# Narrative Review on Methods of Activating Irrigation Liquids for Root Canal Treatment
## 4 Irrigants Activation Techniques
### Laser Activation Techniques  
Lasers utilized for activation of irrigants include diode laser, neodymium-doped yttrium aluminum garnet (ND:YAG) laser, erbium-doped yttrium aluminum garnet (Er:YAG)laser and erbium, chromium-doped yttrium, scandium, gallium, and garnet (Er,Cr:YSGG) laser. We can divide laser activation techniques based on the tip placement: Laser-Activated Irrigation (LAI in which the laser tip is positioned inside the root canal and Photon-Induced Photoacoustic Streaming (PIPS) in which the laser tip is positioned within the pulp chamber. For the latter technique, Er:YAG laser is mainly used. Moreover, lasers might be used for disinfection of the root canal walls without using irrigants. Yet again, pairing two techniques gives a superior result. Using a laser in the canal filled with NaCl1 has a significantly greater antibacterial effect than using a laser [63; 64].  
The LAI cleansing mechanism relies on cavitation in the solution [65; 66]. The tip inserted in a root canal should be composed of glass fiber with a diameter between 200 and 400 m, regardless of the laser used [66]. The root canal shall be processed until at least ISO 30 with a tool expansion of 02. The depth of tip insertion should be 1 mm less than the functional length of the canal [67]. After positioning the tip at the desired depth, the laser must be activated and 1 mm/s of fiber must be removed from the root canal [68]. In the case of broad canals during the removal of the fiber, the operator needs to make sideway, sweeping movements. It is crucial to activate the laser only during the removal from the canal and not while inserting the fiber toward the canal. This allows us to avoid the danger of processing the canal with the laser. Keeping the glass fiber in constant motion in the root canal is equally important and prevents local temperature spikes [69].  
PIPS is an activation technique in which a special Er:YAG laser tip is placed within the pulp chamber and induces cavitation within the irrigant (there is no need to position the instrument at the end of the canal to achieve the disinfecting effect [70]). High-velocity irrigating streams are created at a further distance from the source of activation in comparison with UA [71]. A movement of created follicles in the whole internal part of the multi-root tooth is visible with the laser tip placed just in the pulp chamber [66]. During canal processing, minimal instrumentation is sufficient for effective PIPS activation. It results in ISO 20/25 apical preparation without a specific taper designation, whereas EndoVac requires a minimum of 35/0.04 apical preparation. Despite this, the PIPS results in a more significant potential of pushing NaOCl through the apical foramen than EndoVac [72].  
LAI is more efficient in cleansing the root canals, especially from intracanal bacteria than conventional or UA irrigation [65; 73]. Using this type of activation allows for achieving a smoother surface of the root canal than while using UA. It translates into the creation of stronger bonding between dentin and root canal filler [74]. What is more, PIPS seems to be more effective than UA irrigation in the removal of apically located dentin residue [70]. Satisfactory removal of the smear layer by PIPS was also reported [75; 76] with a high quality of open tubules in the root canal dentin [75]. PIPS appears to be more effective than conventional or sonic activation techniques in killing the bacteria deep in the dentinal tubules [77]. No advantage in terms of disinfection was demonstrated for either LAI or PIPS [66].