DEVELOPMENT OF PRIMARY AND SECONDARY DENTITION

By,

S.Akhila Swetha,

4th BDS.

CONTENTS:

INTRODUCTION PRENATAL DEVELOPMENT STAGES OF TOOTH BUD

DEVELOPMENT ROOT FORMATION ERUPTION SEQUENCE OF PRIMARY

AND SECONDARY DENTIOTION NOLLA’S STAGES OF TOOTH

DEVELOPMENT SUMMARY CONCLUSION

The main purpose of knowing the stages of development is to :

Know the course of normal development.

To detect deviation from the normal.

INTRODUCTION:

Text book of oral histology-Tencate’s

PRENATAL DEVELOPMENT:

28 to 30 days: Epithelium thickening.

30 to 32 days: cells become ovoid to cuboidal in shape.

32 to 34 days: invagination of odontogenic epithelium and dental lamina starts to form.

4th week: position of future dental arches is marked out.

Text book of oral histology-Tencates

STAGES OF TOOTH BUD DEVELOPMENT:

Initiation phase of deciduous tooth- 5th month in utero. phase of permanent tooth-6th month phase of accessional tooth-4th month in utero to

4-5 yrs.ProliferationHisto differentiation.Morpho differentiation.

Apposition.

Text book of oral histology-orban’sText book of pedodontics- shoba tandon

Text book of oral histology-Avery

INIATIATION: Involves the physiologic process of induction.

Induction of ectodermal tissues by the developing mesenchyme. Basement membrane separates the developing oral epithelium

and mesenchyme.

This gives rise to the primary epithelial bands.

It represents the bud stage of tooth development.

Text book of oral histology-Tencate’s

Proliferation:

Marked by the incursion of epithelium into the mesenchyme.

Period of extensive proliferation and growth of the dental lamina.

Forms into tooth buds or oral masses that penetrate into the mesenchyme.

Each tooth bud is surrounded by the mesenchyme Buds + mesenchyme tooth germ and the

associated tissues of the tooth.

Text book of oral histology-Tencate’s

Text book of oral histology-Tencate’s ,orban’s

Definite morphogenic and functional changes.

Formation of dentin and enamel.

Histo differentiation:

Text book of oral histology-Tencate’s ,cawson

Morpho differentiation:

The morphological pattern and basic size is determined. The dentino-enamel junction and dentino-cemental junctionare determined. The size and form of the tooth

crown is etablished before hard tissue formation.

Text book of oral histology-Tencate’s,

Atlas of oral histology- majji jose

APPOSITION:

Deposition of the matrix of the hard dental structures.

Regular and rhythmic deposition of extra cellular matrix.

Periods of active and rest alternate at definite intervals.

Text book of oral histology-Tencate’s

CAP STAGE:

Ingrowth of the oral epithelium into the mesenchyme tooth bud of the dental lamina.

A Depression forms in the deepest part of each tooth bud and forms the cap or enamel organ.

Produces the future enamel below this cap is a condensing mass of mesenchyme – dental papilla.

Text book of oral histology-Tencate’sAtlas of oral histology- majji jose

The basement membrane separating the dental organ and the dental papilla becomes the future site for the dentinoenamel junction (DEJ)

Remaining mesenchyme surrounds the dental/enamel organ and condenses to form the dental sac or the dental follicle.

Text book of oral histology-Tencate’s 6th edition

enamel organ + dental papilla + dental follicle tooth germ

These germs are found in the developing dental arches primary dentition

Text book of oral histology-Tencate’s,

Cap shape then assumes a more bell-like shape

Differentiation produces four types of cells within the enamel/dental organ

1. Inner enamel epithelium

2. Outer enamel epithelium

3. Stellate reticulum

4. Stratum intermedium

BELL STAGE:

Text book of oral histology-Tencate’s,

The dental papilla undergoes differentiation and produces two types of cells

1. Outer cells of the DP – forms the dentin-secreting cells (odontoblasts)

2. Central cells of the DP – forms the primordium of the pulp

Dental sac/follicle increases its collagen content and differentiates at a later stage than the EO and DP

Text book of oral histology-Tencate’s, orban’s

The cells in the center of the enamel organ begin tosynthesize and secreteGAGs.-increasing amount of fluidin the EO forces the centralcells apart-however, they remainconnected via cellular processes which makes themstar shaped = stellate ret.

Text book of oral histology-Tencate’s,

Bell stage – early crown formation

The dental papilla is separated from the enamel organ by a basement membrane.

Immediately below this BM is a region called the acellular zone. This is where the first enamel proteins will be

laid down. The dental lamina begins to break up into discrete

islands of epithelial cells (epithelial pearls)– Separates the oral epithelium from the developing

tooth. The IEE completes its folding and you can begin to

identify the shape of the future crown pattern.Text book of oral histology-Tencate’s, orban’s

Cap and Bell stages & Permanent teeth

During the cap stage the development of the permanent dentition begins

The primordia for these teeth appears as an extension off the developing dental lamina

Its site of origin is called the successional dental lamina

Text book of oral histology-Tencate’s,

These permanent teeth are called succedaneous teeth (anterior teeth and the premolars) Teeth that form with the primary tooth

buds (primary predecessors)

Text book of oral histology-Tencate’s,

Text book of oral histology-Tencate’s, 7th edition

ROOT FORMATION

Takes place as the crown is completely shaped and the tooth begins to erupt.

Therefore the tooth forms from the “top down” – i.e. crown to root.

Root formation is through the formation of a cervical loop.

The CL is the most cervical portion of the enamel/dental organ – two layers consisting of IEE and OEE.

The CL begins to grow down into the dental sac. Text book of oral histology-Tencate’s,6th edition

It forms a Hertwig's root sheath.

This sheath shapes the root and induces dentin formation in the root area by the ODs of the dental papilla.

This sheath lacks the stellate reticulum and stratum intermedium.

Is capable of differentiating into ODs BUT NOT Abs.

Text book of oral histology-Tencate’s,6th edition

Root Dentin:

The root of the tooth is composed by dentin and cementum.

Dentin forms when the outer cells of the dental papilla are induced to differentiation into Ods.

Similar to what occurs at the crown area. Influenced by Hertwig’s root sheath. The ODs then undergo dentinogenesis and

secrete predentin. After dentin formation – the BM disintegrates

along with the Hertwig’s sheath.Text book of oral histology-Tencate’s,

Cementum and Pulp formation:

Cementogenesis in the root area also occurs upon degradation of the H. root sheath.

The degradation allows contact of the dental sac cells with the dentin surface – induces the formation of cementoblast cells.

The CBs cover the root dentin and undergo cementogenesis – laying down cementoid.

The region of contact between cementum and root dentin = dentinocemental junction or DCJ.

While the cementum is forming - the central cells of the dental papilla form the pulp.

Text book of oral histology-Tencate’s,orban’s

Atlas of oral histology- majji jose

Periodontal ligament:

The surrounding tissues of the tooth also develop as the crown and root form.

The mesenchyme of the dental sac condenses to form the periodontal ligament.

Forms adjacent to the new cementum. Ends of these fibers insert into the outer layer of

cementum and surrounding alveolar bone. The cells of the disintegrating H. root sheath

develop into discrete islands of epithelial cells. Become epithelial rests of Malassez. They can be identified in the periodontal

ligament and are responsible for the development of radicular cysts.

Text book of oral histology-Tencate’s,

Text book of oral histology-Tencate’s, 6TH Edition

Multirooted teeth:

Anterior teeth, premolars and molars all begin as a single root – root trunk.

Root of the posterior teeth divides from the trunk into the correct number of root branches.

Differential growth of the H. root sheath results in the division of the root trunk into two or three roots.

Text book of oral histology-Tencate’s,

ERUPTION SEQUENCE OF PRIMARY AND SECONDARY DENTIOTION:

NOLLA’S STAGES OF TOOTH DEVELOPMENT 1952:

Root completion Root almost completed 2/3rd root completion 1/3rd root completion Crown completion Crown almost completed 2/3rd crown completion 1/3rd crown completion Initial calcification Absence of crypt

Text book of pedodontics - Shoba tandon

Text book of oral histology-Tencate’s,

Improper neural crest cells migration leads to treacher collin’s syndrome.

Lack of initiation results in- Complete or partial anodontia. Abnormal initiation Supernumerary teeth. Teeth may develop in abnormal locations like in ovary.

CLINICAL CONSIDERATIONS:

In vitamin A deficiency ameloblasts fail to differentiate properly.

osteodentin forms.

Endocrinal disturbances effect size and form of crown.

Trauma to the tooth during root development causes diacerations.

Genetic and environmental disturbances causes enamel hypoplasia.

CONCLUSION:

Thus it is important to know the normal development of primary and secondary dentition to identify, prevent and treat any tooth abnormalities.