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Azerbaycan Saytlari

 »  Home  »  Endodontic Articles 9  »  Combinations of bacterial species in endodontic infections
Combinations of bacterial species in endodontic infections
Discussion - References.



Discussion.
Anaerobic species were dominant in all root canals and constituted 87% of the isolates. Sundqvist (1992) found 90% and Gomes et al. (1994) 64% strict anaerobes. The most dominant species in our study were P. intermedia, P. micros and A. odontolyticus. These species are commonly found in root-canal infections in most studies where comparable patient material and microbial techniques have been used (Sundqvist 1992, Brauner & Conrads 1995, Gomes et al. 1996a). The Odds ratio calculation is a standard method to measure associations between microorganisms in clinical samples. However, the Odds ratio can be high, suggesting a relationship between species, whilst the sample size is very small. In these cases a wide 95% confidence interval can be present and, therefore, it is necessary to be very cautious about the interpretation of the finding. The Fisher’s exact test offers a calculation to find a relationship between two samples with very small expected frequencies. In this study higher Odds ratios were found for many combinations of bacteria. The Fisher’s exact test, however, contradicted the existence of such relationships inmost instances. When comparing the results of similar studies these factors have to be taken into account (Altman 1991).
Positive correlations between P. intermedia and P. micros and Eubacteriumwere previously found in periodontal pockets by Lewis et al. (1988) and Socransky et al. (1988) as well as in endodontic infections of the root canal (Sundqvist 1992, Gomes et al. 1994). Brook et al. (1991) found a consistent pattern of a combination of Bacteriodes spp. and Peptostreptococcus spp. in periapical abscesses. These findings are in accordance with our study where clear positive relations were found between P. intermedia and P. micros. P. intermedia and P. micros have been described as a pathogenic combination of bacterial species in experimental anaerobic infections in mice (Brook &Walker1983).
Gomes et al. (1994) and Drucker et al. (1992) found that P. oralis was associated with P. melaninogenica whilst in our study P. oralis was positively associated with P. intermedia. The confidence interval in our study, however, was very wide whilst Gomes et al. (1994) did not state the 95% confidence interval associated with the Odds ratio of12.Drucker et al. (1992) did not calculate the Odds ratio but showed a significant relationship between the species (P < 0.05).The positive relation between P.micros and A. odontolyticus was described previously by Sundqvist (1992), who found an Odds ratio of 3 between P. micros and Actinomyces spp. In our study a positive association was also found between Veillonella spp. And Bifidobacterium spp. Both isolates are not considered significant human pathogens (Slot & Taubman 1992). Veillonella parvula was described a shaving no or negative relations to other bacteria (Sundqvist1992) and is associated with less active periodontal sites (Dzink et al. 1988, Socransky et al. 1988, ). This discrepancy between results may be due to the small sample size and very wide confidence interval that was found in the present study.
Specific combinations of bacteria are found in the root canal and they may contribute to population shifts of the flora by different mechanisms of interaction. For example, one species or a combination of species might favour another by providing growth factors or by changing the physical-chemical environment. The newly developed combinations may contribute to the development of clinical signs and symptoms or to apical bone destruction.

References.

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