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Biomedical subjects

W R Laird

Publications and source records attributed to W R Laird.

At least 19 recordsLinked to original sources
PubMed1992

Experience with ITI osseointegrated implants at five centres in the UK.

Experience with the two-part ITI titanium implant system at five centres in the UK is reported. A total of 461 implants were inserted in 176 patients, who received 189 prostheses. Criteria for the assessment of success following implantation are listed. Results over a 3-year period showed a success rate of 94% when implants were used for mandibular overdentures and crown and bridge prosthetics. A lower success rate in the edentulous maxilla was recorded.

Adolescent↗
PubMed1992

Ultrasound in dentistry. Part 2--Periodontology and endodontics.

Ultrasound in the kHz frequency range is used widely in clinical dentistry. The most common uses are in the fields of periodontology and endodontics. The ultrasonic scaler works by the vibratory chipping action of the oscillating tip and is assisted by the presence of cavitational activity in the associated cooling water. When assessing clinical studies it is often difficult to interpret results from different workers due to the lack of standardization of the ultrasonic scaler. Operators should be aware of the oscillatory pattern of different instruments. Endosonics utilizes an ultrasonically oscillating endodontic file to clean and shape the root canal prior to obturation. The cleaning ability of such files is assisted by the occurrence of acoustic microstreaming forces. The endosonic file is prone to constraint when it contacts the canal wall which alters its oscillatory pattern. Clinical techniques should be modified to reduce this problem.

Dental Scaling↗
PubMed1991

Ultrasound in dentistry. Part 1--Biophysical interactions.

Ultrasound has many applications in the field of dentistry. However, it is only recently that the applications and effects of its physical properties have been rationalized and understood. Ultrasound may be generated by either magnetostriction or piezoelectricity, although the former is more commonly used in dental applications. Interactions of ultrasound with biological tissues may be caused by either thermal or mechanical mechanisms. The mechanical forces produced may be a result of cavitation, acoustic microstreaming and radiation pressure forces. An understanding of these interactions allows a more knowledgeable appreciation of the effectiveness, safety limitations and rationale of dental ultrasonic instrumentation.

Biophysical Phenomena↗
PubMed1991

Streaming patterns produced around endosonic files.

Acoustic microstreaming is known to be an important phenomenon associated with the use of clinically available endosonic systems. However, it has proved difficult to calibrate its pattern and effectiveness around the oscillating file. An in-vitro model system consisting of slow setting plaster was developed to demonstrate the activity of streaming around both ultrasonically and sonically activated files. For ultrasonic files, streaming occurred mainly in front of and behind the file, in contrast to the sonic file, where the plaster was disturbed evenly around it. With both types of file most activity occurred around the file tip, and became reduced towards the driver. Streaming patterns associated with the ultrasonic device were found to be dependent on the power setting of the instrument and whether the side of the file was constrained or lightly touched. The sonic device produced a large disturbance around the freely oscillating tip. Under load this streaming occurred along the whole length of the file, and was unaffected by constraint. This investigation demonstrated that streaming does occur with the instruments currently available, although it is dependent on their operating conditions. Clinical users of such equipment should be aware of the characteristic three-dimensional patterns of streaming that occur around these endosonic files, in order to maximize their efficiency.

Acoustics↗
PubMed1990

'The Yankee dodge': some new observations on the discovery of anaesthesia.

The discovery of general anaesthesia is arguably the most important advance in the practice of surgery. To whom the credit belongs has, however, remained controversial. A first-hand account has now indicated that this controversy can finally be resolved, and that the credit for the discovery of anaesthesia should be given to Horace Wells.

Anesthesia, Dental↗
PubMed1990

Effects of cavitational activity on the root surface of teeth during ultrasonic scaling.

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.

Dental Prophylaxis↗
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

The development of criteria for the assessment of complete dentures.

Criteria for the assessment of complete dentures have been published by several groups of workers but none have proved universally reliable. The present study was undertaken in an attempt to develop criteria of proven reliability for the assessment of the occlusion, articulation, retention, stability and appearance of complete dentures and the health of their supporting tissues. The criteria formulated were subjected to a series of evaluations of their reliability followed by attempts at refinement where this was unsatisfactory. Although levels of agreement between independent assessments made using the criteria improved as the study progressed, an acceptable level of reliability was not attained. The possible reasons for this are discussed.

Denture, Complete↗
PubMed1989

Problems in the assessment of complete dentures.

The evidence for the reliability of some of the most widely used criteria for the assessment of complete dentures is reviewed and a number of factors discussed which might account for the contradictory nature of this evidence, including methods of statistical analysis, the wording of criteria and possible extraneous influences on the judgment of observers using the criteria. Adequate and consistent reliability has not been demonstrated for any of the criteria which have been proposed and the development of either more reliable criteria or of objective tests of the performance of complete dentures is a priority if the results of epidemiological surveys of complete dentures are to be regarded as meaningful.

Dental Occlusion, Centric↗
PubMed1989

Jaw relationships and complete dentures.

In order to ensure comfort and efficiency from a denture it is important to record correct intermaxillary relationship both vertically and horizontally. A variety of techniques have been developed to produce accurate records and it would appear that a functional technique is most appropriate. Of the methods available evidence suggests that function of swallowing may be particularly useful in this respect.

Deglutition↗
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↗