Biomedical subjects

G L Powell

Publications and source records attributed to G L Powell.

At least 19 recordsLinked to original sources

PubMed2005

Increase of enamel fluoride retention by low fluence argon laser beam: a 6-month follow-up study in vivo.

BACKGROUND AND OBJECTIVES: The aim of this 6-month in vivo study was to investigate if argon laser irradiation of enamel can increase the retention of fluoride. STUDY DESIGN/MATERIALS AND METHODS: Ninety-eight teeth in 12 patients were randomly divided into three groups: (1) EF group: 40 teeth were only treated with fluoride gel (applied for 5 minutes followed by a 1 minute rinsing with distilled water). (2) EFL group: 40 teeth were treated the same way as in the EF group but they were lased after fluoridation. (3) E group: 18 teeth were kept without any treatment as a control group. In order to quantify the fluoride content in the enamel samples, the teeth were analyzed by proton beam delivered by a tandem accelerator (PIgE, particle induced gamma-ray emission). A low energy density of argon laser beam was used: 10.74 J/cm2 (11 mm of beam diameter, irradiation time of 30 seconds, and an output power of 340 mW in continuous mode). RESULTS: The results after 6 months showed that the lased enamel still retained 52.55+/-8.47 ppm or 14.12% of fluoride after the fluoridation process, whereas the unlased enamel retained only 12.18+/-6.82 ppm or 3.27% of fluoride. The untreated and control enamel (E group: unlased and without fluoride treatment) had 1.16+/-4.27 ppm value of fluoride. The statistical test (ANOVA tests at 95% level) showed that the difference is significant between the fluoride retention in the group EFL and the group EF 6 months after fluoridation. CONCLUSIONS: The use of argon laser at low energy density (10.74 J/cm2) significantly increased the fluoride retention in lased enamel that had approximately 400 times more fluoride than the unlased enamel. We consider this procedure as an alternative clinical procedure to increase the fluoride content of enamel surface.

Acidulated Phosphate Fluoride↗

PubMed2004

External temperature during KTP-Nd:YAG laser irradiation in root canals: an in vitro study.

To avoid the damage of periodontal tissues during laser irradiation of the root canal, the conditions of lasering must be carefully controlled. The aim of this study was to determine the safety parameters of the irradiation conditions during the use of a KTP-Nd:YAG laser in root canals. Root canals of 60 freshly extracted teeth were prepared (step-back technique) and filled with a photosensitiser (Acid Red 52). Different irradiation conditions [output power (P), pulse width (PW), pulse repetition rate (PRR, Hz)] were used. The laser beam was delivered by means of the KTP-Nd:YAG fibre tip with a beam spot-size diameter of 200 microm. The temperature increases were measured on the external apical third of the root surface using a thermocouple. The results showed that the temperature rise was always below 7 degrees C at the following laser settings: (1) single irradiation, P < or = 4 W, PW < or = 2.55 ms and PRR < or = 20 Hz; (2) repetitive irradiation series, five pulses of 1 s each, four resting times of 1 s each, P < or = 2.25 W, PW < or = 2.55 ms and PRR < or = 20 Hz. The use of resting times was necessary so as to avoid thermal cumulative effects. In these in vitro irradiation conditions, the use of the KTP-Nd:YAG laser in endodontics may be considered harmless for periodontal tissues.

Dental Pulp Cavity↗

PubMed2001

Structural characteristics of the patagium of Ptychozoon kuhli (Reptilia: Gekkonidae) in relation to parachuting locomotion.

Ptychozoon kuhli is known for its parachuting/gliding capabilities. In this contribution, we document the allometric scaling properties of its patagium, accessory flaps and folds, and its total body surface area and compare them to similar attributes of the agamine lizard Draco volans. Ptychozoon kuhli has passive patagia that lack skeletal support and muscular control. Patagial area in P. kuhli is smaller than that in D. volans for individuals of identical snout-vent length, but the accessory folds and flaps compensate for this shortfall and overall P. kuhli has equivalent total body surface area to D. volans for equally sized individuals. The structure of the patagium of Ptychozoon kuhli was investigated in terms of its scalation patterns and structural integrity, its relationship to the body wall and its mechanism of erection, and the distribution of mechanoreceptive sensilla across its surface. Scalation patterns and the internal architecture of the patagium indicate how its shape and form are maintained as it erects and becomes exposed to air flow. Its cross-sectional shape, together with that of the entire body indicates how it is able to behave as an airfoil. The distribution of sensilla across the patagial surface reflect positioning indicative of the monitoring of scale-to-scale contact on the dorsal surface, and possibly air pressure and flow on the ventral surface.

Animals↗

PubMed2001

Endoplasmic oleoyl-PC desaturase references the second double bond.

The regiospecificity for the gene product of fad2,(1) the microsomal oleoyl-PC desaturase from higher plants, differs from some previous suggestions. Rather than only referencing the carboxyl group (a Delta(12) desaturase) or the methyl terminus (an omega-6 desaturase), this desaturase locates the second double bond in its substrates by first referencing the existing double bond. This specificity was demonstrated for the oleoyl-PC desaturase cDNA from the developing seeds of peanut (Arachis hypogaea L) expressed in yeast (Saccharomyces cerevisae). The expressed enzyme was capable of desaturating monounsaturated fatty acyl groups in membrane lipids. Endogenous palmitoleate was desaturated to cis, cis 9,12 hexadecadienoate (9(Z)12(Z)C16:2), endogenous oleate to linoleate (9(Z)12(Z) octadecadienoate), and cis 10-nonadecenoate (provided as a supplement in the growth medium) to 10(Z)13(Z)C19:2. The rule, Delta(x+3) where x=9 is the double bond location in the substrate, best describes the consistent placement of the second double bond in the above monounsaturated substrates for the oleoyl-PC desaturase of higher plants.

Cytoplasm↗

PubMed2001

Phospholipid composition of articular cartilage boundary lubricant.

The mechanism of lubrication in normal human joints depends on loading and velocity conditions. Boundary lubrication, a mechanism in which layers of molecules separate opposing surfaces, occurs under severe loading. This study was aimed at characterizing the phospholipid composition of the adsorbed molecular layer on the surface of normal cartilage that performs as a boundary lubricant. The different types of phospholipid adsorbed onto the surface of cartilage were isolated by extraction and identified by chromatography on silica gel paper and mass spectroscopy. The main phospholipid classes identified were quantified by a phosphate assay. Gas chromatography and electrospray ionization mass spectrometry were used to further characterize the fatty acyl chains in each major phospholipid component and to identify the molecular species present. Phosphatidylcholine (41%), phosphatidylethanolamine (27%) and sphingomyelin (32%) were the major components of the lipid layer on the normal cartilage surface. For each lipid type, a mixture of fatty acids was detected, with a higher percentage of unsaturated species compared to saturated species. The most abundant fatty acid observed with all three lipid types was oleic acid (C18:1). Additional work to further quantify the molecular species using electrospray ionization mass spectrometry is recommended.

Animals↗

PubMed2000

Nonlinear electron paramagnetic resonance studies of the interaction of cytochrome c oxidase with spin-labeled lipids in gel-phase membranes.

The interaction of lipids, spin-labeled at different positions in the sn-2 chain, with cytochrome c oxidase reconstituted in gel-phase membranes of dimyristoylphosphatidylglycerol has been studied by electron paramagnetic resonance (EPR) spectroscopy. Nonlinear EPR methods, both saturation transfer EPR and progressive saturation EPR, were used. Interaction with the protein largely removes the flexibility gradient of the lipid chains in gel-phase membranes. The rotational mobility of the chain segments is reduced, relative to that for gel-phase lipids, by the intramembranous interaction with cytochrome c oxidase. This holds for all positions of chain labeling, but the relative effect is greater for chain segments closer to the terminal methyl ends. Modification of the paramagnetic metal-ion centers in the protein by binding azide has a pronounced effect on the spin-lattice relaxation of the lipid spin labels. This demonstrates that the centers modified are sufficiently close to the first-shell lipids to give appreciable dipolar interactions and that their vertical location in the membrane is closer to the 5-position than to the 14-position of the lipid chains.

Animals↗

PubMed2000

Laser curing of dental materials.

Research supports the use of the argon laser in dentistry. Used at powers of 250 mW +/- 50 mW for 10 seconds per increment, the argon laser provides good curing of light-activated restorative materials in a shorter period of time with equal or better physical properties as compared to the conventional halogen curing light. When used at approximately 1.5 W, it is a good soft tissue surgical instrument that cuts with little or no bleeding and minimal postoperative pain. The future looks bright for the use of the argon laser in other areas, such as decay prevention or pulpal treatments for primary teeth as well as an adjunct to endodontic therapy.

Adult↗

PubMed2000

Molecular properties of the oleoyl-phosphatidylcholine desaturase from Arachis hypogaea L.

Deficiencies in the activity of the microsomal oleoyl phosphatidylcholine (oleoyl-PC) desaturase from peanuts are the basis of the high oleate oil. Mutation of aspartate-150 to asparagine and the attendant decrease in activity, together with the loss in expression of the higher activity transcript, was the molecular basis of the high oleate trait. The ability of oleoyl-PC desaturase to desaturate palmitoleate, oleate and 10(Z) nonadecenoate to methylene-interrupted products was not consistent with description of this activity as a Delta(12) or omega-6 desaturase. Electrospray MS was used to examine the intact phospholipid products of desaturation by the oleoyl-PC desaturase. PC and phosphatidylinositol containing unsaturated moieties could be desaturated. The enzyme can act on either sn-1 or sn-2 moieties. Phosphatidylethanolamine was a poor substrate.

Amino Acid Substitution↗

PubMed1999

Laser and curing light induced in vitro pulpal temperature changes.

OBJECTIVE: This study was conducted to compare in vitro pulp chamber temperature changes induced by conventional curing light and argon laser under common conditions. SUMMARY BACKGROUND DATA: Previous in vitro studies have shown that impacting the surface of teeth with either an argon laser or conventional curing light causes pulp temperature increases of various degrees. METHODS: The sample tooth had a class V composite restoration placed with 2.48-mm distance from the surface of the composite to a Thermister Thermometer. The thermometer was inserted into the cutaway pulp chamber to measure the temperature increase from stabilized room temperature, which was caused by exposure to argon laser or conventional curing light. RESULTS: Temperature increases for the argon laser for the recommended curing time were 3 degrees F or less. The longer the exposure times for either method of curing, the higher the temperature increased. CONCLUSION: At recommended curing times, in vitro pulp chamber temperature increases from laser units were significantly lower than those of the conventional curing lights.

Analysis of Variance↗

PubMed1999

Combined effects of acidulated phosphate fluoride and argon laser on sound root surface morphology: an in vitro scanning electron microscopy study.

OBJECTIVE: The purpose of this in vitro scanning electron microscopy (SEM) study was to evaluate the effects of combining low fluence argon laser (AL) irradiation and acidulated phosphate fluoride (APF) treatment on the surface morphology of sound human root surfaces. SUMMARY BACKGROUND DATA: Previous in vitro investigations have shown that combined APF and AL irradiation of root surfaces provided a protective effect against cariogenic challenges. MATERIALS AND METHODS: Twelve extracted human molars were sectioned into quarters, and each quarter assigned to 1 of 4 treatment groups: (1) no treatment/control; (2) low fluence (11.5 J/cm2) AL irradiation; (3) 1.23% APF for 4 minutes; (4) APF treatment followed by low fluence AL irradiation. Surface morphology alterations were compared among groups using SEM techniques. RESULTS: AL irradiation alone produced irregular textured surfaces with adherent globular material and fine microporsities in the background. APF treatment, alternatively, only created relatively smooth surface coatings that masked the original underlying root surface. Combining APF treatment followed by AL irradiation resulted in a surface coating composed of relatively small (2 to 3 microns) spherical to avoid precipitates, morphologically resembling calcium fluoride. CONCLUSION: Combining APF with AL irradiation may create a more reactive surface that possesses fluoride-rich mineral deposits and protects the underlying root surface from cariogenic challenges.

Acidulated Phosphate Fluoride↗

PubMed1999

Effect of phospholipidic boundary lubrication in rigid and compliant hemiarthroplasty models.

Hemiarthroplasty may benefit from materials which produce lower friction and improved boundary lubrication protection during start-up conditions. The purpose of this study was to evaluate the effect of phospholipidic boundary lubrication in both rigid and compliant hemiarthroplasty. An in vitro model was designed to dissociate the relative contribution of implant material compliance and the presence of phospholipid to the overall friction of a hemiarthroplasty contact using bovine articular cartilage. Normal bovine articular cartilage was articulated against four flat materials using reciprocating motion: (a) borosilicate glass: (b) borosilicate glass coated with dipalmitoylphosphatidylcholine (DPPC); (c) polyurethane (PU) elastomer (Tecoflex SG93A, a medical-grade aliphatic thermoplastic PU, Thermedics Incorporated. Woburn, Massachusetts); and (d) surface-coated PU (Tecoflex SG93A substrate coated with lipid-attracting copolymer poly[methacryloyloxyethyl phosphorylcholine (MPC)-co-butyl methacrylate (BMA)]. Tests were conducted in physiologically simulated tribological conditions for a non-conformal point contact. Friction and lubrication analysis was performed using both static and kinetic coefficients of friction mu measured for each group as a function of time for a sliding distance of up to 60 m. Results showed that the inclusion of supplemental phospholipid, DPPC, on a rigid substrate significantly decreased mu in comparison with the control (cartilage-glass). Additionally, removal of phospholipid components from the articular cartilage surface produced a significantly greater start-up mu in comparison with normal cartilage at the test onset. The use of a material with a lower modulus resulted in lower mu for the entire duration of the test. Polyurethane elastomer coated with the lipid-attracting copolymer, poly(MPC-co-BMA), resulted in the lowest frictional response. As seen in this study, the improvement of low-modulus hemiarthroplasty may involve the optimization of chemical modification and incorporation of lipid-attracting MPC copolymers onto compliant materials. However, further tests are warranted to determine whether lipid-attracting MPC copolymers perform as well during long-time, in vivo wear studies.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1998

Cytochrome c-induced increase of motionally restricted lipid in reconstituted cytochrome c oxidase membranes, revealed by spin-label ESR spectroscopy.

Cytochrome c oxidase isolated from beef heart mitochondria was reconstituted in bilayer membranes of the anionic lipid dimyristoylphosphatidylglycerol (DMPG) with varying enzyme/DMPG ratio. Lipid-protein interactions in the reconstituted membrane complexes were studied in the presence and absence of saturating amounts of bound cytochrome c, by both chemical binding assays and spin-label ESR spectroscopy. The ESR spectra from a phosphatidylglycerol probe spin-labeled on C-14 of the sn-2 chain revealed two distinct lipid populations differing in their rotational mobility. The stoichiometry of lipids that were restricted in their rotational motion by direct interaction with the integral protein was 50-60 lipids/cytochrome c oxidase monomer, in the absence of cytochrome c, independent of the total lipid/protein ratio. Cytochrome c alone did not induce a motionally restricted population in the lipid ESR spectra, when bound to bilayers of negatively charged DMPG alone, in the fluid phase (at 36 degreesC). However, the motionally restricted lipid population associated with reconstituted cytochrome c oxidase/DMPG membranes increased on binding cytochrome c, indicating structural/dynamic changes taking place in the membrane. Depending on the DMPG/cytochrome c oxidase ratio, apparent stoichiometries of up to 115 motionally restricted lipid molecules/cytochrome c oxidase monomer were found, when saturating amounts of cytochrome c were bound. Under these conditions, cytochrome c binds to approximately 9 negatively charged DMPG molecules, independent of the cytochrome c oxidase content in the reconstituted system. A likely explanation for these results is that the surface binding of cytochrome c propagates the motional restriction of the lipid chains beyond the first boundary shell of cytochrome c oxidase, possibly creating microscopic in-plane domains.

Animals↗

PubMed1998

Argon laser irradiation effects on sound root surfaces: in vitro scanning electron microscopic observations.

OBJECTIVE: The purpose of this in vitro scanning electron microscopy (SEM) study was to evaluate the effect of low fluence (energy density of 11.5 J/cm2 and 100 J/cm2) argon laser irradiation on the surface morphology of sound root surfaces. SUMMARY BACKGROUND DATA: Previous laboratory investigations have shown that argon laser irradiation of root surfaces provided a protective effect against in vitro cariogenic challenges. METHODS: Root surfaces of extracted human molars were sectioned into treatment quarters: 1) mesiobuccal--no treatment control; 2) mesiolingual--low fluence argon laser irradiation (0.231 Watts, 11.5 J/cm2 for 10 seconds); 3) distobuccal--no treatment control; and 4) distolingual--higher fluence argon laser irradiation (2.0 Watts, 100 J/cm2 for 10 seconds). All surfaces were critical-point dried, coated with platinum and paladium under vacuum, and evaluated qualitatively for intactness, surface morphology, surface deposits, and porosities in a blinded fashion by scanning electron microscope. RESULTS: The argon lased root surfaces demonstrated alterations of root surfaces with creation of surface globular particulate material, microporosities, and depressions. Both low- and high-fluence lased root surfaces showed areas with plaque-like plates with fine punctuate oval particulate material on their surfaces. CONCLUSIONS: Argon laser irradiated root surfaces produce surface granular to globular deposits that may provide readily mobilized tooth mineral, which may become redeposited into the underlying root surface during a cariogenic challenge and enhance resistance to caries formation. In addition, microporosities created by the argon laser may provide a means for bonding fluoride-releasing restorative and preventive materials to root surfaces and further improve the root surfaces' ability to resist cariogenic challenges.

Argon↗

PubMed1998

Combined effects of laser irradiation/solution fluoride ion on enamel demineralization.

OBJECTIVE: The effects of CO2 laser irradiation of dental enamel were evaluated in enamel demineralization experiments in partially saturated solutions (i.e., solutions containing both calcium and phosphate ions) with and without fluoride ions. SUMMARY BACKGROUND DATA: Previous studies had shown that a continuous-wave CO2 laser at an energy density of around 130 J/cm2 may induce an increased acid resistance in human dental enamel as assessed by exposure to severe demineralization conditions (0.1 mol/L acetate buffer, pH 4.5 and ionic strength 0.5 mol/L). METHODS: Enamel blocks were irradiated with a continuous-wave CO2 laser at a wavelength of 10.6 microns using energy densities of from 42.5 to 170.0 J/cm2. The blocks were then exposed to a partially saturated demineralizing solution with or without 0.2 ppm fluoride at a temperature of 30 degrees C for 24 hours. The demineralization was examined both qualitatively by light microscopy and quantitatively by microradiography. RESULTS: A comparison between the lased and the unlased portions of enamel showed increased acid-resistance with increasing laser energy density and, at the highest energy density of 170.0 J/cm2, there was little or no lesion development in the fluoride-free dissolution medium. The demineralization of enamel was reduced dramatically in the presence of 0.2 ppm fluoride for both lased and unlased enamel; there was only modest lesion development observed for unlased enamel and, at an energy density as low as 85.0 J/cm2, the surface of enamel was found to be completely protected. CONCLUSIONS: These findings are consistent with the mechanism that laser irradiation of dental enamel results in significant reduction of the effective solubility of enamel mineral and that there is a significant synergism between laser irradiation and solution fluoride with regard to this effect.

Carbon Dioxide↗

PubMed1997

Evaluation of the frictional properties of an elastomer with enhanced lipid-adsorbing ability.

Wear particle production in load-bearing orthopaedic implants is one of the major factors currently limiting the service life of the implant. Most of the research carried out to date in attempting to solve this problem has used the approach of finding more wear-resistant biocompatible material pairs. In contrast, other researchers have attempted to reduce wear by encouraging elastohydrodynamic film formation through the use of elastomeric bearing surfaces. Unfortunately, these elastomeric bearing surfaces have poor tribological properties when a fluid film is not present. Boundary lubrication of an elastomeric orthopaedic bearing may alleviate some of these difficulties. The purpose of this research was to fabricate and characterize an elastomeric material that had a surface capable of specifically adsorbing a naturally occurring boundary lubricant. Dipalmitoyl phosphatidylcholine (DPPC) has been previously shown to be able to act as a boundary lubricant at stresses that occur in human load-bearing joints such as the hip and knee; therefore, DPPC was chosen for use in this study. It was expected that in an aqueous liposome suspension the static coefficient of friction microseconds of such a material would be lower, and increase less quickly over time, than a similar material without an ability to adsorb specifically DPPC when articulated against a polished chrome steel ball bearing. The lipid-adsorbing elastomer did not possess the desired tribological properties. This result was attributed to the polymer adsorbing the DPPC in the liposome phase and not in the bilayer phase, and interaction among the polymeric surface, DPPC and water. This approach to lubricating orthopaedic bearings was shown to have some merit, but a great deal of work needs to be done before such an approach can be used on a clinically available material.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1997

Dentistry for the 21st century? Erbium:YAG laser for teeth.

The first dental laser for use in cutting human teeth in vivo was cleared by the Food and Drug Administration for marketing in the United States. The authors explored, in summary form, the data provided to the FDA for the clinical use of the erbium:yttrium-aluminum-garnet, or Er:YAG, laser. The authors concluded that using the Er:YAG laser to treat dental hard tissue is both safe and effective for caries removal, cavity preparation and enamel etching.

Adolescent↗

PubMed1997

Root caries in vitro after low fluence argon laser and fluoride treatment.

Because the numbers of dentate elderly are increasing, root caries prevention has become a great concern to the dental profession. This in vitro study evaluates the influence of combining low fluence argon laser treatment and acidulated phosphate fluoride treatment on caries initiation and progression in human root surfaces. The combination of low energy laser treatment and fluoride treatment increased the caries resistance of root surfaces when compared with no treatment and with laser irradiation treatment alone.

Acidulated Phosphate Fluoride↗

PubMed1996

Claw retraction and protraction in the Carnivora: skeletal microvariation in the phalanges of the Felidae.

All carnivorans retract and protract their claws. In felids and some viverrids the claws of digits II through V of both the manus and pes have a larger arc of rotation than those of other carnivorans; the claws retract to the lateral side of the middle phalanx rather than onto its dorsal surface as in most other carnivorans. This condition should be termed hyper-retraction. Morphological features of the middle and distal (ungual) phalanges that have been purported to be necessary for hyper-retraction in felids vary considerably among digits within the manus and pes. These features include the lateral projection of the distal head and the asymmetry of the shaft of the middle phalanx, and the oblique orientation of the articular surface on the distal phalanx. None of these features is necessary in every instance for hyper-retraction, and some of the variation in these features is associated instead with protraction. Differences among digits in the orientation of the articular surface on the distal phalanx are associated with differences in the degree to which the claws must move laterally to rotate from the protracted to the retracted position. Differences in the orientation of the distal head on the middle phalanx are associated with the spreading of the claws during protraction. The manual claws are hook-shaped, whereas the pedal claws are more blade-like; this morphological difference is associated with differences in function between the manus and pes. In the manus the medial claws have a larger radius of curvature and a smaller angle of arc as compared to the more lateral claws; in the pes, the claws on digits III and IV have larger radii of curvature and smaller angles of arc. Digit I of the manus lacks the hyper-retraction mechanism; nonetheless, this digit shares many of the attributes that are associated with this mechanism.

Animals↗