Microdamage accumulation in bone is one of the mechanisms for energy dissipation during the fracture process. Changes in the ultrastructure and composition of bone constituents due to aging or diseases could affect microdamage accumulation. Low concentration(1 m M) of sodium fluoride(Na F) has been used in this study to investigate the effect of ultrastructural changes on microdamage accumulation in mouse tibias following free-fall impact loadings.Twenty-two tibias were divided randomly into control and Na F-treated groups. Free-fall impact loading was conducted twice on each tibia to produce microdamage. The elastic modulus of Na F-treated tibias decreased significantly after the impact loadings, while there was no significant difference in the modulus of untreated samples between pre- and post-damage loadings. Microdamage morphology analysis showed that less and shorter microcracks existed in Na F-treated tibias compared with control bones. Meanwhile, more and longer microcracks were observed in tensile regions in untreated samples compared with that in compressive regions, whereas no significant difference was observed between tensile and compressive regions in Na F-treated bones. The results of this study indicate that more energy is required to generate microcracks in Na F-treated bone thanin normal bone. A low concentration of fluoride treatment may increase the toughness of bone under impact loading.
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