Earticle

Purpose: In this study, thermal properties were observed by measuring the extent of thermal expansion and the amount of thermal residue that appears upon burnout on a workpiece made by using a dental digital light processing (DLP) three-dimensional (3D) printer. Methods: Thermal properties of workpieces manufactured by using two 3D printers were observed. The specimens were designed in cylindrical form with dimensions 10 mm in diameter and 10 mm in height. The control specimen was made of wax, and the experimental specimen was made of resin. The thermal expansion rate was measured by applying heat to three types of specimens, and burnout residue was measured. Results: The thermal expansion rate of the wax pattern (WP) specimen was 0.93%±0.05%, of the RP1 specimen was 1.30%±0.08%, and of the RP2 specimen was 1.20%±0.09%. Measuring the recovered residue yielded residual amounts of 0.2% for the WP specimen, 1.1% for the RP2 specimen, and 1.8% for the RP1 specimen. Conclusion: 1. From measurements of the workpieces manufactured by dental DLP 3D printing, the thermal expansion rate was found to be higher than that of wax. 2. As a result of measuring burnout residues on the workpieces manufactured by dental DLP 3D printing, the required summoning temperature to obtain suitable castings was determined to >750℃.

Purpose: The purpose of this in vitro study was to measure and compare the thickness-dependent color dimensions of digital light processing (DLP) three-dimensional (3D) printer and conventional interim restorative resin. Methods: Specimens (N=60) were fabricated using either subtractive manufacturing (S group) or DLP 3D printing (D group) material. All milled and 3D-printed specimens were allocated into three different groups (n=10) according to different thicknesses as follows: 1.0, 1.5, and 2.0 mm. Color measurements in the CIELab coordinates were made using a spectrophotometer under room light conditions (1,003 lux). The color differences (ΔE*) between the specimen and control target data were calculated. Data were analyzed using the oneway analysis of variance (ANOVA). Post hoc comparisons were conducted using Tukey's honestly significant difference method (α=0.05 for all tests). Results: The ΔL*, Δa*, Δb*, and ΔE* values of interim restorative resin produced by DLP 3D printing were obtained in terms of the specimen's thickness increased compared with the increases by subtractive manufacturing. When the thickness was similar, the color difference between subtractive manufacturing and DLP 3D printing was ≥5.5, which is a value required by the dentist for remanufacturing. Conclusion: Color was influenced by the thickness of the interim restorative resin produced by DLP 3D printing.

Purpose: The purpose of this study was to compare the dimension safety evaluation between a general ultrasonic cleaner and an ultrasonic cleaner equipped with UV-C (ultraviolet-C). Methods: An edentulous model was prepared. A denture base and an occlusal rim were fabricated, and scanning was performed. After scanning, a denture base and full arch artificial teeth were designed. The full arch artificial teeth were printed using a three-dimensional printer (n=10). The residual resin was washed with alcohol and then scanned (reference data). The printed specimens were classified and cleaned using a general ultrasonic cleaner (GU group) and an ultrasonic cleaner equipped with UV-C (UC group). After each washing, a rescan was performed (scan data). Reference data and scan data were superimposed using overlapping software. Data were statistically analyzed using the Mann–Whitney test (α=0.05). Results: In the deviation values of full arch artificial teeth, the GU group showed a high deviation of 18.02 µm and the UC group showed a low deviation of 15.02 µm. The two groups demonstrated a statistically significant difference (p<0.05). Conclusion: Full arch artificial teeth prepared using photopolymerized resin were deformed according to the temperature of water generated in the ultrasonic cleaner. It is judged that there is no deformation according to the UV-C ultrasonic cleaner.

Purpose: The aim of this study was to observe the surface roughness and surface topography of cobalt-chrome (Co-Cr) alloys with grinding time in dental barrel finishing. Methods: This study involved two types of Co-Cr alloys. Specimens were manufactured with the dimensions 10×10×2 mm. Each specimen was cast according to the manufacturer's instructions. The cast alloys were polished for 35 minutes at intervals of five minutes in an automatic barrel finishing. Specimens were imaged with a three-dimensional optical microscope to measure surface roughness. Results: BC specimens and GM specimens had the highest roughness (Ra) values in the ungrained control group, and the lowest Ra values were measured 20 minutes after grinding. Conclusion: The best conditions for grinding Co-Cr alloy using a dental barrel finishing were a weight ratio of polishing media, water, and compound of 150 g:200 g:5 g, and a rotation speed of 450 rpm. Grinding time to obtain appropriate surface roughness should be limited to 15 to 30 minutes.

Purpose: This study aims to examine the stress distribution effect of tightening torques of different abutment screws in a custom-abutment implant system on the abutment-fixture connection interface stability using finite element analysis. Methods: The custom-abutment implant system structures used in this study were designed using CATIA program. It was presumed that the abutment screws with a tightening torque of 10, 20, and 30 Nㆍcm fixed the abutment and fixture. Furthermore, two external loadings, vertical loading and oblique loading, were applied. Results: When the screw tightening torque was 10 Nㆍcm, the maximum stress value of the abutment screw was 287.2 MPa that is equivalent to 33% of Ti-6Al-4V yield strength. When the tightening torque was 20 Nㆍcm, the maximum stress value of the abutment screw was 573.9 MPa that is equivalent to 65% of Ti-6Al-4V yield strength. When the tightening torque was 30 N·cm, the maximum stress value of the abutment screw was 859.6 MPa that is similar to the Ti-6Al-4V yield strength. Conclusion: As the screw preload rose when applying each tightening torque to the customabutment implant system, the equivalent stress increased. It was found that the tightening torque of the abutment influenced the abutment-fixture connection interface stability. The analysis results indicate that a custom-abutment implant system should closely consider the optimal tightening torque according to clinical functional loads.

Purpose: This is to provide fundamental resources for the improvement in the department of dental technology curriculum which will ensure effective preparation for the license examination for dental technicians as well as improvement in the students practical skills. Methods: Research analysis was conducted regarding the 2020 academic curriculum table of the department of dental technology established in 19 universities nationwide, from 5th of October 2020 to 30th of November 2020. Results: Research of the ratio of the establishment credit of the 3-year-course major in department of dental technology to the establishment credits of the license examination subjects showed, second semester of the first year (p<0.05), by academic discipline the whole first year (p<0.05) and second semester of first year, to be statistically significant. Conclusion: Hence, it can be concluded that there is a need for the management of a curriculum with distribution of adequate subjects according to academic year and semester, in order to satisfy not only the preparation for the license examination for dental technicians, but also students’ academic desires.

Purpose: In this study, an attempt was made to identify the extent of dental technicians’ perception of professionalism and examine to what extent the perception of professionalism impacts self-development and professionalism improvement activities. Methods: An online survey was conducted for 391 dental technicians for 20 days (i.e., from October 20 to November 10, 2020). Pearson’s correlation analysis was performed to examine the correlation between the independent variable and the dependent variable, and multiple regression analysis was performed to analyze the degree of influence of independent variables on self-development and professionalism improvement activities. Results: As a result of examining the impact of dental technicians’ perception of professionalism on self-development and professionalism improvement activities, it was revealed that all four subareas of the perception of professionalism, i.e., professional qualification, professional autonomy, social perception, and the sense of calling, were positively impacted. Conclusion: (1) It is necessary to compare and analyze the differences in the perception of professionalism among various dental technologist groups, prepare programs to improve them, and endeavor to ensure the growth of organizational operating system. (2) Self-development and professionalism improvement activities need to be supported so that dental technologists can immerse themselves in their duties with affections for the organization and contemplate and provide educational programs to workers.

Purpose: This study aimed to investigate the perception of dental implant insurance supply and demand for the elderly living in Hongseong-gun and Chungcheongnam-do, as well as the selection criteria regarding dental clinics for dental implant treatment to collect basic data for improving the oral health of the elderly population. Methods: Participants living in Hongseong-gun, Chungcheongnam-do who were at least 55 years old from November 2020 to March 2021 were included in this study. The chi-square test was performed to examine the age-specific perception of insurance-covered dental implants (p<0.05). Results: The age group that was the most interested in implants was the 70s age group, and the difference between this age group and the other age groups was statistically significant. Those in their 70’s, 80’s, and 90’s or older paid about 600,000 won including dental implants covered by insurance, and there was a significant difference (p<0.05). Those in their 60s, 70s, and 80s estimated the highest value of implants covered by insurance as two and showed a significant difference (p<0.05). The awareness of the dental implant insurance by age showed that all age groups, except for the ≥90 years age group, considered the insurance to be mediocre mostly due to the large co-payment (p<0.05). Conclusion: There were differences by age in the awareness of dental implant insurance, co-payments, number of applications, and insurance coverage. The perceptions on dental implant insurance by age showed that all age groups except for those over 90 years and older, they considered the insurance was just mediocre the most.

Purpose: To study the perception and satisfaction of in-person and online classes for dental technology students. Methods: A total of 420 questionnaires were distributed to dental technology students between June 1 and June 30, 2021. Of these, 225 questionnaires were assessed using frequency analysis, one-way analysis of variance, Pearson's Chi-squared test, and independent t-tests via IBM SPSS Statistics ver. 22.0 (IBM). Results: For theory subjects, satisfaction was higher for online classes than in-person classes (p=0.001). For practical subjects, satisfaction was higher for in-person classes than online classes (p=0.002). Both the learning effect and motivation for learning were higher for in-person classes than online classes (p=0.001). Conclusion: When in-person and online classes become coexistent, there should be educational guidelines for improving the quality and effectiveness of learning in these different contexts.