Earticle

Purpose: The purpose of this study was to compare the accuracy of the scan data acquired by the extra-oral and intra-oral scanner. Methods: The maxillary right first molar was made of polymethyl methacrylate (PMMA)specimen. This PMMA specimen was scanned with a engineering scanner and intra-oral scanner. Meanwhile, extra-oral scanner scanned stone die duplicated from PMMA master die. Trueness and precision of scan datas was measuredby3-dimensinal inspection. Independent t-test was conduct to analysis the significant difference.(a=0.05) Results: In the trueness analysis, mean of discrepancies were13.82um for intra oral scanner and16.84 um for extra-oral scanner. In the precision analysis, mean of discrepancies were 11.72 for inta-oral scanner and 9.2 for extra-oral scanner. Both trueness and precision showed a statistically significant difference (Table 1, p<0.05). Conclusion: Intra-oral scanner can show higher trueness than extra-oral scanner, it has lower precision.

Purpose: The purpose of this in vitro study was to evaluation the effect of shade on all ceramic restoration based zirconia according to cooling rate on Firing. Methods: 10 specimens applied to the dentin porcelain were made on the zirconia. After 5 specimens of the first group were burned in the furnace, these were put out rapidly. And after 5 specimens of the second group were burned in the furnace, these were put out slowly later 15 min. All specimens were measured L, a, b using spectrophotometer, there were calculated 10 mean(SD) of descriptive statistics with SPSS program. These data were used for ∆E with color difference equation. Independent t tests were performed between 2 groups. Results: L, a, b of 2 groups was statistically significant respectively (p<0.001), ∆E was 4.55 value. Conclusion: This study showed effect of shade on all ceramic restoration based zirconia according to cooling rate on Firing.

Purpose: The objective of this study was to compare the surface roughness according to polishing process in conventional laboratory techniques used for polishing three different acrylic denture base resins. Materials and methods: Specimen preparation and surface polishing procedures were conducted to manufacturer’s recommendation with three heat-polymerized denture base resins. Surface roughness and gloss were measured by a contact type tester and a LED gloss checker using thickness 2 mm and diameter 10 mm. There were five specimens for each acrylic resin material and polishing procedures. Mean average surface roughness (Ra) values of each specimen group were analyzed using a one-way ANOVA analysis of variance and Scheffe’s post hoc test. Surfaces after surface roughness and gloss testing according to each polishing process were evaluated under a stereoscopic microscope. Results: The highest mean average surface roughness was measured (Ra=2.43± 0.47) for surfaces finished with a denture tungsten carbide bur in Triplex. The lowest surface roughness values (Ra=0.11 ±0.07) were determined in Vertex polished with a lathe. In addition, all materials revealed that surface roughness determined highly in HP1 and HP2 than other procedures. All correlation between surface roughness and gloss showed highly with three heat-polymerized resins. Specially, topmost correlation revealed than other material in Triplex. Significant differences in mean average surface roughness were found between polishing process used high speed lathe and low speed hand-piece. Conclusions: Laboratory polishing used to high speed was found to produce the smoothest surface of heat-polymerized denture base acrylic resin. Therefore, we recommended that high polishing process need to get smooth surface.

Purpose: The purpose of this study compared of reproducibility of prepared tooth impression scanning utilized with white and blue light scanners. Methods: To evaluate reproducibility with white and blue light scanners, the impression of premolar were rotated by 10°~20° and scanned. These data were compared with the first 3-D data (STL file), and the error sizes were measured (n=5). Independent t test was used to evaluation the reproducibility of impression of premolar with white versus blue light scanners through discrepancies of mean, RMS (α=0.05). Results: Discrepancies of mean with regard to reproducibility were 11.2㎛, 5.8㎛, respectively, with white and blue light scanners (p<0.047). And discrepancies of RMS with regard to reproducibility were 33.4㎛, 18.8㎛, respectively, with white and blue light scanners (p<0.045). Conclusion: Our results indicate a good reproducibility of prepared tooth impression digitized with blue light scanner more than that with white light scanner.

purpose : The purpose of this study was to evaluate the effect of the chemical surface treatment on the flexural bond strength of heat curing denture base resin and reliners. Methods: Denture base resin surface was treated with MMA 95% and TEGDMA 5%, MMA 95% and silane coupling agent 5%, heat curing resin monomer. After denture reliners were injected, flexural bond strength was measured. Results: The repair resin of Vertex SC was higher than Lang, hard reliner of Kooliner was higher than Rebase. Soft reliner of Dura base and Coe-soft showed differently according to the surface treatment. The all chemical treatment groups on Vertex SC were significantly higher than control(p<0.05). In Lang group, 5% MPS treated group showed significantly higher flexural bond strength than others(p<0.05). In Kooliner group, all chemical treatment groups showed significantly higher than control(p<0.05). In Rebase group, the 5% MPS and the monomer denture base resin treated groups showed significantly higher than others(p<0.05). In Dura base group, 5% MPS treated group showed significantly higher flexural bond strength than others(p<0.05). In Coe-soft group, all treated groups were significantly higher than control group(p<0.05). Conclusion: TEGDMA, MPS, and the monomer of heat-cured denture base resin were effective to improve the bond strengths between denture base and denture relining materials. Especially, 5% MPS expected to strengthen effectively the bonding property of denture base and denture reliners within the results of this study.

Purpose: The purpose of this study was to analysis the internal fitness of single crown fabricated by additive method technique. Methods: Study models were fabricated. Ten crowns were manufactured by additive method technique (AM group) and another ten crowns using conventional method were manufactured (CM group). The internal fitness of specimens were measured using silicone replica technique. Silicone replicas were sectioned one times (direction: from mesial to distal). The internal fitness were evaluated using by digital microscope. Statistical analyses were performed with independent samples t-test. (α=0.05). Results: Mean(SD) of all internal fitness were 92.1(20.0)㎛ for AM group and 69.7(12.3)㎛ for CM group. Two groups were statistically significant differences (p<0.001). Conclusion: All internal gaps of AM group were ranged within the clinical recommendation (120㎛).

Purpose: The aims of this study are compare with microstructure and mechanical properties of Co-Cr-Mo alloys fabricated by powder metallurgy(P/M) process and casting process respectively. Method: Microstructure and micro-hardness were tested by SEM and Vickers Hardness Tester. The sintered specimen was produced by furnace-coolling after sintering, however the casting specimen were produced thru air-cooling and water-cooling after the casting. For observation of phase transformation during sintering, DSC analyzing was carried out. Results: Mean pore size of sintered Co-Cr-Mo alloy was 4.32㎛ and that of casting alloy was 1.63㎛. Hardness of sintered alloy was lower than water-quenched casting alloy. Conclusion: Proper sintering temperature of Co-Cr-Mo alloy was above 1,200℃ and pore size of casting specimen were finer than sintered specimen, but hardness were similar.

Purpose: The aim of this study was to investigate the shear bond strength between various commercial zirconia coping and veneering ceramic, and to observe the failure mode. Methods: For each zirconia block (iJAM Emerald, LUXEN Smile block, ICE Zirkon transluzent), 10 rectangular specimens were layered with Cercon ceram kiss, IPS e.max ceram, ICE Zirkon ceramic according to recommended by the manufacturer. The shear bond strength tests of the veneering porcelain to zirconia were carried out until fracture by a universal testing machine. After the shear bond tests, failure modes were characterized visually, under a stereomicroscope, such as adhesive, cohesive, or mixed. Data were analyzed with One-way ANOVA followed by Scheffe's tests. Results: The shear bond strength (mean±SD) of zirconia-veneer ceramic were JC group 13.9±3.6 ㎫; JE group 17.7±2.4 ㎫; JI group 15.1±2.5 ㎫; LC group 9.5±1.5 ㎫; LE group 16.2±2.3 ㎫; LI group 12.6±0.8 ㎫; ZC group 16.0±2.3 ㎫; ZE group 18.5±3.4 ㎫; and ZI group 15.3±3.2 ㎫. The One-way ANOVA showed a significant difference between groups (p<0.05). The failure mode in most experimental groups was mixed failure, except for the LC group, which showed adhesive failure, and JE group, LE group and ZE group showed cohesive failure. Conclusion: For IPS e.max ceram, the shear bond strength value was highest for all kinds of zirconia blocks. For ICE Zirkon transluzent, the shear bond strength value was highest for all kinds of veneering ceramics. Most of experimental group interfaces revealed mixed failure mode.

Purpose : The purpose of the study is to investigate the need for the retirement attitude of korean dental technicians. Retirement attitude is important in the study of retirement planning. Methods: A total of 778 dental technicians were selected by proportional stratified by region compared to extraction sampling from a list of korea dental technician association in 2012. The final sample size was 386. Questionnaires consisted of 10 questions general characteristics, 9 questions for the current life satisfaction and retirement preparation, and 4 questions about retirement attitudes on a Likert 5 scale. Cronbach's alpha was 0.812 in the study. All statistical analyzed were performed using SPSS 14.0(Statistical Packages for Social Science Ver. 14.0. Chicago, IL, USA). Results: An average of 3.01 ± 0.8 dental technicians were retirement attitude. To affect retirement attitude marital status, age, subjective health status, assets satisfaction, job type, job satisfaction and the economic outlook was living after retirement (p <0.05). Conclusions: This study suggested that retirement attitude of korean dental technicians was very important and the preparation must be connected with the social welfare policy.

Purpose: This study is intended to survey male and female university students to see if there is correlation between temporomandibular disorder and oral habits known to cause temporomandibular disorder. Methods: A survey was conducted to 400 male and female university students attending two universities located in Daegu Metropolitan City and Gyeongsangbuk-do to examine if there is correlation between oral habits and temporomandibular disorder. Among total 400 questionnaire sheets, 334 (83.5%) sheets were used for final analysis except for those unreliably answered or containing error. Results: Female students showed a higher prevalence rate of temporomandibular joint pain than male students, and those having the habit of resting jaw on hand indicated a higher prevalence rate of temporomandibular joint pain, temporomandibular joint clicking, or trismus than normal students not having it. Also, those having the habit of tooth clenching showed a significantly higher prevalence rate of temporomandibular joint pain or temporomandibular joint clicking than normal students not having it. Conclusion: It can be concluded that the habit of resting jaw on hand is closely related with temporomandibular disorder like temporomandibular joint pain, temporomandibular joint clicking, or trismus, and the habit of tooth clenching is significantly correlated with such symptoms as temporomandibular joint pain and temporomandibular joint clicking.

Purpose: The purpose of this study was to examine the usage of CAD/CAM, which is one of dental technologist duties, in an effort to look for any possible changes in the usage of CAD/CAM. It's specifically meant to compare the results of this study with those of Lee Jong-do, Park Kwang-Sig(2011)'s study in March, 2011, to determine if there were any changes over the past four years. The selected variables that were investigated were the ownership of CAD/CAM, awareness of it, the route of acquiring the first information on it, the merits and demerits of its usage, usage experience and educational experience about it. Methods: An online survey was conducted on the dental technologists who worked in urban communities including metropolitan cities to find out the usage of CAD/CAM in 2015 from July 15 to 31, 2015, after existing questionnaire items were modified. The collected data were analyzed by IBM SPSS statistics 22.0, and statistical data on frequency, percentage, mean and standard deviation for each item were obtained. To figure out the characteristics of the subjects and the relationship between their occupational characteristics and the usage of CAD/CAM, crosstabs, independent-samples t-test and one-way ANOVA were utilized. As for the usage of CAD/CAM in 2011, the results of Lee Jong-do, Park Kwang-Sig(2011)'s study were selected, and then a comparative analysis was made. The level of significance was all set at .05. Results: As a result of analyzing the usage of CAD/CAM that was one of dental technologist duties, there was a great increase in the ownership of CAD/CAM in their workplaces from 2.4 percent in 2011 to 71.7 percent in 2015, and there was an improvement in awareness about it and the necessity of its usage as well. In 2011, the Internet and mass media were the most common route that they got to know about it. They had a strong tendency to acquire related knowledge through education in 2015, and there were some changes in the products that they used or preferred. In both years, the great merit of CAD/CAM was the simplified manufacturing process of restoration, and it had another great advantages in 2015 such as the improved quality of restoration or improved environments for dental technology. Concerning disadvantages, high price was a big problem in 2011. In 2015, not only price but the burden of material costs, frequent breakdown, poor demand among dental clinics and a lack of CAD/CAM professionals were pointed out a lot. In the future, this researcher intends to make research to seek ways of improving CAD/CAM professionals. Conclusion: There was more awareness of CAD/CAM in 2015 than in 2011 when the changes in awareness of it were analyzed, and the finding suggest the necessity of sustained education and concern.

Purpose: The following study analyzes the mediating effects of professionalism on the relationship between major selection conviction and career decision level of dental technology students. It is to be used as basic data for improvement of the students’ career decision level and an effective way to train professionals of the colleges. Methods: The survey was conducted on dental technology students. The collected data was analyzed by the statistical program SPSS 18.0. The results were analyzed by reliability, frequency, multiple-way ANOVA, correlation, multiple regression. To test for significance on each item, p<0.05 has been decided as a standard. Results: The analysis shows that the students’ age and clinical practice experience bring a significant difference in major selection conviction, career decision level and professionalism. Professionalism has been found to bring significance mediating effects in relation to major selection conviction and career decision level. Conclusion: To improve the quality and pride as a professional as well as satisfaction with major selection can be expected to raise the standard of the students' career decision level.