Methods: Rat periapical lesions were induced in male Wistar rats (n=30, 8 weeks of age ) by unsealed pulp exposure of the lower first molars. The animals were humanely sacrificed at 0 (nonexposure control), 1, 2, 3, 4, and 6 weeks after exposure and the lower jaws were extracted. The left molars were used for immunohistochemical staining and the right molars were employed for reverse transcription-polymerase chain reaction (RT-PCR) analyses. In the histological sections, the sizes of periapical lesions were measured. Then, the periapical tissue of the mesial root was histopathologically observed and the numbers of cells immunopositive for MMP-8 and MMP-13 that appeared in the lesions were counted.
Results: Gene expression of MMP-8 was gradually increased compared to the normal state from 1 to 4 weeks, but slightly decreased at 6 weeks. Gene expression of MMP-13 was largely increased compared to the normal state from 1 to 2 weeks. At 3, 4, and 6 weeks, the expression was stronger. The size of periapical lesions gradually increased from 1 to 4 weeks, but decreased at 6 weeks. There were significant differences between normal and pulp exposure groups. Regarding immunohistochemistry, the number of MMP-13 cells expressing was significantly higher than that of MMP-8 cells expressing at 1 and 2 weeks, but not at 3, 4, and 6 weeks.
Conclusion: Expressions of MMP-8 and MMP-13 were increased as rat periapical lesions extended. It was shown that MMP-13 was expressed earlier in comparison with MMP-8. These results suggest that MMP-8 and MMP-13 might be involved in the development of rat periapical lesions.