Disinfection and bacterial extrusion in mesial canals of mandibular molars prepared with intentional foraminal enlargement: an in vitro study.

The preparation limit--and, consequently, the extent of apical widening when instrumentation extends beyond the anatomical limits of the root canal--remains a controversial issue in endodontics. The purpose of this in vitro study was to evaluate the effect of intentional foraminal enlargement on the disinfection of and apical bacterial extrusion from mesial root canals of extracted human mandibular first and second molars. After 21 days of biofilm formation (inoculation with Enterococcus faecalis), 60 mesial root canals of mandibular molars were randomly distributed into 2 groups (n = 30) according to irrigation protocol: conventional irrigation (CI) or passive ultrasonic irrigation (PUI). These groups were subdivided according to apical preparation limit, which was based on the total length (TL) of the root canal (n = 10): TL-1, preparation 1 mm short of the apical foramen; TL=0, preparation up to the apical foramen; or TL+1, preparation 1 mm beyond the apical foramen. After root canal preparation, the roots were sectioned and placed in containers containing phosphate-buffered saline, and the remaining biofilm adhering to the dentinal walls at the apical third was removed by sonication to determine the amount of residual bacteria. In addition, any irrigating solution that leaked through the apical foramen during chemomechanical root canal preparation was collected in Eppendorf tubes. Aliquots of the released bacterial suspension and the leaked irrigating solution were plated to count the colony-forming units. Data were analyzed using Kruskal-Wallis and Dunn statistical tests (α = 5%). With the lowest median value of residual bacteria, PUI/TL+1 promoted significantly greater disinfection than CI/TL+1 (P < 0.05) and PUI/TL-1 (P < 0.05). Neither the irrigation protocol nor the apical preparation limit influenced bacterial extrusion (P > 0.05). In root canals with intentional foraminal enlargement, PUI was more effective than CI in eliminating biofilm without inducing bacterial extrusion.