Bone Strength in Growing Rats Treated with Fluoride: a Multi-dose Histomorphometric, Biomechanical and Densitometric Study.

Bone deformation and fragility are common signs of skeletal fluorosis. Disorganisation of bone tissue and presence of inflammatory foci were observed after fluoride (F-) administration. Most information about F- effects on bone has been obtained in adult individuals. However, in fluorosis areas, children are a population very exposed to F- and prone to develop not only dental but also skeletal fluoroses. The aim of this work was to evaluate the bone parameters responsible for the effect of different doses of F- on fracture load of the trabecular and cortical bones using multivariate analysis in growing rats. Twenty-four 21-day-old Sprague-Dawley rats were divided into four groups: F0, F20, F40 and F80, which received orally 0, 20, 40 or 80 μmol F-/100 g bw/day, respectively, for 30 days. After treatment, tibiae were used for measuring bone histomorphometric and connectivity parameters, bone mineral density (BMD) and bone cortical parameters. The femurs were used for biomechanical tests and bone F- content. Trabecular bone volume was significantly decreased by F-. Consistently, we observed a significant decrease in fracture load and Young's modulus (YM) of the trabecular bone in F--treated groups. However, cortical bone parameters were not significantly affected by F-. Moreover, there were no significant differences in cortical nor trabecular BMD. Multivariate analysis revealed a significant correlation between the trabecular fracture load and YM but not with bone volume or BMD. It is concluded that when F- is administered as a single daily dose, it produces significant decrease in trabecular bone strength by changing the elasticity of the trabecular bone.