Biomedical subjects

E Harrington

Publications and source records attributed to E Harrington.

At least 37 records · Page 2Linked to original sources

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↗

PubMed1996

Taper and stiffness of sonic endodontic files.

The aims of this investigation were to measure the thickness and taper of the different files (Heliosonic 15-40. Shaper 15-40 and Rispisonic 1-6) supplied with the MM1500 sonic instrument and relate this to their stiffness. The diameter of the files (n = 5 for each file type) was measured at 2 mm intervals using light microscopy and a calibrated graticule (mag x 120). A model system was developed for the stiffness testing. The file was held 3 mm from its tip and the load in g required to produce a 45 degrees deflection of the file was recorded. Measurements of file diameter showed that the width of the Heliosonic and Shaper increased in a linear manner and that the file taper was the same for increasing file sizes in accordance with ISO recommendations. The Rispisonic files however showed differing widths and degrees of taper which were not consistent with ISO standards. The stiffness testing results showed the Heliosonic files to be less flexible than the Rispisonic and Shaper files for all sizes (ANOVA, p < 0.001). The differences in stiffness of the Heliosonic, Shaper and Rispisonic files were due to the variation in cross sectional area of metal. In conclusion sonic endodontic files do not have the same taper and stiffness.

Analysis of Variance↗

PubMed1996

Effect of light intensity on polymerisation of three composite resins.

The polymerisation ability of twelve light activation units, a mixture of new and old, was assessed by micro-hardness evaluation of samples of three composite resins cured with the lights. Light intensity was assessed using a commercially available band held dental radiometer. Intensity values were representative of the range of intensities that may be found in clinical practice. When a 2 mm thick sample of a microfilled composite was cured for 40s less than half of the light units evaluated produced an acceptable lower surface polymerisation. All but one of the light units tested produced a satisfactory lower surface cure with the monomodal and the hybrid composites. For the products tested material composition was an important factor in regard to the ability to cure a 2 mm thick increment of material with a 40s irradiation time. A significant correlation was found between lower surface hardness and light intensity. Standardising the area of the light sensing device of the hand held radiometer with respect to the diameter of the specimen to be cured improved the correlation between light intensity and lower surface micro-hardness.

Composite Resins↗

PubMed1995

Light curing unit effectiveness assessed by dental radiometers.

OBJECTIVES: The purpose of this investigation was to assess the effectiveness of five commercially available hand-held dental radiometers and a computer-based experimental radiometer. METHODS: Light intensity of five visible light activation units was determined using the dental radiometers. The influence of curing light intensity on depth of cure of a hybrid composite material was determined using a digital penetrometer. RESULTS: The radiometers evaluated varied with respect to sensor aperture diameter, scale readings (analogue or digital) and the units of measurement (arbitrary or mW cm2). The experimental computer-based radiometer allowed continuous recording of intensity against time; thus the light output could be monitored over the entire irradiation period. CONCLUSIONS: When light intensity readings were normalized with regard to a standardized light sensing device aperture of 4 mm diameter, a linear relationship was found between depth of cure and the logarithm of the intensity of the light. The results of this investigation support the use of dental radiometers for periodically monitoring visible light activation units.

Composite Resins↗

PubMed1995

Apoptosis and the cell cycle.

Apoptosis is an evolutionarily conserved 'suicide' programme present in all metazoan cells. Despite its highly conserved nature, it is only recently that any of the molecular mechanisms underlying apoptosis have been identified. Several lines of reasoning indicate that apoptosis and cell proliferation coincide to some degree: many oncogenes that promote cell cycle progression also induce apoptosis; damage to the cell cycle or to DNA integrity is a potent trigger of apoptosis; and the key tumour suppressor proteins, p105rb and p53, exert direct effects both on cell viability and on cell cycle progression. There is less evidence, however, to indicate that apoptosis and the cell cycle share common molecular mechanisms. Moreover, the interleukin-1 beta converting enzyme (ICE) family of cysteine proteases is now known to play a key role in apoptosis but has no discernible role in the cell cycle, arguing that the two processes are discrete.

Animals↗

PubMed1995

The fracture resistance of dental materials.

A novel test procedure was developed that provides the basis for a standard plain strain fracture toughness test to evaluate fracture resistance of resin-based materials. This procedure utilizes a notched disc specimen. Using this technique, a new concept of Torque to initiate fracture (T)' was suggested. Also, fracture resistance can be assessed by means of critical stress intensity factor (K[IC]). Using this method, the fracture resistance of direct restorative materials, resin-based inlay/onlays and luting cements can be evaluated.

Acrylic Resins↗

PubMed1995

Depth of cure of radiation-activated composite restoratives--influence of shade and opacity.

Inadequate depth of cure may reduce the longevity of visible light-activated composite restorations. Radiation-activated composites, originally marketed for the restoration of anterior teeth, have been developed and refined for restoring occlusal and proximal cavities in posterior teeth. Clinical factors such as the accessibility of the light source, the direction of the light, intervening tooth tissue and cavity depth may limit depth of cure. Unfortunately, a hard top surface is no indication of adequate polymerization at the base of the cavity. The current investigation used a penetrometer to evaluate the depth of cure of a range of recently introduced 'universal' composite materials and assess the influence of shade and opacity on depth of cure. Depth of cure of the enamel opacity is always greater than that of the same shade of dentine for each manufacturer's product range.

Bisphenol A-Glycidyl Methacrylate↗

PubMed1994

Integrated control of cell proliferation and cell death by the c-myc oncogene.

Regulation of multicellular architecture involves a dynamic equilibrium between cell proliferation, differentiation with consequent growth arrest, and cell death. Apoptosis is one particular form of active cell death that is extremely rapid and characterized by auto-destruction of chromatin, cellular blebbing and condensation, and vesicularization of internal components. The c-myc proto-oncogene encodes an essential component of the cell's proliferative machinery and its deregulated expression is implicated in most neoplasms. Intriguingly, c-myc can also act as a potent inducer of apoptosis. Myc-induced apoptosis occurs only in cells deprived of growth factors or forcibly arrested with cytostatic drugs. Myc-induced apoptosis is dependent upon the level at which it is expressed and deletion mapping shows that regions of c-Myc required for apoptosis overlap with regions necessary for co-transformation, autoregulation, inhibition of differentiation, transcriptional activation and sequence-specific DNA binding. Moreover, induction of apoptosis by c-Myc requires association with c-Myc's heterologous partner, Max. All of this strongly implies that c-Myc drives apoptosis through a transcriptional mechanism: presumably by modulation of target genes. Two simple models can be invoked to explain the induction of apoptosis by c-Myc. One holds that death arises from a conflict in growth signals which is generated by the inappropriate or unscheduled expression of c-Myc under conditions that would normally promote growth arrest. In this 'Conflict' model, induction of apoptosis is not a normal function of c-Myc but a pathological manifestation of its deregulation. It thus has significance only for models of carcinogenic progression in which myc genes are invariably disrupted.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

A model system for evaluating filing technique.

The aim of this study was to develop a model system to demonstrate the pattern of load and how much is applied. A lower molar was mounted on a beam and attached to a mandibular phantom head jaw. A strain gauge fitted to the beam allowed loading of the molar to be recorded, during root canal preparation. Ten operators were asked to instrument the distal root canal; after preparation the operators were shown a graphical representation of the loads applied. This formed the basis of discussion and instruction in filing technique. The operators then repeated the filing. The results showed that prior to instruction operators used a push-pull motion, applying a constant lateral force to the canal wall. After instruction and discussion of the graphical representation of the loads applied the stroke rates used were slower and loads applied were higher (two-sample t-test, n = 10, P < 0.01). The experiment was repeated 1 year later and this showed that the change in technique had been retained. In conclusion, this model system allows visual feedback to the operator and can be used as an aid to teaching filing technique.

Analysis of Variance↗

PubMed1994

The distribution and severity of tooth wear and the relationship between erosion and dietary constituents in a group of children.

There is very little published information on the severity of tooth wear in children. The current investigation involved clinical examination of 101 children and an assessment of their dietary habits. Evidence of tooth wear was found in over 80% of maxillary incisor teeth, and 30% of primary molar teeth had some dentine exposed. There were 21 children who were regarded as having 'mild' erosion, 45 'moderate' erosion and 35 'severe' erosion. There were highly statistically significant differences between the three groups in relation to drinking habits; the mean number of carbonated drinks consumed per week by children in the 'mild', 'moderate' and 'severe' erosion groups was 3.9, 5.8 and 13.9 respectively, of fruit drinks 10.3, 16.4 and 18.3, and of all fruit-based drinks 17.9, 27.1 and 39.0. There were also highly significant differences in those having a fruit-based drink at bed-time; 14% in the 'mild' erosion group, 32% in the 'moderate' and 60% in the 'severe' group. Although fresh fruit and yoghurt consumption followed the same trend, this did not reveal statistically significant differences. It is important to identify children who exhibit clinical evidence of erosion so that advice can be given about consumption of acidic dietary constituents.

Adolescent↗

PubMed1994

An in vitro investigation of Thermafil obturation at different temperatures.

The apical leakage of lower premolars obturated with Thermafil at three different temperatures was investigated in vitro. The temperatures were determined after calibration of the Thermaprep oven. The root canals of 35 extracted teeth were prepared chemomechanically and divided into three groups of 10 each with a control group of five. The root canals of the experimental group were obturated using plastic Thermafil obturators at three different temperatures 144, 120 and 100 degrees C with the controls being obturated using laterally condensed gutta percha. The teeth were suspended in indian ink for 28 days prior to being cleared and the degree of apical leakage assessed. The results showed no significant difference (p > 0.05) in the apical leakage of the teeth obturated with Thermafil compared to laterally condensed gutta percha. There was a trend towards less leakage in the teeth obturated with Thermafil at the lower temperatures, this, however, was not significant (p > 0.05).

Dental Leakage↗

PubMed1994

Propofol and thiopental anesthesia: a comparison of the incidence of dreams and perioperative mood alterations.

The purpose of this study was to investigate perioperative mood profiles and the incidence of dreams in patients receiving anesthesia with either propofol (n = 29) or thiopental (n = 27) in combination with nitrous oxide. The study was a prospective, randomized, and double-blind investigation of female patients undergoing outpatient dilation and curettage. Recall of dreams was assessed 1 h postoperatively and the following day by using a questionnaire designed for surgical patients. Mood profiles were quantified using the Multiple Affect Adjective Check List-Revised (MAACL-R), a self-administered questionnaire which was completed preoperatively and 1 h postoperatively. Our results indicate that postoperatively, all patients were significantly less anxious than preoperatively (P < 0.0001). In the postoperative period, patients receiving propofol exhibited sensation-seeking tendencies (i.e., active, adventurous, aggressive, daring, energetic, enthusiastic, merry) when compared to the thiopental patients (P < 0.02). The incidence of dreams was small and equal in both groups. We conclude that patients anesthetized with propofol and nitrous oxide, as compared to patients anesthetized with thiopental and nitrous oxide, were more likely to demonstrate adventurous tendencies in the postoperative period.

Adult↗

PubMed1993

Depth of cure of radiation-activated materials--effect of mould material and cavity size.

A method for determining depth of cure of radiation-activated restorative materials has been developed. The effect of mould material and cavity size on depth of cure was determined using a digital penetrometer method. Values were obtained for three selected shades of three dentine products and, in addition, the same three shades of an enamel variant were assessed. All these values were obtained using a 4 mm diameter x 6 mm deep stainless steel mould.

Analysis of Variance↗

PubMed1993

Variations in stroke rate and loading using hand sonic or ultrasonic instrumentation.

An in vitro model system was developed to investigate the stroke rate and loading during hand, sonic, or ultrasonic instrumentation. The model system consisted of a mandibular molar tooth attached to a strain gauge and interface to a computer. Ten clinicians instrumented the distal canal of lower molar teeth. Stroke rates used and loads applied were measured using different sized files with the three different preparation techniques. There was no significant difference in stroke rates between different file sizes (p > 0.05) within the same generator, however, stroke rate for hand was significantly slower than for sonic or ultrasonic (p < 0.01). Loading of the canal wall rose with increase in file size which was significant for hand (p < 0.01) and sonic (p < 0.05) but not ultrasonic (p > 0.05). There was a tendency for loading to be higher with hand instrumentation, this however was not significant (p > 0.05).

Calibration↗

PubMed1993

Operating variables affecting the working time of a dual-cure composite luting cement.

Dual-cure composite resin luting cements are increasingly being used for the cementation of porcelain veneers, composite and ceramic inlays, onlays and crowns. This investigation assessed the effect of a dual-cure adhesive (Bondlite) on the working time of a dual-cure composite resin luting cement (Porcelite Dual-Cure). An oscillating rheometer was used to measure the working time of the composite resin luting cement with and without prior application of dual-cure adhesive. The results demonstrated that use of the dual-cure adhesive significantly reduced the working time of the manufacturer's dual-cure composite resin luting cement.

Analysis of Variance↗