Development of a periapical infection in the presence of antibiotic therapy

Coaggregation interactions between oral and endodontic Enterococcus faecalis and bacterial species isolated from persistent apical periodontitis

Interactions between Enterococcus faecalis and other species found in root canal infections might be important for the development and persistence of periapical disease. The aim of this study was to investigate the coaggregation interactions between E. faecalis clinical isolates and species previously shown to survive and induce apical periodontitis in monkeys: Peptostreptococcus anaerobius, Prevotella oralis, Fusobacterium nucleatum, and Streptococcus anginosus. Intergeneric coaggregation assays were conducted in duplicate with observations scored immediately at 0 h, 1 h and 24 h after mixing of combinations of strains. All E. faecalis strains (n = 53) coaggregated with F. nucleatum; E. faecalis did not coaggregate with P. anaerobius or S. anginosus. One strain, E. faecalis E1, coaggregated with P. oralis, with aggregates visible at 1 h. Coaggregation interactions between E. faecalis and F. nucleatum observed in this study suggest a potential role for this combination in endodontic infections.

Protective and destructive immune reactions in apical periodontitis

Apical periodontitis is initiated primarily by the mixed microflora of infected root canals. Continuous flow of bacteria and their products through the apical foramen induces influx, activation and coordinated interaction of immune-inflammatory cells within the periapical area. Successful mobilization of host defense mechanisms prevents abundant extraradicular bacterial invasion. However, anti-infective effector mechanisms are not restricted to killing the invading microorganisms but also destroy normal tissue components and induce bone absorption, resulting ultimately in the loss of the affected teeth. Moreover, autocrine and paracrine loops of stimulation may lead to the perpetuation of the local inflammatory lesion and may also alter the function of remote tissues and organs. This review attempts to summarize current knowledge about the pathogenic mechanism of apical periodontitis, focusing on the formation of a special granulation tissue that effectively fights bacteria originated from the infected pulp chamber and, by exerting this protective function, also contributes to harmful local and distant events. The dynamic equilibrium between defensive and destructive mechanisms may provide a pathobiological basis for better understanding of clinical signs and symptoms of various forms of apical periodontitis lesions and influence treatment strategy and practice.

Histological evaluation of the presence of bacteria in induced periapical lesions in monkeys

In endodontic periapical lesions, both presence and location of bacteria are controversial. Various experimental techniques have produced differing results perhaps related to potential artifacts such as contamination during specimen recovery. Our objective was to examine for bacteria in uncontaminated, undisturbed periapical lesions in an animal model. Pulp necrosis was induced by exposing molars in nonhuman primates and closing the exposure after 1 week with amalgam. Lesions developed at 18 apices. After 7 months, block sections including tooth and surrounding tissues were removed, processed histologically, and Gram stained. Bacteria, primarily Gram positive, were consistently identified in necrotic tissue in canals. Two canals demonstrated bacterial masses to the apical foramen. No bacterial colonies, only intracellular microorganisms, were seen periapically. Inflammatory lesions seemed to resist the spread of bacteria, confining them to the canal space. Bacterial masses at the apical foramen could contaminate periapical tissues during surgery or extraction and give a false positive upon microbiological sampling.

Facultative gram-negative enteric rods in persistent periapical infections

A bacteriological investigation has been made in two cases of persistent periapical infections. Neither of the two infections responded to root canal therapy including penicillin or penicillin and erythromycin. Samples were taken aseptically for bacteriological examination through and root canals. Chloroform-washed, sterile paper points were used for sampling. Cultivation was performed immediately at chairside on Kanamycin-Vancomycin laked blood agar (KVLB) and blood agar supplemented with menadione, cysteine and glucose for anaerobic incubation and chocolate agar for aerobic incubation. Enterobacter cloacae was only isolate in case 1; Klebsiella pneumoniae and enterococci were found in case 2. Obligately anaerobic bacteria were not found. The treatment was successful after antibiotic therapy based on susceptibility testing of the isolates. The route of infection by facultative enteric rods is discussed.