Earticle

Application of ceramic materials for fabrication of dental restoration materials has been a focus of interest in the field of esthetic dentistry. The ceramic materials of choice are glass ceramics, spinel, alumina, and zirconia. The development of yttrium tetragonal zirconia polycrystal (YTZP)-based systems is a recent addition to all-ceramic systems that have high strength and are used for crowns and fixed partial dentures. Computer-aided design/ computer-aided manufacturing (CAD/CAM)-produced, YTZP-based systems are popular with respect to their esthetic appeal for use in stress-bearing regions. The highly esthetic nature of zirconia and its superior physical properties and biocompatibility have enabled the development of restorative systems that meet the demands of today’s patients. Many in vitro trials have been performed on the use of zirconia; however, relatively fewer long-term clinical studies have been published on this subject. The use of zirconia frameworks for long-span fixed partial dentures is currently being evaluated; in the future, more in vivo research and long-term clinical studies are required to provide scientific evidence for drawing solid guidelines. Further clinical and in vitro studies are required to obtain data regarding the long-term clinical use of zirconia-based restorations.

Purpose: The purpose of this study is to compare and analyze the accuracy of single crowns based on the type of occlusal surface. Methods: A single crown wax pattern was fabricated in three types of occlusal surface. The prepared wax pattern was replicated with silicone, and stone was injected to create a stone model. The prepared specimens were scanned using a model scanner. Scans were classified into three groups, and each scan was performed six times to analyze the trueness and precision of a single crown. In addition, only the occlusal surface area was analyzed for trueness and precision. Data were analyzed using the Kruskal–Wallis H test, a nonparametric test (α=0.05). Results: With regard to the trueness value of the occlusal scan area, the no occlusal tooth attrition (NA) group showed the largest error of 3.5 μm, and the complete occlusal tooth attrition (CA) group showed the lowest value of 3.1 μm. The NA group had the greatest precision, and the medium occlusal tooth attrition (MA) group and CA group showed a low precision value of 3.2 μm; the difference between the groups was statistically significant (α=0.05). In the color difference map, the CA group showed a lower error than the NA group. Conclusion: The occlusal surface with severe attrition had excellent accuracy, but the accuracy of the group without attrition was low. There were significant differences between groups, but clinically acceptable values were shown.

Purpose: This study is to evaluate the accuracy of gypsum replica models made from various gypsum products. Methods: One main model was made of stainless steel by CNC milling process. Molds were formed from the main model, and the gypsum replica models were made using 8 types of type IV gypsum, 10 pieces each. The main model was digitized by a contact scanner (Incise; Renishaw) and the gypsum replicas were digitized by an optical scanner (E4; 3Shape A/S). The difference between the main model and the gypsum replicas were measured by inspection software (3D Systems). One-way ANOVA was performed to evaluate the statistical significance of differences between groups. In addition, the independent sample T test was performed to determine the difference between the conventional and scannable stone group (n=10, α=0.05). Results: The root mean square of the stone models were 7.24 μm to 10.78 μm, and statistical significance was found between the two groups (SR, FR) and the other 6 groups (IS, SG, CA, CS, ER, EBG) (p<0.05). The accuracy of the gypsum replicas was 9.04 μm and 7.62 μm in the conventional and scannable stone group, respectively. There was statistical significance between the two groups (p<0.01). Conclusion: In the limited results of this study, the product with low setting expansion and the scannable showed high accuracy. Therefore, in order to obtain a stable and accurate scan model, it is more effective in terms of accuracy to use a scannable stone with a low setting expansion.

Purpose: The purpose of this study was to evaluate the effects of various zirconia surface treatment methods on shear bond strength with resin cements. Methods: We prepared 120 cylindrical zirconia specimens (⌀10 mm×10 mm) using computer- aided design/computer-aided manufacturing (CAD/CAM). Each specimen was randomly subjected to one of four surface treatment conditions: (1) no treatment (control), (2) airborne-particle abrasion with 50 μm of Al2O3 (A50), (3) airborne-particle abrasion with 125 μm of Al2O3 (A125), and (4) ZrO2 slurry (ZA). Using a polytetrafluoroethylene mold (⌀6 mm×3 mm), we applied three resin cements (Panavia F 2.0, Super-Bond C&B, and Variolink N) to each specimen. The shear bond strength tests were performed in a universal testing machine. The surfaces of representative specimens of each group were evaluated under scanning electron microscope. We used one-way analysis of variance (ANOVA), two-way ANOVA, and post hoc Tukey honest significant difference test to analyze the data. Results: In the surface treatment method, the A50 group showed the highest bond strength, followed by A125, ZA, and control groups; however, no significant difference was observed between A50 and A125, A125 and ZA, and ZA and control (p>0.05). Among the resin cements, Super-Bond C&B showed the highest shear bond strength, followed by Panavia F 2.0 and Variolink N (p<0.05). Conclusion: Within the limitations of this study, application of airborne-particle abrasion and ZrO2 slurry improved the shear bond strength of resin cement on zirconia.

Purpose: This study aimed to compare three-dimensional adaptation with the rinsing time of the temporary crown produced using the digital light processing method. Methods: The maxillary right first molar abutment was scanned with a dental scanner. A temporary crown was designed with the scanned abutment. The designed crown was made of 10 temporary crowns using a digital light processing printer. The crowns were divided into the 5-minute and 10-minute rinsing groups; 5 temporary crown washes were performed for each group. In order to obtain the internal data, each group was scanned for a temporary crown. The three-dimensional fit was measured by superimposing the scanned internal surface data and the abutment data. The average comparison of three-dimensional adaptation was analyzed using the Mann–Whitney U test. Results: The 5-minute rinsing group showed a significantly higher adaptation of 71.42±3.08 μm as compared to the 10-minute rinsing group (67.52±0.92 μm) (p<0.05). Conclusion: When making a temporary crown with a digital light processing method, a rinsing time of 10 minutes is appropriate.

Purpose: This study aimed to evaluate the effect of post-curing method on the flexural strength of provisional restorative resins produced by a digital light processing printer. Methods: A total of 20 specimens were produced, with a length of 64 mm, width of 10 mm, and thickness of 3.3 mm using a digital light processing printer. Two types of provisional restorative resins made with different post-curing methods were investigated and divided into conventional and vacuum groups. For the flexural strength test, each group was prepared by each method according to ISO 10477, and the flexural strength was measured with a universal testing machine. For statistical analysis, data were analyzed by independent t-test and Mann–Whitney U test. Results: The flexural strengths of the conventional and vacuum groups were 151.89 MPa and 131.94 MPa, respectively, showing a statistically significant difference (p<0.05). Conclusion: Within the limitation of this study, provisional restorative resins produced with vacuum demonstrated lower flexural strength than those produced with conventional postcuring method.

Purpose: Zirconia is differentiated from other ceramics because of its high resistance to corrosion and wear, excellent flexural strength (900~1400 MPa), and high hardness. Dental zirconia with proven mechanical/biological stability is suitable for the manufacture of implants. However, there are limited in vivo studies evaluating stress distribution in zirconia compared with that in titanium implants and studies analyzing finite elements. This study was conducted to evaluate the stress distribution of the supporting bone surrounding zirconia and titanium implants using the finite element analysis method. Methods: For finite element analysis, a single implant-supported restoration was designed. Using a universal analysis program, eight occlusal points were set in the direction of the occlusal long axis. The occlusal load was simulated at 700 N. Results: The zirconia implant (47.7 MPa) von Mises stress decreased by 5.3% in the upper cortical bone compared with the titanium implant (50.2 MPa) von Mises stress. Similarly, the zirconia implant (20.8 MPa) von Mises stress decreased by almost 4% in the cancellous bone compared with the titanium implant (21.7 MPa) von Mises stress. The principal stress in the cortical and cancellous bone exhibited a similar propensity to von Mises stress. Conclusion: In the supporting bone, the zirconia implant is able to reduce bone resorption caused by mechanically transferred stress. It is believed that the zirconia implant can be a potential substitute for the titanium implant by reinforcing aesthetic characteristics and improving stress distribution.

Purpose: In this study, we added two kinds of photoinitiators (CQ and TPO) to prepare two kinds of denture base resins (Bis-GMA series and UDMA series) for three-dimensional (3D) printing to compare and analyze their mechanical and biological properties and to find the optimal composition. Methods: Control specimens were made using the mold made of polyvinyl siloxane of the same size. Light curing was performed twice for 20 seconds on both the upper and lower surfaces with LED (light emitting diode) light-curing unit (n=10). Experimental 3D printing dental resins were prepared, to which two photoinitiators were added. Digital light processing type 3D printer (EMBER, Autodesk, CA, USA) was used for 3D printing. The specimen size was 64 mm×10 mm×3.3 mm according to ISO 20795-1. The final specimens were tested for flexural strength and flexural modulus, and MTT test was performed. Furthermore, one-way analysis of variance was performed, and the post-test was analyzed by Duncan’s test at α=0.05. Results: The flexural strength of both Bis-GMA+CQ (97.12±6.47 MPa) and UDMA+TPO (97.40± 3.75 MPa) was significantly higher (p<0.05) in the experimental group. The flexural modulus in the experimental group of UDMA+TPO (2.56±0.06 GPa) was the highest (p<0.05). MTT test revealed that all the experimental groups showed more than 70% cell activity. Conclusion: The composition of UDMA+TPO showed excellent results in flexural strength, flexural modulus, and biocompatibility.

Purpose: The following study seeks to ascertain the motivations behind students’ academic major selection and to identify the obstacles they encounter in the transition to university life, with the objective of providing information necessary to adapt well to the university and the course. Thereby, we aim to supply basic resources needed in the development of a university adaptation program to prevent academic dropout. Methods: Between October 1, 2019 and November 29, 2019, a self-administered questionnaire was distributed to a study sample consisting of students currently attending dental technology courses in Gangwondo and Gyeonggido. A total of 474 (94.8%) responses to the questionnaire were received and used for the final analysis. Results: Factors including major selection motivation, intrinsic motivation (p<0.001), academic adjustment (p<0.001), social adjustment (p<0.01), and institutional adjustment (p<0.05) all had negative relationships with academic dropout intention. Personal-emotional adjustment (p<0.001), however, showed a positive relationship with dropout intention. The explanatory power of the model was found to be 50.0%. Conclusion: This research shows that intrinsic motivation and personal-emotional adjustment diminish academic dropout intention. Therefore, it is recommended that diverse postenrolment course-adjustment programs should be developed to improve students’ confidence in their choice of study, their adjustment to the course, and their level of satisfaction.

Purpose: The aim of this study is to explore professional ethics and awareness of education among dental technicians. Methods: A total of 250 questionnaires were produced and distributed to dental technicians from June 1 to October 30, 2019. Of these questionnaires, 106 were used in the final analysis. Results: More than half of respondents said that the state-run dental company has very strong ethical values. Higher levels of confidence in the professional mission of dental work were correlated with stronger ethical values. Moreover, those who had greater experience of training in the code of ethics for dental technicians exhibited a firmer sense of their professional mission. Conclusion: In the education process for dental technicians, attention should be given to establishing and practicing professional ethics. Guidelines and programs should be revised accordingly to build awareness of ethical practices in the workplace.

Purpose: This study aimed to explore methods to improve the quality recognition and satisfaction level of non-face-to-face lectures among students in the departments of dental technology and dental hygiene. Methods: This survey was conducted to assess the status and preference of non-face-toface lectures and the level of awareness and satisfaction regarding the quality of these lectures among 179 students of dental technology and 295 students of dental hygiene. Statistical analyses were performed using frequency analysis, independent sample t-test, one-way ANOVA (post-hoc Duncan), Welch analysis (post-hoc Games-Howell), and hierarchical multiple regression analysis. Results: Factors that affected the ability to assess the quality of non-face-to-face lectures were the department, the method of non-face-to-face lectures, the most preferred method for conducting lectures, the level of awareness regarding the quality of face-to-face lecture, and satisfaction level. It has 71.5% explanatory power. Moreover, factors that influenced the satisfaction level of non-face-to-face lectures included the department, grade, the highest satisfied non-face-to-face teaching method, the most effective theoretical non-face-to-face teaching method, the most preferred teaching methods, and the ability to assess quality of face-to-face lectures. It has 46.8% explanatory power. Conclusion: Non-face-to-face classes should be designed and developed for web-based programs to improve the motivation and achievement level of the students and encourage interaction between the professors and students. Our findings suggest that educators should strive to achieve optimal educational effects by efficiently combining face-to-face and nonface- to-face lectures.

Purpose: This study aims to understand the relationship between university major satisfaction and job preference according to DISC behavior patterns. Methods: To conduct our evaluation, we surveyed a group of 118 students from the Department of Dental Laboratory Technology at the college of Jinju city from August 31 to September 11, 2020. The collected data was evaluated through frequency analysis, descriptive statistics analysis, one-way ANOVA, and regression analysis. Results: The analysis revealed that the steadiness type had the highest and the dominance type had the lowest major satisfaction level by DISC behavior type. The job preference was different for each DISC behavior type, and higher the preference for stability and development, the higher the degree of satisfaction with the major. Conclusion: These results suggest that DISC behavior type, major satisfaction, and job preference are all related. Therefore, these factors should be considered when implementing career guidance and educational programs for college students.

Purpose: The present study is an analysis of the extents of class satisfaction of college students who had applied the design thinking technique to capstone design class. Methods: The experimental method involved an analysis of 122 cases of data where advance and post replies were performed for the subject by students who had applied the design thinking technique and students who had not. The students involved had attended the capstone design class as a junior in the Department of Dental Technology at D University. Results: In the satisfaction with performance process of the capstone design class, five questions among nine had a high positive rating, while all eight questions on the satisfaction with performance methods had a high negative rating. Among ten questions on subjective learning outcomes, six showed a high positive rating. After the application of the design thinking class method, all mean values of the group with the application were higher than the group with no application in satisfaction with performance process, satisfaction with performance method, and subjective class outcomes. Hence, the design thinking class did have positive effects on the students’ improvement of class. Conclusion: Based on the results of the study, it is implied that the considerations about diverse class composition methods and operation methods capable of improving the students’ satisfaction are needed for efficient operation of the capstone design class.

Purpose: To understand the students’ level of recognition of online classes in the Department of Dental Technology and to provide the basic data for designing online classes based on the dental technology course. Methods: A survey was conducted among the students of the dental technology department. The collected data was analyzed with the SPSS ver. 25.0 program. To ensure a reliable verification, the α=0.05 significance level was used. The t-test and analysis of variance were also performed. Results: The students’ level of recognition of online classes in the Department of Dental Technology is shown in the rate of recognition for video-based classes for both the theory and experiments. Students displayed high positivity with the video-based learning as it is repeated learning that is not affected by the limitations of time. In addition, video-based learning is highly beneficial in terms of convenience, satisfaction, and achievement for learning. Conclusion: Based on the results, video-based learning is a highly positive learning type for students. It was also recommended that the Department of Dental Technology should offer a post-COVID-19 online class to include the blended methods of a face-to-face class and video-based learning.

This case study is aimed at introducing a full-mouth rehabilitation of a patient with severe tooth wear using fixed prosthesis. This is a case report of a patient with severe wear dentition with changing vertical dimension. In line with using prosthetic treatment, patient adaptation was verified with provisional restorations followed by diagnostic wax-up. Function, esthetics, and occlusal stability were verified during a 4-week follow up period. Prosthodontic reconstruction based on systemic analysis, diagnosis, and treatment plan led to satisfactory results after delivery of definitive prosthesis. Prosthetic treatment of severe wear dentition was functionally and esthetically successful. Dentists and dental technicians would be able to develop better treatment approaches using fixed dental prosthesis.