Comparative Aspects of Development of Dental Hard Structures

¹ Institut Dentaire, Faculté de Médecine, Strasbourg, France

Amelogenesis, dentinogenesis, and cementogenesis were studied in human specimens with the electron microscope and, in part, with routine light microscopy. The odontogenic cells during the active phase of tissue elaboration, show a marked increase in their cytoplasmic organelles. In the odontoblast, the mitochondria are intimately associated with the ergastoplasm. The organic matrices of the dental hard tissues are formed extracellularly and consist of fibrous proteins imbedded in a ground substance. Apatite crystal growth occurs gradually, in close relationship to the fibrous proteins-collagen in the case of dentin and cementum and a type of keratin in the case of enamel. The inter-rod substance of enamel is formed before the adjacent rod cores and sheaths. Calcification commences soon after matrix formation. In the early dentin tissue, the odontoblastic process is surrounded by easily visualized collagen fibrils imbedded in a ground substance. At a later stage in development, they are abruptly masked by a change in electron density. Subsequently, peritubular matrix formation and calcification begin. After considerable root dentin is formed, young mesenchymal cells differentiate into cementoblasts and become entrapped in a calcifying collagenous matrix similar to that of bone.