Laser-activated irrigation using pulsed erbium lasers: principles and physical basis

Aim: To discuss the fundamentals and physical principles of laser-activated irrigation using pulsed erbium lasers. Summary: In recent years, the use of pulsed erbium lasers to activate root canal irrigants within the root canal system has witnessed increased attention. Promising in vitro results in terms of disinfection and removal of intracanal debris and smear layer underlie this interest. Operating such pulsed erbium lasers however is not always straightforward, since the laser allows many parameters to be adjusted, all of which affect the interaction between the beam and the irradiated target. When pulsed erbium lasers are operating within aqueous liquids, different physical phenomena occur around the fibre tip. First, there is the formation of vapour bubbles (cavitation) due to superheating and boiling of the liquid surrounding the fibre tip upon absorption of the laser energy. These bubbles vary considerably in size, shape, location and life span, depending on the fibre tip geometry (flat versus conical fibre tips) and pulse parameters such as pulse length and energy. A second phenomenon is the occurrence of shock waves upon implosion of the vapour bubbles, where the potential energy of the bubble is converted into acoustic energy. Third, secondary cavitation bubbles can be seen long after the laser pulse has terminated. These phenomena are explained and related to physical laws in light of its endodontic application. Key learning points: - pulsed erbium lasers produce vapour bubbles, shock waves and secondary cavitation when emitting in aqueous liquids - these explain the cleaning action within the root canal - bubble shape and dynamics are influenced by fibre tip geometry and pulse parameter