Pathway 15-6 Primary Intraradicular Infection

Primary Intraradicular Infection

• Primary intraradicular infection is caused by bacteria in necrotic pulp tissue of untreated teeth.
• This can develop from previous pulp invasion or from new bacteria colonizing the root canal.
• Primary infections are dominated by anaerobic bacteria.
• The number of bacterial cells can range from 10^3 to 10^8 per root canal.
• Molecular studies have found a mean of 10 to 20 species/phylotypes per infected canal.
• Canals of teeth with sinus tracts can have a much larger number of diverse species.
• The size of apical periodontitis lesions is proportionally related to the number of bacterial species and cells.
• Larger apical lesions have higher bacterial diversity and density.
• The most prevalent bacterial species in primary infections belong to different genera of gram-negative and gram-positive bacteria.
• Approximately 40% to 66% of the endodontic microbiota in primary infections is composed of uncultivated species.
• The structure of bacterial communities in symptomatic teeth, including abscesses, is significantly different from asymptomatic teeth.
• The dominant species in asymptomatic versus symptomatic cases are different, and there are more species in symptomatic cases.
• Levels of specific pathogenic species, like Porphyromonas endodontalis, are significantly higher in abscesses.

Geographic Influence

• Findings from different countries often vary in the prevalence of species involved in endodontic infections.
• Studies have shown a geographical influence in the composition of the root canal microbiota.
• The factors that lead to these differences remain unconfirmed.

Microbial Ecology and the Root Canal Ecosystem

• Necrotic pulp provides a moist, warm, nutritious and anaerobic environment for bacterial growth.
• Root canal walls are nonshedding surfaces, allowing persistent colonization and complex community formation.
• The necrotic root canal is a fertile environment for bacterial growth.
• Only a limited assortment of oral species colonize the root canal, suggesting ecological determinants.
• Major factors influencing the composition of the root canal microbiota: oxygen tension, nutrient availability, and bacterial interactions.
• In the initial stages of infection, facultative bacteria dominate.
• As oxygen is depleted, an anaerobic environment develops, favoring the growth of obligate anaerobic bacteria.
• Anaerobic conditions become more pronounced in the apical third of the canal as time progresses.
• Nutrient sources for bacteria in the root canal system: necrotic pulp tissue, proteins and glycoproteins from tissue fluids and exudate, components of saliva, products of bacterial metabolism.
• The main canal, with its higher volume, harbors the highest concentration of bacteria, particularly fastidious anaerobic species.
• Shifts in the composition of the microbiota can also be dependent upon nutrient utilization.
• Saccharolytic species dominate in the early stages, then outnumber asaccharolytic species, dominating later stages.
• As infection progresses, proteins become the principal nutrient source, favoring the establishment of anaerobic species that utilize peptides or amino acids.

Bacterial Interactions

• Different bacterial species interact due to their close proximity within the root canal.
• Early colonizers play a role in dictating the composition of the community.
• Positive interactions enhance bacterial survival and allow coexistence.
• Nutritional interactions, including food webs and bacterial cooperation, improve metabolic efficiency.
• Negative interactions, like competition and amensalism, limit population densities.
• Coaggregation, a specific interaction where bacteria adhere to bacteria already attached to surfaces, facilitates colonization and metabolic interactions.

Other Microorganisms in Endodontic Infections

• Fungi are occasionally detected in primary intraradicular infections, especially Candida species.
• Archaea, often extremophiles, have been found in some but not all studies of primary endodontic infections.
• No archaea are known human pathogens, and their role in apical periodontitis is unclear.
• Viruses, being inanimate, cannot prosper in the necrotic root canal.
• Viruses have been detected in root canals only in teeth with vital pulps.
• Herpesviruses have been found in some apical periodontitis lesions, but their role in the disease is not well established.

Summary

• The bacterial composition of primary intraradicular infections is complex and influenced by numerous factors, including geographic location and bacterial interactions.
• The shift from a primarily aerobic to anaerobic environment in the necrotic root canal allows different species to dominate at different stages of infection.
• The role of other microorganisms like fungi, archaea, and viruses in endodontic infections remains unclear, requiring further research.

Endodontic Bacterial Communities

• Molecular studies using DGGE, T-RFLP, or HTS analysis have shown differences in the structure of bacterial communities in symptomatic and asymptomatic teeth.
• Symptomatic teeth, including those with abscesses, exhibit significantly different bacterial community structures compared to asymptomatic teeth.

Receptor-Adhesin Interactions

• Species can attach to each other through specific receptor-adhesin interactions.
• These interactions are often lectin-like.
• Lectin-like interactions involve a protein on one species attaching to a carbohydrate on the other.