1. Embryological Development of the Tooth “Odontogenesis”

2. Three Stages:
Bud stage
Cap stage
Bell stage

3. Bud Stage and Dental Lamina
Epithelial thickening (dental lamina) starts at weeks of fetal development
Lamina differentiates into tooth buds
Enamel organ ➙ ameloblasts
Dental papilla ➙ odontoblasts
Dental follicle ➙ cementoblasts, osteoblasts, & fibroblasts
Bud Stage: buds are round or ovoid

4. Cap Stage
Round form starts to invert
Appearance of a cap - cap stage

5. Bell Stage Concavity deepens - bell stage
Most of enamel and coronal dentin laid down; DEJ identifiable
Connection with dental lamina disintegrates
Permanent tooth bud starts forming

6. A: Enamel organ (ameloblasts)
B: Dental papilla (odontoblasts)
C: Dental follicle (cementoblasts, osteoblasts, fibroblasts)

7. Root Development Bell stage ends with formation of CE line
Enamel organ differentiates into Hertwig’s sheath, which forms the root structure

8. Root Completed
Deciduous teeth: at about age 3 (one year from eruption to completion)
Apical foramen becomes constricted

9. Eruption Active eruption: Passive eruption:
Entry of tooth into oral cavity until contact with opposing tooth
Passive eruption:
Continuing adaptation of tooth to changing occlusal relationships
Continues throughout life of the tooth

10. Deciduous Eruption Sequence
1. Central incisors
2. Lateral incisors
3. First molars
4. Canines
5. Second molars
*Rule: mandibular precedes maxillary

11. Positioning of Developing Permanent Teeth
Permanent anteriors develop lingual to primary roots
Premolars develop within root furcations of primary molars

12. Mixed Dentition Period
Presence of both deciduous and permanent dentition (ages )
Mandible/maxilla start growth spurt (age 5)
“Primate” spaces form between teeth
Permanent first molars erupt (age 6) - cornerstones in permanent occlusion

13. Resorption
Permanent teeth start resorption of primary roots (osteoclastic process)
Resorption starts at least one year prior to exfoliation
Ankylosis: root fused to bone, disrupts resorption and exfoliation

14. Exfoliation Root structure mostly resorbed, tooth is loose
Mandibular teeth precede maxillary in exfoliation except:
Primary second molars, all four are lost about same time

15. Deciduous Dentition

16. General descriptions:
Twenty primary teeth (A - T)
Dental formula: I C M
No premolars
Important in maintaining arch space for permanent dentition 2 1 2

17. Comparisons With Permanent Dentition
Generally smaller than permanent
Crowns are shorter relative to total tooth length
Crowns wider M-D relative to height
Facial & lingual HOC closer to cervical line

18. More comparisons… Crowns exhibit more F and L convexity
Crowns more constricted cervically and occlusally in F-L dimensions
Presence of a cervical ridge on facials of all teeth as well as linguals of all anteriors*
Fewer anomalies shapes more consistent

19. Still more comparisons…
Deciduous roots longer relative to crown height
Roots are smaller in other dimensions
Apices of anterior roots are facially inclined
Molar roots are flared - more space for permanent buds
No root trunks - branching occurs close to crown

20. Finally… Deciduous crowns have milk-white color Pulp cavities larger
Enamel and dentin layers thinner

21. Tooth ID #2
Anteriors + Premolars

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