Periodontal Ligament Function Under Orthodontic Forces During Periodontal Inflammation

Objectives: Presence of periodontal infection during orthodontic treatment clinically leads to augmented tissue damage. Still, there is limited informaiton regarding the cellular mechanism which ties periodontal infection and orthodontic forces. The aim of the study was to investigate the functional properties of periodontal ligament cells during mechanical forces, and the fate of such processes under inflammatory conditions.
Methods: Primary human PDL fibroblasts were collected and cultured in 96-well plates. Inflammatory supernatant (sup) was prepared by taking human Neutrophils and inoculating them with Porphyromonas gingivalis. Controls included naïve neutrophils or bactria alone. Sup's were added to the PDL cells and force was induced using centrifugation vs. no-force groups (control). PDL function was investigated using proliferation assay (XTT), cell viability using annexin/PI and FACS, cell cycle using permiability treatment, PI staining and FACS. Furthermore, expression of collagen and OPG/sRANKL were tested by ELISA.
Results: Application of mechanical force on fibroblasts increased metabolic rate compared with control. This phenomenoun was reduced significantly by the presence of inflmmatory sup`s. No changes were observed in appoptosis and necrosis between the groups. Interestigly, orthodontic force shifted cell cycle to arresed (phase G0/G1). This was evident also in the cell number following force vs. no–force controls. Collagen levels after application of mechanical force were higher regardles of the presence of inflammation. Similarly, OPG and sRANK-L levels are higher in the force groups. Strikingly, inflammatory sup arrested OPG expression without any change in sRNAKL levels, resulting in a shift torwards RANKL pathway in the presence of inflammatory sup.
Conclusions: Application of mechanical force in the presence of inflammation causes fibroblasts arrest with elevation in metabolic functions, favoring RNAKL pathway. The results implies that orthodontic forces in the presence of periodontal inflammation leads to osteoclastogenesis and bone destruction, summing to exacerbation of destructive tissue processes.