Earticle

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 trueness of three-dimensional (3D) printed zirconia single crowns using digital light processing with different build angles. Methods: A prepped maxillary right first molar model was scanned using a dental laboratory scanner (E4, 3Shape A/S). The anatomically contoured crown was designed using computer- aided design software (Dental Designer, 3Shape A/S) and saved as a standard tessellation language file. Three build angles (0°, 30°, and 60°) were defined using the slicing software (Zipros, AON). The crowns were printed using a digital light-processing 3D printer (N=30), followed by debonding and sintering to achieve the final shape. The crowns were scanned postprocessing and analyzed for trueness using 3D inspection software. Data were statistically analyzed with the one-way analysis of variance and Bonferroni post hoc tests. Results: The root mean square (RMS) values for the internal segments were 40.23 (0°), 53.01 (30°), and 82.49 (60°) μm. The marginal segments recorded RMS values of 34.63 (0°), 59.97 (30°), and 84.16 (60°) μm. Statistical analysis revealed significant differences among the groups (p<0.001). Conclusion: The results indicate that a 0° build angle with uniform height support structures provides the highest accuracy in digital light processing of 3D printed zirconia crowns.

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: To evaluate the effect of post-curing on the three-dimensional (3D) accuracy of artificial teeth, denture bases, and denture base monoblock manufactured using digital light processing (DLP) technology. Methods: Using an edentulous model, a 3D design was made for complete dentures. Three groups were printed by DLP: artificial teeth, denture bases, and denture base monoblock. The models were scanned, subjected to post-curing, and scanned again. Three-dimensional analysis was performed based on the post-treatment differences among the three groups. Statistical analysis was performed using SPSS Statistics ver. 22.0 (IBM), and the Mann– Whitney U-test and Kruskal–Wallis test were employed as nonparametric tests. Results: The complete denture monoblock (CM) and complete denture artificial teeth (CA) groups showed the lowest and highest errors at 15.13 and 23.37 μm, respectively. The groups did not show significant differences (p>0.05). In the significance test among the three groups, no significance was found in the CA group; however, significant differences were found between the complete denture base (CB) and CM groups. In addition, the three groups showed significant differences (p<0.05). Conclusion: Although deformation may occur during the post-curing process, it is within the clinically acceptable range. Future comparative studies using different 3D printers and searching for ways to minimize errors through optimization of the post-curing process are warranted.

Purpose: To evaluate and compare the dimensional accuracy of maxillary denture bases fabricated using digital light processing (DLP) and liquid crystal display (LCD) 3D printing technologies with the same materials and standardized printing parameters. Methods: A standard edentulous maxillary model was used to design a computer-aided design (CAD)-based denture base, which was then printed using DLP (Asiga Pro 4K, 10 specimens) and LCD (UNIZ NBEE, 10 specimens) printers. After post-processing, all specimens were scanned and analyzed using Geomagic Control X. Dimensional accuracy was assessed by calculating the root mean square (RMS) deviation between the printed and reference CAD data. Data were analyzed using Welch’s t-test (α=0.05). Results: RMS values were significantly lower in the LCD group (98.30±3.41 μm) than in the DLP group (166.59±24.18 μm) (p<0.001), indicating superior geometric fidelity. Color difference maps revealed consistent accuracy across the LCD-printed surfaces, whereas DLPprinted samples showed distortion in margin and palatal regions. Conclusion: Under standardized conditions, the LCD printing method demonstrated higher dimensional accuracy and consistency than the DLP method, suggesting its relative clinical suitability for complete denture fabrication.

Purpose: To evaluate the three-dimensional trueness of upper and lower denture bases produced using a digital light processing (DLP) printer and immersed in a constant-temperature water bath. Methods: An edentulous model was prepared and fitted with denture bases and occlusal rims manufactured using base plate wax. After scanning the model, denture bases, and occlusal rims, complete denture designs were created. Using the designs and a DLP printer, 10 upper and 10 lower complete dentures were manufactured. Each denture was scanned before (impression surface of upper denture base before constant temperature water bath [UBC] and impression surface of lower denture base before constant temperature water bath [LBC] groups) and after (impression surface of upper denture base after constant temperature water bath [UAC] and impression surface of lower denture base after constant temperature water bath [LAC] groups) immersion in the constant-temperature water bath. Scanned files were analyzed by comparing reference and scanned data, with statistical analysis conducted using the Kruskal-Wallis test (α=0.05). Results: Statistical analysis revealed no significant differences between the UBC and LBC groups, nor between the UAC and LAC groups (p>0.05). However, significant differences were observed between the UBC and UAC groups and between the LBC and LAC groups, i.e., before and after the constant-temperature water bath for both maxillary and mandibular denture bases (p<0.05). Conclusion: Denture bases not immersed in the constant-temperature water bath (UBC and LBC groups) exhibited error values within 100 μm, whereas those immersed in the water bath (UAC and LAC groups) showed error values exceeding 100 μm.

Purpose: In this study, thermal properties were observed by measuring the extent of thermal expansion and the amount of thermal residue that appears upon burnout on a workpiece made by using a dental digital light processing (DLP) three-dimensional (3D) printer. Methods: Thermal properties of workpieces manufactured by using two 3D printers were observed. The specimens were designed in cylindrical form with dimensions 10 mm in diameter and 10 mm in height. The control specimen was made of wax, and the experimental specimen was made of resin. The thermal expansion rate was measured by applying heat to three types of specimens, and burnout residue was measured. Results: The thermal expansion rate of the wax pattern (WP) specimen was 0.93%±0.05%, of the RP1 specimen was 1.30%±0.08%, and of the RP2 specimen was 1.20%±0.09%. Measuring the recovered residue yielded residual amounts of 0.2% for the WP specimen, 1.1% for the RP2 specimen, and 1.8% for the RP1 specimen. Conclusion: 1. From measurements of the workpieces manufactured by dental DLP 3D printing, the thermal expansion rate was found to be higher than that of wax. 2. As a result of measuring burnout residues on the workpieces manufactured by dental DLP 3D printing, the required summoning temperature to obtain suitable castings was determined to >750℃.

3D printing has the advantage of being able to process various types of parts by layering materials. In addition to these advantages, 3D printing technology allows models to be processed quickly without any special work that can be used in different fields to produce workpieces for various purposes and shapes. This paper deals to not only increase the utilization of 3D printing technology, but also to revitalize 3D printing technology in applications that require similar cryogenic environments. The goal of this study is to identify the mechanical properties of polylactic acid and photopolymer resin processed by Fused Deposition Modeling (FDM) and Digital Light Processing (DLP) respectively. The entire process is meticulously examined, starting from getting the thermal contraction using an extensometer. A uniaxial tensile test is employed, which enables to obtain the mechanical properties of the samples at both room temperature (RT) and cryogenic temperature of 77 K. As the results, photopolymer resin exhibited higher tensile properties than polylactic acid at RT. However, at cryogenic temperatures (77 K), the photopolymer resin became brittle and failure occurred due to thermal contraction, while polylactic acid demonstrated superior tensile properties. Therefore, polylactic acid is more suitable for lower temperatures.

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: The purpose of this in vitro study was to measure and compare the thickness-dependent color dimensions of digital light processing (DLP) three-dimensional (3D) printer and conventional interim restorative resin. Methods: Specimens (N=60) were fabricated using either subtractive manufacturing (S group) or DLP 3D printing (D group) material. All milled and 3D-printed specimens were allocated into three different groups (n=10) according to different thicknesses as follows: 1.0, 1.5, and 2.0 mm. Color measurements in the CIELab coordinates were made using a spectrophotometer under room light conditions (1,003 lux). The color differences (ΔE*) between the specimen and control target data were calculated. Data were analyzed using the oneway analysis of variance (ANOVA). Post hoc comparisons were conducted using Tukey's honestly significant difference method (α=0.05 for all tests). Results: The ΔL*, Δa*, Δb*, and ΔE* values of interim restorative resin produced by DLP 3D printing were obtained in terms of the specimen's thickness increased compared with the increases by subtractive manufacturing. When the thickness was similar, the color difference between subtractive manufacturing and DLP 3D printing was ≥5.5, which is a value required by the dentist for remanufacturing. Conclusion: Color was influenced by the thickness of the interim restorative resin produced by DLP 3D printing.

Purpose: The aim of this study was to evaluate the accuracy of provisional crowns manufactured using a milling machine and a digital light processing (DLP) printer. Methods: A full-contour crown was designed using computer-aided design software. Provisional crowns of this design were manufactured using a milling machine and using a DLP three-dimensional (3D) printer (N=20). The provisional crowns were digitized with an extraoral scanner, and 3D deviation analysis was applied to the scanned data to confirm their accuracy. An independent t-test was performed to detect the significant differences, and the Kolmogorov-Smirnov test was used for analysis (α=0.05). Results: No significant differences were found among the precision of marginal surface between the printed and milled crowns (p=0.181). The trueness of marginal and internal surfaces of the milled crowns were statistically higher than those of the printed crowns (p=0.024, p=0.001; respectively). Conclusion: The accuracy of provisional crowns manufactured using a milling machine and a 3D printer differed significantly except with regards to the precision of the internal surface. However, all the crowns were clinically acceptable, regardless of the manufacturing method used.

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.

The aim of this study is to investigate the effect of wear resistance with 3D printing of DLP(Digital Light Processing). For this purpose, three wear factor which are wear loss, coefficient of friction and friction force applied to test wear-resistance. Wear test of ball-on-disk has been performed using steel balls to determine the variation of wear characteristics. Finally, the coefficient of wear was calculated by the Archard wear equation with 3D printing of DLP.

The digital light processing (DLP) 3D printing method can be used to achieve continuous ceramic laminations during additivemanufacturing. However, it has limited applications because its green body, which is photocured by adding a resin andphotoinitiator to the ceramic powder, cracks during the debinding process. In this study, we used four types of acrylic resinswith low functional groups and mixed 82 wt% zirconia powder with the photoinitiator and dispersant to prepare a slurry. Under a certain content of photoinitiator, the photocured zirconia green body was prepared by controlling the light intensityconditions of 32 W/m2 and 38 W/m2, and the light exposure time of 3s and 7s, respectively. Furthermore, we conductedexperiments focused on the condition of photocuring green body according to the printing approach based on the UV lightposition, as well as cracking of the green body after the debinding process. The position of the UV light influenced thecontinuous lamination behavior and intervention of oxygen during photocuring, and based on these results, we investigatethe differences in the laminated layer interphase of the photocured green body and its relationship to cracking with thedebinding behavior.

This study aimed to recycle eggshell waste to synthesize hydroxyapatite (HAp) powder and evaluate its potential as a bonesubstitute material using DLP (Digital Light Processing) 3D additive manufacturing method. The synthesized HAp powderexhibited a fine particle size with high crystallinity and specific surface area, which enhances their suitability for use in 3Dadditive manufacturing for complicate shaped bone substitute materials. The sintered HAp scaffolds showed the crack-freeand dense microstructure with 45% sintering shrinkage. In particular, the interfaces between the laminated layers werehealed by the control of slurry composition and processing parameters, such as light exposure time. Cell viability testsdemonstrated the highest cell survival at 7 seconds light exposure time and 14.5 mm disc area, suggesting that optimalexposure time and disc design play crucial roles in enhancing cell attachment and survival. These findings indicate that theuse of sustainable powder resources and advanced 3D additive manufacturing techniques extends the applicability of HApin bone tissue engineering, providing complicated and accurate patterns for clinical applications in the future.

PURPOSE. This study aimed to compare the accuracy (trueness and precision) of interim crowns fabricated using DLP (digital light processing) according to post-curing time. MATERIALS AND METHODS. A virtual stone study die of the upper right first molar was created using a dental laboratory scanner. After designing interim crowns on the virtual study die and saving them as Standard Triangulated Language files, 30 interim crowns were fabricated using a DLP-type 3D printer. Additively manufactured interim crowns were post-cured using three different time conditions-10-minute post-curing interim crown (10-MPCI), 20-minute post-curing interim crown (20-MPCI), and 30-minute post-curing interim crown (30-MPCI) (n = 10 per group). The scan data of the external and intaglio surfaces were overlapped with reference crown data, and trueness was measured using the best-fit alignment method. In the external and intaglio surface groups (n = 45 per group), precision was measured using a combination formula exclusive to scan data (10C2). Significant differences in accuracy (trueness and precision) data were analyzed using the Kruskal-Wallis H test, and post hoc analysis was performed using the Mann-Whitney U test with Bonferroni correction (α=.05). RESULTS. In the 10-MPCI, 20-MPCI, and 30-MPCI groups, there was a statistically significant difference in the accuracy of the external and intaglio surfaces (P<.05). On the external and intaglio surfaces, the root mean square (RMS) values of trueness and precision were the lowest in the 10-MPCI group. CONCLUSION. Interim crowns with 10-minute post-curing showed high accuracy.

Additive Manufacturing technologies have been acknowledged for years as tremendous processing routes for the production of parts with complex shape. While the economic Digital Light Processing (DLP) technology was initially restricted to the production of photopolymer materials, it has a great potential for the manufacture of ceramic and metallic parts, half way between direct prototyping and the conventional powder processing route. The method consists in preparing a powder-loaded photopolymer slurry by conventional ball milling, processing green composite parts by DLP and carrying a debinding and sintering heat treatment. The present report investigates the preparation of a suitable slurry and evaluate the printability by DLP. It was found that viscosity of the slurry significantly increased with increasing powder contents, particularly over 25 vol.%. A 28 vol.% Al2O3 powder containing green composite was successfully processed using a commercial DLP apparatus. However, higher loads of powder are required to allow for appropriate sintering, which suggests optimization of the slurry by addition of solvents and use of finer powder particles to reduce viscosity and enhance printability.

Purpose: The technique introduced in this study describes a technique for surface treatment that applies a photocuring resin to the surface of an interim crown fabricated by three-dimensional (3D) printing without a conventional polishing method. The purpose of this study was to evaluate marginal and internal fit and the intaglio surface trueness of interim crowns after surface treatment of 3D-printed crowns for clinical application. Materials and Methods: An interim crown was fabricated using a 3D printer with digital light-processing technology, and the surface support was removed. After the posttreatment process, the resin was thinly applied to the surface of the interim crown and polymerized to solve the esthetic problem of the surface without the conventional polishing process. In addition, the marginal and internal fits were measured to verify the clinical use of this technique, and the trueness was evaluated to confirm the deformation of the inner surface according to the technical application of the outer surface of the interim crown. The difference before and after the evaluation by a statistical method was verified using an independent t-test (α=0.05). Result: There was no significant difference in the marginal and internal fit before and after the application of this technique (P>0.05). There was no significant difference in intaglio surface trueness before and after the application of this technique (P=0.963). Conclusion: There was no change in the marginal and internal fit or in intaglio surface trueness of the interim crowns to which this technology was applied. This surface treatment technique is a more convenient method for interim crowns fabricated using 3D-printing technology without the conventional polishing process.