The role of mechanical instrumentation in the cleaning of root canals ZVI METZGER, MICHAEL SOLOMONOV & ANDA KFIR The cleaning and shaping of the root canal is a key procedure in root canal treatment. The aim of cleaning is the removal of tissue remnants and bacterial biofilms in order to allow close adaptation of the root filling to the canal walls. In simple straight canals with a round cross-section, this aim is easily attained by mechanical instrumentation and irrigation. The task of cleaning presents a greater challenge in oval canals, curved canals, and in canal systems that contain an isthmus. In areas that are inaccessible to mechanical instrumentation, the cleaning greatly depends on the action of sodium hypochlorite, which is used to dissolve and remove all of the remaining tissues and bacterial biofilms. Traditional irrigation with syringe and needle is often ineffective in cleaning such inaccessible areas. Newer irrigation methods allow for better cleaning by facilitating a more effective flow of irrigants; nevertheless, adequate, larger, mechanical preparations are required for the effective use of these methods. An alternative approach is to use a hollow file that adapts itself to the cross-section of the canal, without excessive enlargement of the canal, thus allowing mechanical scrubbing of the walls with a continuous flow of the irrigant through the file. All cleaning methods reach their limit in cases of long narrow isthmuses that are often inaccessible to mechanical instrumentation; adequate instrumentation is, however, a prerequisite for all cleaning methods. Received 2 August 2013; accepted 22 September 2013. Introduction If root canals could be thoroughly cleaned using irrigation alone and effectively obturated, there would be no need for mechanical instrumentation (1). However, with the currently available technologies, this is not yet clinically possible (2). Various forms of mechanical instrumentation have been used over the years for “cleaning and shaping” root canals. Mechanical instrumentation is often thought of as a means to facilitate root canal obturation by “shaping” the canal to accommodate certain types of master cones or certain types of pluggers. Nevertheless, it is recognized that cleaning and disinfecting of the apical part of the canal with irrigants such as sodium hypochlorite is ineffective unless the canal is instrumented to a given size (3–9). Previously, extensive instrumentation was the hallmark of good endodontic treatment (3,6,10–12). Over the years, it became recognized that extensive removal of dentin tends to weaken the root and should be avoided (13–16). This realization led to a narrower ideal “look” of the root canal filling. The question about the appropriate amount of dentin to be removed for adequate cleaning is still debated (3–9,17). The adequate apical size and proper taper of the rotary instrument are still not settled (6,9,17,18). Recently, a new concept of mechanical instrumentation was introduced to allow effective cleaning while avoiding excessive removal of sound dentin, which potentially could lead to minimally invasive endodontic treatment. The purpose of this review is to look at the targets and challenges for effective cleaning of root canals and Endodontic Topics 2013, 29, 87–109 All rights reserved © 2013 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd ENDODONTIC TOPICS 1601-1538 87