In vitro sodium fluoride exposure decreases torsional and bending strength and increases ductility of mouse femora.

Fluoride exposure in vivo can reduce the material strength of bone, an effect that has been attributed to a change in mineral structure. An in vitro model of fluoride exposure offers the potential to study directly the effects of fluoride on bone mineral. Previous investigators have reported that soaking bones in sodium fluoride in vitro reduces bone strength. However, long soaking times and the absence of physiological buffering ions from their treatment solutions may have caused mineral dissolution that contributed to the decrease in bone strength. Our objectives were to further characterize the effects of in vitro fluoride exposure on bone mechanical properties and to determine if the changes reported in previous studies of bovine cortical bone would be observed for whole rodent bones. We soaked 60 mouse femora in sodium fluoride solutions, with and without physiological buffering ions, and evaluated their torsional and bending properties. Fluoride soaked bones had a 30-fold increase in fluoride content and a 23% increase in water content compared to controls. These changes were associated with average reductions in ultimate load of 45%, reductions in rigidity of 70%, and increases in deformation to failure of 80%. The effect of fluoride was similar for bones treated in buffered and non-buffered solutions, and was observed in both torsion and bending. Our findings confirm those of previous studies and highlight the strong effect that in vitro fluoride exposure has on bone mechanical properties. The in vitro model of fluoride exposure offers a tool to further study the effects of ion substitution in bone.