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Dental Materials : Official Publication... Mar 2022Bulk-fill resin composites are a special group of restorative materials designed to reduce chair time needed to insert a direct composite restoration. However, other...
OBJECTIVE
Bulk-fill resin composites are a special group of restorative materials designed to reduce chair time needed to insert a direct composite restoration. However, other factors determine the clinical success of a restorative material. Clinically the major reasons for failure of direct restorations are secondary caries and fracture of the restoration or the tooth itself. In the long-term composite resin restorations in posterior teeth may be prone to wear. As bulk-fill materials have their own composition that will determine their mechanical properties, the wear resistance may be affected as well. The aim of this in vitro study was to evaluate the wear of bulk-fill composites in comparison with a conventional hybrid composite. The null hypothesis was that there are no differences between the four bulk-fill materials and one traditional highly filled nanohybrid composite for posterior use when subjected to a two-body wear rate test and hardness measurement.
METHODS
Four bulk-fill composites SDR Smart Dentin Replacement (SDR), X-tra base (XBA), FiltekBulk Fill (FUP), Dual-Curing Bulk Composite (FBFL) and conventional nanohybrid resin composite Grandio (GDO) subjected to a two-body wear test against a stainless steel (SS) antagonist wheel. Scanning Electron Microscopy analysis was performed to detect the surface alterations. Microhardness of all samples was tested (n = 5) with a Vickers diamond indenter (5 indentations in each specimen). One-way ANOVA and Tukey's post hoc test (P < 0.01) were used to analyze differences in wear values. The hardness data were submitted to one-way ANOVA test, followed by the Tukey post hoc test (α = 0.05). T-test was applied to compare wear rate in time interval between one day and one month.
RESULTS
The highest wear rate values were recorded for SDR and the lowest wear rate values were for GDO. Hardness was the highest for GDO and the lowest for FBFL.
SIGNIFICANCE
The bulk-fill composites have a higher wear rate and lower hardness than the conventional nanohybrid composite, making them less suitable for stress-bearing restorations.
Topics: Composite Resins; Dental Materials; Hardness; Materials Testing
PubMed: 34972580
DOI: 10.1016/j.dental.2021.12.138 -
Nature Feb 2020The mechanics of the cellular microenvironment continuously modulates cell functions such as growth, survival, apoptosis, differentiation and morphogenesis via...
The mechanics of the cellular microenvironment continuously modulates cell functions such as growth, survival, apoptosis, differentiation and morphogenesis via cytoskeletal remodelling and actomyosin contractility. Although all of these processes consume energy, it is unknown whether and how cells adapt their metabolic activity to variable mechanical cues. Here we report that the transfer of human bronchial epithelial cells from stiff to soft substrates causes a downregulation of glycolysis via proteasomal degradation of the rate-limiting metabolic enzyme phosphofructokinase (PFK). PFK degradation is triggered by the disassembly of stress fibres, which releases the PFK-targeting E3 ubiquitin ligase tripartite motif (TRIM)-containing protein 21 (TRIM21). Transformed non-small-cell lung cancer cells, which maintain high glycolytic rates regardless of changing environmental mechanics, retain PFK expression by downregulating TRIM21, and by sequestering residual TRIM21 on a stress-fibre subset that is insensitive to substrate stiffness. Our data reveal a mechanism by which glycolysis responds to architectural features of the actomyosin cytoskeleton, thus coupling cell metabolism to the mechanical properties of the surrounding tissue. These processes enable normal cells to tune energy production in variable microenvironments, whereas the resistance of the cytoskeleton in response to mechanical cues enables the persistence of high glycolytic rates in cancer cells despite constant alterations of the tumour tissue.
Topics: Actins; Actomyosin; Animals; Bronchi; Cattle; Cell Differentiation; Cell Line; Cellular Microenvironment; Cytoskeleton; Epithelial Cells; Glucose; Glycolysis; Hardness; Humans; Neoplasms; Phosphofructokinases; Proteasome Endopeptidase Complex; Ribonucleoproteins; Stress Fibers; Ubiquitin-Protein Ligases
PubMed: 32051585
DOI: 10.1038/s41586-020-1998-1 -
Orthodontics & Craniofacial Research Aug 2022The aim of this study was to compare the mechanical properties of orthodontic aligners among different commercially available 3D printing devices. (Review)
Review
OBJECTIVE
The aim of this study was to compare the mechanical properties of orthodontic aligners among different commercially available 3D printing devices.
MATERIALS AND METHODS
Five 3D printers (Ka:rv LP 550, Swinwon; "KAR"), (L120, Dazz 3D; "L12"), (MiiCraft 125, Miicraft Jena; "MIC"), (Slash 2, Uniz; "SLS") and (Pro 95, SprintRay; "PRO") were used to prepare orthodontic aligners with dental resin (Tera Harz TC-85DAW, Graphy). The central incisors of each aligner were cut, prepared and evaluated in terms of Martens-Hardness (HM), indentation-modulus (E ) and elastic-index (η ) as per ISO14577-1:2002. Force-indentation curves were recorded and differences among printers were checked with generalized linear regressions (alpha=5%).
RESULTS
Statistically significant differences were seen for all mechanical properties (P < .05), which were in descending order: HM (N/mm ) as median (Interquartile Range [IQR]): SLS 108.5 (106.0-112.0), L12 103.0 (102.0-107.0), KAR 101.5 (97.5-103.0), MIC 100.0 (97.5-101.5) and PRO 94.0 (93.0-96.0); E (MPa) as mean (Standard Deviation [SD]): SLS 2696.3 (124.7), L12 2627.8 (73.5), MIC 2566.2 (125.1), KAR 2565.0 (130.2) and PRO 2491.2 (53.3); and η (%) as median (IQR): SLS 32.8 (32.3-33.1), L12 31.6 (30.8-32.3), KAR 31.3 (30.9-31.9), MIC 30.5 (29.9-31.2) and PRO 29.5 (29.1-30.0). Additionally, significant differences existed between liquid crystal display (LCD) and digital light processing (DLP) printers for HM (P < .001), E (P = .002) and η (P < .001), with aligners from the former having higher values than aligners from the latter printer.
CONCLUSION
Under the limitations of this study, it may be concluded that the mechanical properties of 3D-printed orthodontic aligners are dependent on the 3D printer used, and thus, differences in their clinical efficacy are anticipated.
Topics: Hardness; Materials Testing; Printing, Three-Dimensional
PubMed: 34569692
DOI: 10.1111/ocr.12537 -
Journal of Biomechanics Aug 2022Investigations into teeth mechanical properties provide insight into physiological functions and pathological changes. This study sought to 1) quantify the spatial...
Investigations into teeth mechanical properties provide insight into physiological functions and pathological changes. This study sought to 1) quantify the spatial distribution of elastic modulus, hardness and the microstructural features of dog dentin and to 2) investigate quantitative relationships between the mechanical properties and the complex microstructure of dog dentin. Maxillary canine teeth of 10 mature dogs were sectioned in the transverse and vertical planes, then tested using nanoindentation and scanning electron microscopy (SEM). Microstructural features (dentin area fraction and dentinal tubule density) and mechanical properties (elastic modulus and hardness) were quantified. Results demonstrated significant anisotropy and spatial variation in elastic modulus, hardness, dentin area fraction and tubule density. These spatial variations adhered to a consistent distribution pattern; hardness, elastic modulus and dentin area fraction generally decreased from superficial to deep dentin and from crown tip to base; tubule density generally increased from superficial to deep dentin. Poor to moderate correlations between microstructural features and mechanical properties (R = 0.032-0.466) were determined. The results of this study suggest that the other constituents may contribute to the mechanical behavior of mammalian dentin. Our results also present several remaining opportunities for further investigation into the roles of organic components (e.g., collagen) and mineral content on dentin mechanical behavior.
Topics: Animals; Dentin; Dogs; Elastic Modulus; Hardness; Mammals; Microscopy, Electron, Scanning; Structure-Activity Relationship; Tooth
PubMed: 35834939
DOI: 10.1016/j.jbiomech.2022.111218 -
Journal of the Mechanical Behavior of... Dec 2021Biodentine is a calcium silicate/calcium carbonate/zirconium dioxide/water-based dental replacement biomaterial, significantly outperforming the stiffness and hardness...
Biodentine is a calcium silicate/calcium carbonate/zirconium dioxide/water-based dental replacement biomaterial, significantly outperforming the stiffness and hardness properties of chemically similar construction cement pastes. We here report the first systematic micromechanical investigation of Biodentine, combining grid nanoindentation with ultrasonic testing and micromechanical modeling. Histograms of nanoindentation-probed hardness and elastic modulus, comprising more than 5700 values each, are very well represented by the superposition of three log-normal distributions (LNDs). Most of the data (74%) belong to the intermediate LND, representing highly dense calcite-reinforced hydration products with on-average more than 60GPa elastic modulus and 3GPa hardness. The remaining data refer, on the one hand, to lower density hydration products, and on the other hand, to single-micron-sized unhydrated clinker and zirconium-dioxide inclusions. Micromechanical homogenization of these three material phases delivers elastic properties of the overall cement paste material, which significantly exceed those probed by more than 300 ultrasonic tests performed in the kHz and MHz regime. This indicates the presence of micro-defects, which slightly weaken the otherwise highly optimized biomaterial system.
Topics: Calcium Carbonate; Construction Materials; Glass Ionomer Cements; Hardness; Water
PubMed: 34634693
DOI: 10.1016/j.jmbbm.2021.104863 -
Molecules (Basel, Switzerland) Dec 2022The chemical hardness concept and its realization within the conceptual density functional theory is approached with innovative perspectives, such as the... (Review)
Review
The chemical hardness concept and its realization within the conceptual density functional theory is approached with innovative perspectives, such as the electronegativity and hardness equalization of atoms in molecules connected with the softness kernel, in order to examine the structure-reactivity equalization ansatz between the electronic sharing index and the charge transfer either in the additive or geometrical mean picture of bonding. On the other hand, the maximum hardness principle presents a relation with the chemical stability of the hardness concept. In light of the inverse relation between hardness and polarizability, the minimum polarizability principle has been proposed. Additionally, this review includes important applications of the chemical hardness concept to solid-state chemistry. The mentioned applications support the validity of the electronic structure principles regarding chemical hardness and polarizability in solid-state chemistry.
Topics: Hardness; Density Functional Theory; Molecular Structure
PubMed: 36557957
DOI: 10.3390/molecules27248825 -
Dental Materials Journal Nov 2022The aim of this in vitro study was to evaluate the wear and surface hardness of nine materials for conventional manufacturing, subtractive milling, and 3D printing of...
The aim of this in vitro study was to evaluate the wear and surface hardness of nine materials for conventional manufacturing, subtractive milling, and 3D printing of occlusal splints, as well as to evaluate the differences in wear and surface hardness between rigid and flexible 3D-printed occlusal splint materials. Two-body wear and Vickers hardness tests were performed. The vertical wear depth and Vickers hardness values were statistically analyzed. Vertical wear depth and surface hardness values were statistically significant among the investigated materials (p<0.05). The lowest vertical wear depth was observed for the heat-cured resin (27.5±2.4 μm), PMMA-based milled material (30.5±2.8 μm), and autopolymerizing resin (36.7±6.3 μm), with no statistical difference (p<0.05). Flexible 3D-printed and CAD-CAM milled polycarbonate-based splint materials displayed lower surface hardness and higher wear than the PMMA-based materials. PMMA-based splint materials displayed the most consistent surface hardness and wear resistance regardless of the manufacturing technology.
Topics: Occlusal Splints; Hardness; Polymethyl Methacrylate; Materials Testing; Computer-Aided Design; Printing, Three-Dimensional; Surface Properties
PubMed: 36288940
DOI: 10.4012/dmj.2022-100 -
Nature Communications Oct 2023Stretchability is an essential property for wearable devices to match varying strains when interfacing with soft tissues or organs. While piezoelectricity has broad...
Stretchability is an essential property for wearable devices to match varying strains when interfacing with soft tissues or organs. While piezoelectricity has broad application potentials as tactile sensors, artificial skins, or nanogenerators, enabling tissue-comparable stretchability is a main roadblock due to the intrinsic rigidity and hardness of the crystalline phase. Here, an amino acid-based piezoelectric biocrystal thin film that offers tissue-compatible omnidirectional stretchability with unimpaired piezoelectricity is reported. The stretchability was enabled by a truss-like microstructure that was self-assembled under controlled molecule-solvent interaction and interface tension. Through the open and close of truss meshes, this large scale biocrystal microstructure was able to endure up to 40% tensile strain along different directions while retained both structural integrity and piezoelectric performance. Built on this structure, a tissue-compatible stretchable piezoelectric nanogenerator was developed, which could conform to various tissue surfaces, and exhibited stable functions under multidimensional large strains. In this work, we presented a promising solution that integrates piezoelectricity, stretchability and biocompatibility in one material system, a critical step toward tissue-compatible biomedical devices.
Topics: Wearable Electronic Devices; Hardness
PubMed: 37848410
DOI: 10.1038/s41467-023-42184-8 -
Acta Biomaterialia Oct 2022Structures made by scleractinian corals support diverse ocean ecosystems. Despite the importance of coral skeletons and their predicted vulnerability to climate change,...
Structures made by scleractinian corals support diverse ocean ecosystems. Despite the importance of coral skeletons and their predicted vulnerability to climate change, few studies have examined the mechanical and crystallographic properties of coral skeletons at the micro- and nano-scales. Here, we investigated the interplay of crystallographic and microarchitectural organization with mechanical anisotropy within Porites skeletons by measuring Young's modulus and hardness along surfaces transverse and longitudinal to the primary coral growth direction. We observed micro-scale anisotropy, where the transverse surface had greater Young's modulus and hardness by ∼ 6 GPa and 0.2 GPa, respectively. Electron backscatter diffraction (EBSD) revealed that this surface also had a higher percentage of crystals oriented with the a-axis between ± 30-60, relative to the longitudinal surface, and a broader grain size distribution. Within a region containing a sharp microscale gradient in Young's modulus, nanoscale indentation mapping, energy dispersive spectroscopy (EDS), EBSD, and Raman crystallography were performed. A correlative trend showed higher Young's modulus and hardness in regions with individual crystal bases (c-axis) facing upward, and in crystal fibers relative to centers of calcification. These relationships highlight the difference in mechanical properties between scales (i.e. crystals, crystal bundles, grains). Observations of crystal orientation and mechanical properties suggest that anisotropy is driven by microscale organization and crystal packing rather than intrinsic crystal anisotropy. In comparison with previous observations of nanoscale isotropy in corals, our results illustrate the role of hierarchical architecture in coral skeletons and the influence of biotic and abiotic factors on mechanical properties at different scales. STATEMENT OF SIGNIFICANCE: Coral biomineralization and the ability of corals' skeletal structure to withstand biotic and abiotic forces underpins the success of reef ecosystems. At the microscale, we show increased skeletal stiffness and hardness perpendicular to the coral growth direction. By comparing nano- and micro-scale indentation results, we also reveal an effect of hierarchical architecture on the mechanical properties of coral skeletons and hypothesize that crystal packing and orientation result in microscale anisotropy. In contrast to previous findings, we demonstrate that mechanical and crystallographic properties of coral skeletons can vary between surface planes, within surface planes, and at different analytical scales. These results improve our understanding of biomineralization and the effects of scale and direction on how biomineral structures respond to environmental stimuli.
Topics: Animals; Anisotropy; Anthozoa; Ecosystem; Elastic Modulus; Hardness
PubMed: 35963519
DOI: 10.1016/j.actbio.2022.08.012 -
Frontiers in Cellular and Infection... 2022White spot lesions (WSLs) are prevalent and often lead to aesthetic problems and progressive caries. The objectives of this study were to: (1) develop a novel resin...
OBJECTIVES
White spot lesions (WSLs) are prevalent and often lead to aesthetic problems and progressive caries. The objectives of this study were to: (1) develop a novel resin infiltrant containing smart monomer dodecylmethylaminoethyl methacrylate (DMAEM) to inhibit WSLs, and (2) investigate the effects of DMAEM incorporation on cytotoxicity, mechanical properties, biofilm-inhibition and protection of enamel hardness for the first time.
METHODS
DMAEM was synthesized using 1-bromododecane, 2-methylamino ethanol and methylmethacrylate. DMAEM with mass fractions of 0%, 1.25%, 2.5% and 5% were incorporated into a resin infiltant containing BisGMA and TEGDMA. Cytotoxicity, mechanical properties and antibacterial effects were tested. After resin infiltration, bovine enamel was demineralized with saliva biofilm acids, and enamel hardness was measured.
RESULT
DMAEM infiltration did not increase the cytotoxicity or compromise the physical properties when DMAEM mass fraction was below 5% ( > 0.05). Biofilm metabolic activity was reduced by 90%, and biofilm lactic acid production was reduced by 92%, DMAEM ( < 0.05). Mutans streptococci biofilm CFU was reduced by 3 logs ( < 0.05). When demineralized in acid and then under biofilms, the infiltrant + 5% DMAEM group produced an enamel hardness (mean ± sd; n = 6) of 2.90 ± 0.06 GPa, much higher than 0.85 ± 0.12 GPa of the infiltrant + 0% DMAEM group ( < 0.05).
SIGNIFICANCE
A novel resin infiltrant with excellent mechanical properties, biocompability, strong antibacterial activity and anti-demineralization effect was developed using DMAEM for the first time. The DMAEM resin infiltrant is promising for inhibiting WSLs, arresting early caries, and protecting enamel hardness.
Topics: Cattle; Animals; Methacrylates; Streptococcus mutans; Biofilms; Hardness; Anti-Bacterial Agents; Dental Caries
PubMed: 36519132
DOI: 10.3389/fcimb.2022.1063143