The effect of orthodontic force on the inflammatory periodontal tissue remodeling and the expression of IL-6 in rats

Objective To study the combined effect of orthodontic force and inflammation on the periodontal tissue remodeling by evaluating the expression and distribution of IL-6 in periodontal tissue and the change of the alveolar bone of rats under the condition of orthodontic force and inflammation. Methods 60 SD rats were randomly divided into controlled group(P1),orthodontic tooth movement group (P2),periodontitis group (P3) and orthodontic tooth movement with periodontitis group (P4). 50 gram orthodontic force was loaded on the maxillary left first molars of 25 rats in P2. Experimental periodontitis were established in the other 30 rats of P3,P4. 2 weeks after the establishment of the experimental periodontitis,50 gram orthodontic force was loaded on the maxillary left first molars of P4. Immunohistochemistry and histomorphometric analysis was performed to measure the expression of IL-6 and the loss of alveolar bone of the 4 groups. Results The IL-6 expressed in a low concentration in P1. The expression of IL-6 in P2 was related with the time of orthodontic treatment,which was observed to reach a maximum on day 3 and decline thereafter to the normal standard on day 10. The expression level of IL-6 in P3 increased when periodontitis occurred. Compared with P2,the expression level of IL-6 in P4 increased and reached the maximum on day 5 and then declined slowly under the combined effect of orthodontic force and inflammation. Compared with P1,no obvious alveolar bone loss was detected in the mesial side of P2; Compared with P1 and P2,obvious alveolar bone loss was detected in the mesial side of P3 and P4. Conclusions Both orthodontic force and inflammatory stimulus can stimulate the expression of IL-6. When accompanied by periodontitis,orthodontic force can evoke an uplifting expression of IL-6. But orthodontic force can not cause severe alveolar bone loss as long as the local inflammatory stimulus was eliminated.