ラット抜歯窩の創傷治癒を目的とした炭酸ガスレーザー照射による隣接歯への影響

Abstract

The utility of laser irradiation has been demonstrated in basic and clinical studies, albeit with an associated risk of tissue damage. We previously tested a combination of high reactive level laser therapy (HLLT) and low reactive level laser therapy (LLLT) using a carbon dioxide laser for enhanced post-extraction wound healing and observed irreversible changes in the pulps of the teeth adjacent to the extracted tooth. The aim of this study was to elucidate the histopathological changes in the pulps of teeth adjacent to the site of carbon dioxide laser irradiation performed to achieve enhanced wound healing after tooth extraction; here we report the significance of care for the adjacent tissues in laser irradiation therapy. A total of 20 male Wistar rats (5 weeks old) were divided into an irradiation group that received HLLT combined with LLLT and a non-irradiation (control) group that did not. A tooth socket model was prepared by extracting the maxillary left first molar. HLLT and LLLT were respectively performed immediately and 1 day after tooth extraction. Laser-stimulated tissues surrounding the extracted tooth, namely, the socket and adjacent teeth, were collected from each rat both 7 and 10 days after tooth extraction. The obtained specimens were fixed in 4% paraformaldehyde, decalcified in 10% ethylenediaminetetraacetic solution, and then embedded in paraffin. Serial sagittal sections were stained with hematoxylin and eosin for histopathological examination. Laser-induced injuries, such as enamel ablation and dentin carbonization, were absent 7 days after tooth extraction in both groups. Formation of reparative dentin was observed along the rim of the laser-irradiated area in the dental pulps in the irradiation group but not the control group. Both groups showed no signs of inflammation in pulp tissues. Enamel and dentin injuries were not observed in either group at 10 days after tooth extraction, similar to the findings at 7 days after tooth extraction. Formation of reparative dentin was much more prominent at 10 days after tooth extraction than at 7 days in the irradiation group. In contrast, no formation of reparative dentin was observed at either time point in the control group. These results show that carbon dioxide laser irradiation induces the formation of reparative dentin in the pulps of teeth adjacent to the extracted tooth socket. In sum, carbon dioxide laser irradiation at the low reactive level appears to induce irreversible changes in the tissues surrounding the laser treatment site.