Tooth Development (Odontogenesis)

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Tooth Development(Odontogenesis)
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Dentition

• Primary dentition develops during prenatal
  period
• 20 teeth
• Permanent dentition develops as the jaw grows
  and matures
• 32 teeth
• period in between during the preteen years
• mixed dentition period

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THERE ARE MULTIPLE STAGES IN TOOTH DEVELOPMENT
but three major ones actually

• initiation stage 6th to 7th week
• bud stage 8th week
• cap stage 9th to 10th weeks
• bell stage 11th to 12th weeks
• apposition stage vaires per tooth
• maturation stage varies per tooth

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Tooth formation

• first signs of formation day 11
• thickening of the epithelium where tooth
  formation will occur - on the 1st branchial arch
• more than 90 genes have been identified in the
  oral epithelium, dental epithelium and dental
  mesenchyme!! so exact signaling mechanisms remain
  unclear

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Tooth formation Initial stages
-involves the physiologic process of
induction -induction of ectodermal tissues by the
developing mesenchyme -mechanisms remain
unknown -at the 6th week the stomatodeum is lined
with ectoderm outer portion is the oral
epithelium -this gives rise to the primary
epithelial bands -also is a developing mesenchyme
which contains neural crest cells that have
migrated to the area -a basement membrane
separates the developing oral epithelium and
mesenchyme
The initiation of tooth formation starts around
the 37th day of gestation.
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Primary epithelial bands Horseshoe-shaped bands
that appear approximately around the 37th day of
development, one for each jaw. (corresponds to
future dental arches) -Each band gives rise to
two subdivisions vestibular lamina and dental
lamina -the Dental lamina indicates series of
outgrowths into the mesenchyme -develops in the
future spot for the dental arches -the ingrowths
represent the future sites for each deciduous
teeth -the Vestibular lamina cells rapidly
enlarge and proliferate and then degenerate
forms a cleft that becomes the vestibule of the
oral cavity
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Bud Stage

• Marked by the incursion of epithelium into the
  mesenchyme
• Period of extensive proliferation and growth of
  the dental lamina
• Forms into tooth buds or oral masses that
  penetrate into the mesenchyme
• Each tooth bud is surrounded by the mesenchyme
  packed closely beneath bud

1. Tooth bud
2. Oral epithelium
3. Mesenchyme

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Cap Stage

• characterized by continuation of the ingrowth of
  the oral epithelium into the mesenchyme.
• tooth bud of the dental lamina proliferates
  unequally in different parts of the bud
• forms a cap shaped tissue attached to the
  remaining dental lamina
• this stage marks the beginning of
  histodifferentiation (differentiation of
  tissues)
• the tooth germ also begins to take on form
  start of morphodifferentiation
• a depression forms in the deepest part of each
  tooth bud and forms the cap or enamel organ (or
  dental organ) produces the future enamel
  (ectodermal origin)
• below this cap is a condensing mass of mesenchyme
  dental papilla produces the future dentin and
  pulp tissue (mesenchymal origin)
• the basement membrane separating the dental organ
  and the dental papilla becomes the future site
  for the dentinoenamel junction (DEJ)
• remaining mesenchyme surrounds the dental/enamel
  organ and condenses to form the dental sac or the
  dental follicle

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Cap stage

• together the enamel organ dental papilla
  dental follicle is considered the developing
  tooth germ
• these germs are found in the developing dental
  arches and will develop into the primary dentition

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Bell Stage

• Continuation of histodifferentiation and
  morphodifferentiation
• cap shape then assumes a more bell-like shape
• differentiation produces four types of cells
  within the enamel/dental organ
• 1. inner enamel epithelium
• 2. outer enamel epithelium
• 3. stellate reticulum
• 4. stratum intermedium
• the dental papilla undergoes differentiation and
  produces two types of cells
• 1. outer cells of the DP forms the
  dentin-secreting cells (odontoblasts)
• 2. central cells of the DP forms the primordium
  of the pulp
• dental sac/follicle increases its collagen
  content and differentiates at a later stage than
  the EO and DP

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Differentiation of the Enamel/Dental organ

• outer enamel epithelium (OEE) cuboidal shape
• protective barrier during enamel production
• may also be called the outer dental epithelium
• inner enamel epithelium (IEE)
• short, columnar cells
• differentiates into the enamel secreting cells
  ameloblasts
• separated from the dental papilla below it by a
  basement membrane also
• may also be called the inner dental epithelium
• the IEE and OEE are continuous
• region where they connect curved rim of the EO
  cervical loop
• stellate reticulum
• star-shaped cells in many layers
• center of the enamel organ
• forms a network reticulum
• supports production of enamel
• stratum intermedium
• inner layer of compressed flat to cuboidal cells

OEE
IEE
cervical loop
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Bell Stage
-the cells in the center of the enamel organ
begin to synthesize and secrete GAGs -this pulls
water into the EO -increasing amount of fluid in
the EO forces the central cells apart -however,
they remain connected via cellular processes
which makes them star shaped stellate ret.
B inner dental epithelium (inner enamel
epithelium)
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Bell stage early crown formation

• the dental papilla is separated from the enamel
  organ by a basement membrane
• immediately below this BM is a region called the
  acellular zone
• this is where the first enamel proteins will be
  laid down
• the dental lamina begins to break up into
  discrete islands of epithelial cells (epithelial
  pearls) separates the oral epithelium from the
  developing tooth
• the IEE completes its folding and you can begin
  to identify the shape of the future crown pattern

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Tooth development so far
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Cap and Bell stages Permanent teeth

• during the cap stage the development of the
  permanent dentition begins
• the primordia for these teeth appears as an
  extension off the developing dental lamina
• its site of origin is called the succesional
  dental lamina
• these permanent teeth are called succedaneous
  teeth (anterior teeth and the premolars)
• teeth that form with the primary tooth buds
  (primary predecessors)

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Appositional stage

• secretion of enamel, dentin and cementum
• these tissues are initially secreted as a matrix
  that is partially calcified serves as a
  framework for later calcification

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Maturation stage

• characterized by the completion of calcification

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Ameloblasts and Odontoblasts

• ameloblasts
• the cells of the IEE assume a more columnar shape
  or they elongate
• differentiate into pre-ameloblasts
• the pre-ABs induce the cells of the dental
  papilla to differentiate also
• odontoblasts
• differentiation by the mesenchyme of the dental
  papilla
• occurs after differentiation of pre-ABs begins
• results because the pre-ABs induce
  differentiation of the mesenchymal cells also
• after differentiation the ODs then start
  dentinogenesis

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• At 1 the epithelium is separated from the dental
  papilla by an acellular zone.
• At 2 the cells of the inner dental epithelium
  have elongated, and the acellular zone begins to
  be eliminated as odontoblasts differentiate from
  ectomesenchymal cells in the tooth pulp.
• At 3 the odontoblasts retreat toward the center
  of the pulp, leaving behind formed dentin.
• At 4 the cells of the inner dental epithelium,
  now ameloblasts, begin to migrate outward and
  leave behind formed enamel.
• before dentin forms cells of the EO receive
  blood supply from vessels of the dental lamina
• as dentin forms, it cuts of this papillary source
  of blood/nutrients
• this causes a drastic reduction in the amount of
  nutrients that reach the EO
• but the ABs require extensive nutrients to form
  enamel stellate reticulum collapses and
  invagination of the OEE this brings in blood
  supply from peripheral vessels found outside the
  tooth

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Dentinoenamel junction

• after OD differentiation and the initiation of
  dentinogenesis the BM between the pre-ABs and
  ODs disintegrates
• this allows direct contact between the pre-ABs
  and ODs results in the completion of pre-AB
  differentiation to mature ABs
• ABs then begin amelogenesis apposition of
  enamel matrix
• upon contact of the enamel matrix and dentin
  the disintegrating BM begins to mineralize
  forms the dentinoenamel junction or DEJ
• mineralization of the developing dentin and
  enamel is distinct for each type of tissue

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Timetable for tooth development

• Entire primary dentition initiated between 6 and
  8 weeks of embryonic development.
• Successional permanent teeth initiated between
  20th week in utero and 10th month after birth
• permanent molars between 20th week in utero
  (first molar) and 5th year of life (third molar)

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ROOT FORMATION

• takes place as the crown is completely shaped and
  the tooth begins to erupt
• therefore the tooth forms from the top down
  i.e. crown to root
• root formation is through the formation of a
  cervical loop
• the CL is the most cervical portion of the
  enamel/dental organ two layers consisting of
  IEE and OEE
• the CL begins to grow down into the dental sac
• it forms a Hertwig's root sheath
• grows down to encompass all but the basal portion
  of the pulp
• this sheath shapes the root and induces dentin
  formation in the root area by the ODs of the
  dental papilla
• this sheath lacks the stellate reticulum and
  stratum intermedium
• is capable of differentiating into ODs BUT NOT
  ABs

A, The root is beginning to form as an extension
of the inner and outer dental epithelia in the
cervical loop region (circles) which form a
bilayered structure called Hertwigs epithelial
root sheath. B. formation of dentin by
odontoblasts above the root sheath
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Root Dentin

• The root of the tooth is composed by dentin and
  cementum
• dentin forms when the outer cells of the dental
  papilla are induced to differentiation into ODs
• similar to what occurs at the crown area
• influenced by Hertwigs root sheath
• the ODs then undergo dentinogenesis and secrete
  predentin
• after dentin formation the BM disintegrates
  along with the Hertwigs sheath

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Cementum and Pulp formation

• cementogenesis in the root area also occurs upon
  degradation of the H. root sheath
• the degradation allows contact of the dental sac
  cells with the dentin surface induces the
  formation of cementoblast cells
• the CBs cover the root dentin and undergo
  cementogenesis laying down cementoid
• only upon mineralization of the cementoid can it
  be called cementum
• the region of contact between cementum and root
  dentin dentinocemental junction or DCJ
• while the cementum is forming - the central
  cells of the dental papilla form the pulp
  (Chapter 13)

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Periodontal ligament

• the surrounding tissues of the tooth also develop
  as the crown and root form
• the mesenchyme of the dental sac condenses to
  form the periodontal ligament
• forms adjacent to the new cementum
• ends of these fibers insert into the outer layer
  of cementum and surrounding alveolar bone
• the cells of the disintegrating H. root sheath
  develop into discrete islands of epithelial cells
• become epithelial rests of Malassez (figure
  6-22)
• no known function
• they can be identified in the periodontal
  ligament and are responsible for the development
  of radicular cysts.

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Multirooted teeth

• anterior teeth, premolars and molars all begin as
  a single root root trunk
• root of the posterior teeth divides from the
  trunk into the correct number of root branches
• differential growth of the H. root sheath results
  in the division of the root trunk into two or
  three roots

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