Role of the flat-designed surface in improving the cyclic fatigue resistance of endodontic NiTi rotary instruments

The aim of this study was to investigate the role of the flat-designed surface in improving the resistance to cyclic fatigue by comparing heat-treated F-One (Fanta Dental, Shanghai, China) nickel-titanium (NiTi) rotary instruments and similar prototypes, differing only by the absence of the flat side. The null hypothesis was that there were no differences between the two tested instruments in terms of cyclic fatigue lifespan. A total of 40 new NiTi instruments (20 F-One and 20 prototypes) were tested in the present study. The instruments were rotated with the same speed (500 rpm) and torque (2 N) using an endodontic motor (Elements Motor, Kerr, Orange, CA, USA) in the same stainless steel, artificial canal (90° angle of curvature and 5 mm radius). A Wilcoxon-Mann-Whitney test was performed to assess the differences in terms of time to fracture and the length of the fractured segment between the flat- and non-flat-sided instruments. Significance was set at p = 0.05. The differences in terms of time to fracture between non-flat and flat were statistically significant (p < 0.001). In addition, the differences in terms of fractured segment length were statistically significant (p = 0.034). The results of this study highlight the importance of flat-sided design in increasing the cyclic fatigue lifespan of NiTi rotary instruments

Histidine-assisted reduction of arylnitrenes upon photo-activation of phenyl azide chromophores in the GFP-like fluorescent proteins

The photochemically active sites of the proteins sfGFP66azF and Venus66azF from the green fluorescent protein (GFP) family contain a non-canonical amino acid residue p-azidophenylalanine (azF) instead of Tyr66 in GFP. Light-induced decomposition of azF in these sites leads to the reactive arylnitrene (nF) intermediates followed by formation of phenylamine-containing chromophores. We report the first study of a reaction mechanism of reduction of arylnitrene intermediates in sfGFP66nF and Venus66nF using molecular modeling methods. The Gibbs energy profiles for the elementary steps of chemical reaction in sfGFP66nF are computed using molecular dynamics simulations with the quantum mechanics/molecular mechanics (QM/MM) potentials. Structures and energies along the reaction pathway in Venus66nF are evaluated using the QM/MM approach. According to the results of simulations, arylnitrene reduction is coupled with oxidation of the histidine side chain His148 located near the chromophore

Sonic vs Ultrasonic activation of sodium hypoclorite for root canal treatments. In vitro assessment of debris removal from main and lateral canals

Aim: Aim of this study is to evaluate the efficacy of two different sonic and ultrasonic devices in the elimination of debris from artificial main and accessory canals. Methodology: Two different irrigant activator devices were tested: The sonic handpiece Endo- Activator (Dentsply Maillefer, Baillagues, Switzerland) and the ultrasonic handpiece Ultra X (Eighteeth, Changzhou Sifary Medical Technology Co., Ltd, Changzhou City, China). Two groups of 18 artificial root canals were analyzed (n=36): Main and lateral canals were embedded in a transparent resin model. Canals were filled with organic paste to simulate the necrotic pulp tissues. With both devices, irrigation was performed using 5% sodium hypoclorite and two activation times of 30 seconds each. Sodium hypochlorite was replaced every 30 seconds. After a photographic exam, debris removal was evaluated by a software and assessed in terms of percentage of cleaned canal. Means and standard deviations were calculated and data were statistically analyzed with the Anova test. Results: Under the same experimental conditions (same canal, time and irrigant), both sonic and ultrasonic devices completely cleaned the main canal. On the contrary, a statistically significant difference was noted in the debridement of lateral canals, with ultrasonic device removing more debris than the sonic one (p<0.05). No tested device was able to remove all debris from accessory canals. Conclusions: The cordless ultrasonic handpiece Ultra X used with maximum power showed significantly greater efficacy in cleaning accessory canals when compared to the sonic EndoActivator

Monomerization of the photoconvertible fluorescent protein SAASoti by rational mutagenesis of single amino acids

Abstract Photoconvertible fluorescent proteins (PCFPs) are widely used as markers for the visualization of intracellular processes and for sub-diffraction single-molecule localization microscopy. Although wild type of a new photoconvertible fluorescent protein SAASoti tends to aggregate, we succeeded, via rational mutagenesis, to obtain variants that formed either tetramers or monomers. We compare two approaches: one is based on the structural similarity between SAASoti and Kaede, which helped us to identify a single point mutation (V127T) at the protein’s hydrophobic interface that leads to monomerization. The other is based on a chemical modification of amino groups of SAASoti with succinic anhydride, which converts the protein aggregates into monomers. Mass-spectrometric analysis helped us to identify that the modification of a single ε-amino group of lysine K145 in the strongly charged interface AB was sufficient to convert the protein into its tetrameric form. Furthermore, site-directed mutagenesis was used to generate mutants that proved to be either monomeric or tetrameric, both capable of rapid green-to-red photoconversion. This allows SAASoti to be used as a photoconvertible fluorescent marker for in vivo cell studies