Er:YAG laser promotes gingival wound repair by photo-dissociating water molecules

Objective: The aim of the present study was to show that rapid wound repair following Er:YAG treatment and its bactericidal effect can also be related to reactive oxygen species (MOS) generation in irradiated tissue. Background data: The Er:YAG laser with a wavelength of 2,940 nm (corresponding to the vibrational OH stretch frequency of water) is of great value in dental medicine, owing to its dual ability to ablate soft and hard tissues with minimal damage to surrounding structures. The relatively rapid postoperative healing time seen after ablation of the gingiva is attributed to the very narrow zone of thermal disruption. Methods: Water was irradiated with an Er:YAG laser at an energy of 100-130 mJ/cm² and 10-30-Hz pulse repetition rate The concentration of OH radicals produced following irradiation was assessed by spin trapping coupled with electron paramagnetic resonance (EPR) spectroscopy. Results: We found that the Er-YAG laser dissociates water and generates OH radicals. The concentration of radicals produced was strongly dependent on the pulse repetition rate and energy density per laser pulse. Conclusions: The dissociation of water needed to generate OH radicals is possibly due to intermolecular vibrational (V-V) energy transfer in water, competing with vibrational relaxation, thus leading to water dissociation. High amounts of oxygen radicals (e.g., hydroxyl groups) have a sterilization effect, whereas low concentrations of ROS stimulate fibroblasts, causing collagen and extracellular matrix formation. ROS formation may explain the wound healing effect of the Er-YAG laser in dentistry.