a
Vietnamese population
by
Cameron Freelove
A Thesis Presented to the
FACULTY OF THE USC HERMAN OSTROW SCHOOL OF
DENTISTRY
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
MASTER OF SCIENCE
CRANIOFACIAL BIOLOGY
May 2020

2020 Cameron Freelove
ii

Table of Contents
List of Tables……………………………………………………………………………………..iii
List of Figures…………………………………………………………………………………….iv
Abstract…………………………………………………………………………………………...v
Introduction………………………………………………………………………………………..1
Anthropological Origins…………………………………………………………………..1
Angle Classification……………………………………………………………………….2
Overbite and overjet……………………………………………………………………….2
Shovel shaped incisors…………………………………………………………………….3
Crossbite…………………………………………………………………………………..5
Archform…………………………………………………………………………………..5
Crowding…………………………………………………………………………………..6
Bolton Ratio…………………………………………………………………………….....8
Materials and Methods………………………………………………………………………….....9
Results……………………………………………………………………………………………11
Angle Classification……………………………………………………………………...11
Overbite and overjet……………………………………………………………………...14
Shovel shaped incisors…………………………………………………………………...14
Crossbite…………………………………………………………………………………15
Archform…………………………………………………………………………………17
Crowding…………………………………………………………………………………23
Bolton Ratio…………………………………………………………………………….. 23
Conclusions………………………………………………………………………………………23
References………………………………………………………………………………………..27

iii

List of Tables
Table 1…………………………………………………………………………………………...11
Table 2…………………………………………………………………………………………...17

iv

List of Figures
Figure 1……………………………………………………………………………………………4
Figure 2……………………………………………………………………………………………7
Figure 3…………………………………………………………………………………………..10
Figure 4…………………………………………………………………………………………..12
Figure 5…………………………………………………………………………………………..12
Figure 6………………………………………………………………………………………….13
Figure 7…………………………………………………………………………………………..14
Figure 8…………………………………………………………………………………………..15
Figure 9…………………………………………………………………………………………..16
Figure 10…………………………………………………………………………………………16
Figure 11…………………………………………………………………………………………17
Figure 12…………………………………………………………………………………………18
Figure 13…………………………………………………………………………………………19
Figure 14…………………………………………………………………………………………19
Figure 15…………………………………………………………………………………………20
Figure 16…………………………………………………………………………………………21
Figure 17…………………………………………………………………………………………22
Figure 18…………………………………………………………………………………………22
v

Abstract
Background: Many of the dental norms used in orthodontic treatment planning are based on
Caucasian peoples. There is limited research on dental norms for Vietnamese peoples, which
hinders the orthodontist’s ability to properly treatment plan for Vietnamese patients.
Objective: The purpose of this study is to help create a reference that outlines an overview of the
dental characteristics of the Vietnamese people.
Materials and Methods: Initial records (plaster study models) of 159 patients (49 male, 110
female) of Vietnamese descent were collected from a private orthodontic practice in Southern
California. The inclusion criteria for this study were: subject was to be of Vietnamese descent,
subject had to have complete records, subject had to have not completed any previous
orthodontic treatment, subject had to have had permanent 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. The plaster study models were fabricated from alginate impressions and were
trimmed according to wax bites recorded in centric occlusion. Measurements were taken using
Mitutoyo digital calipers and were rounded to the nearest hundredth of a millimeter. All the
models were analyzed and recorded by two investigators for the following measurements: Angle
classification, overbite, overjet, presence of tooth shaped incisors, presence of anterior and
posterior crossbite, arch form, crowding, and Bolton discrepancy.
Results: Angle classification in the total sample and in the female subdivision exhibited class 1,
2, and 3 malocclusions in decreasing frequency. The male subdivision, however, exhibited class
1, 3, and 2 malocclusions in decreasing frequency. The mean overbite of the sample was 2.6 ±
2.2 mm and the mean overjet was 3.5 ± 3.3mm. Shovel shaped incisors were prevalent in 57.2%
of the subjects. Posterior crossbite was prevalent in 23% of the subjects and anterior crossbite in
vi

32%. Arch form was recorded as follows in decreasing frequency: ovoid, square, tapered. The
average crowding in the sample was 3.2 ± 3.8mm in the mandible and 3.8 ± 3.8mm in the
maxilla. The overall Bolton ratio in the sample was 91.6 ± 2.9% and the anterior Bolton ratio
was 78.8 ± 4.8%.
Conclusions: The subjects showed Angle molar classification in decreasing frequency from
class 1, 2, and 3. The mean overjet and overbite values were greater than established ideal norms.
Shovel shaped incisors were present in 57.2% of the subjects, which is consistent with
Mongoloid dental features. Posterior crossbite of at least one tooth was present in 23% of the
subjects, anterior crossbite of at least one tooth was present in 32% of the subjects. Ovoid was
the most common arch form, followed by square, and then tapered. On average, subjects
exhibited mild to moderate crowding. Bolton’s tooth sized ratios can be used appropriately for
Vietnamese peoples.
1

Introduction
Orthodontic treatment is highly dependent on the goals set forth by the orthodontist
during the treatment planning stage. During this initial period of treatment, the orthodontist
reviews and evaluates the records obtained from the patient and uses these records to formulate a
treatment plan. Based on the orthodontist’s knowledge of normal occlusion and his/her
subjective views regarding esthetics, the orthodontist decides where he or she wants to place the
teeth relative to the patient’s skeletal base and facial soft tissue. These subjective views are very
often influenced by standards and norms established in previous studies that are published in the
orthodontic literature and taught in orthodontic graduate programs across the United States and
the rest of the world. However, many of the norms and values of normal occlusion taught and
accepted by the orthodontic community are based on Caucasian populations. This creates a
problem as many of the patients treated by orthodontists are not Caucasian and are thus defined
by an entirely different set of occlusal norms and even cultural values regarding dental and facial
esthetics.
There are many studies evaluating the characteristics of occlusion in various ethnicities,
however there is a dearth of literature investigating the dental and occlusal characteristics of the
Vietnamese people. The purpose of this study is thus to help create a reference that outlines an
overview of the dental characteristics of the Vietnamese people. The dental characteristics
investigated in this study were Angle classification, overbite/overjet, shovel-shaped incisors,
crossbite, arch form, crowding, and Bolton discrepancy.
Anthropological origins
In The Origin of the Races
1
, anthropologist Carleton Coon categorized humans into five
distinct races: Caucasoid, Mongoloid, Australoid, Negroid, and Capoid. These categories were
2

derived from many factors, including geographical migration and phenotypic features.
Vietnamese peoples are classified under Mongoloid peoples, along with the rest of South Asian
peoples, Native Americans, Polynesians, along with some others. Although diverse, Mongoloids
share many skeletal and dental features, such as an increased tendency towards shovel-shaped
incisors
2
. These differences in dental features are likely due to genetic differences between these
different races and populations. For instance, alterations in the genes Msx1 and Pax9 have been
identified in peoples with molar oligodontia
3
. Other variations in dental phenotypic patterns seen
in Vietnamese peoples include lower mandibular incisor hypodontia
3
.
Angle Classification
Edward Angle formulated the molar Angle classification in 1899
4
, and since then its use
in diagnosis and treatment planning has been ubiquitous in orthodontics. He classified molar
relationships as either Class 1, 2, or 3, depending on the position of the maxillary and mandibular
first molars relative to each other in the sagittal plane.
A systematic review by Alhammadi et al. on global traits of malocclusion
5
combined
studies that looked at the Angle classification of many ethnicities and found that the global
distribution of Angle classification is: Class 1 (72.9%), Class 2 (23.11%), and Class 3 (3.98%).
When separated into individual races, the review found that the prevalence of Angle Class 1, 2,
and 3 in Caucasians were 71.61%, 22.9%, and 5.92% respectively, compared to 74.87%,
14.14%, and 9.63% in Mongoloid populations. This suggests a trend towards higher rate of Class
3 malocclusions in Mongoloid peoples. Previous studies looking at Angle classification in
Vietnamese subjects support this trend towards Class 3. Nguyen et al.
6
found that the prevalence
of Class 1, 2, and 3 were 67%, 17.5%, and 15.5% when looking at groups of 12 and 18 year olds
from Da Nang, Vietnam, while Lee
7
found a prevalence of 55% Class 1, 29% Class 2, and 16%
3

Class 3 when evaluating right molar classification in subjects of Vietnamese ethnicity in
Southern California.
Overbite and overjet
Overbite refers to the vertical overlap of a person’s maxillary incisors relative to the
mandibular incisors, while overjet refers to the horizontal overlap of the maxillary incisors to the
mandibular incisors. In current guidelines and practice, orthodontists strive to set overbite at 1-2
mm and overjet at 2-3 mm in most cases.
8

The systematic review on the global traits of malocclusion
5
found that Caucasians exhibit
deepbite (more than 2.5mm) more often than Mongoloids (22.95% vs 19.5%). Mongoloids were
slightly less likely to exhibit an openbite (zero to negative overbite) than Caucasians (3.27% vs
4.52%). Sathler et al.
9
compared the overbites between Caucasian, Japanese-Brazilian, and
Mongoloid groups, finding that Caucasians exhibited the greatest overbites 2.99 ± 1.15 mm. This
was followed by the Mongoloid group at 2.57 ± 1.11 mm and finally the Japanese-Brazilian
group at 2.23 ± 1.40 mm. This finding supports the notion that Caucasians display deeper bites
than Mongoloid populations. Nguyen’s
6
sample of Vietnamese subjects found that increased
overbite (>3.5mm) existed in 26.3% of the sample, however there was no data on openbite.
Lee’s
7
sample of Vietnamese subjects had a mean overbite of 2.7 ± 1.8mm.
Overjet values found in the systematic review by Alhammadi et al.
5
found that
Caucasians were more likely to have increased overjet (>3mm) when compared to Mongoloids
(22.29% vs 12.87%) for increased overjet. Conversely, Mongoloids were more likely to have
reverse overjet (crossbite of all four incisors) than Caucasians (3.99% vs 10.87%). This trend
towards increased overjet in Causcasians is contradicted by Sathler et al
9
, who found overjet
values of 2.79 ± .76mm for Mongoloids vs 2.66 ± .66mm for Causcasians. Lee’s
7
sample of
4

Vietnamese subjects had a mean overjet of 3.5 ± 2.8mm.
Shovel Shaped Incisors
Shovel shaped incisors are a dental trait in which very prominent lingual marginal ridges
of a maxillary incisor create a scooped out or shovel like appearance of the maxillary incisor.
Fig.1

Shovel shaped incisors are known to be a common feature in Mongoloid populations. Studies by
Dahlberg
10
and Hanihara
11
found shovel incisors to be prevalent in up to 90% of some
Mongoloid populations, compared to less than 2% in Whites. Shovel shaped incisors have been
found to be associated with a missense mutation in the Ectodysplasin A Receptor (EDAR)
gene
12
. This creates the V370A allele isoform of this gene responsible for tooth shoveling. This
5

allele is more heavily present in Mongoloid populations, likely resulting in the greater expression
of the incisor shoveling phenotype. Lee
7
found that 39.5% of Vietnamese displayed shovel
shaped incisors.
Crossbite
Dental crossbite exists in two forms: anterior and posterior crossbite. An anterior
crossbite exists when the maxillary anterior teeth are in a lingual position relative to the
mandibular anterior teeth. A posterior crossbite exists when the buccal cusps of the maxillary
posterior teeth are in a lingual position relative to the buccal cusps of the mandibular posterior
teeth (lingual posterior crossbite) or when the lingual cusps of the maxillary posterior teeth are in
a buccal position relative to the buccal cusps of the mandibular posterior teeth (buccal crossbite).
The systematic review by Alhammadi et al
5
found that 10.87% of Mongoloid populations
had anterior crossbite, compared to 3.99% in Caucasian populations. Their group also found that
Mongoloids had a 7.53% prevalence of posterior crossbite (defined as at least two teeth in
crossbite) compared to a 10.08% prevalence in Caucasians. Mulimani et al.
13
found that 48.2%
of a combined sample of Chinese, Malay, and Indian subjects had posterior crossbite and 30.4%
had anterior crossbite. Nguyen et al.
6
recorded a posterior crossbite prevalence of 22.8% in their
Vietnamese sample. Lee
7
found a prevalence of crossbite (anterior and posterior combined) in
47.9% of Vietnamese subjects.
Arch Forms
Dental arch forms are determined by the anatomy and geometry of a person’s alveolar
ridge and overlying teeth. Mclaughlin and Bennet
14
stated “if the arch form is changed, it tends
to return to its original shape, and the pre-treatment shape of the arch is the best guide to use for
arch form.” With this guiding principle in mind, orthodontists try to treat the patient without
6

changing their pre-treatment arch form in most clinical scenarios. To do so would risk instability.
This means that knowing a certain population’s tendencies when it comes to arch form could be
a valuable clinical tool. To help with treating patients with varying arch forms, Mclaughlin and
Bennet recommend carrying three types of archwire forms: tapered, ovoid, and square. This
allows the orthodontist to use the archwire that is most compatible with each patient’s pre-
treatment arch form.
Most studies show that Caucasians tend towards ovoid and tapered arches, with square
arch forms being the least prevalent. Ferro et al.
15
found that mandibular arch forms were 42.5%
ovoid, 42.5% tapered, and 15.1% square in a sample of Italian subjects. Another study by
Bayome et al.
16
looking at North American Caucasians saw mandibular arch forms that were
42% ovoid, 37% tapered, and 21% square. One more by Nojima et al.
17
found mandibular arch
forms that were 43.8% tapered, 38.1% ovoid, and 18.1% square in a Caucasian sample.
Trang et al.
18
compared arch form prevalence between North American Caucasians and
Vietnamese groups. They found that the Caucasian arch forms were 34.4% tapered, 27.1%
ovoid, and 38.5% square. These results show a higher tendency towards square archforms than
most other studies, however the distribution is still very different from the Vietnamese group
results, showing 13.3% tapered, 23% ovoid, and 63.7% square arch forms. Another study
supports the notion that Vietnamese subjects have a greater inclination towards square arch
forms when compared to Caucasians. Lee et al.
19
found that mandibular arch forms were 26.9%
ovoid, 11.5% tapered, and 61.5% square in a group of Vietnamese subjects. One more study by
Lee
7
contradicts this notion however, as her Vietnamese group showed mandibular arch forms
that were 60% ovoid, 28% square, and 12% tapered.
Crowding
7

Dental crowding is the total overlap between teeth in a dental arch. The orthodontic
treatment modalities used to correct crowding include creation of space through extraction or
interproximal reduction, or through dental arch expansion. These treatment choices have many
considerations, including dental and facial esthetics, periodontal concerns, stability, and patient
desires. Therefore, knowledge of a group’s crowding tendencies combined with an
understanding on that group’s feelings towards certain dento-facial esthetic inclinations can help
inform the orthodontist during treatment planning.
A study by Mulimani et al.
13
compared dental crowding between Malay, Chinese, and
Indian orthodontic patients (Fig 2). They found that in the maxillary arch, 33.3% of Malays, 26%
of Chinese, and 43.8% of Indians had minor (1-3mm) crowding, 16.7% of Malays, 24% of
Chinese, and 21.9% of Indians had moderate (4-6mm) crowding, and 20% of Malays, 26% of
Chinese, and 12.5% of Indians had severe (>7mm) crowding. In the mandibular arch, 36.7% of
Malays, 48% of Chinese, and 31.3% of Indians had minor crowding, 30.0% of Malays, 16% of
Chinese, and 31.3% of Indians had moderate crowding, and 10.0% of Malays, 20.0% of Chinese,
and 12.5% of Indian had severe crowding.

Fig 2

8

Bolton Ratio
The Bolton ratio compares the mesio-distal width of the maxillary teeth from first molar
to first molar to the mesio-distal width of the mandibular teeth from first molar to first molar. At
an ideal ratio, the mandibular teeth will fit well with the maxillary teeth when all other factors
are considered (class 1 cuspid, ideal overbite/overjet, etc). Bolton determined this ratio to be
91.3±1.91 from first molar to first molar and 77.2±1.65 from canine to canine
20
. A ratio greater
than these values indicated mandibular excess and would require mandibular arch shortening
(through extraction or IPR) or maxillary arch lengthening (through restoration) for ideal
occlusion of the arches. A ratio less than these values indicated maxillary excess and would
require maxillary arch shortening and/or mandibular arch lengthening for ideal occlusion of the
arches. Can these ratios be applied to all ethnicities though, or to the Vietnamese?
Fernandes et al.
21
compared Bolton ratios between black, white, afro-Mediterranean, and
Japanese groups. They concluded that there was no statistically significant difference in tooth
size discrepancy except the anterior ratio in the Japanese group was significantly less (maxillary
anterior excess). Endo et al.
22
looked at Bolton ratios in Japanese subjects and found that the
Japanese anterior ratio showed a significant difference with mandibular excess. Nourallah et al.
23

concluded that Bolton’s ratios can be applied to Syrians as there was no significant difference
between the Syrian group and Bolton’s established ratios. Paredes et al.
24
concluded that “tooth
size does indeed have a strong ethnic component” as they determined that Peruvians had a
greater anterior Bolton ratio than Spanish groups. Depending on the ethnicity and the location of
the discrepancy (anterior), it seems there is some credence to the idea of separate Bolton ratio
standards.
Materials and Methods
9

Initial records (plaster study models) of 159 patients (49 male, 110 female) of
Vietnamese descent were collected from a private orthodontic practice in Southern California.
The inclusion criteria for this study were: subject was to be of Vietnamese descent, subject had
to have complete records, subject had to have not completed any previous orthodontic treatment,
subject had to have had permanent 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.
The plaster study models were fabricated from alginate impressions and were trimmed
according to wax bites recorded in centric occlusion. Measurements were taken using Mitutoyo
digital calipers and were rounded to the nearest hundredth of a millimeter. All the models were
analyzed and recorded by two investigators for the following measurements:
1. Angle classification: The molar classification as defined by the Angle classification was
observed and recorded for both the right and left molars of each subject. The extent of the
classification was not recorded, merely which classification existed. The molar Angle
classification is defined as follows for a Class I occlusion: The mesiobuccal cusp of the
maxillary first permanent molar occludes with the mesiobuccal groove of the mandibular first
permanent molar. Any occlusion that was observed with the maxillary first molar mesiobuccal
cusp being mesial or distal to the buccal groove of the mandibular first molar was recorded as a
Class II or Class III relationship, respectively.
2. Overjet and overbite: Overjet and overbite were recorded according to standards set forth by
the American Board of Orthodontics. Overjet was measured as the greatest measurement
between two antagonistic anterior teeth (lateral and/or central incisors) comprising the greatest
overjet and is measured from the facial surface of the most lingual tooth (Mx or Mn) to the
10

middle of the incisal edge of the more facially positioned tooth (Mx or Mn). Overbite was
measured as the greatest distance between the incisal edges of two antagonistic incisors.
Openbites were recorded as negative overbites.
3. Shovel Shaped Incisors: All maxillary central incisors were subjectively evaluated for the
presence or absence of shovel shaped incisors.
4. Crossbite: Subjects were evaluated for the presence or absence of both anterior and posterior
crossbites. The threshold for qualification of crossbite was a single tooth in crossbite. The degree
of any posterior crossbite was not evaluated. The degree of any anterior crossbite was recorded
as negative overjet.
5. Arch Form: All mandibular arch forms were recorded subjectively as either ovoid, tapered, or
square using McLaughlin Bennet archforms as reference.
Fig. 3

6. Archlength discrepancy: Crowding was evaluated in each arch and recorded. Crowding in
each arch was measured by recording and summing the distances of overlap between each tooth
and subtracting the sum of all spaces between teeth in the arch.
7. Bolton discrepancy: Bolton discrepancy was evaluated via the following formula:
11

∑(U6-U6)/∑(L6-6). The sum of the tooth length from first molar to first molar in the maxillary
arch was divided by the sum of tooth length from first molar to first molar in the mandibular
arch.
Ten casts were used to test intraexaminer reliability. The casts were measured for all
measurements taken for the study and then again one week later. The intraclass correlation
coefficient for each measurement were as follows: right molar angle classification (1.00), left
molar angle classification (1.00), overbite (.98), overjet (.99), shovel shaped incisors (.8),
anterior crossbite (1.00), posterior crossbite (1.00), arch form (1.00), maxillary arch length
discrepancy (.98), mandibular archlength discrepancy (.97), and mesio-distal tooth width (.99).
Results:
Angle Classification
Angle Classification was evaluated and categorized as either Class I, Class II, or Class III
for the each the left and right side of the patient’s occlusion. Class 1 occlusion was present on the
right and left sides in 58% and 64% of the subjects respectively, class II occlusion was present
on right and left sides in 23% and 19% respectively, and class III occlusion was present on left
and right sides in 19% and 17% respectively.
Table 1.

Right Molar (n) Left Molar (n)
Class 1 93 102
Class 2 35 29
Class 3 31 28
Total 159 159

12

Fig. 4

Fig. 5

58%
23%
19%
Right Molar Angle Classification
Class 1
Class 2
Class 3
64%
19%
17%
Left Molar Angle Classification
Class 1
Class 2
Class 3
13

Subjects were then assessed for angle classification by sex. Only right molar
classification was evaluated. Males in the study exhibited 51% class 1, 20% class 2, and 29%
class 3 occlusions, while females exhibited 62% class 1, 23% class 2, and 15% class 3
occlusions.
Fig. 6

51%
20%
29%
Right Side Angle Classification Male
Class 1
Class 2
Class 3
14

Fig. 7

Overbite and Overjet
The mean overbite of the subjects was 2.6 ± 2.2 mm, with values ranging from -3.84 to 9
mm. A majority of the subjects had a positive overbite (n=139, 87.4%), leaving (n=20, 12.6%)
with an openbite.
The mean overjet of the subjects was 3.5 ± 3.3 mm, with values ranging from -9.9 to 12.7
mm. A majority of the patients had a positive overjet (n=132, 83.0%), leaving (n=27, 17.0%)
with a negative overjet.
Shovel Shaped Incisors
Shovel shaped incisors were found in 57.2% (n=91) of the subjects.

62%
23%
15%
Right Side Angle Classification Female
Class 1
Class 2
Class 3
15

Fig. 8

Crossbite
Posterior crossbite was present in 23% (n=36) of subjects. Anterior crossbite was present
in 32% (n=51) of subjects.

57%
43%
Shovel Shaped Incisors
Y
N
16

Fig. 9

Fig. 10

23%
77%
Posterior Crossbite
Posterior crossbite present
Posterior crossbite not present
32%
68%
Anterior Crossbite
Anterior crossbite present
Anterior Crossbite not present
17

Arch Form
Mandibular arch form was evaluated for each subject using McLaughlin Bennet arch
forms. Table 2 shows the distribution of arch forms and fig. 11 shows the percentage of each
archform relative to the total number of subjects. Ovoid was the most common archform with
48%, followed by square at 41% and tapered at 11%.
Table 2
Archform (n)
Ovoid 77
Tapered 17
Square 65

Fig. 11

48%
11%
41%
Archform
Ovoid
Tapered
Square
18

Fig 12

Arch form was further categorized by right and left side molar Angle classification. The
ovoid archform was the most common in Class 1 subjects, being present in 51% of both right and
left side molar class 1 subjects. This was followed by square archforms, which consisted of 40%
and 38% of right and left side molar class 1 subjects respectively. Tapered archforms were the
least common in class 1 subjects, being present in 9% and 11% of right and left side molar class
1 subjects.

0
10
20
30
40
50
60
ovoid square tapered ovoid square tapered ovoid square tapered
Class 1 Class 2 Class 3
Arch form by Molar Classification
Right molar Left molar
19

Fig. 13

Fig. 14

51%
40%
9%
Right molar class 1
ovoid
square
tapered
51%
38%
11%
Left molar class 1
ovoid
square
tapered
20

The ovoid archform was most common in left side molar class 2 subjects, however
square and ovoid archforms were equally present in right side molar class 2 subjects. Ovoid
archforms were present in 46% and 56% of right and left side class 2 subjects while square
archforms were present in 40% and 37% of right and left side class 2 subjects. Tapered
archforms were the least common among class 2 subjects, presenting in 14% and 7% of class 2
subjects.
Fig. 15

46%
40%
14%
Right molar Class 2
ovoid
square
tapered
21

Fig. 16

The ovoid archform was the most common in the right side molar class 3 subjects,
however square archforms were more common in left side molar class 3 subjects. Ovoid
archforms were present in 51% and 39% of right and left side molar class 3 subjects while square
archforms were present in 39% and 50% of right and left molar class 3 subjects. Again, tapered
archforms were the least common among class 3 subjects, presenting in 10 and 11% of right and
left side molar class 3 subjects.

56%
37%
7%
Left molar class 2
ovoid
square
tapered
22

Fig. 17

Fig. 18

51%
39%
10%
Right molar class 3
ovoid
square
tapered
39%
50%
11%
Left molar class 3
ovoid
square
tapered
23

Archlength Discrepancy
The mean archlength discrepancy in the maxilla was 3.2 ± 3.8 mm with values ranging
from -9.9 mm to 15.1 mm. The mean archlength discrepancy in the mandible was 3.8 ± 3.8 mm,
with values ranging from -6.7 mm to 16mm.
Bolton Discrepancy
The mean Bolton discrepancy was 91.6 ± 2.9%, denoting a very slight average
mandibular excess of .3%. Anterior Bolton discrepancy was 78.8 ± 4.8%, denoting an average
mandibular excess of 1.6%.
Discussion
The prevalence of Angle Classification in this study showed that class 1 occlusions were
most common, followed by class 2, and least prevalent was class 3 on both left and right sides.
When dividing the groups by sex however, it was found that males had a greater prevalence of
class 3 than class 2 occlusion. Ignoring that, these findings are consistent with the studies
mentioned earlier by Alhammadi
5
, Nguyen
6
, and Lee
7
. While class 3 was the least common
classification, it was more prevalent in this Vietnamese sample than in the white population
studied in Alhammadi’s
5
systematic review. This is also consistent with the same review’s
finding of increased class 3 prevalence in Mongoloid groups.
The mean overbite in the sample was 2.6mm. This is consistent with Sathler’s
9
findings
of 2.57mm in Mongoloids and Lee’s
7
of 2.7mm in Vietnamese. This means that by current
orthodontic guidelines, Vietnamese exhibit a slight deep bite on average. The variability is quite
high however, with a standard deviation nearly as great as the mean. 12.6% of the subjects had
anterior openbite. This is much greater than the values reported by Alhammadi
5
(3.27%).
24

The mean overjet in the sample was 3.5mm. Again, there was high variability with a
standard deviation nearly as great as the mean at 3.3mm. This is greater than Sathler’s
9
finding of
2.7mm but the same as Lee’s
7
at 3.5mm. By current orthodontic guidelines, Vietnamese show an
average tendency towards increased overjet. 17% of the sample had negative overjet, more than
the 10.87% described by Alhammadi
5
in Mongoloids.
57% of the sample exhibited shovel-shaped incisors, making it a common trait in the
studied group. This is consistent with Lee’s
7
finding of 60% and further solidifies the trend seen
of shovel-shaped incisors in Mongoloid peoples.
Posterior crossbite was present in 23% of the subjects. This is very similar to Nguyen’s
6

findings of 22.8% posterior crossbite in Vietnamese subjects, but more than Alhammadi’s
5

7.53% in Mongoloids. The last study only counted crossbite when at least two teeth were in
crossbite however, so a lower value is expected. Anterior crossbite was present in 32% of the
subject in this study. This is consistent with Mulimani’s
13
findings of anterior crossbite in 30.4%
of the combined sample of Chinese, Malay, and Indian groups (all Mongoloid populations), but
much greater than Alhammadi’s
5
10.87%. Again, this study required that all four incisors be in
crossbite to count and so a lower value is to be expected.
Contrary to the studies performed by Trang et al.
18
and Lee et al
19
, where the square arch
form was the most common at 63.7% and 61.5% respectively, our findings showed that the ovoid
arch form was the most common at 48%, with the square arch from next at 41% prevalence.
Tapered arch form was least prevalent at 11%. This is more in line with Lee’s
7
findings of ovoid
arch form at 60%, square at 28%, and tapered at 12% in Vietnamese subjects. Our findings are
somewhere in the middle of the previously reported Vietnamese values and the Caucasian values
reported by Ferro
15
, Bayome
16
, and Nojima
17
. Regardless of ovoid being the more common arch
25

form, this study does support the tendency towards increased prevalence of square arch forms
when compared to Caucasians groups. When arch form was subdivided by Angle classification,
arch form still followed the general trend of decreasing frequency from ovoid to square to
tapered. It was noted however, that when looking at class 3 subjects, there was only one less
subject with square arch form (n=26) than ovoid arch form (n=27) when right and left molar
classification was combined, meaning square arch form were practically as prevalent in class 3
subjects as ovoid arch forms.
Crowding in the mandible was 3.2 ± 3.8mm and 3.8 ± 3.8mm in the maxilla. The average
subject had mild to moderate crowding, however there was a very large amount of variance.
The overall Bolton ratio determined in the study was 91.6 ± 2.9% and the anterior Bolton
ratio was 78.8 ± 4.8%. These values are very similar to Bolton’s values of 91.3 ±1.9 and 77.2 ±
1.65
14
. Therefore, this study supports the notion that the tooth-size discrepancy values produced
by Bolton can be appropriately applied to a Vietnamese population.
A major limitation to this study is that 69% of the sample were female. This limits our
ability to apply our results and conclusions to an entire Vietnamese population, and especially
men. More male subjects would help improve the scope and applicability of our results.
Furthermore, all measurements were taken using digital calipers from stone casts fabricated from
alginate impressions. Alginate impressions and the pouring process used to create stone models
from them introduce a degree of error. There is additional error introduced by manual
measurement via calipers. This could be improved in future studies with computer aided
measurements made from intraoral 3D scans. Another limitation to this study was the degree of
subjectivity involved in our measurements. Angle classification, shovel-shaped incisors,
crossbite, and arch form were all measured subjectively by the two examiners. As said before, if
26

the models could be uploaded digitally, a mathematical algorithm could help create a more
objective way to measure the stone models. Finally, the models were measured by two separate
examiners, which could have led to inconsistencies in the measurement process.
Conclusions
The aim of this study was to help give an overview of the dental characteristics of the
Vietnamese people. With that in mind, here are the takeaways elucidated from the data gathered.
1. The subjects showed Angle molar classification in decreasing frequency from class 1, 2,
and 3.
2. The mean overjet and overbite values were greater than established ideal norms.
3. Shovel shaped incisors were present in 57.2% of the subjects, which is consistent with
Mongoloid dental features.
4. Posterior crossbite of at least one tooth was present in 23% of the subjects, anterior
crossbite of at least one tooth was present in 32% of the subjects.
5. Ovoid was the most common arch form, followed by square, and then tapered.
6. On average, subjects exhibited mild to moderate crowding.
7. Bolton’s tooth sized ratios can be used appropriately for Vietnamese peoples.

27

References
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(2) Adams, Bradley J. (2007). Forensic Anthropology. USA: Chelsea House. Page 44.
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unique form of hypodontia seen in Vietnamese patients: clinical and molecular analysis. J Med
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(4) Angle EH. Classification of malocclusion. Dent Cosmos. 1899;41:248-64. Frazier-Bowers
(5) Alhammadi, Maged Sultan et al. Global distribution of malocclusion traits: A systematic
review. Dental Press J. Orthod. 2018, vol.23, n.6, pp.40.e1-40.e10.
(6) Nguyen, S.M., Nguyen, M.K., Saag, M., and Jagomagi, T. (2014). The Need for Orthodontic
Treatment among Vietnamese School Children and Young Adults. Int J Dent 2014, 132301.
(7) Lee. (2019). An Overview of the Dental and Skeletal Relationships in Individuals of
Vietnamese Ancestry.
(8) Proffit, William R. Contemporary Orthodontics. Elsevier, 2015:7.
(9) Sathler, R., Pinzan, A., Fernandes, T.M., de Almeida, R.R., and Henriques, J.F. (2014).
Comparative study of dental cephalometric patterns of Japanese-Brazilian, Caucasian and
Mongoloid patients. Dental Press Journal of Orthodontics 19, 50-57.
(10) Dahlberg AA. The dentition of the American Indian. In:Laughlin WS, ed. The physical
anthropology of the American Indian. New York:Viking Fund, 1951.
(11) Hanihara K. Mongoloid dental complex in the permanent dentition: Proceedings VIIIth
International Congress of Anthropological and Ethnological Sciences. Tokyo: Science Council
of Japan, 1968:298-300.
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(12) Kimura, R., Yamaguchi, T., Takeda, M., Kondo, O., Toma, T., Haneji, K., Hanihara,
T.,Matsukusa, H., Kawamura, S., Maki, K., et al. (2009). A common variation in EDAR is a
genetic determinant of shovel-shaped incisors. American Journal of Human Genetics 85, 528-
535.
(13) Mulimani, S., Azmi, M., Jamali, N., Basir, N., Soe, H. Occlusal characteristics and ethnic
variations in Malaysian orthodontic patients. Singapore Dental Journal. 38 (2017):71-77.
(14) Bennett, J. McLaughlin, R. Fundamentals of Orthodontic Treatment Mechanics. Le Grande
Publishing. (2014):86.
(15) Ferro, R., Pasini, M., Fortini, A., Arrighi, A., Carli, E., and Giuca, M.R. (2017). Evaluation
of maxillary and mandibular arch forms in an Italian adolescents sample with normocclusion.
European Journal of Paediatric Dentistry 18, 193-198.
(16) Bayome, M., Sameshima, G.T., Kim, Y., Nojima, K., Baek, S.H., and Kook, Y.A. (2011).
Comparison of arch forms between Egyptian and North American white populations. American
Journal of Orthodontics and Dentofacial Orthopedics 139, e245-252.
(17) Nojima, K., McLaughlin, R.P., Isshiki, Y., and Sinclair, P.M. (2001). A comparative study
of Caucasian and Japanese mandibular clinical arch forms. The Angle orthodontist 71, 195-200.
(18) Trang, V.T., Park, J.H., Bayome, M., Shastry, S., Mellion, A., and Kook, Y.A. (2015).
Evaluation of arch form between Vietnamese and North American Caucasians using 3-
dimensional virtual models. Anthropologischer Anzeiger 72, 223-224.
(19) Lee, K.J., Trang, V.T., Bayome, M., Park, J.H., Kim, Y., and Kook, Y.A. (2013).
Comparison of mandibular arch forms of Korean and Vietnamese patients by using facial axis
points on three-dimensional models. Korean J Orthod 43, 288-293.
(20) Bolton, WA 1962The clinical application of a tooth-size analysis. Am J Orthod 48:504-29.
29

(21) Fernandes, TM., Janson, G., Pinzan, A., Sathler, R., de Freitas, LM., de Freitas, MR., (2010)
Applicability of Bolton tooth-size ratios in ratio groups. World Journal of Orthodontics.
11(4):e57-62.
(22) Endo, Toshiya, et al. Applicability of Boltons Tooth Size Ratios to a Japanese Orthodontic
Population. Odontology, vol. 95, no. 1, 2007, pp. 57–60.
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tooth-size harmony in a Syrian population. Angle Orthodontist. 75(6):996-9.
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Populations; Spanish and Peruvian. A Comparative Study.” Medicina Oral Patología Oral y
Cirugia Bucal, 2011, 16(4):e593-9.

Abstract (if available)

Abstract Background: Many of the dental norms used in orthodontic treatment planning are based on Caucasian peoples. There is limited research on dental norms for Vietnamese peoples, which hinders the orthodontist’s ability to properly treatment plan for Vietnamese patients. ❧ Objective: The purpose of this study is to help create a reference that outlines an overview of the dental characteristics of the Vietnamese people. ❧ Materials and Methods: Initial records (plaster study models) of 159 patients (49 male, 110 female) of Vietnamese descent were collected from a private orthodontic practice in Southern California. The inclusion criteria for this study were: subject was to be of Vietnamese descent, subject had to have complete records, subject had to have not completed any previous orthodontic treatment, subject had to have had permanent 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. The plaster study models were fabricated from alginate impressions and were trimmed according to wax bites recorded in centric occlusion. Measurements were taken using Mitutoyo digital calipers and were rounded to the nearest hundredth of a millimeter. All the models were analyzed and recorded by two investigators for the following measurements: Angle classification, overbite, overjet, presence of tooth shaped incisors, presence of anterior and posterior crossbite, arch form, crowding, and Bolton discrepancy. ❧ Results: Angle classification in the total sample and in the female subdivision exhibited class 1, 2, and 3 malocclusions in decreasing frequency. The male subdivision, however, exhibited class 1, 3, and 2 malocclusions in decreasing frequency. The mean overbite of the sample was 2.6 ± 2.2 mm and the mean overjet was 3.5 ± 3.3 mm. Shovel shaped incisors were prevalent in 57.2% of the subjects. Posterior crossbite was prevalent in 23% of the subjects and anterior crossbite in 32%. Arch form was recorded as follows in decreasing frequency: ovoid, square, tapered. The average crowding in the sample was 3.2 ± 3.8 mm in the mandible and 3.8 ± 3.8 mm in the maxilla. The overall Bolton ratio in the sample was 91.6 ± 2.9% and the anterior Bolton ratio was 78.8 ± 4.8%. ❧ Conclusions: The subjects showed Angle molar classification in decreasing frequency from class 1, 2, and 3. The mean overjet and overbite values were greater than established ideal norms. Shovel shaped incisors were present in 57.2% of the subjects, which is consistent with Mongoloid dental features. Posterior crossbite of at least one tooth was present in 23% of the subjects, anterior crossbite of at least one tooth was present in 32% of the subjects. Ovoid was the most common arch form, followed by square, and then tapered. On average, subjects exhibited mild to moderate crowding. Bolton’s tooth sized ratios can be used appropriately for Vietnamese peoples.

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Asset Metadata

Creator Freelove, Cameron (author)

Core Title Prevalence of arch form types and tooth size discrepancy in a Vietnamese population

School School of Dentistry

Degree Master of Science

Degree Program Craniofacial Biology

Publication Date 04/20/2020

Defense Date 02/20/2020

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

Tag archform,Bolton discrepancy,OAI-PMH Harvest,Vietnamese

Language English

Contributor Electronically uploaded by the author (provenance)

Advisor Ahn, Ji (committee member), Paine, Michael (committee member), Sameshima, Glenn (committee member)

Creator Email cameronfreelove50@gmail.com

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c89-282609

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

Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the a...

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