Which factor is NOT associated with the failure of a nonsurgical root canal treatment?

In the context of nonsurgical root canal treatment, having a proper apical seal is crucial for the success of the procedure. A proper apical seal helps to prevent re-infection by sealing the root canal system from the oral environment and maintaining the integrity of the treatment. When the seal is adequate, it minimizes the risk of pathogens entering the root canal after treatment, thus reducing the likelihood of treatment failure.

On the other hand, factors such as perforation, missed canals, and periodontal disease are all associated with treatment failures. Perforations can create pathways for bacteria to enter the canal system, leading to potential reinfection. Missed canals can leave portions of the tooth untreated, allowing continued disease processes that can compromise the overall success of the treatment. Periodontal disease may also contribute to ongoing infection and can complicate the healing process post-treatment.

Therefore, the presence of a proper apical seal distinctly differentiates itself from those other factors, as it is actually associated with increasing the success rate of nonsurgical root canal treatments rather than contributing to their failure.