# Narrative Review on Methods of Activating Irrigation Liquids for Root Canal Treatment
## 3 Types of Irrigants and Irrigation Protocols  
Root canal irrigation during the endodontic treatment aims for the removal of remaining pulp, bacteria, smear layer, and other contaminations. The literature describes irrigation with sodium hypochlorite (NaOCl) in the concentration of 1-6% as a golden standard in endodontics [5], because of its antimicrobial activity, ability to inactivate intracranial bacterial toxins, and to dissolve the organic component of the smear layer [6]. The advantage of this irrigant is its ability to lubricate the root canal with a quick onset of action [7]. However, one needs to be aware of the cytotoxicity of NaOCl when the solution accidentally penetrates  
Figure 1: Schematic division of irrigants activation techniques. into the periapical area or reaches the soft tissue [8]. To prevent the last complication the procedure must be performed with the help of a rubber dam. A dried-out canal should not be subjected to mechanical processing [9]. Working in a dry environment may cause the instrument to break or the physiological apex to end up blocked with dentin debris. While using endodontic instruments it is advised to use an aqueous solution of NaOCl, pure distilled water, or designated lubricants with antibacterial properties [10]. According to the literature, aqueous solutions may be used instead of ready-made lubricants. They are decreasing both the torsional loading and the force generated by nickel titanium (NiTi) instruments during operation [9; 11]. Between the usage of different tools, it is advised to irrigate the root canal with 2 mL of NaOCl [12]. According to reports, NaOCl does not change the surface structure of NiTi instruments with corrosion and does not increase the risk of fracture [13]. The smear layer is composed of organic and inorganic material and is generated during instrumentation. As substances that remove the smear layer, we may include sodium hypochlorite in concentrations of 1% to 6%, which dissolves only organic material, and chelating agents that remove the inorganic portion of the smear layer (Ethylenediaminetetraacetic acid--EDTA in concentrations of 10% to 19% and citric acid in concentrations of 10% to 50%) [13; 14; 15]. Chelating agents are usually advised to be used in the final part of the irrigation protocol [15]. Numerous clinicians identify chlorhexidine (CHX) as an antibacterial agent. Due to the variety of compounds used in endodontic treatment, the procedure must be carried out with the aid of a rubber dam. Many authors do not recommend chelating compound irrigation during root canal processing. It may result in root dentin erosion [16]. Studies acknowledge the importance of chelating agents but suggest that in order to reduce their destructive effects on dentin, they should be applied in small volumes (1 mL) and for a short period of time (1 min) [17; 18]. Using ultrasonic activation (UA) and EDTA irrigation, it is possible to remove the smear layer and contaminations in the apical region of straight root canals in 1 min (lack of difference in comparison with 3 min of activated irrigation) [19]. Irrigation for 10 min with EDTA resulted in excessive peritubular and intrathular dental erosion [18]. After removing the smear layer with the aforementioned solutions, the exposed root canal wall is repeatedly rinsed with NaOCl or CHX to induce bactericidal activity [20]. There is no consensus among researchers regarding the optimal concentration of NaOCl solutions for irrigation. Some studies suggest that a concentration of 5.25% is superior to the eradication of _E.facetalis_ from infected root canals in comparison to 2.5 and 0.5% concentrations (without activation) [21]. On the contrary, another research indicates that there are no significant differences between concentrations. As antibacterial factors, it rather suggests frequent delivery of new liquid and use of relatively large volumes of the solution by the operator [22]. For the final irrigation protocol, some clinicians add CHX solution.