Anatomy of Primary Teeth

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 • 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 • 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 • Prominent MB cervical bulge • Transverse ridge

19. Primary Crown Anatomy • Maxillary 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