Tooth EruptionTooth Eruption

Objectives: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 Content • Definition Definition • Phases of eruptionPhases of eruption• Types of movementsTypes of movements• Theories of eruptionTheories of eruption• Clinical considerations Clinical considerations

Definition: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

Axialmovement

Bodilymovement

Tilting)tipping(

Rotatory

movement

Occlusal movement in the direction of the long axis of the

tooth

Movement to one direction mesial,distalbuccal or lingual

Movement around a

transverse axis

Movement around a

longitudinal axis

Eccentric

growth

One end (crown) of the developing tooth move

toward eruption whereas, other end (growing root) remain

stable. Shift ofthe center

Phases of eruption:Phases of eruption:

Pre-eruptive phase

Eruptive phase

Post-eruptive phase

Phases of eruption:Phases of eruption:

I. Pre eruptive phasePre eruptive phase:

• beginsbegins in the early bell stageearly bell stage •endsends at the beginning of root beginning of root formationformation.

We will talk about• deciduous • permanent anterior premolar molar

First

Pattern of movement of deciduous teethPattern of movement of deciduous teeth:

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

• grow rapidly• become crowded.

Then

I. Pre eruptive phasePre eruptive phase::

This crowding is relieved by

Jaw growth: • In length• In width• In height

I. Pre eruptive phasePre eruptive phase:

1-Anterior forward

All teeth

3-Outward)vestibular(

4-Upward)occlusaly(

Teeth movement

2- E E

backward

I. Pre eruptive phasePre eruptive phase:

1&2 due to growth of the jaw in length ….occur by

bodily movement

3 due to growth of the jaw in width… occur due

to bodily movement.

4 due to growth of the jaw in height …..occur due to

eccentric growth

Pattern of movement of permanentpermanent teeth:A. Anterior teeth 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.

I. Pre eruptive phase:

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 between the divergent roots of the deciduous molars, then below their roots.

Pattern of movement of permanentpermanent teeth:B. Premolars Premolars

I. Pre eruptive phasePre eruptive phase:

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

Deciduous 1Deciduous 1stst molar and molar and permanent 1permanent 1stst premolar premolar

of the mandible from birth to 14 of the mandible from birth to 14 yearsyears

• 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 occlusal surfacessurfaces facing mesiallymesially.

Pattern of movement of permanent teeth:C. Molars Molars

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

I. Pre eruptive phasePre eruptive phase::

Maxillary molarsMaxillary molars in the tuberosity facing distallydistally

Swing around with growth of the maxilla

Mandibular molarsMandibular molarsin the base of the ramus

facing mesiallymesially

tilt to be upwrightwith growth of the mandible

Pattern of movement of permanent teeth:C. Molars

I. Pre eruptive phase:

Histologic changes:

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

remodeling).3.Movement of the developing tooth

within the growing jaw.

I. Pre eruptive phaseI. Pre eruptive phase::

Types of movements:

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

• Bone depositon on the crypt Bone depositon on the crypt wall behind it. wall behind it.

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

• Shift of the center.Shift of the center.

Bodily movement (Drifting( Eccentric growth

I. Pre eruptive phase:

Any questions?? Any questions??

• It beginsbegins :by root formationroot formation • Ends:Ends: when the tooth reaches the

occlusal planocclusal plan.

• This stage is subdevided into:This stage is subdevided into:

1- intraosseous stage.1- intraosseous stage. 2-extraosseous stage.2-extraosseous stage.

II. Eruptive phase:

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

Pressure exerted by the developing tooth Pressure exerted by the developing tooth induces bone resorption.induces bone resorption.

REE produces desmolytic enzymes to REE produces desmolytic enzymes to degrade CT..

REE+ oral epith.= REE+ oral epith.= epithelial plug.. Central cells of this plug degenerate forming an Central cells of this plug degenerate forming an

epithelial lined canal through which the tooth through which the tooth will erupt will erupt without hemorrhage. .

REE shares in the formation of dento-gingival REE shares in the formation of dento-gingival junction.junction.

A. Epithelial plug.

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:

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

Active eruptionActive eruption: : Passive eruptionPassive eruption::

II. Eruptive phase:

II. Eruptive phase:

The above description in eruptive phase is applied to all teeth however the succestional teeth possess an additional anatomic features which are:

1- The Gubernacular canal.

2-The Gubernacular cord.

. .

At first both deciduous and permanent buds occupy the same crypt

But when the deciduous tooth erupt …. The permanent will be completely enclosed by bone except for a small canal .

The canal is filled with a strand of fibrous tissue strand of fibrous tissue “CT” containing remnants of the dental lamina.

This canal it is widened by osteoclast to guide permanent teeth to erupt.

For the anterior teeth the canal open in the lingual bony surface of the jaw.

For premolars, the canals open within the sockets of corresponding deciduous molars.

They have an influence in determining

Eruptive pathEruptive path

Eruptive path:

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:

B. 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:

C. Readjustment of the PL fibers:Readjustment of PL is performed by Readjustment of PL is performed by fibroblasts

which which synthesis and and degrade collagen fibers.collagen fibers. Once root is established PL must be remodeled to Once root is established PL must be remodeled to

accommodate continuous eruption.accommodate continuous eruption.

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

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

II. Eruptive phase:

Characters of PDL fibroblasts:

1- They function as fibroblasts and fibroclasts. So they form and degrade collagen fibers.

2-They have cell contact of adherence type.

3- They contain fibronexus.

What is fibronexus?The fibronexus is cell surface specialization consisting of intercellular actin filament and extracellular fibronectin which is a sticky glycoprotein that can stick to a number

of extracellular component .

D. 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?? Any questions??

III. Post eruptive phase

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

• Its movements occur to:

Accommodation for jaw growth

Compensation for occlusal wear

Accommodation for interproximal

wear

Accommodation for growth

Deposition of bone at the alveolar crest and at the base of the socket

Compensation for

occlusal wear •Axial movement of the tooth•Cementum deposition around the apex

Compensation for interproximal

wear

•By mesial drift

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

III. Post eruptive phase

Any questions?? Any questions??

Mechanisms of Mechanisms of tooth movements tooth movements

(Theories) (Theories)

1.1. Root formation theoryRoot formation theoryThe proliferating root rested on a fixed base which converting apical force to occlusal movement (Cushioned-hammock ligament).Cushion-hammock ligament:•This is a ligament at the base of the socket passing from one bony wall to the other.•This ligament protects the bone at the base from resorption and allows only an outward growth of the tooth.•Act like a FIXED BASE.

I. Root formation theory

Proliferating rootProliferating root impinges on a fixed baseimpinges on a fixed base

Apically directed forceApically directed force

Occlusal movementOcclusal movement

But • No fixed base: Cushioned-hammock ligament is proved to be pulp

delineating membrane

• Force exerted on bone lead to Force exerted on bone lead to resorption..

• Some teeth move a distance Some teeth move a distance greater than the the

length of their roots as upper canine. length of their roots as upper canine.

• Eruption of Eruption of Rootless teeth. teeth.

• When the When the ERSH is surgically removed the tooth is surgically removed the tooth

erupt. .

I. Root formation theory

II. Bone Remodeling theory

Selective bone resorption and deposition Selective bone resorption and deposition causes tooth eruptioncauses tooth eruption. .

In human, the base of the 1st & 3rd molars showing a In human, the base of the 1st & 3rd molars showing a continuous bone resorption in the fundus floor. While, continuous bone resorption in the fundus floor. While,

2nd molar, 1st and 2nd premolars showed bony 2nd molar, 1st and 2nd premolars showed bony deposition in the fundus floordeposition in the fundus floor..

But

II. Bone Remodeling theory

So. . The selective bone remodeling The selective bone remodeling which occur around the root which occur around the root

are the result not the cause of are the result not the cause of tooth movement. 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 stimulates differentiation of

osteoclastsosteoclasts, eruption is prevented because no mechanism for bone removal exists.

Local administration Local administration of this factor permits the differentiation of osteoclasts, and eruption occurs.

Removal of developing premolar Removal of developing premolar without disturbingdisturbing the DF, or if eruption is prevented by wiring the tooth germ wiring the tooth germ down to the lower border of the mandible, an eruptive eruptive pathwaypathway still forms within the bone forms within the bone as osteoclasts widen the gubernacular canal.

If the DF DF is removed removed, however, no eruptive pathway no eruptive pathway forms. Furthermore, if a metal or silicone replica replica replaces the tooth germreplaces the tooth germ, and so long as the DF is retained, the replica will eruptreplica 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 propertiesB. Connection with collagen fibers extra-cellular “fibronexus”C. Oblique alignment of PDL collagen fibers

V. Vascular pressure theory

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

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

• Although no one theory no one theory is yet supported by sufficient sufficient

experimental evidenceexperimental evidence, it is probably multifactorialmultifactorial

in that more than one agent or factor share in the eruptive

movement.

• The dental follicle, REE, the surrounding PDL and The dental follicle, REE, the surrounding PDL and

the alveolar bone the alveolar bone share in the eruption processeruption process.

• The tooth movement tooth movement results from a balancebalance between

tissue destructiontissue destruction (coronal bone, C.T. and surface

epithelium) and tissue formationtissue formation (root, PDL and bone).

Clinical Clinical ConsiderationsConsiderations

Early eruptionbaby teeth

Delayed eruption

Systemic cause: Due to hormonal disturbances

Local causes:1-Premature loss of deciduous teeth…space loss2-missed successor3-Ankylosed deciduas teeth.4-Gingival fibromatosis

Delayed Delayed eruptioneruption

Thank you Thank you