The document describes the stages of tooth formation, starting from the bud stage through to the root formation stage. It details the cellular differentiation involved in the development of enamel and dentin, as well as the interactions between ectoderm and mesoderm. Key processes include the formation of the enamel organ, the role of odontoblasts and ameloblasts, and the transition from baby teeth to permanent teeth.

1. Tooth Formation
Stages of Tooth Formation
A. BUD STAGE
1. Neuro-ectoderm cells (instead of fusing into neural canal) some migrate from
neural crest into mesoderm (will become CT) right under maxillary & mandibular
arches
2. Neuro-ectoderm cells secrete growth factors inducing ectoderm epithelial cells
to divide (enlargement)  forms epithelial tooth buds (10 future deciduous
teeth per arch)
B. CAP STAGE – EARLY
3. Epithelial structure (from oral ectoderm) divides & penentrates mesoderm
forming cavity  future enamel organ
4. Neuro-ectoderm cells mix with mesodermal cells forming neural crest mesoderm
C. CAP STAGE – LATE
5. Future enamel organ remains connected to oral ectoderm by dental lamina
6. Cavity enlarges, cells of enamel organ differentiates into defined layers by going to
different regions :
a. Outer dental epithelium (ODE): squamous
o Some will form a second bud of permanent tooth (@ age 3-4, will push
out baby tooth)
o ODE remains connected to ectoderm
b. Inner dental epithelium (IDE): tall columnar
o At end of late stage, will start recruiting neuroepithelial cells to align
underneath
7. These neurocrest mesoderm cells (mix of ecto + mesoderm cells) start
differentiating into odontoblasts
D. BELL STAGE
8. Enamel organ also differentiates into:
a. Stratum intermedium: cuboidal cells sitting on top of IDE
b. Stellate reticulum: star-shaped cells scattered in space btw ODE +
IDE
9. IDE is formed by ameloblasts which synthesize enamel  shaping the
crown at this stage
10. Cervical loop  transition from IDE to ODE; marks position of neck of
tooth (future crown – root junction), grows deeper into mesoderm
(bordered by IDE + ODE)
11. Odontblasts become aligned beneath IDE, primitive dental papilla (future
pulp) is formed

2. E. ROOT F ORMATION
12. Junction between IDE and odontoblast marks dentin-enamel
junction: from this point odontoblast grows inwardly
o IDE (below original level of cervical loop) will STOP synthesizing
enamel inwards
o Only serves to recuit & align more odontoblasts under
o At the same time, odontoblasts above junction synthesizing
pre-dentin outwards, with cytoplasmic processes growing
longer
o Pulp becomes more narrow & dentin becomes thicker
o Ameloblasts (in IDE above original cervical loop) synthesize
enamel inwards
o Enamel appears BLUE in immature form due to lots of
proteins (enamelins, amelogenins)
o Mature enamel: all proteins gone  after
decalcification will only space remains
13. Below dentin-enamel junction, ODE + IDE starts to disappear
(apoptosis), odontoblasts will induce mesenchyme to differentiate
into cementoblasts which will form cementum
14. Once enamel fully formed, entire enamel organ (ODE, ameloblasts,
IDE, etc.) disappears
15. Forming tooth is in pocket of alveolar bone, between bone &
cementum  periodontal ligament
16. Baby tooth functions until 5-6 years of age
17. Permanent tooth awaits further development until baby tooth
schedule to fall out; develops in same manner
18. Odontoclasts (osteoclasts) erode root of baby tooth to create space
for permanent tooth to grow; this growth occurs at the same time
 when baby tooth falls out, only crown is left