jkap The Journal of Korean Academy of Prosthodontics J Korean Acad Prosthodont 0301-2875 2005-3789 The Korean Academy of Prosthodontics 10.4047/jkap.2014.52.3.222 jkap-52-222 Original Article Comparison of landmark positions between Cone-Beam Computed Tomogram (CBCT) and Adjusted 2D lateral cephalogram SonSoo-Jung ChunYoun-Sic KimMinji ∗ Graduate School of Clinical Dentistry, Ewha Womans University, Seoul, Republic of Korea Corresponding Author: Minji Kim Mokdong Hospital, Ewha Womans University 911-1, Mokdong, Yangcheon-gu, Seoul, 158-710, Republic of Korea +82 2 2650 5112: e-mail, minjikim@ewha.ac.kr 22014 922014 523 222232 20062014 11072014 14072014 Copyright © 2014 The Korean Academy of Prosthodontics 2014 This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract Purpose

This study aims to investigate if 2D analysis method is applicable to analysis of CBCT by comparing measuring points of CBCT with those of Adjusted 2D Lateral Cephalogram (Adj-Ceph) with magnification adjusted to 100% and finding out at which landmarks the difference in position appear.

 Materials and methods

CBCT data and Adj-Ceph (100% magnification) data from 50 adult patients have been extracted as research objects, and the horizontal (Y axis) and vertical (Z axis) coordinates of landmarks were compared. Landmarks have been categorized into 4 groups by the position and whether they are bilaterally overlapped. Paired t-test was used to compare differences between Adj-Ceph and CBCT.

 Results

Significant difference was found at 11 landmarks including Group B (S, Ar, Ba, PNS), Group C (Po, Or, Hinge axis, Go) and Group D (U1RP, U6CP, L6CP) in the horizontal (Y) axis while all the landmarks in vertical (Z) axis showed significant difference (P<.05). As a result of landmark difference analysis, a meaningful difference with more than 1 mm at 13 landmarks were indentifed in the horizontal axis. In the vertical axis, significant difference over 1 mm was detected from every landmark except Sella.

 Conclusion

Using the conventional lateral cephalometric measurements on CBCT is insufficient. A new 3D analysis or a modified 2D analysis adjusted on 19 landmarks of the vertical axis and 13 of the horizontal axis are needed when implementing CBCT diagnosis.

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CBCT image of 3D and MPR (multiplanar projection reformat) for 3D landmark identification.

X, Y, Z axis of CBCT. N, (0,0,0); X axis, (-), right, (+), left; Y axis, (-), anterior, (+), posterior; Z axis, (-), upper, (+), lower.

Y (Horizontal), Z (Vertical) axis of adjusted 2D lateral cephalogram. N (0,0); Y axis, (-), anterior, (+) posterior; Z axis, (-), upper, (+), lower.

Classification of landmarks' position. Group A (Anterior landmark, marked ▲), ANS, A, B, Pog, Gn, Me; Group B (middle and posterior landmark, marked), S, Ar, Ba, PNS; Group C (R, L overlapped landmark, marked ★), Po, Or, Hinge axis, Go; Group D (Dental landmark, marked ■), U1CP, U1RP, U6CP, L1CP, L1RP, L6CP; red round, Nasion.

Horizontal difference between Adjusted Cephalogram and CBCT (values of Y axis) (mm).

Vertical difference between Adjusted Cephalogram and CBCT (values of Z axis) (mm).

Definition of landmarks

Landmark 2D Definition 3D Definition
Group A ANS Tip of the anterior nasal spine Anterior nasal spine
A Deepest point between ANS, and the upper incisal alveolus Deepest point on contour of maxillary alveolar process
B Deepest point between Pogonion, and the lower incisal alveolus Deepest point on contour of mandibular alveolar process
Pog Most anterior point of the symphysis Most prominent point of mentum
Gn Most inferior point of the mandible in the midline Lowest point on mentum
Me Most inferior point on the symphyseal outline Most inferior point of mandible in the midline
Group B S Center of Sella Turcica Center of Sella Turcica
Ar Intersection of inferior cranial base surface and posterior surface of condyle Predicted intersection of inferior cranial base surface and posterior surface of condyle
Ba Most inferior point of the Occipital bone Anterior midpoint on foramen magnum
PNS Tip of the posterior nasal spine Posterior nasal spine
Group C Po Most superior point of the external auditory meatus (R, L) Most superior point of external auditory meatus
Or Most inferior point of the Orbital contour (R, L) Most inferior point of the orbital contour
Hinge Axis Center of rotation of the condyle Center of rotation of the condyle
Go Lowest posterior and most outword point of the mandible (R, L) Lowest posterior and most outward point of the mandible
Group D U1CP Tip of the crown of the upper incisor (R, L) Tip of the crown of the upper incisor
U1RP Tip of the root of the upper incisor (R, L) Tip of the root of the upper incisor
U6CP Mesiobuccal cusp tip of the upper 1 st molar Mesiobuccal cusp tip of the upper 1 st molar
L1CP Tip of the crown of the lower incisor Tip of the crown of the lower incisor
L1RP Tip of the root of the lower incisor Tip of the root of the lower incisor
L6CP Mesiobuccal cusp tip of the lower 1 st molar Mesiobuccal cusp tip of the lower 1 st molar

Horizontal difference between Adjusted 2D Lateral Cephalogram and CBCT (values of Y axis)

Landmark Adj-Ceph (N = 50) Mean ± SD (mm) CBCT (N = 50) Mean ± SD (mm) Mean ± SD of the difference between Adj-Ceph and CBCT (mm) P value
Group A ANS -3.48 ± 4.50 -4.26 ± 2.88 0.78 ± 3.21 .094
A -0.12 ± 4.10 -0.89 ± 2.93 0.77 ± 2.56 .039∗
B 1.95 ± 9.54 0.98 ± 8.38 0.97 ± 3.91 .086
Pog 0.61 ± 10.81 -0.19 ± 9.30 0.80 ± 4.43 .208
Gn 3.14 ± 11.13 4.09 ± 9.55 1.34 ± 4.58 .044∗
Me 7.85 ± 10.73 6.58 ± 9.27 1.27 ± 4.57 .055
Group B S 71.11 ± 4.10 65.01 ± 3.54 6.10 ± 1.53 <.001∗∗
Ar 86.79 ± 5.77 78.49 ± 5.01 8.30 ± 2.83 <.001∗∗
Ba 97.10 ± 6.48 87.93 ± 5.17 9.18 ± 3.19 <.001∗∗
PNS 47.85 ± 4.60 45.24 ± 3.52 2.61 ± 3.10 <.001∗∗
Po 97.16 ± 6.03 87.00 ± 5.05 10.16 ± 3.06 <.001∗∗
Group C Or 12.02 ± 3.07 9.22 ± 2.35 2.79 ± 2.49 <.001∗∗
Hinge Axis 82.38 ± 5.48 75.55 ± 4.75 6.83 ± 2.39 <.001∗∗
Go 76.69 ± 7.54 68.59 ± 6.46 8.10 ± 3.66 <.001∗∗
Group D U1CP -7.87 ± 6.05 -6.99 ± 4.89 -0.88 ± 3.17 .055
U1RP 4.60 ± 4.24 3.24 ± 3.49 1.50 ± 2.78 .001∗∗
U6CP 27.07 ± 5.91 21.52 ± 4.44 5.55 ± 4.11 <.001∗∗
L1CP -6.45 ± 6.93 -6.03 ± 6.25 -0.42 ± 3.14 .346
L1RP 3.79 ± 8.98 2.84 ± 7.87 0.94 ± 9.79 .498
L6CP 21.24 ± 7.33 18.23 ± 6.72 3.01 ± 3.39 <.001∗∗

P<.05,

P<.01.

(-) sign on Mean ± SD of Adjusted 2D Lateral Cephalogram and Mean ± SD of CBCT refers the given landmark is located anterior to the datum point (Nasion / Z axis).

(-) sign on Mean ± SD of Difference between Adjusted 2D Lateral Cephalogram and CBCT means Landmark on Adjusted Cephalogram is more anterior than CBCT.

Vertical difference between Adjusted 2D Lateral Cephalogram and CBCT (values of Z axis)

Landmark Conventional Cephalogram (N = 50) Mean ± SD (mm) CBCT (N = 50) Mean ± SD (mm) Mean ± SD of the difference between Adj-Ceph and CBCT (mm) P value
Group A ANS 60.65 ± 4.56 55.24 ± 3.69 5.45 ± 1.99 <.001∗∗
A 68.93 ± 5.08 61.48 ± 4.36 7.40 ± 2.13 <.001∗∗
B 116.85 ± 8.02 107.01 ± 6.93 9.80 ± 3.36 <.001∗∗
Pog 130.15 ± 8.72 117.84 ± 7.28 12.33 ± 2.96 <.001∗∗
Gn 135.52 ± 8.51 122.39 ± 7.43 13.10 ± 2.72 <.001∗∗
Me 137.46 ± 8.78 124.56 ± 7.43 12.83 ± 2.80 <.001∗∗
Group B S 13.82 ± 3.64 11.75 ± 2.74 0.90 ± 2.99 <.001∗∗
Ar 48.89 ± 5.56 44.85 ± 3.78 2.63 ± 3.71 <.001∗∗
Ba 56.19 ± 6.50 51.41 ± 4.10 3.19 ± 4.10 <.001∗∗
PNS 61.80 ± 5.24 54.77 ± 3.90 6.23 ± 2.83 <.001∗∗
Group C Po 31.66 ± 2.79 29.32 ± 2.15 2.06 ± 2.67 <.001∗∗
Or 31.66 ± 2.79 29.24 ± 2.05 2.15 ± 2.25 <.001∗∗
Hinge Axis 42.71 ± 4.74 36.19 ± 2.81 4.48 ± 4.04 <.001∗∗
Go 100.42 ± 9.65 91.54 ± 7.84 8.00 ± 4.19 <.001∗∗
Group D U1CP 92.88 ± 5.99 84.55 ± 5.12 8.42 ± 2.19 <.001∗∗
U1RP 71.29 ± 5.11 64.21 ± 4.54 6.87 ± 2.16 <.001∗∗
U6CP 87.61 ± 6.02 79.87 ± 4.83 7.33 ± 2.57 <.001∗∗
L1CP 92.04 ± 6.01 83.56 ± 5.54 8.59 ± 1.96 <.001∗∗
L1RP 109.58 ± 6.99 100.84 ± 6.09 8.83 ± 2.51 <.001∗∗
L6CP 88.65 ± 6.20 81.41 ± 5.23 6.94 ± 2.38 <.001∗∗

P<.05,

P<.01.

(+) sign on Mean ± SD of Difference between Adjusted 2D Lateral Cephalogram and CBCT means Landmark on Adjusted Cephalogram is more lower than CBCT.

The difference between conventional cephalogram and CBCT data of duplicated skull model

Landmark Y axis Mean (mm) Z axis Mean (mm)
Group A ANS -0.66 2.14
A -0.48 2.45
B -0.42 4.61
Pog -0.99 4.47
Gn -1.53 4.76
Me -0.69 5.37
Group B S 2.12 -0.26
Ba 2.36 0.78
PNS 1.22 2.02
Group C Po 2.54 0.46
Or 0.94 0.79
Hinge Axis 0.24 5.45
Go 2.83 2.90
Group D U1CP 2.60 2.60
L1CP 2.87 2.87