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Biomedical subjects

K C Lim

Publications and source records attributed to K C Lim.

At least 19 recordsLinked to original sources
PubMed1994

Structure and regulation of the chicken erythroid delta-aminolevulinate synthase gene.

Erythroid cells regulate heme biosynthesis in a manner that is distinct from all other cell types. While heme negatively regulates the synthesis of the housekeeping delta-aminolevulinate synthase (ALAS-N) in all non-erythroid cells, the expression of an erythroid-specific isozyme (ALAS-E) is developmentally regulated in red blood cells. As a first step towards understanding the molecular basis for the transcriptional regulation of ALAS-E during erythropoiesis, we cloned and characterized the chicken ALAS-E locus. This gene spans 18 kbp and is composed of eleven exons. The intron/exon structure of erythroid ALAS was found to be conserved among several vertebrate species. Direct RNA sequencing identified a 5' untranslated region that is derived from two continuous exons and is predicted to form a very stable stem-loop structure that bears resemblance to the ferritin iron-responsive element. Tissue-specific expression of the ALAS-E gene was analyzed by transient transfection assays in hematopoietic cells of both erythroid and non-erythroid origins. These experiments identified distal (-784 to -505 bp) and proximal (-155 to +21 bp) promoter elements which are required for high level, erythroid-specific transcription.

5-Aminolevulinate Synthetase↗
PubMed1993

Expression of the chicken GATA factor family during early erythroid development and differentiation.

The DNA motif WGATAR has been identified within transcriptional regulatory domains of globin and other erythroid-specific genes and the activator proteins that bind to this regulatory element, the GATA factors, belong to a multi-gene family that is expressed in chicken erythroid cells. Here we show that, as in chickens, multiple members of the GATA factor family are expressed in human and murine erythroid cells. During the early stages of chicken embryogenesis (well before blood island formation), each of the GATA family members is transcribed with a unique temporal and spatial pattern. In the primitive erythroid lineage, transcription of the embryonic epsilon-globin gene parallels GATA-1 expression while the switch to beta-globin transcription in definitive erythroid cells is directly preceded by a pronounced increase in GATA-3 accumulation. The timing and pattern of expression of these different mRNAs during avian erythroid development and differentiation suggests that temporally regulated changes in GATA factor expression are required for vertebrate hematopoiesis.

Animals↗
PubMed1992

Effect of operator variability on void formation in impressions made with an automixed addition silicone.

This study examined voids produced in impressions of an automixed addition-reaction silicone. Two operators took the impressions using material dispensed from either intra-oral tips or an impression syringe. The material was also hand-mixed for comparison. There were no differences in the number of voids in the automixed material dispensed using the intra-oral tip or impression syringe. Automixing produced substantially fewer voids than hand-mixing. There was a significant difference in the number of voids in the impressions made by the two operators.

Dental Impression Materials↗
PubMed1991

Effect of interchanging automatic mixing tips on void formation for an automixed addition silicone impression.

This study examined the effect of interchanging mixing tips on void formation for impressions of an automixed addition silicone material. The impressions were made of a series of stainless-steel cylinders by two dentists. The voids were counted at a predetermined site with a binocular microscope. The results showed that there were no significant variations in the number of voids in impressions of the automixed addition silicone using the three different mixing tips. However, one dentist made impressions that had substantially less voids for all three mixing tips.

Air↗
PubMed1990

Microleakage of intermediate restorative materials.

This study compares the microleakage of a glass ionomer cement, Ketac Fil, used without cavity conditioning, with the established intermediate restorative materials, Cavit-W, and a reinforced zinc oxide-eugenol cement, Kalzinol. Microleakage was assessed using an electrochemical technique. At the end of 30 days, the materials tested, listed in decreasing order of microleakage, were Cavit-W, Ketac Fil inserted without cavity conditioning, Kalzinol, and the control group of Ketac Fil inserted into conditioned cavities. There was no significant difference in the microleakage observed in Ketac Fil restorations inserted without cavity conditioning and Kalzinol (p = 0.450), while the differences between the other groups were highly significant (p less than 0.001).

Calcium Sulfate↗
PubMed1989

MRI study of brain changes with short-term abstinence from alcohol.

Magnetic resonance brain scans were obtained from 10 chronic alcoholics within 2 weeks of alcohol withdrawal, and 19 to 28 days later. Age-matched control subjects were scanned at comparable intervals. At the initial scan, the alcoholics had larger lateral ventricles than the controls; at the second scan, their ventricles were significantly smaller than at the first scan. Among the controls, there was no mean change in the size of the lateral ventricles between the first and second scan. This study demonstrates reversibility in ventricular enlargement with short-term abstinence from alcohol. The role of rehydration in this process and the possibility of further changes with continued abstinence remain to be tested.

Alcoholism↗
PubMed1989

Methods of proximal amalgam overhang removal--a comparison of different techniques.

It is widely accepted that the overhanging restoration is an aggravating factor in the initiation and progression of periodontal disease, and when detected, the overhang should be removed. Some methods for removing proximal amalgam overhangs are the EVA reciprocating motor driven system, roto-pro, flame-shaped steel bur, diamond bur and sonic scaler. This article illustrates the trimmed surface after overhang removal with photographs taken at 1:1 magnification. The smoothest surface was produced by EVA system where the overhang was removed with a diamond tip followed by polishing with prophylaxis paste using the plastic tip. The roughest surface was produced by the sonic scaler, whilst the others were intermediate. Of the single step methods, the instrument which combined speed while leaving a reasonable surface was the rotopro.

Carbon↗
PubMed1988

Mystery of the separating tungsten carbide burs.

Three instances of tungsten carbide bur separation, one of which resulted in the patient swallowing the separated bur head are described. This spate of bur heads separating from the shank was associated with a cold sterilising solution used for disinfection.

Corrosion↗
PubMed1986

Some problems encountered in endodontic radiography.

This retrospective survey highlights some of the problems faced by undergraduate students using the bisecting angle technique in endodontic radiography. The radiographs of maxillary incisors and premolars were observed to suffer from a greater amount of distortion than radiographs of the corresponding mandibular teeth. Further, the presence of rubber dam equipment affected the accuracy of the radiographs, and this was more apparent on the radiographs of the maxillary incisors and premolars compared to the mandibular incisors and premolars. Other problems identified included superimposition, indistinct and missed root apices. Methods to overcome these problems are suggested.

Bicuspid↗