1. Anatomy of Primary Teeth
Steven Chussid D.D.S.

2. Lecture Overview Primary Dentition
General Morphological considerations
Implications of Primary tooth morphology

3. Primary Dentition 20 primary teeth as compared to 32 permanent teeth
No premolars in the primary dentition
The primary molars are replaced by the premolars
The permanent molars erupt distal to the primary second molars

4. Eruption Patterns of Primary Teeth
Sequence more important than timing
Symmetrical pattern
Mandibular teeth erupt first

5. Approximate Eruption Schedule
“7+4” Guideline

6. 7 Months = First Tooth Erupts

7. 11 Months = 4 Erupted Teeth 7 months + 4 = 11 months
0 teeth + 4 = 4 teeth

8. 15 Months = 8 Erupted Teeth 11 months + 4 = 15 months
4 teeth + 4 = 8 teeth

9. 19 Months = 12 Erupted Teeth 15 months + 4 = 19 months
8 teeth + 4 = 12 teeth

10. 23 Months = 16 Erupted Teeth 19 months + 4 = 23 months
12 teeth + 4 = 16 teeth

11. 27 Months = 20 Erupted Teeth 23 months + 4 = 27 months
16 teeth + 4 = 20 teeth

12. General Morphologic considerations
Crown
Pulp
Root

13. Crown of Primary Teeth Shorter Narrower occlusal table
Constricted in the cervical portion
Thinner enamel and dentin layers
Enamel rods in the cervical area directed occlusally
Broad and flat contacts
Color is usually lighter

14. Crowns of Primary Teeth
Prominent mesio-buccal cervical bulge seen in primary molars
Incisors have no developmental grooves or mammelons

15. Primary Crown Anatomy Mandibular Central Incisors-
Symmetrically flat when viewed from buccal
Crown about 1/3 length of root
Cingulum present on lingual surface
Mandibular Lateral Incisor
Similar form to central
Usually longer
Incisal edge slopes toward distal and DI angle more rounded

16. Primary Crown Anatomy Maxillary Central Incisor
Only tooth that has a greater mesiodistal width than height
Prominent cingulum
Incisal edge straight
Maxillary Lateral Incisor
Similar form to cental
Smaller and DI angle rounded

17. Primary Crown Anatomy Maxillary Canine Mandibular Canine
Crown constricted at cervical region
Well developed, sharp cusp
Root is long, more than 2X crown
Mandibular Canine
Similar form to maxillary
Crown shorter and narrower labiolingually

18. Primary Crown Anatomy Maxillary First Molar Mandibular First Molar
Unique appearance
Three cusps-MB, DB and Lingual
Prominent MB cervical bulge
Mandibular First Molar
Also unique in appearance
Four cusps-MB, DB, ML and DL
Transverse ridge

19. Primary Crown Anatomy Maxillary 2nd Molar Mandibular 2nd Molar-
Resembles permanent maxillary first molar but smaller
Mandibular 2nd Molar-
Resembles permanent mandibular first molar but smaller

24. Pulps of Primary Teeth Relatively larger
Pulp horns are closer to the outer surface
Great variation in size and location
Mesial pulp horn is higher
Pulp chamber shallow
Form of the pulp follows the external anatomy
Usually a pulp horn under each cusp

25. Pulpal Anatomy

26. Roots of Primary Teeth
Roots of anterior teeth are narrower mesio-distally
Posterior teeth have longer and more slender roots in relation to crown size
Molar roots flare more as they approach the apex
Apical foramina may be larger and accessory canals often larger and more numerous

27. Implications of Primary tooth morphology
The progress of caries is much faster in the primary dentition, so incipient lesions should be restored sooner than later!
Thinner enamel and dentin
Mesial pulp horn higher

28. Procedures in Primary Teeth
Restorative Dentistry
Enamel is thinner, therefore modifications are necessary in the cavity prep
Broad contacts need to be restored
Beware of the mesio-buccal pulp horn
May need to do SSC if both proximal surfaces involved
Preserve the buccal cervical ridge to obtain mechanical retention for SSC

29. Procedures in Primary Teeth
Surgical Procedures
Conical anterior roots facilitate easy removal
Flared roots of the molars - use caution as premolar buds are located between the roots
Pulp Therapy
Pulpotomy- beware of perforations
Pulpectomy
Difficult on molars due to tortuous and irregular pulp canals
Beware of tooth buds

30. Summary Primary teeth have Thinner enamel and dentin layers
Pulp horns closer to the outer surface
Mesial pulp horn much higher
Relatively larger pulps
Enamel rods direct slightly occlusally in the cervical area
Cervical area is constricted significantly
Roots flare as they approach the apex
More tortuous and irregular pulp canals