The apical 3mm of an infected root canal system is considered to be the “Critical Zone” when it comes to the chemomechanical preparation. Mechanical instrumentation and chemical disinfection of the root canal system to its full length significantly affect the outcome of treatment. All endodontists agree that the irrigation phase of the root canal treatment must be accompanied by an agitation technique. These techniques include: sonic agitation (EndoActivator), ultrasonic agitation, multi-sonic agitation (promising area of research currently), and the cheapest and simplest of all, Manual Dynamic Agitation.
The following video demonstrates how the MDA technique (repeated insertion of a well-fitting gutta-percha cone to the WL at a frequency of 100 strokes/min) significantly facilitates debris removal from the apical portion of a root canal system that appears to be fully shaped and cleaned.