Biomedical subjects
Publications and source records attributed to A Harrison.
The historical and general use of shellac is discussed and its particular value in dentistry outlined. The effects of variations in the mica and aluminium content of shellac are evaluated. Measurements of elastic modulus, modulus of rupture and glass transition temperature are reported.
OBJECTIVES: To develop a patient satisfaction system for disablement services centres and to report on how the initial findings have been used in audit to improve their quality of care and services. DESIGN: Interview survey of randomly selected users attending in three centres: Birmingham (centre X), Oxford (centre Y), and Cambridge (centre Z) to establish core topics for developing a patient satisfaction questionnaire with incorporation into a computer patient satisfaction system (PATSAT) to enable collation of responses to the questionnaire. A pilot of the questionnaire was undertaken in the centres to assess the sensitivity of the questionnaire, which was subsequently used as part of clinical audit process during June 1991 and April 1992 in centre X and the patient satisfaction system used to monitor changes in routine practice. PATIENTS: 123 amputees in the development phase, selected by cluster sampling, and 1103 amputees in the pilot study. MAIN MEASURES: Satisfaction scores for components of the service. RESULTS: The questionnaire included 16 core topics contributing to quality of care and services, including comfort of limbs, appointments, interpersonal aspects of care, a system of support and counselling, and organisation. The pilot survey demonstrated high satisfaction scores for aspects of interpersonal care, organisation, and physical surroundings of the centres and lower satisfaction for counselling services, comfort of the limb and the number of alterations made before the limb was considered acceptable. During the audit in centre X these results prompted changes to care and services which produced significant improvements in satisfaction. CONCLUSIONS: The early results suggest that the questionnaire, coupled with PATSAT software system, enable users' views to be expressed, collated, and fed back to staff; the information provided has already prompted change, and the system is sufficiently sensitive to measure changes in satisfaction with the service.
A novel fine wire bone transport system for use with Ilizarov frames has been used in Bristol. It uses parallel wires instead of crossed wires. Its stiffness has been tested and compared with a crossed wire construct. In its basic form it is not as stiff to bending and shear loading, however, by modification it can be made at least as stiff. A parallel wire construct does not transfix as much soft tissue as a crossed wire construct when used in the leg. This is advantageous, because soft tissue transfixion causes pain and limb swelling, which impair patient mobilization.
In this study, the hypothesis examined is that differences in polymer particle size affect the doughing and manipulation times and the mechanical properties of the cured product. Six batches of polymers were used varying in particle size from <38 micrometers diameter to > 75 micrometers diameter. A penetration test was undertaken to investigate the influence of polymer particle size on the doughing and manipulation times of acrylic resin. It was demonstrated that the particle size in the range examined influenced the doughing and manipulation times, the smaller particle sizes having shorter times. No significant difference was demonstrated in the impact resistance of surface hardness of acrylic resin specimens constructed from polymers of varying particle size and although there were some significant differences in the transverse (flexural) strength these were small in real terms. Further, the molecular weight of the polymerised product was found to be consistently higher than that of the original powder component.
An automated image cytometric system is described for the measurement of DNA content and distribution in cells stained with fluorescent DNA binding or intercalating compounds. The quantitative precision of integrated optical intensity (IOI) measurements using this system was estimated to be 2.0%, based on the coefficient of variation (cv) of the IOI of DNA check beads. Using peripheral blood lymphocytes stained with 4'-6-diamidino-2-phenylindole (DAPI), the cv of IOI was found to be 3.5%. Slide to slide variability of the IOI for peripheral blood lymphocytes (cv over 10 slides of the mean IOI) was found to be 2%. The most important sources of error in these measurements were glare, illumination instability, image calibration instability, and staining non-uniformity. These errors were investigated and minimized.
PURPOSE: To determine the extent of reduction of volume of normal tissue structures exposed to high doses of radiation therapy (RT) after administration of neoadjuvant hormonal therapy (NHT) in patients with bulky, geometrically unfavorable prostatic cancers. METHODS AND MATERIALS: Twenty-two patients with bulky prostatic cancers were treated with a 3 month course of neoadjuvant leuprolide acetate and eulexin prior to three-dimensional (3-D) conformal radiotherapy. Patients were included if 3-D treatment planning revealed that either > 30% of the rectal wall would receive 95% of the prescription dose (D95) (n = 13); > or = 50% of the bladder wall would receive D95 (n = 10); or that any volume of small bowel would receive > or = 65% of the prescription dose (n = 16). All patients underwent simulation and conformal treatment planning before and after NHT. Pre and posthormone cumulative dose volume histogram (DVH) calculations for all normal tissue structures were analyzed and compared for each patient. RESULTS: The median percentage of target volume reduction after NHT was 25% (range: 3-52%). Ten of 13 patients (78%) whose prehormone rectal DVH demonstrated > 30% of the rectal wall receiving D95 responded to NHT with a median 25% (range: 16-48%) reduction of rectal volume receiving the D95. A median reduction of 50% (range: 6-64%) of the bladder volume receiving D95 was observed in nine of ten patients (90%), while 13 of 16 (81%) showed a reduction of small bowel volume to a median percentage of 88% (range: 67-100%) of the prehormonal values. CONCLUSION: Neoadjuvant hormonal therapy is an effective method for decreasing the size of bulky prostatic tumors as well as for optimizing the geometry of the target volume in relation to the adjacent normal tissue structures prior to radiation therapy. Such an approach allows for reduction of the volume of normal tissues exposed to high doses in the majority of treated patients. Currently, studies are underway to determine whether NHT will lead to a decreased likelihood of long-term complications associated with radiotherapy of bulky, geometrically unfavorable prostatic tumors, and permit the safe delivery of escalated dose levels using conformal treatment techniques.
The fracture of dentures is an unresolved problem. Despite increasing costs incurred by the nation on the repair of these prostheses, very little has been documented on the type of fracture encountered. This survey was carried out to determine the prevalence of type of fracture by the distribution of questionnaires to three different laboratories. Results obtained showed that 33% of the repairs carried out were due to debonded/detached teeth. Twenty-nine per cent were repairs to midline fractures, more commonly seen in upper complete dentures. The remaining 38% were other types of fractures, the majority of which constituted repairs to upper partial dentures. The latter involved detachment of acrylic resin saddles from the metal in metal based dentures and the fractures of connectors in the all-acrylic resin partial dentures.
The nucleotide (nt) sequence of a 5.3-kb DNA segment containing the Gram- Acinetobacter calcoaceticus catBCIJFD operon is reported. This information completes determination of a 16-kb nt sequence containing the twelve ben and cat structural genes encoding enzymes required for catabolism of benzoate via the beta-ketoadipate pathway. Many of these genes can be traced to a common ancestry with genes from other organisms containing DNA with widely divergent G + C content. The A. calcoaceticus ben and cat genes are arranged in a supra-operonic cluster containing one known regulatory gene and three additional open reading frames (ORFs) that may have regulatory functions. Thirteen of the ben and cat genes, including the three ORFs with unknown function, are typical for A. calcoaceticus in that they possess a G + C content of 44.9 +/- 2.5%. Three exceptional A. calcoaceticus genes (catI, catJ and catF) possess G + C contents of 56.5 +/- 1.3%. These differences in G + C content are reflected in the distinctive patterns of codon usage shared by catI, catJ and catF. Thus, the catIJF region, known to exchange genetic information with the pcaIJF region in the same chromosome directing isofunctional proteins associated with the beta-ketoadipate pathway, has avoided the evolutionary forces that conferred characteristics G + C content upon the other ben and cat genes in A. calcoaceticus.
The rheologic characteristics of different formulations of acrylic resin denture base materials are presented in this study. This is of practical significance in selecting resins with optimum rheologic properties for denture base construction. The materials are characterized in respect to their constituents, mean powder particle size and distribution, molecular weight averages and distributions, and glass transition temperature. A comparison of the polymers indicates that smaller particles saturate with monomer more readily, and this results in a higher viscosity. A higher viscosity for higher molecular weight and lower viscosity for lower molecular weight have been observed. Increasing the percentage of copolymerization increases the viscosity. No correlation has been found between the rheologic properties of denture base polymers and the powder glass transition temperature.
Abrasive wear tests were performed on unglazed, glazed, and polished porcelain stud specimens using human enamel as the opposing plate specimens. The wear tests were carried out on a wear machine that was specifically designed to simulate the masticatory cycle. The amount of enamel wear produced by both glazed and unglazed porcelain was similar; however, that produced by polished porcelain was substantially less. Investigation of the glazed porcelain surface showed that the glaze was removed in less than 2 hours of wear on the machine.
AIM: To review the outcome of infants born following prolonged and preterm rupture of the membranes. DESIGN: retrospective and partially prospective observational study. SETTING: babies born in and referred to a tertiary neonatal centre. PATIENTS: 117 preterm infants, median gestation (range) = 29.5 (25-36) weeks, seen over a 7 year period with membranes ruptured for more than 4 days; median (range) = 9 (4-119) days. OUTCOME MEASURES: survival and cause of death, compression deformities, pulmonary hypoplasia and infection. RESULTS: 23 infants died, 11 from pulmonary hypoplasia and 11 as a direct consequence of prematurity (3 from hyaline membrane disease, 7 from bronchopulmonary dysplasia and one from necrotising enterocolitis developed on day 17). One infant had a lethal congenital abnormality and died untreated of overwhelming infection. No other infants died of infection. 94% of infants were treated with broad-spectrum antibiotics after birth. Compression deformities were seen in 25 infants: median duration of membrane rupture 28 days, range 4-119. In those without deformity, median duration was 7 days, range 4-105. Sixteen infants had pulmonary hypoplasia (median 31, range 14-119), 11 died (median 37, range 21-112) and five survived (median 23, range 14-119). Although the median duration of membrane rupture in infants dying of pulmonary hypoplasia was longer than in those who did not have hypoplasia (31 compared to 7 days), 13 of 27 (48%) of infants whose membranes were ruptured for 4 weeks and 4 of 7 (57%) whose membranes were ruptured more than 70 days survived. CONCLUSION: death from pulmonary hypoplasia is a much more serious problem following preterm prolonged membrane rupture than is infection. Pulmonary hypoplasia is not inevitable even after prolonged periods of membrane rupture.
OBJECTIVES: This study was conducted to measure the effect of viscose rayon esthetic fibers on the flow properties of an acrylic resin denture base material. METHODS: Two testing methods using a needle penetrometer and an oscillating rheometer were employed on weighed proportions (0.1%, 0.2%, 0.8%, and 0.3%) of fiber. RESULTS: The results show that the fibers affect the flow properties of the polymer/monomer mix. Increasing the percentage of fibers decreases the flow of the material and reduces the doughing time. With increasing amounts of fiber, a rapid increase in the viscosity occurs with a corresponding adverse effect on flow properties. SIGNIFICANCE: It is concluded that these properties are important for the successful handling of acrylic materials since they can influence the accuracy and quality of the molded denture.
The fracture of acrylic resin dentures remains an unresolved problem. It is known that eventual fracture of an appliance occurs due to crack initiation and propagation from areas of high stress concentration. In order to understand and overcome the problem of fracture, it is important to identify the regions of stress concentration. A number of different methods are used in stress analysis. However, the finite element method, a numerical technique, appears to overcome most of the problems associated with the earlier experimental methods. This article reviews the different techniques and their application to examining stresses in dentures.
The degree of polymerization of an acrylic resin repair material, as established by residual monomer estimation, was compared using three different polymerization methods, i.e. bench-cure, hydroflask-cure and microwave irradiation cure. The repair strength of a conventional heat-polymerized resin was then assessed following repairs using each of these three methods. The lowest level of residual monomer was achieved with the microwave irradiation cure. It was also demonstrated that of the three methods, polymerization using microwave energy resulted in the strongest repair.
It is known that high levels of residual monomer have a deleterious effect on the properties of denture base polymers and may cause irritation or hypersensitivity of the oral tissues. In the present study variations in determination methodology and their influence on residual monomer levels are evaluated. The results demonstrate that filtration of the sample, sealed storage and incorporation of an appropriate volume of internal standard enhanced the accuracy of the technique.
The most common cause of teeth detaching from the denture base is the presence of impurities along the tooth denture-base interface. However detachment after a period of wear of the denture probably occurs due to the presence of stress concentrations along the interface from which cracks may initiate. The presence of the impurity will inevitably lower the stress threshold for cracks to propagate thereby increasing the risk of tooth detachment. Although this is obvious, there is no evidence to show the effect of impurities on the stress distribution at this interface. This pilot study utilised the finite element method to examine stresses at the tooth-denture base interface in the presence of simulated impurities interspersed along different positions on the interface. Within the limitations of the two-dimensional model used, it was concluded that the presence of an impurity at the edge of the palatal aspect of the interface has a significant effect on the stress magnitude. However, the presence of impurities elsewhere along the interface had no significant effect on the stress magnitude. This would have important implications during the processing of dentures.
Aesthetic fibres are added to denture base polymers to simulate the natural appearance. The aim of this study was to measure the effect of aesthetic fibres on the low strain rate transverse bend strength and the high strain rate impact strength of an acrylic resin denture base material. Varying amounts of 2 and 4 mm Viscose Rayon aesthetic fibres, ranging from 0.1 to 3%, were incorporated into the polymer to evaluate their effect on these strength properties. The results showed that the fibres had minimal physical effect and that bonding of the fibres to the denture base polymer is not uniform or complete.
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