Effects of Irradiation by Carbon Dioxide Laser Equipped With a Water Spray Function on Bone Formation in Rat Tibiae

Abstract

Background/aim: Irradiation of tissue with carbon dioxide (CO₂) laser shows a characteristic thermal effect that causes vaporization of tissue in the target region. However, the thermal effect in places other than the target region induces tissue damage. Two methods are used: high reactive-level laser therapy (HLLT), aimed at surgical treatment, and low reactive-level laser therapy (LLLT), aimed at cell and tissue activation. In both, vaporization of tissue is induced by thermal damage. A water spray function may ameliorate thermal damage from CO₂ laser irradiation. In this study, we irradiated CO₂ laser on rat tibiae with or without a water spray function and examined the effects of this technique on bone metabolism.

Materials and methods: Bone defects were created in rat tibiae by dental bur in a Bur group and by laser in laser irradiation groups with (Spray group) and without (Air group) water spray function. At 1 week postoperatively, histological analyses of tibiae were performed using hematoxylin and eosin staining, immunohistochemical staining (IHC) with anti-sclerostin antibody, and 3-dimensional (3D) observation using micro-computed tomography.

Results: Histological findings and 3D observation confirmed induction of new bone formation following laser irradiation in both the Air and Spray groups. No bone formation was seen in the Bur group. IHC revealed that the activity of osteocytes in the region of irradiated cortical bone was markedly impaired in the Air group, but osteocyte impairment was ameliorated in the Spray group and absent in the Bur group.

Conclusion: The water spray function appears effective in reducing thermal damage to tissues irradiated by CO₂ laser. CO₂ lasers with water spray function may be useful in bone regeneration therapy.

Keywords: CO2 laser; LLLT; bone formation; sclerostin; water spray function.

Figure 1. Laser device with water spray function. The water spray is seen emanating from the apex of the device (A). Laser device without water spray (B).

Figure 2. Tibial surface in the Bur group (A), Air group (B), and Spray group (C). A scratched groove is seen on the tibial surface in the Bur group (A), and carbonized layers are seen on the tibial surface in both the Air (B) and Spray (C) groups.

Figure 3. Hematoxylin and eosin (H&E) stained sections from the Bur group (A and D), Air group (B and E), and Spray group (C and F). Newly formed bone tissue (asterisks) is recognized right below the laser-irradiated regions (B, C, E and F). Bars: A-C, 200 μm; D-F, 100 μm.

Figure 4. Immunohistochemical staining of sections from the Bur group (A and D), Air group (B and E), and Spray group (C and F). Bars: A-C, 200 μm; D-F, 100 μm. Arrows indicate osteocytes expressing sclerostin.

Figure 5. Three-dimensional analysis of rat tibiae in the Bur group (A), Air group (B), and Spray group (C). Newly formed bone tissue is shown by blue color in tibiae. Bars: A-C, 1 mm.