Biomedical subjects

G L Powell

Publications and source records attributed to G L Powell.

At least 55 records · Page 3Linked to original sources

PubMed1991

Comparison of three lasers for dental instrument sterilization.

The sterilization of dental instruments is an area of great interest and recent concern in the field of dentistry. The purpose of this study was to compare the ability of three lasers (argon, CO2, and NdYAG) to sterilize dental instruments. Endodontic reamers were contaminated with microorganisms, lased at various levels of energy, placed in Trypticase soy broth, incubated, and read for growth or no growth to determine sterility. Results indicated that the argon laser is capable of sterilizing selected dental instruments at the lowest energy level (1 watt for 120 seconds) of the three lasers tested. The other two lasers were able to sterilize the instruments also, but at higher energy levels. Results indicated all three lasers capable of sterilizing selected dental instruments; however, the argon laser was able to do so consistently at the lowest energy level of 1 watt for 120 seconds.

Argon↗

PubMed1991

Post polymerization strength values of an argon laser cured resin.

A hybrid composite resin, Prisma APH, and a microfilled composite resin, Silux Plus, were compared regarding diametral tensile strength values following conventional visible light polymerization and argon lasing. The time interval between resin polymerization and physical property testing ranged from 1 hour to 20 days. Results demonstrated considerable mean tensile strength value variation in the earlier phases of the study with a lessening of the differences between the tensile strengths achieved by each method of polymerization as the 20 day interval was approached. It was concluded that composite resin testing protocols should be lengthened to be able to fully assess the effects of the widely variant, time dependent mean test results.

Argon↗

PubMed1991

Application of the argon laser to dentistry.

A review was conducted to determine specific areas of application of the argon laser to dentistry. When appropriate, comparisons between the argon laser and other treatment methods were made. It was concluded that the argon laser has applicability in composite resin placement, in enamel and dentin bonding procedures, in preventive dental therapies, and in endodontic procedures.

Argon↗

PubMed1991

Degree of composite resin polymerization with visible light and argon laser.

A study was conducted to compare the degree of resin polymerization achievable using conventional visible light techniques and argon lasing. High performance liquid chromatography was used to extract unpolymerized resin from microfilled and small particle composite resin samples following photoactivation with visible light and the argon laser. It was determined that a significantly greater degree of microfilled resin polymerization was achievable following argon lasing compared to exposure to conventional visible light techniques. Although the small particle composite resin samples were polymerized as well as, or slightly better, with the argon laser, the differences were found to be insignificant. As a result, the argon laser should be considered a potentially advantageous method of initiating the polymerization of dental composite resin restorations.

Argon↗

PubMed1991

Managing infection control, hazards communication, and infectious waste disposal.

Dentistry entered a new era in the 1980s when the development of the AIDS crisis targeted dental facilities as one source of potential cross-infection with pathogenic microorganisms. As governmental agencies "discovered" dentistry, regulations forced practitioners to assume duties not previously required. Also, substantial costs of compliance became a significant consideration to employers. Managing the compliance and cost considerations of governmental regulation requires dedicating personnel, preferably one person, to the management of infection control, hazards communication, and infectious waste disposal tasks. predictably, this person--the safety supervisor--will develop into the new auxiliary specialist of the 1990s.

Communicable Disease Control↗

PubMed1990

The apparent permeability coefficient for proton flux through phosphatidylcholine vesicles is dependent on the direction of flux.

A dioleoylphosphatidylcholine unilamellar vesicle model system was used to determine proton permeability. The fluorescence of the pH reporter group, pyranine, trapped within vesicles with a difference in pH across the bilayer, was digitized and analyzed with numerical integration. When H+ flux was initiated by the acidification of the external buffer (acid jump), the apparent H+ permeability was found to be a linear function of the reciprocal of the internal H+ concentration with the slope inversely proportional to the initial size of the H+ gradient. When flux was initiated by the alkalinization of the external buffer (base jump), the apparent permeability coefficient was constant for each external H+ concentration. However, the value of the apparent permeability was linearly dependent on the reciprocal of the external H+. The possibility that carbonates (carbon dioxide, carbonic acid, bicarbonate and carbonate) could be acting as proton carriers was tested by adding millimolar concentrations of bicarbonate to solutions greatly reduced in carbonates. The slopes of the graphs of apparent permeability coefficient vs. reciprocal H+ were linear functions of added bicarbonate concentration for both acid and base jump conditions. These observations were interpreted in terms of a model suggesting that carbonic acid or carbon dioxide together with bicarbonate was an efficient proton carrier across phospholipid bilayers.

Arylsulfonates↗

PubMed1990

Activation of beef-heart cytochrome c oxidase by cardiolipin and analogues of cardiolipin.

Beef-heart cytochrome c oxidase lacking endogenous lipids can be prepared by cholate-mediated exchange with dimyristoylphosphatidylcholine (Powell, G. L., Knowles, P. F. and Marsh, D. (1985) Biochim. Biophys. Acta 816, 191-194). These preparations retained practically no endogenous cardiolipin (less than 0.19 mol cardiolipin per mol of oxidase) but in Tween 80 they retained unaltered electron transport activity. Resupplementation of the dimyristoylphosphatidylcholine-substituted cytochrome oxidase with cardiolipin and cardiolipin analogues with different numbers of acyl chains or with a methylated headgroup enhanced the activity of the reconstituted enzyme to an extent dependent on the structure of the cardiolipin derivative. The Eadie-Hofstee plot showed biphasic kinetic behavior for all reconstituted preparations, even those completely lacking cardiolipin. This biphasic substrate dependence of the kinetics was simulated using the model of Brzezinski, P. and Malmström, B. G. (Proc. Natl. Acad. Sci. USA 83 (1986) 4282-4286), which implicates two interconverting enzyme conformations in the proton transport step. The activation of cytochrome c oxidase by the cardiolipin analogues could be explained in terms of an electrostatic enhancement of the surface concentrations of both cytochrome c and protons, and a facilitated interconversion between the two enzyme conformations.

Animals↗

PubMed1990

Incorporation of cytochrome oxidase into cardiolipin bilayers and induction of nonlamellar phases.

Cytochrome oxidase from beef heart has been lipid-substituted with beef heart cardiolipin. The lipid phase behavior and protein aggregation state of the reconstituted complexes have been studied with 31P NMR, freeze-fracture electron microscopy, and saturation-transfer ESR of the spin-labeled protein. In the absence of salt, the lipid has a lamellar arrangement, and the protein is integrated and uniformly distributed in the membrane vesicles and undergoes rapid rotational diffusion. The presence of the protein stabilizes the cardiolipin lamellar phase against salt-induced transitions to the inverted hexagonal phase. The threshold salt concentration becomes higher and the extent of conversion becomes lower with decreasing lipid:protein ratio. In high salt, lamellar-phase lipid with integrated protein coexists with hexagonal-phase lipid free of protein, and the rotational diffusion of the protein is drastically reduced as a result of the high packing density.

Animals↗

PubMed1990

Conformational changes in cytochrome c and cytochrome oxidase upon complex formation: a resonance Raman study.

The fully oxidized complex of cytochrome c and cytochrome oxidase formed at low ionic strength was studied by resonance Raman spectroscopy. The spectra of the complex and of the individual components were compared over a wide frequency range using Soret band excitation. In both partners of the complex, structural changes occur in the heme groups and in their immediate protein environment. The spectra of the complex in the 1600-1700 cm-1 frequency range were dominated by bands from the cytochrome oxidase component, whereas those in the 300-500 cm-1 range were dominated by bands from the cytochrome c component, hence allowing separation of the contributions from the two individual species. For cytochrome c, spectral changes were observed which correspond to the induction of the conformational state I and the six-coordinated low-spin configuration of state II on binding to cytochrome oxidase. While in state I the structure of cytochrome c is essentially the same as in solution, state II is characterized by a structural rearrangement of the heme pocket, leading to a weakening of the axial iron-methionine bond and an opening of the heme crevice which is situated in the center of the binding domain for cytochrome oxidase. The relative contributions of the two cytochrome c states were estimated to be approximately in the ratio 1:1 in the complex.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

Effect of laser irradiation on the dissolution kinetics of hydroxyapatite preparations.

This research investigated the effects of a laser irradiation treatment on the dissolution characteristics of hydroxyapatite (HAP), and the results provide an insight into the relationship between the effects of laser treatment and the two-site dissolution kinetics of HAP samples. The HAP samples prepared by aqueous precipitation and digestion at approximately 100 degrees C were irradiated with a CO2 laser (20-50 W) with a beam diameter of 14 mm for a total of 10-400 s. Dissolution rates of the laser-treated HAP samples were subsequently determined in acetate buffer (pH = 4.5, mu = 0.50) at various levels of partial saturation (0-24% with respect to the HAP thermodynamic solubility of pKsp = 116). The following were the important findings. The X-ray diffraction and the IR spectroscopy results suggested that the HAP crystalline structure was not changed by laser treatment. Laser treatment of HAP powder at 50 W for 400 s, however, caused an approximately 3.5-fold reduction in the specific surface area of HAP and reduced the initial dissolution rate of HAP in acetate buffer by a factor of approximately 22.9. Also, this laser treatment appeared to reduce the dissolution rate of HAP in 16 and 24% partially saturated acetate buffer from substantial levels to essentially zero. These results may be summarized as follows. Laser treatment of HAP results in a reduction in the dissolution rate and also a reduction in the specific surface area of this material. However, the dissolution rate reduction is significantly greater than the reduction in the specific surface area.(ABSTRACT TRUNCATED AT 250 WORDS)

Hydroxyapatites↗

PubMed1990

Carbon dioxide laser oral safety parameters for teeth.

The carbon dioxide laser is used in the oral cavity for a variety of procedures. Although the procedures may not involve the teeth directly, precaution should be exercised to preserve their integrity. The results of this study indicate that the most limiting parameter for oral use of the CO2 laser is damage to the enamel surface, which could be inflicted with as little as 5 W for 0.2 second and a 1 mm beam. Care should be exercised to prevent inadvertent damage to the surface enamel of teeth even at very low energy levels.

Animals↗

PubMed1990

The presence and identification of organisms transmitted to dental laboratories.

The potential for infection of dental personnel in the office and dental laboratory by transmission of microorganisms between dentists' offices and commercial dental laboratories does exist. Sixty-seven percent of all materials sent from dental offices to dental laboratories sampled in four cities were contaminated with bacteria of varying degrees of opportunistic pathogenicity. Dental offices and dental laboratories need to practice adequate infection control procedures to prevent possible cross-contamination.

Bacteria↗

PubMed1990

The structural requirements for anti-cardiolipin antibody binding in sera from patients with syphilis and SLE.

In a search for specific binding patterns of anti-phospholipid (PL) antibody reactivity in sera from patients with systemic lupus erythematosus (SLE), a quantitative assay was used to compare binding curves with those from beef heart cardiolipin (CL) and the following CL analogues: diphosphatidyl propylene glycol (DPPG), which lacks the internal hydroxyl group on the glycerol moiety; acetyl CL (ACL), in which an acetyl group is substituted for the glycerol hydroxyl group; and dimethyl CL (DCL), in which a methyl group is positioned on each phosphate group. In syphilitic sera the plateau level of antibody binding was decreased by 15 and 41% with DPPG and ACL, respectively. Binding to DCL was dramatically suppressed to levels only slightly above baseline. Only the binding curves for CL and DPPG showed saturability, and analysis by Eadie-Scatchard plots showed that the change in binding was primarily due to a more than twofold increase in KD (decreased antibody avidity). Similar patterns were seen with sera from patients with SLE and SLE-like illness, but some uniquely shaped binding curves were observed. Compared to control CL, peak binding levels were 75-88% for DPPG, 16-20% for ACL, and only 1-4% for DCL. These data indicate that the integrity of the CL headgroup, especially at the phosphate moiety, is essential for recognition by anti-CL antibodies from some sources.

Antibodies, Monoclonal↗

PubMed1989

A spin-label electron spin resonance study of the binding of mitochondrial creatine kinase to cardiolipin.

The binding of the mitochondrial creatine kinase to aqueous dispersions of beef heart cardiolipin has been studied via the perturbation of the mobility of spin-labelled cardiolipin, using electron spin resonance (ESR) spectroscopy. In the presence of creatine kinase (1:1 protein/lipid ratio, by mass), the ESR spectra of cardiolipin labelled in a single acyl chain [n-(4,4-dimethyl-oxazolidinyl-N- oxy)stearoylcardiolipin] indicate a restriction of motion both at the C-5 and C-14 positions (n = 5, 14) of the lipid chains. The restriction in mobility was reversed by addition of phosphate or adriamycin, which are thought to inhibit the binding of creatine kinase to the mitochondrial membrane or to displace it from its binding site on the membrane. The effect of the protein on the chain mobility is consistent with surface binding of the protein; no positive evidence was obtained for penetration of the protein into the hydrophobic region of the membrane.

Animals↗

PubMed1989

Effect of acyl chain composition on salt-induced lamellar to inverted hexagonal phase transitions in cardiolipin.

Salt-induced fluid lamellar (L alpha) to inverted hexagonal (HII) phase transitions have been studied in diphosphatidylglycerols (cardiolipins) with different acyl chain compositions, using 31P nuclear magnetic resonance (NMR) spectroscopy. Cardiolipins with four myristoyl chains, tetramyristoyl cardiolipin (TMCL), and with four oleoyl chains, tetraoleoyl cardiolipin (TOCL), were synthesized chemically. TMCL was found to undergo a thermotropic lamellar gel to lamellar liquid-crystalline phase transition at 33-35 degrees C. This lipid exhibited an axially symmetric 31P-NMR spectrum corresponding to a lamellar phase at all NaCl concentrations between 0 and 6 M. In the case of TOCL, formation of an HII phase was induced by salt concentrations of 3.5 M NaCl or greater. These observations, taken together with earlier findings that bovine heart cardiolipin aqueous dispersions adopt an HII phase at salt concentrations of 1.5 M NaCl or greater, indicate that increasing unsaturation and length of the acyl chains favour formation of the HII phase in diphosphatidylglycerols.

Calorimetry, Differential Scanning↗

PubMed1989

Enhancement of physical properties of resin restorative materials by laser polymerization.

A study was conducted to compare the compressive strength, diametral tensile strength, transverse flexural strength, and flexural modulus of a microfilled and a small particle composite resin restorative material following argon laser and conventional visible light polymerization techniques. All physical properties examined in this study were enhanced by laser polymerization. The diametral tensile strength of both types of restorative materials was significantly greater following laser polymerization, as were the transverse flexural strength and the flexural modulus of the microfilled resin restorative material. Additionally, these results were obtained with a laser polymerization time that was one-fourth that used for visible light activation. It was concluded that the argon laser is a potentially advantageous means of initiating the polymerization of dental composite resin restorations.

Acrylic Resins↗

PubMed1989

The accuracy and efficacy of disinfection by spray atomization on elastomeric impressions.

Five disinfectants applied by spray atomization were examined for possible dimensional distortion of elastomeric impression materials, polyether, polysulfide, and addition silicone, and the associated improved, type IV gypsum casts. The disinfectants did not affect, in a clinically significant manner, the three dimensions measured with an instrument accurate to 1 micron on improved gypsum casts that reproduced a stainless steel standard. The master cast represented two teeth of a fixed partial denture prepared for complete veneer retainers. The use of control casts from elastomeric impressions that were not treated with the disinfectants further supported previous investigations reporting the accuracy of dental casts as the function of the impression material. The use of a spray disinfectant will not appreciably alter the dimensional accuracy of improved stone casts made within elastomeric impressions. The most accurate stone cast system was produced by addition silicone impressions disinfected by a surface spray. It was also shown that four of the disinfectants applied by spray atomization were effective in disinfecting the surface of an elastomeric impression material contaminated with selected test organisms.

Aerosols↗

PubMed1989

Pulpal response to irradiation of enamel with continuous wave CO2 laser.

Selected dog's teeth, in vivo, were exposed to carbon dioxide (CO2) laser power densities ranging from 13 to 102 J per cm2. The teeth were extracted 48 h postlasing, fixed with 10% neutral buffered formalin, decalcified with Kristensen's solution, processed, sectioned, stained, and evaluated for pulpal damage. No pulpal damage was observed when compared with nonlased control teeth. It appears that carbon dioxide laser power densities of approximately 13 to 102 J per cm2 could be used to irradiate enamel of teeth without damage to the pulp.

Animals↗