RESUMO
El esmalte dental es el tejido duro más mineralizado del cuerpo humano. En este trabajo se estudiaron las propiedades mecánicas fundamentales de este tejido para terceros molares de pacientes jóvenes colombianos. Se establecieron la dureza, la tenacidad a la fractura aparente y la fragilidad del esmalte dental en función de la profundidad a partir de la superficie oclusal mediante técnicas de medición de microindentación. Se encontró que las mediciones de dureza son altamente dependientes de la carga utilizada, hallándose que para valores de carga pequeños las huellas alcanzan a representar la dureza de un solo prisma de hidroxiapatita, mientras que para valores altos de carga las huellas abarcan un número de prismas suficientes para estimar la dureza general del esmalte. En términos generales los valores de las propiedades medidas son semejantes a los encontrados en estudios realizados en pacientes jóvenes norteamericanos, evidenciando que estas propiedades del esmalte son independientes de las características raciales o étnicas para pacientes jóvenes, lo cual no es necesariamente extensible al comportamiento de estos tejidos en pacientes mayores.
Dental enamel is one of the hardest and most mineralized tissues of the human body. This work studied the main mechanical properties of this hard tissue for third molars obtained from young Colombian patients. The hardness, apparent fracture toughness and brittleness of enamel were measured as a function of distance from the occlusal surface to the Dental Enamel Junction (DEJ) by means of microndentation techniques. It was found that the hardness measurements are highly dependent on the indentation load, with high values of hardness found when low loads were used. This behavior is explained by the size of the indentations which approached the size of single hydroxyapatite prisms for low load values, while for high load values the size of the indents covered several prisms. Overall, the mechanical properties measured on the enamel from young Colombians are close to the properties reported in the literature for young North American patients. Whether these similarities among young patients persist for older patients deserves further investigation.
RESUMO
<p><b>BACKGROUND</b>Chronic heart failure is a significant cause of cardiovascular morbidity and mortality. This study tested the hypothesis that restrictive filling pattern may provide useful prognostic data for identifying patients with chronic heart failure at high risk of all-cause cardiac death.</p><p><b>METHODS</b>Ninety patients with chronic heart failure [70 men and 20 women, mean age (58.1 +/- 11.6) years] were investigated and followed for (18.8 +/- 7.9) months. During this period, 14 patients died of progressive pump failure, 12 patients underwent heart transplantation, 5 patients died suddenly, and 2 patients died of acute myocardial infarction. A new criterion, the restrictive filling index (RFI), was designed to subgroup patients into a restrictive and a nonrestrictive group.</p><p><b>RESULTS</b>Patients with restrictive filling pattern had a more severe left ventricular dysfunction and a higher cardiac mortality. Analysis by the Kaplan-Meier method revealed that patients in the RFI > or = 1 and RFI < 1 groups had a cardiac events-free survival rate of 52% versus 94% at 1 year, and 27.5% versus 92% at 2 years, respectively. The multivariate Cox proportional hazard model selected RFI as the most powerful prognostic factor (chi(2) = 8.8017, P = 0.0030) for all-cause cardiac death.</p><p><b>CONCLUSION</b>These results indicate that RFI is a simple, noninvasive, and specific clinical predictor for adult chronic heart failure patients who are at a high risk for all-cause cardiac death.</p>