• The Journal of Korean Academy of Prosthodontics
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• v.47 no.1
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• pp.29-38
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• 2009

Statement of problem: A casting connection technique is widely used for repair, correction and addition to base metal framework. However, a casting connection technique may increase the risk of failure in clinical situations when high stresses exist. Purpose: The purpose of this study was to investigate the mechanical retentive groove design comparatively to increase the joint strength by using the three-dimensional finite element analysis model of a 3-unit fixed partial denture. Material and methods: Ten finite element models were constructed. (Model A: One retentive groove, Model B: Two retentive grooves, Model C: Three retentive grooves, Model D: Four retentive grooves, Model E: One horizontal groove and two vertical grooves, Model F: Two horizontal grooves and one vertical groove, Model G: One groove with the enlarged dimension, Model H: Two grooves with the enlarged dimension, Model I: One groove with the increased height, Model J: One groove with the increased width of base). The vertical force was applied to the mesial and the distal fossa to the casting connection of mandibular first molar. Results: The main factors, affecting joint strength of casting connection were both the retention between the primary cast and the secondary cast and the thickness of the primary cast remaining after preparing retentive groove. The increase of retentive force, according to the numbers and the dimension of retentive groove had an effect on distributing stress. However, in some cases, the increase of retentive force resulted in the increase of stress by reducing thickness of the primary cast in the connection area. Conclusion: The design of retentive groove that limits number of retentive groove for metal thickness and increases the depth of retentive groove for retention is highly recommended.

• The Journal of Korean Academy of Prosthodontics
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• v.43 no.2
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• pp.218-231
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• 2005

Statement of problem. In the partially edentulous patients, removable partial dentures have been working as a important treatment modality. Clasps, a kind of direct retainers, received some amount of stresses during the insertion and removal of partial denture on the abutment tooth. Purpose. The study is to investigate stresses of the different clasps. Material and methods. In order to investigate the degree of stresses, maxillary partial edentulism (Kennedy Class II modification I) was assumed and removable partial dentures were designed on it with three kinds of metallic materials; cobalt-chromium alloy, type IV gold alloy and commercially pure (c.p.) titanium. Aker's clasp was applied on the left second molar. RPA (mesial rest-proximal plate-Aker's) clasp was on the left first premolar and wrought wire clasp was on the right first premolar. Three dimensional, non-linear, dynamic finite element analysis method was run to solve this process. Results. 1. Cobalt-chromium alloy had the highest von Mises stress value and c.p. titanium had the lowest one irrespective of the types of clasps. 2. In the Aker's clasps, stress on the retentive tips was shown shortly after the appearance of stresses of the middle and minor connector areas. These time lag was much shorter in the RPA clasps than in the Aker's clasp. 3. In general. retentive tips of wrought wire clasps had much less amount of stress than other clasps. Conclusion. The amount of stress was the highest in the RPA clasp and the lowest in the wrought wire clasp, in general.

• Journal of Technologic Dentistry
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• v.44 no.4
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• pp.154-160
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• 2022

The need for repairing removable dentures has grown as the population had aged. The direct methods allow existing dentures to be repaired without interrupting their use. However, if patient compliance is low, direct methods may be challenging. Moreover, attaching an artificial tooth to a metal base is a complicated procedure because it necessitates casting a retentive element and soldering it to a metal base. This clinical report describes how to add an artificial tooth to a metal base, reline denture bases, and reestablish occlusion on relined removable dentures using indirect methods. Existing removable dentures were successfully repaired and their service life was efficiently extended using the methods described.

• The Journal of Korean Academy of Prosthodontics
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• v.45 no.5
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• pp.665-674
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• 2007

Purpose: The purpose of this study was to investigate the effect of sire and shape of retention element on the bond strength of indirect composite resin and metal. Material and method: The metal disk specimens, each 6mm in diameter, were cast from CrCo alloy. They were divided into 8 groups by applied retention element. retention bead group $B2\;({\phi}\;0.2mm),\;B4\;({\phi}\;0.4mm),\;B6\;({\phi}\;0.6mm),\;B8\;({\phi}\;0.8mm)$, retention crystal group C2 (0.2mm), C5 (0.5mm), C8 (0.8mm) and sandblasting group SB ($110{\mu}m\;Al_2O_3$ blasting) as control. Eighty-eight metal specimens were veneered with $TESCERA^{(R)}$ Indirect resin system. One specimen of each group was sectioned and the resin-metal bonding pattern at the interface was observed under measuring microscope. Other specimens were then tested for tensile bond strength on an Instron universal testing machine at a crosshead speed of 2mm/min. Results: 1. Compared to sandblasting, beads or crystals increased the resin-metal bond strength (P<.05). 2. 0.2mm retention crystals were most effective in improving the resin-metal bond strength (P>.05). 3. 0.2mm beads showed the highest bond strength among retention bead groups, but there was no statistically significant difference (P>.05). 4. Retention crystals tend to be higher in bond strength than retention beads due to wider surface area. 5. The larger retention element, the larger the undercut for the mechanical retention, but the gap at resin-metal interface was also increased. Conclusion: Within the limitations of this study, 0.2mm retention crystals were most effective in improving the resin-metal bond strength.

• The Journal of Advanced Prosthodontics
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• v.11 no.6
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• pp.341-349
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• 2019

PURPOSE. A novel retentive type of implant prosthesis that does not require the use of cement or screw holes has been introduced; however, there are few reports examining the biomechanical aspects of this novel implant. This study aimed to evaluate the biomechanical features of cementless fixation (CLF) implant prostheses. MATERIALS AND METHODS. The test groups of three variations of CLF implant prostheses and a control group of conventional cement-retained (CR) prosthesis were designed three-dimensionally for finite element analysis. The test groups were divided according to the abutment shape and the relining strategy on the inner surface of the implant crown as follows; resin-air hole-full (RAF), resin-air hole (RA), and resin-no air hole (RNA). The von Mises stress and principal stress were used to evaluate the stress values and distributions of the implant components. Contact open values were calculated to analyze the gap formation of the contact surfaces at the abutment-resin and abutment-implant interfaces. The micro-strain values were evaluated for the surrounding bone. RESULTS. Values reflecting the maximum stress on the abutment were as follows (in MPa): RAF, 25.6; RA, 23.4; RNA, 20.0; and CR, 15.8. The value of gap formation was measured from 0.88 to 1.19 ㎛ at the abutment-resin interface and 24.4 to 24.7 ㎛ at the abutment-implant interface. The strain distribution was similar in all cases. CONCLUSION. CLF had no disadvantages in terms of the biomechanical features compared with conventional CR implant prosthesis and could be successfully applied for implant prosthesis.

• The Journal of Korean Academy of Prosthodontics
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• v.45 no.5
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• pp.633-643
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• 2007

Statement of problem: Recently there are on an increasing trend of using implants-especially in edentulous mandible of severly alveolar bone recessed. Purpose: The aim of this study was to analyze the displacement and stress distribution of various mandibular implant-retained overdenture models supported by two implants in interforaminal region under the occlusion scheme load. Material and method: FEA models were made by the 3D scanning of the edentulous mandibular dentiform. The three models were named as Model M1, M2, and M3 accord ing to the position of implants: M1, Lt. incisor area, M2, Canine area, and M3, 1st Premolar area. Inter-implant angulation model was named as M4. Conventional complete denture was named M5 and used as a control group. Ball implant and Gold matrice were used as a retentive anchors. The occlusion type loads were applied horizontally over each tooth. Results: 1. In mandibular implant retained overdenture Canine Protected Occlusion type load resulted in higher levels of stress to the implants and female matrices than other types of loads. 2. The overdenture model M1, with implants in lateral incisor areas resulted in lower stress concentration to the implants and female matrices than other models. 3. In mandibular implant retained overdenture the stresses of the implant and female matrice were lower in mesially inclined implant than these of parallel installed implant. Conclusion: Lateral incisor areas could be the best site for the implants in mandibular implant-retained overdenture. The mandibular implant retained overdenture models mentioned above showed to the lowest stress to the implants and female matrices.

• The Journal of Korean Academy of Prosthodontics
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• v.47 no.3
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• pp.328-334
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• 2009

Statement of problem: Pier abutments act as a Class I fulcrum lever system when the teeth are incorporated in a fixed partial denture with rigid connectors. Therefore non-rigid connector incorporated into the fixed partial denture might reduce the stresses created by the leverage. Purpose: The purpose of this study was to evaluate, by means of finite element method, the effects of non-rigid connectors and supporting alveolar bone level on stress distribution for fixed partial dentures with pier abutments. Material and methods: A 2-dimensional finite element model simulating a 5-unit metal ceramic fixed partial denture with a pier abutment with rigid or non-rigid designs, the connector was located at the distal region of the second premolar, was developed. In the model, the lower canine, second premolar, and second molar served as abutments. Four types of alveolar bone condition were employed. One was normal bone condition and others were supporting bone reduced 20% height at one abutment. Two different loading conditions, each 150 N on 1st premolar and 1st molar and 300N on 1st molar, were used. Results: Two types of FPD were displaced apically. The amount of displacement decreased in an almost linear slope away from the loaded point. Non-rigid design tended to cause the higher stresses in supporting bone of premolar and molar abutments and the lower stresses in that of canine than rigid design. Alveolar bone loss increased the stresses in supporting bone of corresponding abutment. Conclusion: Careful evaluation of the retentive capacity of retainers and the periodontal condition of abutments may be required for the prosthetic design of fixed partial denture with a pier abutment.

• Nuclear Engineering and Technology
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• v.39 no.5
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• pp.603-616
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• 2007

Roy Huddle, having invented the coated particle in Harwell 1957, stated in the early 1970s that we know now everything about particles and coatings and should be going over to deal with other problems. This was on the occasion of the Dragon fuel performance information meeting London 1973: How wrong a genius be! It took until 1978 that really good particles were made in Germany, then during the Japanese HTTR production in the 1990s and finally the Chinese 2000-2001 campaign for HTR-10. Here, we present a review of history and present status. Today, good fuel is measured by different standards from the seventies: where $9*10^{-4}$ initial free heavy metal fraction was typical for early AVR carbide fuel and $3*10^{-4}$ initial free heavy metal fraction was acceptable for oxide fuel in THTR, we insist on values more than an order of magnitude below this value today. Half a percent of particle failure at the end-of-irradiation, another ancient standard, is not even acceptable today, even for the most severe accidents. While legislation and licensing has not changed, one of the reasons we insist on these improvements is the preference for passive systems rather than active controls of earlier times. After renewed HTGR interest, we are reporting about the start of new or reactivated coated particle work in several parts of the world, considering the aspects of designs/ traditional and new materials, manufacturing technologies/ quality control quality assurance, irradiation and accident performance, modeling and performance predictions, and fuel cycle aspects and spent fuel treatment. In very general terms, the coated particle should be strong, reliable, retentive, and affordable. These properties have to be quantified and will be eventually optimized for a specific application system. Results obtained so far indicate that the same particle can be used for steam cycle applications with $700-750^{\circ}C$ helium coolant gas exit, for gas turbine applications at $850-900^{\circ}C$ and for process heat/hydrogen generation applications with $950^{\circ}C$ outlet temperatures. There is a clear set of standards for modem high quality fuel in terms of low levels of heavy metal contamination, manufacture-induced particle defects during fuel body and fuel element making, irradiation/accident induced particle failures and limits on fission product release from intact particles. While gas-cooled reactor design is still open-ended with blocks for the prismatic and spherical fuel elements for the pebble-bed design, there is near worldwide agreement on high quality fuel: a $500{\mu}m$ diameter $UO_2$ kernel of 10% enrichment is surrounded by a $100{\mu}m$ thick sacrificial buffer layer to be followed by a dense inner pyrocarbon layer, a high quality silicon carbide layer of $35{\mu}m$ thickness and theoretical density and another outer pyrocarbon layer. Good performance has been demonstrated both under operational and under accident conditions, i.e. to 10% FIMA and maximum $1600^{\circ}C$ afterwards. And it is the wide-ranging demonstration experience that makes this particle superior. Recommendations are made for further work: 1. Generation of data for presently manufactured materials, e.g. SiC strength and strength distribution, PyC creep and shrinkage and many more material data sets. 2. Renewed start of irradiation and accident testing of modem coated particle fuel. 3. Analysis of existing and newly created data with a view to demonstrate satisfactory performance at burnups beyond 10% FIMA and complete fission product retention even in accidents that go beyond $1600^{\circ}C$ for a short period of time. This work should proceed at both national and international level.