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Biomedical subjects

G L Powell

Publications and source records attributed to G L Powell.

At least 37 records · Page 2Linked to original sources
PubMed1996

Tetraoleoylpyrophosphatidic acid: a four acyl-chain lipid which forms a hexagonal II phase with high curvature.

Tetraoleoylpyrophosphatidic acid (bis phosphatidic acid), when hydrated in aqueous buffer, was shown to form an inverted hexagonal phase using 31P NMR. Low-angle x-ray diffraction provided verification of the formation of this phase in dilute aqueous buffer and in 2 M NaCl and permitted comparison of the tube diameter with that of cardiolipin in 2 M NaCl. By using the water cylinder diameters for tetraoleoylpyrophosphatidic acid, bovine cardiolipin, chloroplast monogalactosyl-diglyceride, and dioleoyl phosphatidylethanolamine as a means of estimating the spontaneous curvatures, tetraoleoylpyro-phosphatidic acid was shown to exhibit the greatest curvature of any of the above lipids, equaled only by the calcium salt of cardiolipin. Inverted micelles of hydrated tetraoleoylpyrophosphatidic acid and of cardiolipin in tetradecane were approximately the diameter of the inverted hexagonal tubes. A rationale is given for the differences.

Animals↗
PubMed1996

Effects of argon laser curing on dentin shear bond strengths.

Previous studies have demonstrated the ability of the argon laser to polymerize light-activated materials and improve enamel shear bond strengths. This study was conducted to evaluate the effects of the argon laser on dentin shear bond strengths of current dentin bonding systems. Argon laser (HGM Model 8) at 231 and 280 mW, 5 sec bonding agent, 10 sec composite, and a conventional curing light (Translux EC/Kulzer) at 10 sec bonding agent, 20 sec composite were used to polymerize samples of dentin bonding systems [Scotchbond Multi-Purpose Plus (3M) and Prime Bond (Dentsply/Caulk), both with TPH (Dentsply/Caulk) composite]. A flat dentin bonding site (600 grit) was prepared on the buccal surface of extracted human teeth. Twelve samples were made for each set of parameters for both laser and conventional light totaling 48 samples. Samples were stored in distilled water in light-proof containers for 24 h at 37 degrees C. Shear bond strengths (MPa) were determined for each sample on the Instron testing machine. Mean values were calculated for each set of data and ANOVA with Fisher PLSD were used for statistical analysis. The argon laser provided bond strengths that were 21-24% greater than those of the conventional curing light system.

Analysis of Variance↗
PubMed1996

Surface morphology of sound enamel after argon laser irradiation: an in vitro scanning electron microscopic study.

Argon laser irradiation (ALI) at relatively low fluences (energy densities) enhances the caries resistance of sound enamel. The purpose of this SEM study was to compare the effects of argon laser irradiation at relatively low fluences (11.5 Joules/cm2 and 100 Joules/cm2) on enamel surface morphology. Following a fluoride-free prophylaxis, 12 extracted caries-free human molars were sectioned into tooth quarters. Tooth quarters were treated as follows: 1) Mesiobuccal-ALI at 11.5 J/J/cm2 for 10; 2) Distobuccal-Control; 3) Mesiolingual-ALI at 100 J/J/cm2 for 10; and 4) Distolingual-Control. Enamel surface morphology was compared among the two argon laser irradiation groups and matched non-treated control enamel surfaces by SEM. Argon laser treatment resulted in considerable alterations in the surface morphology compared with matched controls. Control enamel surfaces showed relatively smooth contours with occasional termination of enamel prisms at the surface. Both argon laser treatment groups had intact enamel surfaces lacking prism end markings and cratering of the enamel surface. A discontinuous granular surface permeated by numerous microporosities of < 1.0 micron in diameter was created with both argon laser treatment groups. Globular deposits of approximately 0.5 to 2 microns in maximum dimension composed the surface coatings. These deposits were admixed with areas of fine microporosities. Argon laser irradiation at relatively low fluences produces surface coatings which may act as reservoirs for mineral phases during an acidogenic attach of the enamel and may provide a certain degree of protection against a cariogenic challenge.

Argon↗
PubMed1995

Fabrication and characterization of dipalmitoylphosphatidylcholine-attracting elastomeric material for joint replacements.

Wear debris associated with the polyethylene components of total joint replacements has been shown to induce bone resorption which contributes to implant loosening. In an effort to promote lubrication and reduce wear in artificial hip joints, the use of the cushion bearing concept has been proposed previously; however, an elastomeric material tested as a cushion bearing has been shown to have poor tribological properties during initiation of motion from rest. The goal of this project was to fabricate and characterize an elastomer that has the ability to attract to its surface naturally occurring boundary lubricants from an aqueous solution. The test elastomer and appropriate controls were characterized using fluorescence, electron spin resonance and X-ray photoelectron spectroscopy. The test elastomer was found to have an enhanced ability to attract dipalmitoylphosphatidylcholine, a known physiological boundary lubricant. A cushion bearing that also encourages boundary lubrication represents a potential improvement over currently existing orthopaedic implant-bearing materials.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1995

Effects of argon laser irradiation and acidulated phosphate fluoride on root caries.

PURPOSE: To determine the effects of argon laser irradiation (ArI) and topical acidulated phosphate fluoride (APF) treatment on artificial caries formation in root surfaces. MATERIALS AND METHODS: After soft tissue debridement and fluoride-free prophylaxis, the teeth were divided into quarters and acid-resistant varnish was applied, leaving windows of sound root surface exposed. Each tooth received four separate treatments: (1) Control-mesiobuccal quarter; (2) ArI only--mesiolingual quarter; (3) ArI followed by APF- distobuccal quarter; (4) APF followed by ArI-distolingual quarter. ArI was for 10 seconds at 2W (100J/cm2) and APF treatment was for 4 minutes. After artificial lesion formation, sections were prepared and evaluated with polarized light. Mean lesion depths were determined and compared (ANOVA & DMR for a paired design). RESULTS: Mean lesion depths were: 347 +/- 41 microns--controls; 263 +/- 32 microns--ArI only; 158 +/- 21 microns--ArI followed by APF; and 149 +/- 17 microns -APF followed by ArI. Lesion depths were significantly different (P < 0.05) between the control group and each treatment group, and between ArI only group and either combined APF and ArI groups. No lesion depth difference (P > 0.05) was present between the combined APF and ArI groups. Argon laser irradiation significantly enhanced the resistance of root surfaces to demineralization. Combination of APF treatment with argon laser irradiation provided added protection against a constant artificial caries attack.

Acidulated Phosphate Fluoride↗
PubMed1995

Enamel caries initiation and progression following low fluence (energy) argon laser and fluoride treatment.

The aim of this study was to evaluate the effect of low fluence argon laser (AL) and acidulated phosphate fluoride (APF) treatment on caries initiation (CI) and progression (CP) in human enamel. Twenty caries-free molars were divided into tooth quarters. Tooth quarters from each specimen were assigned to one of four groups: 1) Control; 2) AL Only; 3) AL before APF; 4) APF before AL. AL was at 0.25 watts for 10 seconds (12.0 +/- 0.5 J/cm2). APF treatment was with a 1.23% gel for 4 minutes. Lesions were created in two treated, sound enamel windows per tooth quarter with an acidified gel. After CI and CP, sections were obtained and imbibed with water for polarized light study. Mean body of the lesion (BL) depths were determined and compared among groups (ANOVA & DMR). After CI, BL depths were: 189 +/- 29 micrometers for Control, 133 +/- 23 micrometers for AL only; 91 +/- 17 micrometers for AL before APF; and 83 +/- 14 micrometers for APF before AL. After CP, BL depths were: 321 +/- 43 micrometers for Control, 206 +/- 35 micrometers for AL only; 118 +/- 21 micrometers for AL before APF; and 114 +/- 19 micrometers for APF before AL. After CI and CP, argon laser irradiation alone resulted in significant reductions in lesion depth when compared with controls (p<0.05). APF treatment before or after argon laser exposure resulted in a significant reduction in lesion depth when compared with AL alone or control groups (p<0.05). Caries initiation and progression in vitro are affected to a significant extent when low fluence (energy) argon laser irradiation of sound enamel alone or in conjunction with APF treatment is done. This caries-protective effect occurs at an argon laser fluence (energy) that is capable of polymerizing visible light-cured resins.

Acidulated Phosphate Fluoride↗
PubMed1994

Power density and external temperature of laser-treated root canals.

The purpose of this study was to determine the power and time parameters for an argon laser that would result in the removal of pulpal tissue without excessively elevating the external temperature of the root. External temperatures were measured by attaching thermistors to the surfaces of the teeth at the cemento-enamel junction (CEJ) areas and at the root apices. Results indicate that a 1-W power setting with a pulse duration of 0.1 sec and a 1 sec interval between pulses produced a mean temperature rise of 0.89 +/- 0.27 degrees C at the cemento-enamel junction area and a mean temperature increase of 2.04 +/- 0.47 degrees C at the apex. A 2-W power setting with a 0.1 sec pulse duration and a 1 sec interval between pulses resulted in a mean temperature increase of 1.58 +/- 0.45 degrees C at the CEJ and a mean temperature rise of 2.59 +/- 0.20 degrees C at the apex. Based upon the results of this study, it was concluded that an argon laser operating at 1 or 2 W of power with a 0.1 sec pulse duration could be used to remove pulpal tissue without creating an excessive increase in the external temperature of the tooth.

Dentin↗
PubMed1994

Heat-treatment-induced reduction in the apparent solubility of human dental enamel.

Holcomb and Young (1980) have shown a significant increase in human dental enamel (HE) structural order resulting from heat treatment in the temperature range of from 275 to 400 degrees C. Also, previous work in our laboratory had shown dramatic decreases in the initial dissolution rates (IDRs) of both carbonated apatite (CAP) heated at similar temperatures (from 300 to 500 degrees C) and HE exposed to CO2 laser irradiation for which calculated surface temperatures were in this same range. We hypothesize that thermal treatment shifts the apparent solubility distribution profile of HE toward lower apparent solubilities, paralleling the observed increased in crystal structural order and the decrease in IDRs. Powdered HE was heated in a furnace at temperatures ranging from 150 to 500 degrees C for 24 hours. The apparent solubility distributions of both heated and unheated HE powders were measured by equilibration for 24 hours in a series of partially saturated solutions simulating various amounts of HE dissolved in a pH 4.5 dissolution medium. The apparent solubility distribution for the unheated HE showed a peak at KHAP [the ion activity product based on the Ca10(PO4)6(OH)2 stoichiometry] of 10(121.0). Heat treatment shifted the apparent solubility distribution to lower solubilities. The peak KHAP values were approximately 10(124.8) at 200 degrees C; approximately 10(127.8) at 300 degrees C; and approximately 10(-129.1) from 400 to 500 degrees C. This approximately 8 orders of magnitude decrease in KHAP for HE heated at from 400 to 500 degrees C correlates with the previously observed reduction in the IDR driving force for laser-treated HE experiencing a similar surface temperature.(ABSTRACT TRUNCATED AT 250 WORDS)

Apatites↗
PubMed1993

Argon laser oral safety parameters for teeth.

Argon lasers have been reported to prevent or reduce demineralization of enamel in extracted teeth and to polymerize dental composites (using 25-100 J/cm2). Prior to clinical trials on caries prevention and curing composites, safety parameters for intraoral use of the argon laser need to be established. This study was conducted to determine the enamel damage, pulp temperature changes, and associated pulpal tissue damage following irradiation at various argon laser energy levels using 1.6-6.0 watts, approximately 1 and 2 mm diameter beam for 0.2-5.0 seconds. To evaluate pulpal damage, selected dogs' teeth were irradiated in vivo, extracted 7 days postlasing, fixed, decalcified, sectioned, stained, and read for pulpal damage. Pulp temperature and enamel damage tests utilized extracted dog and human teeth. Temperature probes were inserted in the pulp chambers and temperature changes recorded as enamel surface was lased. Enamel surface damage was evaluated by visual and microscope examination. Results showed that histologic pulpal damage occurred at > 600 J/cm2. Temperature changes were < 6 degrees F in human teeth with approximately 900 J/cm2. No enamel damage was observed at these energy densities. At energy densities needed for proposed uses, no apparent damage would be expected to pulp or enamel.

Animals↗
PubMed1993

Comparison of three lasers on dental pulp chamber temperature change.

Previous studies have reported dental pulp chamber temperature changes using only one beam size per laser. This study was designed to evaluate the effects of beam size, wattage, and energy density on pulp chamber temperature changes of extracted human teeth for three lasers (CO 2, Argon, Nd:YAG). During laser irradiation of the outer enamel surface, a thermocouple was placed in the pulp chamber which measured and recorded the temperature changes. This was done for each combination of lasing dosimetry parameters. In all cases the recorded temperatures increased with the increase in beam size for a given energy density (J/cm 2) and wattage. Also, the recorded temperatures increased with increased energy density for a given wattage and beam size.

Dental Pulp Cavity↗
PubMed1993

Sliding friction analysis of phosphatidylcholine as a boundary lubricant for articular cartilage.

Dipalmitoyl phosphatidylcholine (DPPC), the major lipidic component of the synovial fluid (45 per cent), has been implicated in previous studies in synovial joint lubrication as a potential boundary lubricant for articular cartilage. The purpose of this study was to evaluate the effectiveness of DPPC as a boundary lubricant at physiological stresses experienced by weight-bearing joints (up to 7.5 MPa). The sliding coefficients of static and kinetic friction for glass surfaces coated with DPPC layers of physiological thickness (70 nm) were measured as a function of average contact stress, contact geometry (point and line), applied load and relative velocity (from 25 to 0 mm/s) and compared to the coefficient of friction for clean glass in the same conditions. The coefficient of friction for DPPC-lubricated surfaces was dependent on contact geometry, obeyed Amonton's law (not dependent on axial load or contact area), was dependent on relative velocity within the range stated and was an effective lubricant at physiological stresses. This study showed that dipalmitoyl phosphatidylcholine can be an effective boundary lubricant at stresses observed in load-bearing joints. Because of their surface-active nature, these adsorbed molecules might also act as a protective layer for the articular surfaces.

Animals↗
PubMed1993

Caries-like lesion initiation and progression around laser-cured sealants.

This study evaluated and compared the effects of argon laser and visible light polymerization of a pit and fissure sealant material on caries-like lesion initiation and progression. Following the lesion initiation period, the primary surface lesion depth was significantly less (P < 0.05) for the argon laser-cured group (97 microns) when compared with that for the visible light-cured group (151 microns). Wall lesion occurrence was 5% for both treatment groups. Following lesion progression, the primary surface lesion depth was significantly less (P < 0.05) for the argon laser-cured group (129 microns) when compared with that for the visible light-cured group (232 microns). Wall lesion occurrence was 15% and 5% for visible light-cured and argon laser-cured groups, respectively (P < 0.05). Argon laser-curing of sealant material may enhance the caries resistance of the enamel forming the enamel-resin interface and result in a reduction in caries formation adjacent to sealants.

Argon↗
PubMed1993

Laser in dentistry. Soft-tissue procedures.

Dentistry has entered the 1990s, an era of high technology. The dental laser offers the dentist not only a window, but a door into this high-tech arena. All of the advantages lasers offer, from bloodless procedures to minimal postoperative pain and from reduction of operative time to high patient acceptance, indicate that lasers are great dental instruments for today and the future. As a futuristic idea, the ideal laser for dentistry would be able to work well, not only in soft tissue, but in hard tissue. Envision a laser with multiple wavelengths in the same unit: one for incision, another for removal of hard tissue, and yet still another for making tissue "sticky" for flap placement and tissue welding. So often dentists are associated with pain, fear, and the noise of the high-speed drill. The laser certainly helps to dispel these stereotypes and apprehensions, and to bring dentistry into a new era.

Humans↗
PubMed1992

Characterization of CO2/carbonic acid mediated proton flux through phosphatidylcholine vesicles as model membranes.

The apparent proton permeability coefficient for phospholipid vesicles measured in our laboratory (Norris, F. A. and Powell, G. L. (1990) Biochim. Biophys. Acta 1030, 165-171) for proton flux initiated by rapidly lowering of the external pH (acid jump) was a linear function of the reciprocal internal proton concentration. This behavior was ascribed to the presence of the weak acid carriers, carbonic acid/CO2/bicarbonate. In the present work, a theoretical description, appropriate for proton transport by any weak acid carrier, has been developed which lends itself to novel graphical treatment permitting the separate estimation of the permeability coefficients for protons, hydroxide ions and bicarbonate. The proton permeability coefficient determined by this method was 1.8 x 10(-5) (S.E. 1.3 x 10(-5)) cm/s; that for hydroxide ion was 3.8 x 10(-5) (S.E. 5.6 x 10(-6)) cm/s and a lower limit for the permeability of bicarbonate ion, 4.3 x 10(-6) (S.E. 3.6 x 10(-7) cm/s, can be set. The presence of negative surface charge on the lipid bilayer increased the observed proton permeability coefficient in accordance with Gouy-Chapman theory. The charge was introduced by preparing vesicles containing increasing amounts of negatively charged dioleoylphosphatidylglycerol. The observed proton permeability coefficient increased and the observed permeability coefficients for hydroxide ion and bicarbonate decreased. The addition of the lipophilic cations, valinomycin-K+ and tetrabutylammonium ion increased the slope of P vs. 1/[Hi+]. These changes are analogous to those reported for the permeant weak acid uncouplers FCCP and CCCP. These studies demonstrated that CO2/carbonic acid was an effective carrier of protons across phospholipid model membranes.

Carbon Dioxide↗
PubMed1992

Power and time requirements for use of the argon laser to polymerize composite resins.

A carefully controlled laboratory study was conducted to determine the optimum power setting and polymerization cycle time to cure four commercially available composite resins with an argon laser. Most effective resin polymerization was achieved when Prisma APH was polymerized at 310 mW for 7 seconds, when Herculite was polymerized at 160 mW for 12 seconds, when P-50 was polymerized at 525 mW for 13 seconds and when Silux Plus was polymerized at 270 mW for 13 seconds. The exact parameters of laser power and exposure time seem to be material specific, with greater variation being noted in power setting than in exposure time.

Argon↗
PubMed1992

Initial dissolution rate studies on dental enamel after CO2 laser irradiation.

The influence of CO2 laser irradiation on the dissolution behavior of human dental enamel has been investigated. Human enamel was irradiated by a continuous-wave CO2 laser at 10.6 microns and initial dissolution rates (IDRs) were measured in 0.1 mol/L acetate buffer, pH = 4.5, both with and without calcium and/or phosphate common ion, by means of a rotating disk assembly. The effects of (1-hydroxyethylidene) bisphosphonic acid (EHDP), fluoride (F), and dodecylamine HCl (DAC) at various levels upon the IDR were also determined. All of the findings were consistent with the hypothesis that CO2 laser irradiation converts dental enamel to hydroxyapatite (HAP) possessing site #2 character (Yamamoto et al., 1986). The dissolution driving force function, KHAP = aCa10aPO4(6)aOH2, was found to have a value of 10(-129.9) after being lased, as compared with 10(-121.4) before being lased. The IDR values for EHDP (3 mmol/L) and DAC (3 mmol/L) were essentially zero as expected for site #2 HAP. For solution F, the deduced dissolution driving force function, KFAP = aCa10aPO4(6)aF2 was 10(-128.6) after being lased as compared with 10(-116.3) before being lased. These results all support the hypotheses (1) that laser irradiation may convert the surface of human dental enamel to an apatite of significantly lower effective solubility (i.e., site #2 HAP) than that of unlased enamel; and (2) that there is significant synergism between laser treatment and these chemical dissolution rate inhibitors (again consistent with site #2 HAP). Simple model calculations indicate that, in both the presence and absence of fluoride, these laser-induced changes in the driving force for dissolution should dramatically lessen the susceptibility of enamel to the types of acid challenge that might be encountered in the mouth.

Amines↗