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Notes: The downstream near afterglow region of a hydrogen plasma is used to decompose and convert trimethylarsine (TMAs) into methylarsine homologs [(CH3)3−xAsHx, where x=1,2,3] including that of arsine (x=3). Approximately 30%, 17%, and 10% of the TMAs is converted into dimethylarsine (DMAs), monomethylarsine (MMAs), and arsine, respectively, while 28% remains undecomposed. Hydrogen is replaced by deuterium to isotopically verify that the origin of the arsenic hydrogenation occurring during gas conversion arises from both the plasma gas and fragmented hydrogen from the TMAs. Deuterium tagging of the MMAs, DMAs, and hydrocarbon byproducts is consistent with TMAs decomposition via plasma initiated CH3 radical removal and explains why the predominant light stable hydrocarbon produced is methane while ethane and acetylene account for the main higher hydrocarbons.

Notes: The downstream region of a near afterglow plasma (Δt=100 μs) has been used to decompose trimethylgallium (TMGa) and the products analyzed using a mass spectrometer. The major TMGa dissociation products with a hydrogen plasma were identified as methane and ethane while with a helium plasma ethane, ethylene, and acetylene were the main dissociation species. Time-resolved optical emission originating from the downstream reaction zone shows that decomposition of TMGa occurs primarily via photodissociation with the hydrogen plasma while both photon and metastable species (He 21 S and 23 S) contributed to the TMGa decomposition with the helium plasma. VUV transmitting and VUV absorbing windows placed between the upstream hydrogen plasma and the downstream TMGa source provided further direct evidence of the role of VUV photodissociation in the TMGa decomposition.

Notes: In situ generated arsenic hydrides are reacted downstream with trimethylgallium (TMGa), both in the presence of and in the absence of a downstream hydrogen afterglow plasma. The homoepitaxial activation energy dramatically changes from 62 kcal/mol for the pure thermal to 21 kcal/mol for the plasma-assisted growth. The carbon incorporation mechanism for the plasma-assisted growth at temperatures less than 400 °C has a distinct activation energy for carbon incorporation of 23 kcal/mol, independent of V-III ratios. At temperatures above 400 °C, the level of carbon incorporated in the films reaches a level that appears to be dependent on the gas-phase precursor V-III ratio. The activation energy of the low-temperature region is consistent with the surface decomposition of arsenic hydrides.

Notes: The purpose of this study was to determine if a classification of subgingival plaque into distinct categories of microbial forms would be beneficial for detecting differences in the severity of periodontal disease. Three thousand and thirty-two subgingival plaque samples were collected and evaluated from three different populations having 284, 160, and 180 individuals. Plaque and gingival indices, probing depth, and attachment level were measured at each sampling site. Overall, the results indicated that mean plaque index, probing depth, and loss of attachment were successively higher at sites classified into four distinct microbial categories in the order (1) “Low Motile Organism - High Cocci,” (2) “Low Motile Organism - Low Cocci.” (3) “High Motile Organism - High Motile Rods,” and (4) “High Motile Organism - High Spirochetes.” The consistent pattern of differences in severity of periodontal disease between these microbial categories suggest that microscopic interpretation of plaque may be improved by this classification.

Notes: The association between Actinobacillus actinomycetemcomitans and periodontal disease in juveniles has been well documented. The purpose of this investigation was to determine the prevalence and proportions of A. actinomycetemcomitans in supragingival and subgingival plaque samples from the maxillary first molars of a large number of young adults. The study population included 284 adults, aged 20–40, ranging in periodontal disease status from healthy to moderate periodontitis but with the majority exhibiting early periodontal disease. The clinical characteristics of probing depth, attachment level, plaque index, and gingival index were measured. Supragingival and subgingival plaque samples were evaluated microscopically for microbial forms. They were also cultured on supplemented blood agar and various selective agar media including selective media for A. actinomycetemcomitans. The prevalence of A. actinomycetemcomitans in subgingival and supragingival plaque for individuals in the population was 13.0% (37/284) and 4.9% (14/284), respectively. Proportions of actinobacilli, based on total anaerobic counts, were found at or below 1% in 87% of 47 subgingival sites from 37 subjects. Supragingival and subgingival sites with actinobacilli were compared to sites without actinobacilli. Subgingival sites with A. actinomycetemcomitans had a significantly higher mean plaque index, with 79% of these sites having a plaque index greater than 1.0 compared to 30% of sites without actinobacilli. The mean gingival index, probing depth, and attachment level of sites with actinobacilli were also higher, but not significantly, than those without. Of the microbial forms enumerated, only spirochetes had a significantly higher mean proportion at subgingival sites when compared to sites without actinobacilli. Mean proportions of the cultivable microorganisms, Veillonella spp. and Streptococcus spp., were significantly lower at sites with A. actinomycetemcomitans. Differences in the mean proportions of certain microorganisms were compared between the 47 subgingival sites with actinobacilli divided into three groups by probing depth. Mean proportions of A. actinomycetemcomitans were significantly higher at intermediate probing depths between 3.0 and 5.0 mm compared to deeper sites with probing depths above 5.0 mm. On the other hand, dark-pigmented Bacteroides spp. mean proportions were significantly higher at deeper probing depths than at either intermediate or shallow, less than or equal to 3.0 mm, probing depths. There were no significant differences in the mean proportions of spirochetes between shallow, intermediate, or deeper probing depths of the 47 subgingival sites with actinobacilli.

Notes: This paper presents suggested revisions to the American Dental Association's 1985 guidelines for acceptance of anti-gingivitis chemotherapeutic agents. The areas of study design, choice and quality control of clinical gingivitis measurements, statistical analysis, and minimum strength of effect, are addressed. The revisions articulate certain aspects of study design which were implicit in the 1985 guidelines, clarify language on cross-over designs and independence of studies, and recommend use of a United States population in at least one trial supporting a product. Separate recording and analysis of a product's effect on gingival bleeding is proposed, and quality control of clinical measurements receives enhanced emphasis. Modestly elaborated statistical reporting guidelines and strengthened approval criteria, based on size of estimated effect as well as statistical significance, are advocated.

Notes: The goal of this study was to investigate the relationship between probing depth, total microscopic counts, and specific microbial forms in subgingival plaque from young adults. Subgingival plaque samples were collected and probing depth recorded from 415 mesial surfaces of maxillary first molars in 266 individuals aged 20–40. Using dark field microscopy in a Petroff-Hausser chamber, total organisms in each sample were estimated, as well as proportions of spirochetes, motile and non-motile rods, cocci, and total motile organisms. Limits for decile ranks based on total organisms were determined and the mean percentage of each microbial form within each decile rank was calculated. Correlation coefficients (r) were computed between the dependent variables of microbial forms and the independent variables of total organisms, probing depth, and the combination of total organisms and probing depth. The percentage variability of microbial forms that could be explained by the regression of each dependent variable on each independent variable or combination of independent variables was estimated by r2. The results indicate: (1) differences in bacterial composition of subgingival plaque are associated with differences in total subgingival microorganisms and in probing depths, (2) approximately 15–20% of the variability in the proportions of microbial forms in subgingival plaque can be explained by differences in total subgingival microorganisms, (3) two to four times more variability in the proportions of microbial forms in subgingival plaque can be explained by differences in total subgingival microorganisms than can be explained by differences in probing depths, and (4) considerable variability in proportions of microbial forms in subgingival plaque remains that cannot be explained by either differences in total subgingival microorganisms or by differences in probing depths.

Notes: Abstract The purpose of this study was to determine the prevalence and distribution of 5 bacterial pathogens in subgingival plaque, their relationship with each other and probing depth. Plaque was collected from 6905 sites in 938 subjects. A bacterial concentration fluorescence immunoassay and bacterial specific monoclonal antibodies were used to determine the presence and level of P. gingivalis (Pg), A. actinomycetemcomitans (Aa), P. intermedia (Pi), E. carrodens (Ec) and F. nucleatum (Fn) in each plaque sample. The prevalence in subjects was lowest for Pg (32%) and highest for Ec (49%). The site-based frequency distribution of these bacterial species ranged from 10.3% for Pg to 18.7% for Ec. Pi and Ec were the bacterial combination most often found together in a subject (27.2%). While 64.0% of the sites were without any of the 5 bacterial species evaluated, 20.2% had only 1 of the 5 bacterial species evaluated. The remaining 15.8% of sites had at least 2 bacteria species present. There was a general linear association of the detection level of bacterial species and probing depth. The odds ratios were 3.9 (Pg). 3.0 (Aa), 4.0 (Pi). 2.7 (Ec) and 2.8 (Fn) of finding high levels of these bacterial pathogens at 〉 5 mm probing depth (p≤ 0.01). Mean probing depth at molar sites without a specific bacteria was greater (p≤ 0.01) in subjects wish a specific bacterium compared to molar sites in subjects without the bacteria. The observation that these 5 bacterial species frequently inhabit the subgingival environment, yet are not associated with advanced disease, suggest that a susceptible host is required, in addition to a “pathogenic bacteria”, before disease progression may occur.