• Journal of the Korean Society for Precision Engineering
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• v.12 no.8
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• pp.63-72
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• 1995

Closed-die forging of spur gears with hollow cylindrical billet has been analysed by using the upper-bound method. A kinematically admissible velocity field has been developed, wherein, an involute curve has been introduced to represent the forging die profile. In the analysis, the deformation region has been divided into nine zones. A constant frictional stress has been assumed on the contacting surfaces. Utilizing the formulated velocity field, numerical calculations have been carried out to investigate the effects of various parameters, such as module, number of teeth and friction factor, on the forging of spur gears. Hardness and accuracy of forged gears are measured. The following results have been obtained: (1) It is verified that an axisymmetric deformation zone exists between root circle and center of gear through forged gears. (2) The average relative forging pressure is predominantly dependent on the number of teeth and increases near the final filling stage as the addendum modification coefficient increases. (3) Close agreement was found between the predicted values of forging load and those obtained from experimental results.

• The korean journal of orthodontics
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• v.31 no.1 s.84
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• pp.51-61
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• 2001

Cleft lip and/or palate (CLP) is one of the most common congenital craniofacial anomalies and occurs more frequently in Asian people. Dental abnormalities in number, size, shape, and eruption of teeth are frequently associated with CLP. The purposes of this study were to investigate the effects of CLP on number, size, shape and eruption of teeth and to provide basic clinical data for diagnosis and treatment of the CLP patients. With the orthodontic and cleft charts, diagnostic models, orthopantomograms and intraoral x-ray films from 241 CLP patients who visited Dept. of Orthodontics, Seoul National University Dental Hospital, we evaluated the frequency of congenital missing teeth, supernumerary teeth, Impacted teeth, and microdontia. The results were as fellows ; 1. Frequency of congenital missing was relatively high up to $56.8\%$. Congenital missing occurred frequently in the maxillary lateral incisor and the maxillary second premolar. Among the CLP types, frequencies of congenital missing in cleft lip and Palate group and cleft lip and alveolus group were higher than those of cleft lip group and cleft palate group. And bilateral cleft showed higher frequencies than unilateral ones. 2. Supernumerary tooth was shown in $11.2\%$ of CLP patients. It occurred frequently in the area between the maxillary lateral Incisors and the maxillary canine. Among the CLP types, cleft lip group showed relatively most highest frequency. 3. Impaction was shown in $18.3\%$ of CLP patients. It occurred most frequently In the maxillary lateral incisor and the maxillary canine than other teeth. Among the CLP types, cleft lip group and cleft lip and palate group showed most highest frequencies. 4. Microdontia was shown in $15.8\%$ of CLP patients. It occurred the most frequently In the maxillary lateral incisors and maxillary canines. Among the CLP types, cleft lip and alveolus group and cleft lip and palate group showed relatively higher frequencies. There was no microdontia in cleft palate group.

• Journal of the korean academy of Pediatric Dentistry
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• v.41 no.1
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• pp.1-7
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• 2014

If it is possible to preserve and culture cells from exfoliated deciduous teeth in a readily available storage medium within each family, more stem cells would be obtained. This research is about the effect of storage media and time on pulpal cell viability of exfoliated deciduous teeth. 330 exfoliated deciduous teeth were randomly divided into 11 groups; fresh group, dry group, groups stored in cell culture medium (2, 4, 7 days each), in milk (2, 4, 7 days each), and in saline (2, 4, 7 days each). Primary culture of pulpal cells was conducted in each group and the success rates were compared by calculating the number of teeth with viable cells. The result of primary culture shows that the success rate decreases as the time of storage gets longer. There was no statistical difference between groups stored in the cell culture medium, milk, and saline for 2 and 4 days. However, the groups stored in milk and saline for 7 days showed dramatic decrease in success rate compared to the group stored in the cell culture medium. In conclusion, exfoliated or extracted deciduous teeth can be used to culture pulpal cells when they are stored in milk and saline for a certain period of time; however obtaining viable pulpal cells becomes harder as the storage time gets longer.

• Korean Journal of Health Education and Promotion
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• v.17 no.1
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• pp.95-113
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• 2000

The purpose of this study is to investigate the state of the dental health of adults, used self-reporting qestionnaire as objects of 923 residents living in nine districts at random among the sites of eleven town located in a County. The level of knowledge on dental health of adults in a County was 65.6 points out of 100 points, comparatively low. Accodingly, it is necessary for entire adults to have a dental health-related education and get high standard of knowledge. Especially, educational approach should be performed for groups of 40-49 years old, 50-59 years old, above 60 years old, male, no educational background, having only elementary and middle school education, not having any jobs, engaging in agriculture, doing business on their own and so on. When planning the contents of health education, one actually has to include the habit of amalgam, the factor in influencing on dental health as well as show an example such as how to brush teeth, checking point of proper brushing, how to grip toothbrush. The attitude score related to dental heath was 71.2 points out of 100 points, relatively low. Consequently, the change of attitude related the dental health among entire adults is necessary, particularily, the strategical approach is essential to change dental health connected to attitude positively for groups of male, having high school education background, office workers and the civil service. Besides, among dental health related symtoms, more that 30-40％ of objects showed negative attitude toward as the following cases; in case that plaque or food debris are attached to the teeth (40.8％), upper and lower teeth do not fit together(40.3％), you cannot sleep well because of toothache(31.0％), more than one tooth fall out(31.0％), you have loosing teeth(30.6％), the approach should be conducted to form attitude that dental care is necessry. The state of dental health through dental health related symtoms was 33.3 points out of 100 points, which was fairly satisfactory. However, dental treatment for the state of dental health should be executed in case of comparison of the dental health state according to general characteristics, the group who are above 60 years old, have elementary school education background, engage in aggriculture who are not good in dental health state as opposed to other groups. Furthermore, there should be dental care needs according to dental health related symtoms, particularly, more than 60-70％ of objects have experienced symtoms that plaque or food debris attached to the teeth, tartar is on the teeth so dental treatment should be peformed for a large number of adults. In addition, for the people who have indications that there was a cavity, more than one tooth loss, chilled teeth, toothache when chewing, loose teeth, upper and lower teeth do not fit together, you cannnt sleep well due to the toothach, etc, there should be care through dental treatment. The actual conditions of the hygine of the mouth was relatively good and the difference of the actual state of dental health care in terms of general characteristics showed in only gender; female was more careful in dental health. Comparing the state of oral health synthetically, when they have symtoms, only 34.8％ of objects go to a dentist, 60.7％ are using passive or negative care such as gargling, tolerating or ignoring. There was many symtoms to care through dental therapy such as plaque or food debris get in between the teeth, tartar on the teeth, teeth are very cold, more than one tooth fallout, loose teeth, there is wrong amalgam, and so on, among symtoms to care passively or negatively. Therefore the education for proper treatment program should be performed. As a result of dental health-related knowlege, attitude, health state, verification of correlation between the actual condition of care, the higher the dental heath-related knowldege becomes, the more positive the dental health-related attitude is, and the state of dental health, that is, the standard of the symtom of dental health diminishes. the care for dental health executed through more active method and the more positive dental health-related attitude is, the more active means they performed. Consequently, the high level of dental health-related knowledge should be necessary, the more positive the dental health-related attitude was, the more active method they adopted, therefore, the program is needed to form attitude related to the dental health positively. As the knowledge on dental health is increasing, the attitude is also positive, after all, the plan to increase the standard of knowledge on dental health should be contrived through education program related to dental health.

• The korean journal of orthodontics
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• v.41 no.5
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• pp.346-353
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• 2011

Objective: The purpose of this study was to investigate the prevalence of dental anomalies in outpatient clinics. Methods: The subjects of this study were 3,133 patients who visited the clinic between January 2009 and June 2011. The dental records and panoramic films of the patients and detection of supernumerary, missing, and impacted teeth, transposition, and peg lateralis were reviewed. The results were analyzed according to gender and types and locations of dental anomalies. Results: Among the patients, 362 had dental anomalies, with a prevalence rate of 11.55%. Congenital missing teeth (5.71%) ranked first in the categories, and impacted teeth (3.09%) ranked second. The percentage of patients having supernumerary teeth, peg lateralis, and dislocated teeth were 1.79%, 1.66%, and 0.45%, respectively. Conclusions: Congenital missing teeth and impacted teeth are, respectively, the first and second most common dental anomalies in Korean dental patients.

• Journal of Oral Medicine and Pain
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• v.33 no.1
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• pp.59-66
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• 2008

Ribosomal Protein S4Y(RPS4Y) gene is the human sex-linked gene on the Y chromosome. There are a number of reports on the sex determination using RPS4Y gene analysis for prevention and diagnosis in sex-linked disease. Thus RPS4Y gene is a reliable genetic marker for sex determination in forensic medicine. In general, the sex determination of an unidentified body can be achieved based on anatomical characteristics, but sometimes sex determination was considered to be difficult such as pre-adolescent bodies or decomposed, mutilated bodies. In this case, Sex determination using PCR method in human teeth produces good results. Because human teeth have a great structural durability, the DNA well preserved in the teeth. So author isolated nuclear DNA from the 20 human teeth(10 males, 10 females), performed to detect RPS4Y gene by PCR method. Samples were divided four group(10 pulp and 10 dentinal tissue in male, 10 pulp and 10 dentinal tissue in female). It was found that detection of RPS4Y gene for sex determination was possible in all the male pulp tissues and 6 out of 10 male dentinal tissues. But there was not detected in female pulp and dentinal tissues. In the view of this results demonstrates the possibility that detection of RPS4Y gene with other sex chromosome genes from the human teeth is useful to sex determination in forensic medicine.

• Journal of the korean academy of Pediatric Dentistry
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• v.36 no.2
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• pp.245-252
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• 2009

The congenital missing of teeth is common, which takes place since the proliferation and differentiation are not allowed in that tooth bud fail to start development. The purpose of this study is to research incidence rate, number, and missing part of congenital missing teeth, and to study whether a person who has missing teeth has other abnormality of teeth or not. For this study, 1,520 subjects(aged 2.9$\sim$17) who had visited pediatric dentist department of Chonbuk national university dental hospital within 2 years were examined with an panoramic radiograph; exempting third molar missing state. The obtained results are as follows. 1. 8.88% among total subjects show missing teeth; male 9.05%, female 8.64% 2. The most frequently missing permanent teeth were the mandibular second premolars(22.3%). The most frequently missing primary teeth are mandibular lateral incisors(50%). 3. 43.3% patients have one permanent missing tooth, 34.3% have two, and 10.4% have more than six, respectively. In primary teeth, 86.7% patients have one missing tooth, and 13.3% have two missing teeth. 4. 18 patients(13.3%) have missing teeth as well as hyperdontia, while some patients have microdont, ectopic eruption, and fusion teeth.

• Journal of the korean academy of Pediatric Dentistry
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• v.31 no.2
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• pp.290-298
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• 2004

In children, change in lifestyles such as an increase in participation of physical activities has increased the chance of receiving an injury, harming the child and their parents. This study was carried out to give basic information of traumatic injuries to the upper anterior teeth which can be used in prevention of future complications that may arise. From June, 2002 to May, 2003, of the 8,799 children in their primary and mixed dentition visiting Department of Pediatric Dentistry, College of Dentistry, Yonsei University 955 upper anterior teeth(primary 543, permanent 412) of 487 children(male 316, female 171) with traumatic injures to the upper incisors were studied. The results were as follows: 1. Trauma to the primary teeth prevailed at the age of 1-3 and to the permanent teeth at the age of 7. The male to female ratio was 1.85:1. 2. Trauma to the upper incisors for both the primary and permanent teeth occurred in the afternoon. Primary teeth were injured most frequently in the home(44.1%) and the permanent teeth outdoors, in the street(17.5%). 3. Both the primary and permanent teeth were most injured by fall-down injuries(39.8%, 12.9%), and next were collisions(22.2%, 6.0%). For the primary teeth, high fall, traffic accident, violence and sports are next in order, and for the permanent teeth, violence, sorts, traffic accidents were next. 4. Average number of 1.6 primary teeth and 2.8 permanent teeth were injured with the right central incisor most prevailing. 5. Crown fracture without pulpal exposure and subluxation injures were highest in frequency in both the primary and permanent teeth.

• Journal of Periodontal and Implant Science
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• v.23 no.3
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• pp.564-576
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• 1993

The purpose of this study was to evaluate the effects of Nd:YAG laser treatment on removal of smear layer and exposure of dentinal tubules. The experimental specimens were obtained from root planed surface of 30 human teeth which were extracted due to severe periodontal disease. The specimens were assigned randomly of three groups: root planed group, Tetracycline HCl(100mg/ml, 5min) group, and Nd:YAG laser ($Laser-35^{TM}$, U.S.A. 5 seconds )group. Nd:YAG laser group was divided into 4 subgroups according to 3.0W, 3.5W, 4.0W, 4.5W of power. The surface change of specimens were evaluated by scanning electron microscopy. The number of exposed dentinal tubules and percentage of area occupied by dentinal tubule orifices per unit area between each group was statistically analyzed by paired Student t-test. The results were as follows: 1. By root planing only, dentinal tubule was not exposed, but scale-like smear layer and parallel instrument tracks were resulted. 2. Tetracycline HCl treated surfaces exhibited the small number of partially exposed dentinal tubules with long orifices. The number($3.80{\pm}0.79$) of exposed dentinal tubules on Tetracycline HCl group was significantly less than that in laser groups above 3.5W of power(P<0.001), and the percentage ($0.68{\pm}0.19$) of area occufied by dentinal tubule orifices per unit area($192\;{\mu}m^2$) was significantly lower than that of any laser group(P<0.001). 3. The laser group irradiated with 4.5W of power showed both the most number($10.60{\pm}0.97$) of exposed dentinal tubules among the experimental groups, and the highest percentage($3.75{\pm}0.55\;%$) of area occupied by dentinal tubule orifices. 4. Energy Surge during laser pulsing and overlapping passes of the fiber resulted in melted and resolidified surface textures with lava-like appearance.

• Elastomers and Composites
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• v.44 no.4
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• pp.391-396
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• 2009

This paper presents the numerical analysis of thread rolling. Firstly, the analysis is focused on the effective analysis conditions that guarantee the reliability of the analysis results. The investigated parameters are the number of teeth and the number of elements. Using the analysis results, the number of elements and the number of teeth that guarantee the results are found. And then, the effects of the process parameters such as tool shape and temperature on the thread rolling are investigated. The analysis is carried out using DEFORM-3D. The results show that the flank angle and crest round have an effect on the thread rolling load. It is also shown that temperature have significant effects on the effective strain distribution, rolling load, and crack initiation. The crack initiation is predicted using the Cockcroft-Latham criterion.