Search Results (161)

Chewing gum is a frequently neglected polymer-containing consumer product that can be considered a source of microplastic exposure during chewing, and, upon disposal, a cause of surface contamination. This narrative review summarises the composition of the gum base, particle release during mastication, environmental fate, and the emergence of circular upcycling. Modern gum bases can be characterised by water-insoluble elastomeric and resinous phases designed for mechanical durability, as demonstrated by established evidence. Furthermore, a recent experiment has demonstrated the release of detectable microplastic-sized particles into the saliva after chewing. However, quantitative estimates, such as the apparent highest value of 637 MPs g⁻¹, and the observation that the majority of particles detected are released during the first 8 min, remain tentative, given the limited range of products offered and the lack of replication across different brands, formulations, chewing schedules, and analytical tools. Another proof point that samples of natural and synthetic gums have comparable particle discharge indicates that no amount of natural or plastic-free labelling should mean no particle exposure. The adhesive and hydrophobic nature of gum residues, along with observations of microbial colonisation and surface interaction, is also a key factor for their persistence post disposal. Since no standardised gum disintegration protocols exist, outdoor residence times are unknown. Other under-characterisations occur in nano- and ultra-small plastic fractions, as standard spectrometric analyses have size limits. Emerging materials engineering work indicates that sanitised, chewed gum can be reprocessed with conductive nanofillers to serve as flexible sensing agents. These circular paths are proof-of-concept paths at this point, as we must confirm oxidation stability, cleanliness, scalability, logistics, collection, and lifecycles. This study clearly distinguishes well-known polymer and litter issues from new exposure, degradation, and upcycling proposals. Full article

Epoxy resin (EP) exhibits pronounced intrinsic brittleness arising from the highly crosslinked network formed after curing, thereby restricting its application in load-bearing structures. Although TiO₂ nanoparticles possess the potential for impact-strength improvement, they are highly prone to aggregation, which compromises stress-transfer efficiency within the composite. To overcome this challenge, a ball-milling strategy is adopted to anchor TiO₂ nanoparticles onto three-dimensional graphene oxide (3DGO), leading to the successful fabrication of a 3DGO@TiO₂ hybrid filler. At an ultralow loading of 0.03 wt%, the 3DGO@TiO₂ epoxy resin composite shows a 221.5% increase in impact strength to 19.55 kJ/m² and 33.53% and 32.34% increases in tensile and flexural strength to 64.32 MPa and 96.17 MPa, respectively, relative to neat EP. Morphological analyses indicate that the 3DGO spatial confinement reduces TiO₂ aggregate characteristic length by 55.1% from 1123 nm to 504 nm. Molecular dynamics simulations show that the hybrid filler decreases fractional free volume to 17.6%, induces denser matrix packing, and increases the calculated physical interfacial energy to 1023 kcal/mol, which is 2.2 times that of the pure TiO₂ epoxy resin system. This work confirms that 3DGO simultaneously optimizes nanofiller dispersion and physical confinement, offering a novel strategy for high-performance epoxy composites at ultralow loadings. Full article

Introduction: The goal of this study was to evaluate the influence of combined artificial aging protocols on the surface roughness and Vickers microhardness of bulk-fill resin composites, compared with a nanofilled composite used as a reference. Materials and Methods: A total of 120 cylindrical specimens were prepared from three bulk-fill composites (Tetric EvoCeram Bulk Fill, Filtek One Bulk Fill, Venus Bulk Fill) and one nanofilled composite (Filtek Supreme Ultra). Specimens were allocated into three aging conditions: mechanical wear (A), mechanical wear combined with pH-cycling (B), and mechanical wear combined with thermocycling (C). Surface roughness (Ra) and Vickers microhardness (VHN) were evaluated at two time points (T1: 120,000 cycles; T2: 240,000 cycles). Non-parametric statistical tests were applied (α = 0.05). Results: Aging protocols significantly influenced both Ra and VHN (p < 0.05). Overall, higher surface roughness and lower Vickers microhardness values were observed after cumulative aging, with material-dependent variations between T1 and T2. The greatest post-aging differences were observed under combined mechanical wear and pH-cycling (subgroup B), whereas mechanical wear alone showed the lowest changes. Filtek One Bulk Fill and Filtek Supreme Ultra showed more favorable post-aging Ra and VHN values, whereas Venus Bulk Fill showed less favorable post-aging surface properties. No significant correlation was found between Ra and VHN (rho = −0.009; p = 0.958). Conclusions: Combined aging conditions significantly affected the surface roughness and Vickers microhardness of resin composites, with the greatest post-aging differences observed under acidic challenges. Bulk-fill materials exhibit variable resistance depending on composition, emphasizing the importance of material selection for long-term clinical performance. Clinical relevance: Composite restorations exposed to combined mechanical and acidic challenges may show altered surface roughness and microhardness, highlighting the need for materials with enhanced resistance in high-risk oral environments. Full article

This in vitro study evaluated and compared the shear bond strength (SBS) of three restorative materials bonded to dentin: a glass hybrid ionomer (EQUIA Forte HT), a resin-modified glass ionomer (RIVA Light Cure), and a nanofilled composite resin (Filtek Z350 XT). Additionally, their modes of failure were assessed. Thirty extracted human teeth were prepared and randomly assigned to three groups (n = 10) by restorative material: Group 1: Filtek Z350 XT; Group 2: EQUIA Forte HT; Group 3: RIVA Light Cure. All materials were applied following manufacturer instructions. SBS testing used a universal testing machine, applying a load at the tooth–restoration interface at 1 mm/min until failure. SBS values were recorded in megapascals (MPa). Failure modes were examined under a stereomicroscope at 40× magnification. A one-way ANOVA compared mean SBS among groups, with post hoc tests for pairwise group comparisons. Results: Filtek Z350 XT had the highest mean SBS (21 MPa), followed by RIVA Light Cure (7.5 MPa) and EQUIA Forte HT (7.2 MPa). One-way ANOVA indicated a statistically significant difference in SBS (p < 0.05). Post hoc analysis showed Filtek Z350 XT had significantly higher SBS than the glass ionomer-based materials, while EQUIA Forte HT and RIVA Light Cure did not differ significantly. Conclusions: Filtek Z350 XT demonstrated significantly higher shear bond strength to dentin than the glass ionomer-based materials. No significant SBS difference was found between the resin-modified and hybrid glass ionomers. Full article

This study aimed to address the clinical challenge of secondary caries prevention in dental restorations. Leveraging the sustained fluoride-releasing capacity of calcium fluoride (CaF₂) and the broad-spectrum antibacterial activity of zinc oxide (ZnO), we designed and synthesized a novel core–shell CaF₂@ZnO nanoparticle filler to synergistically enhance the functional performance of dental resin composites. The filler was successfully prepared via a co-precipitation-hydrothermal method, and its well-defined core–shell architecture was systematically confirmed using XRD, SEM, and TEM. When incorporated into the resin matrix at 10 wt.% loading, the composite containing CaF₂@30ZnO demonstrated optimal overall performance. Notably, this formulation enabled sustained fluoride ion release, potent antibacterial efficacy, and excellent in vitro cytocompatibility. Collectively, these findings demonstrate that the CaF₂@ZnO nanofiller confers multifunctional benefits—including improved mechanical integrity, long-term fluoride release stability, and targeted antibacterial action—thereby holding significant promise for clinical application in mitigating secondary caries around resin-based restorations. Full article

Conventional epoxy polymers and their composites are increasingly challenged by environmental concerns, high manufacturing costs, and limited recyclability, necessitating the exploration of sustainable alternatives. Many research groups have sought to develop alternate polymers from various renewable resources, such as lignin, polyphenols, natural resins, saccharides, and plant oils. This new type of polymer has led to the emergence of bio-based polymers, which are often used with different reinforcements as bio-based composites. In this review, the synthesis of different bio-epoxy resins is discussed in detail along with their chemical structures. Subsequently, the enhancements in the properties of these bio-composites with the addition of different nanomaterials such as carbonaceous nanofillers (carbon nanotubes, graphene nanoplatelets, graphene oxide, etc.), cellulose-based nanomaterials, inorganic nano-silica (spherical and mesoporous), and nano-clay is explained. Lastly, the properties of these bio-composites and their applications in civil engineering are highlighted. This review has provided a detailed overview of the developments in bio-composites that can be used as a guide for the development of a new class of bio-composites using other alternate resources. Full article

The present research article deals with the thermal degradation study of epoxy resins filled with hybrid nanostructured forms of carbon under oxidative conditions. In particular, the formulated polymer composites (denoted as HYB_0.1%_CNTs:GNs and HYB_0.5%_CNTs:GNs, respectively) consist of two kinds of fillers, namely multi-walled carbon nanotubes (CNTs) and graphene nanosheets (GNs), mixed together with two different total mass amounts: 0.1 and 0.5%. In both kinds of nanocomposites, three different CNT:GN mixing ratios were considered (5:1, 1:1, and 1:5, respectively), thus providing a total of six hybrid samples. The thermal behavior of these samples was studied by simultaneous thermogravimetry and differential thermal analysis (TG/DTA) under flowing air, and two processes took place in distinct temperature ranges. In each step, about 50% of mass loss is detected with an exothermic effect in the corresponding DTA curve, with the second one accompanied by an intense heat release. The kinetic analysis of the two-stage oxidative thermal degradation was investigated using a model-free isoconversional approach. A non-Arrhenian behavior of the temperature function k(T) was assumed, and lifetime prediction was estimated at temperatures close to those of the possible applications. Isoconversional analysis shows nearly constant activation energies for all composites except HYB_0.1%_5:1 (from 142 to 96 kJ·mol⁻¹), while lifetime predictions indicate that thermal stability increases with graphene content at 0.1% loading (HYB_0.1%_1:5) and with CNT content at 0.5% loading (HYB_0.5%_5:1), with uncertainties below 7%. Finally, because of the π–π bond interactions between the CNTs and the GNs dispersed in the epoxy resin matrix, an effective and remarkable electrical performance was found and a correlation with both electrical and morphological properties was established. In this regard, Tunneling Atomic Force Microscopy (TUNA) proved to be particularly powerful in allowing the simultaneous mapping of topography and localized conductive networks with exceptional sensitivity to nanofiller dispersion, such as CNTs and GNs. DC conductivity increased by up to nine orders of magnitude at 0.1 wt% hybrid loading (up to 3.73 × 10⁻⁴ S/m vs. 1.06 × 10⁻¹³ S/m for CNT-only), with nanoscale TUNA currents (−1.9 to 4.5 pA) mirroring macroscopic trends, while at 0.5 wt% all hybrids reached 10⁻² S/m, indicating reduced synergy once a fully developed conductive network is established. Full article

With the capacity of generators continuing to increase, higher demands are placed on the heat dissipation of epoxy resin (EP), the main insulation material used in stator bars and windings. To overcome its low thermal conductivity, a multiscale hybrid filler strategy was adopted to investigate the effects of spherical Al₂O₃ (10 and 1 μm), platelet BN (1 μm), and SiO₂ (50 nm) on the thermal and insulating properties of EP composites. Unlike conventional studies focusing on individual fillers, this work highlights the synergistic design of fillers with different sizes and morphologies. The filler ratios were optimized by finite element simulation, and the composites were prepared by melt blending. The results show that, at a total filler loading of 38.5 wt%, the EP composite filled with spherical Al₂O₃ particles of 10 and 1 μm, platelet BN of 1 μm, and nano-SiO₂ of 50 nm achieves a thermal conductivity of 0.5497 W/(m·K), corresponding to an increase of 158.2% compared with pure EP (0.2129 W/(m·K)). This enhancement is attributed to the synergistic effect of multiscale and multishape fillers, where large Al₂O₃ particles form the main thermally conductive framework, small Al₂O₃ particles fill the gaps, platelet BN acts as a bridging filler, and nano-SiO₂ improves the interfacial region. In addition, the composite exhibits low relative permittivity and dissipation factor tanδ in the frequency range of 10⁻²–10⁶ Hz, and its breakdown strength reaches 65.99 kV/mm. These results demonstrate that simulation-guided multiscale hybrid filler design is an effective strategy for improving the thermal conductivity of EP while maintaining acceptable insulating performance. Full article

This work presents a comparative study of micro- and nano-scale fillers in liquid composite molding processes, focusing on how particle size and morphology affect resin rheology, flow behavior, and filler filtration within fiber preforms. Glass microspheres and organo-modified montmorillonite were dispersed in epoxy resin and injected through glass-mat preforms at different fiber volume fractions (ranging from 0.27 to 0.47). Our study integrates rheological characterization, in situ flow-front tracking, unsaturated permeability analysis, thermogravimetric quantification of retained particles, and microstructural observations by SEM. Despite their smaller loading, nanoclay suspensions showed a markedly higher viscosity increase than microsphere systems, yet their permeability remained nearly unchanged. In contrast, microsphere-filled resins exhibited strong filtration at the flow inlet, density-driven settling near the lower tool face, and significant permeability loss. The results demonstrate that nano-fillers, although more viscous, maintain homogeneous distribution and flow continuity, whereas micro-fillers promote cake formation and local compaction. This controlled side-by-side comparison clarifies how filler size and shape govern filtration mechanisms in liquid composite molding (LCM), providing design guidelines for processing filled resin systems without compromising part quality. Full article

Background: The aim of this in vitro study is to comparatively evaluate the effects of toothpaste formulations containing and not containing vitamin C on the surface roughness and microhardness of different composite resin materials. Methods: Four different toothpastes (Sensodyne, Colgate, Klorhex, Dentiste) and three composite resin materials (Arabesk—microhybrid, Charisma Smart—nanohybrid, Estelite Sigma Quick—supra-nano filled) were used in the study. Composite discs measuring 10 mm in diameter and 2 mm in thickness were prepared and subjected to brushing simulations equivalent to 1 month (150 s) and 3 months (450 s). Surface roughness was measured using a mechanical profilometer, and microhardness was evaluated with a Vickers hardness tester. Surface morphology was further examined in detail using scanning electron microscopy (SEM) and atomic force microscopy (AFM). For statistical analyses, one-way ANOVA, repeated measures ANOVA, Kruskal–Wallis test, and Friedman test were employed, with the significance level set at p < 0.05. Results: Brushing procedures resulted in statistically significant changes in the surface roughness (ΔRa) and microhardness of the composites across all toothpaste groups (p < 0.05). The increase in surface roughness varied depending on the composite type, with the highest increase observed in the ESQ composite. In the ESQ composite, higher ΔRa values were obtained, particularly in the Dentiste (≈1.70 µm) and Colgate (≈1.52 µm) groups. Microhardness results, however, differed depending on the composite and toothpaste type. While a general trend toward increased microhardness was observed, a significant decrease in microhardness was detected in the Colgate and Dentiste groups of the ESQ composite (p < 0.05). Conclusions: This study demonstrates that the addition of vitamin C to toothpaste formulations increases the surface roughness of restorative materials and results in significant changes in their microhardness properties. These findings highlight the importance of considering the type of toothpaste used by patients in clinical practice, particularly in terms of restorative material selection and the long-term preservation of surface integrity. Full article

In this work, we demonstrate that both carbon nanotubes (CNT) and graphene nanosheets (G) were successfully modified by π-stacking interactions with a pyrene derivative (PY), yielding the functionalized nanofillers CNT-PY and G-PY, which were subsequently dispersed within an aeronautical epoxy matrix. This functionalization is highly effective in preserving the remarkable electronic properties of carbon nanotubes and graphene nanosheets. At the same time, the non-covalent functionalization reduces the resin viscosity, enabling a more effective dispersion of the nanofillers. This results in improved rheological behavior and an overall enhancement of the structural performance of the nanocomposites compared to the resin containing unfunctionalized carbon nanofillers (CNT and G). Additional improvements are also observed in electrical properties, self-healing efficiency, and thermal stability. In particular, the samples containing functionalized carbon nanotubes (TBD + 1%CNT-PY) and functionalized graphene nanosheets (TBD + 1%G-PY) exhibit higher conductivities—0.391 S/m and 0.1 S/m, respectively—than the samples loaded with unfunctionalized carbon nanotubes (TBD + 1%CNT) and unfunctionalized graphene nanosheets (TBD + 1%G), which show conductivity values of 0.292 S/m and 4.82 × 10⁻³ S/m, respectively. The functionalized graphene nanosheets (G-PY) display significantly greater thermal stability, with degradation temperatures reaching 670 °C, compared to 310 °C for unfunctionalized ones (G). The functionalized carbon nanotubes (CNT-PY) show a 10% weight loss at 520 °C due to the degradation of the pyrene groups. Significant improvements in the final properties can be achieved when carbon-based nanofillers are homogeneously dispersed in the matrix and the external load is efficiently transferred through strong filler–polymer interfacial interactions, leading to composites with superior characteristics suitable for advanced applications. Tunneling Atomic Force Microscopy (TUNA) highlights the morphological features of the two types of carbon nanofillers, their dispersion within the polymer matrix and the effect of the functionalization on the electrical pathways and conductivity of the samples at both the micro- and nanometer-scale. The measured electrical conductivities are consistent with the electric currents detected at the micro/nanoscale. Full article

Purpose: Pure three-dimensional (3D)-printed resin for denture base shows strength in comparison with the conventional heat-cured materials. The purpose of this study was to assess how physical and mechanical properties of 3D-printed denture base resins are affected by the addition of cerium zirconium oxide nanofibers (CeZrO₄ NFs), which have a unique combination of thermophysical and mechanical properties. Materials and Methods: The specimens were digitally created utilizing Microsoft Corporation’s 3D builder software through computer-aided design. To meet the test criteria for transverse strength, impact strength, hardness, radiopacity, and degree of conversion (DC), specimens were designed and printed with specific dimensions according to the relevant standards. The 3D-printed denture base resin was mixed with CeZrO₄ NFs (diameter: 300–800 nm, length: 2–10 µm) at weight percentages of 0.5, 1.0%, 1.5%, 2%, and 2.5%. The data were analyzed using Tukey’s post hoc test (α = 0.05) and ANOVA. Field emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectroscopy (EDX) were used to evaluate surface morphologies of the composites and nanofibers, and the dispersion of the NFs within the resin matrix respectively. Results: The results demonstrated that compared with those of the control group, the average transverse strength, impact strength, and hardness values of the CeZrO₄ NF reinforcement groups significantly increased up to a nanofiller concentration of 1.5 wt.%., whereas those of the other reinforcement groups significantly decreased. For example, the impact strength significantly increased from 5.84 kJ/m² (0 wt.%) to the maximum value 8.76 kJ/m² at 1.0 wt.% CeZrO₄ NF. On the other hand, the Shore D hardness increased from 80.84 for the control group to the maximum value 83.27 at 1.5 wt.% CeZrO₄ NF. The radiopacity increased as the NF concentration increased. Although Fourier transform infrared (FTIR) spectroscopy analysis did not show any noticeable change in the chemical structure of the resin after incorporating the NFs, there was a notable improvement in the DC of the nanocomposites with NF concentrations of 0.5, 1.0 and 1.5 wt.%. Energy dispersive X-ray spectroscopy (EDX) and field emission scanning electron microscopy (FESEM) showed evidence of uniform distribution of the CeZrO₄ NFs in the 3D-printed specimens. Conclusions: The properties of the denture bases fabricated from 3D-printed resin were enhanced by the addition of 0.5%, 1 wt.% and 1.5 wt.% CeZrO₄-milled NFs, though the latter two concentrations produced the most significant results. Full article

The increasing popularity of collagen peptide supplements raises concerns about their potential effects on dental restorations. This in vitro study investigated the effects of collagen peptide supplements dissolved in different beverages on the color stability, profile arithmetic mean roughness (Ra), and gloss of various restorative materials. Four restorative materials were tested: a nanofilled composite resin (Filtek Universal), a CAD/CAM composite block (Tetric CAD), a hybrid ceramic (Vita Enamic), and a leucite-reinforced glass-ceramic (IPS Empress CAD). Specimens were immersed in three collagen solutions (Pure Collagen Water Mix, Pure Collagen Coffee Mix, and Purple Collagen) and distilled water (control) for periods simulating 1 and 6 months of daily consumption. Color changes (ΔE₀₀), Ra, and gloss were measured at baseline, after two immersion periods, and following repolishing. Results showed that collagen peptide supplements significantly affected all tested properties, with effects varying by material type and solution composition. Empress CAD demonstrated superior resistance to staining and surface property changes, while Filtek Universal exhibited the highest susceptibility. Collagen supplements mixed with coffee and those containing anthocyanin-rich ingredients produced more pronounced effects than water-mixed formulations. All materials remained within clinically acceptable thresholds for Ra and maintained adequate gloss values. Repolishing improved surface properties in all materials, though resin-based materials showed persistent discoloration due to internal staining. These findings suggest that material selection should be considered carefully for patients who regularly consume collagen peptide supplements, with ceramic and hybrid materials being preferable for aesthetic restorations. Full article

Background/Objective: Resin-based composite (RBC) gained wide popularity in dentistry due to its excellent biocompatibility, superior aesthetics, and good bonding to enamel and dentine. However, they have several shortcomings, including mechanical insufficiency and shrinkage tendency. Many researchers have utilized nanoparticles (NPs) as a reinforcing filler for RBCs. This article focused on assessing the impact of three different nanoparticles, ZrO₂, TiO_2, and SiO_2, with concentrations of 3 wt% and 7 wt%, on the elastic modulus (E) and fracture toughness (K_IC) of one commercial light-activated dental resin composite. Methods: 140 rectangular specimens were constructed according to ISO 4049 with dimensions (25 × 2 × 5 ± 0.03 mm) and (25 × 2 × 2 ± 0.03 mm) for fracture toughness and elastic modulus, respectively. Specimens were categorized into four main groups based on nanofiller types. Control: plain without filler (CC) and three modified ones with ZrO₂ (ZC), TiO₂ (TC), and SiO₂ (SC). Furthermore, modified groups were divided into two subgroups according to nanofiller concentration, 3 and 7 wt% (ZC3, ZC7, TC3, TC7, SC3, and SC7), n = 10. Mechanical testing for fracture toughness was completed using a single-edge notched beam, while a three-point bending test was used for elastic modulus. Analysis of data was based on two-way ANOVA and Bonferroni post hoc (α = 0.05). Results: ZrO₂ provided the most substantial improvement in both E and K_IC, with the optimal performance observed at 3 wt% for stiffness and 7 wt% for toughness. TiO₂ groups also enhanced these properties at both concentrations; however, the gains were less pronounced compared to ZrO₂. SiO₂ improved mechanical performance at 3 wt%, but a higher loading of 7 wt% resulted in reduced values. Conclusions: Resin-based composite modified with 3 wt% of NPs tends to possess higher fracture toughness and modulus of elasticity. Fracture toughness enhancement was concentration-dependent with ZrO₂ NPs, where the best result was obtained with 7 wt%. Nanoparticle-reinforced composite, particularly ZrO₂, may be suitable for prosthodontic applications. Full article

This study evaluated the effect of two-step polishing procedures on the surface roughness of bulk fill restorative materials. Disk-shaped specimens (10 × 1.5 mm) were prepared from four resin composites: Filtek One Bulk Fill (3M ESPE) and Tetric PowerFill (Ivoclar Vivadent), both bulk fill nanohybrid composites; X-tra fil LC (Voco), a bulk fill microfilled composite; and Filtek Supreme (3M ESPE), a conventional nanofilled composite used as a control. Polishing was performed using D-Fine Double Diamond, Sof-Lex Diamond, and A.S.A.P. polishers. Each system was applied for 30 s with a slow-speed handpiece at 10,000 rpm under water cooling. Surface roughness (Ra) was measured before and after polishing using a profilometer, with three readings per specimen, and surface morphology was assessed by scanning electron microscopy. Data were analyzed using two-way ANOVA and Tukey’s HSD test (α = 0.05). Significant differences were observed for the interaction between composite type and polishing system (p < 0.001). The lowest Ra value was obtained for Filtek One polished with Sof-Lex Diamond, while the highest surface roughness was observed for X-tra fil LC polished with D-Fine (0.800 ± 0.072 μm). SEM analysis indicated that composites containing larger filler particles exhibited greater surface roughness. In conclusion, surface roughness after polishing was primarily material dependent, with nanofilled composites demonstrating superior polishability compared to materials with larger filler particles. Full article