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Biomedical subjects

A D Walmsley

Publications and source records attributed to A D Walmsley.

At least 109 records · Page 6Linked to original sources
PubMed1989

Pressures produced in vitro during intraligamentary anaesthesia.

An in vitro investigation measured the pressures produced by an Astra type aspirating syringe (modified Sterling) and a pressure syringe (Ligmaject) during periodontal ligament injections. A pressure transducer (0-6.9 MPa) was adapted to record the pressures generated within both syringes, with the output of the transducer connected to a microcomputer. Thirty-five clinicians (male: female ratio 3:2) were instructed in the technique of the periodontal ligament injection and the pressures that they produced from both syringes were recorded. Measurements of both the peak and time averaged pressures were obtained from computer print-outs of the recordings. Significantly higher pressures (P less than 0.01) were produced with the pressure syringe than with the aspirating syringe. It was also found that male operators produced significantly (P less than 0.1) higher pressure with the aspirating syringe, although there was no significant sex difference (P greater than 0.1) between the pressures recorded with the pressure syringe. Recordings from the pressure syringe revealed that either a multiple high pressure technique or a steady pressure technique was used, the former producing significantly (P less than 0.01) higher pressures.

Anesthesia, Dental↗
PubMed1989

Ultrasonic debonding of composite-retained restorations.

Ultrasonic chisels are used clinically to remove composite-retained bridges from one or both abutment teeth. Displacement amplitude measurements at the tip of the two designs available showed that the curved chisel was twice as powerful as the straight chisel. Investigations were undertaken to assess the efficiency of these chisels in vitro. Cast metal retainers were made, which incorporated particulate roughening of the fitting surface and these were bonded with a composite luting cement to extracted premolar teeth. Ten clinicians were asked to remove the retainers from the teeth and their application forces were measured. Clinicians were able to apply the highest force with the straight chisel design. The time taken to remove the retained restorations under increasing application forces and different power settings of the two chisels was then measured. Optimal time for removal of the retainers (ie with 5-10 minutes' exposure) required the use of high displacement amplitudes of the chisel, together with high application forces. Scanning electron microscopy of the failed bond revealed that composite was removed in those areas where the chisel was applied to the tooth. However, there was a disproportionate amount of tooth surface damage compared to that inflicted upon the metal retainer.

Composite Resins↗
PubMed1989

Effects of constraint on the oscillatory pattern of endosonic files.

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.

Root Canal Therapy↗
PubMed1989

Oscillatory pattern of sonically powered endodontic files.

When operated in air, the sonic endodontic instrument produced a movement at the driver head which resulted in a large elliptical oscillation of the file. This motion had similar properties to ultrasonically operated files in that there was a distinct variability in the magnitude of the vibratory motion between files of different design, length and thickness. When the sonic file was loaded, the elliptical motion was eliminated leaving a pure longitudinal file oscillation. This mode of vibration was particularly efficient as it was largely unaffected by loading, with the displacement amplitude being similar for different types of file used. The oscillatory pattern of the sonic file may offer a useful mode of mechanically assisted root canal preparation.

Root Canal Therapy↗
PubMed1989

A three part sectional denture.

A case is described in which a three-part sectional denture design was used to overcome the problem of severely instanding lower premolar and molar teeth. The design combined the use of a two-part cobalt-chromium lingual plate bolted together by an anterior flange which replaced missing lower anterior teeth.

Denture Design↗
PubMed1988

Applications of ultrasound in dentistry.

An ultrasonic descaler working at kHz frequencies is used in dentistry to remove attached deposits from the teeth. Such devices offer many advantages over conventional hand instruments by reducing both the work and time involved in the clinical descaling process. Although it is a recognised clinical instrument, there has been little attempt to standardise its acoustic power output. A parameter which may characterise adequately the acoustic emission from these instruments is the displacement amplitude of the probe tip. Modification of the ultrasonic descaler generator has led to the further use of the instrument in other dental areas. Diagnostic applications of MHz ultrasound is limited by the structure and arrangement of the dental tissues. Therapeutic ultrasound has been used to treat a variety of dentally related ailments, and ultrasonic cleaning baths are used to clean both dental instruments and materials.

Dental Plaque↗
PubMed1988

Potential hazards of the dental ultrasonic descaler.

The use of a dental ultrasonic descaler may be associated with biological hazards to structures within the oral cavity. Thermal hazards may result from either frictional contact between the oscillating probe and tooth or from absorption of acoustic energy within the tooth. Transmission of ultrasound along the tooth may result in thrombogenic damage to nearby blood vessels. The vibrating probe tip may produce scratching of the tooth surface, and incorporation of oral bacteria within the aerosol generated by the instrument which may result in transmission of infected material. Damage to the ear may arise from the coupling of ultrasound to the bones of the skull via the tooth. Furthermore the electro-magnetic field produced by these devices may interfere with cardiac pacemakers. It is the patient receiving treatment who is mainly exposed to these potential hazards. However, the clinician and his supporting staff may also be at risk.

Dental Plaque↗
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

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

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↗
PubMed1987

Preliminary investigation into the performance of a sonic scaler.

Recently a number of mechanical scalers, known as air or sonic scalers, have been developed. Preliminary investigations were undertaken to observe the operating characteristics of such a sonic scaler including its oscillatory pattern, and how this was affected by changing the design of the scaling tip, the air pressure, and the application load. The oscillatory pattern exhibited an open elliptical movement that was dependent upon the air pressure input to the instrument. Application of a load to the scaling tip resulted in oscillatory damping that increased with the magnitude of the load. The oscillatory performance of the sonic scaler differed from that observed previously with ultrasonic scalers. Investigators using the sonic scaler should indicate the type of scaling tip, the air pressure input, and the application load used to enable meaningful comparisons to be made between the results of different workers. Clinicians should be aware of its operating characteristics to avoid potential damage to the tooth surface.

Dental Prophylaxis↗