3D vs. 2D cephalometric analysis comparisons with repeated measurements from 20 Thai males and 20 Thai females
1 National Electronic and Computer Technology Center (NECTEC), National Science and Technology Development Agency (NSTDA), Pathumthani, Thailand
2 Advanced Dental Technology Center (ADTEC),
National Science and Technology Development Agency (NSTDA), Pathumthani, Thailand
This paper was presented at the 4th Kuala Lumpur
International Conference on Biomedical Engineering, 25-28 June 2008, Kuala Lumpur , Malaysia.
This paper presented 3D cephalometric analysis on DICOM
data from I-CAT CT cone-beam machine consisted of averages and standard
deviations from 20 Thai males from 19 to 70 year (average 33.53 � 14.08 year)
and 20 Thai females from 16 to 70 year (average 32.60 � 15.37 year). The
angular measurements consisted of 49 lateral angular measurements and 9 frontal
angular measurements while linear measurements consisted of 29 lateral linear
measurements, 3 frontal linear measurements, and 8 perpendicular measurements.
Results in 3D were compared with the corresponding 2D results showing that most
midline-to-midline linear measurements and some midline-to-midline angular
measurements were not different, while other types of measurements were
significantly different. The 3D results will be used in the clinical Ceph3D
services as requested by those with interests on cephalometric analysis and
anthropology with focus on Thai subjects while the 2D results will be used for
comparison with cephalometric analyses from other orthodontists. � 2009
Biomedical Imaging and Intervention Journal. All rights reserved.
Keywords: 3D cephalometric analysis; Simplant; cone-beam CT
Cephalometric analysis is one of the essential tools in
orthodontic diagnoses as well as craniomaxillofacial surgery. Two-dimensional
cephalometric measurements from lateral and/or frontal cephalograms were widely
studied in several ethnic groups  including Thai people .
However, 2D-cephalometry is a projection image of
3D-structures, which has several disadvantages including non-homogenous
enlargement and distortion on lateral structures, inaccurate landmark locations
due to overlapping structures, and landmarks that appear on the lateral may not
appear on the frontal image or vice versa. Misaligned head position may lead to
In addition, using average measurements of left and right
structures in 2D-cephalometry as though both sides of the
face are symmetrical is not realistic since human face is rarely symmetrical
. Olszewski et al. has demonstrated that 3D analysis gives the same results
and adequate diagnoses as 2D analysis using the same skull  while Adam et
al. has shown that using a 3D method is more precise with 4-5 times more
accurate than the 2D approach . However, a few 3D cephalometric analysis
researches were focusing on a large number of samples [7-8] including Thai
cephalometric researches [9-10] but most of them did not take landmarks on
facial soft tissue into account.
Hardware and Software
I-CAT cone beam CT scan was used with 512 x 512 matrices,
radiation at 120 kV and 87.75 mAs taken at 0.4 mm slice thickness.
Simplant MasterTM (Materialise N.V.), medical image processing
software, was used for 3D reconstruction from CT DICOM data with 0.4 mm
interpolated slice thickness. All anatomical landmarks were first identified on
the 3D model, and their positions were verified in multi-planar reformat mode
in axial and sagittal views.
The selected means and standard deviations plots of thirty
eight landmark positions from repeated tests can be classified according to
craniofacial landmarks types including 5 Anterior Cranial based, 5
Nasomaxillary Complex, 10 Mandible, 14 Dentition, and 4 Soft tissue to be
listed in details as follows:
- Anterior Cranial Based Landmarks including Nasal (N), Sella (S), Left
Porion (PoL), and Right Porion (PoR)
- Nasomaxillofacial complex landmarks including Subspinal (A), Anterior
Nasal Spine (ANS), Posterior Nasal Spine (PNS), Basion (Ba), Left Orbitale
(OrL), and Right Orbitale (OrR)
- Mandible landmarks including Left Gonion (GoL), Right Gonion (GoR), Left
Condyle Head (CondL), Right Condyle Head (CondR), Center of Left Condyle (CcL),
Center of Right Condyle (CcR), Subspinal (B), Pogonion (Pog), Menton (Me), and
- Dentition Landmarks including Upper left incisor tip (A1L), Upper right
incisor tip (A1R), Upper left incisor apex (ARL),Upper right incisor apex
(ARR), Lower left incisor tip (B1L), Lower right incisor tip (B1R), Lower left
incisor apex (BRL), Lower right incisor apex (BRR), Upper left Canine tip
(A3L), Upper right Canine tip (A3L), Lower left Canine tip (B3L),Lower right
Canine tip (B3R), First Buccal of the first Left Molar (B6L), and First Buccal
of the first Right Molar (B6R)
- Soft Tissue Landmarks including Pronasale (PRN), Labial Superior (Ls),
Labial Inferior (Li), and Soft Tissue Pogonion (PG)
Fifty-eight angular measurements, forty linear
measurements, and a ratio [11-14] based upon thirty-eight landmarks were analyzed
from CT radiographs of 20 men and 20 women, non-severe malocclusion Thai
patients. The ages of 20 males were ranged from 19 to 70 years with the
mean of 33.53 � 14.08 years while the ages of 20 female
patients were ranged from 16 to 70 years with the mean of 32.60 � 15.37
Linear measurements consisted of 31 lateral linear
measurements including 9 midline-to-midline, and 22 lateral-to-lateral, 3
frontal and 8 perpendicular linear measurements to be listed along with the
analysis results in Table 1.
Angular measurements consisted of 49 lateral angular
measurements including 19 three or four points all midline, 10 one point
midline and two point lateral, 6 midline-midline to midline-lateral four
points, 4 midline-lateral to lateral-lateral four points, ���8 midline-midline
to lateral-lateral four points, 2 four point lateral, and 9 frontal angular
measurements to be listed along with the analysis results in Table 2.
Fig 1a and 1b depicted 3D images where 3D cephalometric
analysis was derived from Simplant CMFTM was applied to calculate
default 2D cephalometric analysis in form of lateral x-ray in Fig 1c.
Applying sagittal plane readjustment to display an ��x-ray
image of frontal skull and get 2D frontal analysis as shown in Fig 1d.
Subsequently, 3D cephalometric analysis was compared with corresponding 2D
lateral and frontal analysis.
Analyses and Calculations
Data of 20 males and 20 females were digitized and had
landmarks located five times by the same operator for the test of accuracy and
reliability. Dahlberg�s formula of standard errors was applied to analyze the
positions of 38 landmarks as applied in the work of Hashim  which is the
square of different between mean position and actual results on x, y, and z
The means and standard deviations of landmark positions on
x, y, and z axis will be plotted as ellipsoid along with and a set of 5
landmarks from repeated tests by using MATLAB� as shown for the case of Sella
Turcica (Point S) in Figure 2. After obtaining the linear and angular
measurements, paired T-Test through command TTEST of� Microsoft Excel� was used
to analyze the differences between 3D and 2D measurements and the differences
between 2D and 3D measurements from male examples and the correspondent
measurements from female examples at p<0.05. The differences were shown in
percentage using the formula with the results rounded to integers.
The paired T-Test results will be shown as the
probabilities to be described as follows: NS is for non significant for the
case with probability over 0.05 which implied that the pair of analyzed values
is interchangeable while * is for the case with probability less than 0.05
(p< 0.05), ** is for the case with probability less than 0.01 (p< 0.01),
and ������*** is for the case with probability less than
0.001 (p< 0.001) which implied that the pair of analyzed values is not
The repeated test results of 38 landmarks in males showed
that the highest errors on x-axis were at PNS due to difficulties to pinpoint
the back end of palate (PNS) to be accurate in all axes simultaneously. The
errors on Y‑axis occurred at the highest level at the buccal of the first
right molar (B6R) as well as the left and right gonion (GoL and GoR) due to the
radiographic scattering from the filling that blur both CT images and rendered
3D images, and The highest error on Z axis were the upper lip (Ls) and
lower lip (Li) due to the difficulties to pinpoint the position of these 2 soft
tissue landmarks which required an observer to view both sagittal and lateral
projection simultaneous as a counter-check measure for 3D landmarking.
The repeated test results of 38 landmarks in females
showed that the highest errors on x- axis were at the upper end of right porion
(PoR) due to the limited field of view (FOV). The errors on Y-axis occurred at
the highest level at the buccal of first right molar (B6R) due to the
radiographic scattering from the filling that blurs both CT images and rendered
3D images, and the highest error on Z axis were the subspinal (B), center of
right condyle (CcR), lower lip (Li) and soft tissue pogonion (PG) due to the
difficulties to pinpoint the position of these landmarks which required an
observer to view both sagittal and lateral projection simultaneous as a
countercheck measure for 3D landmarking.
The paired T-test results of linear measurements from 20
males and 20 female along with 2D and 3D comparison were shown in Table 1.
Linear measurement from 20 males showed that most measurements from midline to
midline structures were not significantly different between 3D and 2D
cephalometry as well as N‑ANS/ANS-Me ratio while the other types of
measurements were significantly different. Furthermore, results from 20 males
implied that 2D linear measurements can be substituted by the corresponding 3D
linear measurements in most of midline to midline cases and a few measurements
of lateral to lateral and N‑ANS/ANS-Me ratio.
Results for corresponding linear measurement from 20
females in Table 1 also showed similar results as male counterparts with
noticeable differences in OrL � OrR, Gn � CondL, and Gn � CondR showing that 3D
and 3D linear measurements can be substitute for male cases but not
substitutable in female cases and vice versa.
Linear measurement comparisons in Table 1 showed that
linear measurements from male samples are generally different from the
corresponding linear measurements from female samples, and the 3D linear
measurements are showing larger differences than the corresponding 2D linear
measurements so few 3D linear measurements from male samples are
interchangeable with the corresponding 3D linear measurements from female
samples. The exceptions are the linear measurements on perpendicular distances
that show much smaller differences between 2D and 3D linear measurements;
therefore, most of perpendicular distances from male samples can be
interchanged with the corresponding perpendicular distances from female
The paired T-test results of angular measurements from 20
males and from 20 females along with angular measurements comparisons were
shown in Table 2.���
Results from 20 males implied that few 2D angular
measurements including SNA, SNB, NSBa, U1R to ANS-PNS, U1R to SN, Me to GoL to
CcL, Me to GoR to CcR could be substituted by the corresponding 3D angular
measurements while the other angular measurements could not.
Results from the 20 females also showed similar results as
male counterparts with the additional 2D angular measurement which can be
substituted by the corresponding 3D angular measurements including ANB, L1R to
NB, L1L to SN, L1R to SN, ANS � PNS to SN, A to FHL, and A to FHR.
Angular measurement comparisons showed that most of 2D and
3D angular measurements from male examples could be interchanged with the
correspondent angular measurements from female examples. However, the
differences were the interincisal angles (U1L-L1L, U1R-L1R) which show that the
3D measures from males can be inter-changed with the corresponding results from
females but not interchangeable for the case of 2D angular measurements.
The comparison of 3D and 2D linear measurements derived
from midline structure to midline structure (e.g. A-B, ANS-Me) and measurements
derived from lateral structure to lateral structure (e.g. CcL-GoL, CcR-GoR) as
the example to the measurement of lower face height in Figure 3a with ANS-Me as
the 3D measurement of lower face height and ANS-Me� as the 2D measurement of
lower face height.� However, all 3D measurements derived from midline
structures to lateral structures were larger than those of 2D because 2D
measurements were projected image rather than true measurement. Fig. 3b shows
that Me-GoR represents the right mandibular length in 3D while Me-GoR�
represents the corresponding distance in 2D.
Angular measurements derived from all the landmarks in
mid-sagittal plane (e.g. SNA, SNB) showed similar results between 3D and 2D to
the level that it can be substituted as shown the measurement of sagittal
maxillary position in Fig. 4a and 4b with Fig. 4a shows that SNA� represents
the angular measurement of sagittal maxillary position in 2D while Fig. 4b
shows that SNA represents the angular measurement of sagittal maxillary
position in 3D.� Angular measurements derived from 1point midline to 2 points
lateral (e.g. A to FHL, A to FHR) in 3D showed minor differences from 2D
measurements. However, measurements derived from 4 points in different
planes, 3D and 2D data had significant differences since measurements in 3D
were not measured from the same projected planes as in 2D so angular
measurements in 3D should not be interpreted in the same way as conventional
2D.� Diagrams in Fig. 4c and (D) show different results between 3D and 2D
measurement of the right mandibular height, the angle between right mandibular
length (Me-GoR) and right Frankfort Horizontal plane (FHR) which is the plane
through right porion and right orbitale (PoR-OrR). Fig. 4c shows projected
measurement from 2D onto mid-sagittal plane and Fig. 4d shows that GoR and FHR are
not on the same plane in space.
Landmarks such as left and right porion (PoL, PoR) along
with left and right condylion (CondL, CondR) were difficult to locate due to
the narrow field of view of the CT scan that was too small to cover these
landmarks in patients with big skulls. In general, the standard deviations of
most measurements in this study were higher than previous studies [7-9] due to
the data collected from patient group, which have larger variation than the
data collected from population with normal occlusion.
The results from Ceph3D analyses will be applied in the
clinical Ceph3D services as requested by those with interests on cephalometric
analysis and anthropology with focus on Thai subjects while the 2D results will
be used for comparison with cephalometric analyses from other orthodontists.
Nevertheless, the standard Ceph3D analyses were subjected for the further
revisions to accommodate more types of measurements as well as more data from
Figure 1 2D and 3D cephalometric measurements. (a) 3D Lateral, (b) 3D Frontal, (c) 2D Lateral, and (d) 2D Frontal.
Figure 2 The result from repeated tests on sella turcica (Point S).
Figure 3 The Diagrams showing differences between 3D and 2D linear measurements.
Figure 4 Diagrams showing differences between 3D and 2D angular measurements.
Table 1 Linear cephalometric results from male and female samples.
Table 2 Angular cephalometric results from male and female samples
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|Received 7 May 2009; received in revised form 13 July 2009,
accepted 15 July 2009
Correspondence: Image Technology Laboratory (IMG), Room 217, NECTEC Building, Thailand Science Park, 112 Phahonyothin Road, Klong Luang, Pathumthani, 12120, Thailand. E-mail: firstname.lastname@example.org (Wisarut Bholsithi).
Please cite as: Bholsithi W, Tharanon W, Chintakanon K, Komolpis R, Sinthanayothin C,
3D vs. 2D cephalometric analysis comparisons with repeated measurements from 20 Thai males and 20 Thai females, Biomed Imaging Interv J 2009; 5(4):e21