Changes in human periodontal ligament during orthodontic tooth movement

Introduction Orthodontic tooth movement is the result of a biological response to interference by an externally applied force. The aim of this study was to evaluate periodontal ligament (PDL) collagen types I and IV, fibronectin and vascular endothelial growth factor (VEGF) modification, induced by application of a precalibrated and constant orthodontic strength at different stages of treatment. Materials and methods For the study we utilized a coil spring NiTi 50 gr. and in vivo samples of 20 maxillaries and mandibolar premolars of patients aged from 13 to 18 years subject to orthodontic treatment. These teeth was extracted at 1, 7, 14, 21 and 28 days from application of force respectively. The extraction of the PDL was effectuated scarifying the radicular surface on the pressure and tension side. The results were compared with periodontal ligament samples of the normal homologous teeth (control). Section were observed and photographed using confocal microscope. Were analyzed fluorescence intensity and compared with the control group. Result The signal of type I collagen is negative in tension and pressure side after 1 day, showed an increased respect to control, in the tension and pressure side, until 7, 14 and 21 days . After this stage in both sides maintained the same values of the control. The immunofluorescence of type IV collagen is negative, in both sides, after 1 and 7 days. At 14, 21 and 28 days from treatment, increased gradually in pressure side and maintained the same values of the control in tension side . The observation of fibronectin showed strongly immunofluorescence at all stages of treatment. After 1 and 7 and 14 days the immunofluorescence of VEGF is negative in pressure side, and positive in tension side. In the last observation periods at 21 and 28 days, VEGF signal showing, in both sides, significant increase when compared with the control. Conclusion These findings suggest that: The increase of collagen type I and fibronectin could indicate that the solicitation by orthodontic force could determinate an increase of metabolic activity in the periodontal ligament. The rapid modification after the start of tooth movement, suggest that VEGF may be involved in the early stages of periodontal remodeling during orthodontic tooth movement, when occur rapid changes in local blood circulation. The initial decrease of collagen type IV, indicate a loss of vascular component in the early stages of movement in fact this protein is localized in perivessel zones.