Earticle

Purpose: To perform a comparative study on curing shrinkage according to the thickness of photopolymerization resin. Methods: Stainless steel molds of 2, 4, and 6 mm heights were prepared. The 2, 4, and 6 mm-height molds were classified as the 2H, 4H, and 6H groups, respectively. A photopolymerization resin was injected into the stainless steel mold. Photopolymerization was carried out using a photopolymer machine. During photopolymerization, the wavelength and intensity of 400~405 nm were set to 10, the highest intensity among 1~10. Photopolymerization was performed for 30 min per specimen (each group=10). The inner and outer areas of the specimen were measured. The data were analyzed using one-way ANOVA and Kruskal–Wallis H test (α=0.05). Results: In terms of the inner and outer diameters of the photopolymerization resin specimen, the 2H group contracted the most, whereas the 6H group contracted the least. A statistically significant difference was found between the groups (p<0.05). Conclusion: The amount of light irradiation of the photopolymerization resin must be adjusted according to the thickness.

Purpose: This study aimed to compare the shear bond strength between zirconia cores and veneer ceramics as per the sand blasting and liner treatments. Methods: The following 4 groups of zirconia-veneering ceramic specimens were prepared: (1) Group I, untreated; (2) Group II, with 110 μm aluminium oxide (Al2O3) sandblasting; (3) Group III, with liner (IPS e.max ZirLiner; Ivoclar Vivadent); and (4) Group IV, with 110 μm Al2O3 sand blasting and liner. Surface roughness was measured for all the prepared specimens, and the surface morphology was observed using a scanning electron microscope. All the samples (n=40) were fixed with measuring jigs, and shear bond strengths were obtained using a universal testing machine with a crosshead speed of 0.5 mm/min. The shear bond strength data were analyzed using one-way analysis of variance and t-test. The post hoc comparison was performed using the Tukey’s test (α=0.05). Results: A significant difference in the surface roughness was observed between the specimens of groups I and II (p<0.05). Surface treatment with liner and sandblasting showed higher shear bond strength between zirconia core and veneering ceramic (p<0.05). Conclusion: The sand blasting and liner treatment increased the shear bond strength between zirconia core and veneering ceramic.

Purpose: This study aimed to compare the flexural properties and perform the Weibull analysis of photo-curing three-dimensional (3D) printing resin. Methods: Photo-curing temporary resin (3D polymer) was used as a printing resin. Specimens (65 × 10 × 3.3 mm3) were prepared following the ISO 20975-1 guidelines and according to the different printing orientations using a digital light processing 3D printer (D2 120; Dentium). The flexural strength (FS), flexural modulus, and work of fracture (WOF) were measured using a universal testing machine (Instron 3344; Instron) at a crosshead speed of 5 mm/min. Results: In this study, the 0° orientation exhibited higher FS and WOF than the 45° orientation. Significant differences were found among the printing orientations (p<0.05). Specimens printed at the 0° orientation were the most accurate. In the Weibull analysis, 0° showed the greatest Weibull modulus (m), which represents a higher reliability. Conclusion: 3D printing should be selected and used by considering flexural properties, size accuracy, and reliability.

Purpose: This study aimed to obtain basic data on oral health improvement by investigating the EQ-5D index according to the oral prosthesis status of elderly persons aged 65 years or older in Korea using the Seventh Korea National Health and Nutrition Examination Survey. Methods: In this study, 3,426 elderly persons aged 65 years or older were included to analyze the relationship between the dental prostheses status and EQ-5D index in the collected data. Results: Compared to the “complete denture” in oral prosthesis, EQ in case of no dental prostheses or fixed dental prostheses is comparable to removable prosthetics such as “no dental prostheses,” “one fixed bridge,” and “two or more fixed bridges.” Removable partial denture and complete denture required for the maxillary and mandibular EQ-5D index were significantly higher in “not necessary” than in “complete denture necessary” in all the elderly persons. Conclusion: The condition of the dental prosthesis and the need for a removable partial denture and complete denture for the elderly’s EQ-5D index were confirmed, and it was found that the fixed dental prostheses were more effective than the removable dental prostheses. Therefore, oral health education programs for the elderly should be developed to promote dental function and oral health maintenance.

Purpose: This study was conducted on dental technicians to examine the problems of the dental laboratory registration system and devise a plan to improve it. Methods: For data collection, an online survey was conducted on 14,015 dental technicians registered in the Korea Dental Technologist Association as of October 2020. Among the collected 405 questionnaires, 391 data were used for analysis. Results: We found that dental technicians felt that the dental laboratory opening registration system was unfair. There were problems including the problem of the verification method of job performance, not acknowledging the difference in the job field, and the lack of understanding of the structure of work cooperation between dentistry and dental laboratories. Furthermore, it was recognized that the system was improved by reflecting the change in job area according to the change of the times. Conclusion: There is an urgent need to reorganize the legal system so that the dental technicians can have their professionalism and autonomy recognized while remaining faithful to the public interest of protecting the national oral health by revising the related regulations, thereby ensuring smooth work activities.