Most likely, activated osteoclasts at the initial stage promote the release of TGF-β from the bone matrix and subsequently recruit mesenchymal stem cells to bone resorption pits to differentiate into osteoblasts and form new bone, which is consistent with the transiently increased bone volume and osteoblasts at this stage.45 Further study of TGF-β signalling is required to obtain a deeper understanding of chronic apical periodontitis and to provide insights for possible biological bone regeneration for bone loss in chronic apical periodontitis. The gene discussed is TGFB1; the disease is chronic apical periodontitis.