Purpose: This in vitro study evaluated the flexural strength, impact strength, hardness, and surface roughness of 3D-printed denture base resin subjected to thermal cycling treatment. Materials and Methods: According to ISO 20795-1:2013 standards, 120 acrylic resin specimens (40/flexural strength test, 40/impact strength, and 40/surface roughness and hardness test, n = 10) were fabricated and distributed into two groups: heatpolymerized; (Major.Base.20) as control and 3D-printed (NextDent) as experimental group. Half of the specimens of each group were subjected to 10,000 thermal cycles of 5 to 55°C simulating 1 year of clinical use. Flexural strength (MPa), impact strength (KJ/m 2 ), hardness (VHN), and surface roughness (μm) were measured using universal testing machine, Charpy's impact tester, Vickers hardness tester, and profilometer, respectively. Data were analyzed by ANOVA and Tukey honestly significant difference (HSD) test (α = 0.05). Results:The values of flexural strength (MPa) were 86.63 ± 1.0 and 69.15 ± 0.88; impact strength (KJ/m 2 )-6.32 ± 0.50 and 2.44 ± 0.31; hardness (VHN)-41.63 ± 2.03 and 34.62 ± 2.1; and surface roughness (μm)-0.18 ± 0.01 and 0.12 ± 0.02 for heat-polymerized and 3D-printed denture base materials, respectively. Significant differences in all tested properties were recorded between heat-polymerized and 3D-printed denture base materials (P < 0.001). Thermal cycling significantly lowered the flexural strength (63.93 ± 1.54 MPa), impact strength (2.40 ± 0.35 KJ/m 2 ), and hardness (30.17 ± 1.38 VHN) of 3D-printed resin in comparison to thermal cycled heat-polymerized resin, but surface roughness showed non-significant difference (p = 0.262). Conclusion: 3D-printed resin had inferior flexural strength, impact strength, and hardness values than heat-polymerized resin, but showed superior surface roughness. Temperature changes (thermal cycling) significantly reduced the hardness and flexural strength and increased surface roughness, but did not affect the impact strength.

The reactions of coronene dehydrogenation and fusion upon heat treatment in the temperature range of 500–700 °C were studied using XRD, TEM, Raman, IR, and NEXAFS spectroscopy. The formation of a coronene dimer (dicoronylene) was observed at temperatures 530–550 °C; dicoronylene can easily be separated using sublimation with a temperature gradient. An insoluble and not sublimable black precipitate was found to form at higher temperatures. Analysis of the data shows that dimerization of coronene is followed at 550–600 °C by oligomerization into larger molecules. Above 600 °C amorphization of the material and formation of graphitic nanoparticles was observed. Coronene fusion by annealing is proposed as a road to synthesis of larger polycyclic aromatic hydrocarbons and nanographenes.

Purpose To assess the effect of addition of different concentrations of nanodiamonds (NDs) on flexural strength, impact strength, and surface roughness of heat‐polymerized acrylic resin. Materials and Methods 120 specimens were fabricated from heat‐polymerized acrylic resin. They were divided into a control group of pure polymethylmethacrylate (PMMA; Major.Base.20) and three tested groups (PMMA‐ND) with 0.5%wt, 1%wt, and 1.5%wt of added ND to PMMA. Flexural strength was determined using the three‐point bending test. Impact strength was recorded by using a Charpy type impact test. Surface roughness test was performed using a Contour GT machine. One‐way ANOVA and Tukey's post‐hoc analysis (p ≤ 0.05) were used for statistical analysis. Results Acrylic resin reinforced with 0.5% ND displayed significantly higher flexural strength than the unreinforced heat‐polymerized specimens, acrylic resin reinforced with 1% ND and the 1.5% ND (p < 0.0001). The impact strength of unreinforced heat‐polymerized specimens was significantly higher than all nano‐composite materials (p < 0.0001) with no significant difference between 1% ND and the 1.5% ND (p > 0.05). The addition of 0.5% ND and 1% ND significantly decreased the surface roughness in comparison to both control and the 1.5% ND groups (p < 0.0001) while no significant differences between 0.5% ND and 1% ND (p > 0.05) were reported. Nano‐composite material (0.5% ND) showed significantly lower surface roughness when compared to other specimens. Conclusions The addition of NDs to acrylic denture base improved the flexural strength and surface roughness at low concentrations (0.5%), while the impact strength was decreased with ND addition.

A method to produce suspensions of graphene sheets by combining solution-based bromine intercalation and mild sonochemical exfoliation is presented. Ultrasonic treatment of graphite in water leads to the formation of suspensions of graphite flakes. The delamination is dramatically improved by intercalation of bromine into the graphite before sonication. The bromine intercalation was verified by Raman spectroscopy as well as by x-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations show an almost ten times lower interlayer binding energy after introducing Br2 into the graphite. Analysis of the suspended material by transmission and scanning electron microscopy (TEM and SEM) revealed a significant content of few-layer graphene with sizes up to 30 µm, corresponding to the grain size of the starting material.

Purpose To evaluate the flexural strength (FS), impact strength (IS), surface roughness (Ra), and hardness of 3D‐printed resin incorporating silicon dioxide nanoparticles (SNPs). Materials and Methods A total of 320 acrylic specimens were fabricated with different dimensions according to test specifications and divided into a control group of heat denture base resin, and 3 test groups (80/test (n = 10) of unmodified, 0.25 wt%, and 0.5 wt% SNPs modified 3D‐printed resin. 10,000 thermal cycles were performed to half of the fabricated specimens. FS, IS (Charpy impact), Ra, and hardness were evaluated and the collected data was analyzed with ANOVA followed by Tukey's post hoc test (α = 0.05). Results Incorporating SNPs into 3D‐printed resin significantly increased the FS, IS (at 0.5%) and hardness compared to unmodified 3D‐printed resin (p < 0.001). However, the FS of pure 3D‐printed and 3D/SNP‐0.50% resin and IS of all 3D‐printed resin groups were significantly lower than the control group (p < 0.0001). Hardness of 3D/SNP‐0.25% and 3D/SNP‐0.50% was significantly higher than control and unmodified 3D‐printed resin (p < 0.0001), with insignificant differences between them. The Ra of all 3D‐printed resin groups were significantly higher than control group (p < 0.001), while insignificant difference was found between 3D‐printed groups. Thermal cycling significantly reduced FS and hardness for all tested groups, while for IS the reduction was significant only in the control and 3D/SNP‐0.50% groups. Thermal cycling significantly increased Ra of the control group and unmodified 3D‐printed resin (p < 0.001). Conclusion The addition of SNPs to 3D‐printed denture base resin improved its mechanical properties while Ra was not significantly altered. Thermal cycling adversely affected tested properties, except IS of unmodified 3D‐printed resin and 3D/SNP‐0.25%, and Ra of modified 3D‐printed resin.