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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