Search Results (520)

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 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

Protective coatings are essential for extending the service life of components exposed to harsh conditions, such as pipes used in industrial systems, where wear and corrosion remain constant challenges. This study explores the development of a nano-sized TiO₂-reinforced electroless nickel-based ternary (Ni-W-P) alloy and composite coating on API X60 steel, a high-strength carbon steel pipe grade widely used in oil and gas pipelines, using an alkaline hypophosphite-reduced bath. The surface morphology, microstructure, elemental composition, structure, phase evolution, adhesion, and roughness of the coatings were analyzed using optical microscopy, FESEM, EDS, XRD, AFM, cross-cut tape test, and 3D profilometry. The tribological performance was evaluated via Vickers microhardness measurements and reciprocating wear tests conducted under dry conditions at a 5 N load. The TiO₂ nanoparticle-reinforced composite coating achieved a consistent thickness of approximately 24 µm and exhibited enhanced microhardness and reduced coefficient of friction (COF), although the addition of nanoparticles increased surface roughness (S_a). Annealing the electroless composites at 400 °C led to a significant improvement in their tribological properties, primarily owing to the grain growth, phase transformation, and Ni₃P crystallization. XRD analysis revealed phase evolution from an amorphous state to crystalline Ni₃P upon annealing. Both the alloy and composite coatings exhibited excellent adhesion performances. The combined effect of TiO₂ nanoparticles, tungsten, and Ni₃P crystallization greatly improved the wear resistance, with abrasive and adhesive wear identified as the dominant mechanisms, making these coatings well suited for high-wear applications. Full article

Background: Dental caries is a prevalent dental problem affecting primary and permanent teeth. Early demineralization of enamel lesions can be reversed through remineralization. Many studies have focused on caries prevention and disease progression arrest using silver diamine fluoride (SDF). No in vitro studies have compared the remineralization effects of different 38% SDF solutions on artificially demineralized enamel lesions. This study aimed to compare the remineralization potential of three commercial 38% silver diamine fluoride formulations on artificial enamel lesions in primary teeth using a pH cycling model. The hypothesis was as follows: different commercial SDF formulations would exhibit varying remineralization effects, as measured by surface microhardness, due to potential differences in their compositions. Materials and Methods: In this study, 75 primary molars were randomized into five groups (N = 15): I: baseline, II: SDF Riva Star Aqua^® 38%, III: Riva Star^® 38%, IV: SDF Advantage Arrest^® 38%, and V: control. Artificial caries were created by submerging teeth in 10 mL of demineralization solution (pH 4.5) for three days in a light-resistant container, ensuring distinct visual changes in the enamel as per the International Caries Detection and Assessment System (ICDAS level 2). After pH cycling, all samples underwent a standardized Vickers microhardness test (VMHT) with a 50 g load for 15 s. Data were analyzed using one-way ANOVA and Tukey’s post hoc test, with a significance level set at p ≤ 0.05. Results: The one-way ANOVA test indicated a significant difference in microhardness among the groups (SDF Riva Star Aqua, SDF Riva Star, and SDF Advantage Arrest), with an F-value of 167.73 and p < 0.001. The post hoc Scheffé test showed that SDF Riva Star Aqua and SDF Riva Star were not significantly different (p = 0.388). However, SDF Advantage Arrest had a significantly higher mean microhardness compared to both groups (p < 0.001). Overall, these results show that SDF Advantage Arrest leads to greater microhardness than SDF Riva Star Aqua or SDF Riva Star. Conclusions: SDF Advantage Arrest showed superior performance among the SDF-treated groups, significantly increasing microhardness compared to SDF Riva Star Aqua and SDF Riva Star. This suggests that SDF Advantage Arrest offers enhanced remineralization and structural strengthening, making it the most effective option for managing demineralized primary teeth. Future research should investigate the long-term performance and mechanisms of these treatments to optimize clinical protocols for preserving primary tooth integrity. 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

This study evaluated the physicochemical and morphological properties of tooth enamel in patients with caries-predisposing SNPs (rs4694075 in AMBN and rs2337359 in TUFT1 genes), based on the DMFT index. We included 40 of 120 individuals (aged 19–43), collecting stimulated saliva and 58 healthy teeth extracted for orthodontic/surgical reasons. Saliva DNA was genotyped. Enamel properties were assessed using Vickers microhardness, deposition thickness, and calcium content. Genotype and allele frequencies aligned with the literature. The TUFT1C/C genotype subgroup showed a significantly higher DMFT index (p = 0.03) compared to the T/T genotype, while AMBN showed no such correlation. Calcium content, microhardness, and enamel thickness were similar across all polymorphic variants of both genes. A statistically significant correlation (p = 0.003) was found between reduced enamel calcium content and a higher DMFT index. Despite existing literature on the subject, the studied SNPs did not reflect any correlation with morphological or physicochemical changes in enamel. The above results suggest that genetic variability identifies patients classified by dentists as being at higher risk of caries, even though these patients follow a non-cariogenic diet and adhere to a hygiene regime. As no structural or physicochemical changes in the enamel of this group were observed, the potential cause may be disturbances in the remineralisation mechanisms or enamel surface properties that promote biofilm adhesion in polymorphic patients. Intensive tooth calcification control algorithms using LIF and RVG, as well as remineralisation cycles to increase hydroxyapatite saturation with calcium phosphates and bioadhesive fluoride delivery systems for long-term biofilm control, are used to more effectively prevent or slow down the progression of caries. Full article

This study investigated the effects of color shade and curing time on the degree of conversion (DC) and microhardness of colored compomers. A total of 162 samples (81 for DC, 81 for microhardness) were prepared, with nine samples per color group (gold, blackberry, green, pink, orange, lemon, blue, silver) and for the control. Samples were subdivided into three polymerization subgroups (3 s/3200 mW/cm², 10 s/1000 mW/cm², 20 s/1000 mW/cm²). The DC was analyzed via fourier transform infrared spectroscopy (FTIR) and microhardness was measured using Vickers testing. Statistical analysis included two-way ANOVA and Spearman correlation (α = 0.05). The colored compomers demonstrated a significantly lower DC compared to the control group (p ≤ 0.001). Among the tested colors, green exhibited the lowest DC (33.3%), while orange showed the highest (51.0%). A significant difference in DC was observed across curing times (p = 0.005), with the 3 s and 20 s groups exhibiting significantly higher conversion rates than the 10 s group. Microhardness values exhibited significant variation depending on the color (p < 0.001). Gold compomers demonstrated the lowest microhardness, whereas silver compomers showed comparable performance with the control group (p = 0.154). A moderate correlation between DC and microhardness was observed overall (ρ = 0.42, p = 0.003). However, the observed relationships were color-dependent: orange displayed a strong positive correlation (ρ = 0.78), whereas pink revealed no meaningful association (ρ = −0.15). Color and curing time critically influence compomer performance. High-intensity short curing is viable for lighter colors, while darker colors require extended curing. Customized protocols are essential to optimize clinical outcomes in pediatric dentistry. 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

This study investigates the surface modification of Ti-6Al-4V alloy through the electrical discharge machining (EDM) process to improve its suitability for orthopedic and dental implant applications. The analysis focused on evaluating the morphological, wettability, roughness, hardness, and biocompatibility properties of the modified surfaces. Samples were subjected to different dielectric fluids and polarities during EDM. Subsequently, optical microscopy, roughness measurements, Vickers microhardness, contact angle tests, and in vitro cytotoxicity assays were performed. The results demonstrated that EDM processing led to the formation of distinct layers on the sample surfaces, with surface roughness increasing under negative polarity by up to ~304% in Ra and 305% in Rz. Additionally, wettability measurements indicated that the modified surfaces presented a lower water contact angle, which suggests enhanced hydrophilicity. Moreover, the modified samples showed a significant increase in Vickers microhardness, with the highest value reaching 1520 HV in the recast layer, indicating improvements in the mechanical properties. According to ISO 10993-5, all treated samples were classified as non-cytotoxic, presenting RGR values above 75%, similar to the untreated Ti-6Al-4V alloy. Therefore, it is concluded that surface modification through the EDM process has the potential to enhance the properties and safety of biomedical implants made with this alloy. Full article

The aim of the current study is to investigate the mechanical properties and ballistic performance of HARDOX 450 steel for defense applications in different conditions: uncoated, alumina-coated, and LINE X polyurea-coated. Tensile tests and Vickers microhardness measurements were conducted, along with fracture surface analysis using stereomicroscopy, scanning electron microscopy, and computed tomography. Experimental results showed that uncoated HARDOX 450 steel exhibited the highest strength and hardness, with ductile fracture features. Polyurea-coated HARDOX 450 steel samples retained good mechanical properties and demonstrated effective ballistic protection, including the containment of fragments. In contrast, alumina-coated HARDOX 450 steel samples exhibited reduced strength and ballistic resistance, attributed to the microstructural changes in HARDOX 450 steel caused by the high-temperature deposition process of alumina. Numerical simulations performed with the 5.56 × 45 mm bullet used in the simulation, along with its ballistic impact interaction with the Hardox 450 target model, aligned well with experimental ballistic impact results for all the samples. Overall, LINE X polyurea coating on HARDOX 450 steel proved to be the more suitable coating for applications requiring a balance of mechanical strength and ballistic impact resistance. Full article