It is well known that no irrigant is able to efficiently remove smear layer and organic debris. Therefore, a correct choice of two or more irrigants is essential to enhance the de-bridement effect. During root canal preparation the action of endodontic instruments on the canal walls produces a smear layer, that is compacted directly on the walls. According to several studies (11,12
) the elimination of the smear layer seems to be of great importance, since it could allow NaOCl to penetrate more easily into the dentinal tubules, thus enhancing its bactericidal action. Moreover, endodontic smear layer may affect the sealing efficiency of root canal obturation, acting as a physical barrier interfering with adhesion and penetration of sealers into dentinal tubules. This is a must when adhesive endodontic techniques, i.e. Resilon®
-based material (RealSeal®
, SybronEndo, Orange, Ca, USA) are used. 17% EDTA was used as a final irrigant, following 6% NaOCl throughout instrumentation, to effectively remove soft tissue remnants as well as the inorganic/organic smear layer. The two irrigants were not combined during instrumentation, because they could compete between themselves, reducing their properties. and showed that in most cases canal surfaces are smooth, free of pulpal remnants and hard tissue debris.
On the contrary, a significantly heavier smear layer was observed at all levels in specimens irrigated with the saline group (B). These findings are consistent with the results of other studies. All Ni-Ti rotary instrumentation techniques have been shown to produce moderate to heavy smear layer that needed to be removed with the use of EDTA and NaOCl solutions. The excellent debridement capabilities of these two irrigants, being used as shown in the present study, can be easily evaluated by the comparison of results of Groups A and B specimens. This positive results could be also due to the incorporation of tensioactive agents in the irrigating solutions to improve wettability.
The average good cleanliness of the canal walls produced by the EDTA+NaOCl irrigation technique may be also due to the TF®
crown-down (coronal-apical) preparation technique, in which the coronal and middle thirds are instrumented first, followed by the apical third. Coronal flaring enhances irrigant efficacy as it provides radicular access necessary to position the needle tip effectively. Abou-Rass and Piccinino (13
) stated that in order to be effective, irrigating needles needed to come in close proximity to the material to be removed. Moreover the portion of the canal that has already been shaped acts as a reservoir for the irrigant, to better cleanse the root canal space (3
). The greater coronal space for the irrigating solution and the prolonged contact with the canal walls could explain the statistically significant differences between debridement of the apical and coronal portions.
Regardless of the irrigants, wall surfaces of apical thirds showed a greater amount of superficial debris and smear-layer, confirming previous studies (3,14
), which have cited big challenges to the chemical cleaning of the apical portions of root canals. Anatomic complexities and minimal tissue contact, such as within narrow apical space, limit mechanical cleansing by instruments and debridement capability of irrigants (15
). It have been speculated (16
) that prolonged contact of intracanal chemicals might overcome this limited action. However, NiTi rotary instrumentation is significantly faster than hand-filing, as demonstrated by other research works (8,9
); consequently, tissue-chemical contact is shorter and solvent effect could be reduced.
instrumentation produced good shaping results, aiming at reducing tissue-irrigant contact problems. As it has been previously demonstrated in other studies (17,18
), a crown down instrumentation approach together with the enhanced quality of root canal preparation produces an improved cleanness of the root canal walls, because irrignts could have a better flow in root canal anatomy. Anyway the critical area of the apical third has always demonstrated the worst results if compared with medium and coronal thirds (17–19
). It is a well-known concept that the success of endodontic treatment depends on the canal system being thoroughly cleansed and disinfected, before three-dimensional obturation of this space. Innovative approaches or materials should be used to achieve more effective debridement. Ni-Ti rotary instrumentation gives practitioners a predetermined root canal funnel shape, eliminating all the tedious step-back previously required to create a tapered root canal shape, and saving much time over conventional methods, as well. The saved time should be spent to increase debridement during and after instrumentation (7