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When do primary teeth begin formation?

6 weeks in utero


When does mineralization begin?

4 months in utero


What germ layers does the teeth formed by?

Ectoderm and mesoderm


What does ectoderm and mesoderm turn into?

Ectoderm: Enamel
Mesoderm: Dentin and pulp


What is the tooth germ life cycle?

Growth, calcification, eruption, attrition


What are the stages of growth?

Initiation, proliferation, histodifferentiation, morphodifferentiation, apposition.


What is initiation also called? What happens during this stage?

Bud stage. Epithelial thickening at 20 sites. They will become primary teeth.


What is determined in the initiation, or bud stage?

Tooth number! Lack of initiation or arrest results in congenital tooth absence. Continued budding of enamel organ leads to supernumerary teeth.


What is proliferation also called? What happens during this stage?

Cap stage! Further cell multiplication, creating a cap formation with a dental papilla and dental follicle.


Dental Organ

The cap-like formation. Precursor of enamel.


Dental Papilla

Cell growth below and within the cap. Precursor of pulp and dentin.


Dental Follicle

Mesenchyme around enamel organ and dental papilla. Precursor of cementum and PDL.


What is determined in the proliferation or cap stage?

Tooth number! Missing tooth is a result of lack of initiation or arrest. Congenital tooth absence. An extra tooth can result from excessive cell proliferation. Epithelial rests may become a cyst and with further differentiation, an odontoma or supernumerary tooth depending on the degree of differentiation.


What is stage does histodifferentiation occur in? What happens during histodifferentiation?

Bell stage! Epithelium continues to develop and differentiates into odontoblasts and ameloblasts (papilla). Marks the end of the proliferative stage. Cells no longer can proliferate. If there is abnormal development, you have problems with dentin and enamel.


What stage does Morphodifferentiation occur? What happens?

Advanced Bell Stage! Continued growth of formative cells, that form the ultimate tooth shape.


What do disturbances and aberrations in the advanced bell stage result in?

Abnormal size and shape of teeth including peg laterals, microdontia and macrodontia.


What is Apposition?

The layer like deposition of non-vital extracellular tissue matrix secreted by the formative cells, ameloblasts and odontoblasts. Matrix creates definitive pattern and rate.


Disturbance or local trauma during apposition can result in what?

If injured during enamel formation, it can interrupt or arrest matrix apposition. Enamel hypoplasia is most common and often found with premature infants. Dentin hypoplasia is less common and from severe systemic disturbances.


What is calcification?

Follows matrix deposition and is the precipitation of inorganic calcium salts. Cusps and goes cervically.


What can go wrong in calcification?

Sensitive and lengthy process. Disturbances may result in enamel hypocalcification. Interglobular dentin.


How many years are needed for the calcification process?

4 years!


What is the most favorable eruption sequence of primary teeth?

Central, lateral, 1st molar, canine, 2nd molar


What is the 7 + 4 guideline?

From age 7 months, 4 teeth erupt every four months.


When is the enamel of primary dentition completely formed?

12 months.


At what age should all primary teeth be erupted?

2-3 years.


At what age should all root structures be formed?

3 years.


Why should there idealy be spaces between primary dentition?

Successors are larger.


Does spacing ensure successors will erupt without crowding?

NO! But it may reduce crowding during transition from primary to mixed.


What are the two types of spacing?

Primate and leeway.


What is the primate space?

Space between the MX primary lateral and primary canine and a space between the MN primary canine and primary first molar.