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Biomedical subjects

A M Lacy

Publications and source records attributed to A M Lacy.

87 records · Page 5Linked to original sources
PubMed1981

Time-dependent accuracy of elastomer impression materials. Part I: Condensation silicones.

1. Although condensation silicone elastomers can be used to produce multiple dies from a single impression, one can expect changes in dimensions of dies produced from successive pours. 2. Putty/wash systems exhibit variable behavior among different brands. Some products produce a series of dies of increasing diameter over a 4-day period, while other brands may produce a series of dies whose diameters decrease as they are successively poured. 3. Light-body wash silicone impressions made in adhesive-lined custom acrylic resin trays produce dies which increase in diameter with time. 4. Putty/wash system, in general, show a greater eccentricity of dies than is seen with custom-tray/adhesive/wash systems, but there were some significant exceptions among the brands tested. 5. There does not appear to be any difference in behavior between single-wash and double-mix techniques in the condensation-silicone systems. 6. For maximum accuracy, the condensation-silicone systems should be poured as soon as possible after making the impression.

Adhesives↗
PubMed1981

Bottled mineral waters polluted by protozoa in Mexico.

A survey of protozoa polluting bottled mineral water in Mexico was carried out using samples obtained form the three best-selling brands of bottled mineral water in the country. The organisms were concentrated through filtration procedures and subsequently cultured in the sterile media. The cultures were observed over four weeks, with identification to the level of genus and species. Most commonly found were the amoebae Naegleria gruberi, Acanthamoeba astronyxis, and Vahlkampfia vahlkampfi (trophic as well as cystic stages) plus one flagellate, Bodomorpha minima. No ciliates were detected. The public health importance of the findings is obvious, since some strains of Naegleria and Acanthamoeba have the potential to cause human disease that may lead to death.

Amoeba↗
PubMed1980

Effectiveness of hardening films on die stone.

1. Cyanoacrylate resins and resinous die hardeners effectively improved the hardness and abrasion resistance of stone dies. 2. Application of liquid resins followed by blotting and/or blowing with compressed air produced an improved surface without clinically significant dimensional change. The extent of film buildup was qualitatively related to the viscosity of the resin. 3. Application of multiple coats of resin or simply soaking the dies in resin without further blotting or other mode of removal of the excess produced a thick film which can obliterate surface detail.

Calcium Sulfate↗
PubMed1980

Xeroradiography for imaging biomaterials--A comparison with conventional radiography.

Our visual comparison of dental xeroradiographs versus conventional film radiographs demonstrated the superiority of the dental xeroradiographic technique for the imaging of all radiolucent and mild-to-moderately radiopaque materials. Both systems were equally valuable for the imaging of very dense radiographic materials such as gold and amalgam alloys.

Biocompatible Materials↗
PubMed1970

Histidine-mediated control of tryptophan biosynthetic enzymes in Neurospora crassa.

The formation of the five tryptophan biosynthetic enzymes of Neurospora crassa was shown to be derepressed in histidine-starved cells. This histidine-mediated derepression was not due to a lowered intracellular concentration of tryptophan in these cells. Furthermore, histidine-mediated derepression of tryptophan enzymes was found to be coordinate and not subject to reversal by tryptophan of either exogenous or biosynthetic origin. The synthesis of tryptophan enzymes also was found to be coordinate in cells which were not histidine-starved. Although histidine is clearly involved in regulating the synthesis of tryptophan enzymes, it did not prevent either tryptophan-mediated derepression of tryptophan enzymes or indole-3-glycerol phosphate-mediated derepression of tryptophan synthetase.

Histidine↗
PubMedDate not supplied

Laparoscopic-assisted vs. open colectomy for colorectal cancer: influence on neoplastic cell mobilization.

Laparoscopic surgery for treatment of colorectal cancer has been suggested to enhance tumor dissemination. Recently, molecular techniques have been developed to detect micrometastatic disease in patients with solid tumors, with a higher accuracy than cytologic or immunohistochemical approaches. This study was undertaken to investigate the potential harmful effects of laparoscopic-assisted colectomy on neoplastic cell mobilization in patients with resectable colorectal cancer. Fifty patients with nonmetastatic colorectal cancer were randomly assigned to laparoscopic-assisted (LAC, n = 26) or open (OC, n = 24) colectomy. Peripheral venous blood samples were obtained preoperatively, immediately after tumor removal, and 24 hours later. In 10 patients from each treatment group, portal blood and peritoneal fluid samples were also obtained before and after resection. Neoplastic cells were detected by means of reverse transcriptase-polymerase chain reaction targeted to carcinoembryonic antigen (CEA) transcription. CEA mRNA was detected in peripheral venous blood samples from 35 of 50 colorectal cancer patients preoperatively. Among those 15 baseline-negative patients, four experienced conversion 24 hours after tumor resection (2 [33%] of 6 in the LAC group vs. 2 [22%] of 9 in the OC group; NS). At that time point, clearance of CEA mRNA expression was observed in 14 of the 35 baseline-positive patients (9 [45%] of 20 in the LAC group vs. 5 [33%] of 15 in the OC group; NS). In addition, only one patient in the LAC group with baseline-negative CEA mRNA expression experienced portal blood conversion after tumor removal, although his peripheral blood level remained negative. Finally, baseline peritoneal fluid CEA mRNA expression was never detected, but one patient in each group became positive postoperatively. These results confirm that preoperative and perioperative mobilization of neoplastic cells is a frequent occurrence in patients with colorectal cancer, but the surgical approach (LAC vs. OC) does not seem to be a determining factor.

Adult↗
PubMedDate not supplied

Adhesive monomers for porcelain repair.

The purpose of this investigation was to test the bond strengths of several adhesive systems intended for intraoral resin-to-porcelain and resin-to-metal bonding. All measurements were compared with resin bonding to etched bovine enamel. Based on these data and the authors' own clinical experiences, protocols for intraoral porcelain repair are presented for fractures in porcelain only, fractures with both porcelain and metal exposed, and fractures with all metal exposure.

Dental Bonding↗