Magnetic Hydroxyapatite-Coated Iron-Chromium Microspheres for Dental Surface Polishing and Plaque Removal.

This research aimed to engineer magnetic hydroxyapatite-coated iron-chromium (HAp-FeCr) microspheres to enhance dental surface polishing and plaque elimination. Utilizing a tailored sol-gel approach, the HAp-FeCr microspheres were synthesized and exhaustively characterized via scanning electron microscopy, energy-dispersive X-ray spectroscopy, ζ-potential, X-ray diffractometry, and X-ray photoelectron spectroscopy methodologies. Key findings showcased that these microspheres retained their magnetic properties post-HAp coating, as evidenced by the magnetization curves. An innovative magnetic polishing system was developed, incorporating these microspheres and a 2000 rpm magnet. Comparative evaluations between traditional air-powder polishing and the proposed magnetic technique demonstrated the latter's superiority. Notably, the magnetic polishing led to a substantial reduction in dental plaque on the tooth surface, decreasing bacterial adhesion and early biofilm formation by Streptococcus gordonii and Lactobacillus acidophilus, where the most pronounced effects were observed in samples with elevated HAp content. A significant 60% reduction in dental plaque was achieved with the magnetic method relative to air-powder polishing. Furthermore, the HAp-FeCr microspheres' biocompatibility was verified through cytotoxicity tests and animal studies. In essence, the magnetic HAp-FeCr microspheres present a novel and efficient strategy for dental treatments, holding immense potential for improving oral health.

Microstructure and Mechanical Properties of Friction Stir-Welded Dissimilar Joints of ZK60 and Mg-4.6Al-1.2Sn-0.7Zn Alloys.

In order to clarify the microstructural evolution and the mechanical property of dissimilar friction stir-welded joints of ZK60 and Mg-4.6Al-1.2Sn-0.7Zn magnesium alloys, two types of arrangement with ZK60 at advancing side (AS) or retreating side (RS) were adopted. The macrostructure and the microstructure of the dissimilar welded joints were discussed, and the microhardness and the transverse tensile properties of the joints were measured. There are three stirring sub-zones with different compositions and two clear interfaces within the joints. Due to the effect of both the original grain size of base materials and the growth of recrystallized grains, in the stir zone (SZ), the grain size of ZK60 increased slightly, while the grain size of Mg-4.6Al-1.2Sn-0.7Zn decreased significantly. The dissolution of precipitates was gradually significant from RS to AS within the SZ due to the gradual increase in strain and heat. The grain refinement led to an increase in hardness, while the dissolution of precipitates resulted in a decrease in hardness. The performance of the joints obtained with ZK60 placed on the RS is slightly better than that of that on the AS. The tensile fracture of both joints occurred at the interface between SZ and the thermos-mechanical affected zone at the AS, and showed a quasi-dissociative fracture.