• 대한치과교정학회지
• /
• 제49권1호
• /
• pp.32-40
• /
• 2019

Objective: Precise identification of landmarks on posteroanterior (PA) cephalograms is necessary when evaluating lateral problems such as facial asymmetry. The aim of the present study was to investigate whether the use of lateral (LA) cephalograms can reduce errors in landmark identification on PA cephalograms. Methods: Five examiners identified 16 landmarks (Cg, N, ANS, GT, Me, RO, Lo, FM, Z, Or, Zyg, Cd, NC, Ms, M, and Ag) on 32 PA cephalograms with and without LA cephalograms at the same time. The positions of the landmarks were recorded and saved in the horizontal and vertical direction. The mean errors and standard deviation of landmarks location according to the use of LA cephalograms were compared for each landmark. Results: Relatively small errors were found for ANS, Me, Ms, and Ag, while relatively large errors were found for N, GT, Z, Or, and Cd. No significant difference was found between the horizontal and vertical errors for Z and Or, while large vertical errors were found for N, GT, and Cd. The value of identification error was lower when the landmarks were identified using LA cephalograms. Statistically significant error reductions were found at N and Cd with LA cephalograms, especially in the vertical direction. Conclusions: The use of LA cephalograms during identification of landmarks on PA cephalograms could help reduce identification errors.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
• /
• 제37권1호
• /
• pp.21-29
• /
• 2011

Introduction: To compare the change in frontal ramal inclination (FRI) in laterognathism after orthognathic surgery. Materials and Methods: Twenty four patients (10 men, 14 women; mean age, $22.8{\pm}5.2$ years) with minimal facial canting (${\leq}$ 2 mm) and apparent menton deviation ($5.9{\pm}2.4\;mm$) who had been operated on to correct facial asymmetry and skeletal CIII malocclusion, were selected. On a preoperative posteroanterior (PA) cephalogram, the FRI of the deviated side and non deviated side, L1 deviation amounts and menton deviation amounts were measured. The FRI differences between both sides were compared, and the correlations between the measured deviated elements and the FRI differences were analyzed. On a postoperative PA cephalogram, the shifting amount of L1, shifting amount of L7 and FRI of both sides were measured, and the correlations between the shifting elements and the change in FRI were analyzed. Results: On the preoperative PA cephalogram, the FRI of the non deviated side was significantly greater than those of the deviated side. The differences in FRI, with a menton deviation amount showed a significant correlation. On the postoperative PA cephalogram, the FRI differences between the deviated and non deviated side were decreased significantly and mandibular transverse movement toward central position was noted. The mean shifting amounts of L7 were associated with the amount of change in the deviated side of FRI. Conclusion: Transverse shifting of the mandible through orthognathic surgery decreases the FRI difference, which showed laterognathism, and improves the facial contour.

• 대한치과교정학회지
• /
• 제49권1호
• /
• pp.41-48
• /
• 2019

Objective: This in-vivo study aimed to compare landmark identification errors in anteroposterior (AP) and posteroanterior (PA) cephalograms generated from cone-beam computed tomography (CBCT) scan data in order to examine the feasibility of using AP cephalograms in clinical settings. Methods: AP and PA cephalograms were generated from CBCT scans obtained from 25 adults. Four experienced and four inexperienced examiners were selected depending on their experience levels in analyzing frontal cephalograms. They identified six cephalometric landmarks on AP and PA cephalograms. The errors incurred in positioning the cephalometric landmarks on the AP and PA cephalograms were calculated by using the straight-line distance and the horizontal and vertical components as parameters. Results: Comparison of the landmark identification errors in CBCT-generated frontal cephalograms revealed that landmark-dependent differences were greater than experienceor projection-dependent differences. Comparisons of landmark identification errors in the horizontal and vertical directions revealed larger errors in identification of the crista galli and anterior nasal spine in the vertical direction and the menton in the horizontal direction, in comparison with the other landmarks. Comparison of landmark identification errors between the AP and PA projections in CBCT-generated images revealed a slightly higher error rate in the AP projections, with no inter-examiner differences. Statistical testing of the differences in landmark identification errors between AP and PA cephalograms showed no statistically significant differences for all landmarks. Conclusions: The reproducibility of CBCT-generated AP cephalograms is comparable to that of PA cephalograms; therefore, AP cephalograms can be generated reliably from CBCT scan data in clinical settings.

• 대한치과교정학회지
• /
• 제30권5호
• /
• pp.543-552
• /
• 2000

본 연구는 natural head posture(NHP)를 이용하여 정모 두부 방사선 규격사진 촬영시 재현도를 알아보기 위하여 시행되었다. 두개 안면부의 기형이 없는 25세 전후의 성인 남녀 30명을 대상으로 통상적인 방법(술자 유도법)과 NHP에서 Head Posture Aligner를 이용한 방법(HPA법)으로 정모 두부 방사선 사진을 각기 2주 간격으로 촬영한 후 5개의 고경 계측항목과 9개의 폭경 계측항목을 선정하여 t 검정으로 각 계측항목의 재현도를 비교하는 한편, 정모와 측모 두부 방사선 사진으로3차원 상을 합성시 오차의 요인이 되는 두부의 상하회전 정도 차이를 촬영 방법별로 비교 분석하여 다음과 같은 결과를 얻었다. 1. 시간 간격을 두고 술자 유도법으로 2회 촬영한 정모 두부 방사선 사진의 계측치는 모든 고경 계측항목에서 서로 차이를 나타내어 낮은 재현도를 보였다. 2. 시간 간격을 두고 HPA법으로 2회 촬영한 정모 두부 방사선 사진의 계측치는 모든 고경 계측항목에서 통계적으로 유의한 차이를 나타내지 않아 재현도가 높음을 보였다. 3. 폭경 계측항목의 경우 2회 계측치의 차이를 통하여 살펴 본 재현도에서 술자유도법과HPA방법간에 두드러진 차이를 보이지 않았다. 4. 정모 및 측모 두부 방사선사진으로 3차원상을 합성하기 위한 수직적 두부 위치 보정각을 계산한 결과, 술자 유도법의 경우 $2.5^{\circ}$인 반면, HPA법은 $0.8^{\circ}$로 작게 나타났다. 이상의 결과는 정모 두부 방사선 규격 사진 촬영시 두부 위치의 재현도를 증가시키기 위하여 HPA의 사용이 필요함을 시사하였다.

• 대한치과교정학회지
• /
• 제40권1호
• /
• pp.6-15
• /
• 2010

안면 비대칭의 평가에 있어 과거 정면 두부방사선 규격사진을 이용하던 것과는 다르게 현재는 점차 3D CT를 이용하여 평가하는 것으로 변하고 있다. 본 연구는 3D CT와의 비교를 이용하여 정면 두부방사선 규격사진 분석에서 쉽게 접근할 수 있는 시상 기준 평면을 찾고자 하였다. 임상적으로 안모 비대칭이 발견되지 않은 성인 환자들을 대상으로 3D CT와 정면 두부방사선 규격사진을 촬영하였고, 정면 두부방사선 규격사진 분석에서 이용되어 왔던 5가지 정중 시상 기준 평면을 선택하여 계측을 실시한 뒤 이 값을 3D CT의 Nasion (Na), Sella (S), Basion (Ba)으로 구성된 정중 시상 평면에 대한 계측값과 비교하였다. 그 결과 좌우측 latero-orbitale의 수직이등분선을 정중 시상 기준 평면으로 이용한 정면 두부방사선 규격사진 계측값이 3D CT의 Na, S, Ba으로 구성된 정중 시상 평면을 이용한 계측값과 가장 차이가 작았고 상관관계가 높은 것으로 나타났다. 안면 비대칭 평가 시 좌우측 latero-orbitale의 수직이등분선이 정면 두부방사선 규격사진 분석에서 도움이 되는 정중 시상 기준 평면으로 이용될 수 있을 것이다.

• 대한치과교정학회지
• /
• 제54권1호
• /
• pp.48-58
• /
• 2024

Objective: To quantify the effects of midline-related landmark identification on midline deviation measurements in posteroanterior (PA) cephalograms using a cascaded convolutional neural network (CNN). Methods: A total of 2,903 PA cephalogram images obtained from 9 university hospitals were divided into training, internal validation, and test sets (n = 2,150, 376, and 377). As the gold standard, 2 orthodontic professors marked the bilateral landmarks, including the frontozygomatic suture point and latero-orbitale (LO), and the midline landmarks, including the crista galli, anterior nasal spine (ANS), upper dental midpoint (UDM), lower dental midpoint (LDM), and menton (Me). For the test, Examiner-1 and Examiner-2 (3-year and 1-year orthodontic residents) and the Cascaded-CNN models marked the landmarks. After point-to-point errors of landmark identification, the successful detection rate (SDR) and distance and direction of the midline landmark deviation from the midsagittal line (ANS-mid, UDM-mid, LDM-mid, and Me-mid) were measured, and statistical analysis was performed. Results: The cascaded-CNN algorithm showed a clinically acceptable level of point-to-point error (1.26 mm vs. 1.57 mm in Examiner-1 and 1.75 mm in Examiner-2). The average SDR within the 2 mm range was 83.2%, with high accuracy at the LO (right, 96.9%; left, 97.1%), and UDM (96.9%). The absolute measurement errors were less than 1 mm for ANS-mid, UDM-mid, and LDM-mid compared with the gold standard. Conclusions: The cascaded-CNN model may be considered an effective tool for the auto-identification of midline landmarks and quantification of midline deviation in PA cephalograms of adult patients, regardless of variations in the image acquisition method.