Tooth Develpoment Stages

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odontogenesis

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tooth development
in stages but continious
Week 7-8 primary dentition starts to form devs from interation of the oral epithelial cells and underlying mesenchymal cells

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hypodontia

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fewer than six teeth missing

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oligodontia

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more than six teeth missing

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Stages of tooth development

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Based on apperance of tooth
*initiation stage
*bud stage
*cap stage
*bell stage(cell differentiation giving rise to enamel/dentin formation

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Initiation Stage is

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interaction between 2 different tissues

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In the initiation Stage
teeth develop from what kind of cells?

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2 types of cells
1) oral epithelial = forms enamel organ(enamel dev from enamel organ)
2)Mesenchymal cells=form dental papilla
* neural cells also contribute to tooth dev*

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In the initiation stage neural crest cells contribute to tooth development by

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arising from neural tissue at early stage of dev. and migrate into jaws, intermingling w/ mesenchymal cells. Function by intermingling w/ dental papilla and epithelial cells of the early enamel organ aids in dev of tooth, cells also function in dev of salivary gland, bone, cartilage,nerves,and facial muscles

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dentitions develop from

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embryologic tissue interactions of epithelial and mesenchymal cells

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Oral Epithelium

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derived from ectoderm
2 horseshoe shaped bands become maxillary and mandibular

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Ectomesenchyme

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derived from ectoderm
deep to oral epithelium
*once these tissues interact, initiation stage begins*

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Basement Membrane

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seperates the Oral epithlium and ectomesenchyme

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Week 7 of the Intiation stage

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dental lamina formation
1)dev and arises from oral epithelium(tooth buds)
2)dev into a sheet of epithelial cells that push into the mesenchyme around perimeter of both the maxillary and mandibular jaws

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areas of enlargement

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at the leading edge of the lamina 20 tooth buds
*after primary teeth develop from buds, leading area of lamina continues to grow to dev permanent teeth, which succeed the 20 primary = part of lamina successional lamina

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Successional lamina

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successional dental lamina for permanent teeth Not including molars= formed from leading edge of lamina

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Where does the posterior teeth come from?

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lamina continues posteriorly into the elongating jaw and from it come the posterior teeth.

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Permanent molars form from

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general lamina- develop from behind the primary dentition

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when does the initiating lamina that forms both successional and general lamina begin to function?

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6th prenatal week and continues to function until the fifteenth year producing all 52 teeth (permant forms slightly lingual to primary)

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Bud Stage-Initial stage

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rounded localized epitheal cell growth surrounded by condensing mesenchymal cells

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what happens to the underlying ectomesenchyme during the bud stage?

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undergoes proliferation

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where is the basement membrane during bud stage?

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between the bud and growing ectomesenchyme

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when does the bud stage end and the cap stage begin?

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gradually, as the rounded epithelial bud enlarges, it gains a concave surface, which begins the cap stage

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Cap stage

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Week 9-10- primary detition
the epithlial cells now become the enamel organ & remain attached to the lamina
*Concave surface*

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Dental papilla is formed from

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mesenchyme forms dental papilla which becomes pulp and dentin

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Dental sac (follicle)

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tissue surrounding the enamel organ and dental papilla

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Future DEJ

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basement membrane between enamel organ and dental papilla= basement membrane will be site of DEJ

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tooth germ

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aka dental germ

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at what week does initiation of primary dentition occur?

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Week 10

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Primordium(original entity) for the initially formed permanent teeth appears as an extention of

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dental lamina into ectomeschyme lingual to dev primary tooth germ
*site of origin =successional dental lamina

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succedaneous

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permanent dentition formed after primary predecessors(succeed other teeth)
anterior teeth/premolars-
replace anterior/primary molars
*eruption lingual to primary root if tooth has not shed

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nonsuccedaneous

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no primary predecessors
permanent molars
6 permanent molars per dental arch develop from posterior extension of dental lamina distal to primary M2'sdental lamina and is associated ectomesenchme for each quardarnt

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Bell Stage

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differentiation takes place, looks like a bell, sets stage for histodifferentation

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Histodifferentation

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enamel and dention formation

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Week 11-12 primary dention Oral epithelium differintiates into

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1)Outer enamel epithelium OEE outer cuboidal cells of EO= protective, Cover the enamel organ
2) Inner enamel epithelium IEE differentiate into ameloblast by organizing a network of capillaries that bring nutrition to ameloblasts(form enamel form tooth crown)

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At the bell stage the basement membrane

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is still between the Inner enamel epithelium and the dental papilla

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At bell stage, stellate reticulum

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between the two cell layers (OEE,IEE) star shaped, synthesize GAG glycoamonoglycons drawing water in and streching in to star shape

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At bell stage, Stratum intermedium

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4th layer of the enamel organ, adjacent to IEE( between the stellate & IEE), flat cuboidal cells, assit with IEE, ameloblast to form enamel

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Concavity of enamel organ differentiates into

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1)Odontoblasts( outer cells of dental papilla) dentin forming cells
2) Pulp Primordium- central cells of dental papilla (original)

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Odontoblasts(predentin)

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outer cells od dental papilla, formed form cell in periphery from mesenchymal cells, odontoblasts, elongate become columnar form matrix of collagen fibers called predentin

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Odontobalsts(dentin)

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after 24 hours the (predentin) increment matrix calcifies and becomes dentin. (several layers in process)

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Odontoblasts(amelogenesis)

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after several layers of dentin, the differentiated amelobalsts deposit enamel matrix and amelogenesis begins
*dentiogenesis always preceeds amelogenesis*

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After Enamel organ is differentiated

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the dental lamina disintegrates by undergoing lysis, dental lamina dissappears in the anterior part of the mouth, although it remains active in the posterior region for many years

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Cell signaling

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cells interact through sysytem of effectors, modulators, and receptors
EX: epithelial -mesenchymal interaction in tooth development

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Pulp Primordium

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central cells of the dental papilla

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Dental Papilla

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densley packed cells chatacterize the dental papilla
*become dental pulp
*densley packed cells(fibroblasts)
*Blood vessels (nutrition)
* Nerves
Cellular changes result in formation of hard shell around central papilla which becomes known as pulp

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Dentigenesis

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initial formation of dentin at the cuspal tips and the vascularization of the pulp. the dental follicular cells are differentiationg around the enamel organ and aleovar bone proper is beginning to define the dental crypt.

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where does dentogeneisis develop

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process develops at the proximal ends of the cell, adjacent to the DEJ & cell gradually moves pulpward

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where is dentin formed in dentogenenisis

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increments of dentin are formed along the DEJ

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how is the dental matrix formed

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dental matrix is at first a meshwork od collagen fibers(predentin), but 24 hours after becomes calcified(dentin)

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At the time of calcification, the dental papilla becomes

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dental pulp as dentin surrounds it.

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Dentogenesis takes place in two phases

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1)collagen matrix formation
2) depostition of calcium phosphate( hydroxiapatite) crystals in matrix
* only newly formed band of dental matrix along pulpal border is uncalcified

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amelogenesis

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begins the enamel process production and development

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ameloblasts

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begin enamel deposition after a few micrometers of dentin have been deposited at the DEJ

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Ameloblasts differentiate

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and pass through five functional stages
1) morphogenesis
2)organization and differention
3)secretion
4)maturation
5)protection

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morphogenesis

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look up

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Organization and differentiation begins by

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*the row of ameloblasts maintain oreientation by cell to cell attachments(desomsomes) at both proximal and distal ends of the cell. this maintains the cells in a row as they move peripherally from the DEJ depositing enamel matrix

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Organization and differntiation finishes by

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as the ameloblast differentiates, the enamel matrix is synthesized within the RER, which then migrates to the golgi apparatus where it is condensed and packaged in membrane bound organells

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secretion begins when

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a short conical processess (Tomes' processes) develop at the apical end of the ameloblast, junctional coplexes called the terminal bar apparatus appear at the junction of the cell bodies and Tomes and maintain contact between adjacent cells

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amelobasts begin sercretion when

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the overlying cells of the stratum intermedium change shape from spindal to pyramidal. as amelogenesis proceeds, both of these cells layers(ameloblasts and stratum intermedium) are held together by cell junctional complexes (demosomes), with synthesis of enamel occuring in both cells

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during sercretion,how is the protien amelognin produced

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substance needed for enamel production arrive via blood vessels and pass through the strellate reticulum to the stratum intermedium and ameloblasts

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Maturation

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occurs after enamel production is complete

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in maturation, as amelogeneisis is completed, amelogenin is

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deposited and begins to mineralize

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during maturation, as soon as the small crystals of mineral are deposited,

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they begin to grow in length and diameter (70 % of the mineral in enamels is result of growth of crystals

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during maturation, the protien of the enamel changes or matures and is termed

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enamelin

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in maturation as the ameloblast completes the matrix deposition phase

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it's terminal apparatus disappears, and the surface enamel becomes smooth

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Protection

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closing of maturation; plauque formation and attachment

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during protection ameoblasts secrete

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basal lamina against enamel surface and establish hemidesomes

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hemidesmosomes

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is half of a desmosome attachment of plaque, it relates to the attachment of a cell to a surface membrane

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ameloblasts

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protect the enamel from cellular influences of follicular connective tissue

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ameloblasts shortenand contact

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the stratum intermedium and other enamel epithelium. This cellular organic covering remains on the enamel surface until the tooth erupts into the oral cavity

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apposition

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final stage in odontogenesis
enamel, dentin,cementum, are secreted in successive layers, initially secreted as a matrix(extracellular substance) that is partially calcified and serves as a framework for later calcification

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maturation

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when things fully mineralize, other final stage of odontogenesis, dental tissues subsequently fully mineralize

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crown formation

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tooth development begins at crown and proceeds to root
* root force causes tooth to shoot up & erupt