A R Williams

The University of Manchester, Manchester, England, United Kingdom

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Publications (14)32.48 Total impact

  • A D Walmsley, A R Williams
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    ABSTRACT: The formation of free iodine from the KI/CCl4 chemical dosimeter has been used to quantify the amount of cavitational activity occurring within a 25 kHz cleaning bath under various exposure conditions. The amount of activity occurring within the bath was related to the supply voltage to the cleaning bath, the time of exposure and the volume of solution. An important observation was that the amount of cavitational activity occurring within a glass beaker suspended within a water-filled bath varied by as much as a factor of ten if that beaker contained different volumes of the test solution. Also, the amount of cavitation occurring within the exposure vessel and its contents of an ultrasonic cleaning bath will assist in the cleaning of dental instruments and their accessories.
    Journal of Dentistry 03/1991; 19(1):62-6. · 3.20 Impact Factor
  • A D Walmsley, T F Walsh, W R Laird, A R Williams
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    ABSTRACT: It is recognised that roughness of the root surface will occur during ultrasonic scaling and this has been attributed to the vibrating scaling tip. Although the presence of cavitational activity and acoustic microstreaming forces have been described their effects on the root surface have not been fully evaluated. Utilising an in vitro system of polished gold, it was possible to demonstrate an indentation produced by the scaling tip. However cavitational activity around the tip within the water supply appeared to produce an area of erosion (0.66 +/- 0.3 mm2, 1 SD, n = 10), and the surface appeared pitted. A scanning electron microscope study (SEM) of root surfaces following ultrasonic scaling showed similar areas of erosion. A replica technique was utilised so that control and experimental root surfaces could be observed. Cavitational activity and acoustic microstreaming resulted in a superficial removal of root surface constituents, and this area of removal was measured as 0.7 +/- 0.3 mm2 (1 SD, n = 10), which was not significantly different from that area observed with the gold surface system (p greater than 0.1). It may be concluded that cavitational activity within the cooling water supply of the ultrasonic scaler results in a superficial removal of root surface constituents.
    Journal Of Clinical Periodontology 06/1990; 17(5):306-12. · 3.69 Impact Factor
  • A D Walmsley, A R Williams
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    ABSTRACT: When operated in air, the transverse oscillation of the endosonic file exhibits a series of nodes and antinodes along its length with the greatest displacement amplitude occurring at the unconstrained tip. Endosonic files of varying design, length, and thickness exhibit differences in their oscillation. Preliminary work has revealed that the endosonic file is susceptible to constraint when working within the root canal and a model system was designed to investigate this problem. The constraining influence was found to be greatest when it was applied at those antinodes nearest the tip. This effect was further enhanced if the file was angled. Furthermore, constraint applied at the nodes also influenced the file oscillation. Such results may explain in situ observations on the occasional inefficiency of the system, especially when negotiating the apical third of a curved root canal. Clinical techniques utilizing an endosonic file may require reappraisal in order to minimize such constraint.
    Journal of Endodontics 06/1989; 15(5):189-94. · 2.93 Impact Factor
  • A D Walmsley, W R Laird, A R Williams
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    ABSTRACT: 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.
    Journal Of Clinical Periodontology 11/1988; 15(9):539-43. · 3.69 Impact Factor
  • A R Williams, A D Walmsley
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    ABSTRACT: In low-frequency (20-40-kHz) ultrasonic devices used in dentistry the ultrasound is conducted to the tooth either via a metal waveguide oscillating predominantly in its longitudinal mode or via metal files or reamers driven to vibrate transversely or longitudinally at the same frequency as the transducer. All of these arrangements have unique coupling problems, so that it is difficult to estimate how much ultrasonic energy enters the tooth and therefore what its biological effects might be. As a first step, it is proposed that the maximum displacement amplitudes of that part of the instrument that contacts the tooth be measured to obtain some estimate of the ;acoustic output' of each instrument. These measurements are necessary because of the wide variations in the efficiency of the transduction process between different probe designs (i.e., the interchangeable inserts) powered by the same handpiece, or by the same insert powered by different but compatible generators from the same manufacturer. It is suggested that this information will also improve the ability of clinical users of these devices to reproduce each other's techniques and procedures, and thus make it possible to reduce the number of contradictory claims regarding their clinical efficiency.
    IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 02/1988; 35(2):264-9. · 1.82 Impact Factor
  • A D Walmsley, W R Laird, A R Williams
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    ABSTRACT: 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.
    Journal of oral pathology 06/1987; 16(5):256-9.
  • British dental journal 04/1987; 162(6):221-4. · 0.81 Impact Factor
  • A D Walmsley, A R Williams, W R Laird
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    ABSTRACT: 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.
    Journal of Oral Rehabilitation 02/1987; 14(1):43-50. · 2.34 Impact Factor
  • A D Walmsley, W R Laird, A R Williams
    Dental Materials 07/1986; 2(3):97-100. · 3.77 Impact Factor
  • A D Walmsley, W R Laird, A R Williams
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    ABSTRACT: The displacement amplitudes of three different ultrasonic descaler probe tips were compared when driven by the same ultrasonic generator. Each descaling tip design gave different displacement amplitudes at the same instrument setting. This may be reflected in a difference in clinical effectiveness. A single design of probe tip also gave different displacement amplitudes when used with different generators supplied by the same manufacturer. Furthermore, during operation each particular design of probe tip exhibited differing patterns of oscillation superimposed on the expected longitudinal mode.Therefore, there is a need to measure the displacement amplitude of different probe tips to give a true indication of the acoustic power output of the instrument. Such calibration measurements must be made if users of ultrasonic descalers wish not only to rationalize and improve their clinical performance with the instrument, but also so that any investigative results can be compared in a meaningful manner with those obtained by other workers.
    Journal of Dentistry 07/1986; 14(3):121-5. · 3.20 Impact Factor
  • A D Walmsley, A R Williams, W R Laird
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    ABSTRACT: During descaling procedures temperature gradients were found to be established within the tooth. The measurements of temperature were found to be dependent on the thermal conductive properties of the enamel and dentine and were interpreted in relation to the position of a thermocouple junction within the pulp cavity.Heat produced by frictional contact between the oscillating tip and tooth is largely removed by a flow of cooling water over the probe. However, the presence of water may act as a matching layer between the steel probe and enamel which may allow acoustic energy to pass into the tooth which would travel rapidly throughout the tooth substance and be absorbed to produce relatively uniform heating. Thermocouples positioned furthest away from the point of descaling, therefore, initially registered an excess temperature rise produced only by absorption of the ultrasonic energy conducted into the tooth. This temperature rise within an insulated tooth in vitro was ≅ 2 C, following a 30-s contact at a displacement amplitude of 19 μm. It is suggested that temperature increases produced by acoustic absorption during ultrasonic descaling are unlikely to be high enough to damage the pulpal contents.
    Journal of Dentistry 03/1986; 14(1):2-6. · 3.20 Impact Factor
  • A.D. Walmsley, W.R.E. Laird, A.R. Williams
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    ABSTRACT: There is no commonly accepted method for quantifying the amount of acoustic power emitted by an ultrasonic scaler. The instrument control dial is imprecise and does not provide any meaningful estimate of the acoustic power output. In this study the amount of cavitational activity occurring within the cooling water was measured by means of a chemical dosimetric system (Fricke's solution). The cavitational activity measured was found to be directly related to the displacement amplitude of the probe tip (half the maximum peak to peak excursion), and an apparent ‘threshold’ for the onset of cavitational activity was found at a displacement amplitude of about 12 μm. When the instrument was driven at the same ‘nominal’ power setting, different probe designs oscillated with different displacement amplitudes. The longitudinal displacement amplitude of the probe tip is therefore a meaningful and convenient measure of the acoustic power output from the ultrasonic scaler. It is a direct measure of both the efficiency of the ‘chipping’ action of the probe tip and the amount of cavitational activity occurring within the cooling water. It is also the only means whereby the results of clinical trials using different probe designs and/or different instruments can be compared in a meaningful manner.
    Dental Materials. 01/1986;
  • A.D. Walmsley, W.R.E. Laird, A.R. Williams
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    ABSTRACT: A model system consisting of a thin layer of vacuum-deposited metallic aluminium on a glass microscope slide was developed to demonstrate the effectiveness of cavitational activity (occurring within the cooling water supply of a dental ultrasonic descaler operating at 25 kHz) in the removal of particulate matter from solid surfaces. The pattern of particulate matter removal using this model system demonstrated both the mechanism of bubble activity and the erosive nature of microbubbles.Non-resonant bubbles were formed by surface wave activity and adhered to the surface of the slide. There was some removal of the aluminium metal at the periphery of the bubble (probably by a microstreaming mechanism) giving a ‘ghost’ outline. The majority of aluminium removal was caused by numerous microbubbles of non-resonant sizes (typically 1 to 2 μm diameter) formed by surface wave induced fragmentation of the parent bubble.The damaging and erosive effects of transient cavitational activity appear to be the result of sub-resonant sized microbubble formation from larger parent bubbles.
    Ultrasonics. 01/1985;
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    A D Walmsley, W R Laird, A R Williams
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    ABSTRACT: A model system consisting of vacuum-deposited aluminum on glass was developed to demonstrate the effectiveness of cavitational activity (occurring within the cooling water supply of a dental ultrasonic scaler) in the removal of particulate material from solid surfaces. The amount of solid material removed from the model system by this cavitational activity was quantified by a spectrophotometric technique. It was shown that cavitational activity occurring within the cooling water is an important contributory factor in the cleaning efficacy of the ultrasonic scaler operated under conditions similar to those employed clinically.
    Journal of Dental Research 10/1984; 63(9):1162-5. · 3.83 Impact Factor