Abstract: Objective：To observe the changes of autophagy levels after delayed tooth replantation in rats and investigate the effect of autophagy in inflammatory root resorption after delayed tooth replantation. Methods： Twenty-four 4-week-old SD rats were divided into different groups. Maxillary first molars were extracted, dried for 30 minutes and then replanted into the alveolar sockets. Rats were sacrificed on day 1, 3, 7 and 28 after surgery, the inflammation infiltration situation, root resorption situation, expression of inflammatory cytokines, TNF-α and IL-1β, and expression of autophagy proteins LC3B and Beclin-1 were detected by tissue staining. Immunofluorescence staining was performed on human periodontal ligament fibroblasts (hPDLFs) treated with LPS to detect the expression of LC3B and Beclin1 at different time points. Meanwhile, the inflammation and autophagy-related gene expression in hPDLFs treated with LPS and autophagy promoter (Rapamycin) or autophagy inhibitor (chloroquine) was examined through real-time RT-PCR. Results：Massive inflammatory cell infiltration and inflammatory cytokines TNF-α and IL-1β around the root were observed on the 1st and 3rd day after surgery. On the 7th day, inflammatory infiltration level increased gradually and increased secretion of TNF-α and IL-1β was detected through immunohistochemical staining. The TRAP staining result showed obvious inflammatory resorption on the 7th day. The inflammation alleviated on the 28th day. During this process, autophagy proteins LC3 and Beclin-1 increased significantly on the 1st day after surgery, then declined on the 3rd and 7th day and increased again on the 28th days. In vitro experiments, autophagy proteins LC3B and Beclin-1 were activated in hPDLFs after LPS 24h stimulation, while inhibited after 72h LPS stimulation. The trends of autophagy proteins in vitro were consistent with the in vivo results. Expression of inflammation genes were significantly reduced in hPDLFs treated with autophagy promoter and LPS. Conclusions：Autophagy participates in the development of root inflammatory resorption after delayed tooth replantation, and may play a protective role.

Key words: [Key words] Autophagy, Delayed tooth replantation, Inflammatory root resorption