Abstract: Objective To compare the histologic appearance and the ultrastructure of fibroblast in the healing of ultrapulsed CO_2 laser and scalpel incisions of rats.To explore the mechanism of the ultrapulsed CO_2 laser in the delayed the wound healing;and that to provide a theoretical support for its clinical application.Methods Six W power levels ultrapulsed CO_2 laser and a scalpel were performed in the skin to form two incisions on each of the total seventy two male SD rats.Wounds were harvested at 0,1,2,3,5,7,10,15 and 20 days schedules.Each specimen was prepared for staining with haematoxylin and eosin.Fibroblast of every sections were counted and evaluated independently;and observed the ultrastructure of the fibroblast at 3,5,7,10,15 and 20 days schedules by electron-microscope.Results The average time for the incisions closure of the ultrapulsed CO_2 laser at 6 W level was 12.81 days when the parallel scalpel incisions which healed significant earlier(P<0.01),which healed at 8.94 days.The generation of fibroblasts was inhibited at 5 days,the number of the laser group at 6 W level was(76.625 0±7.153 92),which was less then the scalpel group(101.406 3±20.557 82). There was statistically significant difference(P<0.05).In different periods of wound healing,there were different distribution of different types of fibroblasts by electron microscope.Conclusion The ultrapulsed CO_2 laser may delay the wound healing, due to power setting-dependent tissue thermal damage which lead to the change of the phase on the generation of fibroblast, ultrastructural changes and the inhibition of fibroblasts.

Key words: Ultrapulse CO_2 laser, Healing delay, Fibroblasts, Ultrastructure