Effect of Fluoride on Orthodontically-Induced Root Resorption In Vitro

Fluoride has been suggested to play a role in prevention of orthodontically-induced root resorption. A better understanding of the effect that fluoride has on osteoclast differentiation and mobilisation may lead to improved clinical outcomes in susceptible patients. Objective:   To investigate the effect of fluoride on osteoclast/odontoclast cell number and localisation within the periodontal ligament (PDL) in a 3D mandible slice culture model.  Method:   2mm thick mandible slices were prepared from mandibles dissected from 28 day old male Wistar rats. A calibrated force of 50g was applied to mandible slices through application of a spring prior to culture in Trowel type cultures in differing concentrations of sodium fluoride (0,3,6,9,12,and 24 mM).  Following 7 and 14 days in culture, mandibles were fixed, demineralised and processed prior to histomorphometric analysis and assessment of cell and tissue viability. TRAP staining allowed identification and localisation of osteoclast/odontoclast cells.  Numbers of TRAP positive cells were quantified through digital image analysis. Results: Tissue architecture was maintained under fluoride supplemented culture conditions at both 7 and 14 days.  Viability of the pulp cells was maintained at all fluoride concentrations, with and without orthodontic force application.  A decrease in PDL cell numbers was seen in slices cultured for 14 days, and in those cultured in fluoride concentration of 9mM and above.  Degradation of the extracellular matrix of the PDL observed with increasing fluoride level. Osteoclast/odontoclast cell number did not appear to decrease with increasing fluoride concentration, however more TRAP positive cells were located free within the PDL rather that attached to the alveolar bone with significantly increased numbers observed within the middle third of the PDL and adjacent to the tooth. Conclusion:   Increasing fluoride does not appear to effect osteoclast/odontoclast cell number within cultured mandible slices, however may influence localisation within the PDL.