Osteoblasts are primary bone‐making cells originating from mesenchymal stem cells (MSCs) in the bone marrow. The differentiation of MSCs to mature osteoblasts involves an intermediate stage called preosteoblasts, but the details of this process remain unclear. This study focused on the intracellular density of immature osteoblast lineage cells and hypothesized that the density might vary during differentiation and might be associated with the differentiation stages of osteoblast lineage cells. This study aimed to clarify the relationship between intracellular density and differentiation stages using density gradient centrifugation. Primary murine bone marrow stromal cell cultures were prepared in an osteogenic induction medium, and cells were separated into three fractions (low, intermediate, and high‐density). The high‐density fraction showed elevated expression of osteoblast differentiation markers (Sp7, Col1a1, Spp1, and Bglap) and low expression of MSC surface markers (Sca‐1, CD73, CD105, and CD106). In contrast, the low‐density fraction showed a high expression of MSC surface markers. These results indicated that intracellular density increased during differentiation from preosteoblasts to committed osteoblasts. Intracellular density may be a novel indicator for osteoblast differentiation stages. Density gradient centrifugation is a novel technique to study the process by which preosteoblasts transform into bone‐forming cells.

Apical periodontitis is a disease caused by bacterial invasions through the root canals. Our previous study reported that lithium chloride (LiCl) had a healing effect on apical periodontitis. The aim of this report is to investigate the healing properties and mechanism of lithium ion (Li+) for apical periodontitis using rat root canal treatment model. 10-week-old male Wistar rat’s mandibular first molars with experimentally induced apical periodontitis underwent root canal treatment and were applied lithium carbonate (Li2CO3) containing intracanal medicament. Base material of the medicament was used as a control. Subject teeth were scanned by micro-CT every week and the periapical lesion volume was evaluated. The lesion volume of Li2CO3 group was significantly smaller than that of the control group. Histological analysis showed that in Li2CO3 group, M2 macrophages and regulatory T cells were induced in the periapical lesion. In situ hybridization experiments revealed a greater expression of Col1a1 in Li2CO3 group compared with the control group. At 24 h after application of intracanal medicament, Axin2-positive cells were distributed in Li2CO3 group. In conclusion, Li2CO3 stimulates Wnt/β-catenin signaling pathway and accelerate the healing process of apical periodontitis, modulating the immune system and the bone metabolism.

We previously reported on the restorative properties of lithium chloride (LiCl) for periapical periodontitis using in vivo murine experiment. In this report, looking ahead to potential human clinical applications, we investigated the restorative properties of lithium carbonate (Li2CO3) in the healing process of periapical periodontitis. If the application of Li2CO3 into root canals also confers the healing ability for periapical periodontitis, Li+ has the healing ability for periapical periodontitis. In this report, we used rats instead of mice in our experiments. From rat root canal treatment model experiments, we found that the application of Li2CO3 in the treatment of root canals was not only safe for the rat subjects, but it also conferred restorative properties to accelerate the healing of periapical periodontitis. The application of Li2CO3 induced CD68/CD206-double positive cells (i.e., M2 macrophages) and Foxp3-positive cells (i.e., regulatory T cells) in the rats’ periapical lesions at an early stage of inflammation. After 24 h from the application of Li2CO3, Axin2 positive cells were observed in periapical lesion. Our findings demonstrated that Li2CO3 activates the Wnt/β-catenin signaling pathway and accelerates the healing process, making it a potential novel intracanal medicament for periapical periodontitis.

Apical periodontitis is a disease caused by bacterial invasions through the root canals. Our previous study reported that lithium chloride (LiCl) had a healing effect on apical periodontitis. The aim of this report is to investigate the healing properties and mechanism of lithium ion (Li+) for apical periodontitis using rat root canal treatment model. 10-week-old male Wistar rat’s mandibular first molars with experimentally induced apical periodontitis underwent root canal treatment and were applied lithium carbonate (Li2CO3) containing intracanal medicament. Base material of the medicament was used as a control. Subject teeth were scanned by micro-CT every week and the periapical lesion volume was evaluated. The lesion volume of Li2CO3 group was significantly smaller than that of the control group. Histological analysis showed that in Li2CO3 group, M2 macrophages and regulatory T cells were induced in the periapical lesion. In situ hybridization experiments revealed a greater expression of Col1a1 in Li2CO3 group compared with the control group. At 24 h after application of intracanal medicament, Axin2-positive cells were distributed in Li2CO3 group. In conclusion, Li2CO3 stimulates Wnt/β-catenin signaling pathway and accelerate the healing process of apical periodontitis, modulating the immune system and the bone metabolism.