Biomedical subjects
Publications and source records attributed to R M Browne.
A case of malignant calcifying epithelial odontogenic tumour is reported in a 75-year-old man. Evidence of local tissue invasion and lymph-node metastasis is presented. Immunoperoxidase studies of the neoplastic cells and tumour amyloid were negative for a variety of antigens, including the epithelial markers CEA and keratin. The histological and clinical findings are discussed.
Glycosaminoglycans and proteoglycans were analysed in keratinizing and nonkeratinizing odontogenic cyst fluids. Hyaluronic acid showed the highest incidence and abundance amongst the glycosaminoglycans detected. Appreciable amounts of chondroitin-4-sulphate were also observed, particularly in the dental cysts, with lesser amounts of the other glycosaminoglycans. Heparan sulphate showed a higher incidence and abundance in the keratocyst than the other cysts, whilst chondroitin-6-sulphate could not be detected in any of the cysts. A considerable proportion of the glycosaminoglycans of the fluids appeared to be complexed with protein and was released only after proteolytic digestion. The origin of these macromolecules is uncertain although it is likely that they are derived from both the connective tissue and the epithelium of the cyst wall.
The histological changes following removal of 2 cm discs of buccal mucosa by CO2 laser and conventional surgery were studied over a period of 42 days. The laser wound differed from the conventional wound: there was minimal damage to the adjacent tissue; initially a coagulum of denatured protein formed on the surface; the inflammatory reaction was less; fewer myofibroblasts were present and there was little wound contraction; less collagen was formed and epithelial regeneration was delayed and more irregular.
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The cytotoxic effects of zinc phosphate and silicate cements, Concise composite and zinc oxide/eugenol were evaluated after 24 h in an in vitro system which simulates the clinical usage of the material, and the results compared with those using phenol. Data of gross changes affecting cell viability placed these materials in ranking order of increasing severity: Concise less than zinc phosphate less than Silicap much less than zinc oxide/eugenol. More discrete changes involving alterations in enzyme cytochemistry were assessed and the significance of the results discussed. The presence of dentine powder in the system reduced the cytotoxic effects on these materials.
The in vitro cytotoxicity of two glass-ionomer cements--ASPA and ChemBond--was compared using a model cavity system which simulates the in vivo situation. Both materials were cytotoxic to fibroblasts and macrophages, although differences were observed in the time scale and magnitude of the response elicited.
Interpositional autogenous bone grafting procedures were performed in the mandibles of 12 beagle dogs to assess cell survival within the graft and the superiorly repositioned alveolus, and to monitor the remodeling process. Histologic and radiologic results indicated that the grafts were well accepted and that new bone was rapidly laid down on their trabeculae. However, the osteocytes within the autografts generally did not survive. There was no evidence of necrosis of the superiorly displaced alveolus, nor any resorption of its surface cortex, and it rapidly united with the autograft and the mandible to produce a stable structure. This study confirms that the lingual pedicle of soft tissue is adequate to maintain the viability of the superiorly repositioned alveolus or segment and to allow rapid remodeling of the autogenous bone graft.
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Densely sintered calcium hydroxyapatite has previously been shown to be biocompatible and stable. Its possible role in jaw surgery was investigated using a clinically analogous animal model. The apatite was implanted into the mandible of twelve dogs for 12 weeks, and the healing assessed radiologically and histologically. The new bone which was deposited directly onto the surface of the implants bonded them firmly to the adjacent tissues. There was no fibrous tissue between implant and bone. This material appears to be a suitable substitute for autogenous bone when used as inert 'space filler' in maxillo-facial surgical procedures.
This study compared autogenous bone, freeze-dried homografts, and hydroxyapatite in interpositional grafting of the mandible in beagle dogs. Healing was assessed radiologically and histologically. Results showed that the rate of incorporation of the autografts was greater than that of the homografts, and at both 4 and 12 weeks healing was more advanced. There was also rapid healing around the hydroxyapatite grafts, which became firmly bonded to the surrounding bone. The apatite was not resorbed, and new trabeculae of bone had been deposited onto much of its surface. This investigation confirms that hydroxyapatite is well tolerated and may be a suitable substitute for autogenous bone for augmentation of the atrophic mandible.
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In vitro methods for the biological evaluation of dental restorative materials are discussed, with particular reference to the type of cells used, the physical state of the test material, the method of establishing cell-material contact, and the criteria of cytotoxicity. It is postulated that in vitro methods should provide a reliable assessment of the toxicity of dental restorative materials, but since the current in vitro methods do not mimic in vivo conditions sufficiently closely, the correlation between in vitro and in vivo results is at present poor. The development of in vitro methods more closely simulating in vivo circumstances is advocated.