Ultrastructural evidence of directed cell migration during initial cementoblast differentiation in root formation

Root formation in 14‐day‐old Sprague‐Dawley rats was studied by light and electron microscopy. Special attention was focused on initial cementoblast differentiation. Disruption of the epithelial root sheath appears to be a consequence of directed cell migration by cells of the dental follicle proper which undergo differentiation into precementoblasts. Precementoblasts rapidly develop polarity towards the dentin, exhibiting major cytoplasmic processes rich in cytoplasmic filaments. These processes grow toward and eventually contact the dentin matrix. It is suggested that the cells of the dental follicle proper are cementoblast precursors which respond to chemoattractant substances released from newly deposited dentin matrix‐ and/or basal lamina‐associated material of root sheath origin.