1. ERUPTION OF TEETH
Tooth eruption is defined as the physiological movement of tooth from its site of development within the jaw to its position of function within the oral cavity.

2. Eruption of mandibular incisor
5 months
At birth
1 year
2 years
3.5 years
4.5 years
Figure Source: Dr. Sandra Meyers

3. Mixed dentition

4. Dentition:
Diphodont: two sets of dentition in humans
Primary vs Secondary dentition
Deciduous vs Permanent dentition
Mixed dentition: presence of two dentition
Teeth in primary dentition are smaller and fewer in number than
permanent dentition to conform to the smaller jaw size
Primary dentition: ~ 2 to 6 years of age
Mixed dentition: ~ 6 to 12 years
Permanent dentition: > 12 years

5. Source: http://www.columbia.edu/itc/hs/dental/d9903/lectures/lecture4.pdf

6. Mixed Dentition
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

7. Mixed Dentition: Presence of both dentitions
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

8. The rate of tooth eruption depends on the phase of movement
Intraosseous phase: 1 to 10 µm/day
Extraosseous phase: 75 μm/day
Environmental factors affecting the final position of the tooth:
Muscular forces
Thumb-sucking

10. Directions and rates of tooth eruption
Main direction is axial (i.e. long axis of the tooth)
Also movement in other planes – resulting in tilting and drifting
Eruption rates are greatest during times of crown emergence
Rates will differ based on tooth type – balance between eruptive forces and resistive forces
permanent maxillar y incisors – 1mm/month
mandibular second molars – 4.5 mm in 14 weeks
permanent third molars – 1 mm in 3 months
eruption rates can slow to 1 mm/6 months in crowded dentitions

11. Clinical crown: Anatomic crown:
During eruption, the exposed crown extending from the cusp tip to the area of the gingival attachment
Anatomic crown:
Entire crown, extending from cusp tip to the cementoenamel (CE) junction

12. Eruption
Active eruption :Is the movement of the tooth from its development site to its position in the dental arch.
Passive eruption does not involve tooth movement but occurs due to apical recession of gingival tissues exposing more tooth structure into the oral cavity.

13. PASSIVE ERUPTION
Gingival recession onto & down the cementum with loss of alveolar-crest bone
Raising the banana, then peeling the banana

14. Tooth eruption Eruption takes place in chronological order
involves active eruption – vertical movement of the tooth
as opposed to passive eruption – recession of the gingiva.
root growth, hormonal action, contractile collagen, vascular pressure??
no requirement for the root
Three distinct phases to the development of the dentition
1. pre-eruptive – initiation of tooth development
2. tooth eruption – prefunctional phase
begins as the roots begin to form
3.Posteruptive: development and maintenance of occlusion – functional phase
after the teeth have emerged into the oral cavity

15. END OF CROWN FORMATION
Ameloblasts will finish full thickness of cusp enamel & reduce in height
Dentine widens
DENTAL PAPILLA become pulp process proceeds downs
Stellate reticulum follows Cervical loop down then stops: Crown defined
Odontoblast recruitment site
Cervical loop:

16. Types of movements of tooth during three phases of eruption
1.Axial or occlusal
2.Bodily
3.Tilting
4.Rotation
Excentric

17. covering the recently formed crown
Eruptive phase starts at the beginning of root formation Note the reduced enamel epithelium
covering the recently formed crown
Essentials of Oral Histology and Embryology. James Avery, 2nd edition

18. Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

19. Eruption of mandibular incisor
5 months
At birth
1 year
2 years
3.5 years
4.5 years
Figure Source: Dr. Sandra Meyers

20. Eruption: tooth in bony crypt

21. Eruption phase

22. Eruption phase

23. Post eruption phase

24. The cervical portion of the reduced enamel epithelium is still attached to the neck of the tooth .
-this fused tissue serves as the initial junctional epithelium (thin dotted line) and creates a seal between the tooth and the surrounding tissue

25. Histological phases of eruption:
1) Pre-eruptive phase: It starts at the beginning of tooth development and ends when the crown formation is completed. It is characterized by:
a) Growth of tooth germ i.e. dental (enamel) organ, dental papilla and dental sac. b) Formation of bony crypt. c) Movement of developing tooth within the growing jaw. Different types of movement occurs: bodily, axial, rotational and eccentric( i.e. shifting the long axis of the developing tooth).

26. 2)Prefunctional ( Eruptive) phase:
It starts at the beginning of root formation and ends when the tooth reaches occlusion. It is characterized by: a) Formation of the root. b) Bone apposition especially at the fundus of the crypt. c) Initial organization of periodontal ligament. d) Rapid active eruption

27. 3) Functional ( Posteruptive ) phase:
It starts when the erupting tooth reaches occlusion with its antagonists and lasts throughout the life of the tooth.
It is characterized by: a) Occlusal active eruption (more cementum and alveolar bone apposition). b) Occlusomesial physiological drift .
c) alveolar bone remodeling. d) Organization of periodontal ligament principal fibers.

28. Two types of tooth movement in
pre-eruptive phase:
Total bodily movement
Movement where one part remains fixed while the rest continues to grow leading to change in the center of the tooth germ

29. Eruptive Tooth Movement
4 major events occur:
Root formation. Space is required for root formation
Proliferation of epithelial root sheath
Initiation of root dentin and pulp
Increase in fibrous tissue of the follicle
Movement. Occurs incisally or occlusally
The main reason for movement is so that the
roots can form normally
Reduced enamel epithelium fuses and contacts
the oral epithelium
Penetration of the tooth’s crown tip through the fused
epithelial layers allowing entrance of the crown into the
oral cavity
Intraoral incisal or occlusal movement of the erupting tooth
continues until clinical contact with the opposing crown occurs

30. Post Eruptive Tooth Movement
Movements to accommodate the growing jaws. Mostly occurs
between 14 and 18 years by formation of new bone at the
alveolar crest and base of socket to keep pace wit increasing
height of jaws.
Movements to compensate for continued occlusal wear.
Compensation primarily occurs by continuous deposition of
cementum around the apex of the tooth. However, this
deposition occurs only after tooth moves. Similar to eruptive
tooth movement.
Movements to accommodate interproximal wear. Compensated
by mesial or a proximal drift. Mesial drift is the lateral
bodily movement of teeth on both sides of the mouth.
Very important in orthodontics.

31. Why hemorrhage does not occurs during eruption
Degeneration of connective tissue (decrease in blood vessels and degeneration of nerves) immediately overlying the erupting teeth
Eruption pathway – altered tissue area overlying the teeth
Macrophages destroy cells and fibers by secreting hydrolytic
enzymes

33. Essentials of Oral Histology and Embryology. James Avery, 2nd edition

34. Mechanism(Theories )of tooth eruption
1.Bone remodeling
2.Root formation theory
3.Vascular hydrostatic pressure
4.PDL traction
5.Dental follicle
Multifactorial process but the most important factor is the PDL traction

35. MECHANISMS OF ERUPTION
Construction & Reorganization of PDL
Formation of the root
Deposition of alveolar bone?
Remodelling of bone overall
FURTHER INFLUENCES from: tooth/teeth in occlusion; muscle actions

36. Mechanism of eruption: Theories
1- Root growth ( increase in root length ): Root growth seems to generate a force but it does not cause eruptive tooth movement. Evidence against this theory is that teeth without roots erupt, also some human teeth during eruption move a greater distance than the length of their fully formed roots. Further, teeth continue to erupt after root formation is completed and when root forming tissues were surgically removed in experimental animals, those teeth continued to erupt.

37. 2- Hydrostatic pressure from tissue fluid and blood vessels in periapical tissues:
Experimental evidence indicates that tissue pressure occlusal to an erupting tooth is less than that in the tissues apical to it. This pressure differential seems to favor axial eruptive movements.

38. 3. Bone remodeling theory
Experimental studies using bone markers clearly showed that bone apposition at the bottom of the bony crypt housing an erupting tooth is a result of the occlusal movement of the tooth not a cause for eruption.

39. PDL traction theory Linked to contractility of fibroblasts
Tractional forces are associated with pulling properties of fibroblasts
The tractional force of fibroblast is mediated through collagen fibers of the PDL
Explained as a sailor pulling a rope
Sail=tooth
PDL collagen fiber= a rope
Sailor=fibroblast

40. A sailor pulling a sail Sailor =Fibroblast Sail = Erupting tooth
Rope = Collagen fibers

41. Dental follicle
This theory suggests that the dental follicle has an important participation in tooth eruption.

42. Eruption of permanent teeth
Same as the primary teeth
Additional force generated by fibrous tissue containing remnants of the dental lamina, known as gubernacular cord
The gubernacular cord is the connective tissue link between the crypt and the oral mucous membrane.
Gubernacular cord provides a specific promoting role or a guiding path for eruption of the permanent teeth

43. Eruption of secondary tooth
Loss of primary teeth should occur first
Gubernacular cord: The connective tissue overlying a
successional tooth that connects with the lamina
propria of the oral mucosa by means of a strand of fibrous
connective tissue that contains remnants of dental lamina
Gubernacular canal: Holes noted in a dry skull noted lingual to primary teeth in jaws that represent openings of gubernacular cord .
As the successional teeth erupt, gubernacular canal
Widens enabling tooth to erupt .

44. Essentials of Oral Histology and Embryology. James Avery,
2nd edition
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci,
6th edition

45. Essentials of Oral Histology and Embryology. James Avery, 2nd edition

46. Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

47. ERUPTION: Problems Delayed eruption Early eruption Missing tooth
Impaction - failure to erupt e.g., from too little gap after premature loss of deciduous tooth
Retained root fragment
Malocclusion
Infra-occlusion (not high enough)
Excessive drift
Tilting (can occur early from germ rotation)

48. Problems of Premature Tooth Eruption
Natal and Neonatal Teeth

49. Congenitally Missing
Teeth