Transcript 5391aa89-7a6e-469a-bf45

Tooth Eruption
Tooth eruption is the process by which
a tooth moves from its site of
development within the jaws to its final
functional position in the oral cavity.
it is a continuous process
Phases of tooth eruption
Pre-eruptive phase
Pre-functional eruptive phase
Functional eruptive phase
Pre-eruptive phase
All movements of primary and permanent
tooth germs (crowns)
from
time of their early initiation and
formation to the time of crown
completion
ends with early initiation of root formation
Pre-Eruptive Phase
 Early in the stage, the permanent anterior
teeth begin developing lingual to the
incisal level of the primary teeth. Later, as
the primary teeth erupt, the secondary
teeth are positioned lingual to the apical
third of their roots.
 Permanent premolars shift from a location
near the occlusal area of the primary
molars to a location enclosed within the
roots of the primary molars
Periapical
Permanent molars have no predecessors
Maxillary molars develop within the maxillary
tuberosity with their occlusal surfaces slanted
distally
Mandibular molars develop in the ramus with the
occlusal surfaces slanting mesially
Pre-Functional Eruptive
 Starts with the initiation of root formation and
ends when the teeth reach occlusal contact
 Four major events occur during this phase:
1. Root formation
2. Movement occurs incisally or occlusally
through the bony crept to reach the oral
mucosa
3. Penetration of the tooth crown tip into the oral
cavity
4. Intraoral movement occlusally and incisally
until clinical contact with the opposing crown
occurs.
The rate of tooth eruption depends on the
phase of movement
Intraosseous phase: 1 to 10 μm/day
Extraosseous phase (soft tissue): 75 μm/day
Functional Eruptive
Phase
Takes place after the teeth are
functioning and continues as long as the
teeth are present in the mouth
Post eruptive tooth movement
1. 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 with increasing height of
jaws.
2. Movements to compensate for
continued occlusal wear.
Compensation primarily occurs by
continuous deposition of cementum
around the apex of the tooth.
3. Movements to accommodate
interproximal wear.
Compensated by mesial or approximal
drift.
Mesial drift is the lateral bodily
movement of teeth on both sides of
the mouth.
Very important in orthodontics.
Space loss
Environmental factors affecting the final
position of the tooth:
Muscular forces
Thumb-sucking
Tongue thrust
Palatal crib
Mechanisms of Eruptive
Tooth Movement
Root formation
Bone remodeling
Dental follicle
Periodontal ligament
Role of hydrostatic pressure
Root formation
Should be an obvious cause of tooth
eruption. But studies have not provided
evidence for this.
If a tooth that is continuously erupting is
prevented the root still forms by causing
bone resorption.
Rootless tooth still erupt, some teeth erupt
more than the total length of the roots and
the teeth still erupt after completion of root
formation.
Therefore root formation is accommodated
during eruption and may not be the cause of
tooth eruption.
Root formation produces a force which
causes bone resorption by osteoclast.
Root growth theory suggested the presence of
the cushion hammock ligament at the base of
the socket that transmits the force to cause
eruption but the ligament was never found
histologically
One point of importance is that, the tissue
beneath the growing root resists the apical
movement of the developing root.
This resistance results in the occlusal
movement of the tooth crown as the root
lengthens
Bone Remodeling
An inherent growth pattern of the maxilla and
mandible supposedly moves teeth by
selective deposition and resorption of bone
not sure if bone remodeling plays a significant
role but is involved
Dental follicle
Investigators indicate a pattern of cellular
activity involving the reduced enamel
epithelium (REE) and the follicles associated
with tooth eruption.
Studies have shown that the reduced dental
epithelium initiates a cascade of intercellular
signals that recruit osteoclasts to the follicle.
By providing a signal and chemoattractant for osteoclasts, it is possible that
the dental follicle can initiate bone
remodeling which goes with tooth
eruption.
RDE also secretes proteases, which assist
in breakdown of connective tissue to
produce a path of least resistance.
Periodontal ligament
Periodontal Ligament Traction theory
Formation and renewal of the PDL has been
considered a factor in tooth eruption because
of the traction power of the fibroblasts.
Most accepted theory Due to contraction of
the FB situated in the PDL, a pressure is
created which favors eruption
Hydrostatic Pressure
A number of studies exist to demonstrate that there
is a hydrostatic pressure difference between the
tissue around the erupting crown and its apical
extent
The hydrostatic theory was investigated by Hassel
and McMinn (1972) who demonstrated that the
tissue pressure apically was greater than occlusally
theoretically generating an eruptive force.
No association was found between the rate of
eruption and the pressure gradient.
Shedding of Primary Teeth
Shedding is the loss of the primary dentition caused
by the physiologic resorption of the roots, the
loss of the bony supporting structure and therefore
the inability of these teeth to withstand the
masticatory forces.
Resorption of anterior teeth occurs on the lingual
surface and these teeth are shed with their pulp
chamber intact
Resorption of primary molars occurs in
interradicular dentine with some resorption of the
pulp chamber, coronal dentine and sometimes
enamel
Pattern of Shedding
Resorption of dental hard tissues is
achieved by cells with a histological nature
similar to that of osteoclasts called
Odontoclasts
Pressure plays an important role in the
exfoliation of primary teeth
Stem cells ????
Hormonal Control
Mechanisms
Eruption occurs only during a critical
period between 8pm and midnight or 1am.
During the morning, tooth eruption ceases
or even the tooth intrudes a bit.
This reflects Circadian Rhythm reflecting
the possible involvement and control of
growth hormone and thyroid hormone.
Logan and Kronfeld’s chronology of human dentition (1933)
Eruption sequence
The time of eruption for primary and
permanent teeth varies greatly.
A variation of 6 months on either side of
the usual eruption date may be
considered normal for a given child.
Girls eruption of their permanent teeth
are 5 months earlier than the boys
Tooth eruption has three stages
1. Deciduous dentition
2. Mixed dentition
3. Permanent dentition
Primary dentition
starts on the arrival of the mandibular
central incisors, typically from around six
months,
lasts until the first permanent molars
appear in the mouth, usually at six years.
The primary teeth typically erupt in the
following order: (1) central incisor, (2)
lateral incisor, (3) first molar, (4) canine,
and (5) second molar
Mixed dentition
starts when the first permanent molar
appears in the mouth, usually at five or
six years,
lasts until the last primary tooth is lost,
usually at ten, eleven, or twelve years.
Sequence of eruption
The sequence of calcification is not a sure
clue to the sequence of emergence in the
mouth
Wide variability
Max ( 6-1-2-4-3-5-7/ 6-1-2-4-5-3-7 )
Mand ( 6-1-2-3-4-5-7/6-1-2-4-3-5-7 )
Most common sequence
Max ( 6-1-2-4-5-3-7 ) & Mand ( 6-1-2-3-4-57)
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Abnormal eruption sequence
The permanent dentition
begins when the last primary tooth is
lost, usually at 11 to 12 years,
and lasts for the rest of a person's life or
until all of the teeth are lost
Infant occlusion
Upper anterior gum pad is wider than
lower
Over jet= 5mm
Overbite= 0.5 mm
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Normal features of the
primary dentition
Spaced anterior
Primate spaces
Shallow overbite and overjet1-2mm
Mesial step plane molar relationship
Almost vertical inclination of the ant
teeth
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Primary dentition
occlusion
Types of molar relationship
1- Flush terminal plane:
distal surface of opposing E are at the
same level
37% of primary molar relationship
75% of them result in ideal class I
permanent molar relationship
25% will shift to class II
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2- mesial step:
Distal surface of lower E mesial to distal
of upper
49% of primary of molar relationship
(most common)
mesial step will result in ideal class I
molar relationship
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3- Distal step :
Distal surface of lower E distal to distal
of upper
14% of primary molar relationship
Result in class II molar relationship
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Permanent dentition
occlusion
Molar classification :
Class I mesiobuccal cusp of upper 1st molar
in buccal groove of lower 1st molar 55%
Class II mesiobuccal cusp of upper 1st molar
mesial to opposing one 19%
Class III mesiobuccal cusp of upper 1st molar
distal to opposing one
End-on relation ship : mesiobuccal cusp of
both molars at the same level 25%
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Criteria for ideal
occlusion:
Class I molar relationship
Over jet & overbite = 2 mm
Tight proximal contacts
Coincidental dental midlines
Flat occlusal plane
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