Ch 21 & 22: Root Formation, Eruption & Shedding of Teeth

What does Herwig’s Epithelial Root Sheath (HERS) do? How does this happen?

defines root shape, length, and initiates root dentin formation; signals odontoblast differentiation from papilla (certain papilla cells change into odontoblasts)

1st step of HERS and Dentin Formation

cervical loop forms at the junction of the OEE and IEE

2nd step of HERS and Dentin Formation

HERS develops from the cervical loop

3rd step of HERS and Dentin Formation

HERS grows apically to outline the future root

4th step of HERS and Dentin Formation

tip HERS bends inward to form the epithelial diaphragm which guides the number of roots

5th step of HERS and Dentin Formation

HERS signals outer cells of dental papilla to turn into odontoblasts

6th step of HERS and Dentin Formation

odontoblasts secrete root dentin, and begins dentinogenesis of root

7th step of HERS and Dentin Formation

DEJ is formed at the crown-root junction

What happens if epithelial root sheath fail to disintegrate and remain attached to dentin?

transforms into ameloblasts (prevents dental follicle from contacting the root dentin, prevents cementoblasts)

What do abnormal ameloblasts produce?

depositing enamel causes enamel pearls

What is the consequence of enamel pearl formation?

interferes with periodontal attachment and can lead to periodontal problems

How are accessory root canals formed?

root sheath that fails to grow apically or encounters a blood vessel may produce a horizontal pathway from the tooth to periodontium

What is Epithelial rests of Malassez? What may they eventually form?

root sheath cells that have disnintegrated and detached from dentin but remain in periodontal space next to tooth —> can form periodontal cysts

Describe the beginning of cementum formation.

at the cervical line of the tooth (CEJ) the cementoblasts secrete a matrix that mineralizes and forms cementum

What are the two varieties of cementum formation?

acellular cementum and cellular cementum

Acellular Cementum

• formed first at cervical 2/3rds of the root

• cementoblasts remain on the surface instead of being entrapped, anchorage: attaching periodontal fibers to root

Cellular Cementum

• formed later at middle and apical thirds of the root

• cementoblasts become entrapped as cementocytes, more vital and responsive to repair

From which tissue do periodontal ligaments (PDLs) develop?

mesodermal cells of the dental sac after cementum formation

What do the dental sac cells differentiate into during PDL formation?

differentiate into fibroblasts

What do fibroblasts form in the periodontal ligament?

collagen fibers are formed

How are collagen fibers arranged during early development of the PDL? How do they change as they mature?

initially arranged parallel to the root surface; shift into oblique orientation and eventually bundles between cementum and alveolar bone

What other structures do PDLs contain than fibers?

cells, lymphatics, nerves, and connective tissue cells

What functions do PDLs serve? (3)

1. support the tooth

2. resist occlusal forces

3. transmit sensations: touch, pressure, pain, temperature

Name and describe the three fibers of the PDL

Alveodental fibers: Anchor tooth to bone; alveolar creast, horizontal, oblique, apical, interradical

Transseptal fibers: between adjacent teeth (interproximal contact)

Gingival fibers: in marginal gingiva

Cool Red Oranges: Stages of Tooth Eruption and Function of each

C: Crown formation (Preeruptive)

R: Root development (Eruptive)

O: Occlusion (Posteruptive)

What happens during preeruptive stage?

tooth germs grow, shift within the jaw, and move toward the surface as the crypt develops

What happens during the eruptive stage?

tooth moves toward oral surface, bone is resorbed, and cementum, PDL, alveolar bone form

What is the main function of the posteruptive stage?

to maintain tooth position during jaw growth and compensate for wear or tooth loss

What disintegrates during the eruptive stage?

the epithelial cells covering the crown of the tooth

What happens when Reduced Enamel Epithelium fuses with oral epithelium during eruption?

forms united oral epithelium, while macrophages and osteoclasts break down bone and REE enzymes break down surface epithelium = tooth emerges

What happens when a permanent tooth pushes against a deciduous tooth root?

the pressure forms osteoclasts which break down and cause root resorption (eats away) of the deciduous tooth’s root

Is root resorption constant or intermittent? Besides pressure, what else can cause root resorption?

intermittent (off and on); the enamel organ of the erupting tooth = can also cause deciduous teeth to fall out without a permanent tooth underneath

Exfoliation; why might a primary tooth stay despite a permanent tooth being present?

shedding or loss of a baby tooth; resorption doesn’t always fully happen

What does pressure do to bone during tooth movement? What does tension on periodontal fibers do to bone?

pressure = bone breakdown; tension = buildup (new bone formation)

Where do anterior permanent teeth develop?

develop apically and lingually to primary teeth (underneath root, behind tooth)

Where do permanent premolars develop?

between the roots of primary molars

What is passive eruption? Where is it often seen?

the gradual apical migration of the gingiva that occurs after tooth eruption; absence of clinical inflammation

Stage 1 of Passive Eruption

attachment epithelium at base of gingival sulcus resting entirely on enamel

Stage 2 of Passive Eruption

attachment epithelium primarily on enamel with a bit of cementum

Stage 3 of Passive Eruption

attachment epithelium extends from cementoenamel junction (CEJ) onto cementum

Stage 4 of Passive Eruption

attachment epithelium entirely on cementum apical to CEJ; pathologic, gingival recession