This study aimed to elucidate the optimum usage parameters of low reactive-level laser therapy (LLLT) in a rat incisional wound model. In Sprague-Dawley rats, surgical wounds of 15-mm length were made in the dorsal thoracic region. They were divided into groups to receive 660-nm diode laser irradiation 24 h after surgery at an energy density of 0 (control), 1, 5, or 10 J/cm2. Tissue sections collected on postoperative day 3 were stained with hematoxylin-eosin and an antibody for ED1 to determine the number of macrophages around the wound. Samples collected on day 7 were stained with hematoxylin-eosin and observed via polarized light microscopy to measure the area occupied by collagen fibers around the wound; day 7 skin specimens were also subjected to mechanical testing to evaluate tensile strength. On postoperative day 3, the numbers of macrophages around the wound were significantly lower in the groups receiving 1 and 5 J/cm2 irradiation, compared to the control and 10 J/cm2 irradiation groups (p < 0.01). The area occupied by collagen fibers in day 7 was largest in 5 J/cm2 group, followed by 1 J/cm2 group, although this difference was not significant. The day 7 tensile test demonstrated significantly greater rupture strength in healing tissues from 1 and 5 J/cm2 irradiation groups, compared to the control group (p < 0.05). Thus, LLLT with a 660-nm diode laser with energy density of 1 and 5 J/cm2 enhanced wound healing in a rat incisional wound model. However, a higher radiation energy density yielded no significant enhancement.
Keywords: Collagenous tissues; Diode laser; Low reactive-level laser therapy; Macrophage; Tensile strength; Wound healing.