Introduction
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6th week of intra uterine life
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Stomatodeum (primitive oral cavity) consists of epithelium and
connective tissue
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Complex process involving epithelium & mesenchymal
interactions.
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Connective tissue contains cells derived from neural crest hence
called as ectomesenchyme.
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Horseshoe shaped band like proliferation of epithelium forms the
DENTAL LAMINA
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Dental lamina further forms the enamel organ of the developing
teeth
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Dental lamina further proliferates at 10 points corresponding to 10
decidous teeth.
Lingual extension – permanent successors
Buccal extension – vestibular lamina
Distal extension – permanent molars
Dental lamina Enamel organ
Ectomesenchymal condensation – Dental papillae
Dental follicle / sac
Enamel organ forms
Dental papillae forms
Dental follice forms
ENAMEL
DENTIN & PULP
CEMENTUM, PERIODONTAL LIGAMENT
& ALVEOLAR BONE
Oral epithelium
Dental lamina
Enamel organ
Future dental papilla
Stages of tooth development
Tooth formation is a continuous process based on the shape of the
enamel organ it is divided into stages
 Bud Stage
 Cap Stage
 Early bell stage
 Advanced bell stage
Based on the physiologic phase the development of tooth can be also
divided in to physiologic stages
 Initiation
 Proliferation
 Histodifferentiation
 Morphodifferentiation
 Apposition
BUD stage
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The enamel organ resembles a bud
It consists of peripheral low columnar cells & central polyhedral cells
Ectomesenchymal condensation can be seen
Difference between dental papillae and dental follicle is not evident
CAP Stage
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Unequal proliferation transforms the bud into a cap like structure
Enamel organ shows 3 distinct layers
 Outer enamel epithelium – convex part– cuboidal cells
 Inner enamel epithelium – concave part – columnar cells
 Stellate reticulum - polygonal (star shaped network)
polygonal cells produce albumin
increase in intercellular
fluid
cushion like effect
protects enamel forming cells.
CAP Stage
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Enamel knot, cord, septum, navel – transient structures seen in the
center of enamel organ.
 Enamel knot – knob like accumulation
 Enamel cord – vertical extension of knot
 Enamel septum – knot extending from inner enamel epithelium to
outer enamel epithelium dividing the enamel organ
 Enamel navel – depression on the outer surface of enamel organ
Earlier thought to be only reservoir for dividing cells but now known to
act as signaling center & plays a role in determining the shape of
the tooth.
The ectomesenchyme becomes more cellular and occupies the
concavity of the enamel organ – Dental Papilla
Part of the ectomesenchyme which is more fibrous and surrounds
both the enamel organ & papilla – Dental follicle
Early Bell Stage
Early Bell Stage
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Enamel organ assumes bell shape
4 distinct layers – 3 of cap stage and stratum intermedium.
Inner enamel epithelium converts to ameloblasts
“Reciprocal induction” begins
Cervical loop is appreciated
Dental lamina disintegrates – cell rests of serres (epithelial
pearls)
Dental papilla & dental follicle become more organized.
“Membrana Preformative” – Future dentinoenamel junction
Advanced Bell Stage
Advanced Bell Stage
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Ameloblasts and odontoblasts can be clearly demarcated.
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Enamel and Dentin formation begins (reciprocal induction)
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Stellate reticulum collapses to facilitate nutrition.
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After hard tissue formation dental papilla is known as dental pulp.
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Hertwigs epithelial root sheath proliferates from cervical loop
leading to root formation.
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Fibres of dental sac become more organized to resemble
periodontal ligament.
Reciprocal Induction
Root Formation
Hertwigs epithelial root sheath (HERS) consists of
inner & outer enamel epithelium.
Hard tissue formation reaches the future CEJ [cervical loop]
HERS proliferates downwards
inner cells induce dental papillae cells to differentiate into
odontoblasts
formation of radicular dentin
rupture of HERS [cell rest of mallasez]
Dental follicle comes in contact with dentin
differentiation of cementoblasts & cementum formation.
Formation of multirooted teeth
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Cell rests of mallasez
Enamel pearls & Epithelial pearls
Physiologic stages of tooth development
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Initiation: induction by epithelial – mesenchymal interaction
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Proliferation: increases in size and grows from bud to cap & bell
stages
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Histodifferentiation: basic cells transform into various layers and
assume their functions, i.e. become specialized.
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Morphodifferentiation: basic size and form of the tooth are
determined.
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Apposition: deposition of hard tissues.
Applied aspects
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Enamel hypoplasia
Mottled teeth
Turners hypoplasia
Anodontia
Supernumerary teeth
Taurodontism
Dens invaginatus
Odontogenic cysts & tumors
Dens evaginatus
Enameloma