EFFECTS OF ND-YAG-LASER IRRADIATION ON MONOLAYER CELL-CULTURES

Background and Objective: The clinical applications of Nd:YAG lasers o n oral soft tissues include a wide field of surgical and periodontal p rocedures. This in vitro study focuses on the histological effects of Nd:YAG-laser irradiation on a fibroblast monolayer cell culture especi ally with regard to thermal damage and cell necrosis. The results of t his basic research study provide us with clear power settings for a sa fe soft tissue laser treatment. Study Design/Materials and Methods: Tw o hundred forty multiwell cell cultures and 24 micro-slide Leighton tu bes were laser treated. Laser irradiation was performed with a commerc ial free-running pulse Nd:YAG laser and a quartz fiber with a diameter of 200 mu m on L-929 fibroblast cell cultures. The variable parameter s were pulse energy (30-120 mJ), pulse rate (20-100 Hz), power output (1.5-3.0 W), and time of irradiation (10-60 s). The cultures were anal yzed with help of vital staining, autoradiography, and cytomorphology examination. Results: Depending on the different settings the laser ir radiation caused inhibitions of the DNA metabolism rate and the cell d ivision rate, a degeneratively changed cytomorphology up to cell pykno sis. An increasing pulse energy, pulse rate, or an increased time of i rradiation created an extended diameter of the pyknotic cell zone. Con clusions: The laser beam creates an exactly bordered damage between ce lls. The cells had a very good inherent mobility, but the border betwe en eliminated and unloaded cell zone was sharp, even after an incubati on of 24 h. These stable results prove that the laser can be applied u p to a micrometer distance. With the help of cell clusters it was prov ed that the laser beam is also able to eliminate exactly one monolayer . Cells which had been covered by another cell layer (in a cluster) we re not eliminated. (C) 1998 Wiley-Liss, Inc.