Fig. 2. Analyzing three-dimensional (3D) explant culture with transmission electron microscope. Human dental pulp tissues in 4-week 3D explant culture were subjected to transmission electron microscope analysis. (A) Pulp core showed little cellular content and mostly extracellular matrix. (B) Outgrowth area showed the reticular arrangement of cells with adjoining of two or three pre-odontoblasts, which exhibited maturation of endoplasmic reticulum or Golgi. (C) Mineral deposit area showed the de novo generation of pre-detin and dentin with accumulation of von Korff fibers and secretory granules.