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Biomedical subjects

R N Powell

Publications and source records attributed to R N Powell.

At least 55 records · Page 3Linked to original sources
PubMed1985

Interleukin-2 production and bone-resorption activity in vitro by unstimulated lymphocytes extracted from chronically-inflamed human periodontal tissues.

Lymphocytes isolated from chronically-inflamed tissues were assessed for their ability to produce lymphokines without further stimulation in vitro. Cells were extracted from tissue obtained from 42 patients undergoing periodontal surgery. Cultures were set up in triplicate and supernatants collected after 48 h were assayed for interleukin-2 (IL-2) or bone-resorptive activity. IL-2 was assayed in the cultured supernatants from 20 patients using a previously-standardized T-cell growth assay, with maximally-stimulated peripheral blood-lymphocytes as a positive control. Bone-resorptive activity (BRA) was assessed in culture supernatants from another 22 patients using an in-vitro mouse-calvaria culture-system in which calcium release was measured with a calcium analyser. IL-2 was detected in 12 out of the 20 unstimulated cultures; BRA was detected in 14 of the 22 unstimulated cultures. There appeared to be no relationship between IL-2 production and BRA and the severity of the disease as assessed by loss of attachment. Nevertheless, it seems that most of the cells extracted from chronically-inflamed tissue were producing lymphokines which may indicate stimulation in vivo prior to cell extraction.

Adult↗
PubMed1985

The in vitro effect of retinol on human gingival epithelium. II. Modulation of Langerhans cell markers and interleukin-1 production.

The in vitro influence of retinol on the markers of gingival Langerhans cells (LC) was investigated using an organ culture system. Retinol at a dose of 5 micrograms/ml produced an increase in the density of T6-positive cells within the epithelium which peaked during the first 24 h of culture. LC HLA-DR and ATPase markers were maintained for the same period, while all markers were depressed after 72 h. These effects were not seen in explants cultured in conventional or alcohol-enriched media, in which all markers were lost in an exponential fashion. In addition to modulation of LC markers, retinol treatment also prolonged the expression of HLA-DR antigens by gingival keratinocytes. These findings, together with the augmented production of interleukin-1-like activity by retinol-treated gingival organ cultures suggest that low doses of retinol may alter immune reactions within epithelia via stimulation of both keratinocytes and LC.

Adenosine Triphosphatases↗
PubMed1985

Modulation of HLA-DR antigens in the gingival epithelium in vitro by heat-killed Fusobacterium nucleatum and E. coli lipopolysaccharide.

The in vitro influence of the periodontopathic organism Fusobacterium nucleatum (FN) on gingival tissue was examined using an organ culture system. Treatment of gingival explants obtained from periodontally diseased sites with suspensions of FN, stimulated the expression of HLA-DR antigens by Langerhans cells (LC) in a dose-dependent fashion, and produced a maintenance of the LC markers T6 and ATPase. Similar effects were seen when E. coli lipopolysaccharide (LPS) was substituted for suspensions of FN. With both FN and LPS the expression of HLA-DR by gingival keratinocytes was maintained throughout the 72-h culture period, despite the cytotoxic effects of these agents. Using a variety of immunohistological techniques and a monoclonal antibody specific for the strain of FN used, it was possible to demonstrate the uptake of FN antigens by LC within the gingival epithelium.

Cell Count↗
PubMed1985

Gingival keratinocytes express HLA-DR antigens in chronic gingivitis.

The expression of the histocompatibility antigens HLA-DR and HLA-A, B, C within periodontally diseased tissue was investigated using immunohistological and histochemical techniques. Tissue was obtained from 18 patients with periodontal disease and from 2 healthy volunteers. HLA-DR antigen was expressed by the keratinocytes of the oral epithelium in all inflamed samples but was not a feature of normal tissue where HLA-DR reactivity was confined to Langerhans cells. These results are consistent with an underlying cellular immune process. Using a variety of phenotypic markers it was possible to characterize the macrophage population within the connective tissue into 2 distinct types: an antigen-presenting cell type located subjacent to the oral epithelium and a phagocytic cell type situated deep within the connective tissue.

Chronic Disease↗
PubMed1984

The pulpal response to citric acid in cats.

Citric acid conditioning of dentine has been proposed as an efficacious treatment for promoting re-attachment after periodontal surgery. This study investigated the pulpal reactions to periodontal surgery combined with citric acid (pH 1) demineralization of exposed dentine for 3 min. 9 cats were used as the experimental animals, with each cat providing 1 negative and 1 positive control and 2 experimental canine teeth. Evaluation was over 3 observation periods, with 3 cats in each period being sacrificed at 4, 21 and 83 days. Positive control teeth, which underwent periodontal surgery combining the removal of approximately 3 mm2 of labial bone and vigorous root planning of the exposed root surfaces, displayed mild to moderate pulpal reactions during the short- and intermediate-term periods and only mild to no reactions in the long-term period. The addition of citric acid demineralization, however, resulted in 5 experimental teeth (28%) becoming abscessed or totally necrotic in the intermediate- and long-term periods. At 21 days, the frequency of adverse pulpal responses to surgery and citric acid conditioning was significantly (p less than 0.05) greater than to surgery alone. Although 4 experimental teeth were relatively uninflamed at the long-term period of observation, all showed irritational dentine formation. Penetration of exposed dentinal tubules by plaque bacteria was observed only in the citric acid treated teeth.

Acid Etching, Dental↗
PubMed1984

Surface markers of human gingival fibroblasts in vitro. Characterization and modulation by enzymes and bacterial products.

Surface markers of human gingival fibroblasts in vitro were investigated using monoclonal and heterologous antisera against a range of cell surface antigens, together with rosetting techniques to characterize surface receptors for IgG and C3. WI-38 fibroblasts and human peripheral blood monocytes were used as control cells. Human gingival fibroblasts exhibited complement receptors and beta2-microglobulin, as did WI-38 cells. Ten per cent of the human gingival fibroblasts were positive for HLA-DR antigens and additionally exhibited a granulocyte antigen not apparent on WI-38 cells. Monolayers of the gingival fibroblasts were further exposed for short periods to varying concentrations of enzymes (trypsin, collagenase and neuraminidase), bacterial extracts (lipopolysaccharide and lipoteichoic acid) and crude supra- and subgingival plaque sonicates. Surface-marker analysis was then carried out. The most noticeable effects were obtained with Vibrio cholerae neuraminidase which enhanced C3 receptor and surface antigen expression, and supragingival plaque sonicate which depressed the expression of HLA-DR and granulocyte antigens while not affecting beta2-microglobulin expression. Trypsin reduced antigen expression to a degree, but its effects were mainly on cell adherence.

Antigens, Surface↗
PubMed1984

Loss of Langerhans cells from gingival tissue maintained in organ culture.

Changes occurring in a population of Langerhans cells (LC) were investigated using human gingival epithelium maintained in organ culture. The enzyme adenosine-5'-triphosphatase together with the surface antigens HLA-DR and T6 were used to identify and quantitate these cells. An exponential fall in the expression of each of these markers was seen to occur with increasing incubation time, suggesting that a true loss of these cells is in fact occurring. HLA-DR antigen is shed from LC at a rate significantly greater than that at which LC are lost. A mathematical model which simulates the behaviour of LC within organ culture is presented, and several implications and possible explanations proposed.

Adenosine Triphosphatases↗
PubMed1984

Natural killer (NK) cell activity against human gingival fibroblasts exposed to dental plaque extracts.

Natural killer (NK) cell activity against plaque pretreated human gingival fibroblasts and against the erythroblastoid cell line K562 also pretreated with plaque extract was studied. Supra- and subgingival plaque was collected and extracts prepared by sonication for 10 to 15 minutes at room temperature. The erythroblastoid cell line K562 was given in RPMI (1640) medium, and served as the control. Gingival fibroblasts were grown from an explant of human gingiva. The K562 cells and gingival fibroblasts were incubated in subcytotoxic doses of both supra- and subgingival plaque for 18 hours prior to the NK cell assay in serum free medium. Pretreatment of the K562 cells with both supra- and subgingival plaque was found to reduce NK cell activity. On the other hand pretreatment of the human gingival fibroblasts with plaque extracts seemed to increase their sensitivity to NK cell activity. This suggests that the plaque pretreatment leads to a cytopathic change in the fibroblasts making them more sensitive to NK cell activity, or alternatively that by binding to target cells, plaque modulates the ability of NK cells to bind to, and kill these cells. Nevertheless, these results indicate that NK cell activity could play a role in tissue destruction in chronic inflammatory periodontal disease.

Cell Count↗
PubMed1983

A radiographic study of chronic periodontitis in 15 year old Queensland children.

A retrospective study was carried out to determine the frequency of early periodontal bone loss in 15 year olds as seen in bite-wing radiographs. A total of 468 radiographs of 15 year olds was examined, 246 from 1970-74 and 222 from 1978-80. The alveolar bone crest on the mesial and distal of the first permanent molar teeth was examined for radiographic evidence of early chronic periodontitis. The condition of the adjacent proximal tooth surfaces was also recorded. No significant difference was found between the two groups; 39% of the 1978-80 and 43% of the 1970-74 group showed radiographic evidence of early chronic periodontitis (P less than 0.05). Males and females showed a similar frequency of periodontal disease levels. The mesial interproximal space of the first molars had significantly higher frequencies of radiographic evidence of chronic periodontitis than the distal interproximal spaces in the two groups examined. Fewer proximal restorations with overhangs were noted in the 1978-80 group, however more proximal subgingival calculus was found in this group than the 1970-74 group.

Adolescent↗
PubMed1983

Geographic effects on dental caries prevalence and tooth loss in Australia.

Geographic effects on caries prevalence have been noted in studies in the United States, Australia and South Africa. Australia, because of its large land mass, is a useful standpoint from which to gauge such effects, particularly since countrywide data from the School Dental Service is processed centrally, and since the Australian Bureau of Statistics has recently conducted a nationwide survey of adult dental health status. Both studies reveal a distinct impact of geographical factors on dental morbidity. DMF scores in 12-yr-old children are higher in the southern states, and rates of edentulousness in 35-44-yr-olds in Tasmania (latitude 40(0)-45(0)S) are double those for the more northerly states.

Adult↗
PubMed1983

Experimental gingivitis in humans. A clinical and histologic investigation.

AN EXPERIMENTAL GINGIVITIS STUDY was carried out to relate the clinical parameters (plaque and gingival index) to the histologic appearance of the associated gingival lesions. Fifteen third-year dental students took part in the study. Following the withdrawal of oral hygiene, biopsies were taken on days 0, 4, 8 and 21 of the experimental period. A statistically significant association was found between the plaque and gingival indices and the various time intervals throughout the experimental period (P less than 0.001). At day 0, although all sites had a GI of 0, all but 2 of the 15 specimens showed some degree of inflammation. Histologically, these lesions consisted of over 60% lymphocytes, while plasma cells comprised less than 5% of the infiltrating population. Although the degree of inflammation increased both clinically and histologically throughout the experimental period, the nature of the infiltrate did not change significantly. Lymphocytes remained as the dominant cell type. In fact, no association was seen between the degree of inflammation and the nature of the infiltrating cells.

Dental Plaque Index↗
PubMed1982

A longitudinal study of isolated gingival recession in the mandibular central incisor region of children aged 6-8 years.

A 2-year longitudinal investigation of isolated gingival recession was undertaken in 42 children aged 6-8 years at the commencement of the study. Gingival inflammation was controlled by supervised tooth brushing or professional plaque control. Mandibular anterior crowding considered to have contributed to the degree of recession was untreated in 11 subjects, while in 13 subjects serial extractions had been undertaken. No attempt was made to correct frenal involvement in those subjects (9) where it might have been considered a contributing etiologic factor. After 2 years, improvement in gingival contour was most apparent in those subjects whose gingival inflammation had been controlled. This was achieved more readily with professional plaque control than with supervised tooth brushing. Improvement in arch alignment and gingival contour was greater in untreated subjects than in those receiving serial extractions. WHen gingival inflammation was controlled evidence of frenal involvement declined. Control of gingival inflammation appears to be the most important factor in the treatment of isolated gingival recession in the mandibular central incisor region.

Child↗