Influence of temporal delay in SWEEPS dual-pulse Er: YAG laser-activated irrigation on fluid dynamics in confined domain environment: an in vitro study

Abstract The shock wave-enhanced emission photoacoustic streaming (SWEEPS) technique delivers synchronized dual-pulse Er: YAG laser energy to enhance fluid dynamics during laser-activated irrigation. The temporal delay (Tp) between consecutive pulses is a key parameter, but its influence on fluid dynamics within a confined root canal environment remains unclear. This in vitro study investigated the effects of different Tp settings on bubble morphology and transient apical peak pressure (TAPP) in a simulated root canal model. A transparent single-rooted resin anterior tooth model (apical diameter: 0.30 mm, taper: 6%, root canal length: 12 mm) was fabricated. The root canal was filled with deionized water. SWEEPS dual-pulse Er: YAG laser irrigation (20 mJ/pulse, 20 Hz) was performed at five Tp settings: 120, 210, 300, 400, and 500 µs. Bubble dynamics within the root canal were recorded using a high-speed camera system (200,000 fps). The grayscale integral of bubble images was calculated using MATLAB as a surrogate for relative bubble volume. Simultaneously, TAPP at the root apex was measured using a high-frequency pressure sensor (50 kHz). Four repeated measurements were performed per Tp group. Data were analyzed using one-way ANOVA followed by Tukey’s HSD post-hoc test (α = 0.05). Both bubble morphology and TAPP varied significantly with Tp. At Tp = 120 µs, the bubbles generated by the first and second pulses coalesced into a single larger bubble, whereas at Tp = 300–500 µs, two independent bubbles formed sequentially. The grayscale integral (secondary cavitation volume surrogate) was significantly higher at Tp = 120 µs ((0.074 ± 0.010) ×10 6 pixel) than at 210 µs ((0.052 ± 0.012) ×10 6 pixel), P < 0.05), and significantly higher at 500 µs ((2.767 ± 0.195) ×10 6 pixel) than at 300 µs ((1.926 ± 0.06) ×10 6 pixel) and 400 µs ((1.986 ± 0.135) ×10 6 pixel, both P < 0.05). TAPP followed a similar pattern: 120 µs produced significantly higher apical pressure than 210 µs (3.520 ± 0.291 vs. 2.835 ± 0.047 kPa, P < 0.05), and 500 µs produced significantly higher pressure than 300 and 400 µs (3.398 ± 0.068 vs. 2.807 ± 0.099 and 3.128 ± 0.182 kPa, both P < 0.05). No significant differences in TAPP were observed between 120 and 500 µs (P > 0.05). In this in vitro resin root canal model with deionized water, SWEEPS dual-pulse Er: YAG laser-activated irrigation with Tp = 120 or 500 µs produced greater secondary cavitation volume and higher apical pressure than intermediate Tp values (210–400 µs), indicating that Tp significantly influences fluid dynamics under the tested experimental conditions.