Eruption

Tooth Eruption

Dr. Mona Dnewar Lecture of oral biology department

Objectives:

At the end of this chapter the student should be able to understand the following:

• Phases of tooth eruption.• Theories of tooth eruption.

Content • Definition • Phases of eruption• Types of movements• Theories of eruption• Clinical considerations

Definition:

It is the axial or occlusal movement of teeth from its position within the jaw bone to its functional position in occlusion.

Types of Tooth

Movement

Axialmovem

entBodilymovem

ent

Tilting(tippin

g)

Rotatory

movement

Occlusal movement

in the direction of

the long axis of the

tooth

Movement to one

direction mesial,dist

albuccal or

lingual

Movement around

a transvers

e axis

Movement around

a longitudin

al axis

Eccentric growth

Shift ofthe center

Phases of eruption:

I. Pre eruptive phase

II. Eruptive phase

III. Post eruptive phase

Pre-eruptive phase

Eruptive phase

Post-eruptive phase

Phases of eruption:

I. Pre eruptive phase:

This phase begins in the early bell stage and ends at the beginning of root formation.

Made by the deciduous and permanent tooth germs within tissues of the jaw before they begin to erupt.

First

Pattern of movement of deciduous teeth:

• teeth germs are small• have good space in the jaw

bones

• grow rapidly• become crowded.

Then


This crowding is relieved by Jaw growth: • In length• In width• In height


Anterior forward

All teeth

Outward(vestibular)

Upward(downward)

This crowding is relieved by

EE backward


Pattern of movement of permanent teeth:A. Anterior teeth Permanent incisors and canine,

first develop lingual to the deciduous tooth germs in the same crypt. As the deciduous tooth erupt, they move to be apical in position and occupy their own bony crypts.


Permanent premolars develop lingual to their predecessors at the level of their occlusal surfaces and in the same bony crypt.

Then shift to be situated in their own crypts beneath the divergent roots of the deciduous molars.

Pattern of movement of permanent teeth:B. Premolars


Radiograph of the mixed dentition of a 7-year-old child

Deciduous 1st molar and permanent 1st

premolarof the mandible from

birth to 14 years

• Permanent molars have no predecessors; develop from backward extension of dental lamina.

• Mandibular molars develop in the base of the mandibular ramus with their occlusal surfaces facing mesially.

Pattern of movement of permanent teeth:C. Molars

• Maxillary molars develop in the maxillary tuberosity with their occlusal surfaces facing distally.


Maxillary molars in the tuberosity facing distally

Swing around with growth of the maxilla

Mandibular molarsin the base of the ramus

facing mesially

tilt to be upwrightwith growth of the mandible

Pattern of movement of permanent teeth:C. Molars


Histologic changes :1. Growth of tooth germs.2. Formation of bony crypt (bone

remodeling).3. Movement of the developing tooth

within the growing jaw.


Types of movements :

• Bone resorption on the crypt wall toward which the tooth moves.

• Bone depositon on the crypt wall behind it.

• Bone resorption only occurs on the crypt wall facing the growing tooth germ.

• Shift of the center.

Bodily movement (Drifting)

Eccentric growth


Any questions??

• It begins by root formation and ends when the tooth reaches the occlusal plan.

• Made by a tooth to move from its position within the bone of the jaw to its functional position in occlusion.

II. Eruptive phase:

it happens due to gradual retraction of attachment epithelium from tooth surface.

it is gradual appearance of the tooth in the oral cavity due to axial occlusal movement of the tooth.

Active eruption : Passive eruption:

II. Eruptive phase:

Once the tooth has broken through the oral mucosa, further emergency of the tooth results from active eruption movements and passive separation of the oral epithelium from the crown surface.

So,

Until, it reaches the occlusal plane and meets its antagonist.

II. Eruptive phase:

• The principal direction of movement is occlusal or axial (for deciduous and permanent teeth).

• However, movement in other planes also occur such as bodily, tilting, and rotating movement.

Types of movements :II. Eruptive phase:

Tooth is covered by; REE, CT, bony crypt and oral epith.

Pressure exerted by the developing tooth induces bone resorption.

REE produces desmolytic enzymes to degrade CT.

REE+ oral epith.= epithelial plug.

Central cells of this plug degenerate forming an epithelial lined canal through which the tooth will erupt without hemorrhage.

REE shares in the formation of dento-gingival junction.

A. Epithelial plug.II. Eruptive phase:

B. Eruptive path: Gubernacular cord and Gubernacular canal

Gubernacular cord is a strand of fibrous tissue “CT” containing reminants of the dental lamina.Gubernacular canal into which the cord is enclosed; it is widened by osteoclast to guide permeant teeth to erupt.

II. Eruptive phase:

B. Eruptive path: Gubernacular cord and Gubernacular canal

II. Eruptive phase:II. Eruptive phase:

C. Root Formation:

Apical proliferation of ERSH leads to..

Bone resorption of the crypt floor

Bone deposition on the crypt walls

Organization of PL fibers.

Cementum formation at root surface.

II. Eruptive phase:

D. Readjustment of the PL fibers: Readjustment of PL is performed

by fibroblasts which synthesis and degrade collagen fibers.

Once root is established PL must be remodeled to accommodate continuous eruption.

It was suggested that there was a structure known as intermediate plexus that permits remodeling of the PL fibers at the middle area without the need of fibers to re-embed themselves in cementum and bone.

But recent studies showed that this structure is only present in rodents and not in humans.

II. Eruptive phase:

E. Alveolar ridge:

It grows rapidly by deposition of bone trabeculae parallel to the fundus of the socket to aid in tooth eruption due to incomplete formation of root at this stage.

II. Eruptive phase:

Any questions??


• It begins after the tooth has reached its functional position in the occlusal plane, continues through the whole life of the tooth.

• Its movements divided into three categories: Accommodation

for growthCompensation

for occlusal wearAccommodation for interproximal

wear

Histologic changes :• More cementum and alveolar

bone apposition.• Alveolar bone remodeling due

to an occluso-mesial drift.• Organization of PDL fibers.

Types of movements :• Axial movement• Mesial movement


Any questions??

Mechanisms of tooth

movements (Theories)

I. Root formation theory

Proliferating root impinges on a fixed base

Apically directed force

Occlusal movement

But • Force exerted on bone lead to

resorption.• Some teeth move a distance

greater than the length of their roots as upper canine.

• Eruption of Rootless teeth.• When the ERSH is surgically

removed the tooth erupt.

I. Root formation theory

II. Bone Remodeling

theorySelective bone resorption and

deposition causes tooth eruption .

In human, the base of the 1st & 3rd molars showing a continuous bone resorption in the fundus floor. While, 2nd molar, 1st and 2nd premolars showed bony deposition in the

fundus floor.

But

II. Bone Remodeling

theory

So ..The selective bone

remodeling which occur around the root are the result

not the cause of tooth movement.

II. Bone Remodeling

theory

III. Dental follicle theory

Pattern cellular activity involving the REE and the DF associated with tooth

eruption, which facilitates CT degradation and bone resorption as the

tooth erupts.

III. Dental follicle theory

lack of factors that stimulates differentiation of osteoclasts, eruption is prevented because no mechanism for bone removal exists. Local administration of this factor permits the differentiation of osteoclasts, and eruption occurs. Removal of developing premolar without disturbing the DF, or if eruption is prevented by wiring the tooth germ down to the lower border of the mandible, an eruptive pathway still forms within the bone as osteoclasts widen the gubernacular canal. If the DF is removed, however, no eruptive pathway forms. Furthermore, if a metal or silicone replica replaces the tooth germ, and so long as the DF is retained, the replica will erupt, with the formation of an eruptive pathway.

IV. Periodontal ligament traction

theory cells and fibers of periodontal ligament

possess contractile force Tooth movement is brought about by:

A. Fibroblast contractile properties

B. Connection with collagen fibers extra- cellular “fibronexus”

C. Oblique alignment of PDL collagen fibers

V. Vascular pressure theory

Local increase in blood pressure at apical area lead to occlusal movement of the tooth.

Increased bl. press. rates increase eruption rate & increased number of bl. cap at the apical region in comparison with alveolar crest region.

• Although no one theory is yet supported by sufficient experimental evidence, it is probably multifactorial in that more than one agent or factor share in the eruptive movement.

• The dental follicle, REE, the surrounding PDL and the alveolar bone share in the eruption process.

• The tooth movement results from a balance between tissue destruction (coronal bone, C.T. and surface epithelium) and tissue formation (root, PDL and bone).

Clinical Considerations

Early eruption

Delayed eruption

Any questions??

Thank you

Eruption

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