• Journal of the Korean Society for Precision Engineering
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• v.16 no.12
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• pp.99-108
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• 1999

A four-degree-of-freedom non-linear model with time varying mesh stiffness has been developed for the dynamic analysis of spur gear trains. The model includes a spur gear pair, two shafts, two inertias representing load and prime mover. In the model, developed several factors such as time varying mesh stiffness and damping, separation of teeth, teeth collision, various gear errors and profile modifications have been considered. Two computer programs are developed to calculate stiffness of a gear pair and transmission error and the dynamic analysis of modeled system using time integration method. Dynamic tooth and mesh forces, dynamic factors are calculated. Numerical examples have been given, which shows the time varying mesh stiffness ha a significant effect upon the dynamic tooth force and torsional vibrations.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2004.10a
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• pp.416-421
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• 2004

Off-line feedrate scheduling is presented as the advanced technology to regulate cutting forces at the desired level through change of feedrates. In rough cutting, the feedrate scheduling aims at reducing the machining time, which is the most important factor for better productivity. Thus, the largest force which can avoid breakage of tool shank and tooth is a reference force for feedrate scheduling in rough cutting. In this paper, a calculation method of the reference cutting force for feedrate scheduling is developed. This model calculates rupture plane of tooth using the FEM analysis of a tool and computes the reference force using the transverse rupture strength of a tool. Experiments validate that the presented feedrate scheduling model reduced machining time drastically and regulate cutting forces at the reference cutting force.

• Imaging Science in Dentistry
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• v.49 no.1
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• pp.19-26
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• 2019

Purpose: It has been proposed that using new prediction methods, such as neural networks based on dental data, could improve age estimation. This study aimed to assess the possibility of exploiting neural networks for estimating age by means of the pulp-to-tooth ratio in canines as a non-destructive, non-expensive, and accurate method. In addition, the predictive performance of neural networks was compared with that of a linear regression model. Materials and Methods: Three hundred subjects whose age ranged from 14 to 60 years and were well distributed among various age groups were included in the study. Two statistical software programs, SPSS 21 (IBM Corp., Armonk, NY, USA) and R, were used for statistical analyses. Results: The results indicated that the neural network model generally performed better than the regression model for estimation of age with pulp-to-tooth ratio data. The prediction errors of the developed neural network model were acceptable, with a root mean square error (RMSE) of 4.40 years and a mean absolute error (MAE) of 4.12 years for the unseen dataset. The prediction errors of the regression model were higher than those of the neural network, with an RMSE of 10.26 years and a MAE of 8.17 years for the test dataset. Conclusion: The neural network method showed relatively acceptable performance, with an MAE of 4.12 years. The application of neural networks creates new opportunities to obtain more accurate estimations of age in forensic research.

• The Journal of Korean Academy of Prosthodontics
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• v.38 no.2
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• pp.242-254
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• 2000

Accurate impression is very important to achieve desirable prosthesis and there are many factors in taking a good impression. For example, types of impression material, types of impression tray, impression taking methods and so on. Recently individual tooth tray technique is accepted as obtaining good impression that can be applied to multiple abutment impression, heavy salivated patient, to minimize the effect of natural teeth s undercuts and to reduce pain during cord packing procedures. The purpose of this study was to compare the accuracy according to materials and forms of the individual tooth tray which is clinically applied nowadays. Used materials in experiment were divided into 3 types (acrylic resin. $Futar^{(R)}$ occlusion. $Blu-mousse^{(R)}$) and forms were divided into 2 types (forming occlusal vent hole or not and forming marginal vent space or not). Stone master model from impression body and metal master model were measured by $X-PLAN360d^{(R)}$ to compare occlusal surface discrepancy and marginal discrepancy. The results were as follows: 1. In comparison of occlusal surface discrepancy and marginal discrepancy according to materials, groups with three materials showed no statistical difference 2. In comparison of occlusal surface discrepancy and marginal discrepancy according to occlusal vent hole, groups with occlusal vent hole showed significantly less marginal discrepancy than groups with no occlusal vent hole(p<0.05). 3. In comparison of occlusal surface discrepancy and marginal discrepancy according to 0.5mm-marginal-vent-space, groups with no 0.5mm-marginal-vent-space showed significantly less marginal discrepancy than groups with 0.5mm-marginal-vent-space (p<0.05). In summary these results suggest that individual tooth tray made of 3 types of materials with occlusal vent hole and individual tooth tray made of acrylic resin with no marginal vent space showed good accuracy of impression. In addition, individual tooth tray which is made of bite registration materials may be more useful because of advantage in facility and timesaving aspect of fabrication.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.1
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• pp.101-107
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• 2011

Analytical solution of micro-scale milling process is presented in order to suggest available machining conditions. The size effect should be considered to determine cutting characteristics in micro-scale cutting. The feed per tooth is the most dominant cutting parameter related to the size effect in micro-scale milling process. In order to determine the feed per tooth at which chips can be formed, the finite element method is used. The finite element method is employed by utilizing the Johnson-Cook (JC) model as a constitutive model of work material flow stress. Machining experiments are performed to validate the simulation results by using a micro-machining stage. The validation is conducted by observing cutting force signals from a cutting tool and the conditions of the machined surface of the workpiece.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.21 no.2
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• pp.64-72
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• 2022

Gear designers need to select the proper tolerances for deviations in both the center distance and parallelism of axes because these deviations cause high stresses and lead to fatigue breakage of the teeth. In this study, a three-dimensional finite element analysis model was developed for a helical gear used in metro vehicles, and a bending stress analysis method for gear pairs was established according to the contact position change. Using this model, the effect of shaft misalignment due to the center distance and shaft parallelism deviations on the bending stress of the gear was analyzed. As a result, the magnitude of the bending stress changed nearly linearly with the change in the center distance deviation. The tooth contact of the helical gear is biased toward the end of the tooth width when the parallelism deviations of the shaft occur, and the tooth root bending stress increases.

• Journal of Dental Rehabilitation and Applied Science
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• v.35 no.4
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• pp.220-227
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• 2019

Purpose: The purpose of this study was to compare the degree of tooth preparation abilities of students according to three self-assessment methods. Materials and Methods: forty-eight sophomores in Kyungpook National University College of Dentistry were divided into three experimental groups. Students performed tooth preparation of the left mandibular first molar for full gold crown. They performed self-assessment using the three methods (visual, digital, and putty index self-assessment group), and reperformed tooth preparation. An intraoral scanner was used to scan each tooth model (prepared tooth and unprepared tooth), and data were acquired in standard tessellation language (STL) file format. The STL files of prepared tooth and unprepared tooth were superimposed using the 3-dimensional analysis software (Geomagic control X). And the reduction amount was measured. In the statistical analysis, all values of reduction amount were analyzed with the Wilcoxon signed rank test and Kruskal-Wallis test (α = 0.05). Results: The three self-assessment methods showed statistically significant differences (P < 0.001). The putty index self-assessment group showed the highest reduction in error than the digital self-assessment method. Conclusion: Within limitations of this study, students showed significant differences in improvement of tooth preparation ability according to the three self-evaluation methods.

• The Journal of Korean Academy of Prosthodontics
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• v.29 no.2
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• pp.147-160
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• 1991

The purpose of this study was to examine, by the method of finite element analysis, how implant geometry with or without connection between natural tooth and osseointegrated abutments affected the stress distribution in surrounding bone and osseointegrated prosthesis. The mandibular first and second molars were removed and the two osseointegrated implants were placed in the first and second molar sites. Stress analysis induced by prostheses with connection(Model A)or without connection(Model B) between natural tooth(second bicuspid) and two osseointegrated abutments(first molar and second molar) was performed under vertical point load(Load P1) or distributed point load(Load P2). The results were as follows; 1. Under vertical point load, mesial tilting was shown in both Model A and Model B and inferior displacement of Model A was greater than that of Model B in the second bicuspid. 2. Under vortical point load, the first and second molars showed mesial tilting in both Model A and Model B, and inferior displacement of them was similar in Model A and Model B and was less than that of the second bicuspid. 3. Under distributed point load, mesial displacement was shown in Model A and Model B and inferior displacement of Model A was less than that of Model B in the second bicuspid. 4. Under distributed point load, mesial tilting was shown and inferior displacement of Model A was similar to that of Model B in the first and second molars. 5. In Model A under vertical point load, high stress was concentrated in the corneal portion of first molar and distributed throughout the second molar and the second bicuspid, and the stress distribution of the second molar was greater than that of the second bicuspid. 6. In Model B under vertical point load, high stress was concentrated in the coronal and mesio-cervical portion of the first molar. 7. In Model A under distributed point load, high stress was concentrated in the mesio-cervical portion of the first molar and evenly distributed throughout the second molar and the second bicuspid. 8. In Model B under distributed point load, high stress was concentrated in the disto-cervical portion of the second bicuspid and evenly distributed throughout the first and second molars.

• The Journal of Korean Academy of Prosthodontics
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• v.37 no.3
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• pp.328-342
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• 1999

This study was performed to investigate the factors related to tooth wear. For this study, 78 patients with temporomandibular disorders and 76 dental students without any signs and symptoms of temporomandibular disorders were selected as the patients group and as the normal group, respectively. Preferred chewing side, Angle's classification, lateral guidance pattern, head and shoulder posture were observed clinically. Electromyographic activity of anterior temporalis and masseter muscle were recorded with $BioEMG^{(R)}$ and occlusal status were recorded with $T-Scan^{(R)}$. Wear facet area of each tooth was measured from working model of upper arch corresponding to the occlusal status from T-Scan. Wear facet area were measured with planimeter in $mm^2$. Total area were divided into incisal, canine, posterior tooth area. Anterior wearfacet area was incisor area plus canine area, and unilateral area was anterior area plus posterior area. The data collected were analyzed by SAS statistical program and the results of this study were as follows: 1. There was no significant difference between the two groups in total werafacet area, and male subjects showed tendency to have larger area in the normal group but female subjects showed tendency vice versa. 2. There was no significant difference related to preferred chewing side and Angle's classification, however some difference was observed by lateral guidance pattern. Anterior wear facet area in subjects of canine guidance was the largest in the three subgroups. 3. Subjects with head tilting to right side had larger posterior and total area, and subjects with higher shoulder in right side had larger canine and anterior area than any other subgrous. 4. Electromyographic activity of masseter muscle was more correlated with wear facet area than anterior temporalis muscle, and tooth contact number and force were significantly correlated with wear facet area, but the most important factor affecting tooth attrition was age.

• The Journal of Korean Academy of Prosthodontics
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• v.56 no.4
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• pp.302-307
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• 2018

Multiple tooth loss and excessive occlusal wear can result in damage to occlusal disharmony, functional disorders and esthetic problems, requiring comprehensive prosthetic treatments. Changing vertical dimension harmonized with surrounding muscle tissue is important. In this case, the patient with loss of vertical dimension caused by severe tooth loss and tooth wear was treated with the analysis of vertical dimension, such as diagnostic model, radiography and various clinical exams. the patient was satisfied with favorable functions and esthetics for 1 years of follow-up.