Temporal and spatial mRNA expression of bone sialoprotein and type I collagen during rodent tooth movement

To investigate the mechanism of bone formation during tooth movement, in si tu hybridization was performed with digoxigenin-labelled RNA probes to dete ct bone sialoprotein (BSP) and type I collagen mRNAs in the dentoalveolar t issue of 72 Sprague-Dawley rats. An elastic band was inserted between the f irst and second right maxillary molars, and the teeth experimentally moved for 1, 3, and 7 days. The left first maxillary molar was used as the contro l. For the untreated molars, osteoblasts and osteocytes near the distal sur face of the interradicular septum (IRS) expressed a high level of both BSP and type I collagen mRNAs, while cells on the mesial side of the IRS showed a low level of these mRNAs. For the first molars subjected to experimental tooth movement, a high level of type I collagen mRNA expression was found in the osteoblasts on the tension side of the IRS after 1 day of experiment al tooth movement. A high level of BSP mRNA was detected after 3 days of ex perimental tooth movement. However, a negligible amount of both mRNAs was f ound in cells on the compression side. These results support the hypothesis that BSP may be involved in mineraliza tion during physiological bone remodelling. On application of orthodontic f orce, osteoblasts were activated and induced to express BSP mRNA, which is involved in bone remodelling due to orthodontic force. In addition, respons e to the orthodontic force was observed in osteocytes.