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Biomedical subjects

N Sundaram

Publications and source records attributed to N Sundaram.

4 recordsLinked to original sources
PubMed2005

Stress ratio contributes to fatigue crack growth in dentin.

An experimental study of fatigue crack growth in dentin was conducted, and the influence of stress ratio (R) on the crack growth rate and mechanisms of cyclic extension were examined. Double Cantilever Beam (DCB) fatigue specimens were sectioned from bovine molars and then subjected to high cycle fatigue loading (10(5) < N < 10(6)) under hydrated conditions. The evaluation consisted of Mode I loads with stress ratios that ranged from -0.5 to 0.5. The fatigue crack growth rates were measured and used to estimate the crack growth exponent (m) and coefficient (C) according to the Paris Law model. The fatigue crack growth rates for steady-state extension (Region II) ranged from 1E-7 to 1E-4 mm/cycle. It was found that the rate of cyclic extension increased significantly with increasing R, and that the highest average crack growth rate occurred at a stress ratio of 0.5. However, the crack growth exponent decreased with increasing R from an average of 4.6 (R = 0.10) to 2.7 (R = 0.50). The stress intensity threshold for crack growth decreased with increasing R as well. Results from this study suggest that an increase in the cyclic stress ratio facilitates fatigue crack growth in dentin and increases the rate of cyclic extension, both of which are critical concerns in minimizing tooth fractures and maintaining lifelong oral health.

Animals↗
PubMed2000

Selenium causes growth inhibition and apoptosis in human brain tumor cell lines.

We examined the effect of the trace element selenium on human glioma cell lines: T98G, U373MG, and U87MG, in addition to dermal fibroblast cells. Cultures were incubated with sodium selenite, and the following parameters were studied: cell growth, mitochondrial function, and ultrastructure. Cell growth was assayed by counting the number of viable cells after treatment with selenium. Mitochondrial function was analyzed using the MTT (tetrazolium salt reduction) assay. Apoptosis was determined by evaluating nuclear chromatin condensation by electron microscopy. The results indicated that selenium had a significant inhibitory effect on the growth of the tumor cells but had little effect upon dermal fibroblasts which had been passaged numerous times. Selenium also induced mitochondrial damage as shown by MTT assay in two brain tumor cell lines and in minimally passaged fibroblasts, but it had little effect upon the high-passage fibroblasts. Ultrastructurally, mitochondria had electron-dense inclusions resulting from selenium treatment. High rates of apoptosis were induced by selenium in the tumor cell lines and in the minimally passaged fibroblasts, whereas the fibroblasts with a high number of passages had some resistance to selenium treatment. This study correlates the adverse effects of selenium on mitochondrial function, inhibition of cell growth, and apoptosis and shows that selenium similarly affects three different brain tumor cell lines and minimally passaged fibroblasts. Further, the results with fibroblasts show that some types of cells after repeated passages can develop resistance to selenium damage.

Apoptosis↗
PubMed1992

Stabilization of acute acromioclavicular dislocation by a modified Bosworth technique: a long-term follow-up study.

We reviewed 31 patients who underwent modified Bosworth procedures for grade III acromioclavicular dislocation. Their average age at the time of surgery was 32.5 years (range 18-60 years) and the mean follow-up was 11.6 years (range 5-20.6 years). The operation was performed for young, active individuals engaged in heavy manual work, in those who wished to return to contact sports and in patients with prominent clinical deformity. The results were analysed using the criteria suggested by Imatani et al. (1975). Of the patients, 24 (77 per cent) had excellent or good results and seven (23 per cent) had fair or poor results. There was no correlation between the radiological findings and the clinical results.

Acromioclavicular Joint↗