Odontogenesis

Question 1

Process of odontogenesis

Answer 1

0. Initiation
   Primary epithelial bands form in Week 6 along the Mx and Md processes.
   In Week 7, primary epithelial bands grow into the ectomesenchyme. → gives rise to 2 layers
   Epithelium = dental lamina
   Ectomesenchyme = vestibular lamina
   In Week 8, dental lamina forms localised thick projections, aka dental placodes.
1. Bud stage - Week 8
   Dental placodes proliferate, forming tooth bud.
   Ectomesenchyme condenses around bud.
2. Cap stage - Week 10
   Cells on outside divide faster than cells on inside, causing bud to invaginate and form a cap shape, called enamel organ
   Cap now sits on top of a ball of condensed ectomesenchyme aka dental papilla, the future dentine and pulp
   Surrounding ectomesenchyme is called dental follicle, future cementum and PDL.
   3 types of cells: stellate reticulum, outer enamel epithelium (cuboidal cells) and inner enamel epithelium (columnar cells)
3. Bell stage - Week 12
   Cap invaginates further, forming a bell shape
   Morphodifferentiation: Bell resembles crown of future tooth
   Cervical loop will form future root
   Week 14: Epithelium between IEE and stellate reticuum differentiate to form stratum intermedium (transports nutrients to ameloblasts)
   Histodifferentiation:
   Cells of inner enamel epithelium → ameloblasts → enamel
   Cells of outer enamel epithelium → odontoblasts → dentine
4. Crown stage, apposition and maturation
   Mineralisation of enamel and dentine
   Dental lamina disintegrates, detaching tooth germ
   Successional lamina forms germs for permanent teeth
   Tooth moves into final position, Emergence and eruption

Question 2

Amelogenesis

Answer 2

1) Pre-secretory phase
Cells of inner enamel epithelium differentiate into ameloblasts in Wk 14 - Bell stage.
By undergoing cell polarity change and developing protein-synthesising organelles

2) Secretory phase
Ameloblasts develop extensions on the apical surface, known as Tomes’ processes.
Initial enamel is rodless ie aprismatic
Enamel is immediately partially mineralised ~30%. (because of amelogenin)
Space between enamel is filled with enamel proteins.
The proximal part of Tomes’ process secretes hydroxyapatite crystals in a horizontal direction, forming inter-rod enamel
While distal part of Tomes’ process secretes HAP crystals in a more vertical orientation, forming enamel rods
As ameloblasts secrete enamel underneath them, they move coronally.

3) Maturation phase
Ameloblasts lose TP
Ameloblasts form Basal Lamina, binds to Basal Lamina via hemidesmosomes
Ameloblasts undergo modulation, where they alternate between
Smooth-ended: resorbs proteins and organic material
Ruffle-ended: deposits mineral
Process increases mineral content of enamel and decreases organic content
Process continues until enamel reaches full mineralisation of 96%.

Question 3

Dentinogenesis

Answer 3

Enamel organ sends signals
Dental papilla divides, forming odontoblasts from the outer enamel epithelium
Odontoblasts lay down collagen, forming organic matrix
Forms pre-dentine which matures to dentine.

Question 4

Cementogenesis

Answer 4

When enamel organ has disintegrated
Dental follicle touches dental papilla
Cementoblasts form
Outer: alveolar bone, inner: PDL

Question 5

Developmental defects at each stage of odontogenesis

Answer 5

Initiation - teeth presence/absence - anodontia/oligodontia(>6)/hypodontia(>6), supernumerary

Bud stage - size of teeth - macrodontia, microdontia

Cap stage - tooth bud abnormalities - Dens in dente, gemination (think gemini)

Bell/Apposition/maturation - individual layer - AI, DI, concrescence

Question 6

Amelogenesis Imperfecta (AI) genetics

Answer 6

Hereditary condition - X-inactivated - females display mosaic pattern - banding - wrinkled enamel.

Question 7

Types of Amelogenesis Imperfecta (AI)

Answer 7

Hypoplasia AI
Insufficient enamel matrix deposition
Qty defect

Hypomaturation AI
Insufficient removal of organic content from enamel matrix
Qly defect - brittle enamel

Hypocalcification AI
Insufficient transport of Ca mineral to be secreted into enamel
Qly - soft enamel

Dentinogenesis Imperfecta
Weakly attached enamel to dentine - limited interdigitation

Question 8

Ages of permanent teeth calcification

Answer 8

1 3-4months
2 3-4 months (upper - 1 year)
3 4-5months
4 1.5 - 2.25y
5 2.5-3y
6 Birth
7 2.5-3y
8 8-10y

Question 9

Ages of permanent teeth eruption

Answer 9

6y - 6
6-7y - Md 1s
7-8y - Mx 1s, Md 2s
8-9y - Mx 2s
9-10y - Md 3s
10-11y - 4s, Mx 5
11-12y - Mx 3s, Md 5
12-13y - 7s
17-25y - 8s

Question 10

Ages of primary teeth eruption

Answer 10

A - 6-7mths
B - 7-8mths
D - 1y-1.25y
C - 1.5y-1.7y
E - 2-3y

Question 11

Ages of primary teeth calcification

Answer 11

in utero
A - 12-16 wks
B - 13-16 wks
D - 14-17 wks
C - 15-18wks
E - 16-23wks