Earticle

This study was to propose the clear understanding for stress distribution of supporting bone by use of staggered buccal offset tripodal placement of fixtures of posterior 3 crown implant partial dentures. We realized posterior 3 crown implant fixed partial dentures through finite element modeling and analysed stress effect of implant arrangement location to supporting bone under external load using finite element method. Method: To understand stress distribution of 3 crown implant fixed partial dentures which have 2 different arrangement by finite element analysis. In each model, for loading condition, we applied 45° oblique load to occlusal surface of crown and applied 100 N for 3 crown individually(total 300 N) for imitating possible oral loading condition. at this time, we calculated Von Mises stress distribution in supporting bone through finite element method. Result: When apply 45° oblique load to in-line arrangement model, maximum stress result for 100 N for each 3 crown 47.566 . In tripodal placement, result for 1 buccal offset tripodal placement implant model was maximum distributed load 51.418 , so result was higher than in-line arrangement model. Conclusion: In stress distribution result by placement of implant fixture, the most effective structure was in-line arrangement. The tripodal placement does not effective for stress distribution, gap cause more damage to supporting bone.

This experimental study was to determine the fitness on each cervical margin of recast using crown base metal alloy. The alloy used in this experimental study was a Ni-Cr alloy(Wirolloy, Bego, Germany) for the fabrication of full cast crown prosthesis. Twenty-five copings were divided into the five groups. And the group A, B, C, D and E were cording successively according to the frequency of recast to five times. Each specimen was recasted without adding new metal. The experimental results were as follows: 1. The group A and B showed good fitness had subtle differences in each cervical margin adaptation, in other words, the mesio and disto cervical margin showed worse adaptation than the bucco and linguo cervical margin. 2. The group C got good fitness in bucco and linguo cervical margins, but the mesio and disto cervical margin showed inaccurate fitness. And I could not get good casting bodies without adding new metal. 3. The group D and E showed bad fitness for each cervical margin. Therefore the group D and E lost its function as a dental restoration.

The goal of esthetic restoration is to achieve morphologic, optical, and biologic acceptance. Creation of a natural looking ceramic restoration, which blends harmoniously with surrounding dentition, is not always achieved. A successful color match is an important aspect of any esthetic dental restoration. Since natural enamel has inherent translucency, it is important that ceramic restorations reproduce the translucency and color of the natural teeth. However, the final color match of porcelain crowns to adjacent natural dentition remains some problem. Difficulties related to color matching arise from the structural differences that exist between metal ceramic crowns and natural teeth, the limited range of available ceramic shades, inadequate shade guides, different types of metal alloys, repeated firing, the condensation technique, and varying compositions of ceramic materials. Many factors contribute to the esthetic success of dental restoration: optical properties such as color and its elements of hue, value, and chroma; translucency and opacity; light transmission and scattering; and metamerism and fluorescence. The purpose of this study was to determine the color changes of metal-ceramic system with different veneering porcelain powder after repeated firing. The objectives of this in vitro study were to measure the lightness(L*), chromaticity(a*), chromaticity(b*), chroma(C*), hue(h), reflectance(%), color difference( E). The following conclusions were obtained: 1. An increase in the number of firings resulted in decrease in lightness(L*) but increase in chromacticity(a*) with all porcelain. After the second sintering resulted in decrease in chromacticity(b*) with opaque-dentin porcelain and dentin porcelain but in increase with enamel porcelain and translucency porcelain. And after the second sintering resulted in decrease in chroma(C*) with opaque-dentin porcelain and dentin porcelain, but on the whole side in decrease with enamel porcelain and translucency porcelain. 2. After the second firing, a increase in the number of firings resulted in decrease reflectance(%) in all wavelength. 3. There were noticeable color differences( E) between first sintering and multiple firings(dentin porcelain: 5.29 ~ 8.15, opaque-dentin porcelain: 4.83~8.2, enamel porcelain: 8.93~13.15, translucency porcelain: 9.37~12.91), but the color difference( E) after second sintering were down to 4.87 in all porcelain. 4. Given the NBS Criteria, a ‘'trace’' was not found this study but a ‘'slight’' was found 2-3, 3-5 in dentin porcelain, 2-3 in opaque-dentin porcelain, 3-5, 5-10 in enamel porcelain and translucency porcelain, a ‘'noticeable’' was 2-5, 3-10, 5-10 in dentin porcelain and opaque-dentin porcelain, 2-3, 2-5, 3-10 in enamel porcelain 2-3, 3-10 in translucency porcelain, an ‘'appreciable’' was 1-2, 1-3, 2-10 in dentin porcelain 1-2, 1-3, 2-10, 3-10 in opaquedentin porcelain, 2-10 in enamel porcelain, 2-5, 2-10 in ranslucency porcelain, a ‘'much’' was 1-5, 1-10 in dentin porcelain and opaque-dentin porcelain, 1-2, 1-3, 1-5 in enamel porcelain 1-2, 1-3, 1-5, 1-10 in translucency porcelain, a ‘'very much’' was 1-10 in enamel porcelain.

The purpose of this thesis is to address the imbalance between supply and demand of dental lab technicians and to propose its solutions by analyzing the improvement of employment rate of graduates of dental technology schools in Daegu area and the supply and demand of the technician workforce. Preliminary and full-scale surveys were performed from Aug. 10 to Oct. 10 in 2008 on 150 junior students of dental technology schools who finished their on-the-job-training and 150 dental technicians who were working for dental laboratory in Daegu by self-assessment questionnaire. Followings are the findings of this study. First, regarding the gender of the dental technicians, 32.7% of respondents were female 67.3% were male. Concerning age, respondents younger than 29 years-old occupied the highest percentage(39.3%). With respect to the lab technology school they graduated, DaeguHealthCollege took the largest proportion of 87.3%. With regard to interpersonal relationship at the school, 58.0% of respondents felt their relationship ‘'smooth’'. Second, about the motive of choosing to be a lab technician, the biggest proportion of the respondents(34.7%) replied that ‘'because it is professional’'. Regarding the degree of satisfaction about the profession, ‘'so-so’' was the answer with the biggest percentage(51.3%) followed by ‘'satisfied’'(32.0%) and ‘'unsatisfied’'(16.7%). It showed that respondents were generally satisfied with their major. Third, regarding relevance of on-the-job-training with ‘'preparation for the employment’', highest percentage of both students and lab technicians(50.0%) replied ‘'so-so’'. With respect to ‘'necessity of practical education’', highest percentage of the students and lab technicians replied ‘'relating didactic education in college to the real world’' with 52.7% and 40.7% respectively. With regard to ‘'the aim of on-the-sport-training’', ‘'practical training of didactic education’' was chosen by 54.0% and 47.3% respectively. Fourth, with regard to the ‘'types of college education advantageous for the employment’', both students and lab technicians groups chose ‘'practical training’' with the highest percentage. Concerning ‘'helpfulness of clinical training on employment’', students answered ‘'so-so’' and ‘'helpful’' by 50.0% and 42.7% respectively and dental technicians replied similarly by 50.0% and 46.0% respectively. Fifth, with regard to the influence of financial factors on the supply and demand of dental technician(question #1), 68.0% of respondents agreed that ‘'salary plays key role in the supply and demand of the work force’'. Concerning the question about working condition, respondents requested better working environment. With reference to interpersonal relationship at the laboratory, respondents replied that interpersonal relationship affects the duration of the employment it was found out that there were many conflicts with colleagues or dental office. Sixth, regarding the satisfaction about their profession according to the characteristics of the respondents more respondents were ‘'satisfied’'(10.30 points) with their profession and ‘'unsatisfied’' were 9.47 points and the difference was statistically significant(p<0.05). According to the findings of this study, practical education on campus and -the-job-training are as important as didactic education at class due to the haracteristics of dental technology major. It was found that more practical training is related to higher employment rate. Therefore, efficiency of on-the-job-training by college education should be increased raise employment rate of the graduates and reduce the unemployment. Up-to-date information needs to be promptly delivered and future vision should be presented to the students to raise their satisfaction about the profession. In addition, to reduce dental technician’'s frequent change of their workplace after facing with the reality of the profession after graduation, related organizations should make an effort to present better future than now.

Passive fitting of meso-structure and super-structures is a predominant requirement for the longevity and clinical success of osseointegrated dental implants. However, precision and passive fitting has been unpredictable with conventional methods of casting as well as for corrective techniques. Alternative to conventional techniques, electro discharge machining(EDM) is an advanced method introduced to dental technology to improve the passive fitting of implant prosthesis. In this technique material is removed by melting and vaporization in electric sparks. Regarding the efficacy of EDM, the application of this technique induces severe surface morphological and elemental alterations due to the high temperatures developed during machining, which vary between 10,000~20,000 . The aim of this study was to investigate the morphological and elemental alterations induced by EDM process of casting dental gold alloy and non-precious alloy used for the production of implant-supported prosthesis. A conventional clinical dental casting alloys were used for experimental specimens patterns, which were divided in three groups, high fineness gold alloy(Au 75%, HG group), low fineness gold alloy(Au 55%, LG group) and nonprecious metal alloy(Ni-Cr, NP group). The UCLA type plastic abutment patterns were invested with conventional investment material and were cast in a centrifugal casting machine. Castings were sandblasted with 50 Al2O3. One casting specimen of each group was polished by conventional finishing(HGCON, LGCON, NPCON) and one specimen of each group was subjected to EDM in a system using Cu electrodes, kerosene as dielectric fluid in 10 min for gold alloy and 20 min for Ni-Cr alloy(HGEDM. LGEDM, NOEDM). The surface morphology of all specimens was studied under an energy dispersive X-ray spectrometer (EDS). The quantitative results from EDS analysis are presented on the HGEDM and LGEDM specimens a significant increase in C and Cu concentrations was found after EDM finishing. The different result was documented for C on the NPEDM with a significant uptake of O after EDM finishing, whereas Al, Si showed a significant decrease in their concentrations. EDS analysis showed a serious uptake of C and Cu after the EDM procedure in the alloys studied. The C uptake after the EDM process is a common finding and it is attributed to the decomposition of the dielectric fluid in the plasma column, probably due to the development of extremely high temperatures. The Cu uptake is readily explained from the decomposition of Cu electrodes, something which is also a common finding after the EDM procedure. However, all the aforementioned mechanisms require further research. The clinical implication of these findings is related with the biological and corrosion resistance of surfaces prepared by the EDM process.

Partial or complete prosthesis is needed when teeth are lost due to various kinds of reason. Artificial teeth recover occlusion instead of natural teeth. Artificial teeth are required of esthetics, fragile resistance and abrasive resistance. Artificial tooth is made of acrylic resin or porcelain. Nowadays, acrylic resin artificial teeth are mainly used. Acrylic resin teeth are occluded with natural teeth, gold alloy, Ni-Cr alloy or porcelain etc. Acrylic resin teeth have similar translucency, gloss of natural teeth. And it has good chemical bond with denture base material, but it has low wear resistance. The aim of this study is to compare wear resistance among several denture teeth(Endura, SR-orthosit-PE, Planustar) and between artificial resin denture teeth and opposing 3 restorative materials(gold, Ni-Cr alloy, porcelain). Wear tests were conducted with a rotating wear testing apparatus(pin-on-disk type wear tester) under conditions of rpm 180, 75 minutes and constant loading of 50N. The upper part was the cusp of maxillary first molar and the lower part was a disk type restorative materials. To make similar oral environment, water was supplied continually. The acrylic resin teeth wear was determined by weighing the cusp each 5 minutes during 75 minutes test. Vicker's hardness tester was used to evaluate the surface hardness of test specimens. The SEM was used to evaluate the wear surfaces. The results were as follows: 1. Wear rates of acrylic resin teeth opposing to the restorative materials were high in order of Porcelain, Gold, Ni-Cr alloy (p<.05). 2. Wear resistance rate opposing to the Porcelain disk, was shown in order of Endura, SR-orthosit-PE, Planustar. The wear rate of opposing to porcelain disk was above two times more than that of other groups (p<.05). 3. Wear resistance rates opposing to the Gold, Ni-Cr alloy disk, was shown in order of Endura, SR-orthosit-PE, Planustar (p<.05). 4. A degree of the surface hardness is directly proportional to the degree of wear resistance. There are statistically significant differences between each groups (p<.05).

Objectives: Practice of dental technology poses great potential risk since the manufacturing processes are complex and involve dangerous devices and the students are asked to handle various materials in the casting and processing process. Lacking an understanding of the overall practice process, the beginners of practice are exposed to greater danger due to their unsafe attitudes and poor practice attitudes. This study set out to investigate the students of dental technology for their attitudes toward safety and their practice of safe actions during practice and to provide basic data for safety education to prevent any possible safety incidents during practice. Methodology: The subjects include total 408 dental technology majors in their sophomore and junior year. Based on literature study and previous studies, a structured questionnaire was made, distributed to the subjects right after practice, and gathered on the spot. The questionnaire contained total 60 items, and data were collected from April 20 to May 25, 2006. Results: Collected data were analyzed in frequency and X©˜˜-test using the SPSS 12.0 version. The analysis results show that the students believed that they could prevent safety accidents by following safety rules and guidelines as far as safety attitudes were concerned. However, they did nothing more than paying attention to many practice processes even though they thought they were dangerous. Conclusion: Overall the subjects practiced proper safety actions during practice with significance differences in their behavioral characteristics according to grade, gender and age. The significant differences according to grade seem to derive from safety education before practice, and those according to gender and age have more to do with individual actions and common sense according to gender and age than education. Thus practice teachers need to develop safety education materials for each practice process and provide systematic safety education before practice so that the students can practice safety actions.