ラット脛骨組織の骨形成能に対する炭酸ガスレーザー照射の影響について

抄録

The reactions of cells and tissues following CO₂ laser irradiation are classified into two types: photobiodestructive reaction and photobioactive reaction. It has been suggested that photobioactive reaction can simulate mechanical force, which is used to treat bone disease because bone remodeling is very sensitive to mechanical force. This study histologically evaluated the responses of bone following low-level laser treatment (LLLT) by CO₂ laser in rattibiae. The left tibia and right tibia of each rat received injury by CO₂ laser irradiation and dental bur, respectively. CO₂ laser irradiation was applied for 1.0 second (calculated energy density, 139.8J/cm²). The injury induced by dental bur was approximately 1.0mm in diameter and 0.5mm in depth. On days 3, 5, 10, 15, and 20 after injury, tibiae were removed and serial sections were prepared for osteoid staining (Yoshiki's method) and in situ hybridization to detect mRNA expression of type I collagen, osteopontin (OPN), and osteocalcin (BGP). The sections from tibiae on day 5 after injury were prepared for immunohistochemistry of type II collagen. The specimens on day 20 after injury were examined for bone mineral density (BMD) using dual energy X-ray absorptiometry. None of the sections from tibiae treated by dental bur throughout the experimental period exhibited histological features of newly-formed bone within the marrow cavity. However, sections from tibiae on day 5 after laser irradiation exhibited osteoid deposition within the marrow cavity subjacent to the laser treatment site, and woven bones were formed within the marrow cavity subjacent to the site on day 10 after laser irradiation. The woven bones transformed into lamellar bone in the marrow cavity on day 15 after laser irradiation and finally made contact with the original cortical bone surface subjacent to the laser treatment site. In situ hybridization of the sections from the specimens treated with laser demonstrated that type I collagen, OPN, and BGP mRNA were expressed in the osteoblasts of the newly-formed bone matrix. Type I collagen mRNA expression was recognized in all specimens after laser irradiation throughout the experimental period. However, OPN mRNA expression was recognized in the specimens on days 3, 5, and 10 after laser irradiation, whereas BGP mRNA expression was recognized in the specimens on days 10, 15, and 20 after laser irradiation. BMD of tibiae treated with CO² laser was higher than that of tibiae treated with dental bur on day 20 after the treatments. No evidence of type II collagen expression was found in the newly-formed bone matrix by laser irradiation. These results indicate that LLLT by CO₂ laser accelerates new bone formation within the marrow cavity subjacent to the laser treatment site, and that this bone formation occurs by membranous ossification. The present study suggests that LLLT by CO₂ laser can be used in the treatment of bone.