3. Objectives:
At the end of this chapter the student should be
able to understand the following:
• Phases of tooth eruption.
• Theories of tooth eruption.
9. I. Pre eruptive phase:
This phase begins in the early bell stage and
ends at the beginning of root formation.
Made by the deciduous and permanent tooth
germs within tissues of the jaw before they
begin to erupt.
10. First
Pattern of movement of deciduous teeth:
• teeth germs are small
• have good space in the jaw bones
• grow rapidly
• become crowded.
Then
I. Pre eruptive phase:
11. This crowding is relieved by
Jaw growth:
• In length
• In width
• In height
I. Pre eruptive phase:
13. Pattern of movement of permanent teeth:
A. Anterior teeth
Permanent incisors and canine, first
develop lingual to the deciduous tooth
germs in the same crypt.
As the deciduous tooth erupt, they
move to be apical in position and
occupy their own bony crypts.
I. Pre eruptive phase:
14. Permanent premolars develop lingual to their
predecessors at the level of their occlusal
surfaces and in the same bony crypt.
Then shift to be situated in their own
crypts beneath the divergent roots of the
deciduous molars.
Pattern of movement of permanent teeth:
B. Premolars
I. Pre eruptive phase:
16. Deciduous 1st molar and
permanent 1st premolar
of the mandible from birth to
14 years
17. • Permanent molars have no predecessors;
develop from backward extension of dental
lamina.
• Mandibular molars develop in the base of the
mandibular ramus with their occlusal surfaces
facing mesially.
Pattern of movement of permanent teeth:
C. Molars
• Maxillary molars develop in the maxillary
tuberosity with their occlusal surfaces facing
distally.
I. Pre eruptive phase:
18. Maxillary molars
in the tuberosity
facing distally
Swing around with growth of
the maxilla
Mandibular molars
in the base of the ramus
facing mesially
tilt to be upwright
with growth of the mandible
Pattern of movement of permanent teeth:
C. Molars
I. Pre eruptive phase:
19. Histologic changes:
1. Growth of tooth germs.
2. Formation of bony crypt (bone remodeling).
3. Movement of the developing tooth within the
growing jaw.
I. Pre eruptive phase:
20. Types of movements:
• Bone resorption on the crypt
wall toward which the tooth
moves.
• Bone depositon on the crypt
wall behind it.
• Bone resorption only occurs on
the crypt wall facing the
growing tooth germ.
• Shift of the center.
Bodily movement (Drifting) Eccentric growth
I. Pre eruptive phase:
22. • It begins by root formation and ends when the tooth
reaches the occlusal plan.
• Made by a tooth to move from its position within the
bone of the jaw to its functional position in occlusion.
II. Eruptive phase:
23. it happens due to gradual
retraction of attachment
epithelium from tooth
surface.
it is gradual appearance of
the tooth in the oral cavity
due to axial occlusal
movement of the tooth
Active eruption: Passive eruption:
II. Eruptive phase:
24. Once the tooth has broken through the
oral mucosa, further emergency of the
tooth results from active eruption
movements and passive separation of the
oral epithelium from the crown surface.
So,
Until,
it reaches the occlusal plane and meets
its antagonist.
II. Eruptive phase:
25. • The principal direction of movement is
occlusal or axial (for deciduous and
permanent teeth).
• However, movement in other planes
also occur such as bodily, tilting, and
rotating movement.
Types of movements:
II. Eruptive phase:
26. Tooth is covered by; REE, CT, bony
crypt and oral epith.
Pressure exerted by the developing
tooth induces bone resorption.
REE produces desmolytic enzymes
to degrade CT.
REE+ oral epith.= epithelial plug.
Central cells of this plug degenerate
forming an epithelial lined canal
through which the tooth will erupt
without hemorrhage.
REE shares in the formation of
dento-gingival junction.
A. Epithelial plug.
II. Eruptive phase:
27. B. Eruptive path:
Gubernacular cord and Gubernacular canal
Gubernacular cord is a strand of fibrous tissue
“CT” containing reminants of the dental
lamina.
Gubernacular canal into which the cord is
enclosed; it is widened by osteoclast to guide
permeant teeth to erupt.
II. Eruptive phase:
29. C. Root Formation:
Apical proliferation of ERSH leads to..
Bone resorption of the crypt floor
Bone deposition on the crypt walls
Organization of PL fibers.
Cementum formation at root surface.
II. Eruptive phase:
30. D. Readjustment of the PL fibers:
Readjustment of PL is performed by
fibroblasts which synthesis and
degrade collagen fibers.
Once root is established PL must be
remodeled to accommodate
continuous eruption.
It was suggested that there was a
structure known as intermediate
plexus that permits remodeling of the
PL fibers at the middle area without
the need of fibers to re-embed
themselves in cementum and bone.
But recent studies showed that this
structure is only present in rodents
and not in humans.
II. Eruptive phase:
31. E. Alveolar ridge:
It grows rapidly by deposition of bone
trabeculae parallel to the fundus of the
socket to aid in tooth eruption due to
incomplete formation of root at this stage.
II. Eruptive phase:
33. III. Post eruptive phase
• It begins after the tooth has reached its
functional position in the occlusal plane,
continues through the whole life of the tooth.
• Its movements divided into three categories:
Accommodation for
growth
Compensation for
occlusal wear
Accommodation for
interproximal wear
34. Histologic changes:
• More cementum and alveolar bone
apposition.
• Alveolar bone remodeling due to an
occluso-mesial drift.
• Organization of PDL fibers.
Types of movements:
• Axial movement
• Mesial movement
III. Post eruptive phase
38. But
• Force exerted on bone lead to resorption.
• Some teeth move a distance greater than
the length of their roots as upper canine.
• Eruption of Rootless teeth.
• When the ERSH is surgically removed the
tooth erupt.
I. Root formation
theory
39. II. Bone Remodeling
theory
Selective bone resorption and deposition
causes tooth eruption.
In human, the base of the 1st & 3rd molars showing a
continuous bone resorption in the fundus floor. While,
2nd molar, 1st and 2nd premolars showed bony
deposition in the fundus floor.
But
41. So..
The selective bone remodeling
which occur around the root are
the result not the cause of tooth
movement.
II. Bone Remodeling
theory
42. III. Dental follicle
theory
Pattern cellular activity involving the REE and
the DF associated with tooth eruption, which
facilitates CT degradation and bone resorption
as the tooth erupts.
43. III. Dental follicle
theory
lack of factors that stimulates differentiation of osteoclasts,
eruption is prevented because no mechanism for bone removal
exists.
Local administration of this factor permits the
differentiation of osteoclasts, and eruption occurs.
Removal of developing premolar without disturbing the DF,
or if eruption is prevented by wiring the tooth germ down to
the lower border of the mandible, an eruptive pathway still
forms within the bone as osteoclasts widen the gubernacular
canal.
If the DF is removed, however, no eruptive pathway forms.
Furthermore, if a metal or silicone replica replaces the tooth
germ, and so long as the DF is retained, the replica will erupt,
with the formation of an eruptive pathway.
44. IV. Periodontal ligament
traction theory
cells and fibers of periodontal ligament possess
contractile force
Tooth movement is brought about by:
A. Fibroblast contractile properties
B. Connection with collagen fibers extra-
cellular “fibronexus”
C. Oblique alignment of PDL collagen
fibers
45. V. Vascular pressure
theory
Local increase in blood pressure at
apical area lead to occlusal movement
of the tooth.
Increased bl. press. rates increase
eruption rate & increased number of
bl. cap at the apical region in
comparison with alveolar crest region.
46. • Although no one theory is yet supported by sufficient experimental evidence, it is
probably multifactorial in that more than one agent or factor share in the
eruptive movement.
• The dental follicle, REE, the surrounding PDL and the alveolar bone share in the
eruption process.
• The tooth movement results from a balance between tissue destruction (coronal
bone, C.T. and surface epithelium) and tissue formation (root, PDL and bone).
