Characteristics of Bubble Oscillations During Laser‐Activated Irrigation of Root Canals and Method of Improvement

Abstract

Background and Objectives: Laser-activated irrigation of dental root canals is being increasingly used as its efficacy has been shown to be superior compared with conventional techniques. The method is based on laser-initiated localized fluid evaporation and subsequent rapid bubble expansions and collapses, inducing microfluid flow throughout the entire volume of the cavity. The irrigation efficacy can be further improved if optimally delayed "SWEEPS" double laser pulses are delivered into the canal. This study aims to show that the irrigation efficacy, as measured by the induced pressure within the canal, is related to the double pulse delay, with the maximal pressure generated at an optimal delay. The second aim is to find a method of determining the optimal delay for different cavity dimensions and/or laser parameters. Study Design/Materials and Methods: Experiments were made in transparent models of root canals where Er:YAG laser (λ = 2.94 μm, pulse duration t p = 25 or 50 microseconds, and pulse energies up to E L = 40 mJ) was used with a combination of cylindrical and conical fiber-tip geometries (diameters 400 and 600 µm). Highspeed photography (60,000 fps) and average pressure measurements inside the canal were used for process characterization. Results: The results show that a pressure amplification of more than 1.5 times occurs if the laser pulse delay approximately coincides with the bubble oscillation time. Correlations between normalized oscillation time and canal diameter for a wide range of laser pulse energies (R 2 = 0.96) and between the average pressure within the canal and the bubble oscillation periods (R 2 = 0.90) were found. A relationship between the bubble oscillation time and the diameter of the treated cavity was found depending on the bubble oscillation time in an infinite fluid reservoir. Conclusions: The bubble oscillation time within a constrained volume can be determined based on the known oscillation time in infinite space, which offers a fast and simple solution for optimization of the laser parameters. These findings enable determination of optimal conditions for shock wave generation, and improvement of root canal irrigation at the same dose of laser energy input, leading to improved treatment efficacy and safety. Lasers Surg. Med.

Measurement of Simulated Debris Removal Rates in an Artificial Root Canal to Optimize Laser‐Activated Irrigation Parameters

“…It is to be noted that while the X‐SWEEPS modality achieved three times higher removal rate compared with AutoSWEEPS, its performance strongly depends on the chosen time delay of the second pulse. For optimal flushing rate, the X‐SWEEPS delay must approximately match the bubble oscillation time that varies depending on the treated root canal geometry [30]. When during clinical procedures no feedback or other method is available to optimize the pulse delay for particular tooth geometry, the AutoSWEEPS modality represents a more robust and preferable choice.…”

“…When using X-SWEEPS modality in clinical practice, it is important to consider that the bubble oscillation time (T B ) depends, among other parameters, on the diameter of the cavity [25,30], and that the dimensions of the access cavity vary from tooth to tooth. Therefore, the X-SWEEPS modality requires the practitioner to adjust the X-SWEEPS pulse separation T p to the dimension of the access cavity in order to obtain consistent enhancement.…”

Determination of Optimal Separation Times for Dual‐Pulse SWEEPS Laser‐Assisted Irrigation in Different Endodontic Access Cavities

“…Recently [38], it was shown that for long liquid‐filled cylindrical cavities (i.e., tubes) with diameter D cavity , the bubble oscillation time T B can be well described by a function: where K is the fitting parameter and T B.inf is the bubble oscillation time in an infinite reservoir ( D cavity ≈ ∞) for a particular set of laser and FT parameters. The ratio T B / T B.inf was found to be independent of the laser pulse energy E L , with the best fit obtained for K = 3.52 mm where the statistical coefficient of determination R 2 = 0.96…”

“…When the temporal separation ( T p ) between the two SWEEPS laser pulses is fixed using the “X‐SWEEPS” modality, the largest enhancement of shock waves and internal irrigant pressures occurs when T p does not deviate substantially from the optimal separation time ( T opt ), corresponding to the time when the second laser pulse of the X‐SWEEPS pulse pair is delivered near the end of the collapse phase of the primary bubble generated by the first laser pulse ( T opt ≈ T B ) [ 24 , 38 ].…”

“…A challenge involved in using X‐SWEEPS in dental practice is posed by the fact that the bubble oscillation time T B critically varies depending not only on laser parameters that can be controlled, but also on the endodontic access cavity dimensions that vary depending on the treated tooth, with T B being longer for smaller cavity dimensions [ 24 , 38 ]. As an improved solution, a special AutoSWEEPS laser modality was developed [ 32 , 35 , 37 ] in which the temporal separation between the pair of laser pulses is continuously swept back and forth between T p = 200 and T p = 650 µs.…”