INNER LAYER OF AMELOBLASTS

MIDDLE LAYER OF ENAMEL PULP OUTER LAYER

ENAMELORGAN

DENTALLAMINA

DISINTEGRATINGDENTAL 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 ORGUM EPITHELIUM

MALPIGHIAN LAYER

DERMIS

DENTAL LAMINAOR RIDGE

DENTAL PAPILLAENAMEL

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 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.

CAT DOG BEAR

LAST UPPERPREMOLARS

FIRST LOWERMOLARS

SHARP CUSPS

DENTICULATECROWN

THREE CONES

DENTICULATE

CRABEATERSEAL

TRICONODONT TRITUBERCULATEFOSSIL MAMMALS FOSSIL MAMMALS

B

UNEVEN GRINDING RIDGES OF ENAMEL

CD

A

CARNASSIAL TEETHSECONDONT

LOW ROUNDED CUSPS ON CROWN

ENAMEL

DENTINE

PULP CAVITY

CEMENT

ROOT

NECK

E

BUNODONT MOLAR IN V.S. MAN OR MONKEY

F

BRCHYODONTSELENODONT

TAPIR

CRESCENTIC ENAMEL RIDGES

DENTINE

CEMENTG

BRCHYODONTIN SURFACE VIEW

JJ

LOPHODONTLOPHODONT OF ELEPHANT

IN SURFACE VIEW

ENAMEL

DENTINE

PULPCAVITY

CEMENT

UNWORN WORN

TRANSVERSE RIDGES OR LOPHOS

CRESCENTIC ENAMEL RIDGES

HHYPSODONTSELENODONT

Fig. – 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.

SMALL

CROWN

ROOT

TAILPRISM-LIKE

CROWN