Effects of phosphonoformic acid and 1-hydroxyethylidene-1,1-bisphosphonate(HEBP)on , . distribution of tetracycline in the developing rat molar Fouda N, Kttt I A. Hammarstrom L: Effects of phosphonoformic acid and l-hydroxyethylidene-l,l-bisphosphonate (HEBP) on distribittion of tetracycline in the developing rat tnolar. Scand J Dent Res 1992; 100; 257-65. Tetracycline was used as a marker to study the effect of phosphonoformic acid and l-hydroxyethylidene-l,l-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 fissues 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.