Molecular histological analysis on calcification of alveolar bone during healing process of chronic periapical lesion.

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The effects of Er : YAG laser irradiation and root canal medication on the periapical lesion during root canal treatment were evaluated using Wistar rats (8 weeks old and weighing 200-300g) histopathologically. After root canals were left unsealed for 1 month, root canals were irradiated using an Er:YAG laser at 2 Hz and 34, 68, and 102 mJ/pulse for 30 seconds. Non-irradiated canals prepared by a conventional method of Grossman served as controls. After calcium hydroxide was put into root canals as medication and root canals were sealed with composite resin, the effects of laser irradiation on the periodontal tissues at apical area were evaluated at 0, 2 days, 1, 2, and 4 weeks after irradiation under light microscopy after H・E, TRAP, and ALP staining. At 4 weeks after treatment, no inflammation or resorption was observed in any cases in the control or 34 mJ/pulse-irradiated groups. There was no significant difference of healing process between 2 groups. However, moderate to severe inflammation with resorption of root surface was observed in 4 of 5 cases (80%) in the 102 mJ/pulse-irradiated group, which was significantly different from the control (P<0.01). On the other hand, there was no significant difference of healing process among some intracanal medicaments. These results suggest that thermal effects on periapical tissues during root canal preparation by Er:YAG laser irradiation at infected root canals are minimal, if appropriate parameters are selected. Observation period of longer than 4 weeks will be needed in further research. A role of osteopontin as a marker on calcification process and any medicaments to accelerate calcification will be investigated.