Earticle

Purpose: This study aimed to assess the quality of dental prostheses printed by digital lightprocessing (DLP) technology. Methods: Ten experimental models were prepared. The ten specimens that were printed by DLP technology constituted the DLP group. The ten specimens that were produced in the same model by the casting method constituted the control group. The marginal gaps of the 20 specimens produced were measured. These gaps were measured by a silicon replica technique at two abutments of the specimen. Therefore, 20 marginal gaps were measured in each group. An independent sample t-test was performed to compare the marginal gaps measured in the two groups (α=0.05). Results: According to the results of the measurement, there was a significant difference between the mean marginal gap of the control group (78.8 μm) and that of the DLP group (91.5 μm), p<0.001. Conclusion: Although the mean marginal gaps of dental fixed prostheses produced by the DLP method was higher than the mean marginal gap of those produced by the casting method, it was considered to be within the clinical threshold value suggested by some previous studies.

Purpose: This study is a comparative analysis of the strain according to deposition in a constant temperature water bath after manufacturing ultraviolet (UV)-cured artificial teeth. Methods: As a control group, 10 ready-made artificial teeth were selected as the first molar on the right side of the maxilla (RT group). Silicone was used as a duplicate of the artificial denture teeth. Experimental teeth were prepared in two groups using the prepared silicone mold. In the first experimental group, the UV-cured resin was injected into the negative silicone, followed by irradiation with a UV-curing machine for 5 minutes (5M group). In the second experimental group, the UV-cured resin was injected into the negative silicone, and then irradiated for 30 minutes using a UV-curing machine (30M group). The one-way ANOVA was performed, and post-test was analyzed by Tukey. Results: When immersed in a water bath for 15 days, it was found to be –0.3% in the RT group, –0.6% in the 5M group, and –0.7% in the 30M group. The results revealed –0.2% in the RT group, 0.2% in the 5M group, and –0.2% in the 30M group when they were in the bath for 30 days. Conclusion: In the water bath, the swelling was greater when deposited for 1 to 15 days, but was less when deposited for 15 to 30 days.

Purpose: This study aimed to analyze the shrinkage and expansion strain of ultraviolet (UV)- cured resin according to the wavelength of the light source and compare the shrinkage and expansion. Methods: We prepared the mold with according to the ISO 4049 specimen. The size of the circle in the mold was prepared with a height of 6.02 mm and a diameter of 4 mm. UV-curable resin for three-dimensional (3D) printing was injected into the circular mold. The control group was irradiated with a wavelength of 400~405 nm using UV-curing equipment (400 group), and the experimental group was irradiated with a wavelength of 460~465 nm (460 group). Both groups were produced ten specimens. The produced specimen was first measured with a digital micrometer. After the first measurement, the specimen was immersed in a constant temperature water bath for 15 days, after which the second measurement was performed, and the third measurement was taken after 30 days. The measured values were analyzed using the independent sample t-test (α=0.05). Results: In the non-immersion water tank, the contraction was 0.9% in the 400 group and 1.3% in the 460 group. In the constant temperature bath, the expansion was high at –0.4% in the 400 group for 15 days, and the smallest expansion was –0.03% for the 400 group for 30 days. There were significant differences between the two groups (p<0.05). Conclusion: The 400 group had a lower UV resin specimen strain than the 460 group. Therefore, it is recommended to use the wavelength required by the UV-curing resin.

Purpose: This study aimed to identify the impact of physical surface roughing with a polishing tool onto the pre-sintering yttria-stabilized tetragonal zirconia polycrystals (TZP) core and liner treatment for chemical bonding on the bond strength of TZP core and veneering ceramic. Methods: Overall, 80 specimens were classified into two groups (non-liner, NL; and usingliner, UL ) depending on the use of liner, and these two groups were then subclassified into four groups depending on the polishing tool used. (1) Non-liner groups: NS, non-liner+stone point; NC, non-liner+carbide bur; NP, non-liner+paper cone point; NT, non-liner+silicon point. (2) Using-liner groups: US, using-liner+stone point; UC, using-liner+carbide bur; UP, usingliner+ paper cone point; UT, using-liner+silicon point. The pre-sintering surface roughing values and shapes were observed, and after burning up the veneering ceramic, the shear bond strength was measured using a universal testing machine. For significance testing, a oneway analysis of variance and Tukey’s multiple comparison test were conducted. An optical microscope was used to observe the fracture plane, and the following results were obtained. Results: Surface roughness NP (4.09±0.51 μm) represented a higher value than other groups (p<0.001). In shear bond strength, NS (35.21±1.44 MPa) of the NL group showed the highest bond strength (p<0.001). The UL group did not show a statistically significant difference between groups (p=0.612). Conclusion: Our study findings reveal that the bond strength of TZP core and veneering ceramic was improved by pre-sintering physical surface treatment than by chemical bonding with liner surface treatment.

Purpose: This study aims to investigate the cusp variation pattern of the Korean mandibular second premolar and to determine the difference in tooth diameter and surface area using a virtual three-dimensional model. Methods: Dental casts from 69 students were scanned as a virtual dental models with a three-dimensional dental model scanner. Tooth diameter, absolute and relative individual areas, total crown area, the number of lingual cusps and central groove pattern were analyzed using RapidForm 2004. The Mann–Whitney U-test and the Kruskal–Wallis test were performed to verify sexual dimorphism, the difference in tooth diameter and surface according to the cusp variation pattern (α=0.05). Results: There was no significant difference except in buccolingual diameter (p<0.05) and buccolingual diameter at the cervix (p<0.05). The relative surface area of the total clinical crown was 65.76% for the buccal half and 34.24% for the lingual half, with a ratio of 2:1. In the case of the presence of two lingual cusps, the ratio was 21.47% for the mesiolingual half and 14.12% for the distaolingual half, with a ratio of 3:2. The dominant central groove patterns of the second premolar were the H-pattern (42.0%), followed by the Y-pattern (37.7%), then the U-pattern (20.3%). The relative buccal half was largest in the U-pattern central groove and the relative lingual half was largest in the Y-pattern central groove (p<0.05). Conclusion: This study is significant in that it measured quantitative surface areas and the findings could be a meaningful reference to comprehend dental anatomy in Koreans.

Purpose: This study aimed to assess and compare the marginal fit of ceramic-based hybrid resin restoration (HYB) and zirconia restoration (ZIR) for dental computer-aided design/ computer-aided manufacturing systems. Methods: A stainless steel master model was produced. The impression was first made with silicone, and then stone working models were produced. A total of twenty restorations were fabricated with two different materials: ZIR and HYB. The silicone film thickness of the marginal gap was measured using a digital microscope; digital photos were taken at a magnification of ×160, and then analyzed using a measurement software. The values of the result were evaluated with the independent-sample t-test (α=0.05). All statistical analyses were performed with a statistical software. Results: The mean values for the marginal gap was 37.14±2.96 μm for HYB, compared with 40.37±5.26 μm for ZIR. No significant difference was found between ZIR and HYB (p=0.107). Conclusion: As a result, the marginal fit of the restoration fabricated using the hybrid resin was better than that of the restoration fabricated using zirconia. Also, the marginal fit of all groups was below the clinical acceptable range of 120 μm. Thus, HYB for dental CAD/CAM system in this study is expected to be suitable for clinical use in dentistry.

Purpose: We investigated the marginal fit between abutment and metal copings according to impression technique, wax block types, and metal types. Methods: We selected the traditional impression method of using rubber impression materials and the digital impression method of using oral scanners, three types of wax blocks, and two types of metal, both of which were domestically and commercially available, were selected to produce metal copings, and the marginal fit was determined through the use of silicon replication. Results: The measurements of axial wall fit revealed that the IYV specimens had the best fit, with a mean gap of 24.11±5.95 μm, followed by CEV, CHV, CSS, CSV, CES, CHS, and IYS specimens (mean: 33.44±8.41 μm). The differences were not statistically significant. The marginal gap measurements showed that the CEV specimen had the smallest gap, 17.25±4.13 μm, followed by the CSV, CHV, CSS, CES, CHS, IYV, and IYS specimen (mean: 43.47±15.63 μm). The differences were statistically significant. Conclusion: The axial wall fit of the metal coping (VeraBond2V; Aalba Dent, Inc., Fairfield, CA, USA) produced by the lost wax technique with the traditional impression method was excellent. The marginal fit of the metal coping (VeraBond 2V) produced by wax milling with the use of an oral scanner was also excellent. The marginal fit of the metal coping was within the clinically acceptable limits in all groups.

Purpose: This study aimed to employ a Q-methodological approach that can understand the characteristics of each type according to the subjective structures of humans, to help understand type-specific characteristics and to provide a basis for creating the image of dental technicians among dental technology students based on the characteristics of each type. Methods: The Q-methodology was used for this study. 120 Q-statements were obtained from a qualitative survey of 120 students of the department of dental technology. To select the Qsample, the Q-population was categorized by taking several repeated readings. The selected statements were reviewed and revised by experts and 33 Q-samples were finally selected. The data were then analyzed using the PQ method program. Results: Among 42 P specimens, 22 were classified into type 1, 9 types 2, and 11 types 3. “Type 1” recognizes the image of dental technicians positively and optimistically (Z=1.29) (Z=1.74), but it is named “self-development oriented” in the sense that steady self-development must be underpinned (Z=1.37). “Type 2” agreed strongly that they could work for a lifetime without age or gender discrimination (Z=2.09). This type was referred to as "professional- oriented" because the recognition of dental technicians is more focused on “professional.” “Type 3” was tagged “pride-oriented,” showing the strongest agreement that they can be proud of their job as healthcare workers (Z=1.08). Conclusion: Many studies on such an image should be carried out to determine the importance of occupational images and establish desirable status for dental technicians to continue developing.

Purpose: This study aimed to verify whether blended learning is worth alternating with traditional face-to-face learning for some dental technology students in practice teaching. Methods: A total of 68 students were included in this study. They were divided into two groups to compare blended learning and traditional face-to-face learning. The experiment had been carried out over 15 weeks. The following tests were performed: test of instructional quality, test of learning satisfaction, test of perceived usefulness, and test of learning flow. The IBM SPSS software was used to analyze the data. Results: The learning satisfaction and the perceived useful of blended learning by students appeared to be higher than that of traditional face-to-face learning. However, there was no significant difference in the variables of traditional face-to-face learning and those of blended learning (p<0.05). Conclusion: Blended learning is an alternative to traditional face-to-face learning for some dental technology students in practice teaching.

Purpose: This study aimed to investigate the effect of stress and oral parafunctional habits on temporomandibular joint disorders (TMD) in college students. Methods: An online survey comprising 354 questionnaires was conducted from May 23, 2020, to June 21, 2020. The collected data were analyzed using Student’s t-test, one-way analysis of variance, correlation tests, and multiple regression analysis. Results: The stress symptom score was higher in females than in males. The symptoms of physical stress were significantly higher among students from the Department of Public Health, whereas those of psychological stress were higher among students from the Department of Physical Education. Both TMDs and oral parafunctional habits were higher among females, students of the Departments of Arts and Physical Education, and seniors. The higher the stress symptom level, the higher the scores for TMD and oral parafunctional habits. TMD and oral parafunctional habits were found to be most affected by physical stress. Conclusion: These findings indicate that a reduction in physical stress is required to decrease the prevalence of oral parafunctional habits and TMDs among college students. This can be achieved by the incorporation of physical activity programs, which may aid in reducing the symptoms of physical stress.

Purpose: This study aimed to provide the basic data for improving patient satisfaction and dental services by examining the satisfaction of implant patients who have become important customers of dental treatment due to the increased demand for implants and identifying the factors affecting satisfaction. Methods: Out of 145 questionnaires, excluding 15 questionnaires that were unfaithfully responded to or difficult to analyze, 130 questionnaires were used for the analysis of the satisfaction of the dental patients with implant treatment in 19 dental hospitals and clinics in Gyeonggi-do, South Korea. Results: Implant satisfaction was as high as 3.20 (±0.56) for masticatory function satisfaction, 3.19 for psychological function satisfaction (±0.59), and 3.01 (±0.58) for social function satisfaction. Conclusion: Consistent patient care is important because an implant is not a one-shot cure but ends over a period of several months to several years. It is meaningful in that this study measured the satisfaction of implant prostheses evaluated from a patient's point of view and examined various factors and needs affecting patient satisfaction to provide the basic data for research that can contribute to improving the satisfaction of implant patients.

Purpose: This study aimed to determine dental technicians’ job satisfaction levels and to assess its influence on turnover intention. Methods: We included 230 dental technicians who work within Seoul, Incheon, Daejeon, the Gyeonggi Province, and the Chungcheongnam-do Province. We carried out a self-reported survey using a structured questionnaire. Results: As a result of assessing the research subjects’ job satisfaction level, we found that there was a significant difference in working hours and a dental-work continuing plan sphere (p<0.05). Achievement & self-realization factors, the human relation factor, and growth & development factors were reported to be major job satisfaction indices. The whole average of the job satisfaction level came to 3.11, thereby appearing to be relatively high. In analyzing the research subjects’ turnover intention, there was a significant difference in age, task field, dental-work career, working hours, incumbency, and dental-work continuing plan sphere (p<0.05). The question average for turnover intention was 2.88. As a result of assessing a correlation between job satisfaction and turnover intention, a significant negative (–) correlation was found between job satisfaction and turnover intention. Thus, a higher job satisfaction level was observed to lead to a lower turnover intention. Conclusion: As a result of conducting a regression analysis in order to assess the influence of job satisfaction on a turnover intention, a working condition factor, a human relation factor, and a recognition factor each appeared to have a high impact.

Purpose: This study analyzes the self-efficacy and CAD/CAM practice of dental technology students with the aim of providing data that will be useful for improving CAD/CAM education. Methods: A questionnaire survey on self-efficacy and CAD/CAM practice was given to students who participated in face-to-face classes in the Department of Dental Technology at a college in Daegu and Gyeongsangnam-do. The survey period was two weeks long (June 15, 2020 to July 2, 2020), and 84 students completed the questionnaire. Results: The higher the self-efficacy, the fewer difficulties or mistakes students made in CAD/CAM practice. The most difficult parts of the scanning process were the top and bottom arc operation and the bite match arc insertion. The most difficult part of the design work was the use of (multiple) tools. The difference between the degree of difficulty and the degree of mistakes during the practical course was shown as the margin line setting in the design work. Setting the margin line was not difficult, but the degree of mistakes was nonetheless high. In the CAM process, height control was the most difficult part, but the degree of mistakes did not differ according to students’ self-efficacy. Conclusion: Given that higher self-efficacy correlated with fewer difficulties or mistakes in CAD/CAM practice, students should be encouraged to enhance their self-efficacy. This may be done by improving their satisfaction with their major course of study, forming friendly relations with their colleagues, and increasing the ratio of performance rather than observation in CAD/CAM practice.

Purpose: This study aimed at exploring the impacts of organizational conflict and job satisfaction on the turnover intention among dental technicians. Methods: This study utilized a descriptive research design. A structured questionnaire was administered to 159 dental technicians. Of the collected questionnaires, data from 127 valid questionnaires were analyzed using t-tests, analysis of variance, Pearson’s correlation coefficient, and hierarchical multiple regression using the IBM SPSS 20.0 statistical package. Results: A positive correlation was identified between organizational conflict and turnover intention (r=0.46, p<0.001); however, a negative correlation was shown between job satisfaction and turnover intention (r=–0.50, p<0.001). A hierarchical multiple-regression model was employed to analyze working hours, unfair treatment from dentists and dental hygienists, organizational conflict, and job satisfaction, which contributed to providing an explanation to 39% of the turnover intention of dental technicians (F=14.16, p<0.001). Furthermore, organizational conflict (β=0.32, p<0.001), job satisfaction (β=–0.31, p=0.003), and working hours (β=0.21, p=0.010) were all shown to affect turnover intention. Conclusion: The impact of the negative consequences of organizational conflict and working hours on the turnover intention should be considered within core strategies for increasing the turnover periods for dental technicians.

Here, we studied the sports mouse guard as an oral device system, to minimize the sports related facial and dental injuries, jawbone fracture and brain injury, and by layering the hardened sheets for improving the activity performance and stable wearing. By pressuring and layering 2 soft- and 1 hard-layers of ethylene vinyl acetate (EVA) thermoplastic materials, for a category of martial art, record sports and leports, here we introduce a methodology for thickness control of layers to protect the teeth and oral structure. A personally customized mouse guard optimized for sports by layering a mixture of soft and hardened sheets is not easily detached during the sporting activity, easy to breathe through, comforts to wear, and also improves the sporting record. A designed EVA thermoplastic material for individual sports is used as the mouth guard, which is stably attached, easily removed, and convenient for breathing through the mouth.