RESUMO
Objective To study the effects of fluoride on longitudinal growth and pathological changes of cultured rat metatarsal bone rudiments.Methods Twenty-four neonatal SD rats were divided into four groups according to the random number table,then the second,third and fourth metatarsal bone rudiments were surgically isolated.The left metatarsal bone rudiments were cultured in α-MEM without F-as control group and the right metatarsal bone rudiments from the same rat were cultured in α-MEM with 1 × 10-7,1 × 10-6,1 × 10-5 and 1 × 10-4 mol/L F-.The length and width of the mineralized area of metatarsal were measured on day 0,day 1,day 4 and day 7,respectively,and the pathological changes of metatarsal bone rudiments were observed by the routinely paraffin-embedded sections method on day 7.Results On day 7,the length of the mineralized area was significantly lower of right metatarsal bone [(240.5 ± 139.3)μm] than the left metatarsal bone [(394.1 ± 173.9)μm,t =4.37,P ＜ 0.01] in the 1 × 10-4 mol/L F-group,but the width of the mineralized area [(239.9 ± 119.4)μm] was not different significantly compared to the left metatarsal bone [(223.3 ± 99.9)μm,t =0.44,P ＞ 0.05].The relative vertical growth rate of the mineralized area on day 4 was significantly lower of right metatarsal bone [(2.43 ± 1.44)％] than left metatarsal bone [(8.34 ± 1.74)％,t =3.21,P ＜ 0.01] in 1 × 10-4 mol/L F-group,and the difference was also significant on day 7 [(16.16 ± 2.87)％ vs.(26.52 ± 4.46)％,t =3.13,P ＜ 0.01].Toluidine blue staining results showed that the thickness of cartilage cells of proliferation and hypertrophic layers was significantly lower of right metatarsal bone [(111.33 ± 27.29),(125.33 ± 30.08)μm] than left metatarsal bone [(127.33 ± 38.36),(160.50 ± 42.73)μm,t =4.82,5.81,all P ＜ 0.01] in 1 × 104 mol/L F-group.The ratio of proliferative and hypertrophic layers was significantly higher of right metatarsal bone (0.93 ± 0.36) than left metatarsal bone (0.83 ± 0.32,t =4.42,P ＜ 0.01) in 1 × 10-4 mol/L F-group.Conclusions Our findings indicate that excessive fluoride could cause longitudinal bone growth inhibition.Such growth inhibition is mediated by decreased chondrocyte proliferation and differentiation and the disproportion of proliferation and differentiation.