• The Journal of Korean Academy of Prosthodontics
• /
• v.42 no.1
• /
• pp.83-93
• /
• 2004

Statement of problem : Since the concept of osseointegrated dental implant by $Br{\aa}nemark$ et al was first applied to mandibular full edentulous patients. Recently it is considerated the first treatment option on missing teeth. A common problem associated with dental implant restorations is loosening of screws that retain the prosthesis to the abutment and the abutment to the implant fixture. Purpose : This study is to examine the influence on screw loosening of implant-abutment designs. Material and methods : External hex, cone screw, beveled hex, cam cylinder, cylinder hex by means of evaluating the loosening torques, with respect to a range of tightening torques after repeated loading. Result : 1. Cone screw, beveled hex groups are the highest initial tightening rate and cylinder hex, external hex groups are the lowest initial tightening rate (p < 0.05). 2. Cone screw groups are the highest after repeated loading tightening rate and cylinder hex groups are lowest after repeated loading tightening rate(p < 0.05). 3. Cone screw groups have the highest initial stability and anal stability. 4. All groups are decreased tightening rate after repeated loading.

• Structural Engineering and Mechanics
• /
• v.32 no.2
• /
• pp.351-370
• /
• 2009

This paper presents a computational study for the structural response of blast loaded metallic sandwich panels, with the emphasis placed on their failure behaviours. The fully-clamped panels are square, and the honeycomb core and skins are made of the same aluminium alloy. A material model considering strain and strain rate hardening effects is used and the blast load is idealised as either a uniform or localised pressure over a short duration. The deformation/failure procedure and modes of the sandwich panels are identified and analysed. In the uniform loading condition, the effect of core density and face-sheets thicknesses is analysed. Likewise, the influence of pulse shape on the failure modes is investigated by deriving a pressure-impulse (P-I) diagram. For localised loading, a comparative study is carried out to assess the blast resistant behaviours of three types of structures: sandwich panel with honeycomb core, two face-sheets with air core and monolithic plate, in terms of their permanent deflections and damage degrees. The finding of this research provides a valuable insight into the engineering design of sandwich constructions against air blast loads.

• The Journal of Advanced Prosthodontics
• /
• v.4 no.1
• /
• pp.18-23
• /
• 2012

PURPOSE. The purpose of this prospective study was to evaluate the effect of early loading on survival rate or clinical parameter of anodic oxidized implants during the 12- month postloading period. MATERIALS AND METHODS. Total 69 implants were placed in 42 patients. Anodic oxidized implants (GS II, Osstem Cor., Busan, Korea) placed on the posterior mandibles were divided into two groups, according to their prosthetic loading times: test group (2 to 6 weeks), and control group (3 to 4 months). The implant survival rates were determined during oneyear postloading period and analyzed by Kaplan-Meier method. The radiographic peri-implant bone loss and periodontal parameters were also evaluated and statistically analyzed by unpaired t-test. RESULTS. Total 69 implants were placed in 42 patients. The cumulative postloading implant survival rates were 88.89% in test group, compared to 100% in control group (P<.05). Periimplant marginal bone loss (T: $0.27{\pm}0.54$ mm, C: $0.40{\pm}0.55$ mm) and periodontal parameters showed no significant difference between the groups (P>.05). CONCLUSION. Within the limitation of the present study, implant survival was affected by early loading on the anodic oxidized implants placed on posterior mandibles during one-year follow-up. Early implant loading did not influence peri-implant marginal bone loss, and periodontal parameters.

• Fisheries and Aquatic Sciences
• /
• v.2 no.1
• /
• pp.52-57
• /
• 1999

Air-drived rotating biological contactor (RBC) system, which is effective method in filtering performance, was tested for the nitrification capacity in a recirculating system. At ammonia concentrations between 0.029 and 0.528 mg/l, the effect of ammonia loading rate on ammonia removal rate at three different hydraulic loading rates could be defined by the following first­order regression models: Hydraulic loading rate of $14.8 m^3/m^3/day:\;y=39.2\times+3.4 (r^2=0.9137)$, Hydraulic loading rate of $26.5 m^3/m^3/day: y=53.3\times+4.0 (r^2=0.8686)$, Hydraulic loading rate of $37.3 m^3/m^3/day: y=58.4\times+4.2 (r^2=0.7755)$, where, $\times$ is ammonia loading rate (mg/l), y is ammonia removal rate $(g/m^3/day)$, The equations showed the optimal ammonia removal rate at the hydraulic loading rate of $26.5m^3/m^3/day$. Below the ammonia concentration of 2.72 mg/l, first-order regression models between ammonia loading rate and ammonia removal rate at three different rates of speed are defined as follows: Rotational speed of $0.75 rpm: y=28.5\times+4.7 (r^2=0.9143)$, Rotational speed of $1.0 rpm: y=33.6\times+8.4 (r^2=0.9534)$, Rotational speed of $2.0 rpm: y=28.9\times+3.6 (r^2=0.9488)$, where, x is ammonia loading rate (mg/l), y is ammonia removal rate $(g/m^3day)$. The equations show the ammonia removal rate at the rotational speed of 1.0 rpm is significantly higher than that at the rotational speed of either 0.75 rpm or 2.0 rpm (P<0.05).

• The Journal of Korean Academy of Prosthodontics
• /
• v.28 no.1
• /
• pp.63-94
• /
• 1990

The purpose of this study was to analyze the displacement and the magnitude and the mode of distribution of the stresses in the lower overdenture, the mucous membrane, the abutment tooth and the mandibular supporting bone when various denture base materials, such as acrylic resin and 0.5mm metal base, and various denture base designs were subjected to different loading schemes. For this study, the two-dimensional finite element method was used. Mandibular arch models, with only canine remaining, were fabricated. In the first denture base design, a space, approximately 1mm thick, was prepared between the denture and the dome abutment. In the second denture base design, contact between the denture and the dome abutment was eliminated except the contact of the occlusal third of the abutment. In order to represent the same physiological condition as the fixed areas of the mandible under loading schemes, the eight nodes which lie at the mandibular angle region, the coronoid process and the mandibular condyle were assumed to be fixed. Each model was loaded with a magnitude of 10 kgs on the first molar region(P1) and 7 kgs on the central incisal region (P2) in a vertical direction. Then the force of 10 kgs was applied distributively from the first premolar to the second molar of each model in a vertical direction(P3). The results were as follows. : 1. When the testing vertical loads were given to the selected points of the overdenture, the overdenture showed the rotatory phenomenon, as well as sinking and the displacements of alveolar ridge, abutment and lower border of mandible under the metal base overdenture were less than those under the acrylic resin overdenture. 2. The maximum principal stresses(the maximum tensile stresses) being considered, high tensile stresses occured at the buccal shelf area, the posterior region of the ridge crest and the anterior border region of the mandibular ramus. 3. The minimum principal stresses(the maximum compressive stresses) being considered, high compressive stresses occured at the inferior and posterior border region of the mandible, the mandibular angle and the posterior border region of the mandibular ramus. 4. The vertical load on the central incisal region(P2) produced higher equivalent stress in the mandible than that on any other region(P1, P3) because of the long lever arm distance from the fixed points to the loading point. 5. Higher equivalent stresses were distributed throughout the metal base overdenture than the resin base overdenture under the same loading condition. 6. The case of occlusal third contact of the abutment to the denture produced higher equivalent stresses in the abutment, the mandibular area around the abutment and the overdenture than the case of a 1mm space between the denture and the abutment. 7. Without regard to overdenture base materials and designs, the amounts and distribution patterns of equivalent stresses under the same loading condition were similar in the mucous membrane.

• Journal of the Korean GEO-environmental Society
• /
• v.10 no.5
• /
• pp.69-73
• /
• 2009

In this study, three dimensional numerical analyses were performed with variation of pile spacing (S=3D, 4D, 5D) to compare the behaviour of single pile and pile group with cap in granite soil. In order to compare and analyze the lateral resistance of single pile and pile group by changing pile spacing, the pile group with array of $1{\times}3$ was employed. To reduce the computation time the symmetric boundary condition was used. And Druker-Prager model and elasticity model were used for granite soil and for concrete pile and cap, respectively. Using the analyses results of pile group in granite soil under lateral loading, p-y curve for pile group and single pile with changing pile spacing was drawn. With p-y curve p-multiplier was evaluated. As a result of analysis, the value of p-multiplier was increased with increasing pile spacing under 1.0 due to pile shadow effects.

• Journal of Periodontal and Implant Science
• /
• v.52 no.6
• /
• pp.496-508
• /
• 2022

Purpose: This study aimed to compare the long-term survival rate and peri-implant marginal bone loss between different types of dental implant-abutment connections. Methods: Implants with external or internal abutment connections, which were fitted at Gangneung-Wonju National University Dental Hospital from November 2011 to December 2015 and followed up for >5 years, were retrospectively investigated. Cumulative survival rates were evaluated for >5 years, and peri-implant marginal bone loss was evaluated at 1- and 5-year follow-up examinations after functional loading. Results: The 8-year cumulative survival rates were 93.3% and 90.7% in the external and internal connection types, respectively (P=0.353). The mean values of marginal bone loss were 1.23 mm (external) and 0.72 mm (internal) (P<0.001) after 1 year of loading, and 1.20 mm and 1.00 mm for external and internal abutment connections, respectively (P=0.137) after 5 years. Implant length (longer, P=0.018), smoking status (heavy, P=0.001), and prosthetic type (bridge, P=0.004) were associated with significantly greater marginal bone loss, and the use of screw-cement-retained prosthesis was significantly associated (P=0.027) with less marginal bone loss. Conclusions: There was no significant difference in the cumulative survival rate between implants with external and internal abutment connections. After 1 year of loading, marginal bone loss was greater around the implants with an external abutment connection. However, no significant difference between the external and internal connection groups was found after 5 years. Both types of abutment connections are viable treatment options for the reconstruction of partially edentulous ridges.

• Journal of Korean Society on Water Environment
• /
• v.26 no.2
• /
• pp.311-316
• /
• 2010

We estimated the nitrogen and phosphorus loads of wintering waterfowl feces in Lake Paldang. The average number of individual birds that belonged to Anatidae species was 2,852.5 from 2005 to 2008 in Lake Paldang. The number of Anatidae reached 97.4% of the total number of individual birds. For evaluating the loading amounts of N and P by waterfowl to Lake Paldang, the feces dry weight (g/day) of each Anatidae species was estimated by multiplying the body weight of the each bird by 2.25% and assumed that N and P in feces contain 1.46% and 0.33%, respectively. We assigned probability 1/3 to the nutrient decomposition of the bird feces in water. The nitrogen loading by wintering waterfowl feces was 0.06 ton/year and the phosphorus loading was 0.001 ton/year. These amounts were 0.0002% of all N loadings and 0.0001% of all P loadings. Therefore the wintering waterfowl might have little impact on the water quality in terms of eutrophication in Lake Paldang.

• The Journal of Korean Academy of Prosthodontics
• /
• v.34 no.1
• /
• pp.1-14
• /
• 1996

Abutment screw loosening of dental implant is a major problem in the treatment of dental implant. The purpose of this study was to examine the effect on the prevention of screw loosening according to tightening method and using of washer. In the first experiment, using a implant fixture and precisely fabricated temporary cylinder, the loosening torque was measured by tightening the screw 5 times repeatedly. In the second experiment, the fabricated crown and implant fixture was tightened by the screw that is attatched washer and then the loosening torque was measured after loading it 1800, 12600 times under the force of 150N. The results were as follows. 1. The highest loosening torque appeared after tightening 3 times repeatedly(p<0.01). 2. When the washer was used, the loosening torque was increased significantly under the loading 1800 times(p<0.01), 3. When the washer was used, the loosening torque was increaed under the loading 12600 times, but it is statistically not significant(p<0.01). The first experiment results mean that 3 times repeated tightening screw is most effective clinically. The second results mean that washer is effective in prevention screw loosening, but the effect is decreased with increasing load.

• The Journal of Korean Academy of Prosthodontics
• /
• v.23 no.1
• /
• pp.97-112
• /
• 1985

The purpose of this study was to evaluate the stress patterns developed in supporting structures by removable partial denture with attachment retainers. The attachments tested were Dalbo(miniature) attachment, resilient Ceka attachment, rigid Ceka attachment, precision and sleeve attachment, and R.P.I. clasp as a contrast. 3-dimensional photoelastic stress analysis was used to record the isochromatic and isoclinic fringe patterns and to calculate principal stress components at measuring points. The results showed that: 1. The maximum compressive stress on residual ridge was produced under the loading point with Dalbo and resilient Ceka attachment, distal to the loading point with rigid Ceka and precision and sleeve attachment, and mesial to the loading point with R.P.I. clasp. 2. The Dalbo attachment produced the most stress on residual ridge, and the least stress on abutment teeth. and resilient Ceka attachment showed favorable stress distribution. 3. Rigid Ceka attachment produced higher compressive stress on buccal. alveolar crest, and precision and sleeve attachment produced higher compressive stress on distal alvelolar crest and mesial surface of the root apex in abutment teeth. 4. R.P.I. clasp produced higher compressive stress on mesial alveolar crest.