Influence of chemicals on wear of dental composites

The wear resistance of a commercial dental restorative composite exposed to different chemicals was measured with a pin-disc apparatus. The initial wear rate increased dramatically once the composite had been immersed in chemicals known to soften the cross-linked matrix material, which is a copolymer derived from BIS-GMA and diluent monomer. The increase of wear rate in a chemically softened composite was found to persist over a depth beyond 160 μm for specimens immersed over two wk prior to wear testing.

Relationship between subsurface damage and wear of dental restorative composites

Pin and disc wear measurements were made on a commercial dental composite over a stress range from 2.5 to 20 MPa. The wear rates were found to increase suddenly during wear at times which tended to decrease with increasing stress. The results are interpreted in terms of wear mode conversion which results from the build-up of subsurface damage during wear. Micrographs showing damaged layers are compared with those from restorations worn in vivo.

A silver staining technique for investigating wear of restorative dental composites

A silver staining technique was developed to demonstrate microdefects in dental restorative composites. Fine silver particles were preferentially introduced into the damaged region to provide optical contrast between the damaged and the undamaged regions. The amount of silver deposition determined with an electron probe microanalyzer, provided an indication of the extent of damage within the dental composites. Examples to demonstrate this technique were given with one clinically worn dental composite restoration and one in vitro worn composite sample.

Purification of Torpedo californica post-synaptic membranes and fractionation of their constituent proteins

A rapid methof for preparation of membrane fractions highly enriched in nicotinic acetylcholine receptor from Torpedo californica electroplax is described. The major step in this purification involves sucrose-density-gradient centrifugation in a reorienting rotor. Further purification of these membranes can be achieved by selective extraction of proteins by use of alkaline pH or by treatment with solutions of lithium di-idosalicylate. The alkali-treated membranes retain functional characteristics of the untreated membranes and in addition contain essentially only the four polypeptides (mol.wts. 40000, 50000, 60000 and 65000) characteristic of the receptor purified by affinity chromatography. Dissolution of the purified membranes or of the alkali-treated purified membranes in sodium cholate solution followed by sucrose-density-gradient centrifugation in the same detergent solution yields solubilized receptor preparations comparable with the most highly purified protein obtained by affinity-chromatographic procedures.

Seasonal variations in vasopressin secretion in rats

Plasma vasopressin concentrations and vasopressin content in neurohypophysis in rats show seasonal variations; namely, high in summer and low in winter.

Probabilistic Aspects of Designing with Ceramics

The paper reviews the design methodology for brittle materials which is being developed under the Ford/ARPA contract. Theoretical aspects of designing with high-temperature ceramics are discussed and demonstrated on a turbine rotor system. Statistical treatment of brittle behavior, based on Weibull’s model, is reviewed and relations for predicting probability of failure and material strength requirements for complex ceramic structures are presented. Reliability considerations, uncertainty of predictions, and need for proof testing are discussed. Similarly, a probabilistic treatment of time to failure of a typical turbine structure in the presence of slow crack growth is presented using fracture mechanics and Weibull relations.

Effect of insulin, glucose, and controlled diabetes mellitus on human jejunal function

The effects of serum insulin concentration, serum glucose concentration, and of insulin-dependent diabetes mellitus on human jejunal glucose, Na, and H2O absorption were assessed. Triple-lumen perfusion studies were carried out in 20 nondiabetic and 9 insulin-requiring diabetic male volunteers. In seven normal subjects, sequential elevation of serum insulin concentrations from 20 muU/ml to 50 and 100 muU/ml for 2 h each, with maintenance of constant serum glucose levels, failed to significantly alter glucose, Na, and H2O absorption. Absorption of glucose, Na, and H2O was similar when the serum glucose concentration was maintained at 125 and at 250 mg/100 ml. Glucose absorption results during 26 perfusion studies in 20 control subjects were compared with results obtained during 20 perfusion studies in 9 diabetic subjects. Glucose concentrations in isotonic perfusates were 25, 40, or 75 mM. Na and H2O absorption rates were similar in both groups. Regression lines relating glucose load or geometric mean study segment glucose concentration to glucose absorption were also comparable. These results indicate that insulin-requiring diabetics absorb glucose, Na, and H2O normally.

Radionuclide demonstration of small-bowel anatomy in the afferent-loop syndrome: case report

Radionuclide imaging with I-131 rose bengal and orally administered Tc-99m colloid was successfully used to show the presence of an afferent loop that was not visualized by radiographic, endoscopic, or ultrasonic procedures.