Abstract: Objective: To compare the efficacy of photon-initiated photoacoustic streaming on the removal of smear layer with two power settings. Methods: 52 extracted single-rooted mandibular premolars were instrumented up to ProTaper Universal F4 and randomly divided into 4 groups (n=13) according to the final irrigation techniques: 0.3 W PIPS, 0.9 W PIPS, ultrasonic, and needle irrigation. After the final irrigation, the teeth were split longitudinally into 2 parts and observed under a scanning electron microscope. Images were taken at the coronal, middle, and apical thirds of the teeth at a magnification of 1000× and were scored in the presence of the smear layer using the Hülsmann scoring system. Results: 0.3 W PIPS and 0.9 W PIPS were comparable on the removal of the smear layer (P>0.05). Both groups were better than the ultrasound group, but the difference was not significant (P>0.05), while the difference between the PIPS and the needle irrigation was significant (P<0.05). Conclusion: 0.3 W PIPS and 0.9 W PIPS are comparable on removal of the smear layer and are better than ulrasonic and needle irrigation.

Key words: The photon-initiated photoacoustic streaming, Ultrasonic irrigation, Needle irrigation, The smear layer