Tooth Development

Odontogenesis

Stages of tooth development

initiation stage – 6th to 7th week bud stage – 8th week cap stage – 9th to 10th weeks bell stage – 11th to 12th weeks apposition stage – vaires per tooth maturation stage – varies per tooth

Tooth formation First signs of formation – day 11 Thickening of the epithelium where tooth

formation will occur on the 1st branchial arch Earlier signals – earliest mesenchymal

markers for tooth formation are the Lim-homeobox genes (Lhx-6 and Lhx-7) – expressed as early as day 9 in the neural crest cells of the tooth region

Tooth formation more than 90 genes have been identified in

the oral epithelium, dental epithelium and dental mesenchyme!! so exact signaling mechanisms remain unclear

Tooth formation -initial stage-

involves the physiologic process of induction induction of ectodermal tissues by the

developing mesenchyme mechanisms remain unknown at the 6th week the stomatodeum is lined with

ectoderm – outer portion is the oral epithelium

this gives rise to the primary epithelial bands

Tooth formation -initial stage-

also is a developing mesenchyme which contains neural crest cells that have migrated to the area

a basement membrane separates the developing oral epithelium and mesenchyme

Cross section (A)

Neural crest cells

MESODERM

ECTODERM

ectomesenchymal cells

Basement membrane

Primary epithelial Band

Tooth formation -initial stage-

Primary epithelial bands: Horseshoe-shaped bands that appear approximately around the 37th day of development, one for each jaw.

There are two subdivisions: vestibular lamina and dental lamina

Tooth formation -initial stage-

The dental lamina develops a series of epithelial outgrowths - grow deep into the mesenchyme

develops in the future spot for the dental arches

will form the midline for these arches arches then form posteriorly from this point the ingrowths represent the future sites for

each deciduous tooth

Tooth formation -initial stage-

the vestibular lamina cells rapidly enlarge and then degenerate – forms a cleft that becomes the vestibule of the oral cavity

The initiation of tooth formation starts around the 37th day of gestation.

Early Dental Lamina

Tongue Dental lamina Vestibular lamina©Copyright 2007, Thomas G. Hollinger, Gainesville, Fl

Late Dental Lamina

Tooth type determination Patterning means the determination of

specific tooth type at the correct position.

Homodont are animals with same shaped teeth

Heterodont are the most mammals with different tooth types

Two theories for the determination of tooth type

Tooth type determination The field model theory proposes that

factors responsible for the determination reside within the ectomesenchyme, but graded fields for each tooth

The clone model theory proposes that each tooth is derived from a clone of ectomesenchymal cells programmed by the epithelium to produce a given pattern.

Bud stage marked by the incursion of epithelium into the

mesenchyme period of extensive proliferation and growth of

the dental lamina forms into buds or oral masses that penetrate

into the mesenchyme each tooth bud is surrounded by the

mesenchyme

Bud stage buds + mesenchyme develop into the tooth

germ and the associated tissues of the tooth this developing tooth forms from both the

ectoderm and mesenchyme and from neural crest cells that have migrated into the mesenchyme

Future dental papilla

Bud stage

Tongue

Cap stage characterized by continuation of the ingrowth

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

unequally in different parts of the bud

forms a cap shaped tissue attached to the remaining dental lamina

looks like a cap sitting on a ball of condensing mesenchyme

Cap stage occurs for the primary dentition (during

the fetal period) this stage marks the beginning of

histodifferentiation (differentiation of similar epithelial cells into functionally and morphogically distinct components)

the tooth germ also begins to take on form – start of morphodifferentiation

Cap stage a depression forms

in the deepest part of each tooth bud and forms the cap or enamel organ (or dental organ) – produces the future enamel (ectodermal origin)

Cap stage below this cap is a

condensing mass of mesenchyme – dental papilla – produces the future dentin and pulp tissue (mesenchymal origin)

Cap stage the basement

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

Cap stage remaining mesenchyme

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

Cap Stage of Tooth Development Dental (enamel) organ

Dental papilla

dental follicle

Oral Histology, 5th edition, A R Ten Cate©Copyright 2007, Thomas G. Hollinger, Gainesville, Fl

Cap Stage

©Copyright 2007, Thomas G. Hollinger, Gainesville, Fl

Cap stage together the enamel organ + dental

papilla + dental follicle is considered the developing tooth germ or tooth primordium

these primordium will be housed in the developing dental arches and will develop into the primary dentition

Cap stage Enamel knots are

clusters of nondividing epithelial cells visible in sections of molar cap stage tooth germs.

They play an important role by the cuspal morphogenesis.

Bell stage Continuation of

histodifferentiation and morphodifferentiation

cap shape then assumes a more bell-like shape

differentiation produces four types of cells within the enamel/dental organ 1. inner enamel epithelium2. outer enamel epithelium3. stellate reticulum4. stratum intermedium

Bell stage the dental papilla undergoes

differentiation and produces two types of cells1. outer cells of the DP – forms the

dentin-secreting cells (odontoblasts)2. central cells of the DP – forms the

primordium of the pulp

Differentiation of the Enamel organ

outer enamel (dental) epithelium (OEE): cuboidal shape protective barrier during

enamel production very little cytoplasm cells are separated from

the dental follicle by a basement membrane

Differentiation of the Enamel organ

inner enamel (dental) epithelium (IEE) short, columnar cells differentiates into the

enamel secreting cells = ameloblasts

separated from the dental papilla below it by a basement membrane also

cells accumulate large amounts of glycogen

Differentiation of the Enamel organ

cervical loop: the IEE and OEE are

continuous region where they

connect – curved rim of the EO = cervical loop

Differentiation of the Enamel organ

stellate reticulum star-shaped cells in many

layers center of the enamel

organ forms a network =

reticulum supports production of

enamel

Differentiation of the Enamel organ

stratum intermedium inner layer of compressed

flat to cuboidal cells very high levels of the

enzyme alkaline phosphatase

supports production of enamel

Bell stage – other events

Two important events occur at the bell stage:

1. the dental lamina begins to break up into discrete islands of epithelial cells (epithelial pearls) – separates the oral epithelium from the developing tooth these pearls may form cysts and

delay eruption or they may develop into supernumerary teeth

Bell stage – other events

2. the IEE completes its folding and you can begin to identify the shape of the future crown pattern.

Bell stage – 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

Tooth Development

Odontogenesis