In vivo Dynamics of Dental Tissue Regeneration

Abstract: [Background] Reparative dentin formation is induced in response to severe dental damage. This is a biological defense mechanism to regenerate the damaged hard tissue. In this biological process, dental damage induces odontoblast death, after which dental pulp stem cells differentiate into odontoblast-like cells, contributing to generate reparative dentin. However, how damage induces this regenerative process remains unclear. We hypothesized that odontoblast death induces the regeneration of damaged dental tissue. In this study, we examined the effects of odontoblastic depletion on dentinogenesis activation using a Cre/LoxP-based strategy. [Methods] (1) To induce cell death specifically in odontoblasts using a Cre/LoxP-based strategy, we confirmed the odontoblast-specific expression of green fluorescent protein (GFP) in type I collagen α [(Col1 (2.3)]-GFP mice, in which GFP is expressed under the control of a 2.3-kb fragment of the Col1 promoter. (2) Col1 (2.3)-Cre; ROSA26-loxP-stop-loxP-diphteria toxin (DT) receptor (DTR); Col1(2.3)-GFP mice were generated and administered DT for 1 week to deplete odontoblasts, and the regeneration of odontoblasts and reparative dentin formation were then analyzed. [Results] (1) The expression of Col1 (2.3) promoter-inducible GFP was only detected in odontoblasts in the maxillary first molar, confirming that Col1 (2.3)-Cre was specifically expressed in odontoblasts. (2) Odontoblasts were markedly depleted in maxillary first molars after DT treatment. (3) Depleted odontoblasts significantly recovered in a time-dependent manner. (4) Regenerative odontoblast-like cells generated reparative dentin. [Conclusion] Dentin formation increased in response to odontoblastic cell death in a genetically modified mouse model. This suggests that there is a dental pulp niche environment regulated by odontoblastic cell death and that this regulatory network is essential for the activation of reparative dentin formation.