Three-dimensional Morphology Analysis Based On Cone Beam Computed Tomography For Craniofacial Morphology Of Young People With Normal Occlusion In Xi’an

Nowadays, cephalometrics is important to the orthodontists. Through cephalometric analysis, we can get the information of malocclusion and make the right diagnosis, then develop the treatment plan. We also can perform cephalometric analysis in any treatment stages to supervise the change of patients. At the end of treatment, we can assess the treatment effect by comparing the cephalometric analysis between pre- and post-treatment. After treatment, we can observe the stability or recurrence of the therapeutic outcomes.With the development of 3D diagnosis, CBCT attracts more and more scholars’ attention with its lower price, smaller radiation dose, faster scanning speed and good effect on hard tissue imaging. But, due to the different landmark identification and cephalometric measurements between 2D cephalometric and 3D cephalometric, there is no recognized method for three-dimensional cephalometry.CBCT(cone beam computed tomography) is used in this research for 3D cephalometric. Through evaluate the precision and reliability of 3D cephalometric landmark identification and measurement, we hope to work out a set of analysis method for three-dimensional cephalometric measurement preliminaryly. This research contains three parts:Part 1 Precision and reliability of cephalometric landmark identification in cone-beam computed tomographyObjective: Explore the precision and reliability of cephalometric landmark identification of three-dimension cephalometric measurement.Methods: 20 pre-orthodontic patients were radiographed with cone-beam computed tomography(CBCT) techniques. 31 landmarks were measured using the Invivo Dental 5.2 software. Intra- and inter-observer correlation coefficient(ICC) were used to test the reliability of landmark identification.Results 1. Intra-observer correlation coefficient analysis showed that 47.7%(42/88) coordinate values were greater than 0.99, and 46.6%(41/88) coordinate values fell in between 0.9 and 0.99. B、U1crown_R and U1labial_R had low reliability on X-axis;Zyg Arch_R had low reliability on Y-axis;Ar_R had low reliability on Z-axis. 2. Inter-observer correlation coefficient analysis showed that 31.8%(28/88) coordinate values were greater than 0.99, and 59.1%(52/88) coordinate values fell in between 0.9 and 0.99. A、B、Sella、U1crown_R and U1labial_R had low reliability on X-axis;Zyg Arch_R had low reliability on Y-axis;Ar_L/R had low reliability on Z-axis.Conclusions 1. The precision and reliability of cephalometric landmark identification of threedimension cephalometric measurement based on the MPR were high in both intra-and inter-observer. 2. The stability of landmark identification in intra-observer was higher than inter-observer.Part 2 Study the differences in cephalometric measurements between 3D data based on CBCT images and conventional 2D radiolography.Objective: Compare and analyze the measurements of 3D cephalometry based on CBCT and 2D cephalometry.Methods: 20 volunteers(10males and 10 females, aged from 18-40) who lived in Xi’an region were radiographed with CBCT and conventional lateral cephalograms. The lateral cephalograms were manually analyzed through the winceph8.0 software and the CBCT images were analyzed through the Invivo Dental5.2 software. Performed 23 measurements by the same observer in both 3D and 2D images, and retraced after a week. Paired T-test were accomplished with SPSS19.0 software.Results 1. Interclass correlation coefficient analysis showed that most of the measurements in 2D and 3D cephalometry had high reliability(ICC>0.9), except ANB angle in 2D cephalometry. And the ICC value was higher in 3D cephalometric measurements, except U1-NA(°)、L1-NB(mm)、Go Gn-SN(°)、FMA(°)、IMPA(°)、Go_R-Pog(mm). 2. Except U1-NA(mm), there was a significant difference between 2D and 3D cephalometric measurements(P<0.05). Most of the linear measurements were larger in 3D cephalometry and most of the angle measurements were larger in 2D cephalometry.Conclusions 1. There was high reliability both in 2D and 3D cephalometric measurements. And most of the ICC values were higher in 3D cephalometric measurements, showed that the 3D cephalometry had a higher reliability. 2. Due to the different cephalometric landmark identification, there was a significant difference between 2D and 3D cephalometric measurements, and we were not able to use the data of 2D measurements to analyze the 3D cephalometric measurements.Part 3 Three-dimensional morphology analysis based on CBCT for craniofacial hard tissues of young people with normal occlusion in Xi’an.Objective: Explore a way to study craniofacial morphology in three-dimensional measurement and analyze with three-dimensional reconstructed CBCT image data. And use this method to measure the data of three-dimensional craniofacial shape for youths with normal occlusion in Xi’an.Methods: Took CBCT scan to 150 selected volunteers(75 males and 75 females) which were in individual normal occlusion. Chose and analyzed 43 craniofacial measurements in each person in software Invivo Dental 5.2. Processed and analyzed measurement data in SPSS 19.0.Results 1. In three-dimensional linear measurements: except A-N-Pog(mm)、U1-NA(mm)、L1-NB(mm) and Overjet(mm), there was a significant difference between male and female(P<0.05), and most of them in male were higher than female. 2. In three-dimensional angle measurements: there was a significant difference between male and female in U1-SN(°)、U1-NA(°)、U1-L1(°)、FMIA(°)、IMPA(°)、SN-FH(°)、SN-OP(°) 、 SN-MP(°) 、 Y-(growth) Axis(°) and Ar-Go-Me R(°)(P<0.05), and U1-SN(°)、U1-NA(°)、IMPA(°)、Y-(growth) Axis(°) in male were larger than female.Conclusions: CBCT cephalometric measurements showed that the shape of craniofacial hard tissues of young people with normal occlusion in Xi’an in male was larger than female, and the vertical growth of mandible in female was more obvious than male.