Bacterial taxonomy, which began as a largely intuitive process, has become increasingly objective with the advent of numerical taxonomy and techniques for the measurement of evolutionary divergence in the structure of semantides, i.e., large, information-bearing molecules such as nucleic acids and proteins. These developments have forced the

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A total of 78 bacteriological samples were taken from the supragingival tooth surface after superficial cleaning with toothpicks or from the periodontal sulci of 42 affected sites in 21 adolescents or young adults with severe generalized periodontitis. Of 190 bacterial species, subspecies, or serotypes detected among 2,723 isolates, 11 species exceeded 1% of the subgingival flora and were most closely associated with the diseased sulci. Eleven others were also sufficiently frequent to be suspect agents of tissue destruction. Many of these species are known pathogens of other body sites. In addition, 10 species of Treponema were isolated. One of these and the "large treponeme" were also more closely associated with severe periodontitis than they were with healthy sites or gingivitis. There were highly significant differences between the composition of the flora of the affected sulci and the flora of (i) the adjacent supragingival tooth surface, (ii) the gingival crevice of periodontally healthy people, and (iii) sites with a gingival index score of 0 or 2 in experimental gingivitis studies. The floras of different individuals were also significantly different. There was no statistically detectable effect of sampling per se upon the composition of the flora of subsequent samples from the same sites. The composition of the supragingival flora of the patients with severe generalized periodontitis that had serum antibody to Actinobacillus actinomycetemcomitans was significantly different from the supragingival flora of patients without this serum antibody. However, there was no statistically significant difference in the composition of their subgingival floras.

Statistical comparisons of the floras associated with juvenile periodontitis, severe periodontitis, and moderate periodontitis indicated that differences in the bacterial compositions of affected sites in these populations were not statistically significant. The subgingival flora of affected juvenile periodontitis sites was statistically significantly different from the adjacent supragingival flora and from the subgingival floras of people with healthy gingiva and of children with developing (experimental) gingivitis. However, the subgingival flora of affected juvenile periodontitis sites was not significantly different from the flora of sites with gingival index scores of 1 or 2 in adults with developing (experimental) gingivitis. Of 357 bacterial taxa among over 18,000 isolates, 54 non-treponemal species, 2 treponemal species, and mycoplasma were most associated with diseased periodontal sulci. These species comprised an increasing proportion of the flora during developing gingivitis * Corresponding author.

There is a perception of conflicting data and opinions among research laboratories that are studying periodontal microbiology. In response to this perception I was asked to discuss recent literature in this field at the 1986 Annual Meeting of the American Association of Dental Research. This review is based on that discussion which primarily concerned all of the relevant papers that were available to me and that had been published in the last 2 years (1984 and 1985). In order to determine what the data (rather than what our biases) may tell us, accurate comparisons of published reports in this field require an appreciation of the reasons for different results in different laboratories. Therefore, before we compare data, let's consider some of the reasons why results from different laboratories may differ. The periodontal flora is complex. We have found over 325 distinct bacterial species in the human gingival crevice (1). Many of these species have never been formally described, most of them are ignored by some laboratories, identified differently by others, or lumped together in various groups by still others. Some of the predominant species have special growth requirements and are not detected on some media that are widely used. Identification criteria differ among laboratories. Even with rigorous testing, identification of some species is questionable. With minimal testing it is even less reliable.

SUMMARY Adolescence is often described as a period of heightened reactivity to emotions paired with reduced regulatory capacities, a combination suggested to contribute to risk-taking and susceptibility to peer influence during puberty. However, no longitudinal research has definitively linked these behavioral changes to underlying neural development. Here, 38 neurotypical participants underwent two fMRI sessions across the transition from late childhood (10 years) to early adolescence (13 years). Responses to affective facial displays exhibited a combination of general and emotion-specific changes in ventral striatum (VS), ventromedial PFC, amygdala, and temporal pole. Furthermore, VS activity increases correlated with decreases in susceptibility to peer influence and risky behavior. VS and amygdala responses were also significantly more negatively coupled in early adolescence than in late childhood while processing sad and happy versus neutral faces. Together, these results suggest that VS responses to viewing emotions may play a regulatory role that is critical to adolescent interpersonal functioning.

From replicate trials of experimental gingivitis in four periodontally healthy subjects, 166 bacterial species and subspecies were detected among 3,034 randomly selected isolates from 96 samples. Of these bacteria, Actinomyces naeslundii (serotype III and phenotypically similar strains that were unreactive with available antisera), Actinomyces odontolyticus (serotype I and phenotypically similar strains that were unreactive with available antisera), Fusobacterium nucleatum, Lactobacillus species D-2, Streptococcus anginosus, Veillonella parvula, and Treponema species A appeared to be the most likely etiological agents of gingivitis. Statistical interpretations indicated that the greatest source of microbiological variation of the total flora observed was person-to-person differences in the floras. The next greatest source of variation was the inflammatory status of the sample sites. Person-to-person differences were smallest at experimental day 4. The floras became more diverse with time and as gingivitis developed and progressed. Analyses indicated that sequential colonization by certain species was repeatable and therefore probably predictable. Variation was relatively small between replicate trials, between two sites on the same teeth sampled on the same day, and between the same sites sampled at the same relative time in a replicate trial.