The Effect of Gates-Glidden Drills on the Quality of Root Canal Treatment by Pre-Clinical Dental Students.

Aim: This study was conducted to investigate the effect of applying Gates-Glidden (GG) drill by pre-clinical dental students on root canal treatment quality.

Method: A total of 56 first molars consisting of 168 canals were selected in this study. For this purpose, 56 students who had been formerly trained by two methods of root canal preparation were randomly divided into two groups (n = 28).

Polymorphic transitions of diborane at sub- and near-megabar pressures.

Recent theoretical investigations of high-pressure structures of diborane have yielded many intriguing predictions which have so far remained untested due to challenges of acquiring experimental data at extreme pressures. Here we report new pressure-induced polymorphic transformations of crystalline diborane observed between 36 and 88 GPa by in situ Raman spectroscopy and interpreted using electronic structure calculations. Two previously unknown phase transitions are identified near 42 and 57 GPa, as evidenced by significant changes in the Raman profiles.

Band Gap Reduction in ZnO and ZnS by Creating Layered ZnO/ZnS Heterostructures.

Wurtzite-type zinc oxide (ZnO) and zinc sulfide (ZnS) have electronic band gaps that are too large for light-harvesting applications. Using screened hybrid density-functional methods, we show that the band gaps of ZnO and ZnS can be dramatically reduced by creating layered ZnO/ZnS bulk heterostructures in which m contiguous monolayers of ZnO alternate with n contiguous monolayers of ZnS. In particular, the band gap decreases by roughly 40% upon substitution of every tenth monolayer of ZnS with a monolayer of ZnO (and vice versa) and becomes as low as 1.