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Name and describe the two major theories of general tooth development
Classical theory-The stages in this theory are based entirely on the general microscopic morphology.
Functional theory. The stages here are based on the functional and cellular changes that occur during tooth development
teeth and their supporting structures are formed from what two germ/tissue types of the embryo?
Ectoderm and Ectomesenchyme
The connective tissue in the oral cavity is an embryonic tissue mesenchyme – in the head this is from cells originating in the neural crest and is known as ectomesenchyme.
describe the primary epithelial band, when it arises. it's a rough indication of what?
arising at around 6 wks of development, it is a horseshoe shaped thickening of the oral ectoderm in the developing arches that later becomes the maxilla and mandible. it indicates the general line along with the future teeth will start to develop.
describe Dental Lamina:
arises from the primary epithelial band in the mandibular and maxillary arches. it is a solid sheet of oral ectoderm that grows down and at specific locations will develop into the enamel organs for the indiv. primary teeth.
What are the stages of the classical theory of tooth development?
Bud, Cap, Early Bell, and Late Bell stages
describe the "condensation of ectomesenchyme." when does it occur?
during bud stage, the (ectoderm)epithelium migrates inward/downward, (into the arch), and the ectomesenchyme cells surrounding the incropping migrate close together around the bud.
describe the cap stage.
what is the cap often refered to as?
during cap stage the bud/downward projection flattens/broadens into a cap shape.
at this stage the "cap" is also referred to as the enamel organ or dental organ.
at what stage do the four layers of enamel organ distinguishable on a slide?
at the cap stage.
the cap stage/enamel organ forms a cap over the ectomesenchymal condensation that is called the:
what part of the tooth does this become
cap forms over the ectomesenchymal condensation known as the Dental Papilla, which eventually becomes the dental pulp.
the enamel organ is responsible for two things:
enamel formation AND inducing the formation of other tooth structures.
The enamel organ consists of four layers:
- 1. outer enamel epithelium (OEE)
- 2. Stellate reticulum (SR)
- 3 Stratum intermedium (SI)
- Inner enamel epithelium (IEE)
describe Outer Enamel Epithelium.
what is significance of basement membrane involved?
One to two layers of flattened cells that act as a semi permeable barrier and aid in the transport of nutrients and growth factors from the surrounding vasculature. because this arose from epithelial tissue it is still separated from surrounding tissue by a basement membrane!
Describe Stellate Reticulum
star shaped cells with numerous processes and desmosomal connections to form a 3D network in a thick ECM gel rich in GAGs.
it aids in the maintenance of crown shape until some hard tissue is formed (i.e. it prevents distortion of the crown which could occur due to rapid growth of surrounding tissues).
describe Inner Enamel Epithelium
a single layer of cells that, as development proceeds from cap stage, will differentiate into become preameloblasts then ameloblasts.
what is the cervical loop? how many layers of cells there? what structure is this the origin of?
cervical loop is the "future neck of hte developing tooth. there are only 2 layers there, the IEE and the OEE. It is the origin of Hertwig's epithelial root sheath, responsible for inducing formation of the dentin of the root.
describe stratum intermedium
- two to three layers of cells closely applied to the inner enamel epithelium (btwn SR and IEE)
- SI cells are rich in alkaline phosphatase involved in mineralization.
IEE and SI are regarded as one unit, essential for the formation of enamel.
what is an enamel knot?
Associated with the IEE in the future cuspal region. it is a group of cells believed to be the focal point of a variety of factors in tooth development.
during what stage of development is the shape of the future crown determined?
EARLY BELL STAGE
which layer in the early bell stage "sets the shape of the future crown?" How?
the IEE is responsible for setting the shape of future crown: the IEE cells at the future cuspal regions proliferate at a higher rate than the rest of the IEE cells, resulting in a buckling of the epithelium at the future cusp regions.
What development is the indicator that early bell is over and late bell stage has begun?
Late Bell Stage occurs as soon as ANY hard tissue has been formed and continues for the entire life of the tooth, even if the tooth is no longer vital!
What two key activities/events occur during Late Bell STage?
- 1. Amelogenesis
- 2. Dentinogenesis
- Inner enamel epithelial cells start to differentiate into preameloblasts. This is believed to be under the influence of the stratum intermedium cells.
- IEE cells then induce cells in the peripheral pulp to develop into preodontoblasts.
Preodontoblasts further differentiate and start to secrete dentin matrix. As soon as they start secretion they are known as odontoblasts.
What develops first, Ameloblasts or odontoblasts? which one lays down its product first?
Ameloblasts develop before odontoblasts, but odontoblasts are the first to begin laying down the dentin.
Where on the structure does cell differentiation and hard tissue formation start? what direction does it progress?
Cell differentiation and hard tissue formation starts at the tips of the future cusps and progresses to the cervical loop (future neck of the tooth). Enamel is thickest at the cusps and thinnest at the cervix of the tooth.
Dentin is first formed as a non-mineralized matrix known as predentin which is then fully mineralized.
There is always a layer of predentin on the pulpal surface of dentin.
T/F: Odontoblasts lay down dentin throughout the life of the tooth.
before hard tissue is formed, where do the ameloblasts get their nutrition?
where does it come from after enamel is being laid down? what event occurs to allow this?
before enamel is formed, ameloblasts get nutrition from both (a) developing pulp; and (b) developing dental follicle.
once hard tissue is formed nutrition reaches the ameloblasts only from the developing dental follicle. The enamel organ collapses down at that regioin to form the COLLAPSED DENTAL ORGAN, bringing blood vessels closer to the amelobasts.
what is the reduced enamel epithelium?
once the full thickness of hte enamel has been formed and fully mineralized at the region of the enamel organ (including ameloblasts), these layers form a protective layer over the enamel known as the reduced enamel epithelium.
name all the cell types/layers that comprise the reduced enamel organ:
- Outer enamel epithelium.
- Stellate reticulum**** debate as to whether this layer has disappeared by this stage.
- Stratum intermedium.
- Note that there are no IEE cells left.
name the functions of the REE:
- Protects the fully mineralized enamel until the tooth erupts.
- Combines with the oral ectoderm to form the epithelium of the sulcus.
- Forms the junctional epithelium (epithelial attachment).
List the Enamel Organ Functions:
- Sets the shape of the future crown.
- Initiates differentiation of ameloblasts and the formation of enamel.
- Initiates differentiation of odontoblasts.
- Initiates root formation (HERS).
- Protects the erupting tooth enamel.
- Aids in formation of the epithelial attachment and the sulcular epithelium.
what is successional lamina and where is it located?
successional lamina is a small projection from the dental lamina that breaks off and will form the enamel organ of the permanent tooth. it is always located lingual to its primary tooth. (meaning it is only present w/r/t permanent teeth replacing deciduous teeth)
Name arrows L to R.
- L: Successional lamina
- Mid: Primary dental lamina
- R: Vestibular lamina
Describe Dental Papilla
- Develops from ectomesenchyme.
- Once some hard tissue is formed and it encloses the dental papilla it is usually known as the developing dental pulp.
Due to the continuous formation of dentin throughout the life of the tooth, the dental pulp becomes progressively smaller with age.