Effect of conditioned medium derived from a clone cell of epithelial rests of Malassez on enamel crystallization in tooth germs.

We have previously isolated the epithelial rests of Malassez (ERM) clone cells with strong Amelx expression, named as ERM-2, from the crude ERM cells. In the present study, we examined whether conditioned medium (CM) derived from cultured ERM-2 promotes the crystallization of immature enamel in tooth germs. Tooth germs from postnatal day 3 mice were incubated with ERM-2 conditional medium (CM). ERM-2 cells were transfected with si-RNA targeting specific enamel matrix proteins (EMPs). After 2 days of incubation, each CM was collected and employed to culture the tooth germs. The surface layers of the enamel structure were examined with a scanning electron microscope (SEM). Tooth germs cultured with ERM-2 CM on days 3 and 7 showed elongation and densification of the columnar structures in SEM analysis. The columnar structures became denser and aggregated forming a HAP-like hexagonal columnar structure 14 days after culture in ERM-2 CM. In contrast, no clear columnar structures were observed in ERM-2 CM with si-RNA of each EMPs. In conclusion, the present study demonstrated that CM derived from ERM-2 could form enamel-like structures on the surface of the tooth germ. ERM-2 may provide the possibility for the clinical use of enamel regeneration.