Eruption of teeth

1. Head of oral biology Al-Azhar dental college

2. Tooth eruption is the process by which
developing teeth emerge through the soft
tissue of the jaws and the overlying mucosa to
enter the oral cavity, contact the teeth of the
opposing arch, and function in mastication .
These movement are too complex and do not
cease after reaching the teeth of the opposing
arch, but continue through the whole life span
of the normally functioning teeth.
Tooth eruption begin as far as the crown of
the developing tooth has matured and the
root commences its growth .

3. Physiologic tooth movement ( eruption ) occur in
order to attain and maintain the functional
alignment of teeth in relation to each other in the
same jaw and with those found in the opposing jaw .
Terminology of eruption :
Active eruption : it is the actual movement of the
tooth from its developmental site to its position in
the dental arch.
Passive eruption : does not involve tooth movement
but occurs due to apical recession of gingival tissue
exposing more tooth structure into the oral cavity .
Anatomical crown : it is that part of the tooth which
is covered by enamel.
Clinical crown : it is that part of the tooth exposed to
the oral cavity

4. Phases of tooth eruption
1. Preeruptive phase: which begins in the
early bell stage and ends at the beginning of
root formation.
2. Prefunctional eruptive phase: Starts with
initiation of root formation and completed
when the teeth reached its functional position
in occlusion. This phase has an intraosseous
and extraosseous compartments. 4 stages:
root formation, movement, penetration and
occlusal contact .

5. 3. Functional (Posteruptive) phase: Takes place
after the teeth are functioning to maintain the
position of the erupted tooth in occlusion while
the jaws are continuing to grow and
compensate for occlusal and proximal tooth
wear and ends at the end of life span of the
tooth.

6. Relative position of primary and permanent incisor
teeth.
A, Preeruptive period. B, Prefunctional eruptive period.

7. 1-PATTERN OF TOOTH MOVEMENT IN THE PRE-ERUPTIVE
PHASE:
a- DECIDUOUS TEETH :
At the beginning , the differentiated deciduous
tooth germs have enough space between them.
Rapid growth of deciduous tooth germs utilizes
the available space between them leading to
crowding of the developing deciduous germs
particularly in the incisors and canine region.
This crowding is relieved by :
1-growth of the jaws in length, which provides
room for the deciduous molars to move
backward and for incisors and canine to move
forward toward the midline by bodily or drifting
movement.

8. 2-Increase in width of the jaws ,which leads to
outward movement of the tooth germs labially
or bucally by bodily movement.
3-Increase in height of the jaws, which leads
to the occlusal movement by eccentric growth.
b-PERMENANT TEETH WITH DECIDUOUS
PREDECESSOR:
A-Permanent incisor and canine tooth germs
develop lingual to their predecessors at the
level of their incisal surfaces and in the same
bony crypt. Then the anterior permanent tooth
germs occupy a more apical position as their
predecessor erupt.

9. They lie in their own bony crypt which is
attached to the bone of the lingual plate of the
jaws through a canal called GUBERNACULAR
CANAL which is filled with the gubernacular
cord. This cord consists of C.T. and remnants
of the dental lamina. It is a link between the
crypt of the permanent tooth germ and the
oral mucous membrane.
IT HAS BEEN PROPOSED THAT GUBERNACULAR CANAL
PROVIDE THE DIRECTIONAL PATH FOR ERUPTION.

11. B- The premolars also begin their development
lingual to their predecessors at the level of their
occlusal surface and in the same bony crypt. At
the end of this phase , they shift to a position
beneath the divergent roots of their
predecessors. The opening of the gubernacular
canal of the premolars crypts are found within
the socket of the corresponding deciduous
molars.
C-Permenant molars have no predecessors
show different movements.The maxillary molars
develop in the tuberosity of the maxilla,their
occlusal surfaces facing downward and

12. distally. Then move round when sufficient
space is provided by growth of maxilla at
eruptive phase.
The mandibular molars develop with their
occlusal surfaces inclined mesially.Then
become upright when available space is
obtained.

13. TYPES OF MOVEMENT DURING THE PRE-ERUPTIVE
MOVEMENT :
1- Bodily [drifting] movement of the tooth germ during
which osteoclastic activity with bone resorption on the
surface of the crypt wall in advance of the moving
tooth[i.e. the surface toward which tooth moves],while
bone deposition occurs on the crypt wall behind.
2-Excentric growth : it means that one part of the
developing tooth germ remains stationary and the
remainder continues to grow leading to a shift in its
center e.g. the deciduous incisor maintain their
superfacial position as the jaw grow in height.During
excentric movement only bone resorption occurs and
is found on the surface of the crypt faces the growing
tooth germ.

14. II -PATTERN OF TOOTH MOVEMENT IN THE
ERUPTIVE PHASE :
During this phase the tooth moves from its
position within the bone of the growing jaw to
its functional position in the occlusal plane.
The principle direction of movement is axial or
occlusal. However, movement in other plane
also occurs.
So, during the eruptive phase tooth moves in
different directions which are :
a-Axial [occlusal] movement in the direction
of the long axis of the tooth.

15. b-Drifting [bodily] movement in
distal,mesial,lingual or buccal direction.
c-Tilting or tipping movement: around the
transverse axis of the tooth[ as in case of
permanent molars ].
d-Rotating movement : around the
longitudinal axis of the tooth [in case of lower
central incisors, and lower canines.
THE DEVELOPMENTAL CHANGES OCURRING DURING THE
ERUPTIVE PHASE INCLUDE :
1-ROOT FORMATION
2-FORMATION OF THE ATTACHMENT APPARATUS [P.L.,BONE&
CEMENTUM].
3- DENTOGINGIVAL JUNCTION.

16. III- PATTERN OF TOOTH MOVEMENT IN POST-ERUPTIVE
PHASE :
During this phase the tooth moves to :
1) Maintain its position while the jaw increase in height
. This movement occurs most actively between the age
of 14 -18 years and is associated with condylar
growth, then it ceases when jaw growth is completed .
The principle movement is axial during this period
.Histologically , bone deposition occurs at the alveolar
crest and in the socket floor. This bone is not
responsible for tooth movement because it occurs
latter to tooth movement.
2) Compensate for occlusal and proximal wear of the
teeth which continue throughout the life span of the
tooth. so

17. a. The occlusal wear is compensated by axial
movement of the tooth. It is assumed that the
continuous deposition of cementum around the
apices of the roots is sufficient to compensate for
occlusal wear, but there is no evidence that
deposition of cementum actively move the tooth. It
is only infilling phenomenon.
b. Proximal wear also takes place at the contact
points between teeth. To compensate this wear &
maintain tooth contact ,mesial drift occurs.
Histologically , this mesial drift is seen as selective
deposition and resorption of bone on the socket wall
by osteoblasts & osteoclasts respectively. With
electron microscope collagen remodeling in the
periodontal ligament is seen.

18. MECHANISM OF TOOTH MOVEMENT
The nature of the intrinsic forces involved in
active tooth eruption is not fully understood .
Available experimental evidence seems to
support factors related to tissue tension
theories. Experiments where tooth is wired to
the lower border of the mandible show that
inspite of immobilizing the tooth , an eruptive
path is formed by resorption of the overlying
bone. However ,if the dental follicle associated
with erupting tooth is removed ,no such
pathway in bone is formed this finding lead to
the fact that human teeth according to

19. a sepcific chronology imply the presence of a
programmed mechanism that leads to tooth
eruption. Such mechanism is probably a
multifactorial one that includes control by
specific gene[s],hormones as well as several
growth factors. The mechanism that brings
about tooth movement is not properly
understood.

20. Epithelial/connective tissue interactions and
molecular signaling during tooth eruption:
During active eruption particularly the prefunctional
stage, epithelial/connective tissue interactions have
been demonstrated between the reduced dental
epithelium covering the enamel of erupting teeth and
the adjacent connective tissue; of the dental follicle.
Signals from the reduced dental epithelium lead to
attraction of monocytes to the dental follicle where
CSFI (Colony stimulating factor 1) promotes their
differentiation into osteoclasts. EGF (Epidermal
Growth Factor) which upregulates the expression of
TGF B ( Transforming Growth Factor beta) have been
localized in the dental follicle.

21. The reduced dental epithelium also secretes
proteolytic enzymes which break down the connective
tissue in the pathway of the erupting teeth to facilitate
their movement, path of least resistance to their place
in the dental arch. Another product of the reduced
dental epithelium is IL-I A (Inerleukin 1 alpha) which
promotes bone resorption. At the apical region of the
alveolar bone a transcription factor is expressed in the
dental follicle, namely Cbfa-I (Core binding factor a-I).
This factor is involved in osteoblast differentiation and
these cells form bone at sites of appositin needed for
the remodeling that accompany tooth eruption. At
sites of bone resorption TGF B downregulates the
expression of Cbfa-l.

22. Tooth eruption
ultra-low power section of developing jaw
1 1
2
4
2 2
3
3
3
4
Key: 1 = milk teeth; 2 = developing adult teeth; 1 mm 3 = jaw bone; 4 = gum

23. Tooth eruption

24. Osteoclasts erode jaw bone to make way for erupting adult tooth

25. ERUPTION PATH :
GUBERNACULAR CORD AND CANAL:
The fibrocellular follicle surrounding the
permanent tooth retains its connection with
the lamina propria of the oral mucous
membrane by means of a strand of fibrous
tissue containing remnants of the dental
lamina, known as the GUBERNACULAR CORD.
It is contained in a bony canal known as
GUBERNACULAR CANAL. In the anterior teeth
,these canals are seen in the lingual plate of
bone ,while in premolars the canals are
present in the corresponding deciduous
molars.

26. At a given time, bone resorption by osteoclasts will
occur in this GUBRNACULAR CANAL even if the tooth is
stationary. Consequently, formation of the tooth
eruption pathway is a localized, genetically
programmed event that does not require pressure from
the erupting tooth.
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

27. Diagram of a developing eruption pathway. A, Early
developing eruption pathway. B, Resorption of bone in eruption
pathway.

31. Erupting deciduous tooth

32. Mechanisms of eruptive Tooth Movement
A. MECHANISM OF AXIAL TOOTH MOVEMENT
Several theories have been advocated in regard to the
probable mechanism which may determine and bring
about the axial tooth movements :
1. Root formation theory :
Contention : the growing apical portion of the root
including ( the root sheath, pulp tissue, and root
sheath ) is believed to be concerned with the axial
movements of the tooth .
The growth of these components either collectively or
separately is believed to provide a force . Such force
permits for the axial tooth movements, by pushing
against an apical structure termed cushioned
hammock ligament .

34. This ligament is considered as suspensory structure
found at the base of tooth crypt and serves in
transforming the generated pressure of the
growing root at the bottom of the crypt into
tension so the tooth moves axially .
Fallacies :
a. Some teeth are evidenced to move a distance
greater than the length of the developing root can
ultimately attain for example , the canine .
b. tooth eruption is a process not limited to a
certain period of time .
c. If the root formation is regarded to be responsible
for tooth eruption, it would be expected that the
onset of root formation must coincide with the
commencement of the eruptive tooth movement .

35. d. The concept regarding the cushioned hammock
ligament to act as a fixed base is explained to be not
valid . This is because the hammock ligament is
evidenced to turns around the apical root end , but does
not posses any insertion to the wall of the alveolar socket
e. When the growing components of the apical end of the
root are experimentally removed, the remaining portion
of the tooth is still progressively erupting .
f. When a tooth is experimentally prevented from
eruption by root pinning, the apical root portion is still
growing and create a pressure on the base of the alveolar
socket . Such finding indicate that the root growth
generate a force, however, this force is not exactly
directed to cause tooth eruption .

36. 2. Bone remodeling theory :
Contention : this theory presumes that eruption of the
teeth occurred through selective bone remodeling .
The end result of bone remodeling is a considerable
bone deposition at the bottom of the socket .
Fallacies :
1. It has been evidenced that the alveolar bone
remodeling which occurs around the root, that end by
bone deposition, is the outcome and not the cause of
axial tooth movement because as the tooth
commences its eruptive movement, bone resorption is
initiated at the base of the socket and so bone
mounting is not a cause for eruption but a filling
process occurring after the tooth has been axially
moved .

37. 3. Vascular pressure theory :
Contention : this theory supposes that a local increase
in tissue fluid pressure in the periapical region is
sufficient to move the tooth .
Fallacies : the experimental removal or transection of
the growing apical root portion and the associated
tissue does not interfere with the tooth eruption .
4. Periodontal ligament traction theory :
This theory denotes that the tooth eruption occurs
through the generation of a traction force to bring the
tooth into occlusion . The traction force is presumed to
be established by either the fibroblasts or collagen
fibers found in the periodontal ligament , or by both .
Drugs that interrupt the proper formation of collagen
in the periodontal ligament ( like vit .C deficiency ) lead
to either slowing or ceasation of the eruptive tooth
movement.

38. Furthermore, experimental transection or removal of
the actively growing apical root portion do not cease
the eruption activity of the distal root portion .
Therefore, it is concluded that :
Firstly : the root growth cannot be considered as
the prime mover of tooth to erupt .
Secondly : the only viable tissue in the distal
root portion is the periodontal ligament , thus the
eruptive forces of a tooth is presumed to reside
in this ligament .
 In concern to the collagen fibers of the periodontal
ligament it has been suggested that they bring the
tooth into the oral cavity through their elaborated
contraction while they are formed .
 In regard to the role played by the fibroblasts, it is
presumed that they provided with contractile
elements .

39. These fibroblasts has both extracellular and
intracellular characteristics :
1) Their cytoplasm contain large number of actin
contractile filaments , which when contract translate
its action into forces outside the cell .
2) The cells establishes a firm connection to the
adjacent cells by special cellular junctions .
3) The cell establishes firm connection to the adjacent
collagen fibers by a special structure called
fibronexus which is formed of :
a. intracellular microfilament .
b. Thickening of the fibroblastic cell membrane .
c. Extracellular filaments .
d. A sticky glycoprotein called fibronectin that bind
the cell to the fiber.
So the fibroblasts should contract collectively to insure

40. massive contraction . This contraction can be secured
through the harmonious play-making of the whole
fibroblasts results in summating their contractile forces
which collectively cause tooth eruption .

41. B. MECHANISM OF MESIAL TOOTH MOVEMENT
Several factors control mesial drift :
(a) Contraction of the transseptal (INTERDENTAL) fibers:
These fibers connect the cervical portion of the
adjacent teeth together and as the proximal tooth
surfaces of adjacent teeth become worn from
functional tooth movement, the transseptal fibers of
the periodontal ligament become shorter (due to
contraction) and thereby maintain tooth contact .
(b) Pressure of the oral and para-oral tissues : buccal
mucosa and tongue push teeth mesially

42. (c) Anterior component of masticatory forces : As the
masticatory forces work, the second and third
permanent molars act as a braces to the teeth
anterior to them and this prevent any tendency for
their distal displacement . Therefore, during
mastication, the more pronounced mesial inclination
of the long axes of the mandibular permanent
molars leads to their striking with their
corresponding maxillary teeth through mesially
inclined stresses .
The summation of the anterior component of the
occlusal forces would be transmitted mesially thus
the teeth are forced in the same direction .

43. Thank you
ANY
QUESTION
Dr. Hesham Dameer