Professor, Biomechanics Lab, Dept. of Health Sciences
Niigata University School of Medicine

Makoto Sakamoto, PhD

A novel method for three-dimensional tooth axis andalignment using cone-beam computed tomography【Keywords】

DentistryCone-beam CT

3D jaw and tooth

3D tooth axis

3D tooth alignment■Summary・We developed a global coordinate system based on maxillary and mandibularfeature points from 3D reconstructions using in vivo cone-beam computed
tomographic (CBCT) image data, devised a procedure for automatically calculating
the tooth axis of the maxillary and mandibular anterior teeth and the absolute 3D
position of the tooth alignment.
3D model of world
coordinate system in theintraoral space.

Tooth axis

■Subject Details/Topic・We used 3D principle component analysis to calculate the tooth axis (PCA) as the principal component of the long axis direction of tooth from six
subjects.
・ To evaluate tooth alignment, we determined a 3D global coordinate
system using three feature points comprising the bilateral mental foramina inthe mandible and the incisive canal in the maxilla by representing 3D toothalignment in terms of tooth’s center of gravity (COG).

Central incisor

121121

13

Maxillary teeth(Upper teeth)

22

Lateral incisor

23Canine

14

First premolar

15

Second premolar

16

First molar

26

17

Second molar

27

18

Third molar

28

24
25

Right

Mandibular teeth(Lower teeth)

Left
48

Third molar

38

47

Second molar

37

46

First molar
Second premolar

45

First premolar

44
43

Maxillary incisors tube

36

42 41 31 3235

FDI dental
numberingsystem for
adult teeth.
Gray teeth
are used inthis study.

3D reconstruction modelof tooth from CBCT
images. Red line
represented the principal
component analysis-axis:
PC-A (#3, 41).

3433Canine
Lateral incisor

Central incisor

Maxillary incisors tube

Z-axisMental foramen

Z-axisTem X-axis

(a)

(b)

OX-axisMental foramen

Y-axis(e)

X-axis(c)

Construction of three-dimensional world coordinate system in the intraoral space.
(a) Determination of temporary X–axis (Tem X-axis).
(b) Determination of Z –axis.
(c) Determination of Y–axis.
(d) Determination of X–axis.
(e) World coordinate system seen from the front of the jaw.

(d)0Z [ mm ]-5-1032 31334142

COG
PC-A
Quadratic function
Cubic function
Force-order function

43-15-20-25-20(a)(b)-15-10-5(c)05X [ mm ]101520(d)(a) Typical reconstruction models of maxillary tooth in X-Y plane. (b) Typical reconstruction models of maxillary tooth in X-Z plane. (c) Typical reconstruction models of
mandibular tooth in X-Y plane. (d) Typical reconstruction models of mandibular tooth in X-Z plane.

○ Advantages
・Conventionally, tooth alignment is calculated from feature points on the surface of the tooth crown, using ambiguous target
points. In comparison, tooth alignment is calculated in our method from the center of gravity of the 3D tooth shape, which
gives it the advantage of using unambiguous target points derived from the unique 3D shape of each tooth.

○ Applications
・Orthodontic and prosthetics, especially we will be able to plan of surgical and evaluation of after surgical.

○ Plans
・We will incorporate our proposed method into CBCT's software system.

■We hope to collaborate with…
・It can be used for CBCT and dental companies (including software companies).
Contact us:

Niigata University, Institute for Social Innovation and Cooperation
TEL：025-262-7554 FAX：025-262-7513 E-mail：onestop@adm.niigata-u.ac.jp