Fracture Toughness of Dental Porcelains Evaluated by IF, SCF, and SEPB Methods

Fracture toughness of six dental porcelains with leucite content ranging from 0 to 22 vol% was evaluated by indentation fracture (IF), surface crack in flexure (SCF), and single edge pre-cracked beam (SEPB) methods. The results of the IF method were similar to those of the SCF method for all the porcelains investigated. The results of the SEPB were similar to those of the other two methods only for the glassy porcelains, but for leucite-based porcelains this method resulted in higher values of K _{I c} . Based on microstructure, fractographic analysis, and an additional single edge V-notched beam test, it was concluded that the pre-crack size influences the value of K _{I c} for porcelains reinforced by leucite. For design and failure analysis purposes, the K _{I c} determined by SCF method should be preferred, since fracture of dental restorations usually starts from small surface cracks.     

Hyperhomocysteinemia and polymorphisms of the methylenetetrahydrofolate gene in hemodialysis and peritoneal dialysis patients

Hyperhomocysteinemia has been documented in chronic renal failure (CRF). Premature as well as progressive occlusive vascular disease is common. Mutations or polymorphisms in the gene of the enzyme methylenetetrahydrofolate reductase (MTHFR), as C677T, A1298C and G1793A, are associated with hyperhomocysteinemia and possibly with elevated risk for vascular diseases. This study was conducted on 89 individuals with renal failure on dialysis to determine the allelic and genotypic frequencies of the mutations in the MTHFR gene and hyperhomocysteinemia. Blood samples were colleted for determination of homocysteine and DNA. The C677T, A1298C and G1793A mutations were detected. This study confirmed the high prevalence of hyperhomocysteinemia in patients on dialysis, which was diagnosed in 76 patients (85.39%) and high incidence of the C677T and A1298C mutation, 42 (47.19%) and 29 (32.58%) patients, respectively. Five patients (5.62%) presented the G1793A mutation and hyperhomocysteinemia. The authors concluded that there was no influence of the polymorphisms on homocysteine levels in these patients.     

The Development Process of the Metropolitan Region of Sao Paulo: Contradictory and Accelerated-SP Brazil-Social and Environmental Aspects

This paper addresses the contradictions that can be seen within the process of economic and urban growth experienced by developing countries. Sao Paulo synthesizes these contradictions and is an example of how far people can go on environmental destruction when associated with social inequity.