Do instrument kinematics and the apical preparation limit influence canal disinfection and bacterial extrusion?

This in vitro research assessed the influence of the instrument kinematics (rotary and reciprocating) and the apical preparation limit on the root canal disinfection and apical bacterial extrusion. After 21 days of Enterococcus faecalis biofilm formation in 72 mesial root canals of mandibular molars, the root canals were distributed into 2 groups (n = 36) according to the systems used for preparation: ProDesign S and Reciproc. The groups were redistributed according to the limit of apical preparation (n = 11): (a) 1 mm up to the apical foramen (TL-1); (b) at the apical foramen (TL = 0); (c) 1 mm beyond the apical foramen (TL + 1). After preparation, the remaining biofilm adhered to the dentin walls at the apical third was removed by sonication. The aliquots of bacterial suspension released, and the irrigating solution leaked through the apical foramen during preparation were plated for colony-forming units (CFUs) counting. Data were statistically assessed by the Kruskal-Wallis and Dunn tests (α = 5%). Both systems promoted decontamination of the apical third, regardless the limit of apical preparation (p > 0.05). A larger quantity of bacteria was extruded from the root canals prepared 1 mm beyond the apical foramen, regardless the instrumentation kinematics (p < 0.05). The apical third of the root canal was efficiently decontaminated after preparation, regardless the instrumentation kinematics and the apical limit. However, a larger quantity of bacterial extrusion was observed when preparation was performed beyond the anatomical root canal limits.