Evaluating very high energy electron RBE from nanodosimetric pBR322 plasmid DNA damage.

This paper presents the first plasmid DNA irradiations carried out with Very High Energy Electrons (VHEE) over 100-200 MeV at the CLEAR user facility at CERN to determine the Relative Biological Effectiveness (RBE) of VHEE. DNA damage yields were measured in dry and aqueous environments to determine that ~ 99% of total DNA breaks were caused by indirect effects, consistent with other published measurements for protons and photons. Double-Strand Break (DSB) yield was used as the biological endpoint for RBE calculation, with values found to be consistent with established radiotherapy modalities. Similarities in physical damage between VHEE and conventional modalities gives confidence that biological effects of VHEE will also be similar-key for clinical implementation. Damage yields were used as a baseline for track structure simulations of VHEE plasmid irradiation using GEANT4-DNA. Current models for DSB yield have shown reasonable agreement with experimental values. The growing interest in FLASH radiotherapy motivated a study into DSB yield variation with dose rate following VHEE irradiation. No significant variations were observed between conventional and FLASH dose rate irradiations, indicating that no FLASH effect is seen under these conditions.

Marginal finishing for cast gold restorations: reciprocal-action instrumentation.

This study compared rotary finishing instruments with a set of reciprocating diamond particle instruments. These reciprocating diamond tips were designed for use in a Dentatus EVA contra angle handpiece to finish cast gold margins. They are also recommended for smoothing amalgam and composite restorations, but this capability was not examined. These small-particle size diamond tips could facilitate finishing techniques of cast gold margins for surfaces inaccessible to rotary instrumentation.

Effectiveness of reciprocal-action instrumentation for polishing composite resin: an in vitro study.

This in vitro study investigates the use of reciprocal-action instrumentation for polishing composite resin restorative materials. Electron photomicrographs were made of surfaces of a microfilled and a hybrid composite resin restorative material polished by various reciprocal-action polishing procedures, including several types of polishing pastes used with nonabrasive plastic tips. The best polish on the microfilled composite resin restorative material tested was produced by ending with 3-mu diamond polishing paste. The best polish on the hybrid composite resin restorative material tested was produced by ending with 0.5-mu diamond polishing paste. The surfaces produced were comparable to those produced by polishing discs.