Tooth Development

Crown and Root

Crown- enamal + chewing surface

Root- cemetum+ in jaw + support crown

Name the six stages of Crown Development

Dental Lamina

Bud Stage

Cap Stage

Bell stage

Apposition stage

Maturation stage

Proliferation vs diffreneation

Pro- cell dividing

Diff- cell lose division powers → morph into their functinal assignment

morphogrnisis

estblish of shape and size of future tooth ( acheived by diffrential growth)

Dental lamina

• (1st stage of crown formation)

• ectomesenchyme cells induce(turn on) oral epithelium => forms a horseshoe shaped ridge for both jaws

• The epithelial ridge becomes the dental lamina

think the forming of the shoe

Bud stage

Proliferation of dental epithelial cells

• ten locations on each dl

• Ectomesenchyme induction of primary tooth buds(early enamel organs)= tooth stage u can see when the teeth form

• Ecromesenchyme condenses around epithelial bud

Cap stage

Morphodifferentiation= unequal prolifation of bud cells => form a cap like structure(enamel organ)

Cytodiffrentiation= 4 cell layers

Ectomesenchyme cells still condense around cap => will become dental papilla (DP) and Dental sac(DS)

• tooth germ fully formed

• successional dental lamina on lingual side of dental lamina give rise to enamel ofgans of successsional teeth

Tooth germ contains

• enamel organ

• Dental Papilla

• Dental sac(dental follicle)

Where does successiosnal dental lamina form and what does it give rise to

Where: Lingual side of DL

Forms: Enamel organs of successional teeth

(part of cap stage)

What is the enamel organ and its orgin

• Orgin: oral ectoderm (oral epithelium)

• Forms enamel (via ameloblasts).

Dental Papilla

Origin: ectomesenchyme derived from neural crest cells (NCC)

Forms dentin (via odontoblasts) and dental pulp.

part of tooth germ

Dental sac orgin and job

Origin: ectomesenchyme derived from NCC

Forms cementum, periodontal ligament and alveolar bone. (basically the peiodontium)

part of tooth germ

Bell stage layers + general info

Continued diffrenation of enamal organ into 4 layers (out to in)

• Outer enamel epithelium

• stellate reticulum

• stratum intermedium

• Inner enamel

cervical loop

DP and DS cells are proliferating

Enamel organ: Inner enamel epithelium (IEE)

• Differentiate into Ameloblast (forms enamel)

• induces diffrentiation of adjacent cells of dental papilla into odontoblast

Enamel Organ: Straum intermedium

layer of spindle shaped cells adjacent to IEE cells

Supports enamel mineralization= alkaline phosphate

Enamel organ: stellate reticulum

cells secrete glycosaminoglycans→ GAG draws water into enamel organ→ increases enamel organs volume

Enamel Organ: Outer enamel Epithelium (OEE)

• enamel organ outer protective barrier

• accociated with capillary plexus

Cervical loop

junction of OEE and IEE.

in bell stage

how are DP and DS cells proliferating in the bell stage

Yes

DP:

• outer DP cells (future odontoblast)

• Inner DP cells

DS:

• do proliferate BUT dont become periodontal tissue until later stage

Apposition Stage

• Organic matrix of enamel + dentin are laid down and followed by initial calcificarion

• reciprocal inducrions occur between enamel organ and dental papilla

Reciprocal inductions order

(happens in spposition stage)

IEE become Premeloblast→ premeloblast tell other DP cells to become Preodontablast→ perodontablast then diffrentiate into odontoblast→ odontoblast sectete dentin matrix, predention and induce preameloblast to become secretory ameloblast→ secretory amelobt secrete enamel matrix which immediatlly calcifies to 30%

Dentin forms before enamal

Tomes process

an apical cytoplasmic extension of a secretory ameloblast

has proximal and distal poriton

(apposition stage)

Tomes process Proximal vs distal portion

Proximal - contacts adjacent ameloblasts on their sides and forms interod enamel.

Distal- interdigitates with the forming enamel, and forms enamel rod

(apposition stage)

Secretory ameloblast form what after they lose their tomes process

Final thin layer of enamel formed

(apposition stage)

Enamel rod and inter rod enamel formed by who

secretory ameloblasts with Tomes’ process.

What is enamel rod vs interrod enamel formed by?

secretory ameloblasts with Tomes’ process.

Maturation ameloblast types

Ruffle ended maturation

Smooth ended maturation

Ruffle ended maturation amenoblast

ruffeled apical end

procxilal leaky juctions + distal tught junctions

No laterally folded plasma membrane

Calcium ions pumped into maturing enamel mineralization

Smooth ended maturation ameloblast job and characteristics

• job: Remove water and degraded fragments of enamel proteins

• smooth apical surface

• lateral pilcations

• Proximal tight junctions + distal leaky junctions

What ameloblast stage is enamel fully minealized during

maturation stage

Mature ameloblast modulation

modulation = cycle of the creation, loss, recreation of ruffle ended apical surface

mature ameloblast will alternate between smooth and ruffled mature ameloblast

Protective ameloblast

Ameloblasts become cuboidal to flat and cover mature enamel

Ameloblast functinal phases

Morphogenetic (IEE) → Differentiation (Preameloblast)→ Initial Secretory Ameloblast→Secretory Ameloblast → Ruffle-ended Maturation Ameloblast → Smooth-ended Maturation Ameloblast→ protective ameloblast

Reduced Enamel Epithelium (REE)

• Composed of the flattened ameloblasts and the remnants of the other three layers of enamel organ

• Cover and protect the enamel

Stages of Dentogenesis

Creation of dentin

1. Mantle dentin

2. Circumpupal dentin

3. predentin

4. Dentin

mantle dentin

• 1st formed layer of dentin created by newly differentiated odontoblast

• has type 1 and 3 collagen

  • collogen fibers perpendicular to DEJ

Circumpulpal detin

• dentin under matel dentin

• type 1 predomanint collagen fibers

  • smaller and randomly orientended

Predentin

• organic collagen matrix layer

• unminzeralized

(third phase in dentinogeneses)

Dentin

• Organic collagen matrix

• hydroxyapatite(calcium phosphate) crystals

Patterns of dentin mineralization

globular mineralization

linear mineralization

global mineralization

Calcoshperites:

• spherical foci of hydroxyapatite

• grow and coalesce

Irregular mineralization front

fast dentin deposition rate

seen in mantel and circumpulpal dentin (1 and 2 layers)

Linear mineralization

more uniform mineralization front

slow dentin despotiton rate

only on circumpulpal dentin

dentinogenises Root formation (3)? Faster or Slower rate then coronal dentin?

• HERS

• Epithelial diagram

• Inner layer → induces root odontoblast

  • root odontoblast creat root mantal and circumpulpal dentin

(occurs at a slower rate than coronal dentin)

Formation of Hers? What from the enamel organ is apart of hers?

aft crown fromed, cells in cervical loop grows apically→ forms root sheath(HERS)

• formed when IEE and OEE joins (absence of stellate reticulum and stratum intermedium)

What is the structure that shapes the root of the tooth & induces formation of root dentin

HERS

Root Odontoblast diffrentiation

Hers induces: DP cells→ preodontoblast→ odontablast

cementogenesis

aft first layer of root dentin formed → HERS breaks dorn

• Ectomesenchymal cells of DS move to contact new root dentin→ odontoblast tells ectomesenchy,al cells to diffrentiate to cemetoblast→ cementum blast produce cementum

HERS has to break down for the NCC to touch the root

When does cervical part of HERS hers break down

After first layer of root dentin is formed

How is cementum deposited

Incrementally

Root elongation

Epithelial rooth sheath proliferates cronally at ANGEL of epithelial diaphram(not the tip)

the epitheliam diaphram maintains its constant size

Malassez Epithelial rest form how

remnants of hers turn into Malassez epithelial rest

Multiple root formation

• number of roots determined by number of medial ingrowths/invaginations of HERS

• multiple root sheaths /tunnels

What can create anomalies in the root? what are the 3 anomalies?

HERS

• exposed root dentin

• enamel pearl

• accessory root canal

Exposed Root dentin? how happen? where found?

Area of root doesnt have cementum= exposed

• HERS still aderes to root dentin surface=> Ectomesenchymal cells of dental follicle dont touch dentin root=> no cementoblast diffrentiation = no cementum formed

• can be found anywhere along root surface, especially cervical zone

Enamel Pearl? how formed?

enamel droplet often found between the roots of the permanent molars

• Formed when epithelial rooth sheath remains attached to root dentin surface

  • inner later root sheath cells diffrentiate into ameloblast that form the enamel droplet

Accesory root canal? how formed?where found

A small lateral canal – connecting the PDL with the main root canal

• Formed if epithelial root sheath breaks down before root dentin is formed => no hers to induce dental pulp cells to odontoblast=> no root dentin formation

• anywhere along root

  • typically apical third/furcation of teeth