Fluoride effects on ectopic bone formation in young and old rats

This study evaluated the effect of fluoride on bone fluoride levels and on ectopic bone formation in young and old rats. Eighty male Wistar rats were assigned to four groups (n = 20/g), which differed according to the fluoride concentration in their drinking water (0, 5, 15 and 50 mg/l). When half of the rats were 90 days old, demineralized bone matrix (DBM) was implanted. The other rats received DBM implants when they were 365 days old. The animals were killed 28 days after. Fluoride in the femur surface, whole femur and plasma was analyzed with an electrode. The implants were analyzed histomorphometrically. Data were tested for statistically significant differences by ANOVA, Tukey's test, t-test and linear regression (p < 0.05). Increases in plasma, femur surface and whole femur fluoride concentrations were observed as water fluoride levels increased. There was also a trend for increase in plasma and femur fluoride concentrations as age increased. Significant positive correlations were found between plasma and femur surface, plasma and femur and femur surface and femur fluoride concentrations. The morphometric analyses indicated an increase in bone formation for younger rats that received 5 mg/l of fluoride in the drinking water. However, this was not statistically significant. The younger rats that received 50 mg/l of fluoride showed impairment in bone formation. Bone formation was not significantly affected among the older rats. The results suggest that lower doses of fluoride in the drinking water, which slightly increase plasma fluoride levels, may have an anabolic effect on bone formation in younger rats.