TEETH ERUPTION
Physiological tooth movements consists ofthe following:
Pre eruptive tooth movement
Eruptive tooth movement
Post eruptive tooth movement
Phases of tooth eruption
• Preeruptive phase: made by the deciduous and permanent
tooth germs within tissues of the jaw before they begin to erupt.
• Eruptive phase: Starts with initiation of root formation and
made by teeth to move from its position within bone of the jaw
to its functional position in occlusion. Has an intraosseous and
extraosseous compartments.
• 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.
Pre eruptive tooth movement
Made by the deciduous and permanent tooth germs within tissues
of the jaw before they begin to erupt.
tooth germs grow rapidly
crowded
relieved by lengthening of jaws
deciduous second molar tooth germs move backward
anterior tooth germ moves forward
4
Permanent anterior tooth germs
develop lingual to the primary
anterior teeth and later as
primary teeth erupt, the
permanent crowns lie at the
apical 3rd of primary roots.
Premolars tooth germs located
lingual to deciduous molars
later they positioned between
thedivergentrootsof
deciduous molars.
5
• Preeruptive movements of teeth are acombination of two factors:
(1) Total bodily movement of the tooth germ
(2) Growth in which one part of the tooth germ
remains fixed while the rest continues to grow,
leading to a change in the center of the
tooth germ.
(•)This growth explains, for example, how the
deciduous incisors maintain their position
relative to the oral mucosa as the jaws increase
in height.
• Preeruptive movements occur in an
intraosseous location and are reflected in
the patterns of bony remodeling within the
crypt wall.
A- during bodily movement in a mesial
direction, bone resorption occurs on the
mesial surface of the crypt wall, and bone
deposition occurs on the distal wall as a
filling-in process.
B- During eccentric growth, only bony
resorption occurs, thus altering the shapeof the crypt to accommodate the altering
shape of the tooth germ.
Eruptive tooth movement
• It is initiated by growth ofHERTWIG’s epithelial root
sheath, which initiates the
differentiation of odontoblasts
from the dental papilla.
• The odontoblasts then form root
dentine, bringing about an overall
increase in length of the tooth
that is largely accommodated by
eruptive tooth movement, which
begins at approximately the same
time as root formation is initiated.
• After the onset of root
formation cementum,
periodontal ligament, and
the bone lining crypt wall
are formed.
• Fibroblasts of the
Periodontal ligament
possess as part of their
cytoskeleton intermediate
filaments that consist of
contractile proteins.
• Bone removal is necessary for permanent teeth to
erupt. In case of those teeth with deciduous
predecessors there is an additional anatomic
feature, the GUBERNACULAR CANAL and its
contents, the gubernacular cord, which may have
influence on eruptive tooth movement.
• As the deciduous tooth erupts, the permanent tooth
germ become situated apically and is entirely
enclosed by the bone except for a small canal that is
filled with connective tissue and often contains
epithelial remnants of the dental lamina. This
connective tissue mass is termed the «gubernacular
cord»
• Gubernacular
canal: Holes noted
in a dry skull noted
lingual to primary
teeth in jaws that
represent openings
of gubernacular cord
.
The changes occurring in the
connective tissues affect the
epithelia it sustains and both the
reduced enamel epithelium and
the overlying oral epithelium
begins to proliferate and
migrate into disorganized
connective tissue so that
eventually a solid plug of
epithelium forms in advance of
the erupting tooth. The central
cells of epithelium mass
degenerate and form an
epithelium-lined canal through
which tooth erupts without any
hemorrhage.
• As the tooth pierces the oral epithelium, another
significantdevelopmentoccurs:the dentogingival
junction forms from epithelial cells of the oral
epithelium and the reduced enamel epithelium
• Once the tooth has broken through the oral
mucosa, it continuous to erupt at the same rate
until its reaches the occlusal plane and meet its
antagonist. Rapid eruptive movement then ceases.
Post Eruptive Tooth Movements
Are those movements made by the tooth after it has reached its functional
position
in the occlusal plane.
They may be divided in three categories:
Accomodation for
growth
Compensation for
occlusal wear
Accomodation for
interproximal wear
16
• ACCOMMODATION FOR GROWTH-
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.
• COMPENSATION FOR OCCLUSAL WEAR -
Compensation primarily occurs by continuous
deposition of cementum around the apex of the tooth.
However, this deposition occurs only after tooth moves.
• ACCOMMODATIONFORINTERPROXIMAL
WEAR - Compensated by mesial or approximal drift. 17