Tooth Development(Odontogenesis)

By: Hasu.Chaudhari

Dentition

•Primary dentition – develops during prenatal period

–20 teeth•Permanent dentition – develops as the jaw grows and matures

–32 teethperiod in between – during the preteen years

(mixed dentition period)

TOOTH DEVELOPMENT

Multiple stages:-•initiation stage – 6th to 7th week•bud stage – 8th week •cap stage – 9th to 10th weeks•bell stage – 11th to 12th weeks•apposition stage – varies per tooth•maturation stage – varies per tooth

Tooth formation

•Dental lamina where tooth formation will occur - on the 1st branchial arch.•Dental lamina, even apparent before the alveolar process itself is defined.•Alveolar process – Semicircular in outline•Similarly, Dental lamina – Curved.

BUD STAGE Proliferation of ectoderm lining the Alveolar Process & Epithelium

become thick on convex side of this process form Dental lamina

Dental lamina shows local thickening which results to form 1 milk tooth.

Deeper part of dental lamina enlarges to form enamel organ.

These thickening called enamel organs. 10 in number – 5 on each side of alveolar process.

Stages in the formation of an enamel organ & developing tooth

CAP STAGE As the enamel organ downwards into the mesenchyme its lower

end forms a cup shape appearance. Then cup occupied by mass of mesenchyme called a dental

papilla. This mesenchyme originate from neural crest cells. Enamel organ + Dental papilla = Tooth germ. At this stage developing tooth looks like a cap.

BELL STAGE The cells of the enamel organ that line the papilla become columnar these are

called ameloblasts. Mesodermal cells of the papilla that are adjacent to the ameloblast cells

arrange themselves as a continuous epithelium like layer. Cells of this layer are called Odontoblasts.

The ameloblasts & odontoblasts are separated by a basement membrane. The remaining cells of the papilla form the pulp of tooth. The developing tooth looks like a bell.

APPOSITIONAL STAGE Ameloblasts secrete enamel on the superficial surface of the basement

membrane. The odontoblasts secretes dentine on its deeper surface. The process of secretion of enamel & dentine is similar to that of formation of

bone by osteoblasts. Ameloblasts & odontoblasts move far away from each other by increasing layers

of enamel & dentine.

After the enamel is fully formed, the ameloblast disappear leaving a thin membrane, the dental cuticle, over the enamel.

The odontoblasts, continue to separate the dentine from pulp throughout the life of the tooth.

Alveolar part of the maxillae & the mandible are formed by ossification.

As ossification progresses, roots of the teeth become surrounded by bone.

MATURATION STAGE

The root of the tooth is established by continued growth into underlying mesenchyme.

Odontoblasts in this region secrete dentine (no ameloblasts cells).

As layers of dentine deposited, the pulp space becomes narrower & converted into a canal through which nerves & blood vessels pass into the tooth.

Dentine is covered by mesenchymal cells that differentiate into cementoblasts.

These cells lay down a layer of dense bone called Cementum.

Mesenchymal cells form a periodontal ligament which connects the root with the socket in the jaw bone.

Formation of permanent tooth The dental lamina gives off a series of buds, one of which lies on the medial

side of each developing milk tooth. These buds form the enamel organs. They give rise to permanent incisors, canines & premolars.The permanent molars are formed from buds that arise from the dental lamina

posterior to the region of last milk tooth.

Dental lamina is established in the 6th week of intrauterine life.

The germ of 3rd molar is formed after birth & germ of premolar & 2nd molar are not very developed & rest of all show considerable development at birth.

The developing tooth germs undergo calcification (accumulation of calcium salts in a body tissue).

All the temporary teeth & permanent lower 1st molar begin to calcify before birth.

The permanent teeth begin to calcify at varying ages after birth.

Anomalies of teeth

1. Anodentia :- one or more teeth may be absent or complete absence.

Supernumerary teeth may be present

Gemination :- Two or more teeth may be fused to each other.

Malocclusion :- Alignment of the upper & the lower teeth may be incorrect.

The End :D