The International Journal of Prosthodontics, 07/2024

Purpose: The purpose of this study was to investigate the mechanical properties of acrylic resins at different aging times for denture bases manufactured using the conventional method, microwave processing, milling, and 3D printing. Materials and Methods: A total of 160 rectangular samples (64 Å~ 10 Å~ 3.3 ± 0.03 mm) were prepared, divided among the four main resin groups, and subdivided into four analysis times (T0, T1, T2, and T3), resulting in 10 samples per subgroup. The samples were stored in distilled water at 37º ± 2ºC for 24 hours (T0), then subjected to thermocycling at temperatures of 5º ± 1ºC and 55º ± 1ºC in different numbers of cycles: 5,000 (T1); 10,000 (T2); and 20,000 (T3). The mechanical properties evaluated were surface microhardness, flexural strength, and modulus of elasticity. Statistical differences between resin groups and aging time were evaluated using two-way analysis of variance (P < .05). Results: The 3D-printed resin showed the significantly lowest values of microhardness, flexural strength, and modulus of elasticity compared to other resins (P < .001). Conclusions: The CAD/CAM–milled denture resin showed mechanical properties similar to those of traditional resins (conventional and microwave-processed). The 3D-printing resin did not show adequate mechanical properties for long-term clinical use. Despite this, new studies are developing better properties of this resin for long-term use.

Purpose: To evaluate and compare the accuracy of conventional and 3D-printed casts using five different 3D printers. Materials and Methods: In the control group (CG group, n = 5), five conventional impressions using light- and heavy-body polyvinyl siloxane were obtained from the master model, resulting in five stone models. In the test groups, five different scans were performed by a well-trained and experienced clinician using a TRIOS intraoral scanner. All data were exported in STL file format, processed, and sent to five 3D printers. Five casts were manufactured in each printer group: SG (CARES P20, Straumann); FG (Form 2, Formlabs); WG (Duplicator 7, Wanhao); ZG (Zenith D, Zenith); and MG (Moonray S100, Moonray). Measurements of the accuracy (trueness and precision) of the casts obtained from conventional elastomeric impressions and 3D-printing methods were accomplished using a 3D analysis software (Geomagic Control). Results: The FG group showed the lowest values for trueness (indicating a value closer to real dimensions), which were similar to the SG group only (P > .05). MG, WG, and ZG groups presented higher values and were similar compared to each other. Data on precision demonstrated that all 3D-printed groups showed lower values for precision (smaller deviation) when compared to the CG. Conclusions: The trueness depends on the chosen 3D printer. All of the tested 3D printers were more precise than cast models obtained from conventional elastomeric impressions.

Purpose: To evaluate the effect of polymerization unit, polishing, and coffee thermocycling on the color and translucency of additively manufactured polyurethane-based resins with different viscosities. In addition, their color behavior was compared with the color of the shade tab throughout the fabrication steps and aging. Materials and Methods: Disk-shaped specimens (Ø10 × 2 mm) were fabricated from polyurethane-based resins with different viscosities (Tera Harz TC-80DP and C&B permanent; n = 30 per material). Baseline color coordinates were measured after cleaning. The specimens in each resin group were divided into three subgroups (n = 10 per subgroup) to be polymerized with different polymerization units (Otoflash G171 [FLN], Wash and Cure 2.0 [CLED1], and P Cure [CLED2]), polished, and subjected to coffee thermocycling. Color coordinates were remeasured after each process. Color differences (ΔE00) and relative translucency parameter (RTP) values were calculated. Data were statistically analyzed (α = .05). Results: Time points and polymerization units affected the ΔE00 for each material (P ≤ .049). ΔE00 of each polymerization unit pair had significant differences within and among different time points within each material (P ≤ .024). ΔE00 (when compared with the shade tab) and RTP were mostly affected by polymerization units and time points within both materials (P ≤ .042). Conclusions: Tested polymerization units, polishing, and coffee thermocycling affected the color difference and translucency of tested resins. Color differences ranged from moderately unacceptable to extremely unacceptable, and the differences in translucency values mostly ranged from perceptible to unacceptable, according to previous thresholds. In addition, tested resin–polymerization unit pairs had unacceptable color differences when compared to the shade tab. CLED1 may enable higher color stability for tested resins. 

Purpose: To investigate the insertion/pull-out performance of splints produced by hand casting, thermoforming, milling, and 3D printing. Materials and Methods: A total of 120 identical mandibular splints (n = 8 specimens per group) were manufactured with hand casting, thermoforming, milling, and 3D printing. The splints were stored in water at 37ºC for 10 days and then placed onto cobalt-chromium arches and fixed on one side. Forces were applied to the other side (centric, perpendicular 50 N, 1 Hz) at two different positions (teeth 46 and 44/45) to pull out, and the test was then reset. The number of pull-out cycles until failure was recorded. The fracture behavior of the splints was investigated and characterized as fracture in the loading position, fracture at the fixation, or combined fracture. Splints were pulled off until fracture as a control (v = 1 mm/minute). Finite element analysis was used to verify the results. Statistical analyses were conducted with one-way ANOVA, post hoc Bonferroni, Pearson correlation, and Kaplan-Meier log-rank tests (α = .05). Results: The mean pull-off cycles varied from 7,839 (V-Print) to 1,600,000 (Optimill) at the tooth 46 position (FDI numbering system) and from 9,064 (Splint Comfort) to 797,750 (Optimill) at the 44/45 position. Log-rank test showed significantly (P < .001) different pull-out cycles between the systems (chi-square: 61,792 to 122,377). The thickness of the splints varied between 1.6 ± 0.2 mm (Splint Comfort) and 2.3 ± 0.1 mm (V-Print). Thickness and number of cycles were correlated (Pearson: 0.164; P = .074). The pull-off forces of the control varied significantly (P ≤ .040), ranging from 13.0 N (Keysplint) to 82.2 N (Optimill) at the tooth 46 position and from 25.2 N (Keysplint) to 139.0 N (Optimill) at the 44/45 position. Conclusions: The milled and cast splints survived more pull-off cycles than the printed or thermoformed splints. The pullout performance showed differences among the tested splint systems and indicated the influence of the material properties and processing.

Purpose: This in vitro study evaluated the adaptation of cobalt-chromium (Co-Cr) fixed dental prostheses (FDPs) fabricated by selective laser melting (SLM) with different build angles. Materials and Methods: Maxillary right first premolars and first molars from a typodont were prepared with 1-mm chamfer, 2-mm occlusal reduction, and total taper of 8 degrees to receive three-unit FDPs. After framework design, data were sent to a laser machine, and 30 specimens were fabricated from Co-Cr metal powder by SLM. Specimens were assigned to three groups (n = 10 per group) with different build angles of 0 (A0), 30 (A30), and 45 (A45) degrees. Marginal and internal fit were evaluated. Results were compared among build orientation groups and abutments. Data were analyzed using the Levene test, t test, and analysis of variance (α = .05). Results: A statistical difference was found between different angle groups (P = .015). At the abutment level, a significant difference was found in the gap values between build orientation groups for the molars (P = .048). Group A0 reported the smallest mean discrepancy values, and group A45 the highest. Statistical differences were found between group A45 and groups A0 (P < .001) and A30 (P < .024). Conclusions: The fit of printed metal FDPs was affected by the build orientation but remained clinically acceptable.

Purpose: This study compares the fracture strengths of long-span fixed provisional restorations fabricated via digital additive and subtractive methods to those fabricated via conventional heat-processing techniques. Materials and Methods: A six-unit anterior partial restoration was designed as an anatomical and morphologic structure using a dental CAD/CAM system. The provisional restorations (N = 40) of four different fabrication methods (n = 10 per group) were used for the failure loading test: stereolithography apparatus (SLA), liquid crystal display (LCD), milling (MIL), and heat-processed temporary (HPT). The specimens were subjected to a maximum load-to-fracture test using a universal testing machine, and the representative fracture patterns were observed. Statistical analysis was performed using Shapiro-Wilk, Kruskal-Wallis, Mann-Whitney U, and Bonferroni post hoc tests (P < .05). Results: The four groups showed significant differences in fracture strength according to the materials and manufacturing methods used (P < .001, except between SLA and HPT groups). The fracture strengths of MIL and LCD digitally fabricated groups were significantly higher than that of the HPT group (P < .001). Conclusions: The subtractive method is ideal for fabricating long-span fixed provisional restorations for long-term use. Additionally, LCD additive manufacturing technology could soon be a good alternative for restorations.

Purpose: To evaluate the wear resistance of a printed interim resin manufactured with different printing and postpolymerization parameters. Materials and Methods: Overall, 130 rectangular resin specimens (15 × 10 × 10 mm) were 3D-printed. Among the specimens, 60 were printed with different printing orientations (0, 45, and 90 degrees) and layer thicknesses (50 and 100 μm) to create six groups to investigate the effects of the printing parameters (n = 10 per group). The remaining 70 specimens were used to evaluate the effects of postpolymerization; for this, seven groups were created as follows (n = 10 per group): nonpostpolymerized; postpolymerized for 5, 15, and 30 minutes with an ultraviolet light–emitting diode (LED) device; and postpolymerized for 5, 15, and 30 minutes with an ultraviolet light bulb device. After masticatory simulation, the wear volume loss was calculated with 3D metrology software. One-way and two-way ANOVA were used for intergroup comparisons (α = .05). Results: The group printed with a build angle of 45 degrees showed lower wear volume loss than the 0- and 90-degree groups (P < .01). The wear volume loss in the ultraviolet LED group was significantly greater than that in the ultraviolet light bulb group (P = .04). No significant difference was observed in the wear volume loss of the printed resin with respect to the layer thickness and polymerization time (P > .05). However, the non-postpolymerized group showed significantly greater wear volume loss than the other groups (P < .001). Conclusions: The printed resin showed greater wear resistance when it was printed at a build angle of 45 degrees and postpolymerized with an ultraviolet light bulb device.

Purpose: Low-cost resin 3D printers have been used to produce affordable interim single crowns in public and private dental practices. The purpose of this study was to assess the impact of different computer-aided design (CAD) software programs on 3D trueness, microscopic marginal and internal gaps, time to design, and interproximal contacts of low-cost 3D-printed single crowns. Materials and Methods: This in vitro study was performed on a total of 90 standardized resin-prepared teeth adapted to a dental manikin. For comparison among CAD software programs, 45 tooth preparations received 3D-printed crowns designed with one of three CAD software programs by an experienced technician and identified as groups TRIOS (n = 15), EXOCAD (n = 15), and ZZ (Zirkonzahn; n = 15). To assess interoperator reproducibility, 15 additional crowns were designed by a dental clinician (group ZZ-DENT) and 15 by a dental prosthetic technician (group ZZ-PROS), both with basic 1-week CAD/CAM training. Finally, as a control group, 15 crowns were milled using a high-end five-axis milling device (group ZZ-CONTROL). Statistically significant differences for 3D trueness, microscopic gaps, time to design, and interproximal contacts among groups were assessed with the Kruskal-Wallis test. Results: No statistically significant differences in 3D trueness or marginal or internal gaps were found, either among different software programs or CAD operators (P > .05). However, Group TRIOS took significantly longer to design than EXOCAD and ZZ groups (P = .001). Less-experienced operators were significantly outperformed in time and interproximal contacts (P = .001) by the CAD technician using the same software program. Finally, control milled crowns (ZZ-CONTROL) significantly outperformed the respective 3D-printed copies (ZZ) in all assessed variables (P < .001). Conclusions: Different CAD software programs may affect the time required to design, but they do not significantly affect clinical outcomes of low-cost 3D-printed resin crowns if designed by an experienced CAD technician.

Purpose: To evaluate the effect of food-simulating liquids (FSLs) on the mechanical properties of provisional restoration materials fabricated by 3D printing, milling, and traditional fabricating methods. Materials and Methods: The bar specimens were fabricated with traditional, milling, and 3D-printing methods according to ISO 10477 specifications. Each group of specimens was randomly subdivided into four groups to be immersed in various FSLs: distilled water (control group), n-heptane, 50% ethyl alcohol, and 0.02 mol/L citric acid for 7 days at room temperature (n = 19 per group). The Knoop hardness (KHN) was evaluated, and the specimens were subjected to a three-point bending (3PB) test to evaluate flexural strength (FS) and flexural modulus (FM). One-way ANOVA and Tukey tests were used to analyze the data. Results: Fabrication methods had a significant effect on the mechanical properties of the materials being tested. FSLs had no effect on the FS and FM of materials being tested. The 50% ethyl alcohol solution significantly decreased the hardness of traditional group specimens, and the n-heptane and 50% ethyl alcohol solutions increased the hardness of the 3D-printed specimens significantly (P ≤ .05). Scanning electron microscopy (SEM) revealed that while traditional and milling group specimens showed a ductile fracture type, 3D-printed specimens showed a brittle fracture type. Conclusions: Production methods affected the mechanical properties of provisional restoration materials. Immersion in 50% ethyl alcohol solution decreased the KHN of the traditional specimens. FSLs had no negative effect on the mechanical properties of the milled and 3D-printed specimens.

Purpose: To compare the accuracy of 12 different dental restorations fabricated with milling or 3D-printed molds and robotically controlled casting. Materials and Methods: Twelve dental restorations (11 inlays and onlays and 1 crown) were made per restoration type, one per each of the 12 different teeth models (total of 24 restorations). On each tooth preparation, two restorations were manufactured using different CAD/ CAM techniques: (1) milling and (2) robotically controlled casting and 3D-printed molds. In addition, twolayer restorations were manufactured with 3D-printed molds. The marginal and internal gaps were evaluated at 120 points per restoration based on micro-CT 3D imaging. Internal gaps were evaluated using a replica technique with silicone. Results: Median values (interquartile ranges) for marginal gaps, middle internal gaps, and central internal gaps were significantly lower for 3D-printed mold restorations (44.3 [65.4] μm, 95.4 [96.2] μm, and 104.6 [78.1] μm) compared to milled restorations (58.4 [93] μm, 145.9 [85.8] μm, and 138.6 [65.7] μm). Internal gaps in the 3D-printed mold group were 6% to 51% smaller than in the milled group. Conclusions: The accuracy of restorations fabricated with 3D-printed molds may be preferable compared to milled restorations, except in the case of crown restoration. However, additional studies with a larger number of samples and different types of restorations are needed to confirm the results.

Purpose: To assess crown die trueness using additive manufacturing (AM) based on intraoral scanning (IOS) data and compare it with stone models. Materials and Methods: Crown dies with four finish line types— equigingival shoulder (SAE), subgingival shoulder (SAS), equigingival chamfer (CAE), and subgingival chamfer (CAS)—were incorporated into a reference model and scanned with a coordinate measurement machine (CMM; n = 1 scan). Trios4 (3Shape) scans generated a second reference dataset (IOS; n = 10 scans). Using scans, crown dies were produced with two different 3D printers (MAX UV385 [Asiga] and NextDent 5100 [3DSystems]; n = 10 per system). Stone dies were created from conventional impressions (n = 10). Specimens were digitized with a laboratory scanner (E4, 3Shape). Trueness was evaluated with Geomagic Control X (3DSystems). Data analysis was done using Shapiro-Wilk, Levene, ANOVA, and t tests (α < .05). Results: All crown dies fell within the clinically acceptable trueness range (150 μm). IOS exhibited significantly lower (P < .05; Δ ≤ 21.7 μm) or similar trueness compared to stone models. Asiga dies demonstrated similar and NextDent significantly lower marginal trueness than IOS (P < .05; Δ ≤ 57.3 μm). Most AM margin areas had significantly lower trueness than stone (P < .001; Δ ≤ 57.2 μm). Asiga outperformed NextDent (P < .001). Shoulder trueness surpassed chamfer in optical scans (P = .01). Finish line design and gingiva location did not have a significant impact on AM and stone models (P > .05). Conclusions: Combining IOS and AM achieves clinically acceptable crown die trueness for single molar teeth. The choice of AM device is critical, with Asiga outperforming NextDent. Finish-line design has an impact on optical scans. Finish-line design and marginal gingiva location have little effect on AM trueness.

Purpose: To evaluate the fabrication trueness, intaglio surface adaptation, and marginal integrity of resin-based onlay restorations made via additive manufacturing (AM) or subtractive manufacturing (SM). Materials and Methods: An onlay restoration was designed (DentalCAD Galway 3.0) and saved as an STL file to generate a design STL file (DO-STL). Using this design, 45 onlays were fabricated either with AM (3D-printed resin for definitive [AM-D; Tera Harz TC-80DP] and interim [AM-I; Freeprint temp] restorations) or SM (composite resin, Tetric CAD) technologies. Onlays were scanned with an intraoral scanner (CEREC Primescan SW 5.2), and the scans were saved as test STL files (TO-STLs). For trueness evaluation, TO-STLs were superimposed over the DO-STL, and root mean square (RMS) values of overall and intaglio surfaces were measured (Geomagic Control X). For the intaglio surface adaptation and marginal integrity, a triple-scan protocol was performed. Kolmogorov-Smirnov, one-way ANOVA, and post-hoc Tukey honestly significant difference tests were used to analyze data (α = .05). Results: RMS values of intaglio and overall surfaces, intaglio adaptation, and marginal integrity varied among test groups (P < .001). AM-D had the greatest overall surface RMS (P < .001), while SM had the greatest intaglio surface RMS (P < .001). SM had the highest average distance deviations for intaglio surface adaptation and marginal integrity, whereas AM-D had the lowest (P < .001). Conclusions: AM-D onlays showed lower overall trueness than AM-I onlays and SM definitive onlays. However, AM-D onlays presented high intaglio surface trueness, intaglio surface adaptation, and marginal integrity.

Purpose: To evaluate relevant material properties (flexural strength [σf], elastic modulus [E], water sorption [Wsp] and solubility [Wsl], and biocompatibility) of an additive manufacturing (AM) polymer vs a heat-curing acrylic resin (AR; control) for the manufacture of complete dentures, testing the hypothesis that fabrications from both materials would present acceptable material properties for clinical use. Materials and Methods: The σf, E, Wsp, and Wsl were evaluated according to the ISO 20795-1:2013 standard, and the biocompatibility was evaluated using MTT and SRB assays. Disk-shaped specimens were fabricated and used for Wsp (n = 5), Wsl (n = 5), and biocompatibility (n = 3) testing. For assessment of σf and E, bar-shaped specimens (n = 30) were fabricated and stored in 37°C distilled water for 48 hours or 6 months before flexural testing in a universal testing machine with a constant displacement rate (5 ± 1 mm/minute). Data from σf, E, Wsp, Wsl, and biocompatibility tests were statistically analyzed using Student t test (α = .05). Weibull analysis was also used for σf and E data. Results: Significant differences between the two materials were found for the evaluated material properties. Water storage for 6 months did not affect the flexural strength of the AM polymer, but this material showed inadequate σf and Wsl values. Conclusions: Despite adequate biocompatibility and strength stability after 6 months of water storage, the AM polymer recommended for complete dentures needs further development to improve the material properties evaluated in this study.

Purpose: To evaluate the effect of model resin type and time interval on the dimensional stability of additively manufactured diagnostic casts. Materials and Methods: Ten irreversible hydrocolloid impressions and 10 impressions from an intraoral scanner were made from a reference maxillary stone cast, which was also digitized with a laboratory scanner. Conventional impressions were poured in type III stone (SC), while digital impressions were used to additively manufacture casts with a nanographene-reinforced model resin (GP) or a model resin (DM). All casts were digitized with the same laboratory scanner 1 day (T0), 1 week (T1), 2 weeks (T2), 3 weeks (T3), and 4 weeks (T4) after fabrication. Cast scans were superimposed over the reference cast scan to evaluate dimensional stability. Data were analyzed with Bonferroni-corrected repeated measures ANOVA (α = .05). Results: The interaction between the main factors (material type and time interval) affected anterior teeth deviations, while the individual main factors affected anterior teeth and entire-cast deviations (P ≤ .008). Within anterior teeth, DM had the lowest deviations at T3, and GP mostly had lower values at T2 and lower deviations at T3 than at T0 (P ≤ .041). SC had the highest pooled anterior teeth deviations, and GP had the highest pooled entire cast deviations (P < .001). T3 had lower pooled anterior teeth deviations than at T0, T1, and T4, and higher pooled entire cast deviations than T1 were demonstrated (P ≤ .027). Conclusions: The trueness of nanographene-reinforced casts was either similar to or higher than that of other casts. Dimensional changes were acceptable during the course of 1 month.

Purpose: To evaluate and compare the fracture resistance and elastic modulus of 3D-printed post and core systems and fiber posts and composite cores. Materials and Methods: Endodontic treatment was performed on 30 mandibular premolars, and post space preparation was performed. The teeth were then randomly divided into two groups (n = 15 per group): the 3D-printed (3DP) group and the fiber post and composite core (FPC) group. In the FPC group, fiber posts (Cytec Blanco 43.604, Hahnenkratt) were bonded with resin cement (RelyX U200, 3M), and the composite core dimension was standardized with a silicone index. In the 3DP group, the impression of the post space for each specimen was taken with pattern resin (Pattern Resin, GC America), and the coronal core was produced with the same silicone index. The impressions of the posts and cores were scanned, and then the custom post and core structures were fabricated from permanent crown resin material (Permanent Crown Resin, Formlabs) with a 3D printer (Form3B, Formlabs). Specimens were subjected to load tests with a universal testing machine (M500-25AT, Testometric). After fracture occurred, the fracture force and elastic modulus were calculated. The data were analyzed by independent sample t test (α = .05) Results: There was no statistically significant difference between the two groups in terms of peak fracture force (P = .626) and elastic modulus (P = .125), and no catastrophic root fractures were observed in either group. Conclusions: The fracture resistance of endodontically treated teeth was not significantly influenced by the post material. 3D-printed, custom-made resin posts were as effective as fiber glass posts with regard to fracture resistance.

Purpose: To evaluate the flexural strength (FS) and microhardness of various CAD/CAM restorative materials intended for definitive use. The effect of hydrothermal aging on the mechanical properties of these materials was also investigated. Materials and Methods: A total of 210 bar-shaped specimens (17 × 4 × 1.5 mm ± 0.02 mm) were fabricated via either subtractive manufacturing (SM) methods—reinforced composite resin (SM-CR), polymer-infiltrated ceramic network (SM-PICN), fine-structured feldspathic ceramic (SMFC), nanographene-reinforced polymethyl methacrylate (PMMA; SM-GPMMA), PMMAbased resin (SM-PMMA)—or additive manufacturing (AM) methods with urethane acrylate–based resins (AM-UA1 and AM-UA2). Specimens were then divided into two subgroups (nonaged or hydrothermal aging; n = 15). A three-point flexural strength test was performed, and five specimens from the nonaged group were submitted to microhardness testing. Specimens were subjected to 10,000 thermal cycles, and the measurements were repeated. Results: Regardless of aging, SM-CR had the highest FS (P < .001), followed by SM-GPMMA (P ≤ .042). In nonaged groups, AM-UA2 had a lower FS than all other materials except SM-FC (P = 1.000). In hydrothermal aging groups, AM specimens had lower FS values than other materials, except SM-PMMA. With regard to microhardness, there was no significant difference found between any of the tested materials (P ≥ .945) in the nonaged and hydrothermal aging groups. Conclusions: The effect of hydrothermal aging on FS varied depending on the type of restorative material. Regardless of aging condition, SM-CR showed the highest FS values, whereas SM-FC had the highest microhardness. Hydrothermal aging had no significant influence on the microhardness of the tested materials.

Purpose: To evaluate the effect of material thickness and coffee thermocycling on the optical properties of definitive resin-based materials created via additive manufacturing (AM) and subtractive manufacturing (SM). Materials and Methods: Specimens were prepared in three thicknesses (1, 1.5, and 2 mm) from three AM (3D-CB, 3D-TH, and 3D-CT) and two SM (G-CAM and VE) resin-based materials (n = 15 per material and thickness combination). Color coordinates of each specimen were measured after polishing and after 10,000 cycles of coffee thermocycling. Color differences (ΔE00s) and relative translucency parameter (RTP) values were calculated. After logarithmic transformation, ΔE00 values were analyzed with two-way ANOVA, while RTP values were analyzed with generalized linear model test (α = .05). Results: 3D-TH had the highest pooled ΔE00 and G-CAM had the lowest (P ≤ .004). 3D-CB had higher pooled ΔE00 than VE and 3D-CT (P ≤ .002). For the SM group, the 1.5-mm and 2-mm 3DCT specimens and 1-mm 3D-TH specimens had lower ΔE00 than 1.5-mm and 2-mm 3D-TH specimens (P ≤ .036). Most of the AM specimens and 1-mm VE specimens had higher ΔE00 than 2-mm G-CAM specimens (P ≤ .029). Further, most AM specimens had higher ΔE00 than 1.5-mm G-CAM specimens (P ≤ .006). RTP values increased in order of 3D-CT, G-CAM, VE, 3D-CB, and 3D-TH specimens (P < .001). Increased thickness and coffee thermocycling mostly reduced RTP (P < .001). Conclusions: 3D-TH typically had higher color change values than SM specimens, while G-CAM typically had lower color change values than AM specimens. Only the 1.5-mm and 2-mm 3D-TH specimens had unacceptable color changes. Thickness and coffee thermocycling mostly reduced the translucency.

Purpose: This study investigated the impact of reducing the oxygen concentration via nitrogen injection during the postcuring process of 3D-printed dental materials. Materials and Methods: Resin specimens for dental crown and bridge (15-mm diameter, both 1-mm and 2-mm heights) were 3D-printed and rinsed. Subsequently, the postcuring process was conducted on nine groups categorized according to atmospheric conditions within the curing device (20% [control], 10%, and 5% oxygen) and curing times (10, 15, and 20 minutes). Surface roughness was measured using a gloss meter. Surface polymerization was confirmed through Fourier-transform infrared spectroscopy (FT-IR) analysis, and the flexural strength and elastic modulus of the specimens were measured using a universal testing machine. Water absorption and solubility were determined according to Inernational Organization for Standardization (ISO) standards. All evaluation criteria were statistically analyzed using one-way ANOVA and Tukey’s post hoc test based on oxygen concentration. Results: The elastic modulus did not show statistically significant differences in all groups. However, compared to the control group, the flexural strength, degree of conversion, and gloss significantly increased in the groups with decreased oxygen concentrations. Conversely, water solubility and water absorption significantly decreased in a few groups with reduced oxygen concentration. Conclusions: Reducing oxygen concentration through nitrogen injection during the postcuring process of 3D printing enhances the suitability of the dental prosthetic materials. The significant increase in flexural strength can particularly enhance the utility of these materials in dental prosthetics.