The purpose of this study was to research the relation between different energy patterns on the same output power and wound healing by the pulsed Nd: YAG laser irradiation. Five hairless rats were used on this study. The pulsed Nd: YAG laser was irradiated with different energy patterns on the same output power (Group 1: 60 mJ, 100 pps. Group 2: 100 mJ, 60 pps. Group 3: 200 mJ, 30 pps. ; 6 W) in a duration 5 sec. in dorsal skin of rats. Wound healing process after the pulsed Nd: YAG laser irradiation were evaluated over a period of 28 days by clinical photographs and histological observation. In the early period of wound healing (0, 1, 3 days after the laser irradiation), wound size of Group 1 was narrow compared with Group 2 and 3 by clinical photographs and histological observation. Until 14 days of healing, a difference was found between the Group 1 and the other groups. In Group 2 and 3 of laser irradiation, a delay in wound healing was observed. After 21 days of healing, an extensive reduction of the wound size in each groups was observed. This report showed, even if the laser is irradiated on the dorsal skin at the same output power, the irradiated tissues receive a severe damage and a delay in wound healing would be observed in the high energy irradiation.
