Biomedical subjects

J Chai

Publications and source records attributed to J Chai.

At least 109 records · Page 6Linked to original sources

PubMed1990

[The study on genome size of leptospires].

Determination of genome size is very important in genetic studies and the molecular cloning of leptospires. With pulsed field gel electrophoresis (PFGE), which can be used in the analysis of large DNA molecules, we studied the genome size of leptospires and analysed it with rare cutter restrict endonuclease Not I. The PFGE system used was CHEF-DR II which produced parallel bands in agarose gel. The results showed that the genome size of leptospires was 2000kb and there was no dramatic difference between the 5 strains of 2 genus leptospira. Rare cutter Not I digestion of genome DNA of leptospira resulted in 11 bands and its bands pattern was quite different from that of E. coli, S. choleraesuis, S. typhimurium, and S. dysenteriae genome DNA. It is thought that more information can be obtained about leptospiral DNA with PFGE technique.

Cloning, Molecular↗

PubMed1990

[Rapid restriction mapping of DNA cloned in cosmid or lambda phage vectors].

A procedure for rapid restriction mapping of cosmid or lambda phage clones has been developed. The mapping of cosmid is based on linearization of circular cosmid DNA in vitro by the phage lambda terminase. Partial digestion products are selectively labelled at the right or left cos cohesive termini by hybridization with [32P] oligonucleotides complementary to the single-strand cos end. After gel electrophoresis and autoradiography, the restriction map can be directly determined from the "ladder" of partial digestion products of cosmid or lambda clones with computer program or by hand.

Bacteriophage lambda↗

PubMed1986

Substrate specificity of alkaline phosphatase from human polymorphonuclear leukocytes.

The ability of alkaline phosphatase in purified preparations from human neutrophils and liver to utilize ATP or inorganic pyrophosphate as substrate depended upon the Mg2+ concentration. With pyrophosphate present (1.0 mmol/l), activity peaked at Mg2+ concentrations of 0.25 to 0.50 mmol/l and fell sharply above this. By contrast, p-nitrophenylphosphatase activity was activated with Mg2+ concentration up to 0.75 mmol/l but above this was constant to 5.0 mmol/l. Hydrolysis was abolished by L-levamisole, a specific inhibitor of alkaline phosphatase. Testing butanol extracts of neutrophils from 50 healthy subjects showed good correlation of enzyme activity with p-nitrophenylphosphate and ADP (r = 0.90), and between p-nitrophenylphosphate and pyridoxal phosphate (r = 0.96) as substrate, consistent with hydrolysis of all three phosphoesters by one enzyme. Inhibition studies yielded no evidence of a specific pyridoxal phosphatase. Alkaline phosphatase from human neutrophils has the same broad substrate specificity as other molecular forms of the human enzyme and, like other forms, has little or no activity towards phosphoesters complexed with Mg2+.

Adenosine Diphosphate↗

PubMed1985

Antigenic analysis of Campylobacter flagellar protein and other proteins.

Outer membrane proteins of Campylobacter jejuni and other campylobacter species were analyzed for their antigenic potentials by immunoblotting. Polypeptides were resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, transferred electrophoretically, and reacted with rabbit antisera to C. jejuni. Each Campylobacter species analyzed demonstrated a unique outer membrane protein antigenic profile; interspecies antigen sharing was observed to be compatible with the degree of DNA relatedness between the species. The most highly conserved outer membrane protein antigen was the flagellum (molecular weight, 62,000). An aflagellate mutant was found to be untypable with the heat-labile system, in contrast to its parental isolate. The immunogenic potentials of C. jejuni proteins were examined by immunoblot analysis of sera from infected humans. Sera of convalescent patients, reacted with their homologous C. jejuni isolates, recognized a variety of campylobacter proteins. The most consistent immunogen in human infection was the flagellar protein. Patient sera assayed by the immunoblot technique were easily distinguished from control sera, which did not recognize specific campylobacter antigens. These findings suggest that the campylobacter flagellar protein is an essential determinant of the heat-labile antigen typing scheme and is the dominant immunogen recognized during C. jejuni infections in humans.

Animals↗

PubMedDate not supplied

MR hysterography using axial long TR imaging with three-dimensional projections of the uterus.

A rapid screening technique for the presentation of uterine cavity anatomy obtained with MR is described. MR hysterographic (MRHG) images were generated and evaluated for uterine cavity abnormalities. Six patients referred for MRI evaluation of the uterus for infertility had an MRI using a pelvic phased array coil with axial 3 mm interleaved fast spin echo images (TR 9000 ms, TE 288 ms with fat saturation) processed using maximum intensity projection algorithms to construct MRHG images. Using the conventional MR sequence as the gold standard the MRHG images were evaluated by two reviewers and accuracy calculated. MRHG took less than 3 min, demonstrated the correct diagnosis in all with a quality score of diagnostic to optimal, and with excellent interobserver agreement (kappa 0.9).

Adult↗

PubMedDate not supplied

Structural basis of IAP recognition by Smac/DIABLO.

Apoptosis is an essential process in the development and homeostasis of all metazoans. The inhibitor-of-apoptosis (IAP) proteins suppress cell death by inhibiting the activity of caspases; this inhibition is performed by the zinc-binding BIR domains of the IAP proteins. The mitochondrial protein Smac/DIABLO promotes apoptosis by eliminating the inhibitory effect of IAPs through physical interactions. Amino-terminal sequences in Smac/DIABLO are required for this function, as mutation of the very first amino acid leads to loss of interaction with IAPs and concomitant loss of Smac/DIABLO function. Here we report the high-resolution crystal structure of Smac/DIABLO complexed with the third BIR domain (BIR3) of XIAP. Our results show that the N-terminal four residues (Ala-Val-Pro-Ile) in Smac/DIABLO recognize a surface groove on BIR3, with the first residue Ala binding a hydrophobic pocket and making five hydrogen bonds to neighbouring residues on BIR3. These observations provide a structural explanation for the roles of the Smac N terminus as well as the conserved N-terminal sequences in the Drosophila proteins Hid/Grim/Reaper. In conjunction with other observations, our results reveal how Smac may relieve IAP inhibition of caspase-9 activity. In addition to explaining a number of biological observations, our structural analysis identifies potential targets for drug screening.

Animals↗

PubMedDate not supplied

Epiglottitis. Twenty-year study with tracheotomy.

One hundred and seventy patients with acute epiglottitis were admitted to the Childrens Hospital of Los Angeles between the years 1957 to 1977. No deaths occurred in any of these patients, all of whom were treated with tracheotomy to support and ensure the airway. The records of 147 of these patients were available for review. No serious complications occurred from tracheotomy in any of the patients in this study. Tracheotomy is a safe method for caring for the airway problem in epiglottitis in a setting such as is available at the Childrens Hospital of Los Angeles. The median range of total days with tracheotomy was five to six days, and the median range for total days of hospitalization was six to seven days. Complications were never severe and in the extreme, merely prolonged hospitalization by a few days. This highly lethal disease is curable with antibiotics and an artificial airway, and it is questionable whether conservative medical measures with observation should be acceptable. The establishment of an airway, whether by tracheotomy or endotracheal intubation, is mandatory in the treatment of this disease.

Acute Disease↗

PubMedDate not supplied

Equilibrium strengths of denture polymers subjected to long-term water immersion.

PURPOSE: This study characterized the effect of water immersion on the strength of denture polymers. MATERIALS AND METHODS: Four denture-base polymers and four denture-reline polymers were tested for flexural strength at proportional limits (FSpl) at 24 hours and at monthly intervals. The equilibrium strength of each polymer was estimated. RESULTS: The denture polymers took from 24 hours to 4 months to reach their equilibrium strength. The equilibrium strengths of the denture polymers were significantly different. CONCLUSION: Water immersion affected the strength of most denture polymers. Different denture polymers behaved differently in response to water immersion.

Analysis of Variance↗

PubMedDate not supplied

Comparative mechanical property characterization of 3 all-ceramic core materials.

PURPOSE: The biaxial flexural strength and fracture toughness for 3 representative types of ceramic core materials were studied to (1) ascertain the ranking of the 3 ceramic types for strength and toughness, and (2) provide clinicians with more information to predict clinical outcomes. The former aim was deemed important in view of the importance of flaw size in the relationship between failure stress and fracture toughness of brittle materials. MATERIALS AND METHODS: The 3 representative ceramic types included a leucite-reinforced glass, a glass-infiltrated sintered alumina, and a high-purity, high-density alumina. The biaxial flexural strength was measured with the piston-on-3-ball method. The plane-strain fracture toughness was measured with the short-bar chevron-notch method. RESULTS: The biaxial flexural strengths of the high-purity, high-density alumina and glass-infiltrated sintered alumina ceramic core types were significantly higher than that of the leucite-reinforced glass ceramic type. The glass-infiltrated sintered alumina was significantly higher in fracture toughness than the high-purity, high-density alumina type, which was significantly higher than the leucite-reinforced glass. CONCLUSION: All materials surpassed the minimum strength requirement outlined by the International Standards Organization, and they also had similar strength variability according to their Weibull moduli. The glass-infiltrated sintered alumina and the high-purity, high-density alumina types were significantly stronger and tougher than currently used core materials. However, while the glass-infiltrated sintered alumina had a higher fracture toughness than the high-purity, high-density alumina, it had a lower flexural strength.

Aluminum Oxide↗

PubMedDate not supplied

Bond strength of denture teeth to denture base resins.

PURPOSE: The study examined the bond strength between 2 types of denture teeth and 3 denture base resins. The denture teeth were untreated, prepared with diatorics, or treated with dichloromethane, a solvent. MATERIALS AND METHODS: Conventional denture teeth and cross-linked denture teeth were bonded to either a heat-cured denture base resin, a microwave-cured denture base resin, or a pour-type denture base resin. Compressive load was applied at 45 degrees on the palatal surface of each tooth until fracture. RESULTS: Conventional resin teeth possessed higher bond strength than cross-linked denture teeth. The heat-cured denture base resin significantly surpassed the microwave-cured denture base resin in bond strength. Both materials were better than the pour-type resin. The application of dichloromethane resulted in a significantly better improvement in bond strength compared to the use of diatorics. CONCLUSION: It is recommended that dichloromethane be applied on the denture teeth ridge-lap area prior to denture base processing.

Acrylic Resins↗

PubMedDate not supplied

Bonding durability of conventional resinous denture teeth and highly crosslinked denture teeth to a pour-type denture base resin.

PURPOSE: The study examined the bond strength between 2 types of resin denture teeth and a pour-type denture base resin after thermocycling. The denture teeth were untreated, prepared with diatorics, or treated with a solvent, dichloromethane. MATERIALS AND METHODS: Conventional denture teeth and crosslinked denture teeth were bonded to a pour-type denture base resin. Compressive load was applied at 45 degrees on the palatal surface of each tooth until fracture. The teeth were either thermocycled or not thermocycled. Porcelain teeth were also tested for comparison. RESULTS: There was no significant difference in bond strength between the conventional resin teeth and the crosslinked denture teeth. Thermocycling significantly decreased the bond strength of the 2 types of resin teeth but had no effect on porcelain teeth. The application of dichloromethane significantly improved the bond strength of the 2 types of resin teeth either before or after thermocycling. CONCLUSION: It is recommended that dichloromethane be applied on the denture teeth ridge-lap area prior to denture base processing.

Analysis of Variance↗

PubMedDate not supplied

Strength of relined denture base polymers subjected to long-term water immersion.

PURPOSE: This study was undertaken to characterize the long-term equilibrium flexural strength at proportional limit (FSp) of 4 denture reline polymers processed onto 4 denture base polymers. MATERIALS AND METHODS: A 3-point flexural test was applied on rectangular specimens of each denture base polymer-denture reline polymer. Each specimen was immersed in water for 4 months prior to and 4 months after reline. RESULTS: Significant differences existed among the relined specimens because of the denture base polymer variable, the denture reline polymer variable, and their interaction (P < 0.05). The descending order in FSp according to the denture base polymer, arranged in terms of statistical significance was: Acron approximately Acron MC > Triad > Palapress Vario, where approximately denotes no significant difference between Acron and Acron MC. The descending order in FSp according to the denture reline polymer, arranged in terms of statistical significance was: Triad > Rebaron > Rebaron LC > Tokuso Rebase. Significant difference existed among all of the denture reline polymers. CONCLUSION: The present study showed that the long-term equilibrium strengths of 4 denture reline polymers processed onto 4 denture base polymers were different. The strength of the relined specimen of a denture base is dependent on the strength of the denture base polymer and that of the reline polymer.

Acrylic Resins↗

PubMedDate not supplied

Probability of fracture of all-ceramic crowns.

PURPOSE: The study compared the probability of fracture of 4 systems of all-ceramic crowns fabricated on maxillary central incisors. MATERIALS AND METHODS: The 4 all-ceramic crown systems were: (1) a glass-infiltrated, sintered alumina system (In-Ceram) fabricated conventionally, (2) the same system with machine-milled alumina cores (CEREC 2), (3) a heat-press, leucite-reinforced glass-ceramic system (IPS Empress), and (4) a high-purity, high-density alumina system (Procera). Ten crowns of each system were fabricated and compressed at 45 degrees at the palatal surface until failure. The data were analyzed with the Weibull method. RESULTS: There were no significant differences in the probability of fracture among the 4 systems studied. CONCLUSION: The likelihood of fracture of these crown systems on central incisors should be similar.

Aluminum Oxide↗

PubMedDate not supplied

Shear bond strength of denture reline polymers to denture base polymers.

PURPOSE: This study was undertaken to characterize the shear bond strength established between four denture base polymers and four denture reline polymers. MATERIALS AND METHODS: Cylindric columns of denture reline polymers were bonded to columns of denture base polymers. Specimens were immersed in water for 4 months and then thermocycled. The strength at which the bond failed under shear stress was recorded. RESULTS: Significant differences in bond strength existed among the specimens because of the denture base polymer variable, the denture reline polymer variable, and their interaction (P < .05). A light-activated denture base polymer (Triad) bonded adequately with a light-activated reline polymer (Triad) but less well with the other reline polymers tested. The bond strength established between some denture base polymers and a different light-activated reline polymer (Rebaron LC) was relatively low. CONCLUSION: The type of denture base polymer and denture reline polymer affected the shear bond strength between them.

Acrylic Resins↗

PubMedDate not supplied

Resistance to staining, flexural strength, and chemical solubility of core porcelains for all-ceramic crowns.

PURPOSE: The increased demand for tooth-colored restorations has prompted the use of ceramics in areas that are subject to masticatory stresses. To maximize the strength of these restorations, manufacturers and clinicians advocate placement of core materials in lieu of veneering materials in areas that are more susceptible to fracture. The objectives of this study were to determine the: resistance to staining of three core porcelains used for all-ceramic restorations, Procera, IPS Empress, and In-Ceram, through the use of colorimetry and visual observation; flexural strength of these porcelains under a three-point bend test; and chemical solubility in a controlled environment. MATERIALS AND METHODS: L*a*b* values were obtained for each specimen before and after immersion in a saturated solution of methylene blue in ethanol for 24 hours. Visual observation was also performed to ascertain color differences before and after staining. A three-point bend test was used to determine flexural strength. A reflux-condenser type, three-piece extraction apparatus was used with 4% acetic acid solution for 16 hours to determine solubility. Each sample was weighed before and after the reflux procedure to ascertain percentage weight loss. RESULTS: The mean delta E obtained for IPS Empress was 14.5; In-Ceram was 9.2, and Procera was 9.0. Flexural strength obtained for IPS Empress, In-Ceram, and Procera was 176.9 MPa, 323.4 MPa, and 464.3 MPa, respectively. Weight loss of IPS Empress, In-Ceram, and Procera was 0.056%, 0.734%, and 0.003%, respectively. CONCLUSION: IPS Empress showed the least resistance to staining. IPS Empress had the lowest flexural strength, while Procera had the highest. In-Ceram demonstrated the highest chemical solubility.

Acetates↗

PubMedDate not supplied

Flexural strength of a glass-infiltrated alumina dental ceramic incorporated with silicon carbide whiskers.

PURPOSE: The addition of silicon carbide whiskers has been known to reinforce ceramics. This study compared the flexural strength of a glass-infiltrated alumina dental ceramic with various amounts of silicon carbide whiskers incorporated into the alumina matrix. MATERIALS AND METHODS: Three groups with a total of 30 specimens were included: glass-infiltrated alumina dental ceramic with 0, 0.125, and 0.25 wt% silicon carbide whiskers. The flexural strength was measured using a three-point bending test, and the data were analyzed with one-way analysis of variance. Scanning electron microscopy was used to examine the fracture surfaces of all three materials. RESULTS: There were no significant differences in the flexural strength among the three groups. Glass-infiltrated alumina dental ceramic failed predominantly by transgranular fracture and to a lesser degree by intergranular fracture. CONCLUSION: The addition of silicon carbide whiskers did not change the flexural strength of glass-infiltrated alumina dental ceramic.

Aluminum Oxide↗

PubMedDate not supplied

Fracture resistance and primary failure mode of endodontically treated teeth restored with a carbon fiber-reinforced resin post system in vitro.

PURPOSE: This study was undertaken to characterize the fracture resistance and mode of fracture of endodontically treated incisors restored with cast post-and-core, prefabricated stainless steel post, or carbon fiber-reinforced composite post systems. MATERIALS AND METHODS: Ten endodontically treated teeth restored with each technique were subjected to a compressive load delivered at a 130-degree angle to the long axis until the first sign of failure was noted. The fracture load and the mode of fracture were recorded. RESULTS: The failure loads registered in the three groups were not significantly different. Between 70%, and 80% of teeth from any of the three groups displayed fractures that were located above the simulated bone level. CONCLUSION: The use of carbon fiber-reinforced composite posts did not change the fracture resistance or the failure mode of endodontically treated central incisors compared to the use of metallic posts.

Adhesiveness↗

PubMedDate not supplied

Interchangeability of a semiadjustable articulator.

PURPOSE: The purpose of this study was to investigate whether the interchangeability of new Hanau semiadjustable articulators fulfills the manufacturer's criterion (102 microns) in the mediolateral direction and the defined 166-micron criterion three dimensionally and whether the articulators maintain the same interchangeability as new articulators after a period of function. MATERIALS AND METHODS: The spatial deviations in three dimensions of ten new, ten 18-month-old, and ten 30-month-old Hanau articulators were measured with a field-inspection gauge and compared to those of a master articulator. RESULTS: Compared to the master articulator, nine of 10 new articulators met the manufacturer's criterion of articulator interchangeability in the mediolateral direction. However, only four of the 10 articulators fulfilled the criterion for three-dimensional interchangeability. The articulators were found to be interchangeable among the groups when the spatial deviations of test articulators from the master articulator at the position of the lingual cusp of the right maxillary first premolar were compared. However, using the geometric mean deviations of test articulators, the 30-month group was not interchangeable with the new and the 18-month articulator groups. CONCLUSION: This limited study revealed that most of the articulators tested met the manufacturer's criterion of articulator interchangeability, but most did not pass the three-dimensional interchangeability test. Clinicians should be aware of the amount of occlusal error in the range of 0.2 mm that may result from interchanging dental casts on the articulator system. The articulator system might be able to maintain the same level of interchangeability for up to 18 months of routine use.

Analysis of Variance↗