Comparative bubble dynamics of plasma-mediated Nd: YAG laser-induced optical breakdown and thermally driven Er: YAG laser-activated irrigation in water

PURPOSE: Root-canal anatomy can limit irrigant access. Bubble dynamics in distilled water were examined for plasma-mediated 1064-nm Nd: YAG laser-induced optical breakdown (LIOB) and thermally driven 2940-nm Er: YAG laser-activated irrigation (LAI) to guide confined-model testing. METHODS: LIOB was tested at 100, 200 and 300 mJ/pulse and LAI at 10, 15 and 20 mJ/pulse. Ten independent bubble events per setting were imaged at 50,000 frames/s. Projected size, lifetime, frame-averaged apparent expansion rates, aspect ratio and first rebound were compared using Kruskal-Wallis and Holm-adjusted Mann-Whitney U tests. RESULTS: Chain-like plasma luminescence preceded LIOB bubble formation. Median primary equivalent diameters were 3.21, 4.39 and 4.72 mm in LIOB and 2.24, 2.60 and 2.89 mm in LAI. The LIOB increment was smaller at 200-300 mJ than at 100-200 mJ. Axial apparent expansion was lower and transverse expansion generally higher with LIOB. Rebound-to-primary ratios were 0.65-0.74 for LAI and 0.57-0.61 for LIOB, while absolute rebounds were larger with 200/300-mJ LIOB. CONCLUSION: Under the tested, non-energy-matched configurations, LIOB and LAI produced different bubble sequences and growth patterns. The results provide a free-water benchmark for confined-model experiments, but do not establish pressure safety, cleaning efficacy or superiority.