PAX9 and tooth agenesis: According to clinical reports, tooth agenesis-related pathogenic genes include Wnt10A, Wnt10B, Msx1, Pax9, TGFA and AXIN2, which are involved in multiple signalling pathways, such as Wnt/β-catenin, TGF-β/BMP and Eda/Edar/NF-κB.122–126 Therefore, even if many factors can prevent or interfere with the development of the tooth germ, such as genetic conditions, trauma, radiation and infectious diseases, studies have mostly focused on abnormalities in Wnt, Shh, Bmp and FGF signalling.