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There is a direct correlation between the expanse of the periapical lesion, the number of bacterial strains, and the number individual bacteria within the root canal; teeth exhibiting large periapical lesions are associated with more different types of bacteria as well as higher bacterial density.

The periapical lesion results from a nonspecific infection. Microbiologic experiments have demonstrated that various bacteria are capable of eliciting periapical lesions in various ways. Experiments have also shown that combinations of bacteria, or specific bacteria, play a role in the development of periapical abscess; among these are the black-pigment-ing, gram-negative anaerobic bacteria.

How can these bacteria be eliminated most effectively? The answer is clear: by means of mechanical instrumentation (cleansing), supported by antibacterial solutions (rinsing), as well as the use of antibacterial interim dressings.

One of the most incorrect premises regarding treatment of acute apical periodontitis is that the tooth should be left open between two appointments following trepanation, regardless of the amount of purulent material that was released. There are many facts that speak against leaving a canal open: The canal will be contaminated additionally, food debris will be impacted into the canal, and otherwise avoidable appointments for treatment of the tooth must be planned. The length of time during which the tooth is left open and the number of attempts to render the tooth symptom-free are correlated positively with each other.

The goal of every successful endodontic treatment is to eliminate the bacteria and their metabolic by-products that are responsible for the existence of a periapical lesion, and to create a condition that prohibits reinfection. This is accomplished by mechanical instrumentation (cleansing), antibacterial rinsing, and an effective but biocompatible interim dressing for the time between the treatment appointments.

In cases of acute apical periodontitis, pus should be released via the root canal.

This will be successful in most cases, but in exceptional circumstances, e.g., with a blocked canal or with reduced host-response capacity, an incision through the oral soft tissues may be required. If the decision is made to leave the canal/tooth open, the working length must be determined and the canal must be completely instrumented. The patient must rinse often with saline solution in order to prevent any blockage of the trepanation opening. At the most, 48 hours later, the patient must be reappointed for closure of the coronal opening.

If drainage via the root canal is possible, following trepanation the coronal pulp is removed, the access is expansively enlarged, copiously rinsed with NaOCl and instrumented into the apical segment using a size 15 Hedstrôm file.

If no pus flow occurs, instrumentation 1 mm beyond the apex can be performed. After additional canal rinsing, the tooth is left open for ca. 20 minutes, instrumented up to file size 25, and then finally rinsed with citric acid. Using a lentulo spiral, calcium hydroxide is inserted, the tooth is closed, and the patient is reap-pointed five days later for complete instrumentation. At this time, instrumentation is performed up to the apical constriction to file size 30 (or larger), and closure with well-condensed calcium hydroxide suspension (which can remain in the canal for four to 12 weeks). If the patient remains symptom-free, the canal can be definitively filled at the third appointment.

If the intraoral soft tissue swelling is small, this treatment is usually sufficient; if the swelling in the region of the tooth is large and fluctuant, an additional soft tissue incision is recommended. There is usually no necessity for systemic antibiotic coverage.

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