Embryological Development of the Tooth

1. Embryological Development of the Tooth

2. Three Stages: • Bud stage • Cap stage • Bell stage

3. Bud Stage and Dental Lamina • Epithelial thickening (dental lamina) starts at 6 - 8 weeks of fetal development • Lamina differentiates into tooth buds • 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. Root Development • Bell stage ends with formation of CE line • Enamel organ differentiates into Hertwig’s sheath, which forms the root structure

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

8. Eruption • Active 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

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 6 - 12) • 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. Ankylosis

15. 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

16. Deciduous Dentition

17. General descriptions: • Twenty primary teeth (A - T) • Dental formula: ICM • No premolars • Important in maintaining arch space for permanent dentition 2 2 1 1 2 2

18. 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

19. 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

20. 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

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

22. Deciduous Dental Anatomy Comparative Descriptions To Permanent Dentition

23. Maxillary Primary Teeth

24. Maxillary Central Incisor • No mamelons evident • M-D crown width greater than I-C crown height (only anterior tooth with this characteristic)* • M and D outlines exhibit more convexity than permanent

25. Maxillary central… • Cingulum more prominent • Lingual ridge a possibility • Lingual fossa deeper • Marginal ridges more prominent • Root is longer relative to crown height

26. Maxillary central… • Facial developmental depressions rare • Incisal view: M-D width noticeably wider than F-L dimension (MD>IC>FL) • Root deflected facially • Lingual CE line more apically located • Incisal edge is slightly facial to mid-root axis

27. Maxillary Lateral Incisor • Similar to primary central except: • Crown is narrower M-D than I-C • More incisal angle rounding • More prominent marginal ridges - deeper fossa • Lingual CE line more apically located • M-D width greater than F-L

28. Maxillary Canine • M-D, F-L and I-C dimensions nearly same* • M and D heights of contour at same level* • Lingual CE line more apical • No facial developmental depressions (?)

29. Maxillary canine… • M cusp ridge longer than D cusp ridge* (Cusp tip offset distally) • Cingulum and lingual ridges prominent - ML and DL fossae • Root deflected facially • Cusp tip is facial to mid-root axis

30. Maxillary First Molar • Crown is unique - does not resemble any other molar* • Crown morphology more similar to premolar’s • Crown wider F-L than M-D • Occlusal outine is 5-sided • An oblique ridge connects the ML and DB cusps

31. More first molar… • Facial CE line has depth of curvature towards mesial* • Two prominent cusps: MB and ML (largest) • Mesial marginal ridge prominent • Transverse ridge connects the MB and ML cusps • DL cusp greatly diminished • Three fossae/pits: mesial>central>distal

32. Still more first molar… • Roots are slender and flared • No root trunk (or very small) • Three roots (largest to smallest): L, MB, DB

33. Maxillary Second Molar • Larger in all dimensions than maxillary primary first molar • Closely resembles permanent maxillary first molar* • Cusp of Carabelli present

34. Mandibular Primary Teeth

35. Mandibular Central Incisor • Crown is symmetrical: M and D outlines evenly convex • No mamelons

36. Mandibular central... • Incisal edge in line with root center* • Root apex curves facially • F-L dimension relatively greater than permanent’s • Lingual CE line located more apically

37. Mandibular Lateral Incisor • Similar to primary central except: • Not as symmetrical • DI corner more rounded, slight twist to lingual • Cingulum bulges towards distal

38. Mandibular lateral... • Marginal ridges more prominent, deeper fossa than central • Incisal edge also in line with root center • Root apex has a distal and also a facial inclination

39. Mandibular Canine • Similar to maxillary canine except: • Much narrower F-L • M-D narrower than I-C width • M cusp ridge shorter than D cusp ridge

40. Mandibular First Molar • Crown is unlike any other primary or permanent tooth* • Wider M-D than F-L • Two roots, M and D (mesial much longer and wider) • F and L root surfaces almost parallel

41. More first molar… • CE line contour off-set to mesial • Prominent facial cervical ridge • Four cusps: MB, ML, DB, DL (largest to smallest) • Mesial crown outline straight* • Mesial HOC more cervical than distal*

42. Still more first molar… • Prominent mesial transverse ridge* • Three fossae: mesial, central, distal (?) • Two pits: mesial and central • No distal pit* • Distal of occlusal table wider than mesial • Prominent MB bulge

43. Mandibular Second Molar • Closely resembles permanent mandibular first molar except: • All three facial cusps more similar in size* • Occlusal table narrower F-L • M root much longer and wider than D root • F and L surfaces of M root nearly parallel

44. Lights!

45. Primary DentitionReview

46. Development and Eruption • All 20 primaries begin calcifying 4-6 months in utero (2nd trimester) • Crown completion in all primaries within first year after birth • Eruption from 6 months to 2 years • Mixed dentition from age 6 to 12 • Age 4-5 yrs, primate spaces develop due to growth of maxilla and mandible

47. Eruption Sequence • Mandibular teeth erupt prior to their maxillary counterparts • Sequence: • Centrals • Laterals • 1st molars • Canines • 2nd molars

48. Exfoliation sequence: • Preceeds the eruption sequence of the permanent dentition. • Root resorption begins one year prior to exfoliation • All second molars are lost about the same time

49. Unique Characteristics of Primary Teeth

50. All Primary Anterior Teeth... • Apical 1/3 of root curves facially • Facial crown surface smooth, no mamelons or perikymata • CE line on lingual is more apical than facial • Root is long relative to crown length • Incisal edge is in-line with mid-root axis