Earticle

An investigation was carried out to examine the pores of casting bodies depending on the position of wax pattern in the ring for precious alloy by optical micrographs. From the result of optical micrographs, many pores were found in the Group C that wax pattern is placed in the center of the ring. However, any pores were scarcely found in the Group A, B, D and E that wax patterns are placed out of the center of thermal zone. In comparison with the pores of casting bodies of Group C, many pores were found at the cusp area rather than at the proximal surface. From these examination, it was concluded that wax pattern should be placed out of the center of thermal zone to prevent casting boies from occurring pores.

Gypsum products are used for the preparation of stone casts of oral and maxillofacial structures and as important adjuncts to dental laboratory operations involved in the production of dental prosthesis. Accuracy and dimensional stability over time are properties of concern in fixed prothodontics. Gypsum products used in denstry are a form calcium sulfate hemihydrate and are classified as 1 of 5 types according to International Standard Organization(ISO) 6873. All die materials exhibit some dimensional change during setting, but expansion and contraction during setting and dimensional changes in response to varations in temperature and the water-powder ratio must be minimal. Although numerous investigators have studied the properties of die materials, several products have been introduced recently with manufacturer claims of superior dimensional stalility. The aim of this study was to determine the surface properties using various separating materials of dental gypsum products The results were as follows 1. In the comparison of first and second plaster distances before separation in different separating agent, there was no significant difference except using Trio separating agent. The interface using Trio separating agent forms like to pores. 2. In the comparison of first and second plaster distances after separation in different separating agent, there was significant difference. The interface of plasters using WD-40, Trio and Vaseline was showed some gaps. Each they were measured at average 7.97 2.07 , 63.09 23.25 , 27.59 4.19 . 3. In the comparison of the surface, the surface of control sample(using none seperating agent) showed irregular properties and the surface using Trio and Vaseline become wrinkled. Specially the surface using Vaseline was showed shiny properties. But the surface using MAGIC SEP, Plaster seperating agent, WD-40 showed regular properties.

Cp-Ti and Ti-6Al-4V alloys commonly used dental implant materials, particularly for orthopaedic and osteosynthesis because of its suitable mechanical properties and excellent biocompatibility. This alloys have excellent corrosion behavior in the clinical environment. The first factor to decide the success of dental implantation is sufficient osseointegration and high corrosion resistance between on implant fixture and its surrounding bone tissue. In this study, in order to increase corrosion resistance and biocompatibility of Cp-Ti and Ti-6Al-4V alloy that surface of manufactured alloy was coated with TiN by RF-magnetron sputtering method. The electrochemical behavior of TiN coated Cp-Ti and Ti-6Al-4V alloy were investigated using potentiodynamic (EG&G Co, PARSTAT 2273. USA) and potentiostatic test (250mV) in 0.9% NaCl solution at 36.5 1 . These results are as follows : 1. From the microstructure analysis, Cp-Ti showed the acicular structure of -phase and Ti-6Al-4V showed the micro-acicular structure of + phase. 2. From the potentiodynamic test, Ecorr value of Cp-Ti and Ti-6Al-4V alloys showed -702.48mV and -319.87mV, respectively. Ti-6Al-4V alloy value was higher than Cp-Ti alloy. 3. From the analysis of TiN and coated layer, TIN coated surface showed columnar structure with 800 nm thickness. 4. The corrosion resistance of TiN coated Cp-Ti and Ti-6Al-4V alloys were higher than those of the non-coated Ti alloys in 0.9% NaCl solution from potentiodynamic test, indicating better protective effect. 5. The passivation current density of TiN coated Cp-Ti and Ti-6Al-4V alloys were smaller than that of the noncoated implant fixture in 0.9% NaCl solution, indicating the good protective effect resulting from more compact and homogeneous layer formation.

Recently natural characteristics and esthetics have been interested increasing in clinical dentistry. Thus the evaluation of the shade of dental porcelain has become an important part in dental research. Noritake Super Porcelain EX-3 Vita shade A2 (Noritake, Japan) Vintage HaLo Vita shade A2 (Shofu, Japan), Vita omega 900 Vitapan 3D-master shade 2M2 (Vita, Germany) were conducted for six times for repeated firing in a way to observe the change of color with respect to the number of firing. The repeated firing was implemented with the vacuum firing and air firing, and by using Shade Eye-EX Chroma meter (Shofu, U.S.A.), the changes in values of shade, value and chroma were compared. With the above results, the change of color was not noticed only in Vita when repeated firing was applied.

This study was to evaluate the biaxial flexural strength of zirconia ceramics after glass-infiltration on zirconia core. The zirconia specimens were made with diameter-15mm, thickness-0.6mm using zirconia block which divided into 1) sintered group, 2) heat - treated group, 3) Glass - infiltrated group and experimented fracture strength by each 10 specimens in experimental group. The biaxial flexural test was performed at crosshead speed of 0.1ßÆ min. The experiment result average fracture strength was shown 541.0ßÁ in sintered group and glass-infiltrated group as 662.2ßÁ river of 22.4% rise appear. Weibull coefficient sintered group is 3.462 and glass-infiltrated group improved believability about fracture strength from melting permeation processing of glass by 4.716.

In this study, to provide the fundamental data on stable connection method for successful implants prosthesis, We fabricated the solder joint of gold alloy bar specimens by gas flame soldering method and laser welding and soldering method. It compared and studied the tensile strength of two soldering method by universal testing machine . The results using universal testing machine were as follow : The mean of tensile strength of solder joint bar in gas flame soldering method specimens was 363.89 17.62 , and the mean strength of laser welding and soldering method was 125.91 19.66 , so gas flame soldering method was better than laser welding and soldering method and the finding better way to improve tensile strength is needed in laser welding method. On weak loading condition and the part which is needed an accuracy, laser welding method is more effective and on long-span prosthesis and frequent chewing loading part, laser welding technique is recommended first and applying additional gas flame soldering technique would be better for making much more successful prosthesis.

The purpose of this study was to ascertain the effect of different abutment height and different taper of abutment on retention force of cemented implant-supported prostheses. Test specimens consisted of different abutment height group(3 , 4 , 5 , 6 , 7 ) and different taper(degrees) abutment group(4°, 5°, 6°, 7°, 8°). The surfaces of abutments and crowns were manufactured and finished by automatic lathe(CNC). Luting cement(Tokuso Ionomer) was prepared according to the manufacturer’s instruction. And the cylinders were sealed onto the abutments and loaded in compression at 5 for 10minutes. Excess cement was removed from the abutment-cylinder junction and the specimens were stored at room temparature for 24 hours. Specimens were tested in tension using a universal testing machine. Within the limits of this study, the following conclusions were drawn: 1. The increase in abutment height result in improvement in retention strength(P<0.05). 2. The increase in taper of abutment result in decrease in retention strength(P<0.05). 3. The decrease in abutment height result in decrease in retention strength, besides has a significantly lower retention strength at 3 abutment height. 4. The increase in taper of abutment result in decrease in retention strength, besides has a significantly lower retention strength at 7° abutment.

The use of titanium in the field of dentistry has increased, due to their excellent biocompatibility, appropriate mechanical properties, corrosion-resistance and low price. However, many difficulties with the use of titanium for metal-ceramic crowns remain to be solved. The objective of this study was to evaluate the influence of surface modifications on the bonding characteristics of specific titanium porcelain bonded to cast titanium. The surfaces of Titanium were prepared with 4 test groups, ) sandblasted with particles of different size, ) sandblasted after treated oxidization and oxidized after sandblast. We observed the bond strength and node aspect of titanium and ceramic, and respect to the methods of modifying surface of titanium by the test of mean roughness of surface, Scanning Electron Microscope, and 3-point flexural bend test. The results show that, 1. The specimens, which treated oxidization after process of sandblast with particles of 50um size, were the better for the bond strength in comparison with other specimen. 2. The specimen with process of sandblasting after oxidization treatment were the better for stability of the bond strength. 3. The wettability of titanium surface affect the bond strength.

This study has been analyzed to write an ideal training evaluation table after analyzing validity of content organization and assigning score of evaluating elements of clinical practice of Dept. of dental technology. 220 junior students who are studying dental technology in D university in Daegu were questioned to analyze the relationship of content organization and score of clinical practice evaluation table. The corrected material has been inspected by SAS V8 for Windows. The results are as following. 1. The validity of content organization of clinical practice evaluation table has a result which can be reliable over than 70% but the validity of score shows low reliance. c 2. The validity of content organization of detail elements of clinical practice evaluation shows that overuse of material and attentiveness(3.78) and responsibility (3.60) are high response but in score organization, the validity shows that safety measure(2.36) when controling machines, arrangement(2.98) after use and ability (2.98) of solving problems are very low. 3. In the elements without interpersonal relation, it shows that those are related to each other. its grading is p < 0.01 so it appears to be meaningful. 4. In result of analyzing the effect to ‘studying amount’ mark in clinical practice evaluation mark, it appears the element of attitude for job to affect it. And in result of analyzing the effect to ‘training attitude’ mark, it appears the element of ‘controling machines’ to affect it. For these results, to be a better evaluation tool, it should be modified by continuous research with arranging evaluation elements to be marked differently in between elements.

This study aims to analyze the major factors in their working conditions affecting the enlargement of leisure activities of dental technicians. We also present a need for dental technicians to assign more time many different kinds of leisure activities for their quality life. To this end, we examined the status and the characteristics of dental technicians’ leisure activities among the randomly selected subjects who are working in the area of Seoul, Gyonggido, and Gangwon-do through the analysis of the 311 sheets of self-administered questionnaires. The conclusions from this analysis are as follows; 1. On weekdays, non participants in leisure activities were found to be 64.0%, and in the case of weekends, the participants were reached to 70.7%. Those who enjoy any leisure activities in either of weekdays and weekends were 34.1%, 27.3% of the dental technicians did not have any leisure activities. Therefore, statistical significance was shown in the participations of leisure activities between weekdays and weekends. 2. Of the types of leisure activities in both weekdays and weekends, sports activities were ranked at the top 33.4%, 29.6% respectively, which is followed by going to the cinema/theatre/exhibitions, etc 21.9%, 26.0%, games/entertainment 14.5%, 14.8%, hobbies/cultural activities 14.1%, 12.5%, sightseeing/picnic 6.4%, 7.4%. 3. Of the differences in the characteristics of leisure activities, the types of leisure activities between weekdays and weekends showed difference in gender, company and information regarding leisure activities in age, company and the place of leisure activities, and leisure information in the marital status, career and monthly income in company, company and leisure information in the job position, which is statistically significant (p<.001). However, no statistical significance was found among the other general items of the characteristics of leisure activities. Considering only works on weekdays policy is currently permeating into almost every business sector, dental business owners or managers are advised to consider more effective time management or human resources management, such as keeping reasonable manufacturing time through cooperations with the dentists, regularity of working hours, incentive system, introduction of credible over time payment. Which will provide their staff with more times and opportunities to enjoy their leisure activities. Additionally, the concrete and feasible ways of motivating and activating the leisure activities of dental technicians are in need of further researches and studies.

Objectives; The purpose of the present study is to investigate the difference in levels of satisfaction between dental laboratory owners and employed dental technicians in the area of dental laboratory management. Methods; The samples of seventy-one dental laboratory owners and sixty-six employed dental technicians were selected in a blinded and random manner. Data was collected through self-administered questionnaires and analyzed using average values, the t-test and multiple regression. Results; 1) There was no significant difference in the average values of general satisfaction levels related to dental laboratory management between dental lab owners and employees. 2) The average values of satisfaction levels in 11 specific items scored ‘above average’ among dental lab owners and ‘average’ among employees. 3) The average values of satisfaction levels in 10 specific items except for ‘trust and respect’ showed a significant difference between dental lab owners and employees. 4) Important factors which influenced the satisfaction level of dental lab owners were ‘trust and respect’ and ‘improvement of employee’s benefits’. In the employees group, ‘trust and respect’, ‘improvement of employee’s benefits’ and ‘technical information support’ were important factors. Conclusion; The present study revealed that dental laboratory owners and employees have some gaps between the viewpoints in dental laboratory management. This suggests the necessity to improve management in a transparent and economical way. However this study has some limitation in that the sample size was not massive enough.

The Status of oral health and dental prosthetic treatment in Daegu and Gyoung Buk area was examined. To investigate the correlation between factors such as demographic and socioeconomic characteristics and status of oral health and knowledge about oral preventive measures, a survey was performed. After analyzing the effects of knowledge levels about dental prosthetic treatment on the oral health status and preventive measures, following results were obtained. A Total of 625 people participated in the survey for three months from October 2007 to January 2008. The responses from the survey were then analyzed to assess whether those with less knowledge of preventive measures tended to have more dental prosthetic work. Of those that took part in the survey: 30.2% were in their twenties 56.2% were married 51.4% of respondents had at least a college degree 42.4% had monthly incomes below one million Won 24.3% were students 55.8% were from urban areas After studying the relationship between oral health and various demographics, researchers concluded that respondents’ sex, income, job and place of residence had no effect on the overall status of their oral health. However, those that were divorcees or widows (1.95+/- 0.32), over the age of 70 (1.67+/-0.31), or had little education (0.82+/-0.28), all demonstrated a statistically significant effect on their oral health with a significance level of 0.05.Cross analysis revealed a p-value of 0.000. The correlation between knowledge of oral preventive measures and other factors was examined. No difference was found between men and women but people who were divorced or lost their spouse, people over the age of 60, and people with no education, the results of knowledge of oral preventive measure was poor as 1.74 0.44, 1.85 0.40, 1.85 0.44,and 1.60 0.47 separately. Cross analysis showed that p-value was 0.000 and correlation between knowledge of oral preventive measures and those factors were statistically significant at significance level of 0.05. The status of dental prosthetic treatment was investigated. Women, people with higher income, and married people had more dental prosthetic treatment and it was related to education, income, residential area, and the status of dental prosthetic treatment. The returns of those factors was 32.7%. Respondents°Ø oral hygiene status and knowledge of oral preventive measures was related to demographic or socioeconomic factors. Therefore, a preventive program for oral health care needs to be developed in advanced countries. Knowledge of oral health is below the international average and more research and effort needs to be put in to develop public knowledge of dental prosthetic treatment. Government intervention such as enacting an oral health initiative or dental insurance that covers prosthetic treatments is urgently needed.

The purpose of this research project is to assess students’ stress during clinical rotations and to suggest strategies for enhancing professional skills as well as the quality of clinical rotations among the students of dental technology. The participants included 200 sophomores and juniors from dental laboratory college located in Daegu and Jeju. Data was collected December 7, 2007, and March 7, 2008, by survey samplings. A total of 185 completed surveys were obtained and analyzed for this study. Findings from the study are summarized below. When age and stress were compared, it was found that younger students had higher levels of stress related to their environment, role, and activities. Regarding grade level and stress, students in lower levels were slightly (p<.01) more likely to have stress (Sophomore =2.91, junior =2.49). When the stress level was compared with students’ satisfaction with their major, the less students were satisfied, the higher their level of stress was. The study found a slight (p<.05) difference between groups [satisfaction group (M=2.44), group in between satisfaction and dissatisfaction (M=2.58), and dissatisfaction (M=2.82)) in the relationship between satisfaction with the major and overall stress. Again, it appears that stress levels increase as satisfaction with the chosen major decreases. Third, the intensity of stress was affected by the environment in which students practiced, classmate relationships, roles, goals and values, and activities, and areas of performance. It showed that the groups unsatisfied and in-between with the quality of practice have more intensified stress than the group with satisfaction. The study showed a slight (p<.01) difference amongst groups [(satisfaction group (M=2.17), group in between satisfaction and dissatisfaction (M=2.68), and dissatisfaction (M=2.96)) in the relationship between satisfaction with the quality of the clinical rotation and overall stress. It appeared that higher levels of stress were seen with lower satisfaction with the major. Overall, students’ level of stress was correlated with age and grade level, level of satisfaction in the major and the quality of the clinical rotation. Furthermore, schools need to focus on improving the environment where students practice, classmate relationships, roles, goals and values, and activities, and areas of performance. Dental laboratory colleges should concentrate on the basic case with the quality of clinical rotation and the chosen major. More skillful teaching and properly assigned clinical rotations and classes, along with a strong practical knowledge base applicable to clinical rotations will be needed in order to address these sources of dissatisfaction.

It’s very important to find the most appropriate adhesion technique available, taking into consideration factors such as biocompatibility, non-corrosiveness, mechanical stability, etc. Laser welding is the best choice you can make because from a mechanical viewpoint, a laser welded surface has better particle structure than does a casted particle structure. Furthermore, it requires no additional material and the same metal alloy which is used when casting can be used. Therefore, the resulting mixture will consist of a single alloy, instead of utilizing different alloy combinations. Another benefit is the low economic cost. The most beneficial aspects of laser welding is that it is biologicallly friendlly, doesn't require soldering, can fuse different metal alloys together, and can weld on heat-sensitive spots(E.g. around resin or ceramic). A consistent strong pulse is possible. This technique is capable of welding on master models and creates accurate welds. It is capable of due to its stronger, non-corrosive microscope, which allows 25times magnification during the soldering process. This is possible because of its high stability from the tiny particle structure.