In mature rat pulp tissue, our results showed that BMP9 was mainly expressed in the odontoblast cell layer and the remaining pulp cells, in accordance with our previous results regarding human pulp tissue.13 The expression of BMP9 significantly decreased in the inflammatory area and surrounding odontoblast layer 24 h after the onset of inflammation, showing that the expression of BMP9 was inhibited in the early stage of pulpitis. This evidence concerns the gene GDF2 and pulpitis.