Tooth eruption

1. Development of dentition :

2. Phases of teeth development :
• Pre-eruptive phase : from the initiation of
tooth development to completion of the
crown.
• Per-functional phase : begins once roots
begin to form .
• Functional phase : after teeth have emerged ,
concerned with development and
maintenance with occlusion.

3. • Eruption is the process a tooth moves from its
developmental position into its functional position .
• Permanent 2nd molar has two stages of active eruption :
- 1st stage Occurs 6-12 yrs tooth is emerging into mouth.
- 2nd stage 16 years in association with the adolescent growth
spurt.
• Eruption rates are greatest at the time of crown emergence .
rates differ according to tooth type.
• Main direction is axial . movement occurs in other planes.
• As the tooth erupts : the outer cells of the reduced enamel
epithelium proliferate into connective tissue , secret enzymes
that degrade collagen.
• Reduced enamel epithelium may also be concerned with the
removal of breakdown products resulting from resorption of
C.T .

5. Development of dentogingival junction
:

6. Layer of reduced enamel epithelium and the
basal cell layer proliferate and unite .
Epithelium covering the tip of the tooth
degenerate , enabling the crown to emerge .
Active eruption movement and passive
seperation of oral epithelium from the crown
result in further emergence .
Epithelial seal – the junctional epithelium:
reduced enamel epithelium attached to the
unerupted part of the crown .

8. • Permanent tooth germ situate lingually to the
deciduous tooth …. With continued growth permanent
tooth comes to lie near the root apex
• Gubernacular canal :through which the permanent
tooth germ communicates with the overlying oral
mucosa .
contains the gubernacular cord , composed of central
strand epi. From dental lamina and surrounded by
connective tissue organized to inner and outer layer .
• This cord will increase in thickness and decrease in
length .

10. • Resorption of primary roots :
-Inherent developmental process
-Pressure from the permanent .
-Increased masticatory loads.
• Resorbing of dentine by multinucleated osteoclast like cells
(odontoclast ) lie within resorption lacunae ( howship’s
lacunae ).
• Resorption of dec. teeth is not continous .
there is rest periods reparative tissue may be formed. If
reparative > resorption tooth may become ankylosed .
and then may cause submerged teeth .
•

11. MECHANISM OF TOOTH ERUPTION :
• The rate of eruption represents the balance
between eruptive force and resistive force .
• In brief ; Eruptive mechanism is
- A property of PDL ( the dental follicle).
- Doesn’t need a tractional force pulling the tooth
out.
- Is probably multifactorial
- Involve a combination of the force produced by the
activity periodontal fibroblast through their
contractility and motility ,and vascular and tissue
hydrostatic pressures in and around the tooth are
responsible for eruption .

12. • Initially , there is a period of slow eruption
when the crown is carried to the oral mucosa
.it takes 2-4 years in perm. teeth . then tooth
erupts more rapidly as it enters the oral cavity(
the length of the root is about 2/3 ) . and once
the tooth emerge into oral cavity it takes 1-2
years to reach occlusal plane .
• Dental age is a useful index of maturity .
estimated clinically and radiographically

18. Panoramic radiograph of a child about 7 years of age. This type of examination is of great value in registering an
overall record of development.

19. DEVELOPMENT OF OCCLUSION :
• AT BIRTH , thickened oral mucosa forms mand.
And max. gum pads (rarely come into occlusion ).
• During the first year of life the gum pads grow
rapidly in lateral directions and provide space for
the developing teeth.
• Occasionally a natal tooth is present . its usually
supernumerary tooth.
• The deciduous teeth start to erupt at the age of 6
mnths and dentition is complete by the age of 3
yrs .

20. • Occlusion of dec. dentition differs from perm.
Dentition in the followings :
1. The incisors are more vertically positioned within the
alveolus and are often spaced.
2. The overbite is usually greater .
3. Significant spacing distal to the mandibular canines
and mesial to tha maxillary canines ( primate spaces).
4. Anteroposterior relationships appears that the distal
edges of the maxillary and mandibular deciduous
molars are flush , and the mesiobuccal cusps of upper
D and E occlude in the buccal grooves of the lower D
and E .

23. • The dental arches become wider and longer so deciduous
teeth become more spaced.
• There is a greater forward growth of the mandible than
maxilla ,then the lower arch moves forwards so an edge to
edge incisor relationship is obtained. And distal surfaces of
upper and lower E’s show a slight mesial step.
• Flush terminal plane is the usual relationship in deciduious
dentition.
• Molar relationship tends to shift after E’s are shed and
adolescent growth spurt occurs.
• Change in molar relationship depends upon the leeway
space and mandibular growth .

24. • Ugly duckling stage : when the permanent incisors
incline distally as a result of the pressure on the roots
from the developing canines . the diastema usually
closes after permanent canines eruption .
• By the age of 12 yrs all primary teeth have been shed
and the occlusion appears similar to that in adults.
Space is provided for permanent molars by continued
growth of mandible and maxilla .
• Primate spaces , developmental spaces (increase as
child grows ), generalized spacing ---- requirement for
proper alignment of permanent incisors.

26. • Once a tooth reaches its functional position, it is occupy a position of
equilibrium between the soft tissue of the cheeks and lips and the
tongue .
• Mesial drift :
 During functional phase . and may involve bodily movement of the
tooth .
 The 6 drifts 4mm in a mesial direction between 6-18 years.
 Mechanisms are multifactorial and involve the periodontal tissue .
 Four hypotheses :
I. The mesial inclination of teeth favours mesial drift .
II. Action of certain jaw muscles , as buccinator .
III. Bone deposited preferentially on the distal surface of the socket .
IV. Contraction of gingival connective tissue .