Search PubMed⌕ Search

Biomedical subjects

K H Chung

Publications and source records attributed to K H Chung.

88 records · Page 5Linked to original sources
PubMed1991

Histological and biomechanical studies of hydroxylapatite implant.

Bony defects measuring 12x12x12 millimeters in size were created bilaterally over the proximal end of the femurs of 10 Macaca cyclopis monkeys and implanted with particulate hydroxylapatite. The animals were sacrificed according to a predetermined sequence of post-operative 1, 2, 3, 6, and 8 months. The specimens taken from the implant sites in the two femurs of each animal were chosen randomly either for histological observation or for compressive strength tests under vertical loads. Histological pictures showed only loose fibrous tissue over the interparticular space of the implant site at the first month after surgery. Woven bone could be observed over the basal part of the implant site at the second month. New bone formed over the central part of the implant site at the third month after surgery. Continuing maturation of the bone tissue could be observed over the interparticular space of the implant site until the late stages at the 6th and 8th month after surgery. The results of compressive strength tests were compatible with the histological observations. The value of the elastic modulus was low initially at the first month, but increased gradually with time due to organization of fibrous tissue, condensation of HA particles, and ossification as well as maturation of bone tissue. The value of elastic modulus at the third month was equal to that of cortical bone tissue and even two-fold higher than that of the cortical bone at the eighth month after surgery. These results provide valuable information about the compressive strength of the HA implant in host tissue.

Animals↗
PubMed1990

Interfacial strengths of various alloy surface treatments for resin-bonded fixed partial dentures.

A practical method for bonding or rebonding the resin-bonded retainer is eagerly being sought by general practitioners. This research introduces a new test apparatus for evaluating bond strength of base metal alloys after various alloy surface treatments. Five commercial base metal alloys and a resin luting cement for resin-bonded fixed partial dentures were examined. Sandblasting, oxidation, or etching treatment were determined to be effective in increasing the adhesive strength for the tested alloys. No statistical differences between various surface treatments were found for bonding of Unitbond metal. Inexpensive sandblasting, along with ultrasonic washing, provided superior bonding strengths for Biobond II and Litecast B materials. Electrochemical treatment was suitable for Wiron 77 and Lab metals.

Acid Etching, Dental↗
PubMed1990

Correlation between degree of conversion, filler concentration and mechanical properties of posterior composite resins.

The degree of conversion, filler concentration and mechanical properties of seven proprietary light-cured posterior composite resins were investigated. The degree of conversion of composites ranged from 43.5-73.8%. The weight fraction of filler that was obtained was in the range 66.4-85.2%. The volume fraction varied from 58.2-74.2%. The mean values of the observed compressive and diametral tensile strengths ranged from 242.3-324.7 MPa and from 39.8-62.6 MPa, respectively. The Knoop hardness numbers ranged from 41.8-81.9. Significant correlations were observed between the volume fraction of filler and the diametral tensile strength (r = 0.89), and between the volume fraction of filler and the Knoop hardness number (r = 0.89). No correlation was found between the degree of conversion and any of the mechanical properties of the composite resins tested. Because of the positive correlations between the volume fraction of filler and the diametral tensile strength, and between the volume fraction of filler and the Knoop hardness numbers, it is concluded that the filler concentration plays a prominent role in determining the properties of contemporary posterior composite resins.

Analysis of Variance↗
PubMed1990

The relationship between composition and properties of posterior resin composites.

The effects of filler concentration and resinous components on the properties of highly filled composites were determined for prediction of the durability of the restorative resins. Resinous components of seven proprietary light-cured posterior resin composites were extracted by chloroform solvent and examined by the Fourier Transform Infrared (FTIR) method. Filler concentration was determined by the thermogravimetric method. Diametral tensile strength, Knoop hardness, and Barcol hardness tests for the composite, as well as extracted resinous matrix, were performed by standard experimental procedures. Toothbrush abrasion test of the resin composites was evaluated by a toothbrushing machine giving the equivalent of five years' toothbrushing and examined with a roughness meter. The degree of conversion of resin composites ranged from 43.5 to 73.8%. The volume fraction of filler varied from 58.2% to 74.2%. The ranges of diametral tensile strength and Knoop and Barcol hardness numbers obtained were 39.8 MPa to 60.0 MPa, 41.8 to 81.9, and 76.3 to 89.2, respectively. Significant correlations (p less than 0.01) were obtained between filler fraction and diametral tensile strength (r = 0.89, S.E. = 3.66) and between filler fraction and Knoop hardness number (r = 0.89, S.E. = 8.39). The increase in strength with increased filler concentration might be related to filler/matrix bonding.

Bicuspid↗
PubMed1989

Hardness tests in highly filled composite resins.

The hardness of seven proprietary, light-cured, posterior composite resins was evaluated by three different hardness testers: the Knoop hardness tester, the Barcol indenter and the Rockwell 15T hardness meter. Specimens were measured after light-curing and 24-hour immersion in 37 degrees C water. Barcol hardness numbers ranged from 79.2 to 85.0. The Rockwell 15T hardness data had a range from 73.3 to 80.3 and the Knoop hardness numbers varied from 39.9 to 79.0. Relatively small variations were determined between results of Barcol hardness numbers and Rockwell 15T hardness data. Great variation was revealed in the results from Knoop hardness numbers. According to the dimensions of the indentations, the results of Barcol and Rockwell hardness represent the bulky part of tested composites rather than superficial hardness. Knoop hardness testing is found to be relatively feasible and a suitable measurement for the determination of superficial hardness of highly filled composite resins.

Composite Resins↗
PubMed1988

Creep in a palladium-enriched high-copper amalgam.

Palladium additions to a dispersed phase high-copper amalgam have been shown recently to suppress markedly the eta' (Cu6Sn5) concentration and decrease creep. A detailed study of the dental and 24 h creep for Pd containing high-copper amalgams and six commercial controls as a function of applied temperature and stress was performed. One part of Ag-Cu or Ag-Cu-Pd dispersants with substitutions of up to 20wt/o Pd for either Ag or Cu was blended with two parts of traditional amalgam alloy. Various temperatures from 25 to 60 degrees C and stresses from 36 to 72 MPa were applied to the samples during the test. For commercial controls and experimental amalgams with no Pd, creep is a strong function of temperature and stress. The experimental amalgam containing up to 10wt/o Pd, Pd substituted for Ag, demonstrated essentially constant creep over the temperature and stress range applied.

Chemical Phenomena↗
PubMed1978

Purification, characterization, and action-pattern studies on the endo-(1 linked to 3)-beta-D-glucanase from Rhizopus arrhizus QM 1032.

The extracellular (1 linked to 3)-beta-D-glucanase [(1 linked to 3)-beta-D-glucan glucanohydrolase, EC 3.2.1.6] produced by Rhizopus arrhizus QU 1032 was purified 305-fold in 70% overall yield. This preparation was found to be homogeneous by ultracentrifugation (sedimentation velocity and equilibrium studies), electrophoresis on acrylamide gel with normal, sodium dodecyl sulfate, and urea-acetic acid gels, and upon isoelectric focusing. The amino acid composition of the enzyme has been determined and it possesses a carbohydrate moiety compose of mannose and galactose (in the ratio approximately 5:1) that is linked to the protein through a 2-acetamido-2-deoxyglucose residue. The molecular weight, as determined by equilibrium sedimentation, is 28,800 and this number was confirmed by electrophoresis on gels of sodium dodecyl sulfate. The enzyme does not possess subunit structure. It hydrolyzes its substrates with retention of configuration and possesses transglycosylating ability. The rates of hydrolysis of a wide variety of substrates were determined, and its action pattern on a series of oligosaccharides containing mixed (1 linked to 3)-, (1 linked to 4)-, and (1 linked to 6)-beta-D-glucopyranosyl residues was investigated. The enzyme favors stretches of beta-D-(1 linked to 3) linkages, but it can hydrolyze beta-D-(1 linked to 4) linkages that are flanked on the non-reducing side with stretches of beta-D-(1 linked to 3) links. The enzyme will not act on (1 linked to 6)-beta-D-glucosyl linkages located in stretches of beta-D-(1 linked to 3) and will not act on (1 linked to 3) beta-D-glycosidic linkages involving sugars other than D-glucose.

Glucan Endo-1,3-beta-D-Glucosidase↗
PubMedDate not supplied

New 4-hydroxypyridine and 4-hydroxyquinoline derivatives as inhibitors of NADH-ubiquinone reductase in the respiratory chain.

Many derivatives of 2,3-dimethoxy-4-hydroxypyridine, which were designed from examination of the structure-activity relationship of piericidins, were tested for inhibition of NADH-UQ reductase. The lipophilic side chain of those compounds was indicated to be a key part for activity and its optimal length was conjectured. By the use of two different phases of assay material, intact mitochondria and submitochondria, the size of a membrane effect was shown to depend on the structure of the side chain. 4-Hydroxyquinoline derivatives were also tested for an analogous role in relation to the electron transport function of menaquinone, and they were proven to be inhibitors of NADH-UQ reductase as good as the pyridine derivatives.

Animals↗
PubMedDate not supplied

Radioimmunotherapy of orthotopically transplanted pancreatic cancer with 131I-labeled chimeric monoclonal antibody Nd2.

Recombinant mouse/human chimeric antibody Nd2 was previously reported to have the same specificity and reactivity against pancreatic cancer as murine Nd2 without HAMA production which induced serious problems in clinical application. We established orthotopic SW1990 transplanted mice to represent the progression of pancreatic cancer. We examined anti-tumor effect of 131I-labeled chimeric Nd2 in an orthotopic transplant model. 131I-labeled chimeric Nd2 inhibited the growth of orthotopically transplanted tumors and extended the survival time of the mice. These results suggest that 131I-labeled chimeric Nd2 has high clinical applicability in the therapy of pancreatic cancer.

Animals↗
PubMedDate not supplied

Evaluation of argyrophilic nucleolar organizer regions (AgNORs) in differentiated thyroid carcinoma as an indicator for disease recurrence.

Differentiated thyroid carcinoma (DTC) is one of the least aggressive cancers of the human malignancies, however, recurrent disease is occasionally found and is difficult to determine the risk for recurrence only by clinicopathological features. In the present study, we investigated argyrophilic nucleolar organizer regions (AgNORs) score, a well-known indicator for proliferative potential of the cancer cells, in 89 cases of DTC. In tumors with capsular invasion, or with extended contra-lateral lymph node metastasis, AgNORs score was significantly higher than in tumors without them, while was not correlated with age or gender of the patients, nor the histological type of the tumor (papillary or follicular). Disease recurrence was observed in one-third of the patients in high AgNOR score group (scored more than mean value +/- standard deviation) when the patients were divided into four groups according to the AgNOR score, and a significantly higher risk for disease recurrence was demonstrated in those cases with high AgNOR score than cases with lower score. These results clearly indicated the usefulness of AgNOR score in selecting the patients at high risk for disease recurrence. All 5 recurrent cases displayed local recurrence in high AgNOR score group, while 5 of 7 cases with low AgNOR score did in the manner of hematological metastasis. In conclusion, this method was technically simple and accurate giving an exact value in individual cases. Thus, we believe AgNOR score might be clinically applicable as a useful indicator for disease recurrence in DTC.

Adenocarcinoma, Follicular↗
PubMedDate not supplied

Evaluation of different methods for cleaning and preparing occlusal fissures.

The effectiveness of different methods for cleaning and preparing occlusal fissures before placing sealants was evaluated. Extracted mandibular molars received such treatments as brushing, pumicing, bur preparing, and air abrasion before application of fissure sealants. FluroShield fissure sealant was then applied to the occlusal fissures. Specimens were subjected to thermo-cycling and then immersed in a 10% solution of methylene blue, and finally sectioned. The sections were examined and photographed in a stereomicroscope, and the dye penetration was recorded using a scoring system. The results indicated that only the control (brushing with a dry brush) and the pumicing groups demonstrated dye penetration to the base of the sealant. Teeth prepared with the #1/4 round bur and air abrasion demonstrated a better seal in evaluated fissures. For this study, those three groups (occlusal fissures prepared with the #1/4 round bur and two air abrasion methods), demonstrated significantly better sealing (P < 0.01) than the control group and the other groups tested.

Air Abrasion, Dental↗
PubMedDate not supplied

Inhibition of invasion and lymph node metastasis of gastrointestinal cancer cells by R-94138, a matrix metalloproteinase inhibitor.

BACKGROUND: MMPs have been implicated in the process of metastasis. Matlystatin analogue, called R-94138, isolated from Actinomadura atramentaria, has been reported to inhibit the activity of MMP-2 and -9 specifically. In this study, we investigated the effect of R-94138 on the invasive and lymphnodal metastatic ability of gastric cancer cells. MATERIALS AND METHODS: Three gastric cancer cell lines, MKN-28, MKN-45, MKN-74, and two colorectal cancer cell lines, HT-29, and LS174T were used. The invasion ability of these cell lines were assayed with R-94138 at the required concentration in vitro. The In vivo effect of R-94138 on lymphnode metastasis was examined passaged by orthotopic implantation. RESULTS: All cell lines revealed activity of both 72 and 92 kDa forms of MMPs by gelatin zymography. R-94138 significantly inhibited the invasiveness of all of these cells to the extracellular matrix. The number of lymph node metastases and the amount of body weight loss were significantly decreased by intraperitoneal administration of R-94138. CONCLUSION: MMP inhibitor, R-94138, has a possible application in adjunctive therapy for lymph node metastasis in gastric carcinoma.

Acetamides↗
PubMedDate not supplied

Clinical use of single-dose surfactant TA therapy for premature infants with severe respiratory distress syndrome.

A single dose of surfactant TA was given as rescue therapy to four small premature infants with severe respiratory distress syndrome requiring mechanical ventilation. Birth weights ranged from 810 to 1200 gm. The dose of 100-120 mg/kg was given at the mean age of 5 hours, with range of 3 to 7 hours. Following surfactant therapy, there was a significant improvement (p < 0.05) in a/APO2 (raising from 0.11 +/- 0.05 before treatment to 0.34 +/- 0.19 at 6 hours after treatment). There was also a significant reduction in the severity of respiratory distress syndrome at 24 hours post-therapy. One baby died of sepsis at 40 hours of life; one survived without complications. The other two cases developed severe bronchopulmonary dysplasia later. We concluded that early use of exogenous surfactant is beneficial in small premature infants with severe respiratory distress syndrome.

Female↗