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Cephalometric norms for the Vietnamese: a clinical appraisal

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Cephalometric norms for the Vietnamese: a clinical appraisal

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Cephalometric Norms for the Vietnamese:
A Clinical Appraisal

by
James Spencer Bisbas

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

Copyright 2020 James Spencer Bisbas
ii
Table of Contents
List of Tables…………………………………………………………..…………………...…….iii
List of Figures………………………………………………………….…………………………iv
Abstract……………………………………………………………………...…………………….v
Introduction…………………………………………………………………..……………………1
Materials and Methods……………………….……………………………..………………..……7
Results………………….…………..…………………….…………………………………..……9
a. ANB…………………………………………………………...………………………16
b. Wits……………………………………………………………………………………17
c. SN-GoGn………………………………………………………………………………18
d. U1-NA…………………………………………………………………………………19
e. L1-NA…………………………………………………………………………………20
f. Upper Lip to E-plane………………………………………………..…………………20
g. Lower Lip to E-plane………………………….………………………………………21

Discussion………………………….………………………………………………………….…22
a. Skeletal Classification …………………………………………...……………………22
b. Dental Protrusion……………………………...………………………………………24
c. Incisor Mandibular Plane Angle………...…………….………………………………25
d. Soft Tissue………………………………………………………….…………………25
e. Mandibular Angle……….……………………………….……………………………26

Conclusion………………..……….……………………………………..………………………27
References………..………………………………………………………………………………28

iii

List of Tables
Table 1 ……………………………………………………………………………………………9
Table 2…………………………………………………………………………………….……12
Table 3…………………………………………………………………………………………15

iv

List of Figures
Figure 1……………………………………………………………………………………………3
Figure 2……………………………………………………………………………………………5
Figure 3……………………………………………………………………………………………6
Figure 4……………………………………………………………………………………………8
Figure 5……………………………………………………………………………..……………16
Figure 6………………………………………………………………………………………..…17
Figure 7…….………………...………………………………………………………………..…18
Figure 8…….………………...……………………………………………..……………………19
Figure 9…….………………...………………………………………………………..…………20
Figure 10…….………………...…………………………………………………………………20
Figure 11…….………………...…………………………………………………………………21

v

Abstract
Background: Lateral Cephalometric radiographs are used in many orthodontic offices to
help diagnose the patients. Many of the analyses associated with these are based off of norms
that were established from a Caucasian population. This does not accurately represent other
ethnicities and may actually cause the treating orthodontist to make treatment decisions based off
of assumptions derived from the analyses. There have been attempts to do this in many
ethnicities, but there is limited information for the Vietnamese population in Vietnam. Due to the
rising economy and demand for orthodontic treatment in Vietnam, more representative data is
needed.
Objective: The purpose of this study was to help establish cephalometric measurements
that are more representative of the Vietnamese people while directly comparing and evaluating
the differences to established norms.
Materials and Methods: Lateral cephalometric radiographs were acquired for 159
Vietnamese patients. Inclusion criteria were as follows: permanent dentition with first molars
erupted into apparent occlusion, lips in a relaxed position, no previous or current orthodontic
treatment, no obvious pathology, and void of any craniofacial syndromes. Of the 159 radiographs
acquired, 104 were used in this study. A Steiner, Tweed, and Wits cephalometric analysis was
completed by a single investigator using the Patterson Dental Dolphin Imaging program. Data
collection and input was made using Microsoft Excel. Twenty-eight parameters were recorded
and included. All descriptive statistics and comparisons were also done in Microsoft Excel.
Results: The mean ANB was found to be 2.3 ± 2.8 degrees with 50% of the sample
established as skeletal Class I, 27% as Class II and 23% as Class III. Mean Wits was found to be
-1.8 ± 4.3 mm. The Upper Incisor to the Nasion-A Point angle (U1-NA) mean was found to be

vi

32.8 ± 7.3 degrees with the Lower Incisor to the Nasion-B Point angle (L1-NB) mean found to
be 31.7 ± 6.9 degrees. The mean angle between the Sella-Nasion line and the Gonion-Gnathion
line (SN-GoGn) of the sample was found to be 29.3 ± 6.0 degrees. Soft tissue measurements
were recorded as the lip in relation to the “E plane” and was found to be 1.1 ± 2.6 mm and 3.4 ±
2.7 mm for the upper and the lower lip respectively.
Conclusion: The Vietnamese individuals showed a Class I majority followed by Class II
and Class III, respectively. They also tended to have increased U1-NA and L1-NB measurements
leading to more protrusive dental characteristics. This is consistent with previous literature
showing a more protrusive soft tissue profile when compared to Rickett’s E-plane as well as the
U1-SN (deg) parameter.

1
Introduction
Diagnosis is critical in the orthodontic profession and often dictates the outcome of
treating orthodontic cases. When treatment planning orthodontic cases, it is important to
understand the position of the dentition within the craniofacial complex as well as the growth
and development of each individual as they mature. Cephalometrics has been established as our
profession’s attempt to provide an objective and reproducible technique to evaluate the
parameters of an individual in a subjective science. It is used globally as a technique to help
understand not only where the skeletal components and teeth are at the beginning of treatment,
but also the limitations of where these components can go. Cephalometric landmarks and norms
have already been established, but based off of a Caucasian population. This has an endless
effect on the diagnosis of individuals of other ethnicities.
There have been few attempts to establish more representative characteristics for the
Vietnamese population despite the noticeable limitations of the existing analyses. Attempts at
other ethnicities have been represented such as Bangladeshi (Alam, 2013), European (Miyajima,
1996) and Malaysian (Purmal, 2013), but due to recent economic improvements and the rise of
orthodontics in Vietnam, more accurate analyses are needed in order to prevent further
inaccuracies in diagnoses. The purpose of this study was to help establish cephalometric
measurements that are more representative of the Vietnamese population, while directly
comparing and evaluating the differences to established norms. Twenty-eight parameters were
included within this study, including factors such as ANB angle, upper incisor proclination,
lower incisor proclination, and soft tissue profile.

2
Establishment of Cephalometrics and Landmarks:
In 1931, Broadbent described the basis for the process of a lateral cephalometric
radiograph (Broadbent, 1931) in “A new X ray technique and its application to orthodontia.”
This opened the door for widespread use. Cecil Steiner was an advocate for this technique and its
advantages in the profession of Orthodontia laying out standard planes and angles that could be
used to help assess the patient (Steiner, 1959). This is a standard analysis that many use when
evaluating these radiographs despite any racial or cultural differences that may exist within the
patients and ignore that many of these norms were developed off of Caucasian populations.
Downs was also an advocate for this type of analysis emphasizing that deviations from ideals
affect the harmony seen in the face comparing to patients with excellent occlusions (Downs,
1948).
Tweed established the “Tweed Triangle” in “The diagnostic facial triangle in control of
treatment objectives” (Tweed, 1969). Tweed’s facial triangle is a well-utilized method in
evaluating the face with a focus on the position of the lower incisor position.
In South Africa, Jacobsen introduced a new parameter to help further define the
characteristics of the upper and lower jaw position. The Wits parameter uses A point and B point
on the maxilla and mandible in association to the occlusal plane (Jacobsen, 1975). It is often used
in conjunction with the ANB angle and commonly included in a traditional Steiner Analysis.
Origin:
Carlton Coon described his classification of five races in The Origin of Races. He
establishes the races of Mongoloid, Australoid, Caucasoid, Negroid, and Capoid. Below is an
3
ethnographic map originally taken from the Meyers Konversations-Lexikon:

Fig. 1
The Vietnamese population would be categorized under the Mongoloid population,
which encompasses people of East Asia, Central Asia, Southeast Asia, North Asia, Polynesia and
the Americas (Coon, 1962).
Craniofacial morphology changes with evolution creating common phenotypes of people
located in different areas. Many factors lead to the phenotypic expressions common in many
people of the same race including culture, war, economics, food availability, geographical
separating barriers, and many more. Particular to individuals of Asian descent, it has been seen
that they exhibit flattened nasal bones and flattened craniofacial morphology. These can
contribute to the maxillary prognathism often seen with the upper incisors inclined anteriorly
4
(Yaacob, 1996). These can also contribute to the common Class III skeletal relationship found
(Chan, 1974). These differences will lead to a general difference in norms from one race to
another. Specifically, this would directly affect the angulation of the upper incisor in relation to
the cranial base as well as the commonly used Wits parameter. Findings in this study will show
that these two parameters were positioned in a similar manner, providing further evidence that an
Asian population does not follow the Caucasian norms established and commonly used.
Current Importance:
Vietnam continues to have a population with substantial dental needs. More than 90% of
Vietnamese population has significant dental needs according to the Teeth-Jaw-Face Hospital in
Vietnam, with 85% of the children suffering from tooth decay. The competitive prices in
Vietnam have caused an influx to the dental services industry and have caused dental clinics to
start adapting more contemporary pieces of technology such as digital dentistry and
incorporating 3-D. This also produces revenue in the range of 150-160 million dollars in tourism.
Therefore, the country has been training more residents to enter the dental profession with
currently eight dental schools (Gurugram, 2019).
The government has acknowledged this need and continues to raise awareness through
initiatives and campaigns. Dental services are expected to produce revenue registering with a
5.6% CAGR and 2.0% CAGR for total clinics for the period up to 2023 (Ken Research, 2019).
Difference in Ethnicities:
In 1982, JRE Mills explained in “Principles and Practice in Orthodontics” that genetics
can play a role in the development of malocclusion. As genetics differ greatly between
individuals, applying similar norms to entirely different ethnicities would be erroneous. This
would establish that each ethnicity would be deserving of their own ideals and ranges of what
5
would be considered normal. Cultural perception can also play a large role in these differences
showing that the norms of one ethnicity with a different culture should not be applied to another
ethnicity with inherent genetic differences (Mills, 1982).
Attempts at other Norms:
There have been many other attempts to provide new norms for other ethnicities
attempting to highlight differences including Pakastani (Khan, 2015), Bangladeshi (Alam, 2013),
European (Miyajima 1996), Malaysian (Purmal, 2013), and many others. For example, Japanese
patients were found to have proclined incisors of both jaws as well as mandibular retrusion
(Miura, 1963).
Other studies have been conducted in an attempt to understand the norms of the
Vietnamese population better. In a study done by Anh et al., it was found that Vietnamese adults
of the ages 18-25 years exhibited a more prognathic maxilla when compared to the mandible and
an increased ANB. It was also found that the mandibular plane was reduced in comparison to
Caucasians and there was greater skeletal-dental protrusion in the Vietnamese. The results are as
follows:

Fig. 2
6
Considering the values for SNA, SNB, and ANB, this study concluded that there tends to
be a protrusion of both the maxilla and the mandible in the Vietnamese population. The ANB
value is higher when compared to Caucasians as well (Anh, 2016).
The cephalometric parameters for 100 Vietnamese citizens of age 18-19 years included
SNA, SNB, ANB, U1-SN, and the interincisal angle. The means for the previous parameters
were found and below is a summary of their findings:

SNA 81.99 ± 3.77
SNB 79.66 ± 4.10
ANB 2.33
U1-SN 109.36 ± 6.46
Interincisal Angle 120.02 ±13.06

Fig. 3
Significant differences were found between males and females in all categories except SNA and
U1-SN. This study concluded that Vietnamese individuals tend to have a dentoalveolar
protrusion (Do, 2008).

7
Materials and Methods
A randomized sample of 159 cephalometric radiographs were taken from a private
practice. All patients were of permanent dentition with accompanying plaster casts for models.
The study identification was UP-19-00481 under the University of Southern California
Institutional Review Board. All cephalometric radiographs of patients with any type of
orthodontic appliance or without clear accessible marker points were excluded. All were taken in
centric relation with the lips at rest. 104 lateral cephalometric radiographs were included. Patient
were deidentified and their genders were excluded. Patient profiles were made for each
anonymous patient using a linear number system (1-104) in the Dolphin Imaging program from
Patterson Dental. A Steiner, Tweed, and Wits analysis was performed on each one including
measurements for SNA (deg), SNB (deg), ANB (deg), SND (deg), U1-NA (mm), U1-NA (deg),
L1-NB (mm), Pog-NB (mm), Po & L1-NB Diff (mm), Interincisal Angle (U1-L1, deg), Occ Plan
to SN (deg), SN-GoGn (deg), S-L (mm), S-E (mm), FMA (MP-FH, deg), IMPA (L1-MP, deg),
FMIA (L1-FH, deg) Y-axis (SGn-SN, deg), U1-SN (deg), L1 Protrusion (L1-Apo, mm), Y-axis
length (mm), Upper Lip to E plane (mm), Lower Lip to E-Plane (mm), Wits appraisal (mm), U1-
FH (deg), LFH (ANS-Me II FH, %), and UFH (Na-ANS, %). When tracing incisors, the most
labial tooth and surface was traced.
After marking each radiographic landmark, soft tissue was marked using the embossing
enhancement feature provided with the Dolphin Imaging software. All data was placed into an
Excel spreadsheet and analyzed using means, medians, standard deviations, variance, and ranges.
All other data was analyzed manually. These were compared to the Steiner, Tweed, and Wits
norms established and utilized by Dolphin Imaging. Rickett’s E-plane was used for the
comparison of soft tissue analysis.
8
Each cephalometric tracing was recorded and measured to the tenth decimal place. Below
is an example of a patient profile with recorded values, Dolphin Imaging’s assigned “norms”,
and standard deviation. The parameters are color coded to indicate the severity difference from
the norm and are different per parameter and patient.

Fig. 4

9
Results
Twenty-eight parameters were recorded for 104 lateral cephalometric radiographs and compared
to established Steiner norms. All values were added and recorded into an Excel spreadsheet and
mean values and standard deviations were calculated. Below is a table outlining descriptive
statistics including mean, median, and standard deviation established for each parameter:

Parameter Average Median Standard Deviation
SNA (deg)
84.0 83.8

4.6

SNB (deg)
81.7

81.2

5.2

ANB (deg)
2.3

2.6

2.8

SND (deg)
78.7

77.85

5.2

U1-NA (mm)
8.7

8.75

3.1

U1-NA (deg)
32.8

32.9

7.3

L1-NB (mm)
8.4

8.45

2.6

L1-NB (deg)
31.7

32.4

6.9

Pog-NB (mm)
0.7 0.6 1.4
10

Po & L1-NB Diff
(mm)
7.7

7.7

3.6

Interincisal Angle
(U1-L1)(deg)
113.3

113.1

10.4

Occ Plan to SN
(deg)
14.2

14.7

5.8

SN-GoGn (deg)
29.3

29.5

6.0

S-L (mm)
49.3

46.7

10.1

S-E (mm)
18.2

18.1

3.2

FMA (MP-FH)(deg)
25.4

25.3

5.1

IMPA (L1-
MP)(deg),
97.4

97.2

7.1

FMIA (L1-FH) (deg
57.2

55.1

9.1

Y-axis(SGn-
SN)(deg)
67.6

67.9

4.7

U1-SN (deg)
116.8

115.9

8.2

11
L1 Protrusion (L1-
Apo)(mm)
6.7

6.7

2.8

Y-axis length(mm)
125.5

124.6

7.3

Upper Lip to E
plane (mm)
1.1

1.1

2.6

Lower Lip to E
plane
3.4

3.4

2.7

Wits Appraisal
(mm)
-1.8

-1.8

4.3

U1-FH (deg)
123.9 123.7

7.4

LFH (ANS-Me II
FH) (%)
56.0

55.8

2.6

UFH (Na-ANS) (%)
44.0

44.2

2.6

Table 1.

Here is a comparison of the “norms” set in the Patterson Dolphin Imaging software
compared to the averages found in the population for each parameter:

12

Parameter Average Norm
SNA (deg) 84.0 82.0
SNB (deg) 81.7

80.9
ANB (deg) 2.3

1.6
SND (deg) 78.7

80.0
U1-NA (mm) 8.8

4.3
U1-NA (deg) 32.8

22.8
L1-NB (mm) 8.4

4.0
L1-NB (deg) 31.7

25.3
Pog-NB (mm) 0.7

2.4
Po & L1-NB Diff (mm) 7.7

2.6
Interincisal Angle (U1-
L1)(deg)
113.3

130.0
13
Occ Plane to SN (deg) 14.2

14.4
SN-GoGn (deg) 29.3

32.9
S-L (mm) 49.3

51.0
S-E (mm) 18.2

22.0
FMA (MP-FH)(deg) 25.4

23.9
IMPA (L1-MP)(deg), 97.4

95.0
FMIA (L1-FH) (deg 57.2

64.8
Y-axis(SGn-SN)(deg 67.6

67.0
U1-SN (deg) 116.8

102.8
L1 Protrusion (L1-
Apo)(mm)
6.7

2.7
Y-axis length(mm) 125.5

131.0
Upper Lip to E plane (mm) 1.1 -6.0
14

Lower Lip to E plane 3.4

-2.0
Wits Appraisal (mm) -1.8

-1.0
U1-FH (deg) 124.0

111.0
LFH (ANS-Me II FH) (%) 56.0

54.0
UFH (Na-ANS) (%) 44.0

46.0

Table 2.
To establish a comparison, values that were the same or within the defined normal ranges as the
Dolphin norm were recorded as “Same as norm”, while others were recorded as “Above the
norm” or “Below the norm” depending on their value. Percentages were calculated from the
values to represent how much of the sample was below and how much of the sample was above
the define Dolphin norm. Ranges are also included here to show the variety of numbers found in
each parameter:

15
Parameter Defined Norm
(Dolphin)
Above the norm
(#)
Below the
norm (#)
Range of Data
(Min- Max)
ANB (deg) 1.6 66 36 -4.4 - 8.3
Wits (mm) -1.0 43 58 -11 - 8.7
U1-NA (mm) 4.3 95 8 1.3 - 19.8
U1-NA (deg) 22.8 95 9 10.1 – 51.8
L1-NB (mm) 4.0 100 4 3.3 -14. 8
L1-NB (deg) 25.3 85 19 14.4 – 45.7
IMPA (deg) 95.0 66 37 79.6 – 112.4
Upper lip to E
Plane (mm)
-6.0 104 0 -5.5 – 6.9
Lower lip to E
plane (mm)
-2.0 102 2 -2.2 – 10.1
Pog-NB (mm) 2.4 12 87 -2.5 – 3.6
Sn-GoGn (deg) 32.9 30 74 10.5 – 46
FMA (deg) 23.9 59 44 79.6 – 112. 4
U1-SN (deg) 102.8 100 4 93.6 – 145.9

Table 3.

Below is a depiction of the sample distribution determined to be Class I, Class II and Class III
based on the ANB parameter of Class I consisting of a range of 0-4 degrees.
16
ANB:

Fig. 5
While the majority of the cases were in Class I occlusion, Class II and Class III were close to
equal representation with 27% and 23%, respectively. The normal range of values was
established to be 0-4 degrees of the ANB measurement. As depicted in Table 3, 66 individuals
exhibited an ANB value below the Dolphin Standard of 1.6 and 36 individuals exhibited values
above the average norm.

50%
27%
23%
Skeletal Classification Indicated from ANB
Angle
Class 1
Class 2
Class 3
17
Wits:

Fig. 6
Taking the A point and the B point on the maxilla and mandible, respectively, and
perpendicularly drawing a line to the occlusal plane of maximal intercuspation allows for another
method of skeletal classification called the Wits Appraisal (Jacobsen, 1975). This Wits parameter
illustrated in Table 3, was measure above the norm in 43 of the individuals and below the norm
in 53 of the individuals. The Occl Plane-SN (deg) was recorded with a mean of 14.2 degrees
compared to the Dolphin norm of 14.4 degrees. Another measure of the verticality or steepness
of the face includes the mandibular plane. The mandibular plane here was constructed by a line
from point Gonion to Gnathion. The angle here is taken from this mandibular plane to the line
from Sella to Nasion creating the (SN-GoGn) parameter. Individuals with angles above the norm
were described as “High angle” and individuals with angles below the norm were described as
“Low angle”.
41%
56%
3%
Wits
Above Norm
Below Norm
Same as Norm
18
Sn-GoGn:

Fig. 7
Thirty individuals had angles that were above the Dolphin norm while seventy-four had angles
that were measured below leaving meaning 29% and 71% of the data, respectively.

29%
71%
0%
SN-GoGn
Above Norm
Below Norm
Same as Norm
19
U1-NA (deg):

Fig. 8
Ninety-five individuals measured above the norm for this parameter meaning 91% of the
individuals were above the established norm for this parameter. Nine of the Vietnamese
individuals registered an angle less than the 22.8 degrees norm and represented 9% of the
sample.

91%
9%
0%
U1-NA (deg)
Above Norm
Below Norm
Same as Norm
20
L1-NA (deg):

Fig. 9
Upper lip to E-plane:

Fig. 10
82%
18%
0%
L1-NB (deg)
Above Norm
Below Norm
Same as Norm
100%
0% 0%
Upper Lip to E-Plane
Above Norm
Below Norm
Same as Norm
21
All data points (100%) collected for this parameter were above the norm. All points were greater
than -6mm.
Lower Lip To E-plane:

Fig. 11
102 Vietnamese individuals (98%) were above the norm with only 2 being below the norm. No
points collected were the same the norm of -2mm.

98%
2%
0%
Lower Lip to E-Plane
Above Norm
Below Norm
Same as Norm
22
Discussion
Skeletal Classification:
The average ANB of the sample set was 2.5 degrees. Steiner originally set the ideal
number to 2 degrees with a range of 0 to 4. This would indicate that while the average of the
Vietnamese sample is within the established limits, it is higher than Steiner’s original ideal. Only
52 of the 104 individuals recorded ANB values (50%) were within the range of 0 to 4 degrees.
Twenty-eight individuals recorded measurements greater than 4 degrees and 24 individuals
recorded ANB values of less than 0 degrees. Dolphin Imaging places the ideal norm at 1.6. This
is consistent with previous literature suggesting a higher ANB average and a possibly increased
SNA or decreased SNB, although differences between males and females were not considered
here (Anh, 2016).
Hudson performed a similar assessment of ANB measurement of an American
Vietnamese sample and found a similar result with an increased ANB of 3.1 ± 2.5 (deg) with
values ranging from -5.6 to 8.4 (deg).
Looking at the proportion of skeletal classifications (Fig 2) there is an almost equal
percentage of Class III’s represented as Class II’s with only 50% of the patients exhibiting
skeletal Class I. This would indicate that the sample population would display a greater
proportion of skeletal Class III’s description according to the Dolphin Imaging norms. The range
included was -4.4 (deg) to 8.3 (deg).
Skeletal Class III relationships can come in multiple forms including: mandibular
protrusion, maxillary retrusion, a combination, or a normal relationship. Previous literature by
Sanborn showed that 45.2% exhibited the singular mandibular protrusion category, 33.0%
exhibited the maxillary retrusion, and 9.5% exhibited a combination. Also, a study by Jacobson
23
showed that the majority of Class III’s had mandibular protrusion with normal maxillas,
followed by maxillary retrusion and then two-jaw retrusion, respectively. Ellis and McNamara
found contrasting results in that patients with a combination of maxillary retrusion and
mandibular prognathism made up the majority of Class III patients.
Assessing the skeletal classification based off of the ANB parameter (Fig 2.) does not
give any information about which of the four categories this Vietnamese sample fell into. Other
parameters such as the Facial Angle would be helpful in further breaking down the categories of
Class III exhibited here.
In 1975, “The Wits appraisal of jaw disharmony” added this parameter as an additional
way to assess skeletal classification. This Wits evaluation is often used in conjunction with the
ANB parameter despite not being involved in the original Steiner analysis. The Wits average was
-1.84 mm which is more negative than the original norms of 0 mm and -1 mm (based on sex)
(Jacobsen, 1975). This would indicate a Class III skeletal discrepancy based on an average. Of
the 104 Vietnamese individuals measured, only twelve of them were within the 0 to -1 mm norm
(11.5%) with a range of -10.6 to 8.7 mm.
This is consistent with previous data that Asians exhibit horizontal growth patterns and
tend to have a lower Wits value indicating a more brachycephalic face. This was a more
significant average result than Hudson’s previous literature. The Wits values were calculated
separately at -0.67 ± 3.14 mm (with a range of -10.9 to 6.3 mm) for males and -0.92 ± 3.76 mm
for females (with a range of -16.3 to 9.0).

24
Dental Protrusion:
Many of the parameters measured within the Steiner analysis can be used to help evaluate
protrusion of the denture complex. Assessing the upper and lower dentition in relation to
craniofacial complex usually has indication on facial profile and soft tissue although that will be
discussed in another section. U1-NA (mm) and U1-NA (deg) indicate the harmony of the upper
incisor in relation to the face. U1-NA (mm) average was more than twice that of the Dolphin
norm meaning that the labial surface of the upper incisor was further out in the craniofacial
complex. Also, the U1-NA (deg) average was approximately 10 degrees above the norm. Both of
these values would contribute to the upper incisors being proclined.
In a similar manner, the measurements for L1-NB (mm and deg) quantify the lower
incisor protrusion describing the position of the lower incisor relative to the harmony of the face.
Both the mean linear distance (8.4 mm) and the mean angulation (31.7 deg) of the lower incisor
were increased from the Dolphin norms indicating protrusion of the lower incisor as well. The
Incisor Mandibular Plane Angle (IMPA) is often discussed in the Tweed philosophy and its
concern with the position of the lower incisor. This parameter would also indicate that the lower
incisor is pushed further out in terms of angulation with an average being higher than the norm.
With parameters indicating the angulation and distance of the incisors being higher than
standard, this would conclude that in general this sample population was protrusive compared to
norms established.
The inability to close the lips when at rest (or lip incompetence) is also a concept related
to the upper and lower incisor position. Upper and lower incisors that are deemed to be
protrusive can push the soft tissue further out causing strain in order to completely close the lips.
Both the upper and lower incisor parameters had the majority of individuals presenting with
25
numbers above the Dolphin norm. In order to help alleviate this inability to close the lips at rest,
the denture complex must be pulled back.
Incisor Mandibular Plane Angle (IMPA):
As discussed with dental protrusion, Tweeds analysis of the lower incisor would indicate
this sample would have higher angulation of the lower incisor. This tendency is consistent with
past literature for both Vietnamese and other Asian (such as Japanese) norms using a Steiner
analysis.
Soft Tissue:
The E-plane is defined as a line extending from the soft tissue tip of the nose to the tip of
the soft tissue on the chin point. The measurements of the upper lip and lower lip to this plane
helps to establish profile in conjunction with the position of the incisors. Both the upper lip and
the lower lip to E-plane measurements are positive numbers indicating that they rest in front of
the E-plane where normal values are -6 mm and -2 mm respectively. This in conjunction with
soft tissue glabella would contribute significantly to the overall profile. This would contribute to
a more convex profile as the region of the lips would be more protrusive or “full”. This contrasts
with the lips being further behind this plane contributing to a retrusive look and appearing more
“flat”.
Convexity vs Concavity:
Pog-NB (mm) is a measurement for the shape of the lower third of the face and the
overall profile. Pog-NB (mm) being a lower value than the Dolphin norm would indicate that the
contour of the chin would be flat. The mean value being 0.7 mm compared to the Dolphin norm
of 2.4 mm is consistent with this value being lower than the Dolphin norm. A higher mean would
contribute to a more contoured soft tissue profile in the chin region. This would indicate that the
26
average difference between the most anterior portion of the mandibular symphysis to the most
concave part on the mandibular symphysis is less pronounced. Depending on the soft tissue, this
would contribute to a flatter connection between soft tissue pogonion and soft tissue B point.
This could contribute to indications of profile convexity with the soft tissue B point further
retrusive with less chin contour.
Mandibular angle:
Two parameters recorded can contribute to the interpretation of the mandibular angle
including SN-GoGn and FMA. This contributes to the overall verticality or steepness of the face.
The mandibular plane is a factor often discussed when treatment planning and can influence
permanent treatment decisions such as extractions. 71% of the Vietnamese sample had a SN-
GoGn below the norm with 29% above the Dolphin norm. This is consistent with previous data
that had stated that this could contribute to a more horizontal growth pattern (Anh, 2016).

27
Conclusion: The aim of this study was to help establish more cephalometric characteristics of
Vietnamese people. From the information established, here are conclusions to be taken from the
study:
(1) Vietnamese individuals portrayed a higher protrusion of the upper incisor when measured to
both Nasion-A point line as well as the Sella-Nasion line (U1-NA, mm, deg and U1-SN, deg)
(2) Vietnamese individuals portrayed a higher protrusion of the lower incisor with increased
means for both the angulation to the Nasion-B point line (L1-NB) and the Incisor Mandibular
Plane Angle (IMPA).
(3) These results are consistent with past literature on patients of Vietnamese descent.
(4) The soft tissue profile contained lips that were much more protrusive and further out
contributing to a more convex profile.
(5) The comparatively smaller difference between Pogonion and B-point contribute to the chin
contour and profile.
(6) A more negative Wits parameter is more appropriate for a mean of the Vietnamese sample.
(7) The mandibular planes for the Vietnamese sample was less than Dolphin norms.

28
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Abstract (if available)

Abstract Background: Lateral Cephalometric radiographs are used in many orthodontic offices to help diagnose the patients. Many of the analyses associated with these are based off of norms that were established from a Caucasian population. This does not accurately represent other ethnicities and may actually cause the treating orthodontist to make treatment decisions based off of assumptions derived from the analyses. There have been attempts to do this in many ethnicities, but there is limited information for the Vietnamese population in Vietnam. Due to the rising economy and demand for orthodontic treatment in Vietnam, more representative data is needed. ❧ Objective: The purpose of this study was to help establish cephalometric measurements that are more representative of the Vietnamese people while directly comparing and evaluating the differences to established norms. ❧ Materials and Methods: Lateral cephalometric radiographs were acquired for 159 Vietnamese patients. Inclusion criteria were as follows: permanent dentition with first molars erupted into apparent occlusion, lips in a relaxed position, no previous or current orthodontic treatment, no obvious pathology, and void of any craniofacial syndromes. Of the 159 radiographs acquired, 104 were used in this study. A Steiner, Tweed, and Wits cephalometric analysis was completed by a single investigator using the Patterson Dental Dolphin Imaging program. Data collection and input was made using Microsoft Excel. Twenty-eight parameters were recorded and included. All descriptive statistics and comparisons were also done in Microsoft Excel. ❧ Results: The mean ANB was found to be 2.3 ± 2.8 degrees with 50% of the sample established as skeletal Class I, 27% as Class II and 23% as Class III. Mean Wits was found to be -1.8 ± 4.3 mm. The Upper Incisor to the Nasion-A Point angle (U1-NA) mean was found to be 32.8 ± 7.3 degrees with the Lower Incisor to the Nasion-B Point angle (L1-NB) mean found to be 31.7 ± 6.9 degrees. The mean angle between the Sella-Nasion line and the Gonion-Gnathion line (SN-GoGn) of the sample was found to be 29.3 ± 6.0 degrees. Soft tissue measurements were recorded as the lip in relation to the “E plane” and was found to be 1.1 ± 2.6 mm and 3.4 ± 2.7 mm for the upper and the lower lip respectively. ❧ Conclusion: The Vietnamese individuals showed a Class I majority followed by Class II and Class III, respectively. They also tended to have increased U1-NA and L1-NB measurements leading to more protrusive dental characteristics. This is consistent with previous literature showing a more protrusive soft tissue profile when compared to Rickett’s E-plane as well as the U1-SN (deg) parameter.

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Asset Metadata

Creator Bisbas, James Spencer (author)

Core Title Cephalometric norms for the Vietnamese: a clinical appraisal

School School of Dentistry

Degree Master of Science

Degree Program Craniofacial Biology

Publication Date 04/25/2020

Defense Date 02/20/2020

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

Tag cephalometric,norms,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 jamesbisbas@gmail.com,jbisbas@usc.edu

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c89-287303

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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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