Effects of aging on repair of resin-modified glass-ionomer cements

The effects of aging on the repair bond strengths of resin-modified glass-ionomer cements after different methods of surface conditioning were studied. Surface conditioning methods included the following: maleic acid; maleic acid with resin application; polyacrylic acid; polyacrylic acid with resin application. Shear bond testing between the aged and new material was carried out with an Instron Universal testing machine. Surface conditioning with maleic acid and resin application gave the highest repair bond strengths at 3 and 6 months. There was, however, no statistically significant difference in bond strengths between the different treatment groups after both 3 and 6 months storage. Intergroup comparisons revealed no significant difference in failure modes after both storage periods. For all treatment groups, no significant difference in repair bond strengths was noted between storage after 1 week, 3 and 6 months. There appears to be a general decrease in repair bond strengths for all treatment groups after 3 months storage. The clinical repair of resin-modified glass-ionomer cements after this period of time is therefore not recommended.     

Chemoprevention of spontaneous tumorigenesis in nullizygous p53- deficient mice by dehydroepiandrosterone and its analog 16alpha-fluoro- 5-androsten-17-one

Transgenic mice with both alleles of the p53 tumor suppressor gene product 'knocked out' by gene targeting are susceptible to early development of tumors, chiefly lymphomas and sarcomas. Compared with the control group, administration of dehydroepiandrosterone (DHEA) at 0.3% of the diet to male p53-deficient mice extended their lifespan by delaying death due to neoplasms (from 105 to 166 days on study, P = 0.002), primarily by suppressing lymphoblastic lymphoma (from 45 to 6% of neoplastic deaths, P = 0.010). Treatment with a synthetic DHEA analog, 16alpha-fluoro-5-androsten-17-one (compound 8354), at 0.15% of the diet also increased lifespan, to 140 days for mice that developed tumors (P = 0.037). The effects of these steroids on lifespan and tumor development did not appear to be strongly related to inhibition of food consumption and weight gain, in that a group pair-fed with control diet to the reduced food consumption of the DHEA-treated group developed and died of the same types of neoplasms at the same rate as the controls fed ad libitum. The chemopreventive effect of these steroids has been proposed to be due to suppression of DNA synthesis by inhibition of glucose 6-phosphate dehydrogenase, the rate-limiting enzyme of the pentose phosphate pathway. Although DHEA and its analog are strong non- competitive inhibitors of this enzyme in vitro, treatment with DHEA did not deplete cellular nucleotide pools in the liver, as would have been predicted. The chemopreventive effect of DHEA in this model may be due to steroid-induced thymic atrophy and suppression of T cell lymphoma, permitting these mice to survive long enough to develop tumors with longer latency.      

Failure of ablation of a mediastinal parathyroid adenoma by repeated contrast staining

In a patient with primary hyperparathyroidism an attempt was made to ablate a middle mediastinal parathyroid gland by forceful staining with radiographic contrast material. The gland was stained on two separate occasions, two weeks apart. Both times the serum calcium level temporarily fell to the normal range but reverted to abnormal levels. The patient ultimately required surgery for correction of hypercalcemia. The mechanism of staining and possible reasons for failure as well as potential complications are discussed.     

The transcutaneous measurement of the elastic properties of the human saphenous vein femoropopliteal bypass graft.

The pressure-strain elastic modulus and compliance of 20 reversed saphenous femoropopliteal vein grafts have been measured by a noninvasive, ultrasonic method. The grafts had been in place for an average of 33.6 months, 11 days to 128 months. In this study no correlation was demonstrated between wall stiffness and duration of implantation. It is concluded that the elastic properties of vein grafts may remain stable for considerable periods of time.     

Gallium-67 lung uptake: conjugate-view technique

A conjugate-view technique is derived for calculation of absolute gallium-67 (Ga-67) uptake from scintillation-camera images. The technique combines counts of posterior and anterior images of the lung with an attenuation correction obtained from cobalt-57 (Co-57) transmission imaging. The formulation is such that the effects of Compton scatter build-up are accounted for. Studies utilizing a canine model indicated that, normally, more activity is located in the chest wall than in the lungs. The quantitative technique must therefore accurately account for a variety of Ga-67 distributions, including that in the chest wall. Calculations were performed using a three-component model comparing results obtained with the conjugate-view approach to the actual uptake. These calculations suggest that an assumption of uniform activity distribution allows an accuracy of approximately +/- 10% over a broad range of body-part thicknesses and uptake by the lungs. It was concluded that the conjugate-view technique is necessarily approximate but can provide clinically useful results.