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Biomedical subjects

R J Wilding

Publications and source records attributed to R J Wilding.

At least 19 recordsLinked to original sources
PubMed1999

Increased exposure to pollutant aerosols under high voltage power lines.

PURPOSE: To assess increased exposure to airborne pollutants near power lines by investigating theoretically and experimentally the behaviour of 222Rn decay product marker aerosols in the 50 Hz electric field under power lines. MATERIALS AND METHODS: The behaviour of aerosols in outdoor air including those carrying 222Rn decay products was modelled theoretically in the presence of an AC field. TASTRAK alpha-particle spectroscopy was used to characterize 218Po and 214Po aerosols outdoors. Sampling points were chosen along a line at right angles up to 200 m from a number of high voltage power (transmission) lines. Each sampling point comprised an arrangement of mutually orthogonal TASTRAK detectors. Exposures were carried out at different power line locations in various weather conditions. RESULTS: The model predicts a two- to three-fold increase in deposition of aerosols on spherical surfaces mimicking the human head under high voltage power lines. Experimental measurements using detectors mounted on grounded metal spheres showed an enhanced deposition of both 218Po and 214Po aerosols. Enhanced 218Po deposition on 400 kV lines ranged from 1.96+/-0.15 to 2.86+/-0.32. Enhanced 214Po deposition on 275 kV and 132 kV lines were 1.43+/-0.07 and 1.11+/-0.21, respectively, where the latter value was not significant. CONCLUSIONS: The observations demonstrate a mode of increased exposure to pollutant aerosols under high voltage power lines by increased deposition on the body. The total (indoor + outdoor) 218Po and 214Po dose to the basal layer of facial skin is estimated to be increased by between 1.2 and 2.0 for 10% of time spent outdoors under high voltage power lines.

Aerosols↗
PubMed1999

Corona ions from powerlines and increased exposure to pollutant aerosols.

PURPOSE: To investigate corona ions emitted from high-voltage powerlines and assess their effects on exposure to environmental pollutant aerosols. MATERIALS AND METHODS: The charge density of ions in air required to produce a given change in the observed DC field at ground level was calculated. A DC field mill meter was used to map the DC fields near 132, 275 and 400 kV powerlines. RESULTS: The Earth's natural DC field of around approximately 100 Vm(-1) was significantly modified near powerlines in 8 out of 14 cases. Typically, downwind of the powerlines the field direction was reversed giving values to -340 V m(-1). In one case, the effect extended more than 500 m from a 275 kV line. DISCUSSION: These results can be analysed in terms of the charge density present. This analysis suggests that typically 2000 excess negative charges per cm3 are required to match the measured DC fields. Such space charge will result in unipolar aerosol charging in excess of the normal bipolar steady state charge distribution of pollutant aerosols. This may lead to increased lung deposition on inhalation.

Aerosols↗
PubMed1997

Muscle activity and jaw movements as predictors of chewing performance.

Chewing performance can be defined in terms of the reduction in food particle size after 15 chewing strokes. In this study, the relationship between chewing performance and electromyographic activity was investigated to develop optimal values of electromyographic variables, based on their ability to predict chewing performance. Electrognathographic and electromyographic recordings from surface electrodes over the digastric (abductor), masseter, and temporalis (adductors) muscles were made from 24 subjects while they chewed a hard fruit gum. A moderate negative correlation was found between the food particle size and the root mean square calculation for masseter activity (-.48; P < .01). Weaker positive correlations were found between particle size and the asynchrony of ipsilateral and contralateral anterior temporalis muscles (.36; P < .05). A multiple regression model of electromyographic and electrognathographic variables was able to predict chewing performance with an R2 value of .66. If chewing performance is used as an output measure of masticatory function, it may be possible to determine optimal ranges for electromyographic variables and jaw movements.

Adult↗
PubMed1997

Jaw movement tremor as a predictor of chewing performance.

The purpose of this study was to investigate normal physiologic tremor in jaw movement as a factor that may influence chewing performance more directly than either muscle activity or jaw displacement. Chewing performance was defined in terms of the reduction in food particle size after 15 chewing strokes. Data on chewing particle size and electromyographic activity were available for 24 asymptomatic adults from an earlier study. Jaw movements during chewing were recorded using electrognathography, and velocity and acceleration in three planes were determined. Power spectrum for acceleration was calculated during opening and closing phases of the chewing cycle. The frequency of the peak amplitude in the power spectrum represented physiologic tremor of the jaw. Tremor frequencies during both opening and closing phases of the chewing cycle were strong predictors of chewing performance. A multivariate model composed of variables derived from acceleration, together with electromyographic and jaw movement variables, produced a multivariate model that was able to predict chewing performance with an adjusted R2 value of .78.

Adult↗
PubMed1997

Communication with TB patients; a neglected dimension of effective treatment?

Previous research has shown that patients who are satisfied with their interactions with a health provider tend to adhere to treatment. This study sets out to investigate the quality of the communication in the interactions between clinic nurses at a Western Cape clinic and newly notified tuberculosis patients. Routine interviews between clinic nurses and tuberculosis patients were video-recorded, transcribed and analysed, using a qualitative instrument devised by the researchers. The interactions were evaluated as being essentially nurse-centred; there was an unequal distribution of control, poor receptivity to the patient and little confirmation of the patient. The nursing staff received a period of training in communication skills. After this training their interviews with patients revealed a significant shift towards a more patient-centred approach, resulting in mutual satisfaction of nurse and patient. Training in communication skills should be introduced at TB clinics, in order to improve patients' adherence to therapy.

Analysis of Variance↗
PubMed1995

The use of fractal analysis to reveal remodelling in human alveolar bone following the placement of dental implants.

In order to confirm the presence of adequate bone support for implants it is necessary to examine the surrounding bone at intervals. While this may be attempted by looking for changes in serial radiographs, such comparisons are inaccurate unless standardized procedures are followed which allow subtraction of consecutive digital images. As image textures are less susceptible to magnification distortion, it was decided to examine the fractal dimensions of successive radiographs of bone after implant placement. All available panoramic radiographs for each of 18 patients who had received fixed implant-supported prostheses were digitized. A window of bone adjacent and distal to the most posterior implant was defined as the region of interest; the fractal dimension of the image was calculated. Linear regression was used to investigate whether there were any significant shifts in fractal dimension during the recall period after implantation. A significant increase in fractal dimension was found during the period up to 2 yr after implantation (p < 0.001). The most pronounced increase was in the region of bone around the neck of the implant. An increase in orientation of the image in a direction oblique to the implant was also found during the same period. These changes are consistent with models derived from finite-element analysis that predict the relation between trabecular architecture and strain. One subject's radiographs had a significant negative regression slope, which further monitoring may reveal was an early sign of implant failure. The satisfactory remodelling of bone in response to implant placement may be monitored using a texture analysis of routine orthopantomograms.

Adult↗
PubMed1994

The determination of optimal human jaw movements based on their association with chewing performance.

Chewing performance is an expression of the functional capacity of the jaws and teeth. In a recent study of fully dentate subjects, the variation in chewing performance could not be explained by differences in occlusal contact area. It was now decided to investigate the possibility that chewing performance might be associated with certain patterns of jaw movement. Data from two previous studies using the same subjects were analysed using a step-wise regression to select variables of jaw movement that could predict chewing performance. A multivariate model with an R2 value of 0.79 (p < 0.000) was generated with particle size as the dependent variable. Eight components of jaw movement made up the independent variables. Some of the more dominant variables in the model were those that describe a wide, bilateral chewing cycle with a predominantly lateral path of closure. Another powerful predictor of efficient chewing was a smooth, flowing movement with minimal changes in velocity. The inclusion of occlusal contact area in the model did not enhance its predictive capability. It was concluded that selected jaw-movement variables were significant determinations of chewing performance, and therefore could contribute to developing a baseline for normal masticatory function.

Adult↗
PubMed1993

The association between chewing efficiency and occlusal contact area in man.

Chewing is influenced by a number of factors, which include jaw and tongue movements, the activity of circumoral muscles, bite force and hard oral surfaces, but it is not clear which of these factors is most crucial to efficiency. The mere presence of surfaces such as the hard palate, or teeth, does not insure that chewing will be efficient. The purpose of this study was to explore the relationship between occlusal contact area, and chewing efficiency and to observe the influence of chewing-side preference on efficiency. These variables were recorded for both left- and right-hand sides, in a sample of 26 normal young adults. Chewing efficiency was estimated by the size of food particles collected after a predetermined number of chewing strokes. The particles were measured using image analysis and the median size calculated. Comparisons were made, firstly within subjects, between the left- and right-hand side, and secondly between subjects. Correlations were found between chewing efficiency and occlusal contact area which were more pronounced within, than between, subjects. It was concluded that while occlusal contact area influenced chewing efficiency within the same individual, it could not account for the differences in chewing efficiency found between individuals. Differences in the movement of the jaw and in the bite force may have a greater influence on chewing efficiency than occlusal contact area.

Adult↗
PubMed1992

Absence of association between a preferred chewing side and its area of functional occlusal contact in the human dentition.

Preference for a particular chewing side may be influenced by several factors, one of which could be the functional contact area on each side of the dentition. In this study, interocclusal wax records were made for each of the 30 subjects. A digital image of the transilluminated wax record was analysed to group 'grey' values into categories of wax thickness. The total area for tight and intermediate tooth contacts was calculated for both the left- and right-hand sides of each subject. The chewing-side preference was recorded. No correlation was found between the area of occlusal contact on one side and the preference for chewing on that side. Occlusal contact area does not appear to be a determinant of chewing-side preference.

Adult↗
PubMed1992

Dimensions of the temporal glenoid fossa and tooth wear in prehistoric human skeletons.

Both the mandibular condyle and the glenoid fossa remodel in response to changes in the dentition during life, although the precise relationship between teeth and joint is not clear. This study was undertaken to ascertain changes, if any, occurring in the glenoid fossae in skeletons with much tooth wear. In a collection of skulls from an excavation site on the South African coast, occlusal wear was measured using the scale devised by Molnar. The dimensions of the glenoid fossae were measured using a reflex microscope. Profiles of the glenoid fossa at right angles to a line through its medial and lateral poles provided estimates of the slope of the articular eminence in three places: centrally, and midway between this slope and each of the poles. The mediolateral profile gave an estimate of the height and gabling of the fossa. Central and lateral slope angles showed weak correlation with molar wear, and the medial but not the lateral angel was significantly different from the central. The fossa appears to remodel in response to patterns of forces generated during function, but compared to the condyle, is not as strongly influenced. This may be accounted for if the relative load-bearing areas of the condyle and fossa are considered.

Adult↗
PubMed1991

Changes in mandibular condyle morphology related to tooth wear in a prehistoric human population.

The exact relationship between tooth wear and changes in the shape of the articulating surface of the mandibular condyles is unknown. It is assumed that to some degree these changes are in response to the loads on the joint generated during chewing. Excavated skeletal remains from sites of primitive human habitation provide an opportunity to study the masticatory system of human beings in their natural context, with the features of form and function expressed to their full potential. Accurate measurements of the condylar head can also be made on such remains. A collection of skulls from an excavation site known as Oakhurst on the South African coast provided material for this study. Occlusal wear was measured using the scale devised by Molnar; approximal wear was assessed by measuring the size of the wear facet between the first and second molars. The width of the condyles were measured directly, and a method was devised to measure changes in the proportion of medial and lateral articulating facets. An increase in the size of the lateral facet of the condyle was found to be associated with increased tooth wear. It is suggested that the direction of condylar remodelling may give an indication of the reaction at the joint to optimal mastication.

Adult↗
PubMed1991

A computer analysis of normal human masticatory movements recorded with a sirognathograph.

A method of analysing jaw movements was developed by converting jaw displacements into a matrix of frequency distributions. Low frequencies were first filtered out; then quartiles and modes were used to describe the remaining core. Eight different types of measures (variables) were developed to describe the proportions and density of a core of movement. These variables were repeatable at successive recording sessions, yet accurate enough to reveal differences in chewing patterns between right- and left-sided chewing. All eight variables of jaw displacement were required to discriminate between the chewing sides of 15 subjects. A statistical model was developed to express the principal components of jaw movement. The first component consisted of variables that expressed the shape of the chewing cycle; the second, its distribution about the midline; the third, the prevalence of a bimodal pathway in the sagittal plane. There was a wide variation in patterns of chewing movements, which appear to be consistent with normal masticatory function. A multivariate model appears to be required to describe chewing movements.

Centric Relation↗
PubMed1991

A model for optimum functional human jaw movements based on values associated with preferred chewing patterns.

Jaw movements during voluntary chewing were recorded from 15 normal subjects with a sirognathograph. A computer program was used to provide a graphic display of the closing strokes in the frontal plane. A record was made of the side from which the jaw approached a central occlusal position. An average of 90 closing strokes was recorded for each subject. In 10 of the subjects, statistical differences were found between the use of the right- and left-hand sides. In these subjects this preference was confirmed by analysis of results from a second set of observations. A model was derived, using multiple regression analysis, which identified a relationship between four jaw-movement variables and an index of preference. A broad chewing pathway, with a bilateral distribution, together with a wide sagittal pathway were characteristics associated with preference. An indication of optimal jaw-movement patterns may be derived from identifying movement variables associated with preferred chewing.

Adult↗
PubMed1990

A technique for the construction of complete dentures in two visits. 2. A pilot study to evaluate the opinions of practitioners and patients.

The technique for fabrication of complete dentures in two visits was described in part I. The purpose of the present study was to evaluate both the clinical methods used and patients' acceptance of the resulting dentures. Eleven general practitioners were taught to use the technique and then asked to complete a questionnaire. Most practitioners had some difficulty with some aspects of the technique. The consensus was that the two-visit denture technique would have some application in providing low-cost dentures, provided that the esthetic demands of the patient could be satisfied within the limitations of the technique. The second part of the evaluation was provided by patients, who were asked to indicate a preference between two sets of dentures, one made using a four-visit technique and the other using the two-visit technique. Preferences were divided, but all patients were able to wear both sets of dentures. The final responsibility for providing an adequate denture service remains with the practitioner.

Consumer Behavior↗