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Notes: The first measurements of the microwave surface resistance at 18 GHz of bulk Tl-Ba-Ca-Cu-O superconductors produced by the hot isostatic pressing (HIP) process are reported. The superconducting samples, prepared by solid-state reaction with subsequent sintering and consolidation to obtain ideal density, were measured by replacing the end wall of a TE011 circular mode gold-plated copper cavity with the sample and determining the cavity Q for the temperature range 4–300 K. Results indicated that HIP samples which underwent subsequent annealing exhibit, below the critical temperature, a surface resistance approaching an order of magnitude less than copper.

Notes: The quantum-well electron barrier diode is a device whose current-voltage characteristic originates in the symmetry of the ground-state energies present in a sequence of quantum wells. In this paper, current-voltage (I-V) and capacitance-voltage (C-V) characteristics of the quantum-well electron barrier diode are presented for a number of symmetric and asymmetric configurations fabricated from samples grown by molecular-beam epitaxy. The data demonstrate that the symmetry of the quantum wells determines the symmetry of the I-V characteristic. The effect of doping on the C-V characteristic is also examined. It is shown how the effect of doping can be understood via a solution of Poisson's equation at zero bias.

Notes: The principal factors which limit the bandwidth and noise temperature of the free-electron bolometer mixer have been calculated. The minimum mixer contribution to the effective noise temperature is found to be 33Tlattice under the conditions of rf match, IF match, and constant current bias. This result is independent of the electron-lattice energy relaxation time, and can be achieved without significantly degrading the information bandwidth. The best experimental values from the literature are found to be near this predicted performance.

Notes: The aim of this study was to investigate the effect on subgingival plaque of a simplified oral hygiene regime consisting of instruction in Bass brushing without stress on interdental cleaning, scaling and root planing, in combination with subgingival pulsated jet irrigation with dilute solutions of chlorhexidine, metronidazole or placebos. Twenty-five patients, 14 women and 11 men, each with periodontal pockets ≥ 4 mm, participated in a randomized, double-blind, placebo-controlled study. The patients were assigned to 4 groups: 2 test groups (0.02% chlorhexidine and 0.05% metronidazole) and 2 placebo groups (0.01% quinine sulphate and 0.09% sodium chloride). Subgingival plaque samples were obtained from at least 4 sites in each subject on days 0 (prior to scaling and root planing), 7, 28, 56 and 84. Subgingival irrigation was terminated on d 28. Darkfield microscopy was used to assess the effects of treatment on the subgingival microflora by observing 4 morphologic groups: cocci, motile organisms, spirochetes and others (i.e. non-motile rods and filaments). All the groups showed marked beneficial changes at the end of the 28-d irrigation period, with increases in cocci and decreases in motile forms and spirochetes to less than baseline values. These beneficial effects were maintained for at least 8 weeks after irrigation was stopped. Metronidazole was more effective in reducing motile forms, but the reduction was not significant at d 84. It was concluded that pulsating monojet subgingival irrigation as part of a simplified oral hygiene program, with or without an active antimicrobial agent at low concentration, is effective in reducing the motile and spirochete portions of the subgingival microflora. These effects might be enhanced and prolonged if suitable antimicrobial solutions of higher concentration were used.

Notes: Antibody levels towards sonicated whole cell extracts of selected oral Gram negative bacteria and Actinomyces viscosus were determined in sera from patients with various inflammatory forms of periodontal disease and from healthy control individuals. Antibody titres to two (non-leukotoxin producing) strains of Actinobacillus actinomycetemcomitans were significantly elevated in patients with juvenile periodontitis. Adult patients with severe periodontitis had significantly lower IgG antibody titres to Veillonella parvula (p 〈 0.001) or A. actinomycetemco-mitans strain NCTC 9710 (p 〈 0.01) and patients with mild periodontitis had decreased IgM antibody titres to A. actinomycetemcomitans strain NCTC 10979 (p 〈 0.05) when compared with the control subjects. Young adults with severe periodontitis showed marked individual differences in their humoral responses. Analysis of data revealed that only patients with a history of juvenile periodontitis had elevated IgG antibody titres to Bacteroides gingivalis (p 〈 0.001) and to V. parvula (p 〈 0.01). Hence the profiles of antibody levels to oral microorganisms identified patients who had previously manifested classical “localised” juvenile periodontitis.

Notes: Abstract This study investigates bacterial invasion of the soft tissue walls of deep pockets from cases with adult (AP) and juvenile periodontitis (JP). Transmission electron microscopy was used to examine pocket soft tissue walls removed from extracted teeth from 5 patients with AP and 2 patients with JP. Bacteria were sparse throughout the epithelium and connective tissue, regardless of the level of tissue breakdown. However many inflammatory cells were seen, and these did appear to be located in regions of marked collagen loss. Accumulations of large numbers of bacteria were extremely rare and found only on the epithelial surface or in artefactual spaces within the deeper tissues. The findings indicate that the tissue destruction associated with periodontitis is not directly related to bacterial invasion. The sparse organisms within the pocket tissues probably result from passive entry rather than an invasive action. Under these circumstances, it would seem reasonable to suggest that bacterial metabolic products rather than the micro-organisms themselves penetrate the tissues in periodontitis.

Notes: Abstract. This study considers false results which may arise due to problems in the preparation or examination of specimens for darkground microscopy of subgingival plaque. Subgingival plaque samples obtained with a sterile curette were placed in 0.1–0.3 ml sterile full or 1/4 strength Ringer's solution: 0.85% saline, 1% gelatin in 0.85% saline, formal saline or pyrogen-free water for injection. Test slides were prepared from the original dispersion, and control slides from the corresponding sterile solution. Optimal dispersion solution, syringe dispersion frequency and the effect on motility of delay in processing samples were tested. Slides were also prepared from dispersions of 11 representative subgingival “periodontopathic” organisms. Problems in sampling included variability in counts between sites with comparable pocket depths, contamination of the sample and reduction of the sample volume after scaling. Problems in dispersion included contamination, uneven distribution of the different morphotypes and destruction of delicate organisms. Problems in slide preparation included slide contamination, limitation in the number of samples that can be assessed by one examiner at a given time without loss of activity of motile cells, and preparation of a cell monolayer. Problems in identification and counting included confusion of Brownian movements with motility, coccoid particles with cocci, spirochetes with campylobacter, flagella with flagella-like structures, size of cocci, counting of fragmented spirochetes and non-motile flagellated organisms and motile cells, and also bias in counting. Problems in morpbotype grouping included the observation that many (10 of the 11 representative) periodontitis-related organisms were in the non-motile groups and not all cells of the motile species (Campylobacter, Capnocytophaga) showed motility.The results indicate that each stage of subgingival plaque darkground microscopy, sampling, dispersion, slide preparation, counting, morphotype grouping and interpretation may lead to false results if not representative or reproducible. Procedures are suggested for the minimisation of problems in the preparation and examination of subgingival plaque specimens for darkground microscopy.

Notes: Abstract The aim of this study was to investigate the effects of a simplified system of oral hygiene, comprising Bass brushing, scaling, root planing and subgingival irrigation using a pulsated monojet oral irrigator, in patients with chronic periodontitis.After initial assessment, patients received scaling, root planing and instruction in Bass brushing and in use of a pulsated jet oral irrigator (Water Pik + Imax attachment) to irrigate subgingivally. 11 patients with 262 approximal periodontal pockets used 0.02% chlorhexidine (CH), or a placebo as the irrigating solution once daily for 28 days. Plaque index (P1I), sulcus bleeding index (SBI), and probing pocket depth (PPD) were assessed on days 0, 28, 56 and 84. Within procedure comparisons for all groups showed that the regime was highly effective in reducing P1I, SBI and PPD, improvements being maintained at least until day 84. Between procedure comparisons showed that benefits were improved only marginally by the use of 0.02% CH as the irrigation fluid. The patients found the procedure pleasant and neither injuries nor staining were noted during the study.It was concluded that this simplified oral hygiene system was effective in reducing periodontal inflammation and pocket depth, although no significant added benefit with 0.02% CH was apparent. The technique may be useful in patients who cannot achieve high levels of routine mechanical oral hygiene, particularly interdentally. The effects of using higher concentrations of chlorhexidine should be investigated.

Notes: Abstract Because interdental and subgingival sites are relatively inaccessible to mouthrinsing, they necessitate alternative methods of application of anti-plaque chemicals. These include routine oral hygiene aids, surfactants to enhance uptake and retention of antimicrobials, gels and periodontal dressings. The principal modes of application that have received attention recently, apart from the systemic route, are syringe and pulsated jet irrigation and slow release compounds. Slow release devices currently receiving attention may be classified as membrane diffusion, solution of drug in polymer and solid drug dispersed in polymer matrix. The most widespread dental instance of a slow release device appears to be the use of varnishes and resins to carry fluoride. Recent attempts at devising improved methods of antimicrobial application include the testing of materials for their biodegradability or for their potential to adhere to mucosal surfaces. It is concluded that the potential exists for antimicrobials applied directly to the site of intended action to contribute significantly to dental health, particularly when employed as components of practical oral hygiene regimes.