Effect of aqueous environment on wear resistance of dental glass-ceramics.

BACKGROUND: Wear resistance affects dental ceramics longevity and the functions of the opposing teeth. However, data for the effect of aqueous environment on wear resistance of dental ceramics are lacking. This study evaluated the effect of aqueous environment on wear resistance of typical dental glass-ceramics. METHODS: Disk specimens were prepared from lithium disilicate glass-ceramics (LD) and leucite reinforced glass-ceramics (LEU). The disk specimens paired with steatite antagonists were tested in a pin-on-disk tribometer under both wet and dry conditions with 10 N up to 500,000 wear cycles. The wear analysis of glass-ceramics was performed using a 3D profilometer after 100,000, 300,000 and 500,000 wear cycles. Wear morphologies were analyzed by employing scanning electron microscopy (SEM). The crystalline compositions of specimens stored in a dry environment and subsequently immersed in distilled water for 40 h were separately determined using X-ray diffraction (XRD). The chemical states of the wear surfaces for LD were analyzed by X-ray photoelectron spectroscopy (XPS). The data analysis and multiple pair-wise comparisons of means were performed by using one-way analysis of variance (ANOVA) and Tukey's post-hoc test. RESULTS: LEU in a wet environment exhibited less wear volume loss than that in a dry environment (p < 0.05). The volume loss of LD in a wet environment was higher than that in a dry environment (p < 0.05). The wear volumes of steatite antagonists paired with two glass-ceramics under dry conditions were higher than under wet conditions. CONCLUSIONS: XPS spectra of LD under wet conditions indicated that high wear loss might result from the effect of stress corrosion by water and reaction of water with the ionic-covalent bonds at the crack tip. XPS spectra and SEM images of LD under dry conditions showed a possible formation of tribofilm. Within the limitations of this in vitro study, water was wear-friendly to LEU and all opposing steatites but aggravated wear for LD.

Reactive Oxygen Species-Responsive Polymeric Prodrug Nanoparticles for Selective and Effective Treatment of Inflammatory Diseases.

It is challenging to manage inflammatory diseases using traditional anti-inflammatory drugs due to their limited efficacy and systemic side effects, which are a result of their lack of selectivity, poor stability, and low solubility. Herein, it reports the development of a novel nanoparticle system, called ROS-CA-NPs, which is formed using polymer-cinnamaldehyde (CA) conjugates and is responsive to reactive oxygen species (ROS). ROS-CA-NPs exhibit excellent drug stability, tissue selectivity, and controlled drug release upon oxidative stress activation. Using mouse models of chronic rheumatoid arthritis and acute ulcerative colitis, this study demonstrates that the systemic administration of ROS-CA-NPs results in their accumulation at inflamed lesions and leads to greater therapeutic efficacy compared to traditional drugs. Furthermore, ROS-CA-NPs present excellent biocompatibility. The findings suggest that ROS-CA-NPs have the potential to be developed as safe and effective nanotherapeutic agents for a broad range of inflammatory diseases.

Construction of Nanostructured Glass-Zirconia to Improve the Interface Stability of Dental Bilayer Zirconia.

Bilayer zirconia restoration is one of the most commonly used restorations in dental practice, but the high frequency of the cohesive/adhesive fracture of veneered porcelain is still a problem. This paper focuses on the development of nanostructured glass-zirconia to improve the interface stability of dental zirconia substrate and veneered porcelain. A novel SiO2-Li2O-Al2O3 (SLA) glass was prepared and infiltrated into the surface of fully sintered dental zirconia to obtain nanostructured glass-zirconia structure. The prepared glass-zirconia was analyzed with scanning electron microscopes (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction spectroscopy (XRD). The wettability, roughness and 3D morphology of zirconia were altered, and shear bonding strength (SBS) test demonstrated almost double increase in SBS values of the nanostructured glass-zirconia structure. The failure modes and microstructure characteristics also verified the improved interfacial stability. This investigation provides a promising method for enhancing the structural stability of bilayer zirconia restorations.

Explosible nanocapsules excited by pulsed microwaves for efficient thermoacoustic-chemo combination therapy.

Microwave irradiation is a powerful non-invasive approach for treating deep-seated diseases in a clinical setting. Pulsed microwave-induced thermoacoustic cavitation allows precise cancer treatment with microwave-absorbing materials. This differs from the traditional continuous microwave-induced thermotherapy which may be harmful to off-target tissues. Here we first report the integration of thermocavitation and cytoplasmic drug release into highly explosible cell-penetrating nanocapsules for effective tumor inhibition under pulsed microwave irradiation. The nanocapsules were formulated from arginine-tethered reduction-responsive copolymers, P(ArgMA-co-DMA)-b-PPOPMA, microwave-absorbing AB and chemotherapeutic DOX using a double-emulsion method. The nanocapsules were internalized by cancer cells rapidly via major energy-independent pathways. Upon pulsed microwave irradiation, AB absorbed energy to generate a giant thermoacoustic shockwave, simultaneously decomposing into carbon dioxide and ammonia which enforced the cavitation damage effect. The thermoacoustic shockwave and gas burst also mechanically disrupted the intracellular organelles resulting in high-ratio cell necrosis and promoted the cytosolic release of DOX into the nucleus to initiate cell death. Importantly, in vivo results demonstrated significantly suppressed tumor growth by the pulsed microwave-triggered thermocavitation and drug release, and minimal systemic toxicity from the microwave treatment. Therefore, our study provides a new strategy for effectively engineering pulsed microwave-responsive nanomaterials for smart cancer therapy.

Effect of Added Mullite Whisker on Properties of Lithium Aluminosilicate (LAS) Glass-Ceramics Prepared for Dental Restoration.

In this work, lithium aluminosilicate (LAS) glass-ceramics were prepared from lithium disilicate glass powder and mullite whiskers. Lithium disilicate glass powder (28.6Li-68.6Si-2K-0.8La, mol.%) with contents of 5, 10 and 15 wt.% mullite whiskers were hot-pressed at 860 °C for 1 h. The effects of added mullite on phase composition, microstructure, mechanical properties, coefficient of thermal expansion (CTE) and translucency were systematically studied. Also, the mechanism for phase transformation and grain growth was discussed. The LAS glass-ceramic samples exhibited relative densities above 98% with main crystalline phases of lithium disilicate (Li2Si2O5, LD), lithium silicate (Li2SiO3, LM), and ß-spodumene (LiAlSi2O6). The ß-spodumene whiskers were in-situ synthesized through the reaction between mullite whiskers and glass matrix. As ß-spodumene fraction rose, lithium disilicate crystals content decreased and that of lithium silicate increased, resulting in declined bending strength and improved fracture toughness. The composite containing 10 wt.% mullite whisker showed optimal performance with bending strength above 300 MPa and fracture toughness of 2.7 MPa·m1/2. The formation of ß-spodumene in the obtained composite declined CTE, with values ranging from 10.5×106 °C-1 for LD glass-ceramic to 6.03×10-6 °C-1 for LAS glass-ceramic doped with 15 wt.% mullite whiskers. Finally, though the real in-line transmission of obtained glass-ceramic composites declined as ß-spodumene content rose, the specimens containing less than 10 wt.% mullite whiskers showed favorable translucency, which would suit applications in dental restoration.