Effect of nano-zinc oxide and fluoride-doped bioactive glass-based dentifrices on esthetic restorations.

BACKGROUND: Over time, improvements have been made in dentifrices and recently bioactive components have been added. It is important to address the abrasivity of these dentifrices, which can cause wear of dental restorative materials. OBJECTIVES: A comparative study was conducted to examine the effects of commercial and experimental dentifrices upon commonly used dental restorative materials. MATERIAL AND METHODS: Three types of experimental dentifrices were prepared with variable concentrations of fluoride-based bioactive glass, nano-zinc oxide (ZnO) and titanium dioxide (TiO2) powder as active ingredients. A custom-made toothbrush simulator was used with variable cycles (0; 5,000; and 10,000) to treat samples prepared from dental restorative materials. Prior to and after the treatment cycles, the physical properties of the restorative materials were assessed and compared with commercial toothpaste through micro-hardness, surface roughness and color stability testing. RESULTS: The restorative materials showed an insignificant difference in terms of micro-hardness before and after the treatment with all dentifrices. A significant difference was observed in terms of surface roughness. With respect to color stability, there has been observed an insignificant difference between the control and the other 3 experimental dentifrices for all the cycles - pre, post-5,000 and post-10,000. CONCLUSIONS: Experimental fluoride-containing bioactive dentifrices caused a change in the restorative material properties; however, it was minimal and the properties still met the requirements for clinical applications.

Strain relaxation and ambipolar electrical transport in GaAs/InSb core-shell nanowires.

The growth, crystal structure, strain relaxation and room temperature transport characteristics of GaAs/InSb core-shell nanowires grown using molecular beam epitaxy are investigated. Due to the large lattice mismatch between GaAs and InSb of 14%, a transition from island-based to layer-like growth occurs during the formation of the shell. High resolution transmission electron microscopy in combination with geometric phase analyses as well as X-ray diffraction with synchrotron radiation are used to investigate the strain relaxation and prove the existence of different dislocations relaxing the strain on zinc blende and wurtzite core-shell nanowire segments. While on the wurtzite phase only Frank partial dislocations are found, the strain on the zinc blende phase is relaxed by dislocations with perfect, Shockley partial and Frank partial dislocations. Even for ultrathin shells of about 2 nm thickness, the strain caused by the high lattice mismatch between GaAs and InSb is relaxed almost completely. Transfer characteristics of the core-shell nanowires show an ambipolar conductance behavior whose strength strongly depends on the dimensions of the nanowires. The interpretation is given based on an electronic band profile which is calculated for completely relaxed core/shell structures. The peculiarities of the band alignment in this situation implies simultaneously occupied electron and hole channels in the InSb shell. The ambipolar behavior is then explained by the change of carrier concentration in both channels by the gate voltage.