Development of teeth

Introduction 6th week of intra uterine life Stomatodeum (primitive oral cavity) consists of epithelium and connective tissue Complex process involving epithelium & mesenchymal interactions. Connective tissue contains cells derived from neural crest hence called as ectomesenchyme. Horseshoe shaped band like proliferation of epithelium forms the DENTAL LAMINA Dental lamina further forms the enamel organ of the developing teeth

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 ENAMEL Dental papillae forms DENTIN & PULP Dental follice forms 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 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 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 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 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 Ameloblasts and odontoblasts can be clearly demarcated. Enamel and Dentin formation begins (reciprocal induction) Stellate reticulum collapses to facilitate nutrition. After hard tissue formation dental papilla is known as dental pulp. Hertwigs epithelial root sheath proliferates from cervical loop leading to root formation. 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 Cell rests of mallasez Enamel pearls & Epithelial pearls

Physiologic stages of tooth development Initiation: induction by epithelial – mesenchymal interaction Proliferation: increases in size and grows from bud to cap & bell stages Histodifferentiation: basic cells transform into various layers and assume their functions, i.e. become specialized. Morphodifferentiation: basic size and form of the tooth are determined. Apposition: deposition of hard tissues.

Applied aspects Enamel hypoplasia Mottled teeth Turners hypoplasia Anodontia Supernumerary teeth Taurodontism Dens invaginatus Odontogenic cysts & tumors Dens evaginatus Enameloma

OVERVIEW