Arid J, et al. - Researchers examined the association of genetic polymorphisms for RANK/RANKL/OPG with delayed tooth emergence and evaluated if a correlation exists between the relative expression of this genes and persistent primary teeth. They analyzed saliva samples from 160 children, aged 6-13 years old. They performed qPCR analysis on the periapical tissue from 15 children with persistent primary teeth and from 15 control subjects to test the correlation between gene expression of RANK/RANKL/OPG in children with delayed tooth emergence and persistent primary teeth. They noted at least one permanent tooth with delayed emergence in 56 children with delayed tooth emergence (35%). Data imply the association of the polymorphism rs9594738 in RANKL with delayed permanent tooth emergence. Moreover, persistent primary teeth were noted in correlation to reduced relative gene expression of RANKL in periapical tissue.