• Tunnel and Underground Space
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• v.23 no.6
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• pp.480-492
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• 2013

After the introduction of geothermal power generation technology based on engineering reservoir creation that can be applied on non-volcanic region, industrial need for studies on the efficient and economic execution of costly deep-depth drilling work becomes manifest increasingly. However, since it is very difficult to predict duration and cost of boring work with acceptable reliability because of many uncertain events during the execution, efficient and organized work management for drilling is not easily achievable. Especially, the round trip that discretely occurs because of the abrasion of bit takes more time as the depth goes deeper and it has a great impact on the work performance. Therefore, a technology that can simulate the occurrence timing and depth of round trip in advance and therefore optimize them is essentially required. This study divided the abrasion state of bit into eight steps for simulation cases and developed a forecast algorithm, i.e., TOSA which can analyze the depth and timing of round trip occurrence. A methodology that can divide a unit section for simulation has been suggested; while the Bourgoyne and Young model has been used for the forecast of drilling rates and bit abrasion extent by section. Lastly, the designed algorithm has been systemized for the convenience of the user.

• Journal of Korean society of Dental Hygiene
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• v.8 no.4
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• pp.205-217
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• 2008

The purpose of this study was to provide information on the development of an oral-health promotion program geared toward office workers. The subjects in this study were 240 employees at the headquarters of S construction company. After a survey was conducted in July and August 2008, the answer sheets from 208 respondents were gathered, and 191 answer sheets were analyzed except 17 unanalyzable ones. The findings of the study were as follows: 1. In regard to subjective oral health status, the largest number of the participants that accounted for 37.2% found their mouth to be neither healthy nor unhealthy. The greatest number of them that represented 58.1% had never visited a dentist's office to receive preventive treatment. 2. Regarding relationship between toothbrushing education experience and toothbrushing frequency, the most common toothbrushing frequency was three times a day( 46.5%) among the company employees who had ever received that education. In the event of the office workers without that experience, the most prevalent frequency was three times(63.6%). The toothbrushing frequency was statistically significantly different according to the toothbrushing education experience(p<0.05). As to the relationship of toothbrushing education experience to tooth- brushing method, the largest number(48.2%) of those who had ever received that education brushed their upper and lower teeth along with the gums by rotating the toothbrush downward from the top and upward from the bottom respectively. In the event of the office workers without that experience, 49.4 percent brushed their teeth and gums by rotating the toothbrush up and down. Thus, whether they had ever received education about toothbrushing made a statistically significant difference to their toothbrushing method(p<0.05). 3. As a result of evaluating their oral health belief by utilizing a five-point scale, they got a mean of 2.95. In each area of oral health belief, they got the best marks in benefit(3.66), salience(3.42), barrier(2.84), susceptility(2.58) and seriousness(2.23). Given the above-mentioned finding of the study, two sorts of oral health beliefs, which are benefit and salience, should be stressed in the development of oral health education programs that cater to company employees. And sustained research efforts should be channeled into finding out the relationship between oral health and actual oral health care.

• Journal of Dental Rehabilitation and Applied Science
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• v.30 no.4
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• pp.265-277
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• 2014

Purpose: The purpose of this study was to investigate the differences of displacement pattern depending on type of sliding jig and application method during maxillary molar distalization with temporary anchorage devices (TADs). Materials and Methods: Maxilla with normal tooth size and arch shape was selected to create a 3-dimensional finite element model, which included the bracket, orthodontic main archwire, removable sliding jig (R-jig). The orthodontic mini-implant anchorage was set 8 mm superiorly from main archwire, buccally between the second premolar and first molar. The base experimental design was Condition 1, which was composed $0.019{\times}0.025$ inch stainless steel (SS) of wire size of R-jig, 200 gm force, un-tied state. And the other designs varied to wire size of R-jig, magnitude of force. The results are as follows. Results: As the wire size of R-jig was increased, the deformation of R-jig was decreased. However, the displacement of second molar wasn't different each other. As the force to second molar was increased, the more displacement of second molar was observed, and the more distal tipping movement, vetical displacement was observed. Conclusion: R-jig can get distal teeth movement in orthodontic treatment without side effects.

• Restorative Dentistry and Endodontics
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• v.31 no.5
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• pp.359-370
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• 2006

The objective of this study was to investigate the effect of excessive occlusal loading on stress distribution on four type of cervical lesion, using a three dimensional finite element analysis (3D FEA). The extracted maxillary second premolar was scanned serially with Micro-CT. The 3D images were processed by 3D-DOCTOR. ANSYS was used to mesh and analyze 3D FE model. Four different lesion configurations representative of the various types observed clinically for teeth were studied. A static point load of 500N was applied to the buccal and lingual cusp (Load A and B). The principal stresses in lesion apex, and vertical sectioned margin of cervical wall were analyzed. The results were as follows 1. The patterns of stress distribution were similar but the magnitude was different in four types of lesion 2. The peak stress was observed at mesial corner and also stresses concentrated at lesion apex. 3. The compressive stress under load A and the tensile stress under load B were dominant stress. 4. Under the load, lesion can be increased and harmful to tooth structure unless restored.

• Journal of the korean academy of Pediatric Dentistry
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• v.41 no.3
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• pp.233-240
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• 2014

An in vitro study on cariogenic potential of four over-the-counter nutritional supplements for children was performed. The experimental groups were four over-the-counter nutritional supplements. The positive control group was 10% sucrose solution (S), and the negative control group was artificial saliva (T). The pH of each group, the buffering capacities, acid production, the microhardness changes of the bovine teeth specimens were measured. The pH of all experimental groups were lower than critical pH 5.5 where enamel demineralization starts. The buffering capacity of the Hama Vitamin Pharm (Hamsoa Pharm Co., Korea) was highest, and the Smart Chewable Vitamin A (JW Pharm Co., Korea) had the lowest buffering capacity. The reduction rates of the pH of the experimental groups were significantly higher than that of the negative control group (p < 0.05). The microhardness of enamel of all experimental groups and the positive control group significantly decreased. In contrast, the microhardness of enamel of the negative control group significantly increased after experiment (p < 0.05). The reduction rate of the microhardness of enamel of the Hama Vitamin Pharm (Hamsoa Pharm Co., Korea) was significantly higher and Hikid Plus (Sanga Pharm Co., Korea) was significantly lower than the other experimental groups.

• Journal of the korean academy of Pediatric Dentistry
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• v.41 no.3
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• pp.225-232
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• 2014

The purpose of this study was to compare skeletal maturity index and dental developmental stages based on skeletal malocclusion. A total of 192 patients (89 male and 103 female) between 6 to 14 years old were selected for this study and underwent cephalograms, panorama radiographs, and hand-wrist radiographs. Any syndromic cases were excluded. Selected clinical parameters were dichotomised for statistical analysis. Chi-square, logistic regression analysis, and independent t-tests were used for the statistical evaluation. Canine, first molar, and second molar calcification were significantly associated with skeletal maturity in the logistic regression model (p < 0.05). In addition, patients who had higher skeletal maturity index were 11.43 times more likely to be female than those who had lower skeletal maturity index (p < 0.001). The patients with skeletal class II malocclusion displayed significantly higher dental developmental stage in canines, first premolars, first molars, and second molars than the patients with class III malocclusion (p < 0.05). The dental developmental stage of the patients was significantly associated with skeletal maturity. In addition, there was a significant difference between class II and class III malocclusion with some types of tooth calcification.

• The korean journal of orthodontics
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• v.27 no.1
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• pp.55-63
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• 1997

The purpose of thus study was to measure the changes of arch and dentition of maxillary posterior teeth before and after treatment and postretentios in patients treated with Quad-helix. Measurements and analysis were performed on study model with carlipers. Seventeen cases, eight boys and nine girls, were selected with average ages of 12.7 years. Mean retention period was 4 months, and mean wearing time was. 127 days. The result were as follows 1. The interpremolar widths and intermolar width were significantly increased in maxillary first piennolar and molar when compared between before and after treatment and postretention. The maxillary second premolar resulted in significant increase in interpremolar between after tretment and post retention. 2. The long axis of maxillary first premolar and first molar accompaning buccal tipping was significant increased before and after Tx and post retention. Significant increase of the lingual inclination of maxillary second premolar was obsered both in before and after Tx, and before Tx and post retention. 3. The distance between the height of tooth contour was significantly increased in the first and second premolar before and after Tx, and was significant increased in the first molar before and after Tx and post retention. 4. Intermolar width at the palatal groove was increased in before and after Tx. and post retention. The palatal depth was significant increased in before and after Tx. In conclusion expansion of maxillary dental arch showed no relapse and results were stable retention

• The Journal of Korean Academy of Prosthodontics
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• v.32 no.4
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• pp.484-514
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• 1994

Cantilever bridge is widely used by mny clinicians, but its worst mechanical character, so called Class I lever system, makes dentists hesitate to restore the missing tooth with it. Therefore it is important to study stress of the cantilever bridge. In this study, two models of cantilever bridges that restores the missing mandibular second molar with two abutment teeth were constructed. One model was a type of cantilever bridge supported by a normal alveolar bone, the other one was supported by an alveolar bone resorbed to its 1/3 of root length. Maximum bite force(550N) and funtional maximum bite force(300N) were vertically applied to the distal end of the pontic, distal 1/3, and distal half of the pontic. And each force was also applied to centric occlusal contacts as a distributed force. Total 16 loading cases were compared and analyzed with 3-dimensional finite element method. The results were as follows: 1. The stress was concentrated on the joint of the pontic and the retainer, grooves, and distal cervical margin of the posterior retainer. 2. In case of maximum bite force(550N) at the end of the pontic, the risk of fracture at the joint of the pontic and the retainer was high. 3. In case of distributed force in centric occlusion and functional maximum bite force(300N), the stresses were less than the yield strength of the type VI gold for any loading cases. 4. In case of alveolar bone resorption, the occlusal force to the cantilever pontic caused more stress on the root apex and less stress on the alveolar crest region of the distal surface of the posterior abutment. 5. In case of alveolar bone resorption, the displacement was larger than that of normal alveolar bone in all loading cases.

• Restorative Dentistry and Endodontics
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• v.25 no.1
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• pp.91-108
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• 2000

Most of cervical abrasion and erosion lesions show gingival margin where the cavosurface angle is on cementum or dentin. Composite resin restoration of cervical lesion shrink toward enamel margin due to polymerization contraction. This shrinkage has clinical problem such as microleakage and secondary caries. Several methods to diminish contraction stress of composite resin restoration, such as modifying cavity form and building up restorations in several increments have been attempted. The purpose of this study was to compare polymerization contraction stress of composite resin in Class V cavity subjected to cavity forms and placement methods. In this study, finite element model of 5 types of Class V cavity was developed on computer tomogram of maxillary central incisor. The types are : 1) Box cavity 2) Box cavity with incisal bevel 3) V shape cavity 4) V shape cavity with incisal bevel 5) Saucer shape cavity. The placement methods are 1) Incisal first oblique incremental curing 2) Bulk curing. An FEM based program for light activated polymerization is not available. For simulation of curing dynamics, time dependent transient thermal conduction analysis was conducted on each cavity and each placement method. For simulation of polymerization shrinkage, thermal stress analysis was performed with each cavity and each placement method. The time-temperature dependent volume shrinkage rate, elastic modulus, and Poisson's ratio were determined in thermal conduction data. The results were as follows : 1. With all five Class V cavifies, the highest Von Mises stress at the composite-tooth interface occurred at gingival margin. 2. With box cavity, V shape cavity and saucer cavity, Von Mises stress at gingival margin of V shape cavity was lower than the others. And that of box cavity was lower than that of saucer cavity. 3. Preparing bevel at incisal cavosurface margin decreased the rate of stress development in early polymerization stage. 4. Preparing bevel at incisal cavosurface margin of V shape cavity increased the Von Mises stress at gingival margin, but decreased at incisal margin. 5. At incisal margin, stress development by bulk curing method was rapid at early stage. Stress development by first increment of incremental curing method was also rapid but lower than that by bulk curing method, however after second increment curing final stress was the same for two placement methods. 6. At gingival margin, stress development by incremental curing method was suddenly rapid at early stage of second increment curing, but final stress was the same for two placement methods.

• Archives of Plastic Surgery
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• v.36 no.5
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• pp.531-537
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• 2009

Purpose: Alveolar bone grafting has become an essential process in the treatmemt of alveolar cleft patient for stabilization of the maxillary arch, elimination of oronasal fistula, the reconstruction of the soft tissue nasal base support, and creation of bony support for tooth eruption for implant. The use of Autologous iliac cancellous bone is preferable because of the adequate quantity and high osteoinductive potential. However, even with iliac bone, insufficient osteoregeneration and absorption occur due to several factors such as the patient's age, cleft width, functional stress, and others. In order to increase osteoregeneration where the iliac bone is placed, the present study is associated with bone marrow aspirate (BMA). The experimental study evaluated the efficacy of osteoregeneration in normal cleft rabbits when alveolar bone grafting was performed with autologous iliac corticocancellous bone. Methods: Twenty - four New Zealand White rabbits were divided randomly into 2 groups (BMA, control). All animals underwent harvesting of corticocancellous bone graft from the right posterior iliac crest via standard surgical technique. $1m{\ell}$ of BMA were obtained by scraping the needle and aspirate with $10m{\ell}$ syringe from the contralateral iliac bone wall. The muco - periosteal flap on the palate was elevated. A mixture of Equal bone's volumes with BMA and saline as its control was inserted into the cleft. Animals were sacrificed at 2, 4, and 8 weeks and maxilla was harvested for dental peri - apical X-ray, bone matrix density (BMD),and histologic analysis. Result: BMD of regenerated bone to the cleft in the rabbits was higher than that of the control rabbits. X-ray, histologic analysis showed that increased osteoregeneration and low absorption rate were observed in the BMA group. Conclusion: Our experimental study showed BMA enhanced the osteoregeneration and survival rate of alveolar bone grafting. BMA is easy to extract & cost - time effective. So it can be an effective enhancers for bone grafting mixtures.