Earticle

Purpose: This study aimed to assess the fracture load of anterior crowns fabricated from ceramic–polymer hybrid blocks and lithium disilicate ceramic blocks, both designed for computer-aided design/computer-aided manufacturing wet milling applications. Methods: For fracture load testing, ceramic crown samples were fabricated using lithium disilicate ceramic blocks and ceramic–polymer hybrid blocks (N=15). The ceramic crowns, designed and milled for an abutment manufactured via metal 3D printing, were positioned onto a prepared maxillary right central incisor model (Nissin Dental). The fracture load of the samples was measured using a universal testing machine, and the fracture patterns were examined with a scanning electron microscope (JSM-6701F, Jeol). Differences in fracture load between the two ceramic block types were evaluated using an independent sample t-test (α=0.05). Results: The ceramic–polymer hybrid and all-ceramic materials showed statistically comparable fracture loads (p>0.05). Conclusion: On the basis of the mechanical property evaluations, we can conclude that ceramic– polymer hybrid materials meet clinical standards for use as restorative materials.

Purpose: This study aimed to evaluate the shear bond strength between ceramic materials and metal substructures fabricated through casting, milling, and three-dimensional (3D) printing techniques. Methods: In total, 45 specimens were fabricated using casting, milling, and 3D-printing (N=15 per group), followed by the application of ceramic to the metal substructures; the specimen dimensions followed ISO/CD 9693 guidelines (height=10 mm, radius=6 mm). Shear bond strength was measured using a universal testing machine, with the maximum load recorded at complete fracture. Fracture patterns were examined under a scanning electron microscope (TESCAN MIRA KH-7700, Hirox). Differences in the specimens’ bond shear strength among the three fabrication techniques were assessed using one-way ANOVA, with post-hoc analysis performed using Tukey’s HSD test (α=0.05). Results: Shear bond strength differed significantly among the three fabrication methods (p<0.001). The milling group exhibited significantly higher shear bond strength than the casting and 3D-printing groups (p<0.05). Conclusion: Metal substructures fabricated via milling showed superior bond strength; therefore, milling is recommended when high shear bond strength is a clinical priority

Purpose: This study aimed to analyze and compare the marginal and internal fit of zirconia crowns fabricated using three types of milling tools with different durations of use (0, 50, and >100 hours). Methods: Zirconia crowns were designed using computer-aided design software, and the design files were extracted. Zirconia blocks (Luxen, Dentalmax) were milled using a five-axis milling machine (DWX-52D, Roland). Crowns were fabricated using unused milling tools, tools used for 50 clinical hours, and tools used for >100 clinical hours (n=12). The morphology of the milling tools was examined using a scanning electron microscope (VEGA, TESCAN). The marginal and internal fit of the fabricated zirconia crowns was evaluated using a D2000 scanner (3Shape) via the scanning method. Differences in fit among the crowns fabricated with tools of various usage durations were analyzed using one-way analysis of variance, with post-hoc analysis conducted through Tukey’s honest significant difference test (α=0.05). Results: Significant differences in zirconia crown fit were observed among the three tooluse groups (p<0.001). Milling tools used for >100 hours produced crowns with significantly lower marginal fit (p<0.05). Similarly, reproducibility in the 100-hour group was significantly reduced (p<0.05). Conclusion: Repeated clinical use of milling tools over extended periods may adversely affect the marginal fit and reproducibility of zirconia crowns.

Purpose: This study aimed to compare the marginal and internal fits of metal three-unit fixed dental prosthesis (FDP) cast from wax and resin patterns produced using milling and three-dimensional (3D) printing technologies. Methods: To fabricate three-unit FDPs, the maxillary right first premolar and molar were prepared on an experimental model (AG-3 ZPVK, Frasaco GmbH), which was then duplicated in metal. The metal model was replicated, and working casts were fabricated using a type IV dental stone. These stone models were scanned using a desktop scanner to fabricate virtual models, allowing for the digital design of the three-unit FDPs. Overall, 30 patterns were fabricated using milling and 3D printing technologies (n=15). Subsequently, all patterns were cast into metal FDPs following conventional laboratory procedures. The marginal and internal fits of the fabricated metal FDPs were evaluated by scanning their inner and outer surfaces in situ on the metal model, followed by digital analysis. Differences in the fit between the two groups of FDPs were analyzed using an independent samples t-test (α=0.05). Results: A significant difference in marginal fit was observed between FDPs fabricated using milling and 3D printing technologies (p<0.001). The milling group exhibited superiority to the 3D printing group in terms of marginal fit (p<0.05). Conclusion: For the fabrication of wax patterns, the milling technology showed superiority to the 3D printing technology in terms of marginal fit for metal three-unit FDPs.

Purpose: This study aims to compare the internal and marginal accuracy of provisional crowns fabricated using the digital light processing (DLP) three-dimensional (3D) printing method, considering build directions of 0° and 90°, as well as layer thicknesses of 50 μm, 75 μm, and 100 μm. Methods: Provisional crowns were fabricated using a DLP 3D printer, and six experimental groups were created, each comprising 10 specimens. Provisional crowns were designed with computer-aided design software and printed using a liquid resin material. Internal and marginal accuracy were assessed using root mean square (RMS) values. Statistical analyses, including two-way ANOVA and Tukey HSD tests (α=0.05), were conducted to evaluate the effects of build direction and layer thickness on RMS values. Results: For the trueness of the internal surface, the lowest RMS value (31.56±4.47 μm) was observed at a 0° build direction with a layer thickness of 100 μm. At 90° with 100 μm, the RMS value was 64.72±4.96 μm (p<0.05). Marginal trueness at a 0° build direction with 75 μm showed the lowest value of 31.88±6.89 μm, while at 90° with 75 μm it was 85.40±22.45 μm (p<0.001). Differences between build direction and layer thickness combinations were confirmed for both internal and marginal trueness (p<0.001). Conclusion: The effects of build directions (0°, 90°) and layer thicknesses (50 μm, 75 μm, 100 μm) on the internal and marginal accuracy of printed crowns were analyzed, revealing a significant interaction in both internal and marginal trueness.

Purpose: This study aimed to evaluate the effect of postcuring conditions, such as variations in light intensity and curing time, on the color stability of resins used in three-dimensional (3D)-printed dental restorations. Methods: Using an liquid crystal display 3D printer, 81 specimens in the shape of a 10.0 mm×1.5 mm disk were produced according to the specified parameters. The printed specimens were postcured at various light intensities (17.76, 121.43, and 199.99 mW/cm2) and curing times (5, 10, and 20 minutes). Color was assessed using a color difference spectrophotometer (CM-3600A, Konica Minolta) based on the Lab* color space defined by the International Commission on Illumination, and the L*, a*, b*, C*, and H values and ΔE00 were analyzed. To evaluate the effect of postcuring conditions on the color changes, a twoway analysis of variance was conducted. Tukey’s post hoc test (α=0.05) was performed to assess significant differences. Results: The results showed significant differences in L*, a*, and ΔE00 values based on light exposure and curing time (p<0.001), whereas b* and C* values differed significantly (p<0.05). H values were not significantly different (p=0.231). Conclusion: This study demonstrated that light exposure and curing time significantly influenced the color stability of 3D-printed resin restorations. Thus, light exposure of Lv7 or lower and curing times of ≤10 minutes are recommended for optimal color stability.

Purpose: This study aimed to assess the effect of the hardness of dental barrel finishing media on the polishing amount and surface roughness (Ra) of different resin materials. Methods: Two types of media (Gray [G] and Pink [P]) and three types of resin (thermal polymerization resin [denture base, DB], autopolymerization resin [orthodontic appliance, OA], and photopolymerization resin for three-dimensional printing [crown & bridge, CB]: Vertex Rapid Simplified, Vertex Dental; Ortho-Jet, Lang Dental; Tera Harz TC-85DAC, Graphy) were used. The hardness values of the media and resin specimens were measured. The specimens were barrel-polished at a speed of 450 rpm for 25 minutes, and their weight loss was recorded. The change in Ra values was assessed. Results: The polishing amount was the highest in the G group among all three resins. The lowest Ra value was recorded in the DBP group at 0.21±0.01 μm; however, no significant differences were observed between the samples in either group (p>0.05). Conclusion: High-hardness G media are suitable when high polishing rates and efficiency are required. However, its performance may decline in the presence of substantial hardness mismatch with low-hardness workpieces. Conversely, low-hardness P media demonstrates excellent performance in fine surface polishing and is suitable for achieving smooth and uniform surface finish.

Purpose: This study aimed to quantitatively compare the stress sensitivity of cortical and cancellous bones under varying preload torques and loading directions in zirconia abutment implant systems by finite-element analysis. Methods: A three-dimensional finite-element model of a mandibular implant system was developed, comprising a zirconia abutment, a Ti-6Al-4V screw and fixture, and surrounding bone structures. The model assumed complete osseointegration and linear elastic properties. Three torque conditions (10, 20, and 30 N·cm) and two loading angles (30° oblique, 90° vertical) with a 175 N occlusal force were applied. To assess stress sensitivity, maximum principal stress was measured in the cortical and cancellous bones across all scenarios. Results: The cortical bone consistently exhibited higher absolute stress values than the cancellous bone. However, the cancellous bone showed a markedly greater increase in stress between 20 and 30 N·cm torque, particularly under oblique loading (30°), with the stress increasing by >59.2%. In contrast, the cortical bone demonstrated a more gradual and linear stress response. Both bone types showed intensified stress concentrations at high torque levels and under oblique loading, suggesting increased mechanical vulnerability in the cancellous bone. Conclusion: The cancellous bone is more sensitive to preload torque and loading direction changes than the cortical bone in zirconia abutment systems. This finding underscores the need for cautious torque applications and stress-distributing prosthetic designs, particularly in areas with poor bone quality.

Purpose: This study aimed to evaluate the clinical acceptability of various cement space settings on the marginal and internal fit of cobalt–chromium (Co-Cr) copings fabricated by additive manufacturing. Methods: The maxillary right first molar was used as the master model (AG-3, Frasaco). After scanning the master model using a dental three-dimensional scanner (E3, 3Shape), the stereolithography file was created with different cement space settings of 0, 30, 50, and 100 μm using computer-aided design software (Dental System 2018-1 ×64, 3Shape). A total of 40 single copings were made with the selective laser melting (SLM) method using Co- Cr alloy and were divided into four cement space groups with 10 specimens each. The marginal and internal fit of the four groups were measured using the silicone replica technique. The measurement points were categorized into margin, axial wall, and occlusal. Statistical analyses were performed by the Shapiro–Wilk test, one-way analysis of variance, and Tukey’s honestly significant difference test (α=0.05). Results: In the cement space 50 μm group, the marginal and internal fit was found to be overall superior to that of the cement space 0, 30, and 100 μm groups, and the margin and occlusal points demonstrated significant differences, except the axial wall points. Conclusion: In this study, a cement space setting of 50 μm is recommended to achieve optimal marginal and internal fit for Co-Cr copings fabricated using the SLM technique.

Purpose: This study aimed to evaluate the effect of the internal coloring treatment of monolithic zirconia crowns on marginal and internal adaptation. Methods: A composite resin model of the maxillary first molar was prepared with an occlusal reduction of 2.0 mm, axial reduction with a 1.0-mm offset, a 6° taper, and a chamfer margin for a monolithic zirconia crown. Then, a duplicated epoxy die was fabricated. According to the internal coloring treatment, the zirconia specimens were classified into the nontreatment (NT) group, DMAX white coloring liquid (DT) group, and Kuwotech esthetic liquid (KT) group. The internal data from all crowns were superimposed on the master die file using the “best-fit alignment” method with three-dimensional analysis software. The one-way analysis of variance and Tukey’s honestly significant difference test were performed (corrected α error level=0.05). Results: The gap in the DT and KT groups was significantly larger than that in the NT group (p<0.05). Conclusion: Within the study limitations, although the adaptation varied with the internal coloring treatment, the marginal and internal fits of the monolithic zirconia crown using the inner coloring technique fell within the range of clinical acceptance.

Purpose: This study examines factors influencing the manufacturing and repair of dental prosthetics in middle-aged and elderly individuals. Specifically, it identifies factors how dental treatment and oral health management behavior affect these processes. Methods: The study analyzed data from 4,363 individuals aged 40 and older. A complex sample logistic regression analysis was conducted to assess the impact of dental treatment and oral health management behaviors on dental prosthetic manufacturing and repair. Results: Dental treatments, including oral examinations, simple cavity treatment, root canal therapy, tooth extractions, and intraoral surgery, as well as oral health management behaviors, such as using interdental brushes and brushing teeth after lunch, were significant factors influencing dental prosthetic manufacturing and repair. Conclusion: These findings provide a theoretical basis for developing systematic oral health prevention strategies and models to reduce the need for dental prosthetic manufacturing and repair in middle-aged and elderly individuals. They can also inform age groupspecific oral health programs.

Purpose: This study aimed to analyze the causes of management deterioration in dental laboratories, identify its causes, and develop improvement measures to address the challenges in managing dental laboratories to promote the sustainable development of the industry. Methods: An online survey was conducted from September 2023 to December 2023 targeting managers of dental laboratories (rooms) registered with the Korean Dental Technician Association. Results: Proposed measures for improving the management environment of dental laboratories include unfairly low-price action of huge capital, government support for direct billing of dental prosthesis costs covered by health insurance, and identifying the appropriate number of dental laboratories by region to limit new openings. Conclusion: The results reveal the importance of devising effective measures to enhance the management stability of dental laboratories, establishing self-rescue measures for dental laboratory managers, and creating a support system aimed at advancing the dental laboratory industry. These approaches ensure that all citizens can equally benefit from highquality oral health services.

Purpose: The study aimed to examine the satisfaction level among dental technicians with a computer-based mock national examination. Methods: The study was conducted from September 1 to 30, 2020, targeting 179 students in the department of dental technology. Descriptive statistical analysis, cross-tabulation, paired sample t-tests, ANOVA, and regression analysis was conducted. Data were analyzed using IBM SPSS Statistics version 22.0 (IBM). Results: The overall satisfaction levels of the mock examination were at 3.80 and 3.93 points for the paper-based testing (PBT) and computer-based testing (CBT), respectively (p<0.001). Regarding the ability to demonstrate dental technician knowledge and skills, the satisfaction level was the highest in the CBT at 3.79 points, followed by the PBT at 3.58 points (p<0.001). As regards the correlation between the mock test and the job situation, the satisfaction level was the highest in the CBT at 3.85 points, followed by the PBT at 3.67 points (p<0.001). The “job-relatedness” item also emerged as a significant predictor variable (p<0.001). The Exp (B) value was 1.371, which means that the overall satisfaction level of respondents who said that CBT was closely related to their jobs was approximately 1.37 times higher than the level of those who did not. Conclusion: The CBT showed higher satisfaction overall than the PBT; in particular, job-relatedness and the possibility of actual ability demonstration significantly influence satisfaction. Therefore, job-based scenarios and practical suitability are important when designing future CBT evaluations.