Age-related Differences of OPG Expression and Cytokine Levels in Initial Orthodontic Bone Remodelling

Objectives: To investigate the age-related differences of osteoprotegerin (OPG) expression in rat periodontal ligament cells (PDLCs) and mediators (PGE2, IL-6 and GM-CSF) in gingival crevicular (GCF) during orthodontic tooth movement. Methods: Three 4-week (juvenile) and 24-week (adult) rats were used. The left upper first molars responded to 60g mesial-tipping force, whose alveolar tissues were prepared for in-situ hybridization to examine OPG mRNA expression. 43 juvenile patients (mean-age 11+/-0.7yrs) and 41 adults (mean-age 24+/-1.6yrs) were involved in the clinic observation. One of the lateral incisors of each patient was tipped labially. Mediator levels in GCF were determined by radioimmunoassay. Results: 1) At the tension side during experimental tooth movement, PDLCs which strongly expressing OPG mRNA attended to move to the bone surface in juvenile rat periodontal tissues, which was conformed from the initial experimental period (3h); while in adult rats, it did not show significant change on OPG expression; 2)At the compression side, where OPG expression of PDLCs remained unchanged in both groups, there were OPG positive cells lined on the bone surface in adult rats, but not in juvenile rats. In the late period (24h), osteoclasts were also observed on the alveolar bone surface in adult rats. 3)PGE2 concentrations were significantly elevated in juveniles and adults, while concentrations of IL-6 and GM-CSF were significantly elevated only in juveniles. Total amounts of all three mediators in GCF significantly increased in both groups. Conclusions: The large amount of OPG produced by PDLCs from an adult host could be related to the delay of alveolar bone turnover onset during orthodontic tooth movement. And juveniles are more responsive than adults, which agree with the finding that the initial tooth movement in juveniles is faster than in adults.Supported by Natural Scientific Foundation of China (30070821) and the "985" Foundation of Peking University Health Science Centre.