• Journal of the korean academy of Pediatric Dentistry
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• v.28 no.1
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• pp.185-194
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• 2001

This study was designed to evaluate the effects of angulation changes of head posture on the enlargement ratios of a lateral headfilm depending on the vortical or horizontal rotation of the objects. A device was constructed to measure regional changes of enlargement ratios. The device was held within the cephalostat and cephalograms recorded at each measured degrees of the device tilting, vertically and horizontally. The enlargement ratios of the horizontal, vertical, and angular measurements on the films taken at each tilted angulations were obtained and compared with those on the films taken without rotation. In summary, the enlargement ratios of the horizontal linear measurements were decreased during horizontal rotations. The enlargement ratios of vortical measurements of the right side on the film were increased and those of the left side were decreased by the horizontal rotations. Enlargement ratios of horizontal measurements were affected further than those of vertical measurements by the same angular changes of the horizontal rotations. Therefore, a disruption of parallelism between the object's midsagittal plane and the film could result in distortion of the image while vertical rotation around the object's porionic axis would not significantly affect the enlargement ratios on the headfilm.

• The korean journal of orthodontics
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• v.35 no.4 s.111
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• pp.320-329
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• 2005

The three-dimensional (3D) changes of bone, soft tissue and the ratio of soft tissue to bony movement was investigated in 8 skeletal Class III patients treated by mandibular setback surgery. CT scans of each patient at pre- and post-operative states were taken. Each scan was segmented by a threshold value and registered to a universal three-dimensional coordinate system, consisting of an FH plane, a mid-sagittal plane, and a coronal plane defined by PNS. In the study, the grid parallel to the coronal plane was proposed for the comparison of the changes. The bone or soft tissue was intersected by the projected line from each point on the gird. The coordinate values of intersected point were measured and compared between the pre- and post-operative models. The facial surface changes after setback surgery occurred not only in the mandible, but also in the mouth corner region. The soft tissue changes of the mandibular area were measured relatively by the proportional ratios to the bone changes. The ratios at the mid-sagittal plane were $77\~102\%(p<0.05)$. The ratios at all other sagittal planes had similar patterns to the mid-sagittal plane, but with decreased values. And, the changes in the maxillary region were calculated as a ratio, relative to the movement of a point representing a mandibular movement. When B point was used as a representative point, the ratios were $14\~29\%$, and when Pog was used, the ratios were $17\~37\%(9<0.05)$. In case of the 83rd point of the grid, the ratios were $11\~22\%(p<0.05)$.

• Journal of Korean Academy of Oral and Maxillofacial Radiology
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• v.22 no.1
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• pp.109-116
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• 1992

To determine the horizontal inclination of the condylar long axis without taking the submentovertex radiograph, the author studied the interrelation between the angle formed by the midsagittal plane and the mandibular angle and the horizontal inclination of the condylar long axis. In 56 subjects, the author measured the angle formed by the midsagittal plane and both mandibular angle using the modified Twirl Bow and the horizontal inclination of the both condylar long axis from submentovertex radiographs. The result were as follows: The mean value of the angle formed by the midsagittal plane and the mandibular angle was l8.50±1.48° in right side and 19.30±1.55° in left side. The mean value of the horizontal inclination of the condylar long axis was 19.25±7.56° in right side and 20.27±7.050 in left side. The interrelation of the two angles was represented as follows: y = 20.31-0.0094× (r = -0.482, p<0.01) in right side and y = 20.64-0.066×(r =-0.301, p<0.05) in left side (y; the horizontal inclination of the condylar long axis, x; the angle formed by the midsagittal plane and the mandibular angle).

• The korean journal of orthodontics
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• v.38 no.6
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• pp.427-436
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• 2008

Objective: The purpose of this study is to compare landmark position between cephalometric radiography and midsagittal plane projected images from 3 dimensional (3D) CT. Methods: Cephalometric radiographs and CT scans were taken from 20 patients for treatment of mandibular prognathism. After selection of land-marks, CT images were projected to the midsagittal plane and magnified to 110% according to the magnifying power of radiographs. These 2 images were superimposed with frontal and occipital bone. Common coordinate system was established on the base of FH plane. The coordinate value of each landmark was compared by paired t test and mean and standard deviation of difference was calculated. Results: The difference was from $-0.14{\pm}0.65$ to $-2.12{\pm}2.89\;mm$ in X axis, from $0.34{\pm}0.78$ to $-2.36{\pm}2.55\;mm$ ($6.79{\pm}3.04\;mm$) in Y axis. There was no significant difference only 9 in X axis, and 7 in Y axis out of 20 landmarks. This might be caused by error from the difference of head positioning, by masking the subtle end structures, identification error from the superimposition and error from the different definition.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.04a
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• pp.725-726
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• 2013

• The korean journal of orthodontics
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• v.35 no.6 s.113
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• pp.475-484
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• 2005

This study was performed to investigate the reproducibility of the horizontal and midsagittal planes, and to suggest a stable coordinate system for three-dimensional (3D) cephalometric analysis. Eighteen CT scans were taken and the coordinate system was established using 7 reference points marked by a volume model, with no more than 4 points on the same plane. The 3D landmarks were selected on V works (Cybermed Inc., Seoul, Korea), then exported to V surgery (Cybermed Inc., Seoul, Korea) to calculate the coordinate values. All the landmarks were taken twice with a lapse of 2 weeks. The horizontal and midsagittal planes were constructed and its reproducibility was evaluated. There was no significant difference in the reproducibility of the horizontal reference planes, But, FH planes were more reproducible than other horizontal planes. FH planes showed no difference between the planes constructed with 3 out of 4 points. The angle of intersection made by 2 FH planes, composed of both Po and one Or showed less than $1^{\circ}$ difference. This was identical when 2 FH planes were composed of both Or and one Po. But, the latter cases showed a significantly smaller error. The reproducibility of the midsagittal plane was reliable with an error range of 0.61 to $1.93^{\circ}$ except for 5 establishments (FMS-Nc, Na-Rh, Na-ANS, Rh-ANS, and FR-PNS). The 3D coordinate system may be constructed with 3 planes; the horizontal plane constructed by both Po and right Or; the midsagittal plane perpendicular to the horizontal plane, including the midpoint of the Foramen Spinosum and Nc; and the coronal plane perpendicular to the horizontal and midsagittal planes, including point clinoidale, or sella, or PNS.

• Journal of the korean academy of Pediatric Dentistry
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• v.48 no.1
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• pp.77-94
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• 2021

The purpose of this study was to investigate the three-dimensional characteristics of mesiodens using Cone-beam Computed Tomography(CBCT) and analyze the factors affecting complications and anesthetic methods of extraction. This study evaluated 602 mesiodens of 452 patients who underwent extraction of mesiodens at the department of Pediatric Dentistry in Seoul National University Dental Hospital between 2017 and 2019. The ratio of mesiodens patients over total patient per year was gradually increased over the past 20 years. Mesiodens with labio-palatally horizontal direction while root directing labial were the most common among the mesiodens with horizontal direction. Mesiodens were the most common at the cervical side of the adjacent teeth(37.0%) and mesiodens located in the near-palatal side were observed about 3.83 times higher than the far-palatal side. Most of the mesiodens(82.1%) were in contact with adjacent permanent teeth on all three sides of the CBCT and 46.2% of mesiodens had curved roots. The patient's age, vertical position, presence of complications, and proximity showed a significant difference in the selection of general anesthesia among anesthetic methods. The direction and vertical position of mesiodens had a significant effect on complications. These results provide a better understanding of mesiodens for establishing an accurate diagnosis and treatment plan.

• Journal of the Korean Society of Radiology
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• v.11 no.5
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• pp.313-319
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• 2017

The purpose of this study is to confirm the double of optic foramen in Korean and apply it to the Rhese method. First, the angle between the right optic foramen and the MSP was measured on the axial image using MPR technique of the 3D CT. Second, we measured the angle between the right optic foramen and OML in sagittal of MPR images. As a result, the angle between the optic foramen and the MSP was $39.9{\pm}4.63^{\circ}$ on average, which was different from the $53^{\circ}$ presented by Rhese method(p<0.05). The angle between optic foramen and OML was $40.8{\pm}6.6^{\circ}$. In conclusion, this study confirms that the standard of the Rhese method proposed in current textbook is difficult to apply to Koreans. Therefore, it is necessary to study angle of Korean standard in various general x-ray technique.

• Journal of the korean academy of Pediatric Dentistry
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• v.36 no.3
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• pp.325-336
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• 2009

The purpose of this study was to investigate the eruption pattern of the mandibular first molar in sagittal, frontal and horizontal views using the cone beam CT scanning. CT images were obtained from healthy 83 children (42 boys, 41 girls) between 3 to 10 years of age with a normal dentition according to Nolla stage. 1. In the frontal and horizontal view, the intermolar width decreased continuously with stage and slightly increased at the last stage. 2. In the sagittal and frontal view, eruption distances from occlusal plane were observed the largest change between stage 5 and 7. 3. In the horizontal and sagittal view, mandibular first molar from distal surface of primary second molar moved distally between stage 4 and 6. 4. In the sagittal view, angle from occlusal plane to mesio-distal axis increased between stage 4 and 8. 5. In the frontal view, angle from occlusal plane to bucco-lingual axis increased continuously during all stage. 6. In the horizontal view, angle from midsagittal plane to long axis increased between stage 5 and 8.

• Journal of the Korean Society of Radiology
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• v.16 no.7
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• pp.919-925
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• 2022

This study is an image reconstruction method after cervical CT scan. According to the oblique coronal reconstruction angle, i would like to suggest the reconstruction angle that can best express neural foraminal bony stricture. The angle created by drawing a line passing through the center of the spinal cord in the midsagittal plane of the cervical spine and the uncovertebral joint was measured. A line passing through the center of the spinal cord was drawn from the neural foramen, and the angle formed with the midsagittal plane was measured and compared. At the C4-5 level, the average was 9.2°, at the C5-6 level, the average was 9.9°, and at the C6-7 level, the average was 8.4°, the neural foraminal angle was measured to be larger than the uncovertebral joint angle. There was a statistically significant difference in mean (p<0.01). Also, it was found that the angle increased toward the lower cervical vertebrae. The angle between the neural foramen of the lower cervical vertebrae (C5-6, C6-7) and the center of the spinal cord is between 55 and 60°. Here, if the oblique coronal image is reconstructed to be 90°, the degree of neural foramen stenosis can be observed well. Because it is an image reconstruction using a conventional CT scan image, it does not receive additional radiation exposure. It is of great significance in diagnosing cervical neural foramen bony stenosis.