Search Results (1,150)

Objective: This study aimed to evaluate the color stability and microhardness of two resin composites, a BPA-based composite (Luna) and a BPA-free composite (Luna 2), after immersion in chlorhexidine (CHX), using two different polishing protocols. Methods: Disks (7 mm diameter × 2 mm thickness) were prepared and divided into three groups per material: unpolished, Sof-Lex, and FlexiDisc polished (n = 20 per group). The specimens were immersed daily in either 0.12% CHX or distilled water for 21 days. Color change (ΔE) was measured at 7, 14, and 21 days using a spectrophotometer. Microhardness was evaluated at each time point using a Vickers hardness tester (200 g load, 10 s dwell time). Results: Luna 2 exhibited significant discoloration from day 14, while Luna showed significant color change on day 21 (p < 0.05). After 21 days of CHX immersion, unpolished Luna reached a ΔE value of 6.27 ± 1.69, exceeding the clinically acceptable threshold. At 14 days, Sof-Lex polishing significantly improved color stability compared to unpolished controls for both materials (p < 0.05). No significant differences were observed between the two polishing systems over time (p > 0.05). Luna 2 demonstrated significantly higher microhardness at all evaluated time points (p < 0.001). Both composites exhibited slight reductions in microhardness over time, which were more pronounced in Luna (p < 0.001). Conclusions: Polishing enhanced the color stability of both composites. Luna 2 exhibited superior microhardness compared to Luna, and polishing had no significant effect on this property. Given the increasing clinical shift toward BPA-free materials due to biocompatibility concerns, these findings offer relevant guidance for optimizing the long-term esthetic and mechanical performance of modern resin-based restorations. Full article

The aim of this study was to evaluate the effect of human blood contamination, before and after hardening of the materials, on microhardness of high-viscosity Fuji IX GP Extra (Fuji IX) and resin-modified Fuji II LC (Fuji II) glass-ionomer cement (GIC) and glass-hybrid material EQUIA Forte HT (EQUIA), with and without protective coating EQUIA Forte Coat (Coat), before and after thermocycling. Four groups (n = 40): 1. Fuji IX; 2. Fuji II; 3. EQUIA and 4. EQUIA + Coat were further subdivided into 3 subgroups: (1) Control; (2) blood contamination before hardening; (3) blood contamination after hardening, resulting in a total of 12 groups of 10 samples each. Samples were prepared using teflon molds (5 mm × 2 mm). Microhardness was measured using a Vickers microhardness tester before and after thermocycling (10,000 cycles), and data were statistically analyzed (Kolmogorov–Smirnov test, ANOVA, Scheffe’s test). In the control groups, the highest microhardness was measured for EQUIA+Coat before thermocycling (70.71 ± 8.79) and after thermocycling (68.6 ± 7.65). Within the groups exposed to blood after hardening, the highest microhardness was recorded in the thermocycled EQUIA+Coat group (73.07 ± 8.85). Blood contamination before hardening negatively affected the microhardness of Fuji II, Fuji IX, and EQUIA+Coat. Exposure to blood after hardening increased the microhardness of Fuji IX and EQUIA, thermocycled Fuji IX and thermocycled EQUIA + Coat samples. Full article

In this study, nanocrystalline (NC) aluminum (Al) and magnesium (Mg)-doped Al bulk components were fabricated using a hybrid manufacturing process that combines cryomilling and high-pressure cold spray (HPCS) additive deposition techniques. Yttria-stabilized zirconia (YSZ) was also added during the HPCS process to improve deposition efficiency and build-up thickness via peening. The evolution of morphology, crystallite size, and elemental composition of both cryomilled powders and cold-sprayed (CS’ed) components was systematically characterized using X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). Mechanical characterization was performed using Vickers microhardness and uniaxial tensile testing, while the tribological behavior was assessed using sliding wear tests under dry/lubricated conditions. XRD analysis revealed that increased cryomilling duration led to significant crystallite refinement, which directly correlated with enhanced hardness and strength. This mechanical strengthening was accompanied by an increase in coefficient of friction (COF) and lower wear rates. The results also showed that the Mg-doped Al exhibited superior hardness, tensile strength, and tribological performance compared to pure Al. The study further explores the underlying mechanisms responsible for these enhancements, highlighting the potential of solute-assisted grain boundary stabilization in tailoring high-performance NC Al alloys. Full article

This paper presents the results of wear tests of two types of commercial low-carbon, low-alloy martensitic abrasion-resistant steels, Hardox 450 and XAR 450, which belong to the hardness class 450 HBW. These steels, due to their increased resistance to the abrasive wear mechanism, are used for machine parts for applications in intensive abrasion environments such as construction, mining, and agriculture. The scope of work included microstructure analysis on an optical microscope, chemical composition analysis, Vickers hardness measurements at different loads (HV0.2, HV1 and HV2), and wear testing. Wear tests were carried out by the standard method “dry sand—rubber wheel”, and tests on the Taber abrader device. Microstructure analysis revealed that both steels have a similar non-oriented, homogenous, fine-grained martensitic microstructure. The results of HV2 hardness measurements showed a similar trend for both steels in all examined sections of the plates. For both tested steels, the hardness values of HV0.2 and HV1 are slightly higher than HV2, but the scattering of the results is also greater. Abrasion resistance testing using the standard “dry sand—rubber wheel” method showed that Hardox 450 steel has a lower volume loss of about 8%, but a greater scattering of the results compared to XAR 450 steel. The results of the abrasion resistance test on the Taber abrader device confirmed approximately the same behavior. For both steels, a prediction model was established for a reliable assessment of the wear intensity concerning the grain size. Although examined steels belong to the same hardness class, Hardox steel seems to be a more appropriate choice for the manufacture of machine components exposed to abrasive wear. Full article

Light attenuation and excess handling of light-cured luting agents create problems in bonding veneer restorations. The aim of the present study was to assess the curing capacity of light-cured veneer luting agents (VLA) [Choice 2 (CH2), G-Cem Veneer (GCV), Panavia LC Veneer (PNV), PermaCem LC Veneer (PMS), and Variolink Esthetic LC (VEV)] under lithium disilicate veneers, in the presence or absence of touch-cure primers (Adhese Universal Bond DC for VEV, G Premio Bond + DCA Activator for GCV, and V5 Tooth Primer V5 for PNV) and to evaluate material setting under two tack-curing irradiation modes (contact, distant). The methods used were ATR–FTIR spectroscopy and Vickers hardness (VHN) tests (n = 5/product and test). According to the results, all materials cured under the ceramic demonstrated significantly lower DC% from the controls, with a ranking of VEV, CH2 > GCV, PMS, PNV. The primers improved DC% by 4–13% only in the veneer groups. Tack-curing in contact mode demonstrated conversion and hardness values ranging from 37% to 78% and 31% to 57% of the controls respectively, corresponding to a vitreous state. For the distant mode, very low conversion values were found (0–7% of the controls), with untraceable indentations. It can be concluded that low translucency veneers reduce conversion of VLAs, which can be improved by using touch-cure activators. Tack-curing, as instructed, creates vitrified materials, resulting in difficult removal of set excess, which implies the need for better standardization of the procedure. Full article

This study aimed to evaluate the penetration and bonding performance of three restorative materials—high-viscosity glass ionomer cement (Riva Self Cure HV), resin-modified glass ionomer cement (Riva Light Cure) and a bioactive resin (Activa BioActive Restorative™)—in the healthy and carious dentine of permanent molars. Forty extracted human molars with sound or decayed dentine were restored following standardised protocols and subsequently divided into slices. So, twenty-four samples were used for each group (sound and carious dentine) for interface analysis using confocal laser scanning microscopy, field emission scanning electron microscopy and energy dispersive X-ray spectroscopy, and another eight simples were used for each group (sound and carious dentine) for Vickers microhardness testing. Results showed that both glass ionomer cements achieved consistent chemical bonding in healthy dentine and demonstrated better interfacial adaptation compared to carious dentine, where partially demineralised areas showed weaker bonding. The bioactive resin exhibited good adhesion in sound dentine due to the adhesive system but showed poorer interaction in decayed dentine with signs of interfacial separation. Elemental analysis revealed similar compositions among materials, with no significant differences in material concentrations among the ionomers, while there were significant differences with the other materials. On the other hand, some variations were observed in the sulphur, fluoride and strontium content depending on dentine condition. Microhardness values were higher in healthy dentine than in carious dentine for all materials (p < 0.001), except the high-viscosity glass ionomer, which maintained stable hardness in both substrates (36.33 ± 6.23 VHN vs. 34.56 ± 4.31 VHN; p = 0.605). These findings highlight the relevance of material selection and dentine condition in minimally invasive restorative dentistry. Full article

Boron (B) is widely used as a neutron-absorbing nuclide and has significant applications in the nuclear industry. B₄C/Al composites combine the high hardness of B₄C with the ductility of Al, making them commonly used neutron-absorbing materials. Under current preparation methods, the poor wettability and low reactivity of B₄C with molten Al limit its effective incorporation into the matrix, and the addition of B₄C in B₄C/Al composites has reached its threshold limit, making it difficult to achieve breakthrough improvements in neutron absorption performance. However, incorporating additional B elements into the B₄C/Al composite can break this limit, effectively enhancing the material’s neutron absorption performance. Nevertheless, research on the impact of this addition on the mechanical properties of the composite remains unclear. The requirements for B₄C/Al composites as spent fuel storage and transportation devices include high mechanical strength and certain machinability. This study fabricated B₄C/Al composites with varying B contents (5 wt.%, 10 wt.%, and 15 wt.%), and the influence of B addition on the microstructure and mechanical properties of B₄C/Al composites was investigated. The results demonstrate that the composites exhibit a density of approximately 99% with well-established interfacial bonds. Increasing B content leads to a higher quantity of interfacial reaction products Al₃BC and AlB₂, enhancing the Vickers hardness to 370.93 HV. The bending strength and fracture toughness of composites with 5 wt.% and 15 wt.% B addition decreased, whereas those with 10 wt.% B exhibited excellent resistance to crack growth and high-temperature plastic deformation due to a high content of ductile phase. Full article

The Bi-Sn, Bi-Sn-Ag, and Bi-Sn-Sb solder alloy systems represent lead-free, environmentally friendly alternatives for reliable electronic assembly. These alloys comply with increasingly strict environmental and health regulations, while offering low melting points suitable for soldering temperature-sensitive components. Microstructural analysis revealed distinct phase segregation in all alloys, with Sb promoting coarse Sn₂Sb₃ intermetallic compounds and Ag inducing fine needle-like Ag₃Sn precipitates. Eutectic refinement and compositional contrast were confirmed by SEM-BSE and EDS mapping. Vickers microhardness measurements revealed increased hardness in Sb- and Ag-modified Bi–Sn alloys, with Ag₃Sn dispersion yielding the highest strengthening effect, indicating enhanced mechanical potential. This study also reports the thermal and electrical conductivities of Bi60Sn40, Bi60Sn35Ag5, and Bi60Sn35Sb5 alloys over the 25–140 °C range. Bi60Sn40 showed an increase in thermal conductivity across the full temperature range from 16.93 to 26.93 W/m·K, while Bi60Sn35Ag5 reached 18.28 W/m·K at 25 °C, and Bi60Sn35Sb5 exhibited 13.90 W/m·K. These findings underline the critical influence of alloying elements on microstructure, phase stability, and thermophysical behavior, supporting their application in low-temperature soldering technologies. Full article

Background/Objectives: The dental industry is continuously developing high-performance polymer (HPP) materials with different qualities for denture frameworks. The aim of this in vitro study was to assess how thermal ageing (TA) affects the flexural strength (FS) and microhardness of two different HPP materials: Nanoksa G-plus and Bio-HPP/PEEK. Methods: The TA process was carried out for 5000 cycles at 5 °C and 55 °C in distilled water. To assess FS, a total of 40 bar-shaped specimens measuring 65.0 mm × 10.0 mm × 2.5 mm (20 per group) were obtained; TA and No-TA (NTA) subgroups were prepared for each material group (10 per subgroup); and a three-point bending test was conducted using an Instron universal testing machine. Each specimen that fractured during the FS test was subjected to microhardness measurement using a Vickers hardness tester. The mean FS and microhardness of the TA and NTA specimens were statistically examined using the t-test. Results: Both the TA and NTA Bio-HPP/PEEK specimens exhibited significantly greater (p < 0.0001) microhardness and FS qualities than the Nanoksa G-Plus specimens. The FS and microhardness of the Bio-HPP/PEEK and Nanoksa G-Plus materials significantly decreased (p < 0.05) after TA. Conclusions: The Bio-HPP/PEEK material showed better FS and microhardness properties than the Nanoksa G-Plus material. TA considerably decreased the FS and microhardness of the Bio-HPP/PEEK and Nanoksa G-Plus materials. Full article

Achieving simultaneous enhancement of Vickers hardness and fracture toughness remains a critical challenge in designing oxide ceramic materials due to their partially antagonistic nature. In this study, we address this trade-off by tailoring the microstructure of zirconia (ZrO₂) ceramics through Y₂O₃ doping and high-pressure high-temperature (HPHT) sintering. Nanostructured composites were synthesized using 50 nm monoclinic ZrO₂ and varying Y₂O₃ contents (3, 5, and 7 mol%) under 5 GPa at temperatures ranging from 400 to 2000 °C. Among them, 3 mol% Y₂O₃-doped zirconia (3Y-PSZ) sintered at 1200 °C achieved a well-balanced mechanical performance, with a Vickers hardness of 11.6 GPa and a fracture toughness of 9.26 MPa·m^1/2. These results demonstrate that it is feasible to retain a high hardness while significantly enhancing toughness by controlling phase composition and grain refinement under HPHT conditions. This work offers valuable insights into microstructural optimization strategies for zirconia-based ceramics aiming to overcome the conventional hardness–toughness trade-off. Full article

Interest in surface integrity has grown in the manufacturing industry; indeed, it has become an integral part of the industry. It can be studied by examining surface roughness parameters, hardness variations, and microstructure. However, evaluating all these parameters together can be a challenging task. To address this multi-criteria decision-making model (MCDM), techniques such as Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) and Grey Relational Analysis (GRA) provide a suitable solution for optimizing the machining parameters that lead to improved product quality. This work investigated surface roughness parameters, including arithmetic average surface roughness (2D) (Ra), mean surface roughness depth (2D) (Rz), area arithmetic mean height (3D) (Sa), and maximum surface height (3D) (Sz), in conjunction with Vickers macrohardness (HV) and optical micrographs, to analyze machined surfaces during the turning of X5CrNi18-10 steel. The results suggest that machining with a spindle speed (N) of 2000 rpm or v_c of 282.7 m/min, a feed rate (f) of 0.1 mm/rev, and a depth of cut of 0.5 mm yields the best surface, achieving an “A” class surface finish. These parameters can be applied in manufacturing industries that utilize chromium–nickel alloys. Additionally, the method used can be applied to rank the quality of the product. Full article

This study investigates the effect of Al_x and Ti_x content (x = 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6) on the microstructural evolution and mechanical properties of Co-free high-entropy Al_xTi_xCrFe₂Ni alloys in both as-cast and homogenized conditions. The research focused on the characterization of structural features, melting behavior, and mechanical performance. Microstructural characterization was carried out using optical microscopy, scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), X-ray diffraction (XRD), and differential thermal analysis (DTA). Mechanical properties were evaluated through Vickers hardness testing and uniaxial compression tests. Increasing the Al and Ti content induced a transformation from a single-phase FCC structure to a dual-phase BCC structure, with the primary BCC phase strengthened by spherical precipitates rich in Al, Ti, and Ni. Homogenization annealing at 1100 °C led to an overall improvement in the mechanical properties. The Al_0.3Ti_0.3CrFe₂Ni alloy exhibited the most balanced combination of strength and ductility after annealing, achieving a compressive yield strength of 1510 MPa, a compressive strength of 3316 MPa, and a compressive plastic strain of 45%. Full article

Background/Objectives: In-office bleaching commonly employs high concentrations of hydrogen peroxide (HP) or carbamide peroxide (CP), which may compromise enamel integrity. This in vitro paired-design study aimed to compare the chemical and mechanical effects of three commercial bleaching agents—Opalescence Boost (40% HP), Opalescence Quick (45% CP), and BlancOne Ultra+ (35% HP)—on human enamel. The null hypothesis assumed no significant differences between the control and treated samples. Given the ongoing debate over pH, active ingredients, and enamel impact, comparing whitening systems remains clinically important. Methods: Forty-two extracted teeth were assigned to three experimental groups (n = 14) with matched controls. Each underwent a single bleaching session per manufacturer protocol: Opalescence Boost (≤60 min), Opalescence Quick (15–30 min), and BlancOne Ultra+ (three light-activated cycles of 8–10 min). Enamel chemical changes were analyzed by Fourier transform infrared (FTIR) spectroscopy (phosphate and carbonate bands), and surface hardness by Vickers microhardness testing. Paired t-tests (α = 0.05) assessed statistical significance. Results: FTIR analysis revealed alterations in phosphate and carbonate bands for all agents, most notably for Opalescence Boost and BlancOne Ultra+. Microhardness testing showed significant reductions in enamel hardness for Opalescence Boost (control: 37.21 ± 1.74 Hv; treated: 34.63 ± 1.70 Hv; p = 0.00) and Opalescence Quick (control: 45.82 ± 1.71 Hv; treated: 39.34 ± 1.94 Hv; p < 0.0001), whereas BlancOne Ultra+ showed no significant difference (control: 51.64 ± 1.59 HV; treated: 51.60 ± 2.34 Hv; p = 0.95). Conclusions: HP-based agents, particularly at higher concentrations, caused greater enamel alterations than CP-based products. While clinically relevant, the results should be interpreted cautiously due to in vitro limitations and natural enamel variability. Full article

Efforts to enhance the mechanical and physicochemical properties of conventional glass ionomer cement (GIC) are ongoing. This study aimed to evaluate the effect of incorporating varying concentrations of frankincense and myrrh liquids into conventional GIC on its microhardness and sealing ability. Frankincense and myrrh liquids were prepared by dissolving 25 g of each ground resin in 50 mL of distilled water at 60 °C and allowing the solutions to stand for 8 h. Five experimental groups were evaluated: Group A (conventional GIC), Group B (15% frankincense-modified GIC), Group C (25% frankincense-modified GIC), Group D (15% myrrh-modified GIC), and Group E (25% myrrh-modified GIC). Microhardness was evaluated using a Vickers hardness tester, and sealing ability was evaluated via interfacial gap measurements using scanning electron microscopy (SEM). SEM analysis revealed that all modified GIC groups exhibited significantly smaller interfacial gap sizes (Groups B–E: 6.1, 5.22, 5.9, and 5.34 µm, respectively) compared to conventional GIC (Group A: 6.88 µm). However, there were no statistically significant differences in microhardness among the groups (p > 0.5). The incorporation of 15% and 25% concentrations of frankincense or myrrh liquids into conventional GIC significantly improved sealing ability without compromising hardness. Full article

Background. Physicomechanical properties and clinical service of bulk-fill composites depend on their adequate polymerization and depth of cure. Some manufacturers claim that these composites can be adequately cured when used in bulks exceeding 4 mm. Objective. The aim of this study was to compare Vickers microhardness (VMH) and depth of cure (DOC) of six contemporary bulk-fill resin composites at depths of 4 mm and 6 mm. Material and methods. Six bulk-fill composites were evaluated in this study: 1. Tetric EvoCeram Bulk (Ivoclar Vivadent, Schaan, Liechtenstein), (TEC); 2. Filtek Bulk Fill Posterior (3M ESPE Dental Products Division, St. Paul, MN, USA), (FBF); 3. Filtek One Bulk Fill (3M ESPE Dental Products Division, St. Paul, MN, USA, (FOB); 4. SonicFill 2 (Kerr, Orange, CA, USA), (SF2); 5. Admira Fusion X-tra (Voco, GmbH, Cuxhaven, Germany), (AFX); 6. GrandioSO X-tra (Voco, GmbH, Cuxhaven, Germany), (GSX). The 18 specimens (3 of each composite) were prepared in split Teflon moulds of 4 mm diameter and 6 mm thickness. All composites were cured in standard mode for 20 s using LED LCU (D-Light Duo, RF-Pharmaceuticals Sarl, Geneva, Switzerland; 1200–1300 mW/cm). The VMH was measured using a digital Micro Hardness Tester Shimadzu (HMV-2T E, Shimadzu Corporation, Kyoto, Japan). A 50 g (0.5 N) load force was applied for 30 s. Each specimen was measured at five places selected by chance at each level (N = 15). The hardness ratio or DOC was calculated for all samples as the ratio of bottom and surface microhardness at levels of 4 and 6 mm. Data were analysed using one-way ANOVA and Tukey’s post hoc test. Results. Significant reduction in VMH was observed for all tested materials when comparing top surface and bottom (p < 0.01). The highest VMH was obtained for GSX and AFX, and the lowest for TEC. The results show that the degree of polymerization was adequate for all tested materials at a depth of 6 mm, since the hardness ratio exceeded 0.80 in all cases. The hardness ratio at 4 mm was high for all tested composites ranging from 0.91 for TEC to 0.98 for GSX. All composites showed adequate DOC at the bottom of the 6 mm bulk samples. However, the hardness ratio was the highest for Admira Fusion X-tra (0.96) and GrandioSO X-tra (0.97). Conclusions. All tested materials showed a significant decrease in microhardness from the top surface to the bottom. The DOC was adequate for all bulk-fill composites at a depth of 6 mm cured under standard mode for 20 s. All bulk-fill resin composites evaluated in this study can be used in bulk, up to 6 mm. Full article