Effect of fluoride dosage on bone density, sonic velocity, and longitudinal modulus of rabbit femurs

Summary

Relationships between the fluoride dosage administered to weanling New Zealand white male rabbits and some mechanical properties of the compact bone were investigated for a wide range of dosages. The measured quantities were density, longitudinal sonic velocity in the radial direction, and fluoride ion concentration in compact bone. The longitudinal elastic modulus was estimated from the product of the density and the square of the sonic velocity. The relative static load stress was estimated from the ratio of the final body weight to the cross-sectional area of the femur. These measurements and derived quantities provide quantitative measures of bone quality. A slight peak (2% greater than reference) was determined for the density and a slightly larger peak (5% above reference) for the longitudinal sonic velocity at a dosage of approximately 20 mg/kg/day. The longitudinal elastic modulus exhibited a substantial peak, 14% greater than reference. The relative static load stress showed a very slight peak as a function of dosage and also as a function of fluoride concentration in the bone. When plotted against the elastic modulus, a nonlinear monotonic increase was observed with modulus, showing that the cross-sectional area of the bone is responsive to the stiffness of the tissue. Stiffer tissue produces a smaller cross section, whereas a more compliant tissue requires a marked increase in the area. There appears to be an improvement of bone quality for low fluoride dosage which tends to be masked by biological variability. The derived quantities, longitudinal elastic modulus, and relative static load stress provide the clearest demonstration of the improvement. There is marked deterioration for higher dosage. The conclusions are limited by a need to related the properties of rabbit to human bone, and young growing bone to older osteoporotic bone.