Biomedical subjects
R van Noort
Publications and source records attributed to R van Noort.
In defence of dental materials.
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Drug release from acrylic polymers via channels and cracks: in vitro studies with hydrocortisone.
Release of hydrocortisone sodium succinate from acrylic resin was found to occur readily on elution in water at 37 degrees C. Increasing the degree of hydration of the acrylic resin by the addition of hydroxyethyl methacrylate impaired rather than enhanced the release of drug. The mechanism for the release of drug is believed to be surface release and drug dissolution into and diffusion via cracks and channels which are formed by incorporation of the drug, producing a 'drug-modified polymer'. Diffusion through the polymer matrix is believed to be insignificant. The results obtained are discussed in relation to this proposed model for drug release. A simple method for the manufacture of the core of an intra-oral insert capable of delivering drugs with MW greater than 400 for systemic and topical oral drug delivery is described.
The fracture topography of acrylic dentures broken in service.
The fracture surfaces of full dentures that failed in service, and others broken under controlled conditions, have been examined using scanning electron microscopy. The results allow the direction of crack propagation to be deduced and indicate that brittle impact is the predominant mode of fracture. Improvements in the strength of the denture tooth/denture base bond may be the most effective means of achieving an increase in the strength of full dentures.
Dental materials: 1982 literature review. Part 2.
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Dental materials: 1982 literature review. Part 1.
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The surface finish of composite resin restorative materials.
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Controlled delivery of drugs. A review of polymer-based devices.
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A scanning electron microscope study of Co-Cr partial dentures fractured in service.
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A study of the effects of glutaraldehyde and formaldehyde on the mechanical behaviour of bovine pericardium.
The inherent variability in the mechanical behavior of bovine pericardium causes difficulties in establishing the effects of treatment procedures used in the manufacture of bioprosthetic cardiac valves. A new experimental technique has been developed in which the specimen acts as its own control, obviating the need to perform large numbers of experiments to obtain statistically significant results. The procedure used is described in detail as is the equipment employed. The technique was used to assess the effect of glutaraldehyde and formaldehyde on the stress/strain response of bovine pericardium. The results show that the fixing process in glutaraldehyde is virtually complete within two hours and causes significant changes in the mechanical behaviour of the tissue. The tissue becomes progressively stiffer as the treatment period is extended, which is especially pronounced at low levels of stress. Formaldehyde storage subsequent to fixing in glutaraldehyde was found to have no effect on the stress/strain response of the bovine pericardium.
The physical properties of bovine pericardium: a study of the effects of stretching during chemical treatment in glutaraldehyde.
The uniaxial stress/strain response of bovine pericardium up to a stress of 1 N/mm2 was studied. The tissue was chemically modified in 0.5% buffered glutaraldehyde for 24 hours under various conditions of constraint. Four groups were studied: an unrestricted control group, a group held at their original length, a group stretched to a stress of 0.04 N/mm2, and a group stretched to a stress of 0.4 N/mm2 during treatment. Histological examination revealed changes in structural organization of the collagen, which explained the alterations in the stress/strain response. A significant alteration in mechanical properties after glutaraldehyde treatment was observed, with considerable loss of extensibility for the prestretched tissues. A valve made from such a prestretched tissue may be stenotic and possibly subject to early failure.
A comparative study of scalpel and electrosurgical incision on subsequent wound healing.
The mechanical strength of incisions in the anterior abdominal wall using either scalpel or electrocautery was compared by measuring the bursting stresses of the resulting wounds. Statistically significant differences were shown to occur in the first and thirty-fifth postoperative days. Between the seventh and tenth postoperative days, when wound dehiscence is most likely to occur, no difference in the rupture strength could be detected.
A study of the uniaxial mechanical properties of human dura mater preserved in glycerol.
Heart valve replacements have now been made for some years from human dura mater. While the clinical results have been encouraging there is a considerable lack of information on the mechanical properties of the dura mater and the effects of the glycerol treatment employed. This study revealed that glycerol provided an adequate preserving medium for periods of up to 12 days, with no significant changes in the mechanical properties of dura mater. A wide range in mechanical properties was observed with, for example, the tensile strength varying from 3.28 N/mm2 to 7.86 N/mm2. Although no age-related deterioration in human dura mater could be shown, the results do suggest that dura mater in excess of fifty years of age should be avoided in order to prevent the selection of poor quality material.
The mechanical properties of human dura mater and the effects of storage media.
Data are presented on the tensile strength and ultimate extensibility of human dura mater. Experiments were performed, prior to, and after, storage in glycerol. The results indicate that storage in glycerol has a small effect on the measured mechanical properties, but this was not statistically significant. In addition, storage in saline after glycerol preservation for up to thirty days was found to have no effect on the mechanical properties of dura mater, as long as the tissue had previously been sterilised and sterility was maintained. However, the considerable variability found in the mechanical properties of human dura prevented this being established beyond doubt. The implications of this variability for tissue selection is discussed.
In vitro heart valve evaluation: fact or fantasy?
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An experimental study of the healing of secondary abdominal incisions.
An experimental study of the healing of separate secondary abdominal incisions in rats has been performed. After an initial right subcostal incision, a vertical left-sided abdominal wound was made 1 or 2 weeks later. Wound healing was assessed by measurement of changes in mechanical strength and collagen deposition. The results indicate that an increase in mechanical strength was not effected by initial wounding despite alterations in collagen metabolism.
Mechanical properties of antibacterial silicone rubber for hydrocephalus shunts.
In an effort to find a solution to the serious problem of bacterial colonization of cerebrospinal-fluid shunting devices, room-temperature and heat-vulcanizing silicone rubbers were impregnated with gentamicin sulphate. The effects on the mechanical properties of the two rubbers were studied. Results show that the tensile strength and extensibility of the room-temperature-vulcanizing silicone rubber reduced with increasing concentration of the drug. For the heat-vulcanizing silicone rubber, the tensile strength was also found to decrease with increasing drug content. The extensibility after an initial reduction at low concentrations was found to increase at drug concentrations in excess of 10 mg/g. Nevertheless, the changes in mechanical properties measured are considered not to be so great as to preclude the application of drug-impregnated silicone rubbers to cerebrospinal-fluid shunting devices.
Dental materials: 1995 literature review.
This critical review of the published literature on dental materials for the year 1995 has been compiled by the Dental Materials Panel of the United Kingdom. It continues the series of annual reviews started in 1973 and published in the Journal of Dentistry. Emphasis has been placed upon publications which report upon the materials science or clinical performance of the materials. The review has been divided by accepted materials classifications (fissure sealants, glass polyalkenoate cements, resin composites, dentine bonding, dental amalgam, endodontic materials, casting alloys, investment materials, resin-bonded bridges and ceramo-metallic restorations, all ceramic restorations, denture base and soft lining materials, impression materials, dental implants, orthodontic materials and biomechanics). Three hundred and thirty articles published in 68 titles have been reviewed.