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At least 649 records · Page 36Linked to original sources
PubMed1988

Retention magnets in guiding plates of distal-extension removable partial dentures.

This investigation studied vertically placed magnets that act simultaneously as guiding plates and retentive devices. The retention of vertically placed magnets was less than that of horizontally or obliquely placed magnets, but comparable to that of I-bar retainers. Load-induced stresses were lower, transmitted more axially to the abutments and were generally more equitably distributed than stresses produced by magnets in other orientations to the abutment tooth. The force distribution characteristics were less stressful than those of a comparable RPD with distal guiding plates, mesial rests, and I-bar retainers. Although the investigators were initially concerned about the relative capabilities of the vertically placed magnets, in vitro and in vivo studies demonstrated that retention was as good if not better than that of conventional clasp designs.

Dental Stress Analysis↗
PubMed1988

The effect of the resilient-layer distal-extension partial denture on movement of the abutment teeth: a new methodology.

The new methodology presented in this article is simple, reliable, and accurate. The testing casts represented a reasonable simulation of human dentition. The artificial mouth reproduced major mandibular movement in a physiologic manner and applied controlled load instead of static load. The abutment movement sensor and the strain-gauge configurations suggested showed a higher level of sensitivity, accuracy, and reproducibility. This method was intended to be used for in vitro studies of RPD designs. It allowed recording of occlusal forces around the abutment tooth in the three axes of motion simultaneously.

Alveolar Process↗
PubMed1992

Collateral blood flow from skeletal muscle to normal myocardium.

Collateral blood vessels from skeletal muscle to myocardium might supplement intramyocardial collaterals during periods of acute myocardial ischemia. This study was conducted to verify the existence of such collaterals and to measure their contribution to collateral flow. In 12 male goats, the innate coronary collateral system to a moderate size myocardial risk area was defined with colored microspheres, and a latissimus dorsi pedicle flap was then apposed to the heart. After 3 weeks, skeletal muscle to myocardial collaterals were characterized by (a) creation of vascular casts (three animals); (b) estimation of skeletal muscle to myocardial collateral blood flow (three animals); and, (c) measurement of total collateral blood flow to the risk area (innate plus skeletal muscle to myocardial collateral flow). Under a dissecting microscope the vascular casts revealed direct communications from the skeletal muscle which penetrated deeply into the myocardium. With the coronary artery to the risk area open, the estimated myocardial collateral blood flow derived from the muscle flap was 0.01, 0.02, and 0.04 ml/min. With the coronary artery to the risk area closed, there was no significant increase in total coronary collateral blood flow. Although the quantity of blood flow delivered by skeletal muscle collaterals was small, this study demonstrates that clearly identified collateral blood vessels form between skeletal muscle and myocardium in a cardiomyoplasty model. This raises the possibility that, under conditions more favorable to their development, extramyocardial collaterals from skeletal muscle might be exploited to augment the intramyocardial collateral system.

Animals↗
PubMed1989

Computational issues of importance to the inverse recovery of epicardial potentials in a realistic heart-torso geometry.

In vitro data from a realistic-geometry electrolytic tank were used to demonstrate the consequences of computational issues critical to the ill-posed inverse problem in electrocardiography. The boundary element method was used to discretize the relationship between the body surface potentials and epicardial cage potentials. Variants of Tikhonov regularization were used to stabilize the inversion of the body surface potentials in order to reconstruct the epicardial surface potentials. The computational issues investigated were (1) computation of the regularization parameter; (2) effects of inaccuracy in locating the position of the heart; and (3) incorporation of a priori information on the properties of epicardial potentials into the regularization methodology. Two methods were suggested by which a priori information could be incorporated into the regularization formulation: (1) use of an estimate of the epicardial potential distribution everywhere on the surface and (2) use of regional bounds on the excursion of the potential. Results indicate that the a posteriori technique called CRESO, developed by Colli Franzone and coworkers, most consistently derives the regularization parameter closest to the optimal parameter for this experimental situation. The sensitivity of the inverse computation in a realistic-geometry torso to inaccuracies in estimating heart position are consistent with results from the eccentric spheres model; errors of 1 cm are well tolerated, but errors of 2 cm or greater result in a loss of position and amplitude information. Finally, estimates and bounds based on accurate, known information successfully lower the relative error associated with the inverse and have the potential to significantly enhance the amplitude and feature position information obtainable from the inverse-reconstructed epicardial potential map.

Animals↗
PubMed1989

A Green's function method for analysis of oxygen delivery to tissue by microvascular networks.

A theoretical model is formulated for analyzing oxygen delivery from an arbitrary network configuration of cylindrical microvessels to a finite region of tissue. In contrast to models based on the classical Krogh cylinder approach, this model requires no a priori assumptions concerning the extent of the tissue region supplied with oxygen by each vessel segment. Steady-state conditions are assumed, and oxygen consumption in the tissue is assumed to be uniform. The nonlinear dissociation characteristics of oxyhemoglobin are taken into account. A computationally efficient Green's function approach is used, in which the tissue oxygen field is expressed in terms of the distribution of source strengths along each segment. The utility of the model is illustrated by analyses of oxygen delivery to a cuboidal tissue region by a single segment and by a six-segment network. It is found that the fractional contribution of the proximal segments to total oxygen delivery increases with decreasing flow rate and metabolic rate.

Animals↗
PubMed1990

Plasma skimming in serial microvascular bifurcations.

Red cell distribution in simple two bifurcation networks has been studied experimentally. The results indicate that fractional red cell flux/fractional volumetric flow curves can be asymmetric at the downstream bifurcation. The important parameters affecting this asymmetry are the fractional flow into the upstream branch Q1*, and the ratio of the distance between junctions to the volumetric flow rate, z/Q. The asymmetry is attenuated as z/Q increases. In 50-micron tubes with Q1* of 0.5, symmetric phase separation behavior is regained when z/Q is greater than 200 sec/mm2. In 25-micron tubes symmetry is recovered before z/Q reaches the value of 50 sec/mm2. These results agree with in vivo data of previous studies and provide additional evidence that flow history can be important in microvascular networks if junctions are close together or flow rates are sufficiently high.

Blood Flow Velocity↗
PubMed1977

Polyethylene tubes as a model for the root canal.

Polyethylene tubes, closed at both ends with casting wax and with four perforations in the middle, were implanted subcutaneously in rats and evaluated as a research model simulating the root canal. As controls, wax bars and unperforated tubes were implanted. Attention was given to the reaction of the tissue surrounding the perforated empty tube, the tissue reaction to polyethylene and casting wax, and to the displacement of the tubes.

Animals↗
PubMed1976

Morphology of the bronchial tree in the dog.

Polyester resin casts were made of the bronchial trees from three adult dogs. The branches were ordered by the method of Strahler and the number of branches in each order counted. The length and diameter of each branch was measured and the mean dimensions of branches in each order calculated. When number, mean diameter and mean length of branches in each order are plotted semilogarithmically against order, linear relationships are found. From the data thus obtained a dimensional model of the dog's bronchial tree has been developed.

Animals↗