Glass ionomer cements (GIC) can be used to protect dentine following caries removal. However, GIC have little biological activity on biological repair processes, which means that neo-dentine formation remains reliant on limited endogenous regenerative processes. Wnt/β-catenin signalling is known to play a central role in stimulating tertiary dentine formation following tooth damage and can be stimulated by a range of glycogen synthase kinase (GSK3) antagonists, including lithium ions.
Here, we created lithium-containing bioactive glass (BG) by substituting lithium for sodium ions in 45S5 BG. We then replaced between 10 and 40% of the powder phase of a commercial GIC with the lithium-substituted BG to create a range of formulations of 'LithGlassGIC'. In vitro physical properties of the resulting glasses were characterised and their ability to stimulate reactionary dentine formation in mouse molars in vivo was tested.
Lithium release from LithGlassGIC increased with increasing lithium content in the cement. In common with unmodified commercial GIC, all formations of LithGlassGIC showed in vitro toxicity when measured using an indirect cell culture assay based on ISO10993:5, precluding direct pulp contact. However, in a murine non-exposed pulp model of tooth damage, LithGlassGIC quickly released lithium ions, which could be transiently detected in the saliva and blood. LithGlassGIC also enhanced the formation of tertiary dentine, resulting in a thickening of the dentine at the damage site that restored lost dentine volume. Dentine regeneration was likely mediated by upregulation of Wnt/β-catenin activity, as LithGlassGIC placed in TCF/Lef:H2B-GFP reporter mice showed enhanced GFP activity.
We conclude that LithGlassGIC acts as a biological restorative material that promotes tertiary dentine formation and restores tooth structure.