INNER LAYER OF AMELOBLASTS MIDDLE LAYER OF ENAMEL PULP OUTER LAYER ENAMEL ORGAN DENTAL LAMINA DISINTEGRATING DENTAL LAMINA DISINTEGRATING ENAMELORGAN TOOTH CROWN ENAMEL DENTINE EARLY BELL STAGE OF PERMANENT TOOTH BUD OR GERM OF PERMANENT TOOTH DECIDUOUS OR MILK TOOTH DENTAL SAC OF MESENCHYME DENTAL PAPILLA OR PULP EPIDERMIS OR GUM EPITHELIUM MALPIGHIAN LAYER DERMIS DENTAL LAMINA OR RIDGE DENTAL PAPILLA ENAMEL DENTINE ODONTOBLASTS Fig. – Development of a mammalian tooth (vii) Odontogenesis : In mammals, teeth develop in the gum or the soft tissue covering the borders of premaxillae, maxillae and dentaries. Enamel of tooth is derived from epidermis, while the rest of tooth from dermis or mesenchyme. In the beginning there is a thickening of ectoderm along the margin of Jaw bone. The basal layer of ectoderm, the Malpighian layer , forms a continuous solid ridge- like vertical invagination into the underlying dermis. This forms the dental lamina, which retains its connection with the outer epidermis. Mesodermal cells multiply rapidly beneath the ectodermal ingrowth or dental lamina forming a series of solid bud-like outgrowths at intervals, called tooth germs. Their number is as many as the number of milk teeth. In each tooth germ, the inverted cup- like epithelial cap will secrete the enamel, hence termed the enamel organ. The mesodermal aggregation beneath enamel organ is termed dermal or dental papilla . Its outer columnar cells become differentiated into odontoblasts , which secrete a layer of dentine on their outer surface. The cells of inner epithelial layer of enamel organ similarly become ameloblasts , which form a cap of hard enamel around the top and sides of dentine. No enamel is deposited on the root. Dental papilla is retained as pulp . Its central cavity goes on increasing to become the pulp cavity . Nerves and blood vessels enter the pulp cavity through the basal opening. Upto this stage the tooth remains inside the tissue (gum). Later, its eruption through the overlying epidermis is known as cutting of tooth . Around