L4-Tooth Development 2 (Crown & root formation, eruption and shedding)

Question 1

During the late bell, early crown stage mineralized enamel and dentin begin to form where? How does this progress migrate?

Answer 1

Begins at the tip of cusp or incisal edge on either side of BM (becomes DEJ).
Progressive differentiation continues down the slopes of the cusps, always starting with odontoblasts first.

Question 2

What structure descends from the cervical loop to initiate root formation by inducing dental papilla cells to differentiate into odontoblasts and produce root dentin?

Answer 2

HERS = Hertwig’s Epithelial Root Sheath

Question 3

Eventually, cementoblasts lay down a layer of cementum and the epithelial tissue, HERS, breaks up into Epithelial Rests of Malassez to allow periodontal ligaments to attach the root to the alveolar bone. What structure produces the 3 cell types necessary for this chain of events? What are the cells?

Answer 3

The DENTAL FOLLICLE gives rise to the three essential cells…

1. Cementoblasts - forms cementum
2. Fibroblasts - form periodontal ligaments
3. Osteoblasts - form alveolar bone

Question 4

How are cementocytes oriented to allow them to receive nutrients? How does cementum formation change throughout life?

Answer 4

Cementocytes and their canaliculi are oriented towards the vascularized periodontal ligaments. Cementum forms continuously throughout life, thickening as we age.

Question 5

One of the first steps of eruption is epithelial fusion. What two layers of epithelium are fusing?

Answer 5

Oral epithelium and the Reduced Dental Epithelium

Question 6

What cells are responsible for root resorption?

Answer 6

Odontoclasts

Question 7

What two structures are necessary for Eruption? Why? How do TGF-beta and CSF-1 play a role in eruption?

Answer 7

1. Dental Follicle (DF): controls bone resorption coronally.
   - CSF-1 draws osteoclasts to the coronal side of the DF to break down roots.
2. Reduced Dental Enamel (RDE): Found ONLY on coronal side.
   - Releases TGF-beta, which signals the direction of eruption.

Question 8

Dental epithelium and dental mesenchyme can be separated and recombined with other tissues to grow in organ culture. Provide an example. Specifically, what structures make up dental mesenchyme and epithelium?

Answer 8

Dental Epithelium can be recombined with skin mesenchyme to form skin.

• Dental epithelium is the outer and inner dental epithelium and later Reduced dental epithelium.
• Dental Mesenchyme is the Undifferentiated Dental Papilla region, which contains BV and nerves (becomes pulp).

Question 9

Humans have heterodont and diphyodont dentition. What does this mean?

Answer 9

Heterodont Dentition = Different kinds of teeth (incisors vs molars)
Diphyodont Dentition = Two sets of teeth.

Question 10

Anodontia? Subsets of anodontia; Oligodontia and hypodontia?

Answer 10

Anodontia = Congenitally missing teeth.
Hypodontia = Missing only a few teeth
Oligodontia = Congenital absence of MANY teeth