• The korean journal of orthodontics
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• v.52 no.4
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• pp.287-297
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• 2022

Objective: To investigate the pattern of accuracy change in artificial intelligence-assisted landmark identification (LI) using a convolutional neural network (CNN) algorithm in serial lateral cephalograms (Lat-cephs) of Class III (C-III) patients who underwent two-jaw orthognathic surgery. Methods: A total of 3,188 Lat-cephs of C-III patients were allocated into the training and validation sets (3,004 Lat-cephs of 751 patients) and test set (184 Lat-cephs of 46 patients; subdivided into the genioplasty and non-genioplasty groups, n = 23 per group) for LI. Each C-III patient in the test set had four Lat-cephs: initial (T0), pre-surgery (T1, presence of orthodontic brackets [OBs]), post-surgery (T2, presence of OBs and surgical plates and screws [S-PS]), and debonding (T3, presence of S-PS and fixed retainers [FR]). After mean errors of 20 landmarks between human gold standard and the CNN model were calculated, statistical analysis was performed. Results: The total mean error was 1.17 mm without significant difference among the four time-points (T0, 1.20 mm; T1, 1.14 mm; T2, 1.18 mm; T3, 1.15 mm). In comparison of two time-points ([T0, T1] vs. [T2, T3]), ANS, A point, and B point showed an increase in error (p < 0.01, 0.05, 0.01, respectively), while Mx6D and Md6D showeda decrease in error (all p < 0.01). No difference in errors existed at B point, Pogonion, Menton, Md1C, and Md1R between the genioplasty and non-genioplasty groups. Conclusions: The CNN model can be used for LI in serial Lat-cephs despite the presence of OB, S-PS, FR, genioplasty, and bone remodeling.

• Composites Research
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• v.28 no.1
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• pp.6-14
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• 2015

Polymerization shrinkage stress analysis of dimethacrylate-based composite (Clearfil AP-X, Kuraray) and silorane-based composite (Filtek P90, 3M ESPE) used for dental composite restorations was performed using strain-gage measurement and FEM analysis. A theoretical equation based on Young's modulus and polymerization shrinkage of the composite resin was proposed to predict the polymerization shrinkage stress. Experimental results showed that the maximum shrinkage stress of Clearfil AP-X was about 2.8 times higher than Filtek P90. FEM analysis agreed with such experimental stress behaviours and showed that the maximum Von-Mises stress appeared near the margin of the filled resin adhered with PMMA ring. The stress concentration at the interface on the specimen surface was higher than that in the interior. The maximum error of shrinkage stress by the theoretical equation was reasonable within 5% in comparison to FEM results under plane stress.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.48 no.1
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• pp.21-32
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• 2022

Objectives: Inferior alveolar nerve block (IANB) is commonly used for mandibular dentoalveolar surgery. The objective of this study was to evaluate and compare the effectiveness of coadministration of dexamethasone (4 mg/mL) or adrenaline (0.01 mg/mL) as an adjuvant with lignocaine 2% in IANB during third molar surgery (TMS). Patients and Methods: This double-blind, randomized controlled trial was conducted between March and August 2020. The investigators screened patients needing elective TMS under local anesthesia. Based on strict inclusion and exclusion criteria, patients were enrolled in this study. These patients were assigned randomly into two study groups: dexamethasone group (DXN) or adrenaline group (ADN). Outcome variables were postoperative edema, trismus, visual analogue scale (VAS), perioperative analgesia, onset time, and duration of IANB. Results: Eighty-three patients were enrolled in this study, of whom 23 (27.7%) were eliminated or excluded during follow-up. This study thus included data from 60 samples. Mean age was 32.28±11.74 years, including 28 females (46.7%) in the ADN (16 patients, 57.1%) and DXN (12 patients, 42.9%) groups. The duration of action for DXN (mean±standard deviation [SD], 4:02:07±0:34:01 hours; standard error [SE], 0:06:00 hours; log-rank P=0.001) and for ADN (mean±SD, 1:58:34±0:24:52 hours; SE, 0:04:42 hours; log-rank P=0.001) were found. Similarly, time at which 1st analgesic consume and total number of nonsteroidal antiinflammatory drugs need to rescue postoperative analgesia was found statistically significant between study groups (t (58)=-11.95; confidence interval, -2:25:41 to -1:43:53; P=0.001). Early-hours VAS was also significantly different between the study groups. Conclusion: A single injection of dexamethasone prolongs the duration of action of lignocaine 2% IANB. Additionally, it can be used in cases where adrenaline is contraindicated.

• The Journal of Korean Academy of Prosthodontics
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• v.57 no.3
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• pp.203-210
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• 2019

Purpose: The purpose of this study was to verify the effect of the abutment superimposition process on the final virtual model in the scanning process of single and 3-units bridge model using a dental model scanner. Materials and methods: A gypsum model for single and 3-unit bridges was manufactured for evaluating. And working casts with removable dies were made using Pindex system. A dental model scanner (3Shape E1 scanner) was used to obtain CAD reference model (CRM) and CAD test model (CTM). The CRM was scanned without removing after dividing the abutments in the working cast. Then, CTM was scanned with separated from the divided abutments and superimposed on the CRM (n=20). Finally, three-dimensional analysis software (Geomagic control X) was used to analyze the root mean square (RMS) and Mann-Whitney U test was used for statistical analysis (${\alpha}=.05$). Results: The RMS mean abutment for single full crown preparation was $10.93{\mu}m$ and the RMS average abutment for 3 unit bridge preparation was $6.9{\mu}m$. The RMS mean of the two groups showed statistically significant differences (P<.001). In addition, errors of positive and negative of two groups averaged $9.83{\mu}m$, $-6.79{\mu}m$ and 3-units bridge abutment $6.22{\mu}m$, $-3.3{\mu}m$, respectively. The mean values of the errors of positive and negative of two groups were all statistically significantly lower in 3-unit bridge abutments (P<.001). Conclusion: Although the number of abutments increased during the scan process of the working cast with removable dies, the error due to the superimposition of abutments did not increase. There was also a significantly higher error in single abutments, but within the range of clinically acceptable scan accuracy.

• Journal of the korean academy of Pediatric Dentistry
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• v.49 no.1
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• pp.14-24
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• 2022

The aim of the present study is to evaluate the validity of orthodontic measurements including tooth width, Bolton ratio, overjet and overbite on the digital dental models. Dental models of the subjects aged 12 to 18 were obtained in 3 different forms, which were conventional stone model, digital model created with Freedom HD model scanner, and digital model produced with CS3600 intraoral scanner. After measurements were made on the models, reliability and reproducibility of the measurements were evaluated by using intraclass correlation coefficient, while validity was assessed with paired t-test. As a result, significant reliability and reproducibility were verified, with intraclass correlation coefficient exceeding 0.750 in all groups. Measurements of the model scanned group showed an adequate validity in overall and anterior Bolton ratio, overjet, and overbite. Intraoral scanned models showed an adequate validity in anterior Bolton ratio, and overjet. Measurement on intraoral scanned digital models can be considered as an alternative for young children who have difficulty in taking impression. Furthermore, careful considerations on measurement error should be made in clinical situations.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.36 no.2
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• pp.78-86
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• 2010

Introduction: Cone beam computed tomography (CBCT) has various advantages and is used favorably in many fields in dentistry. Especially, CBCT is being used as basic diagnostic tool for 3-dimensional analysis in orthognathic patient. Two-dimensional cephalograms can be synthesized from CBCT digital imaging and communications in medicine (DICOM) data. In this study, conventional cephalograms and CBCT were taken simultaneously, and representative landmarks were located and analyzed in its accuracy and reproducibility. Materials and Methods: Ten patients who had orthognathic surgery in Wonkwang University Daejeon Dental Hospital participated in this study. For each patient, CBCT and conventional cephalogram was taken. By using Ondemand (Cybermad, Korea), 2-dimensional cephalograms was established on CBCT. In addition, 19 landmarks were designated and measured by 3 orthodontists twice a week. After these landmarks were transferred to a coordinate, distance of landmark and axis, standard error, distribution degree were measured, compared and analyzed. Results: Comparing the CT ceph group and conventional cephalogram group, CT ceph group had shown shorter distance of landmark and axis in S, Hinge axis, Bpt, Ba, Or, Corpus left. Standard error of the mean shows that CT ceph group has better reproducibility in Or, Corpus left, Hinge axis at X axis and Na, U1R, U1T, Bpt, PNS, Ba Corpus left, Hinge axis at Y axis. In both groups, mean error was less than 1.00 mm, no significant difference were found between CT ceph group and conventional cephalogram group in all measurements. Furthermore, comparing two groups, each 17 landmarks out of 19 had its characteristic in distribution degree. Conclusion: No significant difference were found between CBCT composed cephalographic radiograph and conventional cephalograghic radiograph, clinical application may be possible if improved.

• Journal of Dental Rehabilitation and Applied Science
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• v.28 no.1
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• pp.27-36
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• 2012

As the popularity of implant treatment using a variety of problems have been reported. The proper torque values recommended by the manufacturer and the actual tightening force applied to the observed differences. Period for each product used in this study using different torque controllers accuracy for each of the comparisons, were analyzed. Error rate varies by the manufacturer, but all the products used in the reference period for increasing the error rate increased. Repeat the initial tightening, but the reference, showed a value close to the reference value for the width of change was larger. However, increasing the number of repeated tightening of the reference value for the error rate increased, but has reduced the width of the observed changes.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.29 no.6
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• pp.520-526
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• 2007

The accuracy of model surgery is one of important factors which can influence the outcome of orthognathic surgery. To evaluate the accuracy of digitalized model surgery, we tried the model surgery on a software after transferring the mounted model block into a digital model, and compared the results with that of classical manual model surgery. We could get the following results, which can be used as good baseline analysis for the clinical application. 1. We made the 3D scanning of dental model blocks, and mounted on a software. And we performed the model surgery according to the previously arranged surgical plans, and let the rapid prototyping machine produce the surgical wafer. All through these process, we could confirm that the digital model surgery is feasible without difficulties. 2. The digital model surgery group (Group 2) showed a mean error of $0.0{\sim}0.1mm$ for moving the maxillary model block to the target position. And Group 1, which was done by manual model surgery, presented a mean error of $0.1{\sim}1.2mm$, which is definitely greater than those of Group 2. 3. Remounted maxillary model block with the wafers produced by digital model surgery from Group 2 showed the less mean error (0.2 to 0.4 mm) than that produced by manual model surgery in Group 1 (0.3 to 1.4 mm). From these results, we could confirm that the digital model surgery in Group 2 presented less error than manual model surgery of Group 1. And the model surgery by digital manipulation is expected to have less influence from the individual variation or degree of expertness. So the increased accuracy and enhanced manipulability will serve the digital model surgery as the good candidate for the improvement and replacement of the classical model surgery, if careful preparation works for the clinical adjustment is accompanied.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.51 no.2
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• pp.87-93
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• 2002

Accurate acquisition of surface geometries such as machined surfaces, biological surfaces, and deformed parts have been very important technique in scientific study and engineering, especially for system design, manufacturing and inspection. Two-camera method keeps accuracy more than double than mechanical method. In this paper, a new method is studied to acquire 3D geometric data of the small object such as a die in stone model. When the devices, cameras, laser beam and object are in a perfect plane, the calculation is measured by position error 0.025[mm] within. But this paper shows that arbitrarily positioned system can also be used to obtain 3D data. Also, this paper present a method to generate coping surface data with which CAM system can do for milling work.

• Journal of the Korean Institute of Telematics and Electronics
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• v.7 no.2
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• pp.43-48
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• 1970

The precise measurement technique for dielectric constent of high-loss nonmagnetic materials is described. This technique use6 is based upon cavity resonance method and impedance method. Dielectric constant can be calculated from simple formulas without using transcen-dental equations. The error contained in x-band yields loss tangent, 3%, and dielertric constant, 1%, for materials filled in cross section of waveguide.