Wnt activity is associated with cementum-type transition

Background and Objective: Cellular and acellular cementum and the cells that form them are postulated to have different characteristics, and the relationship between these two tissues is not well understood. Based on the hypothesis that Wnt signaling is involved in the determination of cementum type, we examined Wnt activity along the tooth root and analyzed cementum formation in genetic mutant models. Material and Methods: We generated mutant models with Wnt signaling upregulation (^OCCatnb^lox(ex3)/+), downregulation (^OCWls^fl/fl), and a compound mutant (Enpp1^asj/asj;^OCCatnb^lox(ex3)/+) to compare cementum apposition patterns of ectonucleotide diphosphatase/phosphodiesterase (Enpp1) mutant (Enpp1^asj/asj). The analysis of structural morphology and histology was performed with hematoxylin and eosin and immunohistochemical staining and scanning electron microscopy. Results: The cementum type of upper apical region of tooth roots in the molar is altered from the cellular form at the initial stage to the acellular form at the late stage of cementum formation. However, the basal part of this apical region is not altered and retains cellular cementum characters with strong Wnt activity. In the genetic mutant models for Wnt upregulation, cellular cementum is formed at the cervical region instead of acellular cementum. However, Enpp1 mutant mice have clearly different characteristics with cellular-type cementum even with dramatically increased cervical cementum matrix. In addition, we found that acellular-type formation could be altered into cellular-type formation by analyzing Wnt upregulation and compound mutant models. Conclusions: Cementum type is not determined by its specific location and could be transformed with Wnt activity during cementum formation.