Atomic and vibrational origins of mechanical toughness in bioactive cement during setting

Non-invasive detection of hazardous materials with a thermal-to-epithermal neutron station: a feasibility study towards practical application

The growing scale of the devastation that even a single terrorist attack can cause requires more effective methods for the detection of hazardous materials. In particular, there are no solutions for effectively monitoring threats at sea, both for the off-shore infrastructure and ports. Currently, state-of-the-art detection methods determine the density distribution and the shapes of tested subjects but only allow for a limited degree of substance identification. This work aims to present a feasibility study of the possible usage of several methods available on the thermal-to-epithermal neutron station, VESUVIO, at the ISIS neutron and muon spallation source, UK, for the detection of hazardous materials. To this end, we present the results of a series of experiments performed concurrently employing neutron transmission and Compton scattering using melamine, a commonly used explosive surrogate, in order to determine its signal characteristics and limits of detection and quantitation. The experiments are supported by first-principles modelling, providing detailed scrutiny of the material structure and the nuclear dynamics behind the neutron scattering observables.

Applicability of terahertz spectroscopy in dentistry: a scoping review

OBJECTIVE

This study aimed to analyze the scope, nature, and extent of the applicability of terahertz (THz) spectroscopy in dentistry.

STUDY DESIGN

A scoping review was conducted following the 5-step methodology of Arksey and O'Malley, the PRISMA-ScR checklist, and the Evidence Synthesis Manual of the Joanna Briggs Institute. Electronic literature searches were performed in the PubMed/MEDLINE, Scopus, and Cochrane Library databases, including full-text articles with no specific publication period. The following research question was formulated: "What are the applications of THz spectroscopy in the field of dentistry?"

RESULTS

Seventeen laboratory studies were identified, detailing oral and dental applications of THz. In restorative dentistry, 8 investigations sought to identify the properties of human and animal dental tissues and differentiate between healthy and decayed tissue. In oral pathology, 5 articles analyzed the identification of cancer cells in comparison to the identification of these cells in histological or cytological analysis. In biomaterials, 4 papers studied the changes in properties of restorative materials and effects on polymerization.

CONCLUSION

While the potential for early diagnosis using THz spectroscopy in dentistry is evident, our findings underscore its limitations. The studies were exclusively conducted in vitro, emphasizing the need for innovative clinical research using intraoral devices. Bridging this gap is essential to unlock the full potential of this noninvasive technology for early diagnosis and informed clinical decision-making.

Clinical Effectiveness of Ion-Releasing Restorations versus Composite Restorations in Dental Restorations: Systematic Review and Meta-Analysis

BACKGROUND

To compare the clinical effectiveness of ion-releasing restorations (IRR) vs. composite resin (CR) in dental restorations.

METHODS

A systematic search was carried out from articles published until January 2024, in the biomedical databases: PubMed, Cochrane Library, Scielo, Scopus, Web of Science and Google Scholar. Randomized clinical trials were included, with a follow-up time greater than or equal to 1 year, without time and language limits and which reported the clinical effect of IRR compared to CR in dental restorations. The RoB 2.0 tool was used to assess the risk of bias of the included studies and the GRADEPro GDT tool was used to assess the quality of evidence and the strength of recommendation of the results.

RESULTS

The search yielded a total of 1109 articles. After excluding those that did not meet the selection criteria, 29 articles remained for the quantitative synthesis. The analysis found no statistically significant difference when comparing the dental restorations with IRRs or CRs.

CONCLUSION

The literature reviewed suggests that there are no differences between the IRRs and CRs in dental restorations.

Investigation of the Dynamic Behaviour of H2 and D2 in a Kinetic Quantum Sieving System

Porous organic cages (POCs) are nanoporous materials composed of discrete molecular units that have uniformly distributed functional pores. The intrinsic porosity of these structures can be tuned accurately at the nanoscale by altering the size of the porous molecules, particularly to an optimal size of 3.6 Å, to harness the kinetic quantum sieving effect. Previous research on POCs for isotope separation has predominantly centered on differences in the quantities of adsorbed isotopes. However, nuclear quantum effects also contribute significantly to the dynamics of the sorption process, offering additional opportunities for separating H2 and D2 at practical operational temperatures. In this study, our investigations into H2 and D2 sorption on POC samples revealed a higher uptake of D2 compared to that of H2 under identical conditions. We employed quasi-elastic neutron scattering to study the diffusion processes of D2 and H2 in the POCs across various temperature and pressure ranges. Additionally, neutron Compton scattering was utilized to measure the values of the nuclear zero-point energy of individual isotopic species in D2 and H2. The results indicate that the diffusion coefficient of D2 is approximately one-sixth that of H2 in the POC due to the nuclear quantum effect. Furthermore, the results reveal that at 77 K, D2 has longer residence times compared to H2 when moving from pore to pore. Consequently, using the kinetic difference of H2 and D2 in a porous POC system enables hydrogen isotope separation using a temperature or pressure swing system at around liquid nitrogen temperatures.

Influence of Novel SrTiO3/MnO2 Hybrid Nanoparticles on Poly(methyl methacrylate) Thermal and Mechanical Behavior

While dental poly methyl methacrylate(PMMA) possesses distinctive qualities such as ease of fabrication, cost-effectiveness, and favorable physical and mechanical properties, these attributes alone are inadequate to impart the necessary impact strength and hardness. Consequently, pure PMMA is less suitable for dental applications. This research focused on the incorporation of Strontium titanate (SrTiO3-STO) and hybrid filler STO/Manganese oxide (MnO2) to improve impact resistance and hardness. The potential of STO in reinforcing PMMA is poorly investigated, while hybrid filler STO/MnO2 has not been presented yet. Differential scanning calorimetry is conducted in order to investigate the agglomeration influence on the PMMA glass transition temperature (Tg), as well as the leaching of residual monomer and volatile additives that could pose a threat to human health. It has been determined that agglomeration with 1 wt% loading had no influence on Tg, while the first scan revealed differences in evaporation of small molecules, in favor of composite PMMA-STO/MnO2, which showed the trapping potential of volatiles. Investigations of mechanical properties have revealed the significant influence of hybrid STO/MnO2 filler on microhardness and total absorbed impact energy, which were increased by 89.9% and 145.4%, respectively. Results presented in this study revealed the reinforcing potential of hybrid nanoparticles that could find application in other polymers as well.

A Second Glass Transition Observed in Single-Component Homogeneous Liquids Due to Intramolecular Vitrification

On supercooling a liquid, the viscosity rises rapidly until at the glass transition it vitrifies into an amorphous solid accompanied by a steep drop in the heat capacity. Therefore, a pure homogeneous liquid is not expected to display more than one glass transition. Here we show that a family of single-component homogeneous molecular liquids, titanium tetraalkoxides, exhibit two calorimetric glass transitions of comparable magnitude, one of which is the conventional glass transition associated with dynamic arrest of the bulk liquid properties, while the other is associated with the freezing out of intramolecular degrees of freedom. Such intramolecular vitrification is likely to be found in molecules in which low-frequency terahertz intramolecular motion is coupled to the surrounding liquid. These results imply that intramolecular barrier-crossing processes, typically associated with chemical reactivity, do not necessarily follow the Arrhenius law but may freeze out at a finite temperature.

Effect of Storage Temperature on Selected Strength Parameters of Dual-Cured Composite Cements

Direct restorations are currently the most popular restorations used in dental prosthodontics. Due to the increased requirements for materials used in the fabrication of fixed restorations, there is a need for evaluation of strength parameters of these materials, including dental cements. The present study investigated the change in selected strength parameters of four dual-cured composite cements as a function of storage temperature. The following were investigated: three-point flexural strength (FS), flexural modulus in bending (FM), diametral tensile strength (DTS) and Vickers hardness (HV). Four dual-cured composite cements were tested, i.e., Multilink Automix (Ivoclar Vivadent), seT PP (SDI), MaxCem (Kerr), and Bifix Hybrid Abutment (VOCO). Each of the tested cements was stored for 7 days at one of the selected temperatures: 8 °C, 15 °C, 25 °C, or 35 °C, before the samples were made. Strength properties (DTS, FS) are not strongly dependent on the storage temperature in the range of 8-35 °C. Some statistical differences were observed between the hardness of MaxCem and Multilink Automix storage in various temperatures. FS and FM were lowest for Bifix Hybrid Abutment, MaxCem and Multilink Automix storage at 25 °C, and highest for Bifix Hybrid Abutment, MaxCem, and seT PP stored in 35 °C. The cement with the highest filler content (70% by weight) showed the highest FS and HV.

Organelle Imaging with Terahertz Scattering-Type Scanning Near-Field Microscope

Organelles play core roles in living beings, especially in internal cellular actions, but the hidden information inside the cell is difficult to extract in a label-free manner. In recent years, terahertz (THz) imaging has attracted much attention because of its penetration depth in nonpolar and non-metallic materials and label-free, non-invasive and non-ionizing ability to obtain the interior information of bio-samples. However, the low spatial resolution of traditional far-field THz imaging systems and the weak dielectric contrast of biological samples hinder the application of this technology in the biological field. In this paper, we used an advanced THz scattering near-field imaging method for detecting chloroplasts on gold substrate with nano-flatness combined with an image processing method to remove the background noise and successfully obtained the subcellular-grade internal reticular structure from an Arabidopsis chloroplast THz image. In contrast, little inner information could be observed in the tea chloroplast in similar THz images. Further, transmission electron microscopy (TEM) and mass spectroscopy (MS) were also used to detect structural and chemical differences inside the chloroplasts of Arabidopsis and tea plants. The preliminary results suggested that the interspecific different THz information is related to the internal spatial structures of chloroplasts and metabolite differences among species. Therefore, this method could open a new way to study the structure of individual organelles.

CO2-mineralization and carbonation reactor rig: Design and validation for in situ neutron scattering experiments-Engineering and lessons learned

CO2 mineralization via aqueous Mg/Ca/Na-carbonate (MgCO3/CaCO3/Na2CO3) formation represents a huge opportunity for the utilization of captured CO2. However, large-scale mineralization is hindered by slow kinetics due to the highly hydrated character of the cations in aqueous solutions (Mg2+ in particular). Reaction conditions can be optimized to accelerate carbonation kinetics, for example, by the inclusion of additives that promote competitive dehydration of Mg2+ and subsequent agglomeration, nucleation, and crystallization. For tracking mineralization and these reaction steps, neutron scattering presents unprecedented advantages over traditional techniques for time-resolved in situ measurements. However, a setup providing continuous solution circulation to ensure reactant system homogeneity for industrially relevant CO2-mineralization is currently not available for use on neutron beamlines. We, therefore, undertook the design, construction, testing and implementation of such a self-contained reactor rig for use on selected neutron beamlines at the ISIS Neutron and Muon Source (Harwell, UK). The design ensured robust attachment via suspension from the covering Tomkinson flange to stabilize the reactor assembly and all fittings (~25 kg), as well as facilitating precise alignment of the entire reactor and sample (test) cell with respect to beam dimension and direction. The assembly successfully accomplished the principal tasks of providing a continuous flow of the reaction mixture (~500 mL) for homogeneity, quantitative control of CO2 flux into the mixture, and temperature and pressure regulation throughout the reaction and measurements. The design is discussed, with emphasis placed on the reactor, including its geometry, components, and all technical specifications. Descriptions of the off-beamline bench tests, safety, and functionality, as well as the installation on beamlines and trial experimental procedure, are provided, together with representative raw neutron scattering results.

Effect of Biosilicate® Addition on Physical-Mechanical and Biological Properties of Dental Glass Ionomer Cements

This study investigated the influence of incorporating Biosilicate^® on the physico-mechanical and biological properties of glass ionomer cement (GIC). This bioactive glass ceramic (23.75% Na₂O, 23.75% CaO, 48.5% SiO₂, and 4% P₂O₅) was incorporated by weight (5%, 10%, or 15%) into commercially available GICs (Maxxion R and Fuji IX GP). Surface characterization was made by SEM (n = 3), EDS (n = 3), and FTIR (n = 1). The setting and working (S/W time) times (n = 3) and compressive strength (CS) were analyzed (n = 10) according to ISO 9917-1:2007. The ion release (n = 6) was determined and quantified by ICP OES and by UV-Vis for Ca, Na, Al, Si, P, and F. To verify cell cytotoxicity, stem cells from the apical papilla (SCAP) were exposed to eluates (n = 3, at a ratio of 1.8 cm²/mL) and analyzed 24 h post-exposure. Antimicrobial activity against Streptococcus mutans (ATCC 25175, NCTC 10449) was analyzed by direct contact for 2 h (n = 5). The data were submitted for normality and lognormality testing. One-way ANOVA and Tukey's test were applied for the working and setting time, compressive strength, and ion release data. Data from cytotoxicity and antimicrobial activity were submitted for Kruskal-Wallis' testing and Dunn's post hoc test (α = 0.05). Among all experimental groups, only those with 5% (wt) of Biosilicate^® showed better surface quality. Only M5% showed a comparable W/S time to the original material (p = 0.7254 and p = 0.5912). CS was maintained for all Maxxion R groups (p > 0.0001) and declined for Fuji IX experimental groups (p < 0.0001). The Na, Si, P, and F ions released were significantly increased for all Maxxion R and Fuji IX groups (p < 0.0001). Cytotoxicity was increased only for Maxxion R with 5% and 10% of Biosilicate^®. A higher inhibition of S. mutans growth was observed for Maxxion R with 5% of Biosilicate^® (less than 100 CFU/mL), followed by Maxxion R with 10% of Biosilicate^® (p = 0.0053) and Maxxion R without the glass ceramic (p = 0.0093). Maxxion R and Fuji IX presented different behaviors regarding Biosilicate^® incorporation. The impacts on physico-mechanical and biological properties were different depending on the GIC, but therapeutic ion release was increased for both materials.

Brittle-to-ductile transition and theoretical strength in a metal-organic framework glass

Metal-organic framework (MOF) glasses, a new type of melt-quenched glass, show great promise to deal with the alleviation of greenhouse effects, energy storage and conversion. However, the mechanical behavior of MOF glasses, which is of critical importance given the need for long-term stability, is not well understood. Using both micro- and nanoscale loadings, we find that pillars of a zeolitic imidazolate framework (ZIF) glass have a compressive strength falling within the theoretical strength limit of ≥E/10, a value which is thought to be unreachable in amorphous materials. Pillars with a diameter larger than 500 nm exhibited brittle failure with deformation mechanisms including shear bands and nearly vertical cracks, while pillars with a diameter below 500 nm could carry large plastic strains of ≥20% in a ductile manner with enhanced strength. We report this room-temperature brittle-to-ductile transition in ZIF-62 glass for the first time and demonstrate that theoretical strength and large ductility can be simultaneously achieved in ZIF-62 glass at the nanoscale. Large-scale molecular dynamics simulations have identified that microstructural densification and atomistic rearrangement, i.e., breaking and reconnection of inter-atomistic bonds, were responsible for the exceptional ductility. The insights gained from this study provide a way to manufacture ultra-strong and ductile MOF glasses and may facilitate their processing toward real-world applications.

Teeth Restored with Bulk–Fill Composites and Conventional Resin Composites; Investigation of Stress Distribution and Fracture Lifespan on Enamel, Dentin, and Restorative Materials via Three-Dimensional Finite Element Analysis

Objectives: the aim of this study was to examine the stress distribution of enamel, dentin, and restorative materials in sound first molar teeth with restored cavities with conventional resin composites and bulk–fill composites, as well as to determine their fracture lifetimes by using the three-dimensional finite element stress analysis method. Materials and Methods: an extracted sound number 26 tooth was scanned with a dental tomography device and recorded. Images were obtained as dicom files, and these files were transferred to the Mimics 12.00 program. In this program, different masks were created for each tooth tissue, and the density thresholds were adjusted manually to create a three-dimensional image of the tooth, and these were converted to a STL file. The obtained STL files were transferred to the Geomagic Design X program, and some necessary adjustments, such as smoothing, were made, and STP files were created. Cavity preparation and adhesive material layers were created by transferring STP files to the Solidworks program. Finally, a FE model was created in the ABAQUS program, and stress distributions were analyzed. Results: when the bulk–fill composite and conventional resin composite materials were used in the restoration of the cavity, the structures that were exposed to the most stress as a result of occlusal forces on the tooth were enamel, dentin, restorative material, and adhesive material. When the bulk–fill composite material was used in restoration, while the restorative material had the longest fracture life as a result of stresses, the enamel tissue had the shortest fracture life. When the conventional resin composite material was used as the restorative material, it had the longest fracture life, followed by dentin and enamel. Conclusion: when the bulk–fill composite material was used instead of the conventional resin composite material in the cavity, the stress values on enamel, dentin, and adhesive material increased as a result of occlusal forces, while the amount of stress on the restorative material decreased. In the fracture analysis, when the bulk–fill composite material was used instead of the conventional resin composite material, a decrease in the number of cycles required for the fracture of enamel, dentin, and restorative materials was observed as a result of the forces generated in the oral cavity.

Triple-functional bone adhesive with enhanced internal fixation, bacteriostasis and osteoinductive properties for open fracture repair

At present, effective fixation and anti-infection implant materials represent the mainstay for the treatment of open fractures. However, external fixation can cause nail tract infections and is ineffective for fixing small fracture fragments. Moreover, closed reduction and internal fixation during the early stage of injury can lead to potential bone infection, conducive to bone nonunion and delayed healing. Herein, we designed a bone adhesive with anti-infection, osteogenic and bone adhesion fixation properties to promote reduction and fixation of open fractures and subsequent soft tissue repair. It was prepared by the reaction of gelatin (Gel) and oxidized starch (OS) with vancomycin (VAN)-loaded mesoporous bioactive glass nanoparticles (MBGNs) covalently cross-linked with Schiff bases. Characterization and adhesion experiments were conducted to validate the successful preparation of the Gel-OS/VAN@MBGNs (GOVM-gel) adhesive. Meanwhile, in vitro cell experiments demonstrated its good antibacterial effects with the ability to stimulate bone marrow mesenchymal stem cell (BMSCs) proliferation, upregulate the expression of alkaline phosphatase (ALP) and osteogenic proteins (RunX2 and OPN) and enhance the deposition of calcium nodules. Additionally, we established a rat skull fracture model and a subcutaneous infection model. The histological analysis showed that bone adhesive enhanced osteogenesis, and in vivo experiments demonstrated that the number of inflammatory cells and bacteria was significantly reduced. Overall, the adhesive could promote early reduction of fractures and antibacterial and osteogenic effects, providing the foothold for treatment of this patient population.

[Research Progress in the Application of Terahertz Spectroscopy and Imaging Technology in Stomatology]

Terahertz waves, the electromagnetic waves in the range of 0.1 to 10 THz, has the advantages of being damage-free, causing no ionizing radiation injury, and being capable of recognizing the fingerprint spectrum of molecular characteristics, thus holding encouraging prospects for wide applications in the field of biomedicine. Terahertz spectrum can be used to identify and characterize biological structures of different levels, from biomolecules such as proteins to cells and tissues, through the spectral signals and/or restored images of the samples. Herein, we summarized the current stomatogical application of and research progress in terahertz spectroscopy and imaging in dentistry, reported the latest research findings, strengths and limitations from three perspectives, tooth anatomical structure, the extent of caries progression, and oral soft tissue, and suggested possible directions for future exploration.

Damping Behaviour and Mechanical Properties of Restorative Materials for Primary Teeth

The energy dissipation capacity and damping ability of restorative materials used to restore deciduous teeth were assessed compared to common mechanical properties. Mechanical properties (flexural strength, modulus of elasticity, modulus of toughness) for Compoglass F, Dyract eXtra, SDR flow, Tetric Evo Ceram, Tetric Evo Ceram Bulk Fill, and Venus Diamond were determined using a 4-point bending test. Vickers hardness and Martens hardness, together with its plastic index (η_ITdis), were recorded using instrumented indentation testing. Leeb hardness (HLD) and its deduced energy dissipation data (HLD_dis) were likewise determined. The reliability of materials was assessed using Weibull analysis. For common mechanical properties, Venus Diamond always exhibited the significantly highest results and SDR flow the lowest, except for flexural strength. Independently determined damping parameters (modulus of toughness, HLD_dis, η_ITdis) invariably disclosed the highest values for SDR flow. Composite materials, including SDR flow, showed markedly higher reliabilities (Weibull modulus) than Compoglass F and Dyract eXtra. SDR flow showed pronounced energy dissipation and damping characteristics, making it the most promising material for a biomimetic restoration of viscoelastic dentin structures in deciduous teeth. Future developments in composite technology should implement improved resin structures that facilitate damping effects in artificial restorative materials.

Unveiling Non-isothermal Crystallization of CaO-Al2O3-B2O3-Na2O-Li2O-SiO2 Glass via In Situ X-ray Scattering and Raman Spectroscopy

The crystallization in glasses is a paradoxical phenomenon and scarcely investigated. This work explores the non-isothermal crystallization of a multicomponent alumino-borosilicate glass via in situ high-energy synchrotron X-ray diffraction, atomic pair distribution function, and Raman spectroscopy. Results depict the crystallization sequence as Ca₃Al₂O₆ and CaSiO₄ followed by LiAlO₂ with the final compound formation of Ca₃B₂O₆. These precipitations occur in a narrow temperature range and overlap, resulting in a single exothermic peak in the differential scanning calorimetry thermogram. The concurrent nucleation of Ca₃Al₂O₆ and CaSiO₄ is intermediated by their corresponding hydrates, which have dominantly short-range order. Moreover, the crystallization of LiAlO₂ and Ca₃B₂O₆ is strongly linked with the changes of structural units during the incubation stage in non-isothermal heating. These findings clarify the crystallization of multicomponent glass, which have been inferred from ex situ reports but never evidenced via in situ studies.

This work explores the non-isothermal crystallization behaviors of multicomponent alumino-borosilicate glasses via in situ high-energy synchrotron X-ray diffraction, atomic pair distribution function, and Raman spectroscopy.

Ion release and hydroxyapatite precipitation of resin composites functionalized with two types of bioactive glass

OBJECTIVES

To prepare experimental composites with bioactive glass (BG) and investigate their release of calcium (Ca), phosphate (PO₄), and fluoride (F), as well as pH changes and apatite precipitation after immersion.

METHODS

Experimental composites were prepared with 0, 10, or 20 wt% of either BG 45S5 or a customized low-Na F-containing BG. Three commercial ion-releasing materials were used for reference. Material specimens were immersed in lactic acid (pH = 4.0) and artificial saliva (pH = 6.4). Ion concentrations (atomic absorption spectrometry for Ca, UV-vis spectrometry for PO₄, and ion-selective electrode for F) and pH were measured after 4, 8, 12, 16, 20, 24, 28, and 32 days. After immersion, composite specimens were analyzed using scanning electron microscopy (SEM) and Fourier-transform infrared (FTIR) spectroscopy.

RESULTS

Material-dependent concentrations of Ca, PO₄, and F were measured in the lactic acid solution, while a decrease of Ca and PO₄ concentrations was observed in artificial saliva. The uptake of ions from artificial saliva indicates their precipitation on specimen surfaces, which was supported by the results of SEM and FTIR investigations. In experimental composites functionalized with both bioactive glass types and a commercial "alkasite" material, apatite was precipitated not only in artificial saliva but also in the lactic acid solution.

CONCLUSIONS

Experimental BG-containing composites and selected commercial restorative materials demonstrated the potential for releasing multiple ion types and increasing pH.

CLINICAL SIGNIFICANCE

The observed effects can be beneficial for preventing demineralization and promoting remineralization of dental hard tissues, while apatite precipitation can additionally help in sealing marginal discontinuities.

Topological origin of phase separation in hydrated gels

HYPOTHESIS

Depending on their composition, hydrated gels can be homogeneous or phase-separated, which, in turn, affects their dynamical and mechanical properties. However, the nature of the structural features, if any, that govern the propensity for a given gel to phase-separate remains largely unknown. Here, we argue that the propensity for hydrated gels to phase-separate is topological in nature.

SIMULATIONS

We employ reactive molecular dynamics simulations to model the early-age precipitation of calcium-alumino-silicate-hydrate (CASH) gels with varying compositions, i.e., (CaO)_1.7(Al₂O₃)_x(SiO₂)_{1 -x}(H₂O)_{3.7 +x}. By adopting topological constraint theory, we investigate the structural origin of phase separation in hydrated gels.

FINDINGS

We report the existence of a homogeneous-to-phase-separated transition, wherein Si-rich (x ≤ 0.10) CASH gels are homogeneous, whereas Al-rich (x > 0.10) CASH gels tend to phase-separate. Furthermore, we demonstrate that this transition is correlated to a topological flexible-to-rigid transition within the atomic network. We reveal that the propensity for topologically-overconstrained gels to phase-separate arises from the existence of some internal stress within their atomic network, which acts as an energy penalty that drives phase separation.

Studies of the early stages of the dynamic setting process of chemically activated restorative glass-ionomer cements

Objective

To evaluate the early stages of the setting process of chemically activated restorative glass-ionomer cements (GICs).

Material and methods

Five GICs were evaluated (n = 5): Equia Forte (GC), Equia Forte HT (GC), Ketac Universal (3M ESPE), Maxxion R (FGM) and Riva Self Cure (SDI) by Thermography, Fourier Transform Infrared Attenuated Total Reflectance Spectroscopy (FTIR-ATR) and Gillmore needle indentation mechanical testing. The FTIR-ATR spectra showed the formation of metal carboxylates within the cements and enabled the stabilization time (ST) to be determined and the thermographic camera measured the temperature field images in the sample. Data were statistically analyzed by ANOVA and Tukey–Kramer (α = 5%).

Results

The Gillmore needle test showed that the order of hardening was opposite to the order of ST values determined by FTIR. The results with the thermographic camera showed two stages of temperature variation, which coincided with the evolution of specific infrared bands. The exception was Maxxion R, which showed only a single step change in temperature.

Conclusion

The early stages of the GIC setting reaction show temperature changes, both endothermic and exothermic, at specific times, confirming the occurrence of individual chemical reactions. The early setting involves reactions other than carboxylate formation.

Significance: This study gives further detail of the early stages of the setting of GICs, and past research regarding the setting reaction of GIC.

Fracture toughness of a metal-organic framework glass

Metal-organic framework glasses feature unique thermal, structural, and chemical properties compared to traditional metallic, organic, and oxide glasses. So far, there is a lack of knowledge of their mechanical properties, especially toughness and strength, owing to the challenge in preparing large bulk glass samples for mechanical testing. However, a recently developed melting method enables fabrication of large bulk glass samples (>25 mm³) from zeolitic imidazolate frameworks. Here, fracture toughness (K_Ic) of a representative glass, namely ZIF-62 glass (Zn(C₃H₃N₂)_1.75(C₇H₅N₂)_0.25), is measured using single-edge precracked beam method and simulated using reactive molecular dynamics. K_Ic is determined to be ~0.1 MPa m^0.5, which is even lower than that of brittle oxide glasses due to the preferential breakage of the weak coordinative bonds (Zn-N). The glass is found to exhibit an anomalous brittle-to-ductile transition behavior, considering its low fracture surface energy despite similar Poisson’s ratio to that of many ductile metallic and organic glasses.

Metal-organic framework glasses are gaining interest, but large samples are difficult to fabricate and mechanical properties are not well understood. Here, the authors use experiments and simulations to assess fracture toughness and flexural strength of a zeolitic imidazolate framework glass.

Interfacial Interaction between Suolunite Crystal and Silica Binding Peptide for Novel Bioinspired Cement

Cement and concrete have been important construction materials throughout human history. There is an urgent need to explore novel and untraditional cementitious materials to enhance the durability of building materials and structures in response to increased infrastructure demand worldwide. We report an exploratory study on a biocomposite cement based on a large-scale computational study using density functional theory. An explicitly solvated mixture of a mineral calcium silicate hydrate (C-S-H) crystal suolunite (Ca₂Si₂O₅(OH)₂·H₂O) and a silicon binding peptide with amino acid sequence PRO-PRO-PRO-TRP-LEU-PRO-TYR-MET-PRO-PRO-TRP-SER is constructed using ab initio molecular dynamics (AIMD). Detailed analysis on the interface structure, interatomic bonding, mechanical properties, and solvent effect of this model reveals a complex interplay of different types of covalent and ionic bonding, including ubiquitous hydrogen bonding which plays a crucial role in their properties. The use of the total bond order density (TBOD), a single quantum mechanical metric, for assessing the interfacial cohesion for this composite biocement is proposed. We find that the solvated model has a slightly larger TBOD than the dried one. These results could lead to a systematic search and rational design for different types of bioinspired and hybrid functional materials with other inorganic minerals and organic peptides.

Cell physiological effects of glass ionomer cements on fibroblast cells

The cytotoxicity of glass ionomer cements (GICs) was investigated using a novel, cost-effective, easy-to-perform and standardized test. GIC rings were made using in-house designed, custom-made moulds under sterile conditions; 10 with Fuji Equia and 10 with Fuji Triage capsules, placed in direct contact with primary human gingival fibroblasts (HGF) and immortalized human fibroblasts (HFF1). On day 1, 4, 14 and 21, an AlamarBlue® (resazurin) assay was completed towards determining the effects of the GICs on metabolic activities of the cells, whilst cell morphology was examined by light microscopy. The influence of the compounds released from the GIC rings on cell physiological effects (viability, proliferation and adhesion) during 24 h incubation was further investigated by impedimetry. Result trends obtained from this battery of techniques were complementary. At 100 v/v% concentration, the released compounds from Equia were strongly cytotoxic, while at lower concentration (0, 4, 20 v/v%) they were not cytotoxic. In contrast, Triage elicited only slightly transient cytotoxicity. The method proposed has been proved as being efficient, reliable and reproducible and may be useful in quick testing of the cytotoxicity of similar biomaterials by using an immortalized cell line.

Composition-Nanostructure Steered Performance Predictions in Steel Wires

Neutron scattering in combination with scanning electron and atomic force microscopy were employed to quantitatively resolve elemental composition, nano- through meso- to metallurgical structures and surface characteristics of two commercial stainless steel orthodontic archwires—G&H and Azdent. The obtained bulk composition confirmed that both samples are made of metastable austenitic stainless steel type AISI 304. The neutron technique’s higher detection sensitivity to alloying elements facilitated the quantitative determination of the composition factor (CF), and the pitting resistance equivalent number (PREN) for predicting austenite stability and pitting-corrosion resistance, respectively. Simultaneous neutron diffraction analyses revealed that both samples contained additional martensite phase due to strain-induced martensite transformation. The unexpectedly high martensite content (46.20 vol%) in G&H was caused by combination of lower austenite stability (CF = 17.37, p = .03), excessive cold working and inadequate thermal treatment during material processing. Together, those results assist in revealing alloying recipes and processing history, and relating these with corrosion resistance and mechanical properties. The present methodology has allowed access to unprecedented length-scale (μm to sub-nm) resolution, accessing nano- through meso-scopic properties. It is envisaged that such an approach can be extended to the study and design of other metallic (bio)materials used in medical sciences, dentistry and beyond.

Revisiting the Dependence of Poisson's Ratio on Liquid Fragility and Atomic Packing Density in Oxide Glasses

Poisson's ratio (ν) defines a material's propensity to laterally expand upon compression, or laterally shrink upon tension for non-auxetic materials. This fundamental metric has traditionally, in some fields, been assumed to be a material-independent constant, but it is clear that it varies with composition across glasses, ceramics, metals, and polymers. The intrinsically elastic metric has also been suggested to control a range of properties, even beyond the linear-elastic regime. Notably, metallic glasses show a striking brittle-to-ductile (BTD) transition for ν-values above ~0.32. The BTD transition has also been suggested to be valid for oxide glasses, but, unfortunately, direct prediction of Poisson's ratio from chemical composition remains challenging. With the long-term goal to discover such high-ν oxide glasses, we here revisit whether previously proposed relationships between Poisson's ratio and liquid fragility (m) and atomic packing density (Cg) hold for oxide glasses, since this would enable m and Cg to be used as surrogates for ν. To do so, we have performed an extensive literature review and synthesized new oxide glasses within the zinc borate and aluminoborate families that are found to exhibit high Poisson's ratio values up to ~0.34. We are not able to unequivocally confirm the universality of the Novikov-Sokolov correlation between ν and m and that between ν and Cg for oxide glass-formers, nor for the organic, ionic, chalcogenide, halogenide, or metallic glasses. Despite significant scatter, we do, however, observe an overall increase in ν with increasing m and Cg, but it is clear that additional structural details besides m or Cg are needed to predict and understand the composition dependence of Poisson's ratio. Finally, we also infer from literature data that, in addition to high ν, high Young's modulus is also needed to obtain glasses with high fracture toughness.

Non-destructive quantitation of hydrogen via mass-resolved neutron spectroscopy

This work introduces the use of mass-selective neutron spectroscopy as an analytical tool for the quantitative and non-destructive detection of hydrogen in bulk media. To this end, systematic measurements have been performed on a series of polyethylene standards of known thickness and density, in order to establish optimal data-acquisition protocols as well as associated limits of detection and quantitation. From this analysis, we conclude that state-of-the-art epithermal-neutron instrumentation enables the detection of aeral molar densities of bulk hydrogen in the μmol cm^-2 range. We also discuss potential improvements on the horizon, with a view to broadening the scope of the technique across chemistry, materials science, and engineering.

Nanoscale Mobility of Aqueous Polyacrylic Acid in Dental Restorative Cements

Hydrogen dynamics in a time range from hundreds of femtoseconds to nanoseconds can be directly analyzed using neutron spectroscopy, where information on the inelastic and quasi-elastic scattering, hereafter INS and QENS, can be obtained. In this study, we applied these techniques to understand how the nanoscale mobility of the aqueous solution of polyacrylic acid (PAA) used in conventional glass ionomer cements (GICs) changes under confinement. Combining the spectroscopic analysis with calorimetric results, we were able to separate distinct motions within both the liquid and the GICs. The QENS analysis revealed that the self-diffusion translational motion identified in the liquid is also visible in the GIC. However, as a result of the formation of the cement matrix and its setting, both translational diffusion and residence time differed from the PAA solution. When comparing the local diffusion obtained for the selected GIC, the only noticeable difference was observed for the slow dynamics associated with the polymer chain. Additionally, over short-term aging, progressive water binding to the polymer chain occurred in one of the investigated GICs. Finally, a considerable change in the density of the GIC without progressive water binding indicates an increased polymer cross-linking. Taken together, our results suggest that accurate and deep understanding of polymer-water binding, polymer cross-linking, as well as material density changes occurring during the maturation process of GIC are necessary for the development of advanced dental restorative materials.

A metal-organic framework with ultrahigh glass-forming ability

Glass-forming ability (GFA) is the ability of a liquid to avoid crystallization during cooling. Metal-organic frameworks (MOFs) are a new class of glass formers (1-3), with hitherto unknown dynamic and thermodynamic properties. We report the discovery of a new series of tetrahedral glass systems, zeolitic imidazolate framework-62 (ZIF-62) [Zn(Im_2-x bIm _x )], which have ultrahigh GFA, superior to any other known glass formers. This ultrahigh GFA is evidenced by a high viscosity η (10⁵ Pa·s) at the melting temperature T_m, a large crystal-glass network density deficit (Δρ/ρ_g)_network, no crystallization in supercooled region on laboratory time scales, a low fragility (m = 23), an extremely high Poisson's ratio (ν = 0.45), and the highest T_g/T_m ratio (0.84) ever reported. T_m and T_g both increase with benzimidazolate (bIm) content but retain the same ultrahigh T_g/T_m ratio, owing to high steric hindrance and frustrated network dynamics and also to the unusually low enthalpy and entropy typical of the soft and flexible nature of MOFs. On the basis of these versatile properties, we explain the exceptional GFA of the ZIF-62 system.

Nonlinear Oscillatory Dynamics of the Hardening of Calcium Phosphate Bone Cements

Here we report on the nonlinear, oscillatory dynamics detected in the evolution of phase composition during the setting of different calcium phosphate cements, two of which evolved toward brushite and one toward hydroxyapatite as the final product. Whereas both brushite-forming cements contained ion-doped β-tricalcium phosphate as the initial phase, the zinc-containing one yielded scholzite as an additional phase during setting and the oscillations between these two products were pronounced throughout the entire 80 h setting period, long after the hardening processes was over from the mechanical standpoint. Oscillations in the copper-containing system involved the amount of brushite as the main product of the hardening reaction and they progressed faster toward an equilibrium point than in the zinc-containing system. Initially detected with the use of in situ energy-dispersive X-ray diffractometry, the oscillations were confirmed with a sufficient level of temporal matching in an in situ Fourier transform infrared spectroscopic analysis. The kinetic reaction analysis based on the Johnson-Mehl-Avrami-Kolmogorov model indicated an edge-controlled nucleation mechanism for brushite. The hydroxyapatite-forming cement comprised gelatin as an additional phase with a role of slowing down diffusion and allowing the detection of otherwise rapid oscillations in crystallinity and in the amount of the apatitic phase on the timescale of minutes. A number of possible causes for these dynamic instabilities were discussed. The classical chemical oscillatory model should not apply to these systems unless in combination with less exotic mechanisms of physicochemical nature. One possibility is that the variations in viscosity, directly affecting diffusion and nucleation rates and accompanying growth and transformation from the lower to the higher interfacial energy per the Ostwald-Lussac rule, are responsible for the oscillatory dynamics. The conception of bone replacement materials and tissue engineering constructs capable of engaging in the dynamics of integration with the natural tissues in compliance with this oscillatory nature may open a new avenue for the future of this type of medical devices. To succeed in this goal, the mechanism of these and similar instabilities must be better understood.

Modified Glass Ionomer Cement with "Remove on Demand" Properties: An In Vitro Study

Objectives: To investigate the influence of different temperatures on the compressive strength of glass ionomer cement (GIC) modified by the addition of silica-coated wax capsules; Material and Methods: Commercially-available GIC was modified by adding 10% silica-coated wax capsules. Test blocks were fabricated from pure cement (control) and modified cement (test), and stored in distilled water (37 °C/23 h). The compressive strength was determined using a universal testing machine under different temperatures (37 °C, 50 °C, and 60 °C). The maximum load to failure was recorded for each group. Fractured surfaces of selected test blocks were observed by scanning electron microscopy (SEM); Results: For the control group, the average compressive strength was 96.8 ± 11.8, 94.3 ± 5.7 and 72.5 ± 5.7 MPa for the temperatures 37 °C, 50 °C and 60 °C respectively. The test group reported compressive strength of 64.8 ± 5.4, 47.1 ± 5.4 and 33.4 ± 3.6 MPa at 37 °C, 50 °C and 60 °C, respectively. This represented a decrease of 28% in compressive strength with the increase in temperature from 37 °C to 50 °C and 45% from the 37 °C to the 60 °C group; Conclusion: GIC modified with 10% silica-coated wax capsules and temperature application show a distinct effect on the compressive strength of GIC. Considerable compressive strength reduction was detected if the temperature was above the melting temperature of the wax core.

Simulations reveal the role of composition into the atomic-level flexibility of bioactive glass cements

Bioactive glass ionomer cements (GICs), the reaction product of a fluoro-alumino-silicate glass and polyacrylic acid, have been in effective use in dentistry for over 40 years and more recently in orthopaedics and medical implantation. Their desirable properties have affirmed GIC's place in the medical materials community, yet are limited to non-load bearing applications due to the brittle nature of the hardened composite cement, thought to arise from the glass component and the interfaces it forms. Towards helping resolve the fundamental bases of the mechanical shortcomings of GICs, we report the 1st ever computational models of a GIC-relevant component. Ab initio molecular dynamics simulations were employed to generate and characterise three fluoro-alumino-silicate glasses of differing compositions with focus on resolving the atomic scale structural and dynamic contributions of aluminium, phosphorous and fluorine. Analyses of the glasses revealed rising F-content leading to the expansion of the glass network, compression of Al-F bonding, angular constraint at Al-pivots, localisation of alumino-phosphates and increased fluorine diffusion. Together, these changes to the structure, speciation and dynamics with raised fluorine content impart an overall rigidifying effect on the glass network, and suggest a predisposition to atomic-level inflexibility, which could manifest in the ionomer cements they form.