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Biomedical subjects

W J Houston

Publications and source records attributed to W J Houston.

At least 19 recordsLinked to original sources
PubMed1992

The effect of mechanical deformation on the distribution of potassium ions across the cell membrane of sutural cells.

Ionic concentrations of potassium, sodium, and chloride were determined in osteocytes of the rat calvarium. The values were determined by fluorescent microscopy of both intra- and extracellular concentrations. Following the baseline determination, the calvaria were placed in tension by retraction of a microelectrode manipulator, and the fluorescence of the cells were measured again. A statistically significant change in the derived ion distribution was found. Thus, the tensile forces affected the distribution of ions across the cell membranes, increasing intracellular sodium and decreasing intracellular potassium. This would have an effect on the resting cell membrane potential with a change of potential of 8 mV. This has implications in the interpretation of clinical findings.

Animals↗
PubMed1991

Bases for the analysis of cephalometric radiographs: intracranial reference structures or natural head position.

The inherent variability of intracranial cephalometric reference structures makes analysis based upon them potentially misleading with serious implications for orthodontic and orthognathic surgical treatment planning. These problems can be avoided by using natural head position and relating measurement to the true horizontal. The lack of suitable norms has been a barrier to this approach. This paper demonstrates that norms can be derived from existing data, enabling the clinical application of analyses related to the true horizontal.

Cephalometry↗
PubMed1990

Long-term stability of the lower labial segment relative to the A-Pog line.

Cephalometric records of 47 cases treated with the Begg technique were examined with a view to assessing both the effects of treatment and long-term change. The cases were treated by a single operator (Dr H. Brouwer) whose long-term records were taken on average over 10 years out of retention. Special reference was made of the use of A-Pog line as a guide to lower incisor stability. There was marked individual variation in both response to treatment and long-term change. Though all the results were clinically stable the A-Pog line was not found to be a reliable guide to lower incisor stability. In 62 per cent of the cases examined, the lower incisors tended to return towards their original positions after retention, whilst in the remaining cases the changes were extremely variable.

Adolescent↗
PubMed1990

A preliminary study of facial growth and morphology in unoperated male unilateral cleft lip and palate subjects over 13 years of age.

This paper investigates the effects of surgery on facial growth and morphology in Sri Lankan males with unilateral cleft lip and palate who were over 13 years of age at the time of study with cephalometry and dental study models. Three separate subgroups were analyzed: those who had totally unrepaired cleft lip and palate, those who received lip repair in infancy but not palatal repair, and those who had lip and palate repair in infancy. Twenty-three healthy noncleft Sri Lankan males over 13 years formed a control group from the same racial background. The results show that subjects who had no surgery had a potential for normal maxillary growth. Subjects who have had lip repair in early infancy show relatively normal maxillary growth, but maxillary hypoplasia is common when the palate has also been repaired early.

Adolescent↗
PubMed1990

A study model analysis of adult unoperated Sri Lankans with unilateral cleft lip and palate.

The maxillary arch-form of 41 Sri Lankan adults with unoperated complete unilateral cleft lip and palate (8 female and 33 male) were compared to a control group of 100 normal Sri Lankan adults (45 female and 55 male). The teeth in the cleft group were smaller than their equivalents in the control group, the most marked difference being found in the central and lateral incisors. Arch widths of the cleft groups were reduced, more anteriorly than posteriorly, resulting in more V-shaped arches. No differences were found in the arch length or chord lengths between the groups. Crossbites occurred in 19.5 percent of the cleft group as compared to none of the controls. The overjet was greater in the cleft group than in the controls. A higher percentage of missing teeth was recorded in the cleft group.

Adolescent↗
PubMed1990

An in vivo assessment of muscular activity and the importance of electrical phenomena in bone remodelling.

Modified orthopaedic pins were placed close to the medial and distal epiphyses of the tibia in 4 anaesthetised rabbits, in order to allow the application of controlled external loading cycles. Rosette strain gauges were placed at midshaft level, where the greatest compressive and tensile strains were expected during loading. Two weeks later, following stabilisation of the pins by bone healing, the animals were anaesthetised again and silver-silver chloride electrodes were attached close to the strain gauges in order to measure the changes in electrical potential difference. A sinusoidal load cycle was exerted between the pins with peak levels of 100 N or 250 N depending on the age of the animal. A fluctuation in potential difference, in synchrony with the strain recorded by the strain gauges, was recorded. The maximum potential difference was 2.2 mV, and it was not possible to exceed this with increased bone strain. After demonstration of the piezoelectric effect, repeated stimuli were applied to the sciatic nerve, producing a twitch in the muscles adjacent to the tibia. The electric potential difference from the muscles completely overwhelmed the local potential difference at the bone surface. A further two animals were prepared as previously described, and one electrode was placed on the endosteal surface. The electrical events mirror the changes found across the limb. The stimulus to bone remodeling, as distinct from growth, is usually loading in association with muscular activity. The fact that the changes in electrical fields at the bone surface are predominantly those originating in the muscles indicates that local electrical phenomena generated by bone strain cannot be the factors initiating the cellular response that is responsible for bone remodeling.

Animals↗
PubMed1989

Le Fort I maxillary osteotomies in cleft palate cases. Surgical changes and stability.

Surgical and postsurgical changes in maxillary position following transpalatal osteotomy at the le Fort I level in 30 patients with clefts of lip and palate were evaluated cephalometrically. By superimposing on natural reference structures, a more accurate and detailed evaluation of change in maxillary position was possible than by using conventional cephalometric analyses. The mean horizontal advancement was 9 mm, with a mean vertical change of 3 mm. While it is customary to express postsurgical relapse as a percentage of surgical change (in this case 7% mean horizontal relapse and 23% mean vertical relapse), the most remarkable finding to emerge from this study was the variability in surgical and postsurgical change which would be obscured by concentrating on descriptive statistics. Postsurgical change was related to the amount of surgical change, but the correlation coefficients are quite low, and so other factors must be responsible for a significant proportion of any relapse.

Adolescent↗
PubMed1989

Incisor edge-centroid relationships and overbite depth.

Interincisor angulation is commonly held to be a critical factor in determining overbite depth, where there is incisor contact. In this study significant correlations between these variables were found in Class II, division 2 malocclusions although interincisor angle explained less than a third of the variance in overbite depth. It was found that the anteroposterior relationship of the lower incisor edge to the upper incisor root centroid is more strongly related to overbite depth and it is suggested that this is a useful factor to take into account in planning treatment in Class II cases.

Dental Occlusion, Centric↗
PubMed1987

The Goslon Yardstick: a new system of assessing dental arch relationships in children with unilateral clefts of the lip and palate.

The Goslon (Great Ormond Street, London and Oslo) Yardstick is a clinical tool that allows categorization of the dental relationships in the late mixed and or early permanent dentition stage into five discrete categories. Cases are allocated to these categories on a value judgment basis by reference to the anchor groups of the Goslon Yardstick. The categorization was sufficiently sensitive to distinguish the treatment results at different centers in this study. It is proposed that the Goslon Yardstick should facilitate cross-center studies.

Cleft Lip↗
PubMed1983

The analysis of errors in orthodontic measurements.

The sources of error in cephalometric measurement and their analyses are discussed. The importance of distinguishing bias and random errors is emphasized, and methods of control are discussed. Randomization of record measurement is one of the most important methods of avoiding bias, but it is rarely undertaken in cephalometric studies. Random errors are particularly important in the evaluation of individual radiographs, and a measurement that has a high error in relation to its total variability will be of little value in clinical assessment. In serial studies of facial change, the error variance is always a major part of the total variance and thus results have to be interpreted with caution. In cross-sectional studies it is not possible to specify exactly the acceptable limits of random errors, because this will depend on the difference between groups that would be of interest and on the number of cases. The judicious replication of measurements can be important in the control of random errors. In many papers, adequate error evaluation and control is lacking. In these circumstances, the results are of limited value because it is not possible to tell whether an apparent effect is the result of bias in measurement or whether a real effect is being obscured by random errors. It is incumbent on authors to consider how their measurement errors should affect the interpretation of results.

Cephalometry↗