Mechanisms of Tooth Eruption & Mammalian Teeth 3 Categories on the Basis of Eruptive Charateristics
1. Mechanism of Tooth Eruption
2. Mammalian Teeth 3 Categories on the
Basis of Eruptive Characteristics
Eruption is the movement of the developing
teeth through the bone and the overlying
mucosa of the jaws to appear in the oral
cavity and reach the occlusal plane.
A Close Look at Tooth Eruption
Baby teeth are lost naturally due to the pressure of the permanent teeth
erupting from below. This process is called root resorption. Note the
continued development of the permanent crown and root as it erupts.
1. Pre-eruptive phase
2. Eruptive or Pre-functional phase
3. Post-eruptive or Functional phase
Preparatory to the
It consists of the
movements to the
germs within the
During this phase, the growing teeth move in various
directions to maintain their position in the expanding
jaws. This is accomplished by both bodily movement
eccentric growth. Bodily movement is a shift of the
entire tooth germ, which causes bone resorption in
the direction of tooth movement and bone apposition
from behind. These movement occur as the jaws
Early in the pre-eruptive phase, the successional
permanent teeth develop lingual to, and near the
incisal or occlusal level of, their primary
At the end of this phase, the developing
anterior permanent teeth are positioned
lingually and near the apical third of the
primary anterior teeth.
The premolars are located under the roots of
the primary molars.
The upper molars develop in the tuberosities
of the maxilla, with their occlusal surfaces
slanting distally. The lower molars develop in
the base of the mandibular rami, and their
occlusal surfaces slant messially.
Two types of tooth movement in pre-
1. Total bodily movement
2. Movement where one part remains
fixed while the rest
◦ continues to grow leading to change
in the center of the
◦ tooth germ
Begins with the initiation of root formation
and ends when the teeth reach occlusal
Five major events take place during this
1. The secretory phase of amelogenesis is
completed just before the onset of root formation
and perfunctional eruption. There is realtion
between the cessation of mineralization and
activation of the epithelial cells beyaond the
2. The intraosseous stage occurs when the root
formation begins as a result of the
proliferation of both the epithelial root sheath
and the mesenchymal tissue of the dental
papilla and dental follicle.
3. The supraosseous stage begins when the erupting
tooth moves occlusally through the boneof the crypt
and the connective tissue of the oral mucosa, so that
the reduced enamel epithelium covering the crown
comes into contact with the oral epithelium.
As this occurs, the
epithelium of the
and forms a firm
attachment with the
oral epithelium. A
epithelial layer over
the erupting crown
is then formed.
4. The tip of the crown enters the oral cavity by
breaking through the center of the double -layered
epithelial cells. This breakthrough is accomplished by
the cusp tip causing degeneration of the membrane
and is the beginning stage of clinical eruption.
The crown erupts
further, and the
lateral borders of the
oral mucosa become
The reduced enamel
surrounding the crown like
a cuff, becomes known as
the junctional or attchment
epithelium. When the tip of
the crown appears in the
oral cavity, about one-half
to two-thirds of the roots
5. The erupting tooth continues to move
occlusally at a maximum rate, and there is
gradual exposure of more of the clinical
Begins when the teeth reach occlusion, and continues
for as long as each tooth remains in the oral cavity.
Alveolar processes increase in height and the roots
continue to grow.
Teeth continue to move occlusally, which
accomodates jaw growth and allows for root
elongation. The most marked changes occur as
occlusion is established.
Alveolar bone density increases, and the principle
fibers of the periodontal ligaments establish
themselves into separate groups oriented about the
gingiva, the alveolar crest, and the alveolar surface
around the root.
The diameter of the fiber bundles increase from
delicate, fine groups of fibers to heavy, scurely
When root canal narrows, as a result of root tip
maturation, apical fibers develop to help cushion
the forces of occlusal impact.
Later in life,
wear down the
of the teeth.
The teeth erupt
compensate for loss
of tooth structure
and to prevent
If the occlusal wear
on the apical third of
the root; it is
deposited in the
furcation region of
no gross separation between the anatomical
crown & anatomical root.
continuous growth of the tooth at the apex
& continuous eruption occur throughout the
life of the animal.
clinical crown is constantly replaced by root
covered with enamel in the progressive
stages of development.
with the loss of tooth substance due to
occlusal attrition, more tooth substance is
extruded from the socket to maintain the
this form of tooth is characteristic of
animals with rapid occlusal wear &
(ex. Rodent incisor teeth)
has a defined crown & anatomical root.
as the tooth is worn, more of the
anatomical crown extrudes & epithelial
attachment migrates apically.
since no new tooth structure is being
formed, it results to gradual loosening &
final exfoliation of the tooth.
this tooth form is characteristic of the lower
incisors of sheep & cattle.
eruption does not
occur by enlargement
of the clinical crown
but rather by addition
to the alveolar
this is characteristic
of human teeth.