Multiple use of ProTaper S1 pre-disposed the instrument to microcrack formation and wear of the cutting edges. There was a low prevalence of plastic deformation and most ProTaper S1 instruments failed without discernible sign of unwinding of the flutes. Further studies should address the mode of failure and the role of debris particles in the fracture mechanism.

No abstract

The bone marrow microenvironment facilitates the proliferation and survival of leukemia cells, contributing to disease relapse. Bone marrow-derived mesenchymal stem cells (MSCs) are well known to promote cancer chemoresistance via soluble factors and cell adhesion. However, little is known about the effects of MSCs on the mitochondrial dynamics of T-cell acute lymphoblastic leukemia (T-ALL) cells, or how this may influence the chemoresistance of these cells. Here, we tested both indirect (Transwell) and direct coculture strategies, and found that MSCs protected T-ALL cells from chemotherapeutic cell death and cytotoxicity under both culture conditions. In addition, cell viability was higher in the direct contact system compared with the Transwell system. We further showed that exposure of T-ALL cells to MSCs decreased mitochondrial reactive oxygen species (ROS) levels and promoted a pro-glycolytic shift that was characterized by increased glucose uptake and lactate production with concomitant reductions in adenosine triphosphate production and mitochondrial membrane potential. In T-ALL cells cocultured with MSCs, the mitochondrial morphology of T-ALL cells were altered from elongation to fragmentation because of the extracellular signal-regulated kinase activation-mediated phosphorylation of the pro-fission factor, dynamin-related protein 1 (Drp1), at residue S616. Consistent with this, the expression of S616-phosphorylated Drp1 recapitulated the mitochondrial dynamics, mitochondrial ROS levels, metabolic switching and chemoresistance seen in T-ALL cells cocultured with MSCs. These findings suggest that the ability of MSCs to trigger Drp1 activation-induced changes in mitochondrial dynamics is crucial to their ability to protect cells against chemotherapeutic agents.

No abstract