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Biomedical subjects

A R Williams

Publications and source records attributed to A R Williams.

At least 127 records · Page 7Linked to original sources
PubMed1988

Dental plaque removal by cavitational activity during ultrasonic scaling.

Photomicrographs of the surfaces of recently extracted teeth stained with erythrosin dye were obtained. The stained surfaces were treated with an ultrasonic scaler using two different types of scaling tips driven by the same instrument operated at a medium power setting. Small areas of stained plaque removal occurred when the stationary scaling tip was operated without water cooling. Additional areas of removal were observed where a water coolant was present, which were larger than those produced by the non-water cooled tip. These additional areas were influenced by the type of scaling tip used, it's orientation to the tooth surface and it's displacement amplitude. Cavitational activity in the cooling water supply of the ultrasonic scaler is able to remove dental plaque from tooth surfaces and may be a useful adjunct to the mechanical action of the instrument.

Dental Plaque↗
PubMed1987

Effects of MHz ultrasound on electrical pain threshold perception in humans.

An electrode system was developed consisting of two 8 mm long 0.2 mm diameter silver-coated copper wires arranged parallel to each other 8 mm apart and held in contact with the skin by means of an acoustically transparent plastic adhesive tape. This system was attached to the upper arms of young adult volunteers who increased the voltage of the rectangular electrical pulses supplied to the electrodes until a reproducible sharp prickling pain sensation was perceived. A one inch diameter physiotherapy transducer was positioned over the electrode site so that ultrasound could be administered throughout the measurement period. The experiments were performed single blind to eliminate any subjective bias on the part of the volunteers. Preliminary experiments established that highly reproducible (+/- 3 to 4%) pain threshold perception values could be obtained, and that these values were not affected by changes in (a) the duration of the "on" time of the electrical pulses between 1.5 and 48 ms, (b) the contact pressure between the transducer and the electrode site, (c) the time interval between successive threshold measurements (providing that an unacceptable level of oedema was not produced around the electrodes), and (d) whether or not a test measurement was preceded by a control. Ultrasound exposure via a direct contact technique consistently produced a statistically significant (p less than 0.05) decrease in the perception threshold for electrical pain. This effect usually developed within 30-60 s and its magnitude increased both with increasing intensity (rising to 20.7 +/- 0.57% at an SATA intensity of 0.43 W/cm2 at 1.1 MHz) and with increasing frequency at the same ultrasonic intensity. Delivering the same amount of ultrasonic energy in the form of 2 ms bursts at several different peak intensities produced exactly the same reduction in pain threshold perception. These results indicate a thermal interaction mechanism, and similar threshold changes could be obtained by heating or cooling the electrode site by nonacoustic means. The inclusion of a thermocouple junction between the electrode wires showed that temperature increases of up to 10 degrees C could be produced when the transducer was in direct contact with the tape over the electrodes. The volunteers were not aware of these temperature increases which were primarily caused by heating of the transducer face. If the temperature of the skin surface is kept constant by interposing a thermostatted water path between the transducer and the electrode system, then similar ultrasound exposures had no detectable effects upon the electrical pain perception threshold.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1987

The air-powder dental abrasive unit--an evaluation using a model system.

Air-powder abrasive systems are used in dentistry to remove dental plaque, calculus and stain from the surfaces of teeth. A model system consisting of a thin layer (14 micron) of vacuum-deposited aluminium was used to demonstrate the effectiveness of such a system. Photomicrographic analysis showed two distinct areas of removal: an inner area where removal of aluminium was complete, surrounded by an area where removal was incomplete. With the aid of a relocation pin attached to the nozzle of the instrument it was demonstrated that nozzle-target distance, the air pressure input, the flow of water and the time of operation were all factors which affected the clinical efficiency of the instrument.

Bicarbonates↗
PubMed1987

The role of mean corpuscular haemoglobin concentration in limiting the storage life of human blood.

Human erythrocytes stored for more than 21 days in citrate phosphate dextrose with adenine (CPDA-1) at +4 degrees C had a decreased cell volume, an increased cell density, an elevated mean corpuscular haemoglobin concentration (MCHC) and hence an elevated internal viscosity. These changes are normally masked by the reversible cell swelling which accompanies storage in CPDA-1. Incubation of stored cells for 24 h at 37 degrees C in fresh autologous plasma mimics the effects of reinfusion and causes the artificially swollen cells to shrink to their true volume. Thus, incubated cells which had been stored in CPDA-1 for more than 21 days exhibited a decreased filterability through Nuclepore membranes in vitro, which is apparently correlated with a decreased survival time in vivo.

Adenine↗
PubMed1987

The use of nystatin to restore the flow properties of time-expired stored erythrocytes.

Human erythrocytes stored for more than 21 days in citrate phosphate dextrose with adenine (CPDA-1) exhibited a marked reduction in volume following incubation for 24 h at 37 degrees C in fresh autologous plasma. This incubation apparently mimics the effects of reinfusion of the stored cells in vivo. These shrunken stored cells have a decreased filterability as measured by their increased transit times through a 5-microns diameter Nuclepore filter. The polyene antifungal agent nystatin was used to reinflate these shrunken cells with different concentrations of potassium ions. A concentration of 90 mM potassium chloride was found to reinflate the shrunken stored cells so that their mean cell volume, mean corpuscular haemoglobin concentration and average densities were the same as those of fresh cells. This reinflation also restored the filterability of the shrunken stored cells so as to be similar to that of fresh cells.

Adenine↗
PubMed1987

The effects of reinflation on the survival of time-expired stored rabbit erythrocytes in vivo.

Rabbit blood cells stored for prolonged periods in citrate phosphate dextrose with adenine (CPDA-1) at +4 degrees C show the same decreased volume, increased cell density and decreased filterability as human cells stored under similar conditions. As with human erythrocytes, the stored rabbit cells had to be incubated with autologous fresh plasma for 24 h at 37 degrees C before these changes could be observed (this incubation process apparently mimics the effects of reinfusion). These shrunken stored rabbit cells could also be reinflated using nystatin, so that their mean cell volume, mean corpuscular haemoglobin concentration, average cell densities and filterabilities were restored to normal values. This in vitro reinflation of the stored cells significantly prolonged their in vivo survival rate as determined by radiochromium labelling studies. This reinflation technique may therefore have an application in the prolongation of the useful storage life of human blood.

Adenine↗
PubMed1987

Intra-vascular thrombosis associated with dental ultrasound.

Ultrasonic instruments used in dentistry generally operate at frequencies of 25 to 42 kHz. A wire oscillating at these ultrasonic frequencies immersed in a liquid produces local flow patterns termed acoustic microstreaming. Large shear forces are produced which are able to rupture erythrocytes and platelets both in vitro and in vivo. This results in activation of the blood coagulation system with subsequent thrombus formation. The probe tip of an ultrasonic scaler was positioned to touch a mammalian mesenteric artery. The probe was operated for 10 to 20 s at a displacement amplitude of 15 micron. Acoustic microstreaming occurred which disturbed blood flow and this microstreaming ceased when the power was switched off. After continued operation of the probe, thrombi were formed against the vessel wall with fragments embolising downstream. These thrombi eventually grew to occlude the vessel. Furthermore, an in situ model demonstrated that acoustic energy was transmitted through the tooth during typical ultrasonic scaling procedures. As a consequence of these observations, it is possible that acoustic microstreaming fields may be generated within the blood vessels entering the tooth apex which are large enough to induce platelet damage. Therefore there is a potential hazard from the use of the ultrasonic scaler which may induce similar thrombi formation within the pulpal or perapical tissues of the teeth. If this were to occur it could result in tooth death which might not become evident until a long time after the ultrasonic exposure.

Acoustics↗
PubMed1986

Children at risk: perinatal events, developmental delays and the effects of a developmental stimulation program.

This paper reports the findings of two studies done between 1977 and 1981 in the Philippines. The first study examined the performance of 911 children, with histories of perinatal risk events, on a restandardized Philippine (Metro-Manila) version of the Denver Developmental Screening Test (DDST) which was developed in 1980. This study established that the children performed significantly below Philippine norms. A second study, cognizant of the findings of the first, introduced nursing interventions designed to address some needs of preterm infants and their mothers. Findings suggest that development stimulation can significantly improve the developmental status of preterm infants.

Child↗
PubMed1986

Effects of therapeutic ultrasound on the activity of the mononuclear phagocyte system in vivo.

Therapeutic intensities of continuous wave ultrasound applied over the umbilical area of female rats resulted in a decrease in the rate of removal of 99mtechnetium radio-labelled sulphur colloid by the mononuclear phagocyte system. The magnitude of this effect increased both with increasing intensity of ultrasound and with the duration of exposure, and was found to be dependent upon the total amount of energy deposited within the umbilical area. This effect appeared to be initiated by an effect of ultrasound upon circulating lymphocytes since isolated lymphocytes sonicated in vitro at therapeutic intensities and then injected intravenously resulted in a decrease in the rate of colloid removal in vivo similar to that observed when the umbilical area had been sonicated in vivo. The mechanism by which this is thought to occur is discussed.

Animals↗
PubMed1986

Haemolysis in vivo by therapeutic intensities of ultrasound.

Therapeutic intensities of MHz ultrasound directed at the upper abdominal area of rats in vivo resulted in damage to the circulating red blood cells. This damage was detected as free haemoglobin in the plasma as well as microspheres and spherocytic cell fragments which are characteristically produced when blood is heated to more than 49 degrees C. The magnitude of this effect increased with increasing frequency of the ultrasound and was dependent upon the time-averaged intensity, even when the ultrasound was delivered as bursts of high spatial peak intensities. Thermal lesions were found above 10 W/cm2 SP at 1 MHz and above 3 W/cm2 SP at 3.4 MHz. These results show that the observed blood cell damage is primarily a thermal effect which occurs as the blood perfuses anatomical structures which are being heated by the ultrasound beam.

Animals↗
PubMed1986

The detection of temperature induced structural changes in T4B and T7 bacteriophages by means of high precision acoustic velocity measurements.

High precision measurements of the velocity of 7-7.5 MHz ultrasonic waves in suspensions of both T4B and T7 bacteriophages as a function of temperature revealed the presence of a distinct transition in the physiological range of 35-45 degrees C. Data from acoustic measurements, sedimentation analysis and electron microscopy enabled us to identify this transition as being caused by the protein component of the phage and not the DNA. This transition does not depend on the position of the long tail fibers and may be part of some normal physiological process within the bacteriophage which presumably enhances its recognition and attachment to its host cell.

Acoustics↗