PAX9 is a transcription factor belonging to the PAX family, which is composed of nine members defined by the presence of a paired box domain responsible for DNA binding. PAX9 is expressed at the E10 stage and downregulated at the bell stage. It is controlled by Fgf/Bmp signaling and plays an essential role in tooth development. PAX9 deficient mice fail to form teeth and show developmental arrest at the bud stage. In humans, heterozygous mutation in PAX9 is associate with tooth agenesis. These findings support the role of PAX9 in tooth development.