EFFECTS OF FLUORIDE ON RAT CANCELLOUS BONE

Female Wistar rats were divided into four groups each fed ad libitum regular rodent chow and fluoridated water at four levels (0, 2, 4, 6 mmol/l) for 3 months. There were significant differences in ash weights between control and fluoridated vertebrae (P < 0.01). Intact bone fluoride (F) values observed were: 0.04 ± 0.01% fat-free dry weight (ffdw) for control vertebrae and 0.22 - 0.34 ± 0.03% ffdw for fluoridated vertebrae. Deproteinized fluoridated vertebral bone had significantly lower specific surface area (SSA) (from 100 ± 19 m2/g, P < 0.01, down to 80 ± 20 m2/g, P < 0.001) than the control group (120 ± 10 m2/g); a finding in support of our hypothesis that more of the bone mineral units in fluoridated bone are older (hence denser) than in normal bone. Static morphometric analysis of toluidine blue-stained sections of the femoral metaphyses showed that both cancellous bone volume/tissue volume (Cn-BV/TV) and trabecular thickness (Tb.Th) increased linearly with NaF dosage (R = 0.99 and 0.97, respectively); with Cn-BV/TV increasing from 21 ± 7 to 33 ± 6% (P < 0.01) and Tb.Th from 76 ± 8 to 98 ± 9 μm (P < 0.01). Similar Cn-EV/TV results were also obtained from von Kossa-stained sections. Analysis of the toluidine blue sections also showed that both bone formation and bone resorption were inhibited by NaF at these experimental levels, with cancellous osteoid surface/bone surface decreasing from 10 ± 2 to 4 ± 1% (P < 0.005), cancellous osteoblast surface/bone surface decreasing from 5 ± 2 to 1 ± 1% (P < 0.05) and cancellous eroded surface/bone surface decreasing from 1.3 ± 0.6 to 0.2 ± 0.1% (P < 0.01). Even with reduced formation, NaF increases rat cancellous bone volume through trabecular thickening in a dose-dependent manner, probably due to a more severely reduced resorption. NaF also increases the bone mineral packing density and perhaps the size of individual bone mineral crystallite, both capable of producing a more brittle bone. © 1990.