Oral Histo 9th Lec Pt2

8/2/2019 Oral Histo 9th Lec Pt2

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Eruption & Establishment of the Dentition

Many of the slides of this topic will be canceled

Reminder ,At the picture these are different stages of tooth formation bud stage

,cap stage ,bell stage And during the late period of bell stage we begin to see

hard tissue formation until the full crown is formed and after that the root starts

to form the tooth starts to go up ,so the going up of the tooth related to tooth

formation


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Tooth Eruption

Its a process whereby a tooth moves from its developmental position in thejaw into its functional position in the mouth, asa result its a continuous

process, for example sometimes we call the tooth when the tooth starts to

appear in the mouth eruption which is wrong,it should be called emergence

..now whats the difference ?!

^^Emergence ..when the first part of the tooth appears in the mouth which

is one of the stages of eruption(brief stage of eruption)

^^Eruption ..is a continous process that has many stages

^^functional eruption ..when the tooth reaches contact with the opposite

tooth

Its also The process by which developing teeth emerge through theoverlying bone, soft tissues & oral mucosa

In Addition .. its found that even if the root reaches contact ,if the apposing

tooth is removed the tooth may erupt for one or two mm that means

eruption doesnt end so we dont have an evidence that eruption ceases

after occlusal contact because sometimes teeth may go over-eruption or

super eruption upon removal of antagonist tooth

Thats why is A continuous process ending only with the loss of the tooth


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Purpose of tooth eruption

Entering the oral cavity Contacting teeth of the opposing arch Functioning in occlusion & mastication

Phases of eruption

Generally we have 3 different stages ..

Pre-eruptive phaseIts the phase that begins from the Initiation of tooth development

until crown is completed

Pre-functional eruptive phaseIts the phase that begins from Initiation of root development until

the Establishment of occlusal contact and the tooth is not in functionyet

Post-eruptive functional phase protracted phaseIt starts when the occlusal contact is established and afterwards ,

Note: tooth erupt after they reach contact because if the apposing

tooth is removed they can go up slightly ,the tooth is all the time

erupting and what prevents the tooth from erupting is the apposing

tooth

Concerned with development & maintenance of occlusion


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Now What happens in these phases ?!

Pre-eruptive Phase

Movements in response to positional changes of adjacent developing

crowns ,sometimes the tooth it self before the crown is completed

can move because of the response to adjacent crowns

Sometimes we have Movements in response to changes in the

maxilla and the mandible as the face grows downwards and

forwards,when the face grows downwards and forward the jaw

changes it position these momvements can be medial lateral

anterior posterior not necessarily vertical movement

Usually Teeth make mesial and distal movements during lengthening

of the jaws

Also when the successor teeth moves in relation to theirpredecessors this cause changing in the position of the predecessor

tooth


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Movement of successors

at first they share the same crypt and later own each tooth has it own crept ,,at

the picture .. first its located lingual to it after that it goes down and the other

tooth starts to erupt and occupies a position below and lingual to the tooth

In the case of deciduous molar the premolar located lingual to it with time the pre

molar will come inside between the roots of the deciduous tooth ,which is

important clinically because when the anterior deciduous teeth are lost ,the

resorption is obliquely because of that in some children we see deciduous tooth

and permanent successor tooth appearing in the mouth at the same time,but in

premolar the resorption is not oblique but horizontal


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Movement of permanent molars

These teeth dont have predecessor so they erupt by them self because they are

not successors

Maxillary molars

Develop within the tuberositiesFirst we have first molar development then its moves ,then the

tuberosity will be free for the second molar to develop then moves

forward then its free for the third molar,this third molar remains

within the tuberosity

Usally Occlusal surfaces slanting distally


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mandibular molar

Develop in the rami

Occlusal surfaces slanting mesially


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Movement of teeth

All of these are pre-eruptive ,before the vertical movement

From this picture the doctor emphases that the important thing we should know

that , the crown of this lower permanent canine its very close to the inferior

border of the mandible

the incisor it develops in the middle area of the occlousal plane and the inferior

border of the mandible ..then it keeps moving ,but some teeth like mandibular

canine goes down


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Rates of eruption

teeth dont erupt at the same rate

Theres A balance between eruptive & resistive force,because when theteeth erupt they face resisitance so we should have balance

Resistance (factors affecting eruption rate) Overlying soft tissues & alveolar bone Viscosity of surrounding PDL Occlusal forces

But finally if the tooth wants to erupt the amount of eruptive force should be

more than the amount of resistance

TOOTH ERUPTION RATE

Upper central incisors 1 mm / month

Lower 2nd

premolars 4.5 mm / 14 weeks

3rd

molars 1 mm / 3months

Crowded dentition < 1 mm in 6 months

Lower second premolar is among the fastest teeth that erupt which is 4.5 among

14 weeks (in one month 1.5 mm)


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Rate of eruption

Slow eruption until the tooth reaches the oral mucosaIts takes about 2 to 4 years for permanent teeth

Note : the rate of eruption from the beginning until the end is not the

same

Rapid eruption as the tooth enters the oral cavity,once the toothpenetrate the oral cavity it penetrates fast

When the tooth reaches the emergence 2/3s of root length hasformed

The Maximum rate is usually 1 mm / month ,but during to the studypermanent molar may only need two months from emergence to

functional eruption ,and as the time the tooth emergence become

late the time needed to the functional eruption becomes longer

Eruption slows as the tooth approaches the occlusal plane/contactNo sex difference

Racial differences may exist

Active eruption vs. passive eruption

ActiveAxial movement of the tooth

Passive Retraction of adjacent soft tissues


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Pre-functional Eruptive Phase

Starts with the initiation of root formation

Ends when reaching occlusal contact

The process of Root formationProliferation of Epithelial Root Sheath

Initiation of dentinogenesis in the root

Formation of the pulp tissues

An increase in follicular fibrous tissue

Movementat the root formed the tooth started to go up axially ,when the root is

forming it needs a space it cannot penetrate but it moves up so there will

be

o Elongating for the rootso And usually when the tooth is moving enamel is protected by

the Reduced enamel Epithelium , but once the tooth reaches

very close to the oral mucosa the reduced enamel epithelium

fuses with the oral epithelium creating an epithelial line canal

through which the tooth erupts thats why the penetration

without bleeding


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PenetrationIt involves ..

Entrance into the oral cavity Enamel cuticle covers enamel No bleeding because of the fusion of the epithelial tissue

Intra-oral occlusal/incisal movement Until contact with opposing crown occurs Clinical crown vs. Anatomical crown

Reminder ..

The clinical crown the part of the crown that appears clinically in the mouth

,usually that part of crown is covered by some gingivae thats why the clinical

crown is shorter than the anatomical crown which is the actual crown of the tooth

,with age the amount of the visible crown becomes bigger so with age clinical

crown becomes bigger than anatomical crown


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Changes in tissues

Overlying erupting teeth Surrounding erupting teeth Underling erupting teeth

Overlying erupting teeth

The tooth is moving up , the thing that happens to the area above

the tooth is called eruption pathway, The tooth is a maxillary tooth

so it wants to go down ,they found that this area is an inverted

triangle ,its a degeneration area because we dont see nerves we

dont see blood vessels

Zone of degeneration Blood vessel decrease in number Nerves break down and degenerate


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Inside the degeneration zone we can identify an area calledGubernacular cord at the periphery of the degenerative zone

Imagination ..imagine this is the tooth and this tooth issurrounded by bone the area that is above the cusp of the

tooth which located at the apex of bone this is the orifice of

bone that the tooth has to pass through this area is called

Gubernacular cord ,its a part that fills a space above the

tooth called Gubernacular canal

Note .. Gubernacular canal is only related to permanentteeth(including successor and non successor teeth in order to

these to erupt they have to penetrate bone they have to create

their own canal ) , deciduous teeth always erupt without

overlying bone

as the tooth approximate the surface of bone the canal becomes

bigger and bigger ,the canal for the central is bigger than the one to

the lateral

Follicular fibers directed toward the mucosa Gubernacular canal contains the gubernacular cord The cord is composed of a central strand of epithelium its

important because when the tooth reaches close the

mucosa to connect between the reduced enamel

epithelium and the outer epithelium which is important

for the tooth to reupt without bleeding , and the cord is

surrounded by connective tissue


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cells that are important in eruption ..

OsteoclastsTheir function is ..

Resorption of overlying bone (In successor teeth) resorption of the root of the predecessor

Osteoblasts Build up of resorbed areas after tooth movement

Resorption of primary teeth

o Begins within 1 year of root completion,permenant teeh doesntundergo resorption

o Similar to bone resorptiono Dentine and cementum are reabsorbed but not enamelo By osteoclasts cells


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Factors affecting rate of root resorption

Increased masticatory loads

Less resorption when deciduous teeth are splinted,because when

they are splinted(put them together ) the load will distribute, after

removal of successor germs

Resorption is not continous all the time we have Rest periods and active

periods

Reparative tissue may be formed

But always resorption is more dominant than repair ,if something

goes wrong when repair is the dominant over resarption this leads to

the loss of the PDL & ankylosis to surrounding bone for the

deciduous tooth ..(the tooth becomes attached directly to te bone)

Ankylosed primary teeth,,

Important ,, the most teeth affected the mandibular second deciduous molars

Failure of continuing eruption Position remains constant in the jaw Height of alveolar bone increases Tooth sinks gradually below the levels of adjacent teeth Called submerged teeth


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Submerging may continue to an extent where teeth become completelyburied within bone

Shedding of primary teeth The tooth got lost when the root of this tooth is lost ,because it has no

mechanism of attachment

Primary dentition from about 2 to 7 years ,when last deciduous tootherupts and starts t function which is the second molar , until the first incisor

is lost

Mixed dentition from 7 to 13 years During mixed dentition period nearly 50 teeth are accommodated in the

jaw

this picture shows a fusion betweenreduced enamel epithelium and oral mucosa


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Development of dentogingival junction

The tooth continues to go up until fusion ,it goes up without bleeding the area of

REE remains at the tooth ,when the tooth finally erupted part of the enamel is still

fused with the reduced enamel epithelium ,this epithelium is called junctional

epithelium ,its The part of epithelium that covers the cervical margin of enamel,

and its the remnant of REE

REE, these cells are exhaustive (weak and very old they are not able to protect)

They are the remnants of enamel organ , they are the cells that build the crown

they can easily penetrated by bacteria ,causing gingivitis

Sorry for any mistakes.

What others think of you is not your business

Time heals almost everything, give the time

Some time ;)

Alaa Adas ,!

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Oral Histo 9th Lec Pt2