Within the tooth population studied, accuracy of identifying mesial root canal configuration was influenced greatly by the evaluation method and the type of anatomy. Detection of type I configurations in cleared teeth was significantly lower, whilst type II configurations were detected in all specimens by both methods. In mesial roots with variable anatomical configurations, neither CBCT nor clearing methods were accurate for detecting the actual root canal anatomy.

None of the instrumentation methods were able to completely remove root filling material. Ultrasonic activation improved the removal of root filling material in all groups.

Filling materials were not completely removed by any of the retreatment procedures. The use of xylene and PUI after mechanical instrumentation enhanced removal of materials during endodontic retreatment of anatomically complex teeth.

NaOCl alone or associated with HEBP were the most effective irrigant solutions in dissolving and killing E. faecalis biofilms.

In this Brazilian subpopulation, C-shaped canal configuration of the root canal system was found in 67% of extracted first mandibular premolars with radicular grooves. Vertucci's types I and V were the most prevalent anatomical variations. C-shaped cross-sections were more prevalent in the middle third, and the presence of apical deltas was the most common feature in the apical third.