ABSTRACT
Exposure to elevated particulate matter (PM) concentrations in ambient air has become a major health concern over urban areas worldwide. Reactive oxygen species (ROS) generation due to ambient PM (termed as their oxidative potential, OP) is shown to play a major role in PM-induced health effects. In the present study, the OP of the ambient PM2.5 samples, collected during summer 2019 from New Delhi, were measured using the dithiothreitol (DTT) assay. Average volume-normalized OP (OPV) was 2.9 ± 1.1 nmol DTT min-1 m-3, and mass-normalized OP (OPm) was 61 ± 29 pmol DTT min-1 µg-1. The regression statistics of OPv vs chemical species show the maximum slope of OPV with the elemental carbon (EC, r2 = 0.72) followed by water-soluble organic carbon (WSOC, r2 = 0.72), and organic carbon (OC, r2 = 0.64). A strong positive correlation between OPm and secondary inorganic aerosols (SIA, such as NH4+ and NO3- mass fractions) was also observed, indicating that the sources emitting NO2 and NH3, precursors of NO3- and NH4+, also emit DTT-active species. Interestingly, the slope value of OPv vs OC for aged aerosols (OM/OC > 1.7, f44 > 0.12 and f43 < 0.04) was 1.7 times higher than relatively fresh organic aerosols (OA, OM/OC < 1.7, f44 < 0.12, f43 > 0.04). An increase in OPv and OPoc with f44 indicates the formation of more DTT active species with the ageing of OA. A linear increase in OPoc with increasing Nitrogen/Carbon (N/C) ratio suggests that nitrogenous OA have higher OP.
ABSTRACT
The Purpose of this study was to evaluate the effect of polymerizable and non-polymerizable dentine desensitizers on retention of complete cast crowns cemented with three different types of cements. Freshly extracted human molars (n = 90) were prepared for standardized crown preparation (6-degree taper 4-mm height). The axial surface area of each preparation was determined and specimens were distributed equally among groups (n = 10). Dentine desensitizers, cementing agents, glass ionomer cement and compomer cement. Teeth were prepared and individual castings were made using high noble porcelain-metal alloy. Castings were cemented, thermo-cycled and removed along the path of insertion using a universal testing machine. Tooth surface as well as inner surface of the casting was examined and nature of cement failure was determined. Compomer cement exhibited the highest retentive strength and all dentine treatments resulted in significantly different retentive values. Zinc phosphate was the least retentive. Crown retentive values of Compomer cement were improved with Prime & Bond NT and Gluma Desensitizer Retentive values of zinc phosphate cement with Prime & Bond NT were decreased and not affected with Gluma Desensitizer Retentive values of Glass ionomer cement were not affected by any of the desensitizers used in the study.
