Micro-CT study on the removal of accumulated hard-tissue debris from the root canal system of mandibular molars when using a novel laser-activated irrigation approach

Aim To compare the efficacy of ultrasonically activated irrigation (UAI), photon-induced photoacoustic streaming (PIPS) and shock wave enhanced emission photoacoustic streaming (SWEEPS) activation for the removal of accumulated hard-tissue debris (AHTD) from the root canal system of mandibular molars when assessed using microcomputed tomography (micro-CT). Methodology A total of 30 mandibular first and second molars with joining mesial root canals containing an isthmus and a single distal canal were subjected to three micro-CT scans (before and after canal instrumentation and after final irrigation) at a resolution of 15 mu m. Mesial canals were prepared up to a ProTaper F3 rotary file, and distal canals were prepared up to a ProTaper F4 rotary file. Teeth were randomly assigned to three groups according to the irrigant activation method (n = 10): the UAI group, the PIPS group and the SWEEPS group. The final irrigation procedures were performed using a total of 15.5 mL of 1% NaOCl for each tooth with an activation time of 3 x 30 s. After three-dimensional model reconstruction and volumetric measurement of root canals, the percentage reduction (%Rd) of AHTD was calculated. The %Rd of AHTD was analysed statistically using one-way analysis of variance and nonparametric tests at a significance level of 5%. Results There were no significant differences between the three groups in terms of canal volume before or after instrumentation, or the volume of debris after canal preparation (P > 0.05). In the mesial canals, irrigation with SWEEPS reduced the overall debris by 84.31%, which was significantly more than the reduction associated with PIPS and UAI (58.79% and 50.27%, respectively). In the distal canals, the %Rd of AHTD was significantly different between PIPS and SWEEPS and between UAI and SWEEPS (P < 0.05), but was not significantly different between PIPS and UAI groups (P > 0.05). The SWEEPS was associated with a greater %Rd of AHTD than the PIPS and UAI groups. Conclusions SWEEPS was associated with significantly less debris compared than PIPS and UAI, especially in isthmus-containing mesial roots. None of the activation techniques completely removed debris from root canal systems.