The success of endodontic therapy depends on cleaning and shaping the root canal system.

There are two approaches to the root canal system debridement:

Start at the apex and progressively enlarge the apical portion and then work coronally with increasingly larger instruments, or start with cervical flaring of the root canal and then progress apically using smaller instruments. The instrumentation is always associated to an irrigant solution, which is why the procedure is called chemo-mechanical preparation. The aim of this study was to compare and evaluate two manual instrumentation techniques (step-back and Crown-down) using different size irrigation needles (27G y 30G) and how this influences in the irrigant behavior. The study design was experimental with a nonprobabilistic convenientce sampling, with a 48 sample simulated in standardized transparent acrylic blocks of resin which were instrumented with the different techniques already mentioned and irrigated with different needle calibers after being divided in four groups. The data was obtained through a photographic record of each stage, they were also saved in a file and electronic forms to be analyzed later. The results obtained show that the lime more frequently allows that the irrigant occupies all the length of the conduct. Lime number 30 is used when implementing the telescopic technique; this is in the fifth stage of the process. However, the lime number 55 is used when implementing the Coronal-apical technique; this corresponds to the first stage. What is remarkable when implementing the Telescopic and Coronal-apical manual techniques of instrumentation associated to the conventional irrigation using 27G or 30G caliber irrigation needles is that it does not produce an appropriate irrigant liquid in the entire apical third.