Effect Of Short Exposure To High Levels Of Fluoride On The Expression Of Dsp In Odontoblasts Of Mouse Molar

Background The development of tooth germ is a multi-step and complex process of interaction between epithelial and mesenchymal tissues. Although dentin, unlike enamel, is derived from mesenchyme, which involves secretion of mainly type I collagen and several noncollagenous proteins to form a collagenous scaffold.Next, carbonate apatite crystals are deposited on the existing scaffold. Dentin sialoprotein(DSP) is in majority of the noncollageous proteins(NCPs) ,which play essential roles in the growth and development of dentinogenesis. During the tooth development, however, intaking excessive amounts of fluoride through acute and chronic ways can induce dentin differentiatiation of the odontoblasts and secretion of matrix.This lead to the abnormal development of dentinogenesis,but the specific mechanisms could not be determined.Objective To study the effect of short exposure to high levels of fluoride induces structural changes and the expression of DSP in odontoblasts of mouse molar, further more,explore the mechanism for action of overdose fluoride on odontoblasts, the changes of the biological activities of DSP.Methods Thirty-two ICR mice ( postnatal day four, PND4 ) from eight different litters were used. The mice from each litter were divided randomly into two groups. The experimental animals and the control animals shared equal numbers in each group. The experimental animals were received a single intraperitoneal dose of 20 (n=8) and 10 mg (n=8) NaF/kg b.w. respectively, equal doses of NaCl were given to the controls. The injected volume was kept constant (10μl/g b.w.). After the injections, the mice were returned to their respective mothers. Both the experimental and control animals were weighed before and after the experiment to check the effect of fluodide on body weight. After twenty-four hours all mice were sacrificed. Hematoxylin-eosin stain was used to observe the structural changes and to explore the differences of sensitivity to fluodide in odontoblasts of mandibular first molars of mice at different stages. Immunohistochemi -cal stain was used to detect theexpression of DSP in the odontoblasts of control and experimental groups. Bio-image analysis system was employed to measure density value of corresponding results. The data were analyzed with SPSS 13.0 software.Results No animal died during the experiment. Mean body weight of the animals twenty-four hours after fluoride injection was not statistically different among experimental and control animals. HE stains showed that in control groups ( both 10 and 20 mg /kg b.w. of NaCl ), the secretory odontoblasts were arranged neatly with high columnar, the nucleuses were away from basement membrane with the dentein matrix was stained in red uniformly and the dentianl tubules. The maturation odontoblasts conversed gradually from high columnar to short cube-shape. The fluoride induced changes in the dentin organ of the 10 and 20 mg NaF/kg b.w. groups were almost identical, but different in severity. Sometimes, some secretory stage odontoblasts with vaculation were disorganized, disordered and appeared degenerative.The cells arranged irregularly and the height was reduced.The dentin surface uuper the affected odontoblasts had irregular changes. No obvious abnormalities were observed in maturation odontoblasts in both groups. The immunohistochemistry results demonstra -ted that the expression of DSP was observed in the ameloblasts, the odontoblasts and pulp tissue.Compare with control groups the expression of DSP could be found in the predentin and dentin in experimental group,which were more intense positive staining in experimental group, and statistics showed there were significant differences between the two groups ( P<0.01 ). The expression of DSP increased as the concentration of the fluoride increased,which showed dose-dependent effects.No remarkable differences were found in maturation odontoblasts ( P>0.05 ).Conclusions Short exposure to high levels of fluoride can cause changes in differentiatiation of the odontoblasts,and enhance the expression of DSP in the secretory odontoblasts, disturb the signalings between epithelial and mesenchymal and lead to the abnormal development of dentinogenesis. No apparent differences were found in maturation odontoblasts.