Biomedical subjects

E Harrington

Publications and source records attributed to E Harrington.

At least 19 recordsLinked to original sources

PubMed2003

Cuspal movement and microleakage in premolar teeth restored with a packable composite cured in bulk or in increments.

INTRODUCTION: The aim of this study was to investigate the effect of two novel curing systems (a plasma arc light, and a 'turbo-boosted' conventional curing light) on cuspal movement and gingival microleakage of 'packable' resin-based composite (RBC) restorations placed in extracted maxillary premolar teeth. MATERIALS AND METHODS: Forty sound extracted upper premolar teeth were subjected to standardised preparation of a large mesio-occlusal-distal cavity before restoration with a RBC. Four curing regimens were used. Either the RBC was placed in bulk and light-cured in one increment using (a). the plasma arc light; (b). the 'turbo-boosted' curing light, or the RBC was placed in eight increments using (c). the plasma arc light; (d). the 'turbo-boosted' curing light. A deflection measuring gauge allowed a measurement of cuspal deflection at each stage of polymerisation. Restored teeth were thermocycled before immersion in a 0.2% basic fuchsin dye for 24 h. After sagittal sectioning of the restored teeth in a mesio-distal plane, the sectioned restorations were examined to assess cervical microleakage. RESULTS: Cuspal deflection measurements were significantly increased when the 'turbo-boosted' halogen curing light was compared with the plasma arc light. Total mean cuspal deflection measurements obtained with incremental cure were significantly increased compared with bulk cure for both light sources. Gingival microleakage for bulk restored teeth was significantly increased compared with teeth restored incrementally. Incremental restoration with the plasma arc light had significantly increased gingival microleakage compared with the 'turbo-boosted' halogen curing light. CONCLUSIONS: The packable composite tested could not be cured adequately to a depth of 5 mm with the plasma arc light within the specified irradiation time. Under the test conditions of the current investigation, bulk curing only appeared to be practical with the high intensity halogen light (40 s activation). Incremental build-up and polymerisation optimised marginal seal for the high intensity halogen light but led to greater cuspal deflection.

Bicuspid↗

PubMed2002

A pilot investigation of operator variability during intra-oral light curing.

OBJECTIVE: To test the hypothesis that operator experience influences the efficacy of light curing in a typical posterior intra-oral location. To investigate whether short cure cycles affect performance. DESIGN: A cross-sectional single-centre study designed to assess the efficacy of experienced and inexperienced operators when undertaking simulated intra-oral curing. SETTING: An in vitro laboratory based investigation conducted in a dental school during 2001. MATERIALS AND METHODS: A computer-based technique was used to monitor light intensity in a clinical simulation. Dentists and student operators were tested for their ability to cure a posterior restoration effectively. Relative light intensity was assessed against time for each operator and test run. RESULTS: Experienced (qualified) operators produced more effective and consistent cure results than less experienced undergraduate students. Operator performance was not affected by variations in irradiation time. CONCLUSIONS: This cross-sectional pilot investigation demonstrates that operator experience is a factor in successful clinical photo-curing of posterior restorations. Stable and accurate light guide positioning are required throughout the entire irradiation cycle to optimise intra-oral cure of light-activated restorations. Further investigations are planned to assess the potential of this novel method of assessment for use as a routine teaching aid in clinical practice.

Analysis of Variance↗

PubMed2001

M channel KCNQ2 subunits are localized to key sites for control of neuronal network oscillations and synchronization in mouse brain.

Mutations in the potassium channel subunit KCNQ2 lead to benign familial neonatal convulsions, a dominantly inherited form of generalized epilepsy. In heterologous cells, KCNQ2 expression yields voltage-gated potassium channels that activate slowly (tau, approximately 0.1 sec) at subthreshold membrane potentials. KCNQ2 associates with KCNQ3, a homolog, to form heteromeric channels responsible for the M current (I(M)) in superior cervical ganglion (SCG) neurons. Muscarinic acetylcholine and peptidergic receptors inhibit SCG I(M), causing slow EPSPs and enhancing excitability. Here, we use KCNQ2N antibodies, directed against a conserved N-terminal portion of the KCNQ2 polypeptide, to localize KCNQ2-containing channels throughout mouse brain. We show that KCNQ2N immunoreactivity, although widespread, is particularly concentrated at key sites for control of rhythmic neuronal activity and synchronization. In the basal ganglia, we find KCNQ2N immunoreactivity on somata of dopaminergic and parvalbumin (PV)-positive (presumed GABAergic) cells of the substantia nigra, cholinergic large aspiny neurons of the striatum, and GABAergic and cholinergic neurons of the globus pallidus. In the septum, GABAergic, purinergic, and cholinergic neurons that contribute to the septohippocampal and septohabenular pathways exhibit somatic KCNQ2 labeling. In the thalamus, GABAergic nucleus reticularis neurons that regulate thalamocortical oscillations show strong labeling. In the hippocampus, many PV-positive and additional PV-negative interneurons exhibit strong somatic staining, but labeling of pyramidal and dentate granule somata is weak. There is strong neuropil staining in many regions. In some instances, notably the hippocampal mossy fibers, evidence indicates this neuropil staining is presynaptic.

Animals↗

PubMed2001

Ataxia telangiectasia mutated is essential during adult neurogenesis.

Ataxia telangiectasia (A-T) is an autosomal recessive disease characterized by normal brain development followed by progressive neurodegeneration. The gene mutated in A-T (ATM) is a serine protein kinase implicated in cell cycle regulation and DNA repair. The role of ATM in the brain and the consequences of its loss on neuronal survival remain unclear. We studied the role of ATM in adult neural progenitor cells in vivo and in vitro to define the role of ATM in dividing and postmitotic neural cells from Atm-deficient (Atm(-/-)) mice in a physiologic context. We demonstrate that ATM is an abundant protein in dividing neural progenitor cells but is markedly down-regulated as cells differentiate. In the absence of ATM, neural progenitor cells of the dentate gyrus show abnormally high rates of proliferation and genomic instability. Atm(-/-) cells in vivo, and in cell culture, show a blunted response to environmental stimuli that promote neural progenitor cell proliferation, survival, and differentiation along a neuronal lineage. This study defines a role for ATM during the process of neurogenesis, demonstrates that ATM is required for normal cell fate determination and neuronal survival both in vitro and in vivo, and points to a mechanism for neuronal cell loss in progressive neurodegenerative diseases.

Animals↗

PubMed2001

Effect of exposure intensity and post-cure temperature storage on hardness of contemporary photo-activated composites.

OBJECTIVES: The effect of variation in post-exposure storage temperature (18 vs. 37 degrees C) and light intensity (200 vs. 500mW/cm(2)) on micro-hardness of seven light-activated resin composite materials, cured with a Prismetics Mk II (Dentsply) light activation unit, were studied. METHODS: Hardness values at the upper and lower surfaces of 2mm thick disc shaped specimens of seven light-cured resin composite materials (Herculite XRV and Prodigy/Kerr, Z100 and Silux Plus/3M, TPH/Dentsply, Pertac-Hybrid/Espe, and Charisma/Kulzer), which had been stored dry, were determined 24h after irradiation with a Prismetics Mk II (Dentsply) light activation unit. RESULTS: Hardness values varied with product, surface, storage temperature, and curing light intensity. In no case did the hardness at the lower surface equal that of the upper surface, and the combination of 500mW/cm(2) intensity and 37 degrees C storage produced the best hardness results at the lower surface. CONCLUSIONS: Material composition had a significant influence on surface hardness. Only one of the seven products (TPH) produced a mean hardness values at the lower surface >80% of the maximum mean upper surface hardness obtained for the corresponding product at 500mW/cm(2) intensity/37 degrees C storage temperature when subjected to all four test regimes. Despite optimum post-cure storage conditions, 200mW/cm(2) intensity curing for 40s will not produce acceptable hardness at the lower surface of 2mm increments of the majority of products tested.

Analysis of Variance↗

PubMed2001

Relative merits of narrow versus standard diameter light guides.

The purpose of this study was to assess the relative effectiveness of narrow versus standard diameter light guides at curing the initial increment of composite in a deep cavity. The micro-hardness of 2 mm thick samples of a light activated microfilled posterior composite was determined. Composite was irradiated at 0, 1 or 6 mm light guide tip/composite surface distances. Light intensity was measured with a computer-based radiometer. Lower surface cure was reduced with increasing light guide tip distances. Narrow diameter guides offered no advantage over standard guides for polymerisation of the initial increment of composite in the base of a cavity.

Analysis of Variance↗

PubMed1999

The influence of cyclic loading on the wear of a dental composite.

The load applied to a tooth surface during mastication is not a constant force and the objective of the research reported in this paper was to evaluate the impact of variable masticatory loads on the mechanisms involved in the wear of a dental composite. A new wear testing machine has therefore been developed, which incorporates a sine cam mechanical system to generate an alternating sine curve load at the wear surfaces to simulate the loading produced by masticatory process. The basic wear pattern is generated by positioning a disc shaped specimen against a rotating cylindrical ring with a normal load applied to the upper surface of the specimen. This approach allows different combinations of static and sine curve loads to be applied, thereby facilitating the study of different wear situations. It was found that the wear behaviour associated with variable loading patterns differed from that of static loading.

Composite Resins↗

PubMed1999

The diagnostic accuracy of ex vivo MRI for human atherosclerotic plaque characterization.

Recent evidence indicates that the type of atherosclerotic plaque, rather than the degree of obstruction to flow, is an important determinant of the risk of cardiovascular complications. In previous work, the feasibility of using MRI for the characterization of plaque components was shown. This study extends the previous work to all the plaque components and shows the accuracy of this method. Twenty-two human carotid endarterectomy specimens underwent ex vivo MRI and histopathological examination. Sixty-six cross sections were matched between MRI and histopathology. In each cross section, the presence or absence of plaque components were prospectively identified on the MRI images. The overall sensitivity and specificity for each tissue component were very high. Calcification and fibrocellular tissue were readily identified. Lipid core was also identifiable. However, thrombus was the plaque component for which MRI had the lowest sensitivity. A semiautomated algorithm was created to identify all major atherosclerotic plaque components. MRI can characterize carotid artery plaques with a high level of sensitivity and specificity. Application of these results in the clinical setting may be feasible in the near future.

Algorithms↗

PubMed1998

Temperature rise during polymerization of light-activated resin composites.

There has been a steady rise in the use of resin-based composites in the restoration of large posterior cavities. Visible light-activated materials have come to dominate the market for direct posterior composites because of the convenience offered to the operator by their command set nature. Manufacturers have produced more powerful light-activation units in response to concerns over inadequate depth of cure. However, some authors have warned of the danger to the dental pulp induced by excessive heat generated during polymerization. Variables governing heat generation include output intensity of the light-activation unit, quality of light filter, irradiation time, material composition and material surface-light guide exit window distance, residual dentine thickness and cavity dimensions. This in vitro study assessed the relative influence of some of these factors under controlled conditions. The findings suggest that minimum irradiation times should be used when curing bonding agents in unlined cavities where residual dentine thickness is limited and high output intensity light-activation units are employed. Material composition is identified as an important variable in determining the magnitude of the temperature rise.

Analysis of Variance↗

PubMed1998

Mechanism of extracellular ATP- and adenosine-induced apoptosis of cultured pulmonary artery endothelial cells.

Apoptosis may be important in the exacerbation of endothelial cell injury or limitation of endothelial cell proliferation. We have found that extracellular ATP (exATP) and adenosine cause endothelial apoptosis and that the development of apoptosis is linked to intracellular metabolism of adenosine [Dawicki, D. D., D. Chatterjee, J. Wyche, and S. Rounds. Am. J. Physiol. 273 (Lung Cell Mol. Physiol. 17): L485-L494, 1997]. In the present study, we investigated the mechanism of this effect. We found that exATP, adenosine, and the S-adenosyl-L-homocysteine (SAH) hydrolase inhibitor MDL-28842 caused apoptosis and decreased the ratio of S-adenosyl-L-methionine to SAH compared with untreated control cells. Using release of soluble [3H]thymidine as a measure of DNA fragmentation, we found that the effect of adenosine on soluble DNA release was potentiated by coincubation with homocysteine. These results suggest that the mechanism of exATP- and adenosine-induced endothelial cell apoptosis involves inhibition of SAH hydrolase. exATP-induced apoptosis was enhanced by an inhibitor of adenosine deaminase, whereas exogenous adenosine-induced apoptosis was partially inhibited by an adenosine deaminase inhibitor. These results suggest that adenosine deaminase may also be involved in the mechanism of adenosine-induced endothelial cell apoptosis. Adenosine and MDL-28842 caused intracellular acidosis as assessed with the fluorescent probe 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. The cell-permeant base chloroquine prevented adenosine-induced acidosis but not apoptosis. Thus, although intracellular acidosis is associated with adenosine-induced apoptosis, it is not necessary for this effect. We speculate that exATP- and adenosine-induced endothelial cell apoptosis may be due to an inhibition of methyltransferase(s) activity. Purine-induced endothelial cell apoptosis may be important in limiting endothelial cell proliferation after vascular injury.

Adenosine↗

PubMed1997

Effectiveness of battery powered light activation units.

OBJECTIVE: To investigate the effectiveness of chargeable light curing units and their ability to sustain a high radiant output following successive discharge cycles. SETTING: University based research investigation assessing the output intensity of three battery powered light activation units and the effect of successive discharge cycles, without intervening periods of recharging, on light output and depth of cure of resin composite. MATERIALS AND METHODS: Mean light intensity (mW/cm2), through a 4 mm aperture, was measured with a computer based radiometer. Two commercially available resin composites (one hybrid and one microfilled resin) were used for the depth of cure determinations using a digital penetrometer. RESULTS: Depths of cure were significantly greater for the hybrid resin composite. Output intensity diminished over the period of battery discharge for two of the three units and this finding was paralleled in the depth of cure results. The battery light units tested varied significantly with regard to their length of discharge cycle and recharge times from complete discharge. CONCLUSIONS: Output intensity diminishes over the period of battery discharge for some makes of battery light units. However, many other factors including handpiece size and weight and unit cost and reliability are important considerations when choosing a unit.

Composite Resins↗

PubMed1997

The effects of midazolam on propofol-induced anesthesia: propofol dose requirements, mood profiles, and perioperative dreams.

UNLABELLED: This study examined the effects of midazolam on the doses of propofol required for the induction of hypnosis and the maintenance of propofol/nitrous oxide anesthesia. In addition, the effects of midazolam on the time to patient recovery, perioperative mood profiles, incidence of perioperative dreams, patient satisfaction scores, and requirement for postoperative analgesics were assessed. This investigation was a prospective, randomized, and double-blind study of female patients undergoing dilatation and curettage. Patients received midazolam (30 microg/kg, n = 30) or an equal volume of placebo (n = 30) immediately before the induction of anesthesia. Recall of dreams was assessed immediately postoperatively, in the postanesthesia care unit (PACU), and on the day after surgery using a questionnaire designed for surgical patients. Mood profiles were quantified using the Multiple Affect Adjective Check List-Revised, which was completed preoperatively and 1 h postoperatively. The Client Satisfaction Questionnaire-8, an eight-item self-administered version of the Client Satisfaction Questionnaire, was used to assess patient satisfaction on the day after surgery. Our results indicate that although the time to the loss of the lid reflex was significantly shorter in patients receiving midazolam (43.8 +/- 2.7 vs 74.7 +/- 7.6 s, P < 0.0003), there was no significant difference in the dose of propofol required to induce hypnosis or maintain anesthesia. There were no group differences in postoperative sedation and orientation scores, perioperative mood profiles, incidence of dreams, and patient satisfaction scores. More patients who received midazolam requested analgesics in the PACU (11 vs 4, P < 0.05). In conclusion, midazolam did not reduce the anesthetic dose requirement of propofol in patients undergoing anesthesia with nitrous oxide, nor did it accelerate patient recovery. Our results call into question the benefit of coinducing anesthesia with propofol and midazolam. IMPLICATIONS: Midazolam, administered immediately before anesthetic induction with propofol, did not decrease the dose of propofol necessary for hypnosis, nor the maintenance of surgical anesthesia, in female patients undergoing diagnostic dilatation and curettage. In addition, midazolam did not alter patient recovery characteristics, postoperative mood, incidence of perioperative dreams, or patient satisfaction. The use of midazolam was associated with an increased need for postoperative analgesics. Our study calls into question the benefit of administering midazolam immediately before anesthetic induction with propofol.

Affect↗

PubMed1997

Continuous monitoring of salivary flow rate and pH at the surface of the dentition following consumption of acidic beverages.

Use of a splint-mounted flexible pH electrode has allowed reliable continuous monitoring of pH at the surface of the dentition whilst still enabling subjects to drink normally. pH was monitored at the palatal upper left central incisor and upper right first permanent molar sites after drinking 1% (w/v) citric acid. A maximal decrease in pH to values of 2-3 was observed after 1 min followed by a slower recovery which was above pH 5.5 within 2 min at the former site and in 4-5 min at the latter site. A sharp rise in parotid saliva flow rate was seen at 1 min after drinking the same concentration of citric acid by glass, straw or feeder cup, which returned to resting levels within 6 min although the fall-off of flow rate was slower with the feeder cup. Thus, after dietary acid intake the pH at the surface of the dentition is below the critical pH for enamel dissolution for shorter periods than previously suggested, which is probably a reflection of salivary neutralisation and washing.

Adolescent↗

PubMed1996

Guidelines for the selection, use, and maintenance of visible light activation units.

New light-cured dental materials are constantly being developed and marketed in response to the increasing demand for aesthetic dentistry. Therefore light activation units are now a standard item of equipment in everyday dental practice. Many factors are involved in the selection of a light unit and among these is the need for the unit to polymerise light-activated resin restorations effectively. This article reviews recent developments in the design of visible light activation units and outlines the desirable features such units should possess. In addition, factors influencing the effectiveness of light-activation units are discussed and recommendations made regarding their routine testing, use and maintenance.

Composite Resins↗

PubMed1996

Echocardiographic assessment of left ventricular filling during isoflurane anaesthesia.

PURPOSE: To determine the effect of isoflurane on left ventricular diastolic function, as assessed by Doppler echocardiography. METHODS: Ten patients with normal cardiovascular function were enrolled. Doppler measurements of mitral inflow velocities, and pulmonary venous blood flow velocities were measured preoperatively (transthoracic echocardiography), and intraoperatively (transesophageal echocardiography) at isoflurane MAC 1 and MAC 1.5. Heart rate and blood pressure were measured concomitantly. Variables were compared with repeated measures ANOVA. RESULTS: Isoflurane at both doses caused equal decreases in mitral inflow A(atrial systole) velocity (control: 43 +/- 12.3 cm.sec-1 vs MAC 1: 31 +/- 6.0 cm.sec-1 and MAC 1.5: 31.3 +/- 7.9 cm.sec-1 P < 0.01), the deceleration time of the mitral inflow E (early) velocity (control: 178 +/- 31.7 msec versus MAC 1: 127 +/- 38.3 msec and MAC 1.5: 137 +/- 28.4 msec, P < 0.01), and mean blood pressure (control: 91.1 +/- 15.4 mmHg versus MAC 1: 76.1 +/- 8.8 mmHg and MAC 1.5: 71.9 +/- 6.2 mmHg, P < 0.002). Isoflurane at both doses caused an equal increase in the E/A ratio (control: 1.5 +/- 0.57 vs MAC 1: 2.0 +/- 0.6 and MAC 1.5: 2.2 +/- 0.78, P < 0.01). No changes in mitral inflow E or pulmonary venous velocities were seen. CONCLUSION: The changes in Doppler velocities of mitral inflow and pulmonary venous flow with isoflurane are not consistent with prolonged left ventricular relaxation nor increased myocardial restriction, but are more likely the result of alterations in left ventricular loading conditions and atrial systolic function.

Adolescent↗

PubMed1996

Factors affecting the cutting ability of sonic files.

The aim of this study was to investigate the cutting ability of sonic files. A model system was developed and the following variables evaluated: file type. Heliosonic or Shaper; file length, 21 or 29 mm; power, air inlet ring opening of half or fully open; stroke length, 2 or 4 mm; stroke rate, one or two cycles per second; and load 50 or 100 g. A 2(6) full-factorial analysis with two replications into the effect of the above variables on the cutting ability of the MM1500 sonic instrument was performed. A new size 25 file was used for each cut, together with water irrigation, and the substrate used was 1-mm thick sections of bovine bone. The differences between the variables were significant (ANOVA, P < 0.001). However, examination of the F-values showed that the most significant variable to affect cutting was load, followed by power, file type, stroke length and stroke rate, with the least significant variable being file length. The most significant interaction was between rate and length of stroke. An increase in stroke rate from one to two cycles per second at a stroke length of 2 mm produced an increase in cutting for both the Heliosonic and Shaper files. However, at the longer stroke length of 4 mm, the same increase in rate resulted in a decrease in cutting for the Shaper files. Therefore, it is suggested that operators should press the file against the canal wall and move it slowly to maximise cutting.

Analysis of Variance↗

PubMed1996

Intra-canal cutting ability of MM1500 files.

The aims of this study were to develop a model system capable of monitoring lateral forces during root canal preparation and to measure the cutting ability of files activated by the MM1500 sonic handpiece. Forces were monitored by a calibrated model system which utilized a combination of spring steel beams fitted with strain gauges, these were interfaced through two strain gauge amplifiers to an x-y recorder. Single rooted canine teeth (n = 36; 32 experimental, four control) were mounted in a two-part acrylic mould (which was an integral part of the model system) prior to sectioning horizontally 11 mm from the tooth apex. A 2(4) full factorial experiment with two replications was performed. Four variables were selected for evaluation, load (50 and 100 g), power (air inlet ring half or fully open), file type (Heliosonic or Shaper) and stroke rate (1 or 2 cycles per second). A new file (size 25) was used for 1 min in each canal with water irrigation. The control group was not instrumented. The cross-sectional root canal area was measured before and after instrumentation using image analysis and increase in area was used as an indication of cutting ability. The results showed that the increase in load, power and the Shaper file all produced a significant increase in cutting ability (ANOVA, P < 0.001). However, stroke rate was not found to have a significant effect (P > 0.05). None of the interactions between the variables were significant and there was no significant difference in the control group (P > 0.05). In conclusion, this work has developed a model system to monitor lateral forces and has shown that instrument design and operator usage affect dentine removal from a root canal wall.

Analysis of Variance↗

PubMed1996

Light-activated restorative materials: a method of determining effective radiation times.

The aim of this investigation was to develop a test method that allows an operator to determine the appropriate radiation time for any light-activated material, irrespective of the characteristics of the light-activation unit or material to be cured. A computer-based radiometer was used to monitor the radiation energy transmitted through a number of light-activated materials during irradiation, and a method was devised to determine the predicted radiation time for any given material/shade/light unit combination based upon the change in transmission against time that occurred as the material polymerized. Additional test samples were cured for the predicted radiation times and upper and lower surface microhardness measurements were taken to verify the validity of the test method. Predicted times varied from 16 to 44 s for 2 mm thick samples of the materials/shade/light-activation units used. This method may allow operators to determine appropriate radiation times for any new light-activated restorative they decide to use with their own light-activation unit.

Amplifiers, Electronic↗