RANKL is associated with persistent primary teeth and delayed permanent tooth emergence.

Background: Tooth eruption is a process that is not fully understood.

Aim: To evaluate whether genetic polymorphisms for RANK/RANKL/OPG are associated with delayed tooth emergence. To evaluate whether the relative expression of this genes is associated with persistent primary teeth.

Design: To evaluate whether genetic polymorphisms for RANK/RANKL/OPG could be involved in delayed tooth emergence, saliva samples from 160 children, aged 6-13 years old, were analysed. To test if there is correlation between gene expression of RANK/RANKL/OPG in children with delayed tooth emergence and persistent primary teeth, periapical tissue from 15 children with persistent primary teeth and from 15 control subjects were collected for qPCR analysis.

Results: Fifty-six children with delayed tooth emergence (35%) had at least one permanent tooth with delayed emergence. The T allele in RANKL (rs9594738) increased the risk of delayed tooth emergence (P = 0.02; OR = 1.71, 95%CI 1.09-2.75). The relative gene expression for RANKL and the ratio RANKL/OPG in children with delayed tooth emergence and persistent primary teeth were lower compared to controls (P = 0.02 and P = 0.005, respectively).

Conclusions: Data suggest that the polymorphism rs9594738 in RANKL is associated with delayed permanent tooth emergence. Moreover, reduced relative gene expression of RANKL in periapical tissue is associated with persistent primary teeth.