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Biomedical subjects

K H Chung

Publications and source records attributed to K H Chung.

At least 73 records · Page 4Linked to original sources
PubMed1996

Renal apoptosis and clusterin following ureteral obstruction: the role of maturation.

PURPOSE: Unilateral ureteral obstruction (UUO) increases renal apoptosis as well as clusterin, which in turn is modulated by angiotensin II. The present study was designed to investigate the role of maturation in these responses. MATERIALS AND METHODS: Neonatal and adult Sprague-Dawley rats underwent UUO or sham operation. Fourteen days later, renal apoptosis was quantitated by flow cytometry, and renal messenger RNA (mRNA) was quantitated for renin and clusterin. Apoptotic cells, macrophages, clusterin and Dolichos biflorus agglutinin were localized by immunohistochemistry. RESULTS: Following ipsilateral UUO, renal DNA content increased in the adult but decreased in the neonate. Renal macrophage infiltration induced by UUO was 2-fold greater in adults than in neonates, while distal tubular apoptosis was 2-fold greater in neonatal than in adult kidneys. Unilateral ureteral obstruction markedly increased renal renin mRNA expression in the neonate, but not in the adult, while clusterin expression was greater in adults than in neonates. Clusterin was localized to some, but not all, distal tubules containing apoptotic cells. CONCLUSIONS: We conclude that, compared with the adult, UUO in the neonate induces greater apoptosis, which in turn contributes to reduced renal DNA. This may be modulated by relative suppression of clusterin in the obstructed neonatal kidney due to greater activation of the renin-angiotensin system.

Aging↗
PubMed1995

Regulation of renal growth factors and clusterin by AT1 receptors during neonatal ureteral obstruction.

Unilateral ureteral obstruction (UUO) in the neonate impairs growth of the ipsilateral kidney. Since renal renin expression is increased by UUO, we hypothesized that, by activation of AT1 receptors, angiotensin II (ANG II) regulates expression of transforming growth factor-beta 1 (TGF-beta 1) and epidermal growth factor (EGF) in the obstructed kidney. Sprague-Dawley rats underwent left UUO or sham operation within the first 48 h of life and received losartan, 40 mg.kg-1.day-1, or saline. After 14 days, steady-state renal mRNA was determined for renin, TGF-beta 1, EGF, and clusterin. Losartan reduced the DNA content of the intact kidneys but did not further decrease that of the obstructed kidney. Losartan increased renal renin expression and decreased EGF expression by 80%, regardless of UUO. In contrast, losartan reduced TGF-beta 1 expression by 34% in obstructed kidneys but did not affect TGF-beta 1 in intact kidneys. Losartan increased clusterin expression by 60% in obstructed kidneys and seven-fold in intact kidneys. We conclude that activation of the ANG II AT1 receptor is necessary for normal renal growth and that TGF-beta 1 is regulated by AT1 receptors in the obstructed, but not intact, kidneys. Through AT1 receptors, endogenous ANG II stimulates EGF and inhibits clusterin expression.

Angiotensin II↗
PubMed1994

Effects of finishing and polishing procedures on the surface texture of resin composites.

OBJECTIVES: This study was designed to investigate the effects of finishing and polishing procedures on the roughness and color of resin composite surfaces. METHODS: Four composites and three different polishing systems were evaluated. Forty disc (10 mm x 2 mm) specimens of each composite were prepared. Thirty of them were ground wet through 320-grit paper, and the ground surfaces were used as the base line for the finishing procedure. Ten Mylar-covered specimens were used as controls. A color meter was applied to determine the color differences and a roughness meter was used to measure the surface roughness (Ra). RESULTS: Microfilled composite demonstrated significantly less roughness (p < or = 0.01) than hybrid composite systems as tested by ANOVA and Scheffé's tests. Polishing procedures produced a decrease in the roughness, ranging from 26 to 74%. Relative to the shade guide, the mean color difference values for all the composites after polishing were significantly greater than for the controls (p < or = 0.01) and ranged from 1.08 to 8.15 units. A positive relationship between mean color differences and Ra values was determined by regression analysis (r = 0.55). SIGNIFICANCE: A Mylar strip can create a smoother surface than the other types of tested polishing procedures. Because of the greater values in color differences and surface roughness, the shades of tested resin composites were lighter after the polishing procedures. A custom-made shade guide is suggested based on the results of this study.

Acrylic Resins↗
PubMed1994

Hepatocellular carcinoma metastasizing to the brain and orbit: report of three cases.

Hepatocellular carcinoma rarely metastasizes to the brain or orbit. We report 3 clinically manifest examples, one of which occurred in a 13-yr-old boy. In 2 cases the intracranial metastasis was the initial presenting lesion. The 2 cases of brain metastasis both presented with intracerebral hemorrhage. Light microscopic examination of these tumors revealed a trabecular hepatocellular carcinoma of Edmondson grade II with focal hemorrhage and necrosis. Their immunohistochemical profile was identical to that described for primary hepatocellular carcinoma. The differential diagnosis from other intracranial metastatic tumors is discussed.

Adolescent↗
PubMed1994

The luminance-response function of the dark-adapted rabbit electroretinogram.

The Naka-Rushton equation of the form, R = Rmax I(n)/(I(n)+Kn), has been used to describe the b-wave luminance-response function of the scotopic electroretinogram. Rmax is the asymptotic value of the b-wave amplitude as a function of stimulus luminance I, K is the luminance that produces a b-wave amplitude that is one-half Rmax, and n is a dimensionless constant that controls the slope of the function. These three parameters are often used in research laboratories, since it can show selective changes in each parameter. The present study describes these parameters (Rmax = 354 +/- 28 uV, n = 0.80 +/- 0.06, log K = -2.26 +/- 0.15 log cd. sec/m2) and the values obtained from the derivative analysis of Naka-Rushton equation (Anastasi et al) in 20 normal pigmented rabbit eyes. However, Naka-Rushton equation accurately describes the function only at low to moderate flash luminances. At high flash luminances, a second amplitude increase appears in the function.

Animals↗
PubMed1994

Adult presentation of congenital cystic adenomatoid malformation of the lung: a case report.

Adult presentation of congenital cystic adenomatoid malformation(CCAM) of the lung is so rare that only 5 cases have been reported in the literature to date. We report the case of a 19-year-old female with CCAM in the left lower lobe. Computed tomography showed a multilobulated cystic lesion with multiple air-fluid levels and also showed focal enhancement of the solid component in the eccentrical portion of the lesion. Thoracic aortogram and selected bronchial arteriograms show a slightly enlarged and tortuous bronchial artery feeding the multilobulated cystic lesion. We present the clinical and radiological features of our case with a brief review of the literature.

Adult↗
PubMed1994

A study of bond strength of dentin bonding agents to human dentin.

BACKGROUND: Marginal leakage of restoration induced by polymerization shrinkage of composite resin can be prevented if the dentin bonding agent is strong enough to counteract the force of polymerization shrinkage. METHODS: Fifty molar teeth obtained due to periodontal problem were used in this investigation. Crown portion of the teeth was grounded perpendicular to the long axis of the teeth until a complete layer of dentin surrounded by enamel was created. The teeth were then mounted with dental stone, and divided into five groups randomly. Dentin bonding agent was applied to the dentinal surface and a gelatin capsule mold was used to apply composite resin material. After incubation, the bonded composite specimens were tested with Instron universal testing machine in order to determine the shear strength of the composite bonding result. The fracture patterns were examined with scanning electron microscope. RESULTS: The Universal bond 3 combined with the AP.H composite exhibited the highest shear bond strength (10.76 MPa). The fracture pattern of the Universal Bond 3 combined with AP.H was mainly that of cohesive failure in the composite resin part instead of adhesive failure in the other groups tested. CONCLUSIONS: The shear bond strength of these five dentin bonding agents ranged from 2.89MPa to 10.76MPa. The fracture pattern of the tested groups was mainly that of adhesive failure at the interface between dentin bonding agent and its corresponding composite resin instead of cohesive failure disclosed in the composite resin part of Universal Bond 3 combined with AP.H group.

Biomechanical Phenomena↗
PubMed1994

Metal release from high-copper amalgams containing palladium.

BACKGROUND: High-copper amalgam containing palladium has been successfully developed. However, the effect of palladium on the release of corrosion products remains unknown. We studied the effect of palladium addition on the electrochemical properties of amalgams by measuring the amount of the elements released from the experimental Pd-containing amalgams into Ringer's solution. METHODS: A series of specimens of high-copper amalgams containing different concentrations of palladium, from 0.42 w% to 3.33 w% in the final amalgam, fabricated from a blend of traditional amalgam alloy and copper-silver-palladium ternary alloy, were subjected to free corrosion in Ringer's solution at 37 degrees C for 3 months. Aliquots of 10 microL of electrolyte were removed serially with time, and the concentrations of Ag, Sn, Cu, Pd and Zn were evaluated by graphite furnace atomic absorption technique. In addition, dissolved Hg was evaluated by cold vapor atomic absorption technique in the same aliquotes. Various kinds of commercial amalgam including traditional (Spheraloy), high-copper blends (Dispersalloy and Valiant-Ph.D.) and high-copper spherical (Valiant) were employed as controls. RESULTS: Ag and Sn cations released from the amalgams containing palladium were similar in concentration to those released from the commercial amalgams. The concentrations of released Cu and Hg cations decreased as a function of increased Pd concentration in the experimental amalgams. Averaging an order of magnitude of released Cu and Hg cations less than commercial controls for amalgam containing 1.7 w% Pd. Detection of Pd was essentially below the resolution of the technique and Zn was only detected in case of Dispersalloy. CONCLUSIONS: Pd addition to high-copper amalgam alloy reduces the release of mercury and copper from the Pd-containing amalgam.

Copper↗
PubMed1993

Microleakage of endodontic temporary restorative materials.

This study compared the sealing of Caviton, Cavit, and IRM at two powder to liquid ratios of 6 g/ml and 2 g/ml. Standard endodontic access preparations were made in 140 noncarious, nonrestored crowns of extracted human molars. They were divided into six groups, including positive and negative controls. Microleakage assessment was evaluated by basic fuchsin dye penetration after thermal cycling (5 to 55 degrees C for 100 cycles). The results indicated that Caviton provided the best seal, followed by Cavit. Cavit demonstrated better sealing than IRM at the powder to liquid ratio of 6 g/ml and 2 g/ml. There was a statistically significant difference in leakage between the Cavit group and IRM (powder to liquid = 6 g/ml), between the Cavit group and IRM (powder to liquid = 2 g/ml) group (p < 0.05). However, no statistically significant difference between the two different powder to liquid ratio groups of IRM was disclosed.

Analysis of Variance↗
PubMed1993

The properties of metal-reinforced glass ionomer materials.

The physical properties and bond strengths of two glass ionomer materials reinforced with silver and amalgam alloy powders were compared with those of a conventional material from the same manufacture as well as two commercially available products. The diametral tensile strength, hardness and bonding strength are improved with the addition of either commercial available silver particles or fabricated high-copper amalgam alloy powders to the glass. Simple mixture of the metal or alloy powders with the glass ionomer cement seems to be feasible to improve the properties of the regular cement. However, further studies in formulating an optimal composition of metal or alloy, setting characteristics and long-term clinical evaluation are necessary before proposing uses for this new material.

Cermet Cements↗
PubMed1993

Shear bond strength of ceramic brackets with two bonding adhesives.

The shear bond strength of two adhesives (Concise and Dyna-Plus bonding system) with one type of ceramic bracket was determined in this study. There were statistically significant differences between the bond strengths, with Concise recording higher levels than Dyna-Plus. Failure sites of Dyna-Plus were revealed at the enamel/resin, resin/resin, and resin/bracket interfaces; that of the Concise was mainly at the resin/bracket interface.

Ceramics↗
PubMed1992

Characterization of a complementary DNA for rat liver aryl sulfotransferase IV and use in evaluating the hepatic gene transcript levels of rats at various stages of 2-acetylaminofluorene-induced hepatocarcinogenesis.

A complementary DNA (cDNA) for rat hepatic aryl sulfotransferase IV (AST IV) was isolated, characterized, and used as a hybridization probe to evaluate the molecular basis for the differential expression of AST IV during 2-acetylaminofluorine (2AAF)-induced hepatocarcinogensis. The AST IV cDNA clone was obtained by immunochemical screening of a male Sprague-Dawley rat liver cDNA library. The AST IV cDNA was found to be 1.3 kilobases long and to encode a fusion protein which was reactive with an antibody to AST IV and enzymatically able to generate the sulfuric acid ester of N-hydroxy-2AAF. Sequence analysis of the AST IV cDNA showed it to be 1127 residues in length and to have essentially complete homology with PST-I cDNA, a previously reported (S. Ozawa, et al., Nucleic Acids Res., 18: 4001, 1990), 1028-base cDNA for an uncharacterized rat liver aryl sulfotransferase. Comparison of the PST-I/AST IV cDNA-deduced amino acid sequence with data from a partial (51%) amino acid sequence analysis of purified AST IV showed complete amino acid homology, confirming the identity of the cDNA and establishing that AST IV was an N-blocked, 291-amino acid protein with a molecular mass of 33,909 daltons. The AST IV cDNA sequence differed from the PST-I cDNA in two principal ways: the 5' end lacked 18 coding bases, and the 3' end contained a 190-base extention in the untranslated region, including a consensus sequence for signalling polyadenylation. Studies of AST IV gene transcript levels showed that the livers of rats fed 2AAF for 3 wk (early stage hepatocarcinogenesis) and hyperplastic nodules from the livers of rats fed 2AAF for 19 wk (intermediate stage hepatocarcinogenesis) displayed transcript levels similar to those of livers from normal rats. This contrasted with the 60 to 70% lower than normal capacity of the mRNA fractions to express AST IV observed during in vitro translation. These results indicated that modulation of AST IV expression at early and intermediate stages of hepatocarcinogenesis involved regulatory mechanisms at the translational level. In contrast, mRNA fractions isolated from some 2AAF-induced liver tumors or from known chemical carcinogen-derived rat hepatoma cell lines showed losses of both AST IV transcript level and in vitro translation capacity, suggesting that regulation at the transcriptional level may become important at late stages of 2AAF-induced hepatocarcinogenesis. These results indicated that the molecular mechanisms for the 2AAF-mediated down regulation of AST IV expression during 2AAF-induced hepatocarcinogenesis involved alterations in regulation at both translational and transcriptional levels.

2-Acetylaminofluorene↗
PubMed1992

Effects of posts on dentin stress distribution in pulpless teeth.

A finite element analysis was carried out to study the roles of posts in reducing dentin stress in pulpless teeth. Two-dimensional plane strain models of the midlabiolingual section of a human maxillary central incisor were first analyzed. The results showed that the gold alloy post reduced maximal dentin stress by as much as 30%. However, the integrity of the dentin was compromised and the effects of the post were likely to be exaggerated in such models. In an effort to correct for these problems, plane stress models with side plates and axisymmetric models were analyzed. Posts were found to reduce maximal dentin stress by only 3% to 8% when the teeth were subjected to masticatory and traumatic loadings in these latter models. Although posts reduced maximal dentin stress by as much as 20% when the teeth were loaded vertically, teeth such as incisors and canines normally are not subjected to vertical loadings. Thus the reinforcement effects of posts seem to be doubtful in these teeth.

Bite Force↗
PubMed1992

Microstructures of admixed amalgams produced from Pd-containing dispersants.

Blended Pd-containing dental amalgams were developed by substituting Pd for up to 20 w/o Ag or Cu in the Ag-Cu eutectic alloy. Melted ingots were lathe-comminuted to a particle size distribution of 1-45 microns. Alloy blends were created from two parts of a traditional amalgam and one part of experimental Ag-Cu-Pd particles. Amalgams with from 0.42 to 1.67 w/o Pd were fabricated by trituration of alloys and mercury at a Hg/alloy ratio of 1:1 with a mechanical triturator at 5000 rpm for 10 s and hand-condensed. XRD studies of these amalgams revealed the suppression of eta' (Cu6Sn5) phase with Pd addition and no gamma 2 (Sn8Hg) phase found. At 3.3 w/o Pd, the eta' (Cu6Sn5) concentration of the amalgam was below the detection limit of the instrumentation (1%). SEM micrographs revealed that reaction zones around eutectic particles decreased with increased Pd concentration.

Dental Amalgam↗
PubMed1992

The feasibility of castable ceramic material in dental bridge construction.

This study was to investigate the feasibility of dental bridges constructed with castable ceramic material (Dicor). A dental bridge model was designed similar to the clinical situation. The marginal fit of Dicor crown and a three-unit bridge was evaluated and no statistically significant differences in marginal openings between Dicor crowns and bridges were determined except the mesial and distal end surfaces of the bridge works. The fracture strengths of different thicknesses of Dicor test bars were measured with a three-point bending technique in a jig mounted in a universal testing machine. The results revealed that the bridge design with the thickest (6mm) connector and the shortest (8 mm) width of the pontic had the highest fracture resistance. In addition, pores with size up to 50 microns were disclosed in the fractured interface. The optimal design of Dicor bridge is determined according to the results of this study along with the clinical trial.

Animals↗
PubMed1991

The urine urokinase concentration in end stage renal disease with acquired renal cyst.

To see whether there was any difference in the urine urokinase concentration between acquired cystic kidney disease (ACKD) group and control (non cyst) group in end stage renal disease patients (ESRD), we evaluated fifty ESRD patients who had been maintained on chronic hemodialysis for various period. The urine urokinase concentration was higher in the ACKD group (17.5 +/- 14.7 unit/ml, range 13.5-47.0 unit/ml, n = 9) than the control group (4.1 +/- 3.4 unit/ml, range 0.5-12.0 unit/ml, n = 36) (p less than 0.001), and polycyst group (2.6 +/- 1.8 unit/ml, range 1.0-5.1 unit/ml, n = 5) (p less than 0.01). But there was no difference between the control group and polycyst group. In the control group and the ACKD group, there was a direct relation between the dialysis duration and the urokinase concentration and the longer the dialysis duration, the higher the urine urokinase concentration (r squared = 0.424, p = 0.0001). The hemodialysis duration was longer in the ACKD group (42 +/- 17.0 months) than the control group (20.0 +/- 12.5 months) (p less than 0.005). These findings suggest that urokinase may be responsible for cystogenic degeneration in ESRD.

Adult↗
PubMed1991

Assessment of microleakage of cervical restorations.

Cervical lesions restored with composite resin seem to be more susceptible to marginal leakage, because the gingival margin is usually placed in cementum and/or dentin. The purpose of this study was to evaluate the effectiveness of five dentinal bonding agents, four composite resins and a glass ionomer cement in eliminating marginal gaps in an extraoral model. This study was accomplished using extracted human teeth and dye penetration method. The results indicated that none of the available dentinal bonding agents was able to eliminate marginal gaps completely. The cavities restored with the two component type dentinal adhesives leaked less than the negative control, glass ionomer cement.

Dental Cements↗