Shock wave-enhanced emission photoacoustic streaming versus photon-induced photoacoustic streaming modes for clearing root canal bacteria using erbium-doped yttrium aluminum garnet lasers: An in vitro study

Background: The root canal cleaning efficacy of the photon-induced photoacoustic streaming (PIPS) mode in erbium-doped yttrium aluminum garnet (Er:YAG) lasers is controversial. Shock wave-enhanced emission photoacoustic streaming (SWEEPS), a novel mode in Er:YAG lasers, creates a strong shock wave in a narrow container. We accordingly hypothesized that it may effectively eliminate bacteria from narrow root canals. The present study aimed to compare the bacterial clearance efficacy between the SWEEPS and PIPS modes for Er:YAG lasers designed for root canal treatment. Methods: : The distal and palatal roots of 130 freshly extracted human molars were used. The smear layer was first removed by conventional root canal preparation. All samples were then sterilized in an autoclave. The samples were subsequently exposed to Enterococcus faecalis and incubated for 4 weeks to establish E. faecalis infection models. The models were divided into three groups according to the irrigation method (n = 40 per group): 3% sodium hypochlorite (NaOCl) activated using the SWEEPS Er:YAG laser mode, 3% NaOCl activated using the PIPS Er:YAG laser mode, and 3% NaOCl without activation. Results: : The bacterial clearance efficacy, based on the colony-forming unit count, was significantly higher in the SWEEPS group than in the PIPS and NaOCl groups. Moreover, scanning electron microscopy after irrigation revealed that the SWEEPS group had the least number of bacteria. Conclusions: : The SWEEPS mode is more effective than the PIPS mode for eradicating E. faecalis from root canals.