This study evaluated the superoxide dismutase (SOD) activity, copper and zinc levels in saliva of caries-active and caries-free individuals. Eighty healthy adults were divided according to WHO criteria: caries-free (DMFT = 0) and caries-active (DMFT >10). Saliva collected was estimated for SOD activity as well as copper and zinc levels using the atomic nitro blue tetrazolium chloride reduction method and absorption spectrophotometry, respectively. The Student t test was applied. In conclusion, SOD activity as well as copper and zinc levels increased in the caries-active group and showed statistically significant results.

In wet anisotropic etching, the etched profile of undercut convex corners depends on the type of etchant. A considerable amount of research has been carried out to explain this convex corner undercutting and to identify the orientation of undercut planes. However, it is not clearly understood why differently shaped undercut fronts appear with different etchants. Moreover, there has been no descriptive explanation regarding the distinct shape of the undercut convex corner in both KOH and TMAH. In this work, corner undercutting on the surface of a Si{100} wafer is thoroughly investigated. The undercutting behavior is examined for two different kinds of etchants (KOH and TMAH). The study is performed by analyzing the etching characteristics of different kinds of convex corners on the mask patterns. One type of corner in the mask design is formed by <110 > directions, while other types are formed by the intersection of different directions, which shapes the undercut convex corner profile. Furthermore, the appearance of etchant-dependent beveled directions at convex corners is clearly explained using the contour plot of the etch-rate data of a silicon hemisphere.

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Wet bulk micromachining is a popular technique for the fabrication of microstructures in research labs as well as in industry. However, increasing the throughput still remains an active area of research, and can be done by increasing the etching rate. Moreover, the release time of a freestanding structure can be reduced if the undercutting rate at convex corners can be improved. In this paper, we investigate a non-conventional etchant in the form of NH2OH added in 5 wt% tetramethylammonium hydroxide (TMAH) to determine its etching characteristics. Our analysis is focused on a Si{1 0 0} wafer as this is the most widely used in the fabrication of planer devices (e.g. complementary metal oxide semiconductors) and microelectromechanical systems (e.g. inertial sensors). We perform a systematic and parametric analysis with concentrations of NH2OH varying from 5% to 20% in step of 5%, all in 5 wt% TMAH, to obtain the optimum concentration for achieving improved etching characteristics including higher etch rate, undercutting at convex corners, and smooth etched surface morphology. Average surface roughness (Ra), etch depth, and undercutting length are measured using a 3D scanning laser microscope. Surface morphology of the etched Si{1 0 0} surface is examined using a scanning electron microscope. Our investigation has revealed a two-fold increment in the etch rate of a {1 0 0} surface with the addition of NH2OH in the TMAH solution. Additionally, the incorporation of NH2OH significantly improves the etched surface morphology and the undercutting at convex corners, which is highly desirable for the quick release of microstructures from the substrate. The results presented in this paper are extremely useful for engineering applications and will open a new direction of research for scientists in both academic and industrial laboratories.

Potassium hydroxide (KOH) and tetramethylammonium hydroxide (TMAH) are most extensively used etchants for wet anisotropic etching process. Amongst these two etchants, KOH is a low cost etchant and provides high etch rate anisotropy between Si{111} and Si{100} planes. Increasing the etch rate is an important research problem for both academic and industrial applications. In this research, we study the effect of hydroxylamine (NH2OH) in 20 wt% KOH on the etching characteristics of Si{100}. This type of wafer orientation (i.e. Si{100}) is selected owing to its popularity in fabricating planar semiconductor devices (e.g. diode, transistor, complementary metal oxide semiconductor (CMOS), etc.) and MEMS components (e.g. cantilever, diaphragm, etc.). A systematic parametric analysis of various concentrations of hydroxylamine (from 0 to 20% in step of 5%) added 20 wt% KOH is carried out and its effect on the etching characteristics is discussed. We have found that the etch rate of Si{100} is increased threefold when 15% NH2OH is added to 20 wt% KOH solution. Additionally, this concentration also exhibits improved etching characteristics including undercutting rate, etch selectivity, and surface morphology. We have obtained improved etching characteristics when NH2OH is added to 20 wt% KOH. Due to an improvement in etching characteristics, present research is very useful to pave the path toward application in microfabrication industries as well as academic research laboratories.

Total antioxidant capacity of saliva has a linear relation with caries, i.e., as the severity of caries increases, the TAC level also increases.

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