Tooth development Flashcards
How are deciduous teeth different to permanent ones.
A, B, C = 1, 2, 3
E = a small 6
D = unique in morphology.
Crowns are more bulbous
Teeth are smaller
Roots are more flared (so perm teeth can grow under)
Roots show more resorption
Occlusal/incisal surfaces show more attrition
Larger pulp chamber (and smaller dentine layer)
Whiter enamel bc is less mineralized.
The time frame for a developing deciduous tooth (until root completion)
Crown calcification = 12 months before eruption (E-12)
Crown completion = 6 months before eruption (E-6)
Eruption/roots half formed = E
Root completion = 18 months after eruption (E+18)
Order of deciduous teeth eruption
A, B, D, C, E
The time frame for a developing permanent tooth (until root completion)
Crown calcification begins = E-6 years
Crown completion = E-3 years
Eruption = E
Root completion = E+3 years
Order of eruption for permanent teeth
6, 1, 2, 4, 5, 3, 7, 8
Development of the canines/eruption
Canines/ 3’s don’t erupt until roots are complete so eruption and root completion both occur 6 years after crown completion/around 11 years of age.
Do maxillary or mandibular teeth erupt first
Mandibular
When are the teeth germ present for permanent dentition
Present at birth apart from for the 7’s and 8’s.
What are the stages of tooth development
Initiation Further development Morphodifferentiation Cytodifferentiation Root formation
What are the stages of initiation
- ~7 weeks after fertilization and after the maxillary arch has developed.
- Ectoderm band thickens= primary epithelial band
- Primary epithelial band grows and proliferates into the underlying lamina propria.
- The formation of the primary epithelial band induces the condensation of ectomesenchyme cells around the thickened band.
- The primary epithelial band splits into the dental lamina (w/ the ectomesenchyme cells) and the vestibular lamina. Both continue to grow deeper.
- The deep part of the dental lamina proliferates = a ball/bud stage. Superficial cells of the vestibular lamina die and cause a groove to form.
Growth factors/genes needed for the initiation stage of tooth development
Bone morphogenic proteins and fibroblast growth factors expressed from the ectoderm interact w/ ectomesenchyme = right number of tooth germs.
DLX gene coding = tissue differntiation and positioning
Homeobox genes at specific places on arch = type of tooth.
What is the result of initiation being disrupted
Initiation causes the right number of teeth in the right place, =
adontia (no teeth)
Hypodontia (not enough teeth, 8>5>2)
Hyperdontia (too many teeth, can be accessory or supplemental)
What happens during further development
Ectoderm = enamel organ
Ectomesenchyme = dental papilla
Enamel organ covers the dental papilla = called a tooth germ now.
Stages of morphodifferentiation
Needed to produce the correct shape of the crown.
- Changes are lead by the dental papilla/ectomesenchyme (not enamel organ/ectoderm, like in initiation)
- BMP and FGF induce selective mitosis of the internal dental epithelium of the EO = change in shape.
- The enamel knot does the same thing but only refines the shape e.g. determines if 2nd or 3rd molar.
- The enamel knot disappears.
- The permanent tooth bud grows from the enamel organ.
- The dental lamina disintegrates.
- The dental follicle surrounds the tooth germ (makes the cementum and PDL)
The enamel organ layers
Internal and external dental epithelium (cervical loop where they meet/are continuous)
Stellate reticulum
Stratum intermedium.
(CT layer under the internal dental epithelium)
Function/structure of the external dental epithelium
Cuboidal cells
Regulates entry of nutrients into the EO
Function/structure of the stellate reticulum
Star shaped cells joined by desmosomes.
Space packing w ECM which provides vital nutrients to the avasuclar enamel organ.
Function/structure of the stratum intermedium
2-3 layers of squamous cells needed for enamel production.
Function/structure of the internal dental epithelium
Differentiates into ameloblasts which secrete enamel.
What happens during cytodifferentiation
- Internal dental epithelium induces the dental papilla cells to differentiate into odontoblasts (odontoblasts look more columnar, dental papilla looks like fibroblasts)
- Oodontoblasts secrete dentine
- The dentine induces the internal dental epithelial cells to differentiate into ameloblasts.
- The ameloblasts secrete enamel.
Root formation
Happens as the crown is completing the formation
- The cervical loop where the internal and external dental epithelium are continuous grows (mitosis happening at the tip) = the epithelial root sheath.
- The root sheath grows between the dental papilla and the dental follicle and forms a cylinder around the dental papilla (and divides if its a multi-rooted tooth)
- As it grows, it stretches out causing islets of cells/rests of malassez to occur meaning the root sheath is in contact w the dentine/dental follicle
- As the dentine and dental follicle are both derived from ectomesenchyme, they cant induce each other. The root sheath (derived from ectoderm) induces the dental follicle to differentiate into cementoblasts and fibroblasts (to make cementum and PDL) by secreting a thin hyaline layer of cartilage onto the root dentine
Dentine features
70% mineralized (if wasn’t mineralized it would be less resistant to abrasion and erosion)
30% Collagen type 1 (and ECM + proteins)
Organic matrix = compressable and high tensile strength so acts as a shock absorber and compensates for brittle enamel.
Vital and v sensitive (but doesn’t have many nerves)
Odontoblasts in quiet state at the pulp-dentine border and their processes extend w dentine forming around them = tubules.
Dentinogenesis
- Dental papilla cells differentiate into pre-odontoblasts (not fully differentiated yet) due to signals from the internal dental epithelium (BMP, FGF)
- Preodontoblasts secrete a mantle dentine layer (not mineralised dentine matrix) which stays as a layer under the future ADJ.
- Preodontoblasts fully mature to odontoblasts (cuboidal cells to polarised columnar)
- As the odontoblasts retreat they extend their processes and dentine forms around them = tubules.
- Pre-dentine begins to mineralize = dentine.
What is mantle dentine
A layer under the ADJ.
The first dentine secreted (by preodontoblasts).
Unmineralised dentine matrix - contains less collagen and more ECM.