[Fluoride therapy. Influence on the microarchitecture and biomechanical properties of bone]

Fluoride, in the form prescribed as sodium or monophosphate fluoride for the treatment of vertebral osteoporosis, modifies the microscopic structure and biomechanical properties of bone tissue. For cancellous bone, the main effect of fluoride is a stimulation of bone formation leading to a hypertrophy of the remaining trabeculae. It may also have a beneficial effect by improving interconnections within the trabecular network. Although the mechanisms have yet to be fully understood, the process is probably dependent on the quality of the remaining network. The biomechanical properties of bone after fluoride therapy also are partly dependent on these modifications in the bone microstructure but also on fluoride's effect on bone minerals. When the concentration of fluoride becomes too high in bone, mineralization defects can occur causing major loss in mechanical resistance despite an increase in bone mass. Thus the beneficial effect of fluoride on wedge fractures of the spine in osteoporosis is probably the result of a balance between the effects of increased trabecular bone mass and modifications in bone mineralization. The respective intensities of these two phenomena also depend on the concentration of fluoride accumulated within the bone. This concentration is a function of the level of fluoride salt intake and its biodisponibility during treatment.