Laser-activated irrigation: Cavitation and streaming effects from dental lasers

Abstract

IntroductionThe aim of the present study was to assess the generation of laser-activated irrigation (LAI) with a 9,300-nm CO2 laser, a 455- and 970-nm diode laser as well as an 810- and 980-nm diode laser with and without carbon-coated “hot-tips” for improved irrigation in endodontics. Therefore, the formation of cavitation bubbles at the laser tip-ends in different liquids was evaluated and compared to the traditionally applied Er:YAG laser.MethodsThe CO2 laser was applied at different power settings at a repetition rate of 14 Hz, SIROLASE for each wavelength at 10% Duty Cycle, and WISER with both wavelengths at different power settings and wavelengths. The LAI was videotaped with a high-speed camera. To measure the streaming velocity due to cavitation, all lasers were loosely coated with carbon particles and activated in pure water. Then, due to LAI, moving particles were videotaped with the same high-speed camera set-up. To determine the streaming velocities, the movement of one carbon particle was tracked with the help of a measuring tool in ImageJP software and streaming velocities were calculated.ResultsWith both diode laser devices at four wavelengths, it was only possible to introduce clear cavitation bubbles with low-power parameters (180 mW for the SIROLASE and 200 mW average power for the WISER laser), with the black coating of the laser tips. The 9,300-nm CO2 laser produced clear cavitation bubbles with all tested parameters. Consequently, all tested lasers produced streaming of the liquid, with decreasing velocities at increasing distances from the laser tip: Er:YAG laser 6.4 m/s, CO2 laser up to 5 m/s, and diode lasers in the range of 0.01–0.09 m/s. LIA with the Er:YAG and 9,300-nm CO2 laser generated high and similar streaming velocities. The diode lasers tested generated significantly lower streaming velocities.

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“…Er:YAG and CO 2 lasers were activated within the pulpal chamber. Both lasers are very well-absorbed by water-based irrigants and introduce relatively large vapor bubbles and high streaming velocities [19]. Other investigations showed that the temperature increase of the irrigant after 20 s of activation within the coronal part of an artificial plastic root model ranged between 7°C with the Er:YAG and 15°C with the CO 2 laser with 0.4 W power input [20].…”

“…Er:YAG (Light Touch, Light Instruments Ltd, Yokneam, Israel) and CO 2 laser (Solea, Convergent dental, Waltham, MA, USA) tips were activated at the root canal entrance while the tips of diode laser SIROLASE (Sirona dental systems GmbH, Bensheim, Germany) and diode laser WISER (Lambda SpA, Brendola, Italy) were inserted up to the working length minus 2 mm and moved in coronal to apical direction in continuous helical movements at 1 mm/s (see Figure 1). Diode laser tips were coated black prior to use with carbon particles (Carbon black, acetylene 100%, compressed, 99.9+%, Alfa Aesar, Kandel, Germany) that were glued with a transparent glue-spray (Toolcraft, Conrad Electronic AG, Wollerau, Switzerland) [19]. During activation, the liquid level in the access cavity was constantly controlled and replenished when needed.…”

“…Canal walls of the positive control group were etched with phosphoric acid after mechanical preparation to open dentinal tubules to a maximum. The conventional group was rinsed with NaOCl during instrumentation and received a final rinse with EDTA and NaCl [19].…”

“…The coated laser tip heats up and increases the temperature of the surrounding liquid until it starts to boil and forms vapor bubbles. The implosion of these bubbles leads to secondary cavitation and introduces movements of the liquid [19].…”

“…Recently, a new 9,300 nm CO 2 laser system became popular in its application for dental hard tissue and surgical treatments. Research showed promising results for activation of endodontic irrigants [19].…”