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Given the importance of bacteria in the development of periradicular lesions, the eradication of the root canal infection is paramount in endodontic treatment. This study evaluated the in vitro intracanal bacterial reduction produced by instrumentation and irrigation with 1%, 2.5%, and 5.25% sodium hypochlorite (NaOCl) or saline solution. Root canals inoculated with Enterococcus faecalis were instrumented and irrigated with the solutions tested. Canals were sampled before and after preparation. After serial dilution, samples were plated onto Mitis salivarius agar, and the colony-forming units grown were counted. Inhibitory effects of the three NaOCl solutions on E. faecalis were also evaluated by means of the agar diffusion test. All test solutions significantly reduced the number of bacterial cells in the root canal (p < 0.05). There was no significant difference between the three NaOCl solutions tested (p > 0.05). Nonetheless, all NaOCl solutions were significantly more effective than saline solution in reducing the number of bacterial cells within the root canal (p < 0.05). The three NaOCl concentrations showed large zones of inhibition against E. faecalis. The results of this study suggest that regular exchange and the use of large amounts of irrigant should maintain the antibacterial effectiveness of the NaOCl solution, compensating for the effects of concentration.

Although fungi, archaea, and viruses contribute to the microbial diversity in endodontic infections, bacteria are the most common micro-organisms occurring in these infections. Datasets from culture and molecular studies, integrated here for the first time, showed that over 460 unique bacterial taxa belonging to 100 genera and 9 phyla have been identified in different types of endodontic infections. The phyla with the highest species richness were Firmicutes, Bacteroidetes, Actinobacteria, and Proteobacteria. Diversity varies significantly according to the type of infection. Overall, more taxa have been disclosed by molecular studies than by culture. Many cultivable and as-yet-uncultivated phylotypes have emerged as candidate pathogens based on detection in several studies and/or high prevalence. Now that a comprehensive inventory of the endodontic microbial taxa has been established, future research should focus on the association with different disease conditions, functional roles in the community, and susceptibility to antimicrobial treatment procedures.

The purpose of this prospective study was to evaluate the incidence of postoperative pain after intracanal procedures based on an antimicrobial strategy. Data were examined from 627 teeth that had necrotic pulps or required retreatment. Information was obtained for each patient treated with regard to presence of preoperative pain. Occurrence of periradicular bone destruction detected by radiographs was also recorded. The operators consisted of undergraduate students, who were in their first year of clinical training. Root canals were instrumented and then medicated with a calcium hydroxide/camphorated paramonochlorophenol paste. No systemic medication was prescribed. Approximately 1 week after the initial appointment, patients were asked about the occurrence of postoperative pain and the level of discomfort was rated as no pain, mild pain, moderate pain, or severe pain. Data were statistically analyzed using the Chi-square test. Mild pain occurred in 10% of the cases, moderate in 3.3%, and severe (flare-up) in 1.9%. Postoperative pain was significantly associated with the treatment of previously symptomatic teeth without periradicular lesions (p < 0.01). No other correlations were detected between the occurrence of postoperative discomfort and other clinical conditions. There was also no difference regarding the incidence of postoperative pain between treatment and retreatment (p > 0.01). The intracanal procedures used in this study to control root canal infections showed a small incidence of postoperative pain, particularly flare-ups, even performed by inexperienced undergraduate dental students.

The purpose of the present study was to use terminal restriction fragment length polymorphism analysis and the 16S rRNA gene clone library to investigate the diversity of the microbiota associated with asymptomatic and symptomatic endodontic infections and to compare the bacterial community structure in these two clinical conditions. Samples were taken from asymptomatic endodontic infections associated with chronic periradicular lesions and from symptomatic infections clinically diagnosed as acute abscesses. 16S rRNA genes from DNA isolated from clinical samples were used to construct clone libraries or were subjected to terminal restriction fragment length polymorphism analysis. Sequence analysis of 186 clones revealed 42 taxa; 23 (55%) were uncultivated phylotypes, of which seven were unique to endodontic infections. Clone sequencing and terminal restriction fragment length polymorphism analysis revealed that the most commonly detected taxa were Fusobacterium nucleatum (including terminal restriction fragment types 1 and 2), Peptostreptococcus micros/Peptostreptococcus sp. oral clone AJ062/BS044/FG014, Prevotella species, Dialister species, Mogibacterium species, Lachnospiraceae oral clone 55A-34, Filifactor alocis, Megasphaera sp. oral clone CS025/BS073, and Veillonella sp. oral clone BP1-85/Veillonella dispar/V. parvula. Bacteroides-like sp. oral clone X083/Bacteroidales oral clone MCE7_20 and Dialister sp. oral clone BS016/MCE7_134 were detected only in asymptomatic teeth. On the other hand, F. nucleatum terminal restriction fragment type 2, Prevotella intermedia, Dialister pneumosintes, and some phylotypes were exclusively detected in symptomatic samples. Bacterial profiles of symptomatic endodontic infections generated by terminal restriction fragment length polymorphism analysis were clearly different from those of asymptomatic infections. Overall, the average number of terminal restriction fragments in symptomatic samples was significantly larger than in asymptomatic samples. Molecular analysis of the microbiota associated with symptomatic or asymptomatic endodontic infections indicates that the endodontic bacterial diversity is greater than previously described by culture methods and that the structure of the microbiota differ significantly between asymptomatic and symptomatic infections.

Data from culture studies have revealed that Enterococcus faecalis is occasionally isolated from primary endodontic infections but frequently recovered from treatment failures. This molecular study was undertaken to investigate the prevalence of E. faecalis in endodontic infections and to determine whether this species is associated with particular forms of periradicular diseases. Samples were taken from cases of untreated teeth with asymptomatic chronic periradicular lesions, acute apical periodontitis, or acute periradicular abscesses, and from root-filled teeth associated with asymptomatic chronic periradicular lesions. DNA was extracted from the samples, and a 16S rDNA-based nested polymerase chain reaction assay was used to identify E. faecalis. This species occurred in seven of 21 root canals associated with asymptomatic chronic periradicular lesions, in one of 10 root canals associated with acute apical periodontitis, and in one of 19 pus samples aspirated from acute periradicular abscesses. Statistical analysis showed that E. faecalis was significantly more associated with asymptomatic cases than with symptomatic ones. E. faecalis was detected in 20 of 30 cases of persistent endodontic infections associated with root-filled teeth. When comparing the frequencies of this species in 30 cases of persistent infections with 50 cases of primary infections, statistical analysis demonstrated that E. faecalis was strongly associated with persistent infections. The average odds of detecting E. faecalis in cases of persistent infections associated with treatment failure were 9.1. The results of this study indicated that E. faecalis is significantly more associated with asymptomatic cases of primary endodontic infections than with symptomatic ones. Furthermore, E. faecalis was much more likely to be found in cases of failed endodontic therapy than in primary infections.

SUMMARY Acute apical abscess is the most common form of dental abscess and is caused by infection of the root canal of the tooth. It is usually localized intraorally, but in some cases the apical abscess may spread and result in severe complications or even mortality. The reasons why dental root canal infections can become symptomatic and evolve to severe spreading and sometimes life-threatening abscesses remain elusive. Studies using culture and advanced molecular microbiology methods for microbial identification in apical abscesses have demonstrated a multispecies community conspicuously dominated by anaerobic bacteria. Species/phylotypes commonly found in these infections belong to the genera Fusobacterium , Parvimonas , Prevotella , Porphyromonas , Dialister , Streptococcus , and Treponema . Advances in DNA sequencing technologies and computational biology have substantially enhanced the knowledge of the microbiota associated with acute apical abscesses and shed some light on the etiopathogeny of this disease. Species richness and abundance and the resulting network of interactions among community members may affect the collective pathogenicity and contribute to the development of acute infections. Disease modifiers, including transient or permanent host-related factors, may also influence the development and severity of acute abscesses. This review focuses on the current evidence about the etiology and treatment of acute apical abscesses and how the process is influenced by host-related factors and proposes future directions in research, diagnosis, and therapeutic approaches to deal with this disease.