ABSTRACT
<p><b>OBJECTIVE</b>To investigate the timing and location of the expression of bone sialoprotein (BSP) and osteopontin (OPN) in developing dental tissues of rats.</p><p><b>METHODS</b>Every three neonatal rats were sacrificed at day 1, weeks 1, 2, 3, 5 and 8. The mandibles were dissected and the first molar and the surrounding tissue were fixed, then demineralized with 15% EDTA. Immunohistochemical technique was used to determine the expression of BSP and OPN in dental tissues and the surrounding bone at different time points.</p><p><b>RESULTS</b>Immunoreactivitis of BSP and OPN were present in matured ameloblasts, dentinoblasts, cementoblasts, osteoblasts, and the matrix. The expression of BSP and OPN in cementum and alveolar bone was stronger than that in enamel and dentine. In cementum and alveolar bone, BSP appeared to be concentrated in unmineralized and mineralized tissues, but OPN was concentrated in the mineralizing frontier and reversal line.</p><p><b>CONCLUSIONS</b>BSP and OPN play an important role in the development and mineralization of rat mineralized tissues. The expression of BSP was different from OPN, indicating their different functions.</p>