• The Journal of the Korean dental association
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• v.48 no.1
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• pp.45-55
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• 2010

Purpose: The aim of this study was to evaluate 1 year cumulative survival rate of implants placed on augmented sinus using Osteon$^{(R)}$, bone graft material and to assess height of the grafted material radiographically. Material and Methods: 10 maxillary sinuses were augmented in 10 patients and 25 implant fixtures were installed simultaneously or after 6 months healing period. The height of the sinus graft material was measured using panoramic images immediately after augmentation and up to 19 months subsequently. Changes in the height of the sinus graft material were calculated with respect to implant length and original sinus wall height. Results: The cumulative survival rate was 100% in all 25 implants. Additionally, normal healing process without any complication was observed in all patients. The mean crown/Implant ratio was 1.25. The mean marginal bone loss was 0.95mm and the mean resorption rate of Osteon$^{(R)}$ was 0.05mm/month. The fastest resorption site of Osteon$^{(R)}$ is the first molar area. The grafted material was well maintained in sinus and decreased slightly over 1 year. Conclusion: In conclusion, It can be suggested that Osteon$^{(R)}$ may have predictable result when it was used as a grafting material for sinus floor augmentation.

• The Journal of Advanced Prosthodontics
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• v.10 no.5
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• pp.381-387
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• 2018

PURPOSE. Cement-retained implant prostheses can lack proper retrievability during repair, and residual cement can cause peri-implantitis. The purpose of this in vitro study was to evaluate the influence of abutment height and convergence angle on the retrievability of cement-retained implant prostheses with lingual slots, known as retrievable cement-type slots (RCS). MATERIALS AND METHODS. We fabricated six types of titanium abutments (10 of each type) with two different heights (4 mm and 6 mm), three different convergence angles ($8^{\circ}$, $10^{\circ}$, and $12^{\circ}$), a sloped shoulder margin (0.6 mm depth), a rectangular shape ($6mm{\times}6.5mm$) with rounded edges, and a rectangular ledge ($2mm{\times}1mm$) for the RCS. One monolithic zirconia crown was fabricated for each abutment using a dental computer-aided design/computer-aided manufacturing system. The abutments and crowns were permanently cemented together with dual-curing resin cement, followed by 24 hours in demineralized water at room temperature. Using a custom-made device with a slot driver and torque gauge, we recorded the torque ($N{\cdot}cm$) required to remove the crowns. Statistical analysis was conducted using multiple regression analysis and Mann-Whitney U tests (${\alpha}=.05$). RESULTS. Removal torques significantly decreased as convergence angles increased. Multiple regression analysis showed no significant interaction between the abutment height and the convergence angle (Durbin-Watson ratio: 2.186). CONCLUSION. Within the limitations of this in vitro study, we suggest that the retrievability of cement-retained implant prostheses with RCS can be maintained by adjusting the abutment height and convergence angle, even when they are permanently cemented together.

• Korean Journal of Environment and Ecology
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• v.18 no.2
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• pp.210-220
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• 2004

The purpose of this study is to propose the raw data of conservation and restoration by analyzing the environmental and growth characteristics in Abeliophyllum distichum habitats. The types of soil were sandy loam, loam and silty clay loam and the correlation on chemical characteristics of soil appeared that T-N and C.E.C were highly correlative. In case of growth characteristics, height and diameter in 1st site, crown in 2nd site, number of leaves in 5th site and number of seeds in 4th site were better than other sites. In the results of correlation on growth characteristics, height and diameter were highly correlative. In case of growth and chemical characteristics, EC and height were highly correlative. In the results of regression analysis, R-square of height and EC was some 70.4％ and that of number of leaves and T-N was some 70.2%. To conserve and restore Abeliophyllum distichum habitats, there were demanded that the accurate environmental analysis that considered such diverse factors as light intensity, temperature, genetic quality and so forth.

• The Journal of Advanced Prosthodontics
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• v.5 no.2
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• pp.187-197
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• 2013

PURPOSE. The purpose of this study was to evaluate various core designs on stress distribution within zirconia crowns. MATERIALS AND METHODS. Three-dimensional finite element models, representing mandibular molars, comprising a prepared tooth, cement layer, zirconia core, and veneer porcelain were designed by computer software. The shoulder (1 mm in width) variations in core were incremental increases of 1 mm, 2 mm and 3 mm in proximal and lingual height, and buccal height respectively. To simulate masticatory force, loads of 280 N were applied from three directions (vertical, at a $45^{\circ}$ angle, and horizontal). To simulate maximum bite force, a load of 700 N was applied vertically to the crowns. Maximum principal stress (MPS) was determined for each model, loading condition, and position. RESULTS. In the maximum bite force simulation test, the MPSs on all crowns observed around the shoulder region and loading points. The compressive stresses were located in the shoulder region of the veneer-zirconia interface and at the occlusal region. In the test simulating masticatory force, the MPS was concentrated around the loading points, and the compressive stresses were located at the 3 mm height lingual shoulder region, when the load was applied horizontally. MPS increased in the shoulder region as the shoulder height increased. CONCLUSION. This study suggested that reinforced shoulder play an essential role in the success of the zirconia restoration, and veneer fracture due to occlusal loading can be prevented by proper core design, such as shoulder.

• Journal of Korean Society of Forest Science
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• v.90 no.3
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• pp.338-345
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• 2001

This study was conducted to elucidate the relationship between the root structure and the crown structure of Norway spruce(Picea abies [L.] Karst), and thereafter to obtain the regression equation for the estimation of relative root and needle biomass using the tree height and diameter at breast height(DBH) without measurement of root and needle biomass. The study site was Barbis stands of Harz region located in central part of Germany. Five dominant and three co-dominant trees of 30 to 40 year-old Norway spruce were selected and tree height, diameter at breast height, clear bole length, weight of total needle and branch, cross section and sapwood area at breast height for biomass of above ground part and also the length of root, the number of root, the weight of root, the cross section area of root etc. by dividing the horizontal and vertical roots for below ground part of tree were measured. The significantly correlation was shown between the biomass of most of variables of above ground parts and those of below ground parts. For the diameter of breast height to the weight of total root, regression equation was Y = 3.56X - 45.94 and decision coefficient was 0.96 showing highly correlation. The weight of total branches and needles, and the tree height etc. of above ground parts showed highly positive relationship with below ground biomass. The results obtained from this study can be used to the estimating of biomass of below ground using variables of above ground such as DBH in the 30 to 40 year-old Norway spruce stands.

• Korean Journal of Environmental Biology
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• v.29 no.4
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• pp.345-352
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• 2011

We investigated 12 plots using Herles' diversity of structure feature calculation method, which is based on the Shannon-Weaver-Index for estimation of species diversity. This study sought to facilitate a more systematic understanding of the structure of the forest stands in the Korean fir natural forest in Naeseorak. Although the change in the forest structure is dependent on the change in phase, factors of the natural forest were confirmed by associating individual structure features. As shown in the results of diversity of structure features, the diversity of the structure of the fir tree natural forest in Naeseorak was relatively low. The association between species diversity and overall factors (diversity) related with the change in the structure was found to be weak. The association between the number of trees and the diversity of forest structure stands was moderate, showing that the higher the number of trees, the less diverse the forest structure is. In most of the investigated plots, stem volume and volume of dead tree were associated with the height of natural regeneration, but these were not associated with other factors. Height of natural regeneration was found to be correlated to stand density, crown area and crown class, whereas tree height and BHD did not have any association with other factors. Overall, the results of the investigation are helpful in understanding the change in the structure of Korean fir natural forest. Further investigation with more plots is required.

• Journal of Korean Dental Science
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• v.17 no.1
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• pp.45-52
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• 2024

Purpose: To investigate the 5-year outcome of dental implants placed in a grafted maxillary sinus using recombinant human bone morphogenetic protein-2 (rhBMP-2). Materials and Methods: We retrospectively analyzed 27 implants after maxillary sinus floor augmentation (MSFA) using rhBMP-2 in 16 patients between January 2016 and March 2017. The study evaluated two outcome variables: (1) 5-year cumulative survival and success rate of the implant after functional loading and (2) marginal bone loss (MBL) for implant failure. Results: The average residual bone height was 4.78±1.53 mm. The healing period before loading was 8.35±2.34 months. The crown-to-implant ratio was 1.31±0.26. The 5-year cumulative survival and success rate after functional loading were 100% and 96.3%, respectively. The 5-year average MLB was 0.89±0.82 mm. Conclusion: Placing dental implants with MSFA using rhBMP-2 is a reliable procedure with favorable long-term survival and success rates.

• The Journal of the Korea Contents Association
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• v.10 no.7
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• pp.285-296
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• 2010

This study was implemented among 100 students of C College of Public Health who have healthy permanent dentition in order to measure the morphology and sizes of clinical crowns of permanent maxillary molars. The following are conclusions of this study. 1. The cusp height, crown width, crown thickness of clinical crowns appeared to be bilaterally symmetrical. 2. The strong development of the buccal groove showed to be superior in the right first molar. The appearance rate of the buccal pit was high in the right first molar also. 3. The type 4th cusp appeared as 100% in the left and right first molars, and 78%, 75% in the left and right second molars respectively. 4. The distal lingual cusp(DLC) size were bilaterally symmetrical in the type 4th cusp. 5. As for the distance between two cusp tips, it was large between mesial cusp tips in all of the first and second molars at both sides. 6. Development of the Carabelli's cusp was high in both the left and right first molars. 7. The appearance rate of the oblique ridge was 87.0% in the right first molar, 73.0% in the right second molar, 88.0% in the left first molar, and 73.0% in the left second molar. This is considered to be caused by people who have mild dental crown caries in their first molars. 8. The appearance rate of the mesial marginal ridge tubercle(DMRT) was high in both of the left and right first molars. That of the distal tubercle was 16.0% in the right first molar, 26.0% in the right second molar, 14.0% in the left first molar, and 21% in the left second molar.

• Restorative Dentistry and Endodontics
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• v.19 no.2
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• pp.549-567
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• 1994

Restoration of severly damaged teeth after endodontic treatment had been an interest to many dentists, and it is a fact that there have been lots of studies about it. In these days, although we have used Para-Post, pins, threaded steel post, cast gold post and core, and so on, as a method of restoration frequently, it has been in controversy with the influence of them on the teeth and surrounding periodontal tissue. In this study, we assume that the crown of the upper incisor have severly damaged, so, after the root canal therapy, 4 types of restoration had been carried out; 1) coronal-radicular amalgam restoration, 2) after setting up the Para-Post, restore with composite resin core only, 3) after setting up the Para-Post; restore with amalgam core, then cover with the PPM crown 4) after setting up the Para-Post, restore with composite core, then cover with the PPM crown. After restoration, in order to observe the concentration of stress at internal portion of the teeth and the sourrounding periodontal tissue, developing a 2-dimensional finite element model of labiopalatal section, then loading forces from 3 direction - direction of 45 degrees from lingual side near the incisal edge, horizontal direction from labial height of contour, vertical direction at the incisal edge-were applied. The analyzed results were as follows: 1. Stress of the normal central incisor was concentrated on the dentin aroundpulp chamber, labiocervical portion of a tooth and root apex, but with the alveolar bone, in the case of load from the direction of 45 degrees from lingual side near the incisal edge showed remarkable concentration of stress: 2. Coronal-radicular amalgam technique -showed less concentration of stress on the root and surrounding periodontal tissue than the restoration with the Para-Post. 3. The von Mises equivalent stress on the Para-Post showed maximum value at root-core junction rather than both ends and model with PPM restoration with amalgam core showed the least concentration of stress. Only the force from horizontal direction showed large shear stress on internal portion of the root, root apex and alveolar bone. 4. PPM crown with composite core rarely showed the concentration of stress on root and periodontal tissue. 5. As for alveolar bone, remarkable shear stress was concentrated on labial and palatal side by horizontal load.

• Magazine of the Korean Society of Agricultural Engineers
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• v.40 no.5
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• pp.91-99
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• 1998

The widespread use of thin shell structures has created a need for a systematic method of analysis which can adequately account for arbitrary geometric form and boundary conditions as well as arbitrary general type of loading. Therefore, the stress and analysis of thin shell has been one of the more challenging areas of structural mechanics. A wide variety of numerical methods have been applied to the governing differential equations for spherical and cylindrical structures with a few results applicable to practice. The analysis of axisymmetric spherical shell is almost an every day occurrence in many industrial applications. A reliable and accurate finite element analysis procedure for such structures was needed. Dynamic loading of structures often causes excursions of stresses well into the inelastic range and the influence of geometry changes on the response is also significant in many cases. Therefore both material and geometric nonlinear effects should be considered. In general, the shell structures designed according to quasi-static analysis may fail under conditions of dynamic loading. For a more realistic prediction on the load carrying capacity of these shell, in addition to the dynamic effect, consideration should also include other factors such as nonlinearities in both material and geometry since these factors, in different manner, may also affect the magnitude of this capacity. The objective of this paper is to demonstrate the dynamic characteristics of spherical shell. For these purposes, the spherical shell subjected to uniformly distributed step load was analyzed for its large displacements elasto-viscoplastic static and dynamic response. Geometrically nonlinear behaviour is taken into account using a Total Lagrangian formulation and the material behaviour is assumed to elasto-viscoplastic model highly corresponding to the real behaviour of the material. The results for the dynamic characteristics of spherical shell in the cases under various conditions of base-radius/central height(a/H) and thickness/shell radius(t/R) were summarized as follows : The dynamic characteristics with a/H. 1) AS the a/H increases, the amplitude of displacement in creased. 2) The values of displacement dynamic magnification factor (DMF) were ranges from 2.9 to 6.3 in the crown of shell and the values of factor in the mid-point of shell were ranged from 1.8 to 2.6. 3) As the a/H increases, the values of DMF in the crown of shell is decreased rapidly but the values of DMF in mid-point shell is increased gradually. 4) The values of DMF of hoop-stresses were range from 3.6 to 6.8 in the crown of shell and the values of factor in the mid-point of shell were ranged from 2.3 to 2.6, and the values of DMF of stress were larger than that of displacement. The dynamic characteristics with t/R. 5) With the thickness of shell decreases, the amplitude of the displacement and the period increased. 6) The values of DMF of the displacement were ranged from 2.8 to 3.6 in the crown of shell and the values of factor in the mid-point of shell were ranged from 2.1 to 2.2.