Development of tooth

DEVELOPMENT OF TOOTH

INTRODUCTION

* The primitive oral cavity or stomodeum, is the line by the stratified squamous epithelium called the oral ectoderm.

* The oral ectoderm contacts the endoderm of the forget to form buccopharyngeal membrane .

* At about 27 day of gestation buccopharyngeal membrane reptures and the primitive oral cavity established a connection with the foregut .

* Most of connective tissue cells underlying the oral ectoderm are of neural crest .

* These cells induce the overlying ectoderm to start tooth development .

* Which begins in anterior portion of what will be the future maxilla and mandible and prooced posteriorly .

GERM LAYER

Enamel organ: This develops from the dental lamina and hence is ectodermal in origin and is primarily involved in formation of enamel.

Dental papilla: This component is ectomesenchymal in origin and gives rise to dentin and pulp.

Dental follicle or sac: This is also an ectomesenchymal component and is
responsible for formation of cementum, periodontal ligament and part of the alveolar socket.

Enamel organ + Dental papilla + Dental sac / follicle

DEVELOPMENTAL STAGES

The developmental history of the tooth can be 

divided into the following stages on the basis of 

the shape of the enamel organ:

1. Bud stage

2. Cap stage

3. Bell stage

4. Advanced bell stage

BUD STAGE

* Enamel organ is bud shaped ( round & ovoid) with peripheral cuboidal cells & central polyhedral cells.

* All cells are attached to each other by desmosomal junction.

* Ectomesenchymal condensation adjacent to enamel organ forms the dental papilla .

* Marginal condensation of ectomesenchymal cells enclosing dental papilla and enamel organ is called dental follicle or dental sac.

CAP STAGE

* Enamel organ increase in size and attain the shape of a cap by invagination of deep portion of the bud .

* Cells lining the convexity or the periphery  of the cap are cuboidal in shape and called outer enamel epithelium .

* Cells lining the concave or invagination portion change to columnar cells named as inner enamel epithelium .

* The central polyhedral cells transformed into a network of star shaped cells called stellate reticulum .

* Dental papilla gets partially enclosed by the invaginated portion of enamel organ .

*Dental follicle show further condensation of ectomesenchymal cells . It become more fibrous and denser in cap stage .

 BELL STAGE

* Enamel organ enlarge further and invigilation deepens changing the shape to that of a bell longitudinal section .

* Cells lining the invaginated portion the inner enamel epithelium is composed of single layer to tall columnar cells that differentiate to ameloblast (enamel forming cells) .

* During bell stage a new layer appears which is called stratum intermedium . This layer is located between inner enamel epithelium and is composed of 2 to 3  layers of squamous cells .

* Stellate reticulum expand further in early bell stage .

* Cells of outer enamel epithelium lining the periphery of enamel organ flatten to low cuboidal cells .

* All the cells are attached to each other by a desmosomal junction .

* During early stage in enamel loses its connection to oral ectotherm due to degenerate of dental lamina remnants of dental lamina are called cell rest of serrus .

* Successional lamina develops at this stage which is the primordium for the permanent successor .

Dental papilla : The dental papilla is fully enclosed in the invigilated portion of the enamel organ in this stage .

* Peripheral cells of dental papilla differentiated into odontoblast (dentin forming cells) .

* Dental follicle become more fibrous with three layer, i.e inner cellular , outer fibrous layer and middle loose connective tissue .

ADVANCED BELL STAGE

Differentiating features between early and advanced bell stage is formation of hard tissue .

ENAMEL ORGAN shows four different layers :-

1. Inner enamel epithelium (ameloblast)
2. Stratum intermedium
3. Stellate reticulum
4. Outer enamel epithelium

* Hard tissue (enamel & Dentin) formation :

Dental papilla : show differentiated odontoblast at the periphery .

Dental follicle : is distinct enclosing enamel organ and dental papilla .

ROOT FORMATION

Root formation  begins in advanced bell stage after the enamel and dentin formation reaches the cervical region at future cemento-enamel junction. At this stage, the enamel organ at the cervical loop proliferates giving rise to a structure called Hertwig’s epithelial root sheath (HERS) .

                                     Summary