Ultramicroscopy of hypomineralized responses in rat incisor dentine to injected strontium

The structure of dentine after the injection of strontium chloride by backscattered electron imaging in the scanning electron microscope

The subcutaneous injection of 0.5 ml of 20% aqueous strontium chloride produced a distinct calciotraumatic response in rat incisor dentine. In both the labial and lingual dentine this consisted of an unmineralized layer comprising continuous interglobular spaces. Lingually this unmineralized layer was sharply defined and about 1-2 microns in width but labially it was more irregular, diffuse and difficult to measure. Labially and lingually the dentine formed after the unmineralized layer hypomineralized in comparison to the rest of the dentine. Within the hypomineralized labial dentine a diffuse, more intensely hypomineralized layer was often present. The appearance of the unmineralized layer probably reflects the differences in structure between labial and lingual dentine, that is, small linear calcospherites lingually and large irregular calcospherites labially.

Effects of phosphonoformic acid and 1-hydroxyethylidene-1,1-bisphosphonate (HEBP) on distribution of tetracycline in the developing rat molar

Tetracycline was used as a marker to study the effect of phosphonoformic acid and 1-hydroxyethylidene-1,1-bisphosphonate (HEBP) on the mineralization of the developing dental hard tissues. Groups of young rats were given a single subcutaneous injection of tetracycline and at the same time were injected with a single dose of either phosphonoformic acid or HEBP (10 mg P/kg b.w.). Alternatively, rats were injected with the tetracycline after different time intervals from the phosphonate injection. Rats were sacrificed at intervals ranging from 1 to 4 days. Frozen-sections were obtained at the level of the maxillary first molar and prepared for light and fluorescence microscopy. The results of the present study indicate that the distribution pattern of tetracycline in the developing dental hard tissues is greatly affected by the pathologic changes induced by phosphonoformic acid and HEBP. Both drugs caused similar changes in the pattern of tetracycline uptake in the developing enamel. There seems to be a direct relation between the presence of developmental defects of enamel and the degree of discoloration induced by tetracycline. Aberrations in the mineralization of dentin were caused only by HEBP. As demonstrated by this study, HEBP is capable of inducing a provisional inhibitory effect on dentin mineralization.

1-Hydroxyethylidene-1,1-bisphosphonate (HEBP) simultaneously induces two distinct types of hypomineralization in the rat incisor dentine

Effects of 1-hydroxyethylidene-1,1-bisphosphonate (HEBP) on the dentinogenesis of the rat maxillary incisor were microradiographically examined 96 hours after a single subcutaneous injection. HEBP produced hypomineralized incremental bands in the enamel (HPOe) and in the dentine (outer HPO1 and inner HPO2) in a dose-dependent manner. In the labial dentine, both HPO1 and HPO2 did not extend apically beyond the apical limit of the HPOe and were thus located in the circumpulpal dentine. The two lesions in the labial dentine fully developed with a dosage of 10 mg/ P/kg or larger, and with 15 mg P/kg or larger, gross hypoplastic lesions developed. Therefore, histological analysis at shorter postinjection intervals was carried out on the labial dentine with 10 mg P/kg of HEBP. The HPO1 appeared along the dentine-predentine junction by 24 hours and was characterized by reduced numbers of inorganic crystals and 10 nm particles which invested the collagen fibrils. Therefore, the HPO1 was judged to be produced by the disturbance of transformation of the predentine to dentine. The precursor lesion of HPO2 appeared in the proximal predentine by 4 hours, and was characterized by reduced number of collagen fibrils and unusually coarse interfibrillar stippled material. This lesion migrated to the dentine by 96 hours and became the HPO2, which was characterized by reduced number of collagen fibrils. Individual collagen fibrils in the HPO2 were invested by as many inorganic crystals and 10 nm particles as in the normal dentine. The HPO2 is considered to be produced by the disturbance of organic matrix formation.