Post on 15-Jan-2016
Embed Size (px)
(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.
INNER LAYER OF AMELOBLASTSMIDDLE LAYER OF ENAMEL PULPOUTER LAYERENAMELORGANDENTALLAMINADISINTEGRATINGDENTAL LAMINADISINTEGRATINGENAMELORGANTOOTH CROWNENAMELDENTINEEARLY BELL STAGE OF PERMANENT TOOTHBUD OR GERM OF PERMANENT TOOTHDECIDUOUS OR MILK TOOTHDENTAL SAC OF MESENCHYMEDENTAL PAPILLA OR PULPEPIDERMIS ORGUM EPITHELIUMMALPIGHIAN LAYERDERMISDENTAL LAMINAOR RIDGEDENTAL PAPILLAENAMELDENTINEODONTOBLASTSFig. Development of a mammalian tooth
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 the root of tooth appears cement or cementum, which is a modified bone. Odontoblasts become inactive when tooth is fully formed. However in rodents, lagomorphs, etc. the odontoblasts remain active throughout life and teeth continue to grow.
CATDOGBEARLAST UPPERPREMOLARSFIRST LOWERMOLARSSHARP CUSPSDENTICULATECROWNTHREE CONESDENTICULATECRABEATERSEALTRICONODONTTRITUBERCULATEFOSSIL MAMMALSFOSSIL MAMMALSBUNEVEN GRINDING RIDGES OF ENAMELCDACARNASSIAL TEETHSECONDONTLOW ROUNDED CUSPS ON CROWNENAMELDENTINEPULP CAVITYCEMENTROOTNECKEBUNODONT MOLAR IN V.S. MAN OR MONKEYFBRCHYODONTSELENODONTTAPIRCRESCENTIC ENAMEL RIDGESDENTINECEMENTGBRCHYODONTIN SURFACE VIEWJJLOPHODONTLOPHODONT OF ELEPHANTIN SURFACE VIEWENAMELDENTINEPULPCAVITYCEMENTUNWORNWORNTRANSVERSE RIDGES OR LOPHOSCRESCENTIC ENAMEL RIDGESHHYPSODONTSELENODONTFig. Modifications of cheek teeth. A Carnassial teeth (secondont). B Denticulate molar. C Triconodont tooth. D Tritubercular tooth showing arrangement of cusps. E Bunodont molar in V.S. F Brachodont selenodont molar. G Surface view of crown of brachyodont molar. H Sypsodont selenodont molars. I Hypsodont teeth in V.S. J Lophodont molar.SMALLCROWNROOTTAILPRISM-LIKECROWN