Tooth Development and Eruption

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Tooth development

odontogenesis

What is the time span for initiation?

6th to 7th weeks

What happens during initiation?

Ectoderm lining stomodeum gives rise to the oral epithelium and then to the dental lamina, adjacent to deeper ectomesenchyme, which is influenced by the neural crest cells. Both tissues are seperated by a basement membrane

What is the time span for the bud stage?

8th week

What is the main process involved in initiation?

induction

What is the main process involved in the bud stage?

proliferation

What happens during the bud stage?

Growth of the dental lamina into bud that penetrates growing ectomesenchyme

What is the time span for the cap stage?

9th to 10th weeks

What are the processes involved in the cap stage?

proliferation, differentiation, morphogenesis

What happens during the cap stage?

Enamel organ forms into cap, surrounding mass of dental papilla from the ectomesenchyme and surrounded by mass of dental sac also from the ectomesenchyme. Formation of the tooth germ.

What is the time span for the bell stage?

11th to 12th weeks

What processes are involved in the bell stage?

differentiation, proliferation, morphogenesis

What happens during the bell stage?

Differentiation of enamel organ into bell with four cell types and dental papilla into two cell types.

What processes are involved with the apposition stage?

induction, proliferation

What happens during the apposition stage?

Dental tissues secreted as matrix in successive layers.

What happens during the maturation stage?

Dental tissues fully mineralize to their mature levels.

What is the process involved in the maturation stage?

maturation

What is the outer portion of the ectoderm in the initiation stage?

oral epithelium

What is the important acelluar structure that seperates the oral epithelium and the ectomesenchyme?

the basement membrane

The oral epithelium is induced by the ectomesenchyme to produce what?

the dental lamina

The stage named for extensive proliferation of the dental lamina into oval masses penetrating into the ectomesenchyme?

The bud stage

What else undergoes proliferation in the bud stage besides the dental lamina?

the ectomesenchyme

The buds of the dental lamina, together with the surrounding ecto mesenchyme, will develop into what?

Tooth germ

What happens to the thickened non tooth producing portions of the dental lamina eventually?

it disintegrates as the developing oral mucosa comes to line the oral cavity

In the cap stage the tooth bud does not grow, what happens?

there is unequal growth in different parts of the tooth bud

What is the predominate process of the cap stage?

morphogenesis

When does the tooth bud become a tooth germ?

in the cap stage

What are the major components of the tooth germ?

the enamel organ, dental papilla, dental sac

What is the cap in the cap stage?

the enamel organ

Where is the enamal organ originally derived from?

the ectoderm

What is the inner mass in the cap stage that forms a concavity of the enamel organ?

dental papilla

What will the dental papilla eventually form?

future dentin and pulp tissue

Where is the dental papilla originally derived from?

the ectomesenchyme, which was influenced by the neural crest cells

What is the site for the future dentioenamel junction?

the basement membrane that seperates the enamel organ and dental papilla

The remaining ectomesenchyme surrounding the outside of the enamel organ condenses into what?

the dental sac

What is another name for the dental sac?

dental follicle

What will the dental sac give rise to?

the cementum, PDL, and alveolar bone

Where is the dental sac originally derived from?

the ectomesenchyme

What is the primordium of the tooth?

the tooth germ

Where does the primordium of the permanent dentition develop?

the successional dental lamina, an extension of the dental lamina that extends out lingually to the primary tooth germs

What are succedaneous teeth?

permanent teeth formed with primary predecessors, the anterior teeth and the premolars

Which teeth are nonsuccedaneous?

the permanent molars

What is the predominate process in the bell stage?

differentiation

How many types of cells are found in the enamel organ in the bell stage?

4 types

What are the cell layers found in the enamel organ in the bell stage?

the outer enamel epithelium, the inner enamel epithelium, the stellate reticulum, and the stratum intermedium

What kind of cells occur in the outer enamel epithelium in the bell stage?

cuboidal cells

What layer serves as protection for the enamel organ?

the outer enamel epithelium

What kind of cells occur in the inner enamel epithelium?

tall columnar cells

What wll the inner enamel epithelium differentiate into?

enamel secreting cells (ameloblasts)

Which layer in the bell stage has star shaped cells?

the stellate reticulum

The stellate reticulum is located inner or outer?

outer

What kind of cells reside in the stratum intermediate?

compressed layer of flat to cuboidal cells

The stratum intermediate is located inner or outer?

inner

What are the 2 layers in the dental papilla within the concavity of the enamel organ?

the outer cells of the dental papilla and the central cells of the dental papilla

What will the outer cells of the dental lamina differentiate into?

dentin secreting cells (odontoblats)

What will the inner cells of the dental lamina differentiates into?

the primordium of the pulp

What happens during the appositional stage?

the enamel, dentin, and cementum are secreted in successive layers

What is matrix?

an extracellular substance that is partially calcified, yet serves as a framework for later calcification

What stage does the dental tissues subsequently fully mineralize

maturation

What conveys communications between the cells of the enamel organ, the dental papilla, and the dental sac allowing tissue interactions?

the basement membrane

When the inner epithelial epithelium columnar cells elongate and repolarize they differentiate into what?

preameloblasts

The preameloblasts induce dental papilla cells to differentiate into what?

into odontoblasts

What do the odontoblasts do?

dentinogenesis, which is the apposition of dentin matrix, or predentin, on the other side of the basement membrane

Do odontoblasts start their secretion of matrix before the ameloblasts?

yes, this is why the dentin is thicker in the mature tooth structure than the enamel

What causes the induction of the preameloblasts to differentiate into ameloblasts?

the disintegration of the basement membrane allows the preameloblasts to come into contact with the newly formed predentin

What is amelogenisis?

the apposition of the enamel matrix

Where is the enamel matrix secreted from by the ameloblasts?

the Tomes' process, a tapered portion of each ameloblast that faces the disintegrating basement membrane

Odontoblasts leave attached cellular extensions in the length of the predentin called what?

odontoblastic process

What are the odontoblastic processes is contained in what?

a mineralized cylinder, the dentinal tubule

What cell bodies are involved in the eruption and mineralization process but will be lost after eruption?

the ameloblasts

When does the process of root development take place?

after the crown is completely shaped and the tooth is starting to erupt into the oral cavity

What is the structure responsible for root development?

the cervical loop

What does the cervical loop consist of?

a bilayer rim that consists only IEE and OEE

What is the function of the Hertwig's epithelial root sheath?

to shape the root (or roots) and induce dentin formation in the root area so that it is continuous with coronal dentin

When root formation is completed the portion of the basement membrane disintegrates its cells may become what?

epithelial rests of Malassez

What is cementogenisis?

apposition of the cementum

When the undifferentiated cells of the dental sac come into contact with the root dentin they differentiate into what?

cementoblasts

What is the cementum matrix called?

cementoid

What are entrapped cementoblasts called?

cementocytes

How is the dentinocemental junction formed?

as a result of the apposition of cementum over dentin

What is the embryological background for enamel?

enamel organ

What is the embryological background for dentin, cementum and alveolar bone?

dental papilla

What type of tissue is enamel?

epithelial

What type of tissue is dentin, cementum, and alveolar bone?

connective

What are the formative cells for enamel?

ameloblasts

What are the formative cells for dentin?

odontoblasts

What are the formative cells for cementum?

cementoblasts

What are the formative cells for alveolar bone?

osteoblasts

What are the incremental lines for enamel?

lines of Retzuis

What are the incremental lines for dentin?

imbrication lines of von Ebner

What are the incremental lines for cementum and alveolar bone?

arrest and reversal lines

What are the mature cells for enamel?

there are none, they are lost with eruption

What are the mature cells for dentin?

only dentinal tubules with processes

What are the mature cells for cementum?

cementocytes

What are the mature cells for alveolar bone?

osteocytes

What are the resorptive cells for enamel, dentin, cementum and alveolar bone?

odontoclasts

What hard tissue is can not have tissue formation after eruption?

enamel

What hard tissue has vascularity?

alveolar bone

What hard tissue is innervated by nerves?

dentin and alveolar bone

What stage does anodontia occur?

initiation stage

What is anodontia?

absence of single or multiple teeth

What are the etiological factors for anodontia?

hereditary, endocrine dysfunction, systemic disease, excess radiation exposure

What are the clinical ramifications of anodontia?

may cause disruption of occlusion and aesthetic problems, may need partial or full dentures, bridges, and/or implants

What stage does supernumerary teeth occur?

initiation

What are supernumerary teeth?

development of one or more extra teeth

What are the etiological factors for supernumerary teeth?

hereditary

What are the clinical ramifications of supernumerary teeth?

occurs commonly between the maxillary centrals, distal to the 3rd molars and premolar region. may cause crowding, failureof normal eruption and disruption of occlusion

When does macro/microdontia occur?

bud stage

What is macrodontia?

abnormally large teeth

What is microdontia?

abnormally small teeth

What are the etiological factors for micro/macrodontia?

hereditary in localized form. endocrine dysfunction is complete

What are the clinical ramifications of micro/macrodontia?

commonly involves permanent maxillary lateral incisor and 3rd molars

When does dens in dente occur?

during the cap stage

What is dens in dente?

enamel organ invaginates into the dental papilla

What are the etiological factors for dens in dente and gemination?

hereditary

What are the clinical ramifications of dens in dente?

commonly affects the permanent maxillary lateral incisor. tooth may have deep lingual pit and need endodontic therapy

What are the developmental disturbances of the cap stage?

dens in dente, gemination, tubercle, and fusion

What is gemination?

tooth germ tries to divide

What is fusion?

union of 2 adjacent tooth germs

What are the etiological factors for fusion?

pressure on the area

What are the clinical ramifications of gemination?

large single rooted tooth with one pulp cavity and exhibits "twinning" in crown area. normal number of teeth in dentition. may cause problems in appearance and spacing

What are the clinical ramifications of fusion?

large tooth with two pulp cavities. one fewer tooth in dentition. may cause problems in appearance and spacing

What is tubercle?

extra cusp due to effects on enamel organ

What are the etiological factors of tubercle?

trauma, pressure or metabolic disease

What are the clinical ramifications?

common on permanent molars or cingulum of anterior teeth

What are the development disturbances of the apposition and maturation stages?

enamel pearl, enamel dysplasia, and concresence

What is an enamel pearl?

sphere of enamel on root

What are the etiological factors for enamel pearl?

displacement of ameloblasts to root surface

What are the clinical ramifications of enamel pearl?

may be confused as calculus deposit on root

What is enamel dysplasia?

faulty development of enamel from interference involving ameloblasts

What are the etiological factors of enamel dysplasia?

local or systemic or hereditary

What are the clinical ramifications of enamel dysplasia?

pitting or intrinsic color changes in enamel. changes in thickness of enamel possible. problems in function and aesthetics

What is concrescence?

union of root structure of two or more teeth by cementum

What are the etiological factors of concrescence?

traumatic injury or crowding of teeth

What are the clinical ramifications of concrescence?

common with permanent maxillary molars

Active eruption

the actual vertical movement of the tooth

Passive eruption

when the gingiva recedes and no actual tooth movement takes place

After the enamel apposition ceases the crown area of each primary or permanent tooth what happens?

the ameloblasts place an acellular dental cuticle on the new enamel surface

How is the reduced enamel epithelium created?

the enamel organ is compressed

What happens when the reduced enamel epithelium is created?

the primary tooth can now erupt into the oral cavity, the REE fuses with the oral epithelium, then enzymes from the REE disintegrate the central portion of the epithelial tissue leaving an epithelial tunnel for the tooth to erupt

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