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The introduction of glass matrix ceramics in dental restorations has revolutionized dental aesthetics. A key challenge in the development of dental glass ceramics is achieving nanocrystalline glass ceramics with superior mechanical properties without compromising translucency. In this study, ZrO2-SiO2 glass ceramics doped with amorphous Al2O3 were investigated to address these requirements. The results indicate that the segregation of Al3+ at the grain boundaries of ZrO2 crystallites and the nano-domains of amorphous Al2O3 significantly influences the microstructure, including the grain size and stabilization of tetragonal ZrO2, as well as the translucency and mechanical properties. The composition with 10 mol% Al2O3 exhibits the highest toughness of 8.05 MPa center dot m1/2 while maintaining excellent translucency. Moreover, the composition with 5 mol% Al2O3 demonstrates lower translucency but achieves a high flexural strength of 960 MPa. Overall, the mechanical properties of these translucent glass matrix ceramics surpass those of commercially available dental glass ceramics, highlighting their potential for dental restoration applications.

Periodontal disease caused by bacterial accumulation is a critical issue affecting the longevity of related materials and implants. Enhancing the antibacterial properties of glass ceramics remains a significant challenge. Due to their excellent mechanical properties, ZrO2-SiO2 glass ceramics have shown great potential in dental restoration. Here, to endow ZrO2-SiO2 glass ceramics with antibacterial properties, nitrogen ion implantation was performed to modify their surfaces. The effects of nitrogen fluence on the microstructural, mechanical and antibacterial properties were investigated. The results showed that phase transformation from tetragonal to monoclinic phase occurred after ion implantation. Surface hardening was observed in the sample under the low fluence ion implantation. Partial amorphization and blistering were observed at the highest fluence of 6.0  1017 ions/cm2. XPS analysis revealed that the implanted nitrogen ions mainly form O-Zr-N, N-Si-O and Si-N bonds. Staphylococcus aureus testing showed that the antibacterial properties of ZrO2-SiO2 glass ceramics can be enhanced after implantation, which may be attributed to the formation of reactive nitrogen species. The results show that nitrogen implantation can enhance the antibacterial properties of ZrO2-SiO2 glass ceramics without compromising their mechanical properties.

Solid-state reaction (SSR) is frequently used to fabricate bulk high-entropy ceramics (HECs). However, a high temperature and a long dwelling time are typically required to allow the occurrence of SSR. Meanwhile, conventional HECs were typically composed of single-phase solid solution with micrograins. It is of great interest to develop nanocrystalline dual-phase HECs under mild conditions. Here, we fabricated entropy-mediated crystalline-amorphous dual-phase ceramic nanocomposites, and the fabrication process showed significantly higher energy and time efficiency than the conventional SSR. The nanocomposites were composed of entropy-mediated nanoparticles (EM-NPs) embedded in an amorphous SiO₂ matrix. The constituent elements were homogeneously distributed in the EM-NPs at the atomic level. The EM-NPs were dislocations-free but with lattice strain, and they showed a strong coarsening tendency during annealing. The nanocomposites showed a significant solid solution hardening effect. The reported results would provide useful guidance to fabricate nanocrystalline HECs with crystalline-amorphous dual-phase microstructure. Formation mechanism of traditional single-phase HECs and the new crystalline-amorphous dual-phase HEC. image

Zircon (ZrSiO4) ceramics have been widely used in many fields due to their excellent physical and chemical properties. However, ZrSiO4 ceramics typically possess moderately low mechanical properties, which hinders their wider application. Meanwhile, elevated temperatures (similar to 1500 degrees C) are required to obtain high-purity synthetic ZrSiO4 ceramics, which is time- and energy-consuming. In the present study, we prepared mechanically robust ZrSiO4 ceramics at low temperature (similar to 1170 degrees C) with a low doping level of Mn dopant (<2 mol%). The ZrSiO4 ceramic processed by hot isostatic pressing with .5 mol% Mn dopant achieved the highest flexural strength (512 MPa), elastic modulus (341 GPa), and nanohardness (20.8 GPa). These values are significantly higher than conventional ZrSiO4 ceramics. The strengthening mechanisms of the prepared ZrSiO4 ceramics were attributed to the formation of homogeneously-distributed nanopores due to incomplete densification and submicron ZrSiO4 grains (similar to 300 nm). The nanopores avoided stress concentration and deflected microcracks during loading, and the submicron ZrSiO4 grains endowed the ZrSiO4 ceramics with grain refinement strengthening. The results reported in this study would offer guidance to fabricate mechanically robust ZrSiO4 ceramics at low temperatures with a low doping level of dopant.

Silicon nitride-based bioceramics have been investigated for biomedical applications due to their good thermo-mechanical, tribological and antibacterial properties. However, biological properties, such as bioactivity that promotes the interaction with tissue, are also important. Silicon dioxide has been found to promote bioactivity. With the aim of combining both advantages, a new Si₃N₄-SiO₂ glass ceramic was developed. Three different compositions were synthesized and sintered by spark plasma sintering. The results showed that β-Si₃N₄ crystalline is well distributed in the SiO₂ matrix. 70SiN samples exhibited the highest mechanical properties with a flexural strength of 452 ± 33 MPa and a toughness of 6.4 ± 0.5 MPa∙m^1/2. 50SiN samples exhibited the best bacteriostatic effect due to the synergistic effect of surface chemistry and topography. Apatite was observed on the surfaces of all groups. This study shows that the newly developed Si₃N₄-SiO₂ glass ceramics exhibit promising mechanical and biological properties for biomedical applications.

Injectable poly (methyl methacrylate) (PMMA) bone cements are widely used in orthopaedics to stabilize fractures and for implant fixation. However, bacterial attachment to bone cements leads to significant complications that can create a need for implant revision. Common attempts at reducing bacterial attachment are through the addition of antibiotics or antibacterial nanometals to the bone cements. However, clinical data is inconclusive on the effectiveness of antibiotic-loaded bone cements and a negative osteoblastic response has been reported for certain additive concentrations. There is therefore a need for an additive that can positively affect osteoblastic behaviour while inhibiting bacterial attachment. Silicon nitride (Si3N4) could be such an additive, with initial studies showing promise in achieving antipathogenic properties. The aim of this study was hence to investigate the possibility of creating a bone cement that can support osteoblast growth while reducing bacterial attachment by introducing silicon nitride powders into an injectable PMMA cement. To this end, commercially available bone cements were doped with 5%, 10% and 20% weight/weight (w/w) of Si3N4. Their mechanical properties were examined through compression testing and their radiopacity was evaluated through fluoroscopy imaging. The samples that fulfilled compressive strength requirements had their biological properties tested using Staphylococcus epidermidis bacteria for antibacterial properties and MC3T3-E1 preosteoblasts for the examination of cytotoxicity. Bone cements that were doped with up to 20% w/w Si3N4 were radiopaque (only 13% reduction in optical density compared to radiopaque controls) and retained their compressive strength (85.35 ± 2.1 MPa compared to 83.4 ± 1.9 MPa for the commercial cements), while significantly reducing bacterial attachment by more than 90% compared to commercial cements and achieving a similar level of preosteoblast metabolic activity. This study supports further evaluation of Si3N4 as an additive to injectable bone cements as a way to create mechanically stable, radiopaque, bacteriostatic bone cements that could improve osteointegration.

Silica-based glass ceramics have been extensively used in biomedical applications due to their superior biocompatibility and controllable properties. However, their low mechanical strength limits their application. This could be addressed by optimizing the crystalline phase which determines their final properties. Silicon nitride has attracted attention due to its combination of good mechanical and biological properties. Therefore, to combine the advantage of silica-based glass and silicon nitride ceramic, this study developed a silicon nitridesilicon dioxide (Si3N4-SiO2) glass ceramics. The effects of spark plasma sintering parameters on the structural and mechanical properties of Si3N4-SiO2 glass ceramics were investigated. Full densification was reached at a sintering temperature of 1300 degrees C, a holding time of 10 min and an applied pressure of 80 MPa (relative density = 99.19 %). No silicon oxynitride (Si2N2O) crystalline phase was formed in the sintered glass ceramics, as confirmed by XRD. The interface between the (3-Si3N4 crystalline and amorphous SiO2 was investigated by HRTEM, and the results indicated that an amorphous interfacial oxide was formed at the interface. The mechanical properties increased with increasing sintering temperature, as a result of the increased density. The Si3N4-SiO2 glass ceramics sintered at 1500 degrees C exhibited the highest value of toughness and flexural strength, at 4.6 +/- 0.28 MPa m1/2 and 360 +/- 27 MPa. The indentation cracks observed by SEM showed that the large (3-Si3N4 grains promoted crack deflection, while the equiaxed Si3N4 grains with a lower aspect ratio led to transgranular fracture. The mechanical properties of these Si3N4-SiO2 glass ceramics are comparable to commercial glass ceramics, indicating their promising aspects in biomedical applications.

Calcium phosphate crystals were synthesized via chemical precipitation with strontium (Sr) ionic doping, and starting solutions with at.% Sr 19 % (A), 40 % (B), and 53 % (C) in an acid environment (pH 6.0), resulting in the crystal without Sr with plate morphologies, sample A: Sr similar to 7.8 % and Ca similar to 92,2 % with plate+petaloid crystals, sample B showed two morphological groups: Sr similar to 12,5 % and Ca similar to 87,5 % (B-1) with plate+petaloid crystals and with Sr similar to 32,5 % and Ca similar to 67,9 % (B-2) with petaloid+pseudo-hexagons crystals, and sample C: Sr similar to 48,8 % and Ca similar to 51,2 % with higher symmetric hexagonal crystals. The samples were characterized by X-ray diffraction, SEM, and EDS. The calcium phosphate crystallographic phase family (Ca-P) includes brushite (DCPD), monetite (DCPA), and hydroxyapatite (HAP) surrounding the nucleating crystals that had plate, petaloid, and pseudo-hexagonal or hexagonal morphologies. Crystal growth nucleation by Sr inclusion ions induces preferential orientation with overlapping layer plates forming pseudo-hexagonal or hexagonal crystals with high symmetry when there is ion equilibrium between Ca and Sr. This result indicates biomimicry crystals found in nature (abalone gastropod shell), resulting in promising materials for further advances in mechanical properties and performance.

This paper describes novel and innovative amorphous calcium magnesium fluoride phosphate (ACMFP) core-shell microparticles that may be applied in preventive dentistry for the prevention of caries and the treatment of dentin hypersensitivity. The particles can be synthesized with varied fluoride content, up to approximately 6 wt%, without any observable differences in morphology or crystallinity. Fluoride release from the particles is correlated to the fluoride content, and the particles are readily converted to fluoride-substituted hydroxyapatite or fluorapatite in a simulated saliva solution. The remineralization and dentin tubule occlusion potential of the particles was evaluated in vitro on acid-etched dentin specimens, and treatment with the ACMFP particles resulted in complete tubule occlusion and the formation of a dense mineralization layer. The acid resistance of the mineralization layer was improved compared to treatment with analogous particles without fluoride inclusion. A cross-sectional evaluation of dentin specimens after treatment revealed the formation of high aspect ratio fluorapatite crystals and poorly crystalline hydroxyapatite, respectively. The particles of the current study provide a single source vehicle of readily available calcium, phosphate, and fluoride ions for the potential remineralization of carious lesions as well as exposed dentin tubules for the reduction of hypersensitivity.

Hollow microstructured-and nanostructured-materials (also known as core-shell particles) have got great attention as advanced materials due to their fascinating physicochemical properties and favourable application prospects in many fields. In recent years, a variety of synthesis strategies have been explored to fabricate core-shell particles with different morphologies, compositions, microstructures, and thereby versatile functionalities. Among the synthesis strategies, soft-templating with the usage of nanobubbles is a feasible and effective one. Many inorganic core-shell particles have been prepared by using nanobubbles as a template. Nevertheless, studies in this field have not been reviewed comprehensively yet. Herein, the paper firstly reviewed several critical aspects of nanobubbles, such as the formation methods, stability and stabilization strategies of nano-bubbles; Secondly, characteristics of core-shell particles prepared by using nanobubbles soft template were summarized, including formation mechanisms, morphologies, etc.; Lastly, concerns regarding nanobubbles as soft templates were also briefly discussed.