Earticle

Purpose: The purpose of this study was to identify the source of specific pollutants in dental laboratory wastewater and to suggest management methods for wastewater in such settings. Methods: Test samples (81 types) were created from wastewater generated during prosthetic fabrication using plaster products. The water quality of these samples was tested three times by an authorized testing agency, and the results were categorized based on plaster manufacturer and the prosthesis-making method. Results: In the model plaster group and related samples, lead (Pb) was not detected. In the dental stone group, Pb was detected in sample 50 at 152 times more than the water quality standard, and in sample 51, Pb was detected at a level below the standard. In the highstrength stone group, Pb was detected in two out of three samples. In the high-strength stone test group, after trimming, the concentrations of copper (Cu) and Pb in the gypsum sludge increased. In the mixed gypsum group, after 30 days, the concentrations of mercury (Hg) and hexavalent chromium (Cr6+) increased. Conclusion: Some of the tested gypsum samples exceeded hazardous substance standards, indicating that these gypsum products should not be used in prosthetic fabrication. Additionally, the concentration of hazardous substances increases before and after plaster trimming, necessitating a thorough management of plaster trimming machines. Since the concentration of hazardous substances in wastewater from the plaster trap increases over time, it is critical to maintain cleanliness in the plaster trap at all times.

Purpose: This study aimed to evaluate the impact of pressurization on the three-dimensional accuracy—trueness and precision—of full-arch type IV dental stone models used in prosthodontics. Methods: Dental stone models were categorized into three groups based on the applied pressurization levels during the setting process: 0 bars (0B group), 2 bars (2B group), and 4 bars (4B group). A dental pressurization system was employed to maintain pressure levels of 0, 2, and 4 bars, respectively. The models were analyzed using three-dimensional scanning and superimposition techniques, comparing them with a master model. A colordifference analysis was performed, with a 10-μm tolerance for green zones to standardize error evaluation. Results: The 2B group (2 bars) exhibited the highest accuracy, with minimal mean errors in trueness and precision relative to the 0B and 4B groups. The 0B group demonstrated significant deformation, attributed to microbubble formation and structural instability during the setting process. In contrast, the 4B group experienced increased internal stress and uneven curing, leading to slight distortions. Conclusion: Moderate pressurization at 2 bars significantly enhances the accuracy of type IV dental stone models by reducing deformations and minimizing trueness and precision errors. These findings suggest that controlled pressurization during the setting process improves the overall quality of dental prostheses.

Purpose: This study was conducted to evaluate the accuracy of the internal and marginal surfaces of metal copings manufactured using lost-wax casting (LWC) and selective laser melting (SLM) methods. Methods: A prepared upper left incisor on the master model was selected as the abutment tooth and scanned using a model scanner. Copings were fabricated by casting with cobalt– chromium (Co–Cr) alloy or three-dimensional (3D) printing with Co–Cr powder (n=20). The manufactured specimens were scanned and saved in standard tessellation language format. Accuracy was measured using a 3D analysis program. Statistical analyses were conducted using the SPSS (IBM). Significant differences were evaluated using the Shapiro– Wilk test. The Mann–Whitney U-test, a nonparametric method, was used because normality was not satisfied (α=0.05). Results: The mean root mean square (RMS) values of trueness of the internal and marginal surfaces in the LWC method were 37.12±1.21 and 59.92±4.48 μm, respectively, which were higher than the values of 20.73±1.07 and 44.61±2.67 μm, respectively, in the SLM method, with the difference being statistically significant (p<0.001 and p=0.023, respectively). The internal surface mean RMS values of precision in the LWC and SLM groups were 22.39±2.87 and 21.16±1.25 μm, respectively, which showed no statistically significant difference (p=0.872); however, the marginal surface mean RMS values were 50.97±2.24 and 22.11±1.19 μm, respectively, indicating a statistically higher precision in the SLM group (p<0.001). Conclusion: The internal and marginal surfaces of metal copings manufactured using LWC and SLM methods showed significantly different accuracy, except for internal surface precision. Both methods yielded clinically acceptable values.

Purpose: This study analyzed the mechanical properties of dental zirconia blocks as a function of the size of artificially introduced initial cracks. Methods: Rectangular specimens (30×4×3 mm) were prepared, and cracks were introduced using a Vickers hardness tester under 0 (no applied load), 5, 20, and 30 kg loads. The crack lengths and indentations were measured microscopically, and the fracture toughness was calculated. Results: The Vickers hardness ranged from 1,414.9 to 1,515.5 kgf/mm2, and the fracture toughness ranged from 5.2 to 8.2 MPaㆍm1/2. The higher the load, the larger the cracks created. Further, the bending strength of zirconia decreased considerably as the cracks propagated. Uncracked specimens had a strength of 1,147~1,244 MPa, whereas cracked specimens with 5, 20, and 30 kg loads exhibited values of 237~290, 179~191, and 140~152 MPa, respectively. The fatigue life also reduced drastically with the crack appearance, falling to ≤1,060 cycles, compared with the over 1 million cycles observed for the intact specimens. Conclusion: Initial cracks considerably decreased the bending strength and fatigue life of zirconia. The size of the initial cracks increased with the indentation load, resulting in a decrease in the bending strength and fatigue life.

Purpose: This study aimed to evaluate soldiers’ oral health practices and trust in military medical serviceswhile proposing strategies to enhance awareness and expand the roles of dental hygienists. Methods: An online survey using Naver Forms (Naver) was conducted from June 1 to July 14, 2024, targeting soldiers in Army Unit Y. Data from 134 respondents were analyzed. Results: Soldiers with greater interest in oral health were more likely to undergo regular dental check-ups, scaling, and brushing (p<0.05). Both dental check-ups and scaling increased post-enlistment (p<0.05), but only 15.6% of those highly interested in oral health utilized military dental services (p=0.784). Trust in military medical services declined with longer service, particularly among sergeants (p<0.001). Most soldiers primarily viewed dental hygienists as dental assistants (56.0%), reflecting limited awareness of their broader roles. Among those who used military dental facilities, 42.9% reported neutral satisfaction, whereas 57.1% expressed willingness to reuse the services. Conclusion: These findings emphasize the need to broaden the roles of dental hygienists in the military, particularly as oral health educators, to support the development of effective education and policy initiatives for oral health promotion.

analyzing factors influencing satisfaction and dissatisfaction with field training for dental technicians and college students. The aim was to provide useful data for optimizing field training operations. Methods: An online survey was conducted from July 21 to July 23, 2024, targeting dental technology students across the country who had experienced field training. A total of 111 responses were analyzed. The reliability of the satisfaction factor items for field training was Cronbach’s α=0.853, and for the dissatisfaction factor items, Cronbach’s α=0.850. Data were statistically analyzed using SPSS 21.0 (IBM). Results: Higher satisfaction with field training resulted in stronger, positive, statistically significant correlations with educational content (p=0.001), expertise and program (p=0.003), communication (p=0.001), and other factors, such as evaluation and ethics (p=0.004). Negative correlations were observed between satisfaction with field training and dissatisfaction factors related to educational content (p=0.020), distance (p=0.038), environment (p=0.026), and welfare (p=0.034). Conclusion: Competency indicators and behavioral characteristics of field training leaders were identified. The final result included five competencies and 14 behavioral indicators.

Purpose: This study aimed to investigate the perception of the application of computerbased testing (CBT) in the National Examination for Dental Technicians. Methods: Duly filled survey questionnaires were received from 180 third- and fourth-grade student volunteers from all over the country and 30 professors and 32 clinicians who were identified from a convenience sample from September 15, 2020 to September 23, 2020. In total, 242 questionnaires were analyzed. Depending on the characteristics of the data, frequency, percentage, and one-way ANOVA were performed. Scheffe test was used as a post-hoc test, and the significance level was set at 0.05. The collected data were analyzed using SPSS version 21.0 (IBM). Results: Compared with paper-based testing, CBT significantly increased immersion and concentration on the test and prevented cheating during the examination (p<0.05). Students, professors, and clinicians expressed significant opinions on the validity of applying CBT to the National Examination for Dental Technicians (p<0.05). Conclusion: The use of CBT can improve job evaluations for dental technicians efficiently and accurately, and reflect the actual work environment by combining job performance evaluation with digital technology. The introduction of CBT may improve the quality of dental technician job evaluations and cultivate talents who can adopt digital technology.

Purpose: This study aimed to analyze the association between the dental prosthesis condition and oral health problems in older Koreans. Methods: This study used primary raw data from the 9th (2022) National Health and Nutrition Examination Survey. A total of 1,323 people aged ≥65 years were included in the study. Frequency and cross-analyses were performed (p<0.05). Data were analyzed using IBM SPSS version 21.0 (IBM). Results: Among the older group, 33.6% complained of chewing problems and masticatory discomfort, and 12.7% reported speech problems. The presence of upper and lower jaw implants and the need for partial and full dentures were significantly associated with chewing problems (p<0.05) and masticatory discomfort (p<0.05). The presence of upper and lower jaw implants and the need for dentures were significantly associated with speech problems (p<0.05). This indicates that the type and presence of dental prostheses are closely related to speech problems. Conclusion: Oral healthcare and prosthesis management for older people are essential to maintain oral health and improve the quality of life in an aging society. This study provides useful data for the establishment of policies promoting the oral health of older people and the development of dental prosthesis management programs.

This study aimed to examine advancements in dental prosthesis fabrication using digital technology, particularly in implant systems. Digital tools have expanded their application in implant surgery and prosthesis creation, even for edentulous patients. Initially focused on single-tooth restorations, digital implant technology currently encompasses a wider range of treatments, with ongoing research into its limitations and potential. A 70-year-old edentulous patient sought occlusal reconstruction with implants. After years of denture use, the patient experienced significant alveolar bone resorption. A digital implant system based on the “all-on-4” concept was planned, utilizing a digital surgical guide for flapless surgery. Six implants were placed—four anteriorly and two posteriorly—optimizing the prosthodontic plan to reduce the load on the cantilevered areas. The patient’s occlusal function and esthetics were improved significantly. This treatment strategy enhanced the quality of life of the patient, providing a natural smile and demonstrating the benefits of digital technology in dental prosthetics.