• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.4
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• pp.387-393
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• 2012

A roller rack pinion (RRP) system, which consists of a rack-bar and a cam pinion, transforms a rotation motion into a linear one. The rack-bar has a series of roller trains, and meshes with the cam pinion. This paper first proposes the exact tooth profile of the cam pinion and the non-undercut condition to satisfy the required performance by introducing the profile shift coefficient. The paper then investigates the load stress factors under various shape design parameters to predict the gear surface fatigue limit, which was strongly related to the gear noise and vibration at the contact patch. The results show that the pitting life can be extended significantly with an increase in the profile shift coefficient.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.11
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• pp.1125-1130
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• 2017

The tooth shapes of serration-type and spline-type reactors are optimized using finite element methods to improve the working life of the part and to lower the stress concentration during rotation resulting from contact with the outer race for a reactor operating with $170^{\circ}C$ transmission oil. The results of thermal expansion analyses between an Al reactor and the steel outer race indicate that, before optimization, the gap between the two parts increases further as the serration-type reactor expands by 0.1 mm and the spline-type one strains by 0.08 mm. Because of shape optimization, a trapezoidal shape is obtained from the initial triangular serration and the rectangular spline of the two reactors. The maximum von Mises stress of the serration-type convertor decreased by 24.5 ％, and by 9.3 ％ for the spline-type convertor. In addition, there is a 13 ％ reduction in the axial thickness, as compared to the initially designed model.

• Korean Journal of Materials Research
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• v.2 no.2
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• pp.119-125
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• 1992

Oxygen segregation in horizontal-magnetic-field-applied Czochralski (HMCZ) silicon crystals has been studied as a function of magnetic field strength (B) and crucible rotation rate (C). Along the axis of 57mm din. <100> crystals grown under B=2, 3, 4 kG and C=4-15rpm, the oxygen distribution was usually saw-tooth shaped and fluctuated unevenly. Compared to the conventional CZ method, this result seems to indicate that the horizontal magnetic field, at levels used in the present experiment, had a destabilizing influence on oxygen transport to the growth interface. On the other hand, as C increased, the oxygen fluctuation lessened, and [0] increased overall. At B=2 kG, an oxygen profile in a level of 27-36 ppma was achieved by a programmed ramp of C. Oxygen precipitation behavior of the HMCZ silicon during a simulated device manufacturing process was compared and found to be inferior to that of typical CZ silicon. The uneven oxygen profile in the as-grown state was identified as the major source of poor precipitation uniformity in the HMCZ silicon.

• Structural Engineering and Mechanics
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• v.88 no.4
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• pp.389-403
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• 2023

In order to explore the influence of tooth root cracks on the dynamic characteristics of multi-stage planetary gear transmission systems, a concentrated parameter method was used to construct a nonlinear dynamic model of the system with 30-DOF in bending and torsion, taking into account factors such as crack depth, length, angle, error, time-varying meshing stiffness (TVMS), and damping. In the model, the energy method was used to establish a TVMS model with cracks, and the influence of cracks on the TVMS of the system was studied. By using the Runge- Kutta method to calculate the differential equations of system dynamics, a series of system vibration diagrams containing cracks were obtained, and the influence of different crack parameters on the vibration of the system was analyzed. And vibration testing experiments were conducted on the system with planetary gear cracks. The results show that when the gear contains cracks, the TVMS of the system will decrease, and as the cracks intensify, the TVMS will decrease. When cracks appear on the II-stage planetary gear, the system will experience impact effects with intervals of rotation cycles of the II-stage planetary gear. There will be obvious sidebands near the meshing frequency doubling, and the vibration trajectory of the gear will also become disordered. These situations will become more and more obvious as the degree of cracks intensifies. Through experiments, the theoretical results are in good agreement with experimental results, verifying the correctness of the theoretical model. This provides a theoretical basis for fault diagnosis and reliability research of the system.

• The korean journal of orthodontics
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• v.29 no.4 s.75
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• pp.457-466
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• 1999

It has been reported that skeletal relapse and dental change after mandibular setback do occur not only after intermaxillary fixation(IMF) removal but also during IMF The side effects of skeletal relapse during IMF have clinical importance because they can cause many Postoperative orthodontic Problems. Generally, the Prevention of solid union between segments, compensatory tooth movement, anterior openbite, etc. have been cited as the side effects of jaw displacement. The purpose of this study was to evaluate the skeletal relapse and dental change during IMF. The material consisted of 28 patients who were treated by BSSRO(bilateral sagittal split ramus osteotomy), wire osteosynthesis, IMF for correction of mandibular prognathism. Through cephalometric analysis, the amount and direction of surgical movement, skeletal relapse and dental change during IMF were measured. The correlation between surgical movement and skeletal relapse, between skeletal relapse and dental changes were evaluated. The following conclusions were obtained; 1. Distal segment was repositioned backward and upward, proximal segment showed clockwise rotation during surgery. 2. During ]m, anterior portion of distal segment was displaced backward and posterior portion was displaced upward. Proximal segment was displaced upward with forward movement of p-Go(gonion of proximal segment). Backward surgical movement of p-GO was significantly correlated with forward displacement of p-Go. 3. Overjet and overbite were not changed during IMF. The compensatory tooth movements during IMF were characterized by retroclination of upper incisors md retroclination, extrusion of lower incisors. These compensatory tooth movements had statistically significant correlation with upward displacement of d-Go (gonion of distal segment).

• Journal of the korean academy of Pediatric Dentistry
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• v.35 no.2
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• pp.268-277
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• 2008

Authors evaluated 1171 patients at the department of Pediatric Dentistry in Kyoungpook National University Hospital through clinical records and radiographs. And the following features were studied ; age, sex distribution, number of mesiodens per patients, cause of discovery of mesiodens, location, status of eruption, shape and orientation of crown, complication, dental age of adjacent upper incisor tooth at the time of surgical extraction of mesiodens and the relationship between the resolution rate of complication after extraction of mesiodens and the dental age of adjacent upper incisor tooth, length of diastema, the eruption status of lateral incisor and the crowding status of premaxilla. The followings are the results : 1. The cause of discovery of mesiodens were as follows ; delayed eruption of the permanent incisors in 13.8%, midline diastema in 11.6%, radiographs taken for other reasons in 23.4% and for caries treatment in 15.1%. 2. Complication due to the presence of mesiodens did not occur in 36.8%, delayed eruption of adjacent teeth was observed in 16.1%, midline diastema in 34.4%, rotation in 8.8%, displacement in 2.4%, and crowding in 1.0% of all evaluated patients. 3. As for the dental age of adjacent upper incisor tooth at the time of surgical extraction of mesiodens, below 1/3 of total root length were observed in 3.5%, $1/3{\sim}1/2$ of total root length in 19.9%, $1/2{\sim}2/3$ of total root length in 54.7% and over 2/3 in 21.9% of all evaluated patients. 4. Resolution rate of delayed eruption after the extraction of mesiodens was significant higher in the group with the root length below 1/2. Resolution rate of midline diastema was significant higher in the group with diastema width below 3mm and with non-crowding of adjacent upper incisor teeth.

• The korean journal of orthodontics
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• v.31 no.6 s.89
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• pp.559-566
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• 2001

This study was undertaken to demonstrate the forces in the mandibular alveolar bone generated by activation of the mandibular posterior crossbite appliance in the treatment of buccal crossbite caused by lingual eruption of mandibular second molar. A three-dimensional photoelastic model was fabricated using a photoelastic material (PL-3) to simulate alveolar bone. We observed the model from the anterior to the posterior view in a circular polariscope and recorded photogtaphically before and after activation of the mandibular posterior crossbite appliance. The following results were obtained : 1. When the traction force was applied on the buccal surface of the mandibular second molar, stress was concentrated at the lingual alveolar crest and root apex area. The axis of rotation also was at the middle third of the buccal toot surface and the root apex, so that uncontrolled tipping and a buccal traction force for the mandibular second molar were developed. 2. When the traction force was applied on the lingual surface of the mandibular second molar more stress was observed as opposed to those situations in which the force application was on the buccal surface. In addition, stress intensity was increased below the loot areas and the axis of rotation of the mandibular second molar was lost. In result, controlled tipping and intrusive tooth movements were developed. 3. When the traction forte was applied on either buccal or lingual surface of the second molar, the color patterns of the anchorage unit were similar to the initial color pattern of that before the force application. So we can use the lingual arch for effective anchorage in correcting the posterior buccal crossbite. As in above mentioned results, we must avoid the rotation and uncontrolled tipping, creating occlusal interference of the malpositioned mandibular second molar when correcting posterior buccal crossbite. For this purpose, we recommend the lingual traction force on the second molar as opposed to the buccal traction.

• The korean journal of orthodontics
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• v.37 no.6
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• pp.407-420
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• 2007

The aim of this study was to compare the differences in closing extraction spaces between maxillary first premolar and second premolar extractions using 3-dimensional finite element analysis (FEA). Methods: Maxillary artificial teeth were selected according to Wheeler's dental anatomy. The size and shape of each tooth, bracket and archwire were made from captured real images by a 3D laser scanner and FEA was performed with a 10-noded tetrahedron. A $10^{\circ}$ gable bend was placed behind the bull loop on a $0.017"{\times}0.025"$ archwire. The extraction space was then closed through 12 repeated activating processes for each 2mm of space. Results and Conclusions: The study demonstrated that the retraction of anterior teeth was less for the second premolar extraction than for the first premolar extraction. The anterior teeth showed a controlled tipping movement with slight extrusion, and the posterior teeth showed a mesial-in rotational movement. For the second premolar extraction, buccal movement of posterior teeth was highly increased.

• Journal of the korean academy of Pediatric Dentistry
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• v.30 no.3
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• pp.363-372
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• 2003

Supernumerary teeth are found frequently in the dental office causing many dental complications. They are one of the many dental abnormalities that may occur during tooth development. Inversely impacted supernumerary teeth in the midpalatal area are especially important clinically because they occur with high frequency and many complications. Though many previous clinical and radiographical studies exist, the sample numbers were small and the evaluation of shape, location, and effects to its surrounding tissue may not be accurate due to the solitary use of intraoral radiographs or panoramic radiographs. Among the patients who visited department of pediatric dentistry, yonsei dental hospital, from July, 1998 to June, 2002, those with inversely impacted supernumerary teeth took computerized tomography for a more accurate diagnosis. Their dental chart, panoramic radiograph and computerized tomography were evaluated for this study. The number, form, convexity, location, distance, and complications of inversely impacted supernumerary teeth in the midpalatal area were recorded. This study show that when the supernumerary teeth is tuberculated with a curved root and is in close proximity to the adjacent teeth, it causes complications such as eruption disturbance, rotation, displacement of adjacent teeth, and diastema. Such factors must be considered in making decisions for diagnosis and treatment.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.36 no.5
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• pp.375-379
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• 2010

Introduction: In the management of dentofacial deformities, variable movement of the maxilla can be made possible by a Le Fort I osteotomy. Posterior impaction of the maxilla necessary for rotation of the maxillomandibular complex enhances the functions and esthetic results. In cases of posterior impaction of the maxilla, an increase in the figure of the occlusal plane angle and incisor inclination can occur. This study reports the relationship between the amount of posterior impaction and the change in the occlusal plane angle and incisor inclination in a Le Fort I osteotomy by preoperative and postoperative lateral cephalograms. Materials and Methods: Twenty patients who had undergone orthognathic surgery in Dong-A University Medical Center participated in this study. Lateral cephalometrics, within 3 weeks prior to surgery and 3 days after surgery, were used for analysis. Pre and postoperative measurements of the occlusal plane angle and incisal inclination based on the Frankfort horizontal (FH) plane were performed. X and Y were defined as the amount of vertical change in the upper incisor tip and the amount of vertical change in the upper first molar mesial cup tip through the operation. The amount of final posterior maxillary impaction was determined by subtracting Y from X, which is the difference in vertical height. According to the amount of posterior maxillary impaction, the change in the occlusal plane angle and incisal inclination was measured. Results: The average posterior maxillary impaction was 2.91 mm and the average change in the occlusal plane angle and incisal inclination was $6.54^{\circ}$after surgery. As a result, each mm of posterior maxillary impaction changed the occlusal plane angle and incisal inclination by $2.25^{\circ}$. Statistically, there was high significance. Two cases were observed: one with the same amount of posterior maxillary impaction performed on both the right and left showing $2.20^{\circ}$, and the other with a different amount of posterior maxillary impaction performed showing $2.35^{\circ}$. In this case, there was no significance difference between the two cases. Conclusion: Each mm of posterior maxillary impaction changes the occlusal plane angle and incisal inclination by an average of $2.25^{\circ}$. In posterior maxillary impaction, there was no significant difference in the amount of change in the occlusal plane angle and incisal inclination regardless of whether there was an equal amount of posterior maxillary impaction on both sides. This study is expected to help in the presurgical orthodontic preparation and presurgical treatment planning.