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The use of titanium alloys as biomaterials is increasing due to their superior biocompatibility and enhanced corrosion resistance compared to conventional stainless steels and cobalt-based alloys. Ti-6Al-4V (α + β type) alloy instead of pure titanium ( type) is being widely used as biomaterials has some characteristics such as high fatigue strength, tensile strength and corrosion resistance. But it has been reported recently that the vanadium element expresses cytotoxicity and the aluminium element is related with dementia of Alzheimer type and neurotoxicity. In order to overcome their detrimental effects, β-phase stabilizer Nb was chosen in the present study. This paper was described the influence of phase changes of Ti-Nb alloys on mechanical properties. Ti-3wt.%Nb( α type),Ti-20wt.%Nb( α+ β type) and Ti-40wt.%Nb( β type) alloys were melted by vacuum arc furnace. The specimens were homogenized at 1050℃ for 24hr and were then hot rolled to 50% reduction. Each alloys were solution heat treated at β zone and α+ β zone after homogenization and then were aged. The mechanical properties of Ti alloys were analysed by hardness test, tensile test, elongation test and SEM test. The results can be summarized as follows: 1) The higher hardness value of α+ β type alloy was obtained compared to the α, β type alloys. 2) The aged treated showed better hardness compared to the solution heat treated, homogenized. 3) In the case of solution and aging treatment at β region, the α+ β type alloy showed the most highest tensile strength and β type alloy showed the best elongation.

Ti6Al4V alloy have been mainly used as implant materials. Ti-6Al-4V alloy instead of pure Ti is being widely used as biomaterials has some characteristics such as high fatigue strength, ensile strength. But it has been reported recently that vanadium component expresses cytotoxicity and carcinogenicity and aluminium component is related with dementia of Alzheimer type. In order to overcome their detrimental effects, -phase stabilizer Nb was chosen in the present study, in addition Ta and Hf were added to Ti-40wt.%Nb alloy to improve its mechanical properties. This paper was described the influence of heat treatment of Ti-40Nb alloys with 2wt%Ta, 2wt%Hf on the mechanical properties. Specimens of Ti alloys were melted in vacuum arc furnace and homogenized at 1050 for 24 hr. and then were aged after solution heat treat at + and regions. The mechanical properties of Ti alloys were analysed by hardness test, tensile test, elongation test and SEM test. The results can be summarized as follows: 1. The mechanical properties Ti-40wt.%Nb were improved when 2wt.% Ta and 2wt.%Hf were added. 2. The higher tensile strength value and elongation at solution heat treat was higher than solution heat treat and then were aged.

This study is to show the qualitative analytic methods of facial asymmetry with threedimensional morphometry and find out asymmetry change resulted from enlarging three local regions. Steel balls (1.2 in diameter) were attached in twenty seven landmarks of a symmetrical artificial human skull. This artificial human skull was used as experimental materials. Twelve different asymmetrical artificial human skulls were formed by gradually enlarging the mandibular body length, gonial angle, and ramus height of the left hemiface. From the three-dimensional morphometry of each skull type, nine local area measurements and three total sum area measurements(representing the mandibular area, maxillary area, and lower facial area) were acquired and made into the surface area asymmetry degree. Menton deviation itself was used as the surface area asymmetry degree while right-left percentages were used in the other measurements. These surface area asymmetry degrees were compared with each other to find out asymmetry change according to the degree of actual facial asymmetry. Through the statistical analysis, following results were obtained. The results were as follows: 1. Left maxillary area of artificial human skull was 7.13 0.26% larger while mandibular area was 4.14 0.12% smaller than each those of right hemiface. After all, left lower facial area was 1.44 0.07% larger than those of right hemiface.(n=7) 2. Among the reduce rates of surface area asymmetry degree resulted from enlarging three local regions, ramus height was similar to mandibular body length while it was bigger than those of gonial angle. 3. Among the increase rates of menton deviation resulted from enlarging the local regions, ramus height was the biggest, mandibular body length was the second and gonial angle was the smallest. These results suggest that three-dimensional morphometry can be used to qualitatively analyse facial asymmetry and the asymmetry degree is more influenced by enlarging the ramus height, mandibular body length than those of gonial angle.

This study is to investigate the increasing membership rate against the previous year among the members registered as representative members and general members of the Korea Dental Technician Association from 1990 to 2004. With this study, we aim to provide more systematic data about the current status of each members in the KDTA and reconsider the needs for the practical and distinguishing management of the members. Results of the study are as follows; 1. The increasing rate from 1990 to 2004: whole members; 2.14, representative members; 2.22, general members; 2.11. Average of increasing rate against the previous year: general members; 6.10%, whole members; 5.94%, representative members; 5.91%. 2. The increasing rate in the city branch from 1990 to 2004: whole members; 2.12, representative members; 2.03, general members; 2.15. Average of increasing rate against the previous year: general members; 6.63%, whole members; 6.05%, representative members; 5.23% 3. The increasing rate in the province branch from 1990 to 2004: whole members; 2.21, representative members; 2.74, general members; 2.01. Average of increasing rate against the previous year: representative members; 7.58%, whole members; 5.99%, whole members; 5.35%. 4. Mean ratio between representative members and general members from 1990 to 2004: 1:2.6 against the whole members, 1:2.8 in the city branch, 1:2.3 in the province branch. The ratio between representative members and general members in the year 2004: 1:3.1 in Kyoungnam province, 1:3.0 in Inchon, 1:2.9 in Kwangju that indicates a high ratio between two members and in the case of Chongbuk, the ratio between two members is rather low as shown in 1:1.1.

Experimental Ti-13%Zr and Ti-13%Zr-5%Cu alloys were made in an argon-arc melting furnace. The grade 2 CP Ti was used to control. To investigate the surface reaction layers produced by the reaction with mold materials and the influence of the reaction layers on the hardness of castings, A phosphate bonded SiO2 base investment was used as mold material, and microstructure observation and hardness test were performed. The surface reaction layers of Ti-13%Zr and Ti-13%Zr-5%Cu alloys were thinner than that of CP Ti had a clearly multiple structure. A difference of the hardness between surface and inner of the Ti-13%Zr and Ti-13%Zr-5%Cu alloys became less than that of CP Ti. From the results, it was found that the Ti-Zr-(Cu) based alloys were possible to cast with SiO2 base investment without the great changes of mechanical properties of the castings.

Experimental Ti-13%Zr and Ti-13%Zr-5%Cu alloys were made in an argon-arc melting furnace. The grade 2 CP Ti was used to control. The alloys were cast into phosphate bonded SiO2 investment molds using an argon-arc casting machine, and The hardness and microstructures of the castings were investigated in order to reveal their possible use for new dental casting materials and to collect useful data for alloy design. The hardness of the Ti-13%Zr-5%Cu alloy(379Hv) became higher than that of Ti-13%Zr(317Hv) alloy, and the hardness of this alloys became higher than that of CP Ti(247Hv). Increasing in the hardness of the Ti-13%Zr-5%Cu alloy was considered to be solid solution hardening as the Ti-Zr system shows a completely solid solution for both high temperature phase and low temperature phase and also the inclusion of the eutectoid structure( Ti+Ti2Cu). No martensitic structures are observed in the specimen made of CP Ti, but Ti-13%Zr and Ti- 13%Zr-5%Cu alloys show a kind of martensitic structure. Ti-13%Zr-5%Cu shows the finest microstructure. From these results, it was concluded that new alloys for dental casting materials should be designed as Ti-Zr-Cu based alloys.

The surface-reacted layer of titanium castings greatly affects their mechanical properties. This study analyzed the interfacial zone of Ti-20%Zr-5%Cr alloy castings obtained from phosphate bonded investment and examined the relationship between the surface-reacted layer and hardness. The Vickers hardness of cast disks were tested at 20 ㎛ intervals from the surface to 120 ㎛ in depth. The cross-section was observed metallurgically, and line profile of the reacted layer was conducted under the EDX. The surface-reacted layer of Ti-20%Zr-5%Cr alloy is showed a similar tendency to Ti-6%Al-4%V alloy in thickness, and also Si diffusion in multiple reacted layer of Ti-20%Zr-5%Cr alloy is less than cp Ti and similar to Ti-6%Al-4%V alloy. The Vickers hardness in the surface layer was greater than in the inner part, and the Vickers hardness of Ti-20%Zr-5%Cr alloy ranged 650 to 390 and cp Ti ranged 810 to 160, Ti-6%Al-4%V alloy ranged 710 to 530 respectively.

This study was performed to investigate the surface properties of electrochemically oxidized pure niobium by anodic oxide and hydrothermal treatment technique. Niobium specimens of 10 10 in dimension were polished sequentially from #600, #800, #1000 emery paper. The surface pure niobium specimens were anodized in an electrolytic solution that was dissolved calcium and phosphate in water. The electrolytic voltage was set in the range of 250 V and the current density was 10 / . The specimen was hydrothermal treated in high-pressure steam at 300 for 2 hours using an autoclave. Then, specimens were immersed in the Hanks' solution with pH 7.4 at 37 for 30 days. The surface of specimen was characterized by scanning electron microscope(SEM), energy dispersive X-ray microanalysis(EDX), potentiostat/galvanostat test, and cytotoxicity test. The results obtained was summarized as follows; According to the result of measuring corrosion behavior at 0.9% NaCl, corrosion resistance was improved more specimens treated with anodic oxide than in hydrothermal treated ones. The multi-porous oxide layer on surface treated through anodic oxidation showed a structure that fine pores overlap one another, and the early precipitation of apatite was observed on the surface of hydrothermal treated samples. According to the result of EDX after 30 days deposition in Hanks solution, Ca/P was 1.69 in hydrothermal treated specimens. In MTT test, specimens treated through anodic oxidation and hydrothermal treated ones showed spectrophotometer similar to that of the control group. Thus no significant difference in cytotoxicity was observed (P>0.05).

In the manufacture of ceramo-metal crown, difference of fracture strength according to the metal depth has been known to be an important influence on enough intensity and internal stress to endure an occlusion-pressure as well as aesthetics of rehabilitating similar colour such as natural teeth. Depth of ceramic material could be determined by that of metal in three groups: first case of thin depth, second case of thick depth, and third case of constant depth. For the enhancement of the fracture strength between metal and ceramic materials and aesthetic satisfaction, a study on the bonding force, fracture strength, and aesthetics have been required more. In this study, therefore metal coping were made in three groups of A, B and C by using both ceramic powder of Norithe and metal of Columbium, which have been used primarily in the market. A group was made in 0.2 10 10 , B group was made in 0.4 10 10 , and, C group was made in 0.8 10 10 , respectively. The number of metal coping in each group was 10, and total sample numbers used in this study were 30 metal copings. After thesemetal coping tissue were in the process of build-up in 1.5mm constant depth of porcelain, firing, and glazing, the fracture strength about each metal coping tissue was investigated using oil press. It was found that the average values of durable occlusion pressure for separation of ceramic material in the porcelain fused to metal crown (PFM) in the each group showed the increasing order of A group (30 bar), B group (42 bar), and C group (44 bar), respectively. Proper depth of metal coping in the PFM was considered to be 0.4 in the B group because this metal size showed higher durable property to the occlusion pressure and better coupling strength in the ceramo-metal crown.

The effect of Nb on interfacial bonding characteristics of Ni-Cr alloy for porcelain fused to metal crown (PFM) has been studied in order to investigate oxide layer. A specimens , which is 0.8 in thickness, were fired at 1,000 with four tests such as air, vacuum, air for 5 minutes and vacuum for 5 minutes in order to examine an oxide behavior of alloy surface generated by the adding of Nb to be controlled at a rate of 0, 1, 3 and 5. It observed oxide film form of the fired specimens with optical microscope and scanning electron microscope (SEM), and chemical formation of them with energy disperse X-ray spectroscopy (EDX). The other specimens, which is 2 in thickness, were fired at 1,000 with air and vacuum in order to analyze the diffusion behaviors of alloy-porcelain interface by X-ray dot mapping. The results of this study were as follows: 1. The observation of microstructure of specimens by SEM showed that the more Nb content is high, the more much intermediate compound of rich Nb is observed. 2. The surface morphology of oxide film is most dense in 3% Nb. The heat treatment in air constitutes denser oxide film than heat treatment under vacuum. 3. The diffusion behavior of oxide layer by X-ray dot mapping showed that Si, Al of porcelain diffuse toward metal.

The purpose of this study is to evaluate the effect of loading at three different occlusal surface position of the gold alloy crown on the stress distributions in surrounding bone, utilizing 3- dimensional finite element method. A three dimensional finite element model of an implant with simplified gold alloy crown and supporting bone was developed for this study. A oblique or vertical load of 100 N was applied at the following position at each FE model : 1) center of occlusa surface, 2) a point on the buccal side away from center of occlusal surface (COS) by 2.8 , 3) a point on the lingual side away from COS by 2.8 . In the results, Minimum von Mises stresses under vertical load or oblique load of 100N were about 6MPa at the center of occlusal surface and about 40MPa at the point on the buccal side, respectively. From the results we could come to the conclusion that occlusive loading position could be an important factor for establishment of structural safety of supporting bone.

The purpose of this study was to identify injury characteristics happened in the college dental laboratory technique classes and to provide the empirical accident findings for safety education development for the college dental technology classes. The research data were collected from a self-administered survey distributed to the conveniently selected college students. The study participants were 476 freshmen, sophomore and junior students whose major was the dental laboratory technology of the 4 colleges in 2 metropolitan cities and 2 midium-size cities. All collected survey responses were encoded and analyzed in SPSS 12.0. The findings were as follows. The accidents happened to the college students during the dental laboratory technology classes: 1. The accident rate was the highest in the sophomore and the freshmen, junior in order. 2. The body parts frequently injured were hands, face, eyes, arms, and legs in order. 3. The frequent injury types were cut, burnt, stuck, wound, and suffocated in order. 4. The treatment methods for their accidents were the simple first-aids, no treatment, and the emergency room visits in order. 5. The laboratory training conditions inducing the accidents were significantly frequent under wire-related, and wax-related, iron-related, alcohol-related jobs in order, but not frequent in investing material-related, porcelain-related, resin-related, and agar-related jobs. Polishing was the most accident-prone job explaining 63% of the laboratory accidents and then, model producing, wax patterning, casting, burning, and investing jobs in order. In summary, the college dental laboratory accidents had the certain patterns by the training level and by the material or machine involved in each class. Thus, the planned and organized safety education programs should be produced and investigated for college students before their major laboratory classes.

The purpose of this study was to identify the accidents happened in the college dental laboratory technique classes and to realize the level of safety education for the dental laboratory techniquemajor students. The research data were collected from a self-administered survey distributed to the conveniently selected college students whose majors were dental laboratory technology in Suwon, Daejeon, Daegu, Kimcheon, and Icsan. The study participants were 422 freshmen, sophomore and junior students in the selected cities. All collected survey responses were encoded and analyzed in SPSS 12.0. The findings were as follows. 1. The students who had any accidents in their laboratory classes were 36% and the other 64% answered ‘no.’ 2. Most injuries which the participants had were not significant. 3. The medical treatment periods of most injury cases were less than one week; however, approximately 20% of the self-reported injury cases reported that their treatment periods were longer than one week. 4. The body parts frequently injured from accidents were hands with 84.7% and arms, eyes, face, head, and legs in order. 5. Concerning the materials involved in the laboratory classes, most accidents happened when working with wax in 59.9%, with plaster in 52.3%, with wire in 39.8%, with alcohol in 34.6%, and casting iron in 22.2% in order. 6. The accident-prone laboratory methods were polishing with 53.5%, pickling or sanding with 17.4%, and casting or burning with 5.8% in order. 7. Most students wore their laboratory gowns well; however, few students wore mask before dust-involved jobs. Furthermore, only 57.1% students answered their laboratory fans worked during the polishing job. 8. Approximately 54% participant students answered that they took laboratory safety education when necessary only from the class instructors. 9. The 76.1% students responded that they needed laboratory safety education at least 1-2 times every semester. 10. The survey participants answered that the primary factors for injury prevention in their laboratory were taking safety education, wearing safety equipments, and providing safety-focused facilities. Concludingly, comprehensive evaluation and monitoring for potential risk factors from both the human side and the environment side should be continually provided to minimize the college laboratory accidents.

The market of dental materials industry in Korea will over 10 bilians $. If think concern of world market, we can know the possibility of market growth. In Korea, the technique of dental materials industry is low status. Then, special items income advanced countries. But advanced countries had been developed dental materials industry into high beneficial. Otherwise, Daegu Kyungbuk have several good points in dental materials industry. 1st, national dentisty university and three dental lab. college supplies abilitable human resources. 2nd, the possibility of support on basic industrial technology. Finally, the possibility of selection & attraction from many dental company. Then if Daegu Kyungbuk would be select & supported of dental materials Industrial special region, it can be think that will empower local economy, further national constitutional power. So we propose following three points, 1st. the deeper study on righteous of Daegu Kyungbuk dental materials industrial specialization. 2nd. investment on R & D of the region dental materials industrial. final, the support of venture circle.